Photodynamic therapy for colorectal cancer: an update and a look to the future

Citation: Rodrigues, J.A.; Correia, J.H. Photodynamic Therapy for Colorectal Cancer: An Update and a Look to the Future. Int. J. Mol. Sci. 2023,24, 12204. https://doi.org/ 10.3390/ijms241512204 Academic Editor: Carmine Stolfi Received: 10 July 2023 Revised: 24 July 2023 Accepted: 27 July 2023 Published: 30 July 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). International Journal of Molecular Sciences Review Photodynamic Therapy for Colorectal Cancer: An Update and a Look to the Future JoséA. Rodrigues 1,2,* and JoséH. Correia 1,2 1CMEMS-UMinho, University of Minho, 4800-058 Guimarães, Portugal; [email protected] 2LABBELS—Associate Laboratory, 4800-122 Braga, Portugal *Correspondence: jr[email protected] Abstract: This review provides an update on the current state of photodynamic therapy (PDT) for colorectal cancer (CRC) and explores potential future directions in this field. PDT has emerged as a promising minimally invasive treatment modality that utilizes photosensitizers and specific light wavelengths to induce cell death in targeted tumor tissues. In recent years, significant progress has been made in understanding the underlying mechanisms, optimizing treatment protocols, and improving the efficacy of PDT for CRC. This article highlights key advancements in PDT techniques, including novel photosensitizers, light sources, and delivery methods. Furthermore, it discusses ongoing research efforts and potential future directions, such as combination therapies and nanotechnology-based approaches. By elucidating the current landscape and providing insights into future directions, this review aims to guide researchers and clinicians in harnessing the full potential of PDT for the effective management of CRC. Keywords: photodynamic therapy; colorectal cancer; photosensitizers; light sources; combination therapies; nanotechnology 1. Introduction Colorectal cancer (CRC) is the third most common cancer worldwide (second most common cancer in women and third in men) and the second most common cause of cancer death. The widespread use of colonoscopy has led to an increase in the diagnosis of CRC in both early and late stages and a decrease in the mortality rate [ 1 – 3 ]. According to the World Health Organization (WHO), in 2020, there were 1.93 million newly diagnosed cases of CRC worldwide, resulting in 916.000 deaths attributed to CRC [ 4 ]. Generally, in CRC, 71% are in the colon and 29% in the rectum. [ 1 ]. Several factors contribute to the development of CRC. Age (over 50 years old), family history of CRC, and certain inherited genetic conditions, such as Lynch syndrome and familial adenomatous polyposis (FAP), increase the risk. Lifestyle factors, including a low-fiber and high-fat diet, consumption of red meat, consumption of processed meat, sedentary lifestyle, obesity, and smoking, are also risk factors for CRC [ 1 – 3 ]. CRC is categorized into four distinct stages. These stages provide information about the extent/spread of the disease and guide treatment decisions [5–7]: • Stage 0: This is the earliest stage of CRC. At this stage, the abnormal cells are confined to the mucosa of the colon or rectum and have not spread to nearby tissues. • Stage I: The primary polyps have grown through the mucosa of the colon or rectum and may have invaded the muscle layer. However, they have not spread to the lymph nodes or distant sites. • Stage II: The cancer has spread beyond the muscle layer and may have invaded nearby tissues. However, it has not reached the lymph nodes or distant organs. Stage II CRC tumors are further classified into stages II a, b, and c, regarding the cancer spread to the serosa or nearby organs. Int. J. Mol. Sci. 2023,24, 12204. https://doi.org/10.3390/ijms241512204 https://www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2023,24, 12204 2 of 21 • Stage III: The cancer has spread to nearby lymph nodes but has not metastasized to distant sites. Stage III CRC tumors are further subdivided into stages III a, b, and c, regarding the cancer spread to the serosa, inner and middle layers of the colon, and neighboring lymph nodes. • Stage IV: This is the most advanced stage of CRC. At this stage, the cancer has metastasized to distant organs, such as the liver, lungs, or other parts of the body. The diagnosis of colon cancer involves a combination of screening tests, diagnostic imaging, and pathological analysis. Common screening methods include colonoscopy, flexible sigmoidoscopy, digital rectal exam, and stool-based tests, such as fecal immunochemical test (FIT) and fecal occult blood tests (FOBTs), which look for genetic material (i.e., blood or DNA) in the stool. Colonoscopy is currently the most widely used and cost-effective technique for detecting CRC and taking biopsies for further histopathological evaluation [ 1 , 3 , 6 ]. Artificial intelligence techniques have been integrated into colonoscopy procedures to increase their effectiveness in detecting and evaluating colorectal polyps [ 3 , 8 , 9 ]. The implementation of a computer-aided diagnostic (CAD) system using deep-learning technology has shown promising results in accurately determining polyp histology (from the range of 63.8–71.8% to the range 82.7–84.2%) [3,8]. In addition, the use of narrow-band imaging (NBI) in colonoscopy can also improve polyps detection relative to white light colonoscopy (accuracy 95% vs. 74%) [ 3 ]. When conventional colonoscopy cannot be performed or is contraindicated or rejected by patients, colon capsule endoscopy (CCE) offers an alternative option for screening patients at moderate risk of CRC. CCE is an ingestible, wireless, and disposable capsule that takes multiple pictures of the colon, allowing for a painless and radiation-free study of the entire colon without sedation or gas insufflation. Although CCE has shown promise as a screening tool, it is important to note that it is not as comprehensive as colonoscopy in terms of detecting smaller polyps or providing therapeutic interventions. CCE is not recommended as a first-line screening or diagnostic method for CRC [ 3 , 9 , 10 ]. Diagnostic imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) are used to evaluate the extent of tumor involvement and detect metastasis [ 11 ]. Tissue samples obtained through biopsy or surgical resection are examined histologically to confirm the presence of cancer and determine its stage [3]. The treatment of CRC depends on various factors, including the stage of the disease, location of the tumor, and the overall health of the patient. The conventional treatment modalities include surgery, chemotherapy, radiotherapy, and immunotherapy [ 2 , 6 , 12 ]. Table 1shows the treatment modality commonly used at each stage of CRC [ 1 , 5 – 7 ]. Surgical resection (open or laparoscopic) of the tumor is the main curative treatment option. Overall, these therapies are typically most effective when the disease is diagnosed at an early stage (approximately 90% survival rate). However, when CRC is detected at a late stage, patients often experience a poor prognosis (approximately 15% survival rate in stage 4), indicating the need for improved detection methods and more effective treatment options [2,6]. Table 1. Treatment of CRC at different stages. Stage of CRC Treatment Stage 0 Surgical removal of the polyp or abnormal tissue through endoscopic procedures or minimally invasive surgery Stage I Surgical resection of the tumor Stage II Surgical resection of the tumor. Adjuvant chemotherapy depending on specific tumor characteristics and overall health of the patient Stage III Surgical resection of the tumor and lymph nodes, followed by adjuvant chemotherapy Stage IV Monotherapy or a combination of chemotherapy, biologic targeted therapy, immunotherapy, palliative surgery, radiotherapy, and radiofrequency ablation Int. J. Mol. Sci. 2023,24, 12204 3 of 21 Despite the availability of several conventional treatment approaches for CRC, these methods often have limitations, such as severe side effects, invasiveness, and limited efficacy in late-stage CRC [ 6 ]. Photodynamic therapy (PDT) is an emerging minimally invasive treatment that shows promise in improving CRC treatment outcomes. PDT involves the administration of a photosensitizing agent, which selectively accumulates in the cancer cells. Subsequent exposure to light at specific wavelength activates the photosensitizer (PS), leading to the production of reactive oxygen species (ROS) that cause localized cell death and tumor destruction [ 13 , 14 ]. In the case of colon cancer, PDT offers several advantages. First, it is a minimally invasive procedure that can be performed during endoscopic procedures, such as colonoscopy, allowing for targeted treatment directly at the tumor site. This localized approach reduces the potential damage to healthy tissues around the tumor. Another advantage is the ability to administer multiple dosages with minimal side effects. Unlike some conventional treatments, which can cause serious side effects due to their systemic nature, PDT can be repeated without cumulative toxicity. This flexibility in dosage administration allows for more effective treatment plans [6]. 2. Principles of PDT and Photosensitizers PDT is a non-invasive modality that can be used to treat various types of cancers effectively. The therapy involves the integration of three key components: PS, light at specific wavelength, and oxygen [ 13 – 15 ]. First, a PS is administered to the patient (topically or intravenous), which selectively accumulates in the tumor tissues. After a period of time, called “drug-light interval”, the tumor region is illuminated by a specific light source, typically in the red spectral region ( λ≥ 600 nm), and the PS becomes activated. This light source is carefully chosen to match the absorption properties of the PS, allowing for optimal activation. Upon exposure to the light, the activated PS undergoes a photochemical reaction with the molecular oxygen surrounding the tumor [ 13 , 16 , 17 ]. This reaction generates cytotoxic singlet oxygen ( 1 O 2 ) and other ROS, such as superoxide radical (O 2−• ), hydroxyl radical (HO • ), and hydrogen peroxide (H 2 O 2 ), which are highly destructive to the tumor tissues. These ROS cause oxidative damage to the tumor cells, leading to their destruction and subsequent tumor regression [ 13 , 17 , 18 ]. Two types of photodynamic reaction can occur in PDT. The type I reaction occurs when the excited state of the PS (PS*) reacts directly with a substrate, such as a cell membrane or a molecule, leading to hydrogen atom abstraction or electron transfer reactions. This interaction results in the generation of free radicals and radical ions. These radicals can react with other molecules, e.g., molecular oxygen, producing ROS [ 13 , 14 , 17 – 19 ]. The type II reaction occurs when the excited state of the PS transfer energy directly to the molecular oxygen, forming the singlet oxygen. Approximately all PSs have a high quantum yield in this reaction [ 13 , 14 , 18 , 19 ]. The relative contributions of type I and type II reactions to PDT can vary depending on several factors, such as the PS properties, oxygen concentration, and the binding affinity of PS to the substrate. Understanding and optimizing both types of photodynamic reactions are important for maximizing the therapeutic outcomes of PDT [ 13 , 14 , 19 , 20 ]. Figure 1illustrates the principles involved in PDT. Int. J. Mol. Sci. 2023, 24, x FOR PEER REVIEW 4 of 22 Figure 1. Principles of PDT. The products resulting from both photodynamic reactions lead to tumor destruction and the overall therapeutic effect of PDT via three interrelated mechanisms: direct cytotoxic effects on tumor cells, indirect damage to the tumor-associated vasculature, and induction of an inflammatory response and activation of an immune response [14,18,20]. The reactive species generated during the photodynamic reactions can directly damage the tumor cells. These reactive species can induce cellular stress, disrupt cellular components, and trigger apoptotic pathways, leading to programmed cell death (apoptosis) or cell death by other mechanisms (necrosis) [13,15,17,20]. Photodynamic reactions can also affect tumor-associated vasculature. The reactive species, particularly singlet oxygen, can damage the blood vessels supplying the tumor, leading to vascular rupture and the subsequent deprivation of oxygen and nutrients to the tumor cells. This indirect damage to the tumor-associated vasculature contributes to the overall destruction of the tumor [13,17,20]. An inflammatory response in the treated area can also be induced. The cellular damage caused by PDT triggers the release of inflammatory mediators and the recruitment of immune cells. This inflammatory response can further enhance the destruction of tumor cells and contribute to the activation of the immune system against the tumor. The immune response can recognize and target the tumor cells, leading to immune-mediated clearance and potentially providing long-term protection against tumor recurrence [13,20,21]. Oxygen plays a crucial role in the production of ROS during PDT. Tumor tissues often have an altered microenvironment with reduced levels of oxygen (hypoxia), affecting the effectiveness of PDT. Innovative strategies have been developed to overcome hypoxiarelated limitations and improve the effectiveness of PDT. These strategies aim to increase oxygen levels in the target tissue, either by improving local oxygen generation (e.g., H2O2decomposition, water-splitting, and photosynthetic oxygen production) or by increasing the oxygen-carrying capacity of the blood (e.g., perfluorocarbons and hemoglobin). Fractionated PDT can also help in tumor hypoxia, i.e., delivering light in multiple fractions instead of all at once [13,14,18,21]. The choice of light source for PDT depends on the specific location of the cancerous tissue and the PS used. Commonly used light sources include lasers and lamps; however, there is a growing trend towards the use of laser-emitting diodes (LEDs). Interestingly, even natural sunlight has been used as a light source in a variation of PDT known as daylight PDT [13,14,22,23]. Table 2 shows the main advantages and disadvantages of the light sources used in PDT. Light can penetrate biological tissues with minimal absorption and scattering at the tissue optical window (600–1200 nm), allowing for deeper tissue penetration. However, wavelengths greater than approximately 850 nm generally contain insufficient energy to generate a strong photodynamic effect and require solutions such as the upconversion of photons for sufficient singlet oxygen quantum yields. Thus, the phototherapeutic window predominantly used in PDT ranges from 600 to 850 nm [13,14,22]. In addition to this window, there are two other significant biological windows in the nearinfrared (NIR) spectrum, known as NIR-II (1000–1350 nm) and NIR-III (1500–1800 nm). Figure 1. Principles of PDT. Int. J. Mol. Sci. 2023,24, 12204 4 of 21 The products resulting from both photodynamic reactions lead to tumor destruction and the overall therapeutic effect of PDT via three interrelated mechanisms: direct cytotoxic effects on tumor cells, indirect damage to the tumor-associated vasculature, and induction of an inflammatory response and activation of an immune response [ 14 , 18 , 20 ]. The reactive species generated during the photodynamic reactions can directly damage the tumor cells. These reactive species can induce cellular stress, disrupt cellular components, and trigger apoptotic pathways, leading to programmed cell death (apoptosis) or cell death by other mechanisms (necrosis) [ 13 , 15 , 17 , 20 ]. Photodynamic reactions can also affect tumorassociated vasculature. The reactive species, particularly singlet oxygen, can damage the blood vessels supplying the tumor, leading to vascular rupture and the subsequent deprivation of oxygen and nutrients to the tumor cells. This indirect damage to the tumorassociated vasculature contributes to the overall destruction of the tumor [ 13 , 17 , 20 ]. An inflammatory response in the treated area can also be induced. The cellular damage caused by PDT triggers the release of inflammatory mediators and the recruitment of immune cells. This inflammatory response can further enhance the destruction of tumor cells and contribute to the activation of the immune system against the tumor. The immune response can recognize and target the tumor cells, leading to immune-mediated clearance and potentially providing long-term protection against tumor recurrence [13,20,21]. Oxygen plays a crucial role in the production of ROS during PDT. Tumor tissues often have an altered microenvironment with reduced levels of oxygen (hypoxia), affecting the effectiveness of PDT. Innovative strategies have been developed to overcome hypoxia-related limitations and improve the effectiveness of PDT. These strategies aim to increase oxygen levels in the target tissue, either by improving local oxygen generation ( e.g., H2O2-decomposition, water-splitting, and photosynthetic oxygen production) or by increasing the oxygen-carrying capacity of the blood (e.g., perfluorocarbons and hemoglobin). Fractionated PDT can also help in tumor hypoxia, i.e., delivering light in multiple fractions instead of all at once [13,14,18,21]. The choice of light source for PDT depends on the specific location of the cancerous tissue and the PS used. Commonly used light sources include lasers and lamps; however, there is a growing trend towards the use of laser-emitting diodes (LEDs). Interestingly, even natural sunlight has been used as a light source in a variation of PDT known as daylight PDT [ 13 , 14 , 22 , 23 ]. Table 2shows the main advantages and disadvantages of the light sources used in PDT. Light can penetrate biological tissues with minimal absorption and scattering at the tissue optical window (600–1200 nm), allowing for deeper tissue penetration. However, wavelengths greater than approximately 850 nm generally contain insufficient energy to generate a strong photodynamic effect and require solutions such as the upconversion of photons for sufficient singlet oxygen quantum yields. Thus, the phototherapeutic window predominantly used in PDT ranges from 600 to 850 nm [13,14,22]. In addition to this window, there are two other significant biological windows in the near-infrared (NIR) spectrum, known as NIR-II (1000–1350 nm) and NIR-III (1500–1800 nm). These additional windows also offer advantages as they demonstrate reduced auto-fluorescence, light scattering, and light absorption. NIR light proves to be more advantageous compared to visible light when dealing with tissue depths greater than 0.5 mm [24]. Table 2. Advantages and disadvantages of the light sources used in PDT [13,14,16,23,25–28]. Light Source Advantages Disadvantages Laser High light intensity Monochromatic light Efficient coupling to optical fibers Expensive Bulky Int. J. Mol. Sci. 2023,24, 12204 5 of 21 Table 2. Cont. Light Source Advantages Disadvantages Lamps Low cost Portable Easy to use Wide illumination field Thermal effect Wide spectral width Needs optical filtering Low-light intensity Limited to easily accessible places LEDs Low cost Small Thermally nondestructive Available in flexible arrays Less powerful (compared to laser) Large beam divergence Broad spectral width Daylight Cheaper Minimal patient discomfort Shorter clinical visits Scheduling difficulty Difficult to control light exposure PSs are substances that are capable of absorbing light at specific wavelengths and triggering photochemical reactions [ 14 ]. An ideal PS should demonstrate high purity and chemical stability, selective tumor targeting, low dark toxicity, strong absorption with a high molar extinction coefficient ( ε ) for higher light wavelengths (600 to 800 nm), high singlet oxygen quantum yield ( Φ∆ ), and rapid clearance from the body [ 14 , 17 , 29 ]. PSs can be categorized into three generations based on their complexity and successful application outcomes [ 6 , 13 , 14 ]. First-generation PSs includes hematoporphyrin derivative (HpD) and porfimer sodium. These early PSs were derived from porphyrins and exhibited broad absorption spectra but had limited selectivity, low molar extinction coefficient, and prolonged skin photosensitivity [ 6 , 18 ]. Second-generation PSs aimed to improve upon the limitations of first-generation compounds. These PSs were often synthetic modifications of porphyrin and chlorin structures, leading to enhanced selectivity, increased phototoxicity, and reduced skin photosensitivity. Examples of second-generation PSs include chlorins, protoporphyrin IX (PpIX), benzoporphyrins, hypericin, phthalocyanines, and 5-aminolevulinic acid (5-ALA) [6,16]. Third-generation PSs have emerged with improved tumor selectivity. This is achieved through the incorporation of targeting molecules (antibody conjugation) or encapsulation into carriers (such as nanoparticles or liposomes), enhancing their specificity for tumor regions. These advancements allow for more precise and targeted photodynamic therapy, maximizing the therapeutic effect while minimizing off-target effects [ 6 , 13 , 14 ]. Tables 3and 4show the PSs approved for clinical applications in PDT and some PSs under clinical investigation, respectively. Table 3. PSs clinically used in PDT [13–16,22,30,31]. Photosensitizer Wavelength (nm) Approval Applications Porfimer sodium (Photofrin®)630 Worldwide Esophageal cancer, Barrett’s esophagus, and non-small cell lung cancer 5-aminolevulinic acid (Levulan®/Ameluz®)635 Worldwide Actinic keratosis and superficial basal cell carcinoma Methyl aminolevulinate (Metvix®/Metvixia®)570–670 Worldwide Actinic keratosis and basal cell carcinoma Verteporfin (Visudyne®)690 Worldwide Age-related macular degeneration Temoporfin (Foscan®)652 Europe Advanced head and neck cancer LUZ11 (Redaporfin®)749 Europe Biliary tract cancer Int. J. Mol. Sci. 2023,24, 12204 6 of 21 Table 3. Cont. Photosensitizer Wavelength (nm) Approval Applications Padeliporfin (TOOKAD®)753 Europe Prostate cancer Hexyl-aminolevulinate (Hexvix®/Cysview®)360–450 Europe, USA, Canada Bladder cancer detection Talaporfin sodium (Laserphyrin®)664 Japan Lung and esophageal cancers and brain tumors Table 4. PSs under clinical investigation [13,14,30–32]. Photosensitizer Wavelength (nm) Applications Radachlorin®662 Skin cancer Photochlor®664 Head and neck cancer Purlytin®664 Age-related macular degeneration Fotolon®665 Nasopharyngeal sarcoma Photosens®670 Lung, liver, breast, skin, and gastrointestinal cancer Lutrin®732 Coronary artery disease Today, PS progresses towards the improvement of PDT specificity and efficacy, involving the use of porous carriers for sensitizers, such as liposomes [ 33 ], silica nanoparticles [34,35], polymers [ 36 – 38 ], metallic nanoparticles [ 39 – 41 ], quantum dots [ 42 – 44 ], and carbon nanomaterials [45,46], that can be encapsulated into a large number of PS [ 15 , 22 , 47 , 48 ]. Table 5shows the main properties of the nanoparticles used as carriers of PSs in PDT. Table 5. Main properties of the nanoparticles used as carriers of PSs in PDT [15,47,49,50]. Nanoparticle Properties Liposomes Delivery of hydrophobic agents Good biocompatibility and biodegradability Silica nanoparticles High biocompatibility and biodegradability Highly hydrophilic Easy surface functionalization Trigger ROS production Polymers Biocompatibility Delivery of hydrophobic agents High permeability through cell membranes Loading of multiple agents Metallic nanoparticles Amplification of PS excitation Enhance ROS production Surface modification to bind to PS Quantum dots Photostability Light-re-emitting properties High quantum yields Carbon nanoparticles High immobilization of PSs Water solubility Biocompatibility Int. J. Mol. Sci. 2023,24, 12204 7 of 21 3. PDT and CRC The increased resistance of tumor cells to conventional chemotherapeutic and biologic drugs used in CRC treatment, along with their non-specific toxicity to healthy tissues, highlights the need for alternative therapeutic approaches. One such approach is PDT, which offers several advantages in the treatment of CRC [51]: •Minimally invasive treatment [15,52]; • Minimization of damage to healthy tissues, reducing the risk of systemic side effects, through the targeted and localized approach of PDT [6,51,52]; • Overcoming the issue of multidrug resistance encountered with conventional chemotherapy, as PSs preferentially accumulate in CRC cells [51,52]; • Activation of immune responses against CRC. The release of tumor-associated antigens and the induction of immunogenic cell death triggered by PDT can stimulate an antitumor immune response, leading to the destruction of residual tumor cells and providing long-term therapeutic benefits [53]. In recent years, extensive preclinical and clinical research has been conducted on PDT for the treatment of CRC. This research has yielded valuable insights into the potential of PDT as a therapeutic approach for CRC. Moreover, there has been growing interest in combining PDT with other treatment modalities, such as surgery and radiotherapy. By integrating PDT with established treatment methods, a synergistic effect can be achieved, leading to improved outcomes for patients with CRC [32]. 3.1. Preclinical Research 3.1.1. In Vitro Studies Most preclinical studies investigating the potential application of PDT in colon and rectal cancer have focused on assessing the phototoxic effects of PSs on in vitro cultured colorectal tumor cells. One notable advantage of in vitro methods is the ability to directly use human cells, eliminating the need for translation from animal to human. These in vitro studies serve as a valuable starting point for evaluating the efficacy and selectivity of different PSs in targeting and destroying colorectal tumor cells. By exposing tumor cells to PSs and subsequent light activation, researchers can assess the cytotoxic effects and determine the optimal conditions for PDT treatment. In these preclinical studies, various parameters are investigated, including the choice of PS, optimal concentration, light dose, and treatment duration. Additionally, these in vitro studies provide insights into the underlying mechanisms of PDT in CRC. Researchers investigate the cellular and molecular responses triggered by PDT, such as apoptosis, necrosis, and the generation of ROS. Understanding these mechanisms is crucial for optimizing PDT protocols and developing more effective treatments [ 51 , 54 ]. Monolayer cultures, while valuable for investigating treatment effects, lack the complexity needed to replicate the heterogeneous nature of in vivo conditions. To address these limitations, three-dimensional tumor models have emerged as a partial solution, allowing for long-term studies of single-model tumors and single cells overtime. Three-dimensional tumor models provide a more realistic representation of the tumor microenvironment, incorporating factors such as cell–cell interactions, extracellular matrix components, and nutrient gradients. However, it is important to recognize that three-dimensional tumor models also have their limitations. They do not fully replicate the complexity of in vivo tumor growth, metastasis, and immunological interactions. Additional factors, such as a lack of vasculature or immune cell infiltration, may affect the translation of findings to clinical settings [ 54 ]. Table 6shows some preclinical in vitro studies of PDT performed in colorectal tumor cells. Int. J. Mol. Sci. 2023,24, 12204 8 of 21 Table 6. Preclinical in vitro studies of PDT in colorectal tumor cells. Ref. Tumor Cell Line Photosensitizer Irradiation Conditions Year [55] HT-29 Porfimer sodium, 2.5–10 µg/mL 585 nm, 9.2 W/m2, 2700 J/m22001 [56] Colo 201 Temoporfin, 0.125–1 µg/mL 500 nm, 7 mW/cm2, 1–15 J/cm22002 [57] HCT-116 Phthalocyanine Pc 4, 0–300 nM 670–675 nm, 200 mJ/cm22005 [58] HT-29 Hypericin, 0.04–0.1 µM530–620 nm, 4.4 J/cm22006 [59] HCT-116 PpIX 1, 0.5–10 µg/ml 633 nm, 2 J/cm22007 [60] LoVo Pyropheophorbide-a or verteporfin conjugates with scFvs 2, 0.25–100 µM680 nm, 13.4 J/cm22008 [61] HT-29 SN-38-loaded CSBC 3micelles, 0.001–1000 µg/mL 660 nm, 19.5 mW/cm2, 7 J/cm22009 [62] HCT-116 Newly synthesized phenyl porphyrin derivatives, temoporfin, 1 µg/mL White light, 20 mW/cm2 630 nm, 0.6 mW/cm22009 [63] SW-480 TCPP 4, TCPP nanoparticles or TCPP-loaded PLGA 5 nanoparticles, 1 µ M 400–440 nm, 141 mW/cm2, 15 J/cm22009 [64] HT-29 Ce6-aptamers 6, 0.1–100,000 nM 664 nm, 20–30 mW/cm2, 12 J/cm22009 [65] HCT-116 DH-II-24, 5 µg/mL 630 nm, 1.45 mW/cm 2 , 0.02–0.17 J/cm 22009 [66] LoVo Porfimer sodium, 15–30 µg/mL 633 nm, 3–6 J/cm22010 [67] HT-29 Pheophorbide a, 0–2 µM630 nm, 2 J/cm22010 [68] HCT-116 PpIX silica nanoparticles, 5 µM630 nm, 4 mW/cm22010 [69] HT-29, HCT-116 H 2 TFPC-SGlc or Talaporfin sodium, 1 µ M 633 nm, 37 mW/cm2, 16 J/cm22011 [70] CaCo-2 GaPcCl 7, 2–100 µg/mL 661 nm, ≈90 mW/cm2, 2.5–8.5 J/cm22012 [71] DLD-1 ZnPcSmix 8, 5–40 µM 680 nm, 5 J/cm22012 [72] WiDr TPPS2a 9, 0.1 µg/mL 435 nm, 13.5 mW/cm22013 [73] HT-29 PpIX, 1 µg/mL 633 nm, 1 and 5 J/cm22014 [74] C-26 Ce6, 0.5 µg/mL 662 nm, 105 mW/cm2, 3–12 J/cm22015 [75] SW-620 5-ALA, 3 mM 630 nm, 60 mW/cm2, 4.5 J/cm22016 [76] SW-620, SW-480 Temoporfin, 0.18–11.76 µM650 nm, 60 mW/cm2, 1.5–6 J/cm22017 [77] HCT-116 PMMA@PorVa 10, 0.1–100 nM Visible light, 158.4 J/cm22018 [29] RKO, HCT-15 Temoporfin, 0.5–10 µg/mL 653 nm, 11 mW/cm2, 2.5–10 J/cm22019 [78] HT-29 PGL NPs 11, 0–8 µM 650 nm, 200 mW/cm22020 [79] CT-26 Ce6, 0.1–1.8 µM PI3Kγ12 inhibitor IPI-549, 0.5–9.3 µM660 nm, 800 mW/cm2, 48 J/cm22021 [80] HCT-116 BC4 13, 0–100 µM 761 nm, 30 mW/cm2, 48 J/cm22022 [81] CaCo-2 ZnPcS4/Ag@mSiO2, 0–0.5 µM674 nm, 9.5 mW/cm2, 10 J/cm22022 [82] CaCo-2 AlClPcTS41, 0.125–0.75 µM636 nm, 10 J/cm22023 [83] HCT-15 Porphyrin-based photosensitizers (0–50 µM) + low dose of doxorubicin (0.5 µM) 600–720 nm, 50 mW/cm2, 20 J/cm22023 [84] HCT-116 CFN-gel 14, 0–5 µM 660 nm, 50 mW/cm2, 9 J/cm22023 1 Protoporphyrin IX; 2 single-chain variable fragment; 3 chlorin-core star-shaped block copolymer; 4 meso-tetra (carboxyphenyl) porphyrin; 5 poly (lactic-co-glycolic acid); 6 chlorin e6; 7 gallium (III) phthalocyanine chloride; 8 zinc sulfophthalocyanine; 9 meso-tetraphenylporphine with two sulphonate groups on adjacent phenyl rings; 10 poly-methyl methacrylate nanoparticles covalently loaded with the porphyrin; 11 porphyrin-grafted lipid nanoparticles; 12 phosphoinositide 3-kinase gamma inhibitor IPI-549; 13 meso-tetrakis [1-(2 0 -bromoethyl)-3pyridyl]-bacteriochlorin tetrabromide; 14 fucoidan-based theranostic nanogel. Int. J. Mol. Sci. 2023,24, 12204 9 of 21 3.1.2. Animal Studies In vitro studies are essential for establishing the foundations of PDT in CRC research; however, further investigations are needed to validate these findings in animal models and eventually in clinical trials. A prerequisite for starting a clinical trial is evidence of a positive impact of the technique or drug on animals. The complexity of in vivo tumor microenvironments and the potential influence of factors such as blood flow, immune response, and tissue architecture require further studies to assess the full potential of PDT in the treatment of colon and rectal cancer [ 51 , 85 ]. The choice of animal model is therefore very important and should mimic the human situation as much as possible. The most commonly studied animals are rats and mice [ 85 , 86 ]. The selection of an appropriate cell line is another crucial aspect. Many pharmacological studies use nude animals bearing humanderived tumors [ 85 ]. Nude animals, lacking a functional immune system, are commonly used to avoid immune rejection of human tumor cells. Due to the greater susceptibility of these mice to infections, the cell lines must be free of mouse pathogens and the mice must be maintained under specific pathogen-free conditions [ 86 , 87 ]. Human tumor cells are cultured in vitro and then injected directly into the animal, usually subcutaneously, on the desired tumor location. A large number of human CRC cell lines grown as xenograft tumors at a subcutaneous location in nude mice have been subjected to PDT [ 86 ]. The advantages of this model include relatively rapid tumor development and easy observation. It allows the evaluation of genes and signaling pathways that drive tumor growth. The most important drawbacks, however, are the lack of immune response, no infiltration of adjacent tissues, and rarely observed metastases. To overcome some of those obstacles, the cells are sometimes implanted orthotopically [ 88 – 90 ]. Table 7shows some preclinical animal studies of PDT performed in colorectal tumors. Table 7. Preclinical animal studies of PDT in colorectal tumors. Ref. Animal Model Photosensitizer Irradiation Conditions Year [91]Female nu/nu–athymic mice xenografted with SW-480 tumor cells Phthalocyanine Pc4, 1 mg/kg intravenously (i.v.) 670 nm, 150 mW/cm2, 150 J/cm22000 [92]Male athymic nude mice bearing HT-29 tumor cells Porfimer sodium or liposomal pheophorbide a, 30 mg/kg intraperitoneally (i.p.) 636 or 665 nm, 200 mW/cm 2 or 150 mW/cm2, 100 J/cm22002 [93]Female C57BL/6NCr mice bearing Colo-38 tumor cells NPe6 1, 5 mg/kg i.v. 664 nm, 9 mW/cm2, 61 J/cm22005 [94]Female BALB/c and C57Bl/6 mice xenografted with CT-26 tumor cells ATX-S10 Na(II), 5 mg/Kg i.v. 670 nm, 150 J/cm22006 [95]Female BALB/c–nu/nu athymic nude mice bearing WiDr tumor cells PP(Arg)22, 2 and 10 mg/kg i.v. 632 nm, 250 mW/cm2, 150 J/cm22007 [65]Female BALB/c nude mice bearing HCT-116 tumor cells DH-II-24, 1 mg/kg i.v. > 630 nm, 154 J/cm22009 [96] Female BALB/c, BALB/nude and NOD/scid mice bearing CT-26 tumor cells WST11, 9 mg/kg i.v. 755 nm, 100 mW/cm2, 30 J/cm22009 [69] Female BALB/c Slc-nu/nu nude mice xenografted with HT-29 and HCT-116 tumor cells H2TFPC-SGlc or Talaporfin, 6.25 µmol/kg i.v. 633 nm, 37.5 J/cm22011 [97]Female BALB/c mice bearing CT-26 tumor cells Hypericin, 50 or 200 µg i.v. 600 nm, 27 or 50 mW/cm2, 14 or 60 J/cm22011 [98]Female Swiss nude/nude mice xenografted with HT-29 tumor cells 5,10,15-tri{para-O-[2-(2-O-αD-Manosyloxy)-ethoxy]- ethoxy-phenyl}-20-phenyl porphyrin, 0.6 mg/kg i.v. 650 nm, 75 J/cm22012 Int. J. Mol. Sci. 2023,24, 12204 16 of 21 Acknowledgments: This work was supported by project CMEMS-UMinho Strategic Project UIDB/04436/2020 and UIDP/04436/2020, and MPhotonBiopsy PTDC/FIS-OTI/1259/2020. Conflicts of Interest: The authors declare no conflict of interest. References 1. Ahmed, M. Colon Cancer: A Clinician’s Perspective in 2019. Gastroenterol. Res. 2020,13, 1. [CrossRef] [PubMed] 2. Ali Koc, M.; Utku Celik, S.; Akyol, C. Colon Cancer. In Current Trends in Cancer Management; IntechOpen: London, UK, 2019. 3. Sawicki, T.; Ruszkowska, M.; Danielewicz, A.; Nied´zwiedzka, E.; Arłukowicz, T.; Przybyłowicz, K.E. A Review of Colorectal Cancer in Terms of Epidemiology, Risk Factors, Development, Symptoms and Diagnosis. Cancers 2021,13, 2025. [CrossRef] 4. Cancer. Available online: https://www.who.int/news-room/fact-sheets/detail/cancer (accessed on 15 May 2023). 5. Nkune, N.W.; Kruger, C.A.; Abrahamse, H. Possible Enhancement of Photodynamic Therapy (PDT) Colorectal Cancer Treatment when Combined with Cannabidiol. Anti-Cancer Agents Med. Chem. 2021,21, 137–148. [CrossRef] [PubMed] 6. Simelane, N.W.N.; Kruger, C.A.; Abrahamse, H. Photodynamic diagnosis and photodynamic therapy of colorectal cancer in vitro and in vivo. RSC Adv. 2020,10, 41560–41576. [CrossRef] [PubMed] 7. Kim, S.; Buddolla, V.; Lee, K. Recent insights into nanotechnology development for detection and treatment of colorectal cancer. Int. J. Nanomed. 2016,11, 2491–2504. [CrossRef] 8. Song, E.M.; Park, B.; Ha, C.-A.; Hwang, S.W.; Park, S.H.; Yang, D.-H.; Ye, B.D.; Myung, S.-J.; Yang, S.-K.; Kim, N.; et al. Endoscopic diagnosis and treatment planning for colorectal polyps using a deep-learning model. Sci. Rep. 2020 ,10, 30. [CrossRef] [PubMed] 9. Kanth, P.; Inadomi, J.M. Screening and prevention of colorectal cancer. BMJ 2021,374, n1855. [CrossRef] 10. Spada, C.; Hassan, C.; Bellini, D.; Burling, D.; Cappello, G.; Carretero, C.; Dekker, E.; Eliakim, R.; de Haan, M.; Kaminski, M.F.; et al. Imaging Alternatives to Colonoscopy: CT Colonography and Colon Capsule. European Society of Gastrointestinal Endoscopy (ESGE) and European Society of Gastrointestinal and Abdominal Radiology (ESGAR) Guideline—Update 2020. Eur. Radiol. 2021 , 31, 2967–2982. [CrossRef] 11. Buccafusca, G.; Proserpio, I.; Tralongo, A.C.; Giuliano, S.R.; Tralongo, P. Early colorectal cancer: Diagnosis, treatment and survivorship care. Crit. Rev. Oncol. Hematol. 2019,136, 20–30. [CrossRef] 12. Simelane, N.W.N.; Abrahamse, H. Nanoparticle-Mediated Delivery Systems in Photodynamic Therapy of Colorectal Cancer. Int. J. Mol. Sci. 2021,22, 12405. [CrossRef] 13. Correia, J.H.; Rodrigues, J.A.; Pimenta, S.; Dong, T.; Yang, Z. Photodynamic Therapy Review: Principles, Photosensitizers, Applications, and Future Directions. Pharmaceutics 2021,13, 1332. [CrossRef] [PubMed] 14. Rodrigues, J.A.; Correia, J.H. Enhanced Photodynamic Therapy: A Review of Combined Energy Sources. Cells 2022 ,11, 3995. [CrossRef] 15. Niculescu, A.-G.; Grumezescu, A.M. Photodynamic Therapy—An Up-to-Date Review. Appl. Sci. 2021,11, 3626. [CrossRef] 16. Gunaydin, G.; Gedik, M.E.; Ayan, S. Photodynamic Therapy for the Treatment and Diagnosis of Cancer–A Review of the Current Clinical Status. Front. Chem. 2021,9, 686303. [CrossRef] 17. Fitzgerald, F. Photodynamic Therapy (PDT): Principles, Mechanisms and Applications; Nova Science Publishers, Inc.: New York, NY, USA, 2017. 18. Hu, T.; Wang, Z.; Shen, W.; Liang, R.; Yan, D.; Wei, M. Recent advances in innovative strategies for enhanced cancer photodynamic therapy. Theranostics 2021,11, 3278–3300. [CrossRef] [PubMed] 19. Sobhani, N.; Samadani, A.A. Implications of photodynamic cancer therapy: An overview of PDT mechanisms basically and practically. J. Egypt. Natl. Cancer Inst. 2021,33, 34. [CrossRef] 20. Gunaydin, G.; Gedik, M.E.; Ayan, S. Photodynamic Therapy—Current Limitations and Novel Approaches. Front. Chem. 2021 , 9, 691697. [CrossRef] 21. Yanovsky, R.L.; Bartenstein, D.W.; Rogers, G.S.; Isakoff, S.J.; Chen, S.T. Photodynamic therapy for solid tumors: A review of the literature. Photodermatol. Photoimmunol. Photomed. 2019,35, 295–303. [CrossRef] 22. Huis in ‘t Veld, R.V.; Heuts, J.; Ma, S.; Cruz, L.J.; Ossendorp, F.A.; Jager, M.J. Current Challenges and Opportunities of Photodynamic Therapy against Cancer. Pharmaceutics 2023,15, 330. [CrossRef] 23. Mosaddad, S.A.; Namanloo, R.A.; Aghili, S.S.; Maskani, P.; Alam, M.; Abbasi, K.; Nouri, F.; Tahmasebi, E.; Yazdanian, M.; Tebyaniyan, H. Photodynamic therapy in oral cancer: A review of clinical studies. Med. Oncol. 2023,40, 91. [CrossRef] 24. Bhandari, C.; Guirguis, M.; Savan, N.A.; Shrivastava, N.; Oliveira, S.; Hasan, T.; Obaid, G. What NIR photodynamic activation offers molecular targeted nanomedicines: Perspectives into the conundrum of tumor specificity and selectivity. Nano Today 2021 , 36, 101052. [CrossRef] 25. Kim, M.M.; Darafsheh, A. Light Sources and Dosimetry Techniques for Photodynamic Therapy. Photochem. Photobiol. 2020 , 96, 280–294. [CrossRef] [PubMed] 26. Algorri, J.F.; Ochoa, M.; Roldán-Varona, P.; Rodríguez-Cobo, L.; López-Higuera, J.M. Light Technology for Efficient and Effective Photodynamic Therapy: A Critical Review. Cancers 2021,13, 3484. [CrossRef] [PubMed] 27. Lee, C.-N.; Hsu, R.; Chen, S.; Wong, T.-W. Daylight Photodynamic Therapy: An Update. Molecules 2020 ,25, 5195. [CrossRef] [PubMed] Int. J. Mol. Sci. 2023,24, 12204 17 of 21 28. Piksa, M.; Lian, C.; Samuel, I.C.; Pawlik, K.J.; Samuel, I.D.W.; Matczyszyn, K. The role of the light source in antimicrobial photodynamic therapy. Chem. Soc. Rev. 2023,52, 1697–1722. [CrossRef] 29. Rodrigues, J.A.; Amorim, R.; Silva, M.; Baltazar, F.; Wolffenbuttel, R.; Correia, J.H. Photodynamic Therapy at Low-Light Fluence Rate: In vitro Assays on Colon Cancer Cells. IEEE J. Sel. Top. Quantum Electron. 2019,25, 1–6. [CrossRef] 30. Šoši´c, L.; Selbo, P.K.; Kotkowska, Z.K.; Kündig, T.M.; Høgset, A.; Johansen, P. Photochemical Internalization: Light Paves Way for New Cancer Chemotherapies and Vaccines. Cancers 2020,12, 165. [CrossRef] 31. Karges, J. Clinical Development of Metal Complexes as Photosensitizers for Photodynamic Therapy of Cancer. Angew. Chem. Int. Ed. 2022,61, e202112236. [CrossRef] 32. Algorri, J.F.; Ochoa, M.; Roldán-Varona, P.; Rodríguez-Cobo, L.; López-Higuera, J.M. Photodynamic Therapy: A Compendium of Latest Reviews. Cancers 2021,13, 4447. [CrossRef] 33. Jin, C.S.; Zheng, G. Liposomal nanostructures for photosensitizer delivery. Lasers Surg. Med. 2011,43, 734–748. [CrossRef] 34. Mesquita, Q.M.; Dias, C.J.; Neves, M.G.P.M.S.; Almeida, A.; Faustino, M.A.F. Revisiting Current Photoactive Materials for Antimicrobial Photodynamic Therapy. Molecules 2018,23, 2424. [CrossRef] 35. Lin, J.-F.; Li, J.; Gopal, A.; Munshi, T.; Chu, Y.-W.; Wang, J.-X.; Liu, T.-T.; Shi, B.; Chen, X.; Yan, L. Synthesis of photo-excited Chlorin e6 conjugated silica nanoparticles for enhanced anti-bacterial efficiency to overcome methicillin-resistant Staphylococcus aureus.Chem. Commun. 2019,55, 2656–2659. [CrossRef] [PubMed] 36. Späth, A.; Leibl, C.; Cieplik, F.; Lehner, K.; Regensburger, J.; Hiller, K.-A.; Bäumler, W.; Schmalz, G.; Maisch, T. Improving Photodynamic Inactivation of Bacteria in Dentistry: Highly Effective and Fast Killing of Oral Key Pathogens with Novel Tooth-Colored Type-II Photosensitizers. J. Med. Chem. 2014,57, 5157–5168. [CrossRef] [PubMed] 37. Songca, S.P.; Adjei, Y. Applications of Antimicrobial Photodynamic Therapy against Bacterial Biofilms. Int. J. Mol. Sci. 2022 , 23, 3209. [CrossRef] 38. Park, H.; Lee, J.; Jeong, S.; Im, B.N.; Kim, M.-K.; Yang, S.-G.; Na, K. Lipase-Sensitive Transfersomes Based on Photosensitizer/Polymerizable Lipid Conjugate for Selective Antimicrobial Photodynamic Therapy of Acne. Adv. Health Mater. 2016 , 5, 3139–3147. [CrossRef] [PubMed] 39. Lavaee, F.; Motamedifar, M.; Rafiee, G. The effect of photodynamic therapy by gold nanoparticles on Streptococcus mutans and biofilm formation: An in vitro study. Lasers Med. Sci. 2021,37, 1717–1725. [CrossRef] [PubMed] 40. Zhu, F.; Tan, G.; Zhong, Y.; Jiang, Y.; Cai, L.; Yu, Z.; Liu, S.; Ren, F. Smart nanoplatform for sequential drug release and enhanced chemo-thermal effect of dual drug loaded gold nanorod vesicles for cancer therapy. J. Nanobiotechnol. 2019,17, 44. [CrossRef] 41. Calavia, P.G.; Bruce, G.; Pérez-García, L.; Russell, D.A. Photosensitiser-gold nanoparticle conjugates for photodynamic therapy of cancer. Photochem. Photobiol. Sci. 2018,17, 1534–1552. [CrossRef] 42. Uprety, B.; Abrahamse, H. Semiconductor quantum dots for photodynamic therapy: Recent advances. Front. Chem. 2022 , 10, 946574. [CrossRef] 43. Winnik, F.M.; Maysinger, D. Quantum Dot Cytotoxicity and Ways To Reduce It. Accounts Chem. Res. 2012 ,46, 672–680. [CrossRef] 44. Alavi, M.; Jabari, E.; Jabbari, E. Functionalized carbon-based nanomaterials and quantum dots with antibacterial activity: A review. Expert Rev. Anti. Infect. Ther. 2021,19, 35–44. [CrossRef] 45. Banerjee, I.; Mondal, D.; Martin, J.; Kane, R.S. Photoactivated Antimicrobial Activity of Carbon Nanotube − Porphyrin Conjugates. Langmuir 2010,26, 17369–17374. [CrossRef] 46. Hong, G.; Diao, S.; Antaris, A.L.; Dai, H. Carbon Nanomaterials for Biological Imaging and Nanomedicinal Therapy. Chem. Rev. 2015,115, 10816–10906. [CrossRef] [PubMed] 47. Badran, Z.; Rahman, B.; De Bonfils, P.; Nun, P.; Coeffard, V.; Verron, E. Antibacterial nanophotosensitizers in photodynamic therapy: An update. Drug Discov. Today 2023,28, 103493. [CrossRef] 48. Lee, D.; Kwon, S.; Jang, S.-Y.; Park, E.; Lee, Y.; Koo, H. Overcoming the obstacles of current photodynamic therapy in tumors using nanoparticles. Bioact. Mater. 2022,8, 20–34. [CrossRef] [PubMed] 49. Montaseri, H.; Kruger, C.; Abrahamse, H. Inorganic Nanoparticles Applied for Active Targeted Photodynamic Therapy of Breast Cancer. Pharmaceutics 2021,13, 296. [CrossRef] [PubMed] 50. Hong, E.J.; Choi, D.G.; Shim, M.S. Targeted and effective photodynamic therapy for cancer using functionalized nanomaterials. Acta Pharm. Sin. B 2016,6, 297–307. [CrossRef] [PubMed] 51. Kawczyk-Krupka, A.; Bugaj, A.M.; Latos, W.; Zaremba, K.; Wawrzyniec, K.; Kucharzewski, M.; Siero´n, A. Photodynamic therapy in colorectal cancer treatment—The state of the art in preclinical research. Photodiagnosis Photodyn. Ther. 2016 ,13, 158–174. [CrossRef] 52. Hodgkinson, N.; Kruger, C.A.; Abrahamse, H. Targeted photodynamic therapy as potential treatment modality for the eradication of colon cancer and colon cancer stem cells. Tumor Biol. 2017,39, 1010428317734691. [CrossRef] 53. Kaleta-Richter, M.; Kawczyk-Krupka, A.; Aebisher, D.; Bartusik-Aebisher, D.; Czuba, Z.; Cie´slar, G. The capability and potential of new forms of personalized colon cancer treatment: Immunotherapy and Photodynamic Therapy. Photodiagnosis Photodyn. Ther. 2019,25, 253–258. [CrossRef] 54. Evans, C.L. Three-dimensional in vitro cancer spheroid models for photodynamic therapy: Strengths and opportunities. Front. Phys. 2015,3, 15. [CrossRef] 55. Hanlon, J.G.; Adams, K.; Rainbow, A.J.; Gupta, R.S.; Singh, G. Induction of Hsp60 by Photofrin-mediated photodynamic therapy. J. Photochem. Photobiol. B Biol. 2001,64, 55–61. [CrossRef] Int. J. Mol. Sci. 2023,24, 12204 18 of 21 56. Leung, W.N.; Sun, X.; Mak, N.K.; Yow, C.M.N. Photodynamic Effects of MTHPC on Human Colon Adenocarcinoma Cells: Photocytotoxicity, Subcellular Localization and Apoptosis. Photochem. Photobiol. 2002,75, 406–411. [CrossRef] [PubMed] 57. Chiu, S.-M.; Xue, L.-Y.; Azizuddin, K.; Oleinick, N.L. Photodynamic therapy-induced death of HCT 116 cells: Apoptosis with or without Bax expression. Apoptosis 2005,10, 1357–1368. [CrossRef] 58. Kleban, J.; Szilárdiová, B.; Mikeš, J.; Horváth, V.; Saˇcková, V.; Brezáni, P.; Hofmanová, J.; Kozubík, A.; Fedoroˇcko, P. Pre-Treatment of HT-29 Cells with 5-LOX Inhibitor (MK-886) Induces Changes in Cell Cycle and Increases Apoptosis after Photodynamic Therapy with Hypericin. J. Photochem. Photobiol. B Biol. 2006,84, 79–88. [CrossRef] [PubMed] 59. Zawacka-Pankau, J.; Issaeva, N.; Hossain, S.; Pramanik, A.; Selivanova, G.; Podhajska, A.J. Protoporphyrin IX Interacts with Wild-type p53 Protein in Vitro and Induces Cell Death of Human Colon Cancer Cells in a p53-dependent and -independent Manner. J. Biol. Chem. 2007,282, 2466–2472. [CrossRef] 60. Bhatti, M.; Yahioglu, G.; Milgrom, L.R.; Garcia-Maya, M.; Chester, K.A.; Deonarain, M.P. Targeted photodynamic therapy with multiply-loaded recombinant antibody fragments. Int. J. Cancer 2007,122, 1155–1163. [CrossRef] 61. Peng, C.-L.; Lai, P.-S.; Lin, F.-H.; Wu, S.Y.-H.; Shieh, M.-J. Dual chemotherapy and photodynamic therapy in an HT-29 human colon cancer xenograft model using SN-38-loaded chlorin-core star block copolymer micelles. Biomaterials 2009 ,30, 3614–3625. [CrossRef] 62. Gariboldi, M.B.; Ravizza, R.; Baranyai, P.; Caruso, E.; Banfi, S.; Meschini, S.; Monti, E. Photodynamic effects of novel 5,15-diaryltetrapyrrole derivatives on human colon carcinoma cells. Bioorganic Med. Chem. 2009,17, 2009–2016. [CrossRef] 63. Hu, Z.; Pan, Y.; Wang, J.; Chen, J.; Li, J.; Ren, L. Meso-tetra (carboxyphenyl) porphyrin (TCPP) nanoparticles were internalized by SW480 cells by a clathrin-mediated endocytosis pathway to induce high photocytotoxicity. Biomed. Pharmacother. 2009 , 63, 155–164. [CrossRef] 64. Ferreira, C.S.M.; Cheung, M.C.; Missailidis, S.; Bisland, S.; Gariépy, J. Phototoxic aptamers selectively enter and kill epithelial cancer cells. Nucleic Acids Res. 2009,37, 866–876. [CrossRef] 65. Lim, Y.-C.; Yoo, J.-O.; Park, D.; Kang, G.; Hwang, B.-M.; Kim, Y.-M.; Ha, K.-S. Antitumor effect of photodynamic therapy with chlorin-based photosensitizer DH-II-24 in colorectal carcinoma. Cancer Sci. 2009,100, 2431–2436. [CrossRef] [PubMed] 66. Kulbacka, J.; Chwiłkowska, A.; Bar, J.; Poła, A.; Bana´s, T.; Gamian, A.; Saczko, J. Oxidative alterations induced in vitro by the photodynamic reaction in doxorubicin-sensitive (LoVo) and -resistant (LoVoDX) colon adenocarcinoma cells. Exp. Biol. Med. 2010 , 235, 98–110. [CrossRef] [PubMed] 67. Xu, C.; Leung, A.; Liu, L.; Xia, X. LED-activated pheophorbide a induces cellular destruction of colon cancer cells. Laser Phys. Lett. 2010,7, 544–548. [CrossRef] 68. Simon, V.; Devaux, C.; Darmon, A.; Donnet, T.; Thiã © Not, E.; Germain, M.; Honnorat, J.; Duval, A.; Pottier, A.; Borghi, E.; et al. Pp IX Silica Nanoparticles Demonstrate Differential Interactions with In Vitro Tumor Cell Lines and In Vivo Mouse Models of Human Cancers. Photochem. Photobiol. 2010,86, 213–222. [CrossRef] [PubMed] 69. Tanaka, M.; Kataoka, H.; Mabuchi, M.; Sakuma, S.; Takahashi, S.; Tujii, R.; Akashi, H.; Ohi, H.; Yano, S.; Morita, A.; et al. Anticancer effects of novel photodynamic therapy with glycoconjugated chlorin for gastric and colon cancer. Anticancer. Res. 2011,31, 763–769. [PubMed] 70. Maduray, K.; Odhav, B. Efficacy of Gallium Phthalocyanine as a Photosensitizing Agent in Photodynamic Therapy for the Treatment of Cancer. In Optics in Health Care and Biomedical Optics V; Luo, Q., Gu, Y., Li, X.D., Eds.; SPIE: Bellingham, WA, USA, 2012; Volume 8553, p. 85530G. 71. Manoto, S.L.; Sekhejane, P.R.; Houreld, N.N.; Abrahamse, H. Localization and phototoxic effect of zinc sulfophthalocyanine photosensitizer in human colon (DLD-1) and lung (A549) carcinoma cells ( in vitro ). Photodiagnosis Photodyn. Ther. 2012 ,9, 52–59. [CrossRef] 72. Weyergang, A.; Selbo, P.K.; Berg, K. Sustained EKR inhibition by EGFR targeting therapies is a predictive factor for synergistic cytotoxicity with PDT as neoadjuvant therapy. Biochim. Biophys. Acta Gen. Subj. 2013,1830, 2659–2670. [CrossRef] 73. Wei, M.-F.; Chen, M.-W.; Chen, K.-C.; Lou, P.-J.; Lin, S.Y.-F.; Hung, S.-C.; Hsiao, M.; Yao, C.-J.; Shieh, M.-J. Autophagy promotes resistance to photodynamic therapy-induced apoptosis selectively in colorectal cancer stem-like cells. Autophagy 2014 , 10, 1179–1192. [CrossRef] [PubMed] 74. Li, P.-T.; Ke, E.-S.; Chiang, P.-C.; Tsai, T. ALAor Ce6-PDT induced phenotypic change and suppressed migration in surviving cancer cells. J. Dent. Sci. 2015,10, 74–80. [CrossRef] 75. Ziółkowska, B.; Wo´zniak, M.; Ziółkowski, P. Co-expression of autophagic markers following photodynamic therapy in SW620 human colon adenocarcinoma cells. Mol. Med. Rep. 2016,14, 2548–2554. [CrossRef] [PubMed] 76. Abdulrehman, G.; Xv, K.; Li, Y.; Kang, L. Effects of meta-tetrahydroxyphenylchlorin photodynamic therapy on isogenic colorectal cancer SW480 and SW620 cells with different metastatic potentials. Lasers Med. Sci. 2018,33, 1581–1590. [CrossRef] [PubMed] 77. Ballestri, M.; Caruso, E.; Guerrini, A.; Ferroni, C.; Banfi, S.; Gariboldi, M.; Monti, E.; Sotgiu, G.; Varchi, G. Core–shell poly-methyl methacrylate nanoparticles covalently functionalized with a non-symmetric porphyrin for anticancer photodynamic therapy. J. Photochem. Photobiol. B 2018,186, 169–177. [CrossRef] 78. Liang, X.; Chen, M.; Bhattarai, P.; Hameed, S.; Dai, Z. Perfluorocarbon@Porphyrin Nanoparticles for Tumor Hypoxia Relief to Enhance Photodynamic Therapy against Liver Metastasis of Colon Cancer. ACS Nano 2020 ,14, 13569–13583. [CrossRef] [PubMed] Int. J. Mol. Sci. 2023,24, 12204 19 of 21 79. Ding, D.; Zhong, H.; Liang, R.; Lan, T.; Zhu, X.; Huang, S.; Wang, Y.; Shao, J.; Shuai, X.; Wei, B. Multifunctional Nanodrug Mediates Synergistic Photodynamic Therapy and MDSCs-Targeting Immunotherapy of Colon Cancer. Adv. Sci. 2021 ,8, 2100712. [CrossRef] 80. Karshieva, S.S.; Glinskaya, E.G.; Dalina, A.A.; Akhlyustina, E.V.; Makarova, E.A.; Khesuani, Y.D.; Chmelyuk, N.S.; Abakumov, M.A.; Khochenkov, D.A.; Mironov, V.A.; et al. Antitumor activity of photodynamic therapy with tetracationic derivative of synthetic bacteriochlorin in spheroid culture of liver and colon cancer cells. Photodiagnosis Photodyn. Ther. 2022,40, 103202. [CrossRef] 81. Montaseri, H.; Simelane, N.W.N.; Abrahamse, H. Zinc Phthalocyanine Tetrasulfonate-Loaded Ag@mSiO2 Nanoparticles for Active Targeted Photodynamic Therapy of Colorectal Cancer. Front. Nanotechnol. 2022,4, 928010. [CrossRef] 82. Simelane, N.W.N.; Matlou, G.G.; Abrahamse, H. Photodynamic Therapy of Aluminum Phthalocyanine Tetra Sodium 2Mercaptoacetate Linked to PEGylated Copper–Gold Bimetallic Nanoparticles on Colon Cancer Cells. Int. J. Mol. Sci. 2023 , 24, 1902. [CrossRef] 83. Chilakamarthi, U.; Mahadik, N.S.; Koteshwar, D.; Krishna, N.V.; Giribabu, L.; Banerjee, R. Potentiation of novel porphyrin based photodynamic therapy against colon cancer with low dose doxorubicin and elucidating the molecular signalling pathways responsible for relapse. J. Photochem. Photobiol. B Biol. 2023,238, 112625. [CrossRef] 84. Shin, Y.-K.; Park, Y.-R.; Lee, H.; Choi, Y.; Eom, J.B. Real-Time Monitoring of Colorectal Cancer Location and Lymph Node Metastasis and Photodynamic Therapy Using Fucoidan-Based Therapeutic Nanogel and Near-Infrared Fluorescence Diagnostic– Therapy System. Pharmaceutics 2023,15, 930. [CrossRef] 85. D’Hallewin, M.; Helle, M.; Garrier, J.; Bezdetnaya, L.; Guillemin, F. Animal Models for Photodiagnosis and Photodynamic Therapy. Isr. J. Chem. 2012,52, 706–714. [CrossRef] 86. Silva, Z.S.; Bussadori, S.K.; Fernandes, K.P.S.; Huang, Y.-Y.; Hamblin, M.R. Animal models for photodynamic therapy (PDT). Biosci. Rep. 2015,35, e00265. [CrossRef] 87. Yu, R.; Maswikiti, E.P.; Yu, Y.; Gao, L.; Ma, C.; Ma, H.; Deng, X.; Wang, N.; Wang, B.; Chen, H. Advances in the Application of Preclinical Models in Photodynamic Therapy for Tumor: A Narrative Review. Pharmaceutics 2023 ,15, 197. [CrossRef] [PubMed] 88. Olek, M.; Machorowska-Pieni ˛a˙ zek, A.; Olek, K.; Cie´slar, G.; Kawczyk-Krupka, A. Photodynamic therapy in the treatment of oral squamous cell carcinoma—The state of the art in preclinical research on the animal model. Photodiagnosis Photodyn. Ther. 2021 , 34, 102236. [CrossRef] [PubMed] 89. Ruggeri, B.A.; Camp, F.; Miknyoczki, S. Animal models of disease: Pre-clinical animal models of cancer and their applications and utility in drug discovery. Biochem. Pharmacol. 2014,87, 150–161. [CrossRef] 90. Méry, B.; Rancoule, C.; Guy, J.-B.; Espenel, S.; Wozny, A.-S.; Battiston-Montagne, P.; Ardail, D.; Beuve, M.; Alphonse, G.; Rodriguez-Lafrasse, C.; et al. Preclinical models in HNSCC: A comprehensive review. Oral Oncol. 2017,65, 51–56. [CrossRef] 91. Whitacre, C.M.; Feyes, D.K.; Satoh, T.; Grossmann, J.; Mulvihill, J.W.; Mukhtar, H.; Oleinick, N.L. Photodynamic therapy with the phthalocyanine photosensitizer Pc 4 of SW480 human colon cancer xenografts in athymic mice. Clin. Cancer Res. 2000 , 6, 2021–2027. 92. Hajri, A.; Wack, S.; Meyer, C.; Smith, M.K.; Leberquier, C.; Kedinger, M.; Aprahamian, M. In Vitro and In Vivo Efficacy of Photofrin ® and Pheophorbide a, a Bacteriochlorin, in Photodynamic Therapy of Colonic Cancer Cells. Photochem. Photobiol. 2002 , 75, 140–148. [CrossRef] 93. Webber, J.; Leeson, B.; Fromm, D.; Kessel, D. Effects of photodynamic therapy using a fractionated dosing of mono-l-aspartyl chlorin e6 in a murine tumor. J. Photochem. Photobiol. B: Biol. 2005,78, 135–140. [CrossRef] 94. Saji, H.; Song, W.; Furumoto, K.; Kato, H.; Engleman, E.G. Systemic Antitumor Effect of Intratumoral Injection of Dendritic Cells in Combination with Local Photodynamic Therapy. Clin. Cancer Res. 2006,12, 2568–2574. [CrossRef] 95. Bugaj, A.; Kwitniewski, M.; Iani, V.; Juzeniene, A.; Juzenas, P.; Ma, L.W.; Moan, J. Photodynamic therapy with di-l-arginine protoporphyrinate on WiDr human colon adenocarcinoma xenografts in athymic nude mice. Photodiagnosis Photodyn. Ther. 2007 , 4, 237–241. [CrossRef] [PubMed] 96. Preise, D.; Oren, R.; Glinert, I.; Kalchenko, V.; Jung, S.; Scherz, A.; Salomon, Y. Systemic antitumor protection by vascular-targeted photodynamic therapy involves cellular and humoral immunity. Cancer Immunol. Immunother. 2009 ,58, 71–84. [CrossRef] [PubMed] 97. Sanovic, R.; Verwanger, T.; Hartl, A.; Krammer, B. Low dose hypericin-PDT induces complete tumor regression in BALB/c mice bearing CT26 colon carcinoma. Photodiagnosis Photodyn. Ther. 2011,8, 291–296. [CrossRef] [PubMed] 98. Poyer, F.; Thomas, C.D.; Garcia, G.; Croisy, A.; Carrez, D.; Maillard, P.; Lupu, M.; Mispelter, J. PDT induced bystander effect on human xenografted colorectal tumors as evidenced by sodium MRI. Photodiagnosis Photodyn. Ther. 2012 ,9, 303–309. [CrossRef] [PubMed] 99. Hatakeyama, T.; Murayama, Y.; Komatsu, S.; Shiozaki, A.; Kuriu, Y.; Ikoma, H.; Nakanishi, M.; Ichikawa, D.; Fujiwara, H.; Okamoto, K.; et al. Efficacy of 5-aminolevulinic acid-mediated photodynamic therapy using light-emitting diodes in human colon cancer cells. Oncol. Rep. 2013,29, 911–916. [CrossRef] 100. Bae, B.-C.; Yang, S.-G.; Jeong, S.; Lee, D.H.; Na, K.; Kim, J.M.; Costamagna, G.; Kozarek, R.A.; Isayama, H.; Deviere, J.; et al. Polymeric photosensitizer-embedded self-expanding metal stent for repeatable endoscopic photodynamic therapy of cholangiocarcinoma. Biomaterials 2014,35, 8487–8495. [CrossRef] Int. J. Mol. Sci. 2023,24, 12204 20 of 21 101. Tanaka, M.; Kataoka, H.; Yano, S.; Sawada, T.; Akashi, H.; Inoue, M.; Suzuki, S.; Inagaki, Y.; Hayashi, N.; Nishie, H.; et al. Immunogenic cell death due to a new photodynamic therapy (PDT) with glycoconjugated chlorin (G-chlorin). Oncotarget 2016 , 7, 47242–47251. [CrossRef] 102. Gao, S.; Wang, J.; Tian, R.; Wang, G.; Zhang, L.; Li, Y.; Li, L.; Ma, Q.; Zhu, L. Construction and Evaluation of a Targeted Hyaluronic Acid Nanoparticle/Photosensitizer Complex for Cancer Photodynamic Therapy. ACS Appl. Mater. Interfaces 2017 ,9, 32509–32519. [CrossRef] 103. Gavrina, A.I.; Shirmanova, M.V.; Aksenova, N.A.; Yuzhakova, D.V.; Snopova, L.B.; Solovieva, A.B.; Timashev, P.S.; Dudenkova, V.V.; Zagaynova, E.V. Photodynamic therapy of mouse tumor model using chlorin e6polyvinyl alcohol complex. J. Photochem. Photobiol. B Biol. 2018,178, 614–622. [CrossRef] 104. Peng, C.-L.; Lin, H.-C.; Chiang, W.-L.; Shih, Y.-H.; Chiang, P.-F.; Luo, T.-Y.; Cheng, C.-C.; Shieh, M.-J. Anti-angiogenic treatment (Bevacizumab) improves the responsiveness of photodynamic therapy in colorectal cancer. Photodiagnosis Photodyn. Ther. 2018 , 23, 111–118. [CrossRef] 105. Bretin, L.; Pinon, A.; Bouramtane, S.; Ouk, C.; Richard, L.; Perrin, M.; Chaunavel, A.; Carrion, C.; Bregier, F.; Sol, V.; et al. Photodynamic Therapy Activity of New Porphyrin-Xylan-Coated Silica Nanoparticles in Human Colorectal Cancer. Cancers 2019 , 11, 1474. [CrossRef] [PubMed] 106. Chiarante, N.; Duhalde Vega, M.; Valli, F.; Zotta, E.; Daghero, H.; Basika, T.; Bollati-Fogolin, M.; García Vior, M.C.; Marino, J.; Roguin, L.P. In Vivo Photodynamic Therapy with a Lipophilic Zinc(II) Phthalocyanine Inhibits Colorectal Cancer and Induces a Th1/CD8 Antitumor Immune Response. Lasers Surg. Med. 2021,53, 344–358. [CrossRef] [PubMed] 107. Huis in ‘t Veld, R.V.; Lara, P.; Jager, M.J.; Koning, R.I.; Ossendorp, F.; Cruz, L.J. M1-Derived Extracellular Vesicles Enhance Photodynamic Therapy and Promote Immunological Memory in Preclinical Models of Colon Cancer. J. Nanobiotechnol. 2022 , 20, 252. [CrossRef] 108. Ann Kruger, C.; Abrahamse, H. Targeted Photodynamic Therapy as Potential Treatment Modality for the Eradication of Colon Cancer. In Multidisciplinary Approach for Colorectal Cancer; IntechOpen: London, UK, 2019; Volume 39, pp. 1–17. 109. Kashtan, H.; Papa, M.Z.; Wilson, B.C.; Deutch, A.A.; Stern, H.S. Use of photodynamic therapy in the palliation of massive advanced rectal cancer. Dis. Colon Rectum 1991,34, 600–605. [CrossRef] 110. Loh, C.S.; Bliss, P.; Bown, S.G.; Krasner, N. Photodynamic Therapy for Villous Adenomas of the Colon and Rectum. Endoscopy 1994,26, 243–246. [CrossRef] [PubMed] 111. Mikvy, P.; Messmann, H.; Debinski, H.; Regula, J.; Conio, M.; MacRobert, A.; Spigelman, A.; Phillips, R.; Bown, S. Photodynamic therapy for polyps in familial adenomatous polyposis—A pilot study. Eur. J. Cancer 1995,31, 1160–1165. [CrossRef] 112. Taber, S.W.; Fingar, V.H.; Coots, C.T.; Wieman, T.J. Photodynamic therapy using mono-L-aspartyl chlorin e6 (Npe6) for the treatment of cutaneous disease: A Phase I clinical study. Clin. Cancer Res. 1998,4, 2741–2746. 113. M´ lkvy, P.; Messmann, H.; Regula, J.; Conio, M.; Pauer, M.; Millson, C.E.; MacRobert, A.J.; Bown, S.G. Photodynamic therapy for gastrointestinal tumors using three photosensitizers--ALA induced PPIX, Photofrin and MTHPC. A pilot study. Neoplasma 1998 , 45, 157–161. 114. Privalov, V.A.; Lappa, A.V.; Seliverstov, O.V.; Faizrakhmanov, A.B.; Yarovoy, N.N.; Kochneva, E.V.; Evnevich, M.V.; Anikina, A.S.; Reshetnicov, A.V.; Zalevsky, I.D.; et al. Clinical Trials of a New Chlorin Photosensitizer for Photodynamic Therapy of Malignant Tumors. In Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XI; Dougherty, T.J., Ed.; SPIE: Bellingham, WA, USA, 2002; Volume 4612, pp. 178–189. 115. Nakamura, T.; Fukui, H.; Ishii, Y.; Ejiri, K.; Ejiri, M. Photodynamic therapy with polypectomy for rectal cancer. Gastrointest. Endosc. 2003,57, 266–269. [CrossRef] 116. Hamdan, K.A.; Tait, I.S.; Nadeau, V.; Padgett, M.; Carey, F.; Steele, R.J. Treatment of Grade III Anal Intraepithelial Neoplasia With Photodynamic Therapy. Dis. Colon Rectum 2003,46, 1555–1559. [CrossRef] 117. Lustig, R.A.; Vogl, T.J.; Fromm, D.; Cuenca, R.; Alex Hsi, R.; D’Cruz, A.K.; Krajina, Z.; Turi´c, M.; Singhal, A.; Chen, J.C. A Multicenter Phase I Safety Study of Intratumoral Photoactivation of Talaporfin Sodium in Patients with Refractory Solid Tumors. Cancer 2003,98, 1767–1771. [CrossRef] [PubMed] 118. Vogl, T.J.; Eichler, K.; Mack, M.G.; Zangos, S.; Herzog, C.; Thalhammer, A.; Engelmann, K. Interstitial photodynamic laser therapy in interventional oncology. Eur. Radiol. 2004,14, 1063–1073. [CrossRef] [PubMed] 119. van Duijnhoven, F.H.; Rovers, J.P.; Engelmann, K.; Krajina, Z.; Purkiss, S.F.; Zoetmulder, F.A.N.; Vogl, T.J.; Terpstra, O.T. Photodynamic Therapy With 5,10,15,20-Tetrakis(m-Hydroxyphenyl) Bacteriochlorin for Colorectal Liver Metastases Is Safe and Feasible: Results From a Phase I Study. Ann. Surg. Oncol. 2005,12, 808–816. [CrossRef] [PubMed] 120. Hahn, S.M.; Fraker, D.L.; Mick, R.; Metz, J.; Busch, T.M.; Smith, D.; Zhu, T.; Rodriguez, C.; Dimofte, A.; Spitz, F.; et al. A Phase II Trial of Intraperitoneal Photodynamic Therapy for Patients with Peritoneal Carcinomatosis and Sarcomatosis. Clin. Cancer Res. 2006,12, 2517–2525. [CrossRef] 121. Allison, R.R.; Sheng, C.; Cuenca, R.; Bagnato, V.S.; Austerlitz, C.; Sibata, C.H. Photodynamic therapy for anal cancer. Photodiagnosis Photodyn. Ther. 2010,7, 115–119. [CrossRef] [PubMed] 122. Welbourn, H.; Duthie, G.; Powell, J.; Moghissi, K. Can photodynamic therapy be the preferred treatment option for anal intraepithelial neoplasia? Initial results of a pilot study. Photodiagnosis Photodyn. Ther. 2014,11, 20–21. [CrossRef] 123. Sun, B.; Li, W.; Liu, N. Curative effect of the recent photofrin photodynamic adjuvant treatment on young patients with advanced colorectal cancer. Oncol. Lett. 2016,11, 2071–2074. [CrossRef] Int. J. Mol. Sci. 2023,24, 12204 21 of 21 124. Zhang, S.-Q.; Liu, K.-J.; Yao, H.-L.; Lei, S.-L.; Lei, Z.-D.; Yi, W.-J.; Xiong, L.; Zhao, H. Photodynamic therapy as salvage therapy for residual microscopic cancer after ultra-low anterior resection: A case report. World J. Clin. Cases 2019,7, 798–804. [CrossRef] 125. Kruger, C.A.; Abrahamse, H. Utilisation of Targeted Nanoparticle Photosensitiser Drug Delivery Systems for the Enhancement of Photodynamic Therapy. Molecules 2018,23, 2628. [CrossRef] [PubMed] 126. Qiu, H.; Tan, M.; Ohulchanskyy, T.Y.; Lovell, J.F.; Chen, G. Recent Progress in Upconversion Photodynamic Therapy. Nanomaterials 2018,8, 344. [CrossRef] 127. Shen, Y.; Shuhendler, A.J.; Ye, D.; Xu, J.-J.; Chen, H.-Y. Two-photon excitation nanoparticles for photodynamic therapy. Chem. Soc. Rev. 2016,45, 6725–6741. [CrossRef] 128. Gao, W.; Wang, Z.; Lv, L.; Yin, D.; Chen, D.; Han, Z.; Ma, Y.; Zhang, M.; Yang, M.; Gu, Y. Photodynamic Therapy Induced Enhancement of Tumor Vasculature Permeability Using an Upconversion Nanoconstruct for Improved Intratumoral Nanoparticle Delivery in Deep Tissues. Theranostics 2016,6, 1131–1144. [CrossRef] 129. Xu, J.; Yang, P.; Sun, M.; Bi, H.; Liu, B.; Yang, D.; Gai, S.; He, F.; Lin, J. Highly Emissive Dye-Sensitized Upconversion Nanostructure for Dual-Photosensitizer Photodynamic Therapy and Bioimaging. ACS Nano 2017,11, 4133–4144. [CrossRef] 130. Xu, J.; Gulzar, A.; Liu, Y.; Bi, H.; Gai, S.; Liu, B.; Yang, D.; He, F.; Yang, P. Integration of IR-808 Sensitized Upconversion Nanostructure and MoS 2 Nanosheet for 808 nm NIR Light Triggered Phototherapy and Bioimaging. Small 2017 ,13, 1701841. [CrossRef] 131. Chu, Z.; Tian, T.; Tao, Z.; Yang, J.; Chen, B.; Chen, H.; Wang, W.; Yin, P.; Xia, X.; Wang, H.; et al. Upconversion Nanoparticles@AgBiS2 Core-Shell Nanoparticles with Cancer-Cell-Specific Cytotoxicity for Combined Photothermal and Photodynamic Therapy of Cancers. Bioact. Mater. 2022,17, 71–80. [CrossRef] 132. Kuipers, E.J.; Grady, W.M.; Lieberman, D.; Seufferlein, T.; Sung, J.J.; Boelens, P.G.; Van De Velde, C.J.H.; Watanabe, T. Colorectal Cancer. Nat. Rev. Dis. Prim. 2015,1, 51–58. [CrossRef] 133. Yuan, Z.; Fan, G.; Wu, H.; Liu, C.; Zhan, Y.; Qiu, Y.; Shou, C.; Gao, F.; Zhang, J.; Yin, P.; et al. Photodynamic therapy synergizes with PD-L1 checkpoint blockade for immunotherapy of CRC by multifunctional nanoparticles. Mol. Ther. 2021 ,29, 2931–2948. [CrossRef] [PubMed] 134. He, C.; Duan, X.; Guo, N.; Chan, C.; Poon, C.; Weichselbaum, R.R.; Lin, W. Core-shell nanoscale coordination polymers combine chemotherapy and photodynamic therapy to potentiate checkpoint blockade cancer immunotherapy. Nat. Commun. 2016 , 7, 12499. [CrossRef] 135. Xu, J.; Xu, L.; Wang, C.; Yang, R.; Zhuang, Q.; Han, X.; Dong, Z.; Zhu, W.; Peng, R.; Liu, Z. Near-Infrared-Triggered Photodynamic Therapy with Multitasking Upconversion Nanoparticles in Combination with Checkpoint Blockade for Immunotherapy of Colorectal Cancer. ACS Nano 2017,11, 4463–4474. [CrossRef] [PubMed] 136. McQuade, R.M.; Stojanovska, V.; Bornstein, J.C.; Nurgali, K. Colorectal Cancer Chemotherapy: The Evolution of Treatment and New Approaches. Curr. Med. Chem. 2017,24, 1537–1557. [CrossRef] [PubMed] 137. Su, M.; Tian, H.; Zhou, L.; Li, Q.; Wang, S.; Haung, C.; Nice, E.C.; Zheng, S.; Li, J. Brigatinib-repurposed chemo-photodynamic therapy nanoplatform via effective apoptosis against colorectal cancer. Mater. Des. 2023,226, 111613. [CrossRef] 138. Hashemkhani, M.; Demirci, G.; Bayir, A.; Muti, A.; Sennaroglu, A.; Hadi, L.M.; Yaghini, E.; Loizidou, M.; MacRobert, A.J.; Acar, H.Y. Cetuximab-Ag 2 S quantum dots for fluorescence imaging and highly effective combination of ALA-based photodynamic/chemo-therapy of colorectal cancer cells. Nanoscale 2021,13, 14879–14899. [CrossRef] [PubMed] 139. Chen, M.; Liang, X.; Gao, C.; Zhao, R.; Zhang, N.; Wang, S.; Chen, W.; Zhao, B.; Wang, J.; Dai, Z. Ultrasound Triggered Conversion of Porphyrin/Camptothecin-Fluoroxyuridine Triad Microbubbles into Nanoparticles Overcomes Multidrug Resistance in Colorectal Cancer. ACS Nano 2018,12, 7312–7326. [CrossRef] 140. Seo, S.-H.; Kim, B.-M.; Joe, A.; Han, H.-W.; Chen, X.; Cheng, Z.; Jang, E.-S. NIR-Light-Induced Surface-Enhanced Raman Scattering for Detection and Photothermal/Photodynamic Therapy of Cancer Cells Using Methylene Blue-Embedded Gold Nanorod@SiO2 Nanocomposites. Biomaterials 2014,35, 3309–3318. [CrossRef] 141. Wang, X.; Ouyang, X.; Chen, J.; Hu, Y.; Sun, X.; Yu, Z. Nanoparticulate photosensitizer decorated with hyaluronic acid for photodynamic/photothermal cancer targeting therapy. Nanomedicine 2019,14, 151–167. [CrossRef] [PubMed] 142. Yang, X.; Xue, X.; Luo, Y.; Lin, T.-Y.; Zhang, H.; Lac, D.; Xiao, K.; He, Y.; Jia, B.; Lam, K.S.; et al. Sub-100 nm, long tumor retention SN-38-loaded photonic micelles for tri-modal cancer therapy. J. Control. Release 2017,261, 297–306. [CrossRef] Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.