Aptamer-drug conjugates: A new frontier in targeted cancer therapy

 Corresponding author: Afif Abyad Hossain Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Aptamer-drug conjugates: A new frontier in targeted cancer therapy Afif Abyad Hossain *, Md Roknuzzaman Faisal, Md Shorif Uddin, Adib Azwad Hossain, Nosib Khan and Md Inzamam Ul Haque School of Pharmaceutical Sciences, Zhengzhou University, Henan, China. World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 Publication history: Received on 03 April 2025; revised on 11 May 2025; accepted on 13 May 2025 Article DOI: https://doi.org/10.30574/wjbphs.2025.22.2.0503 Abstract Targeted cancer therapies strive to eliminate cancer cells while minimizing harm to healthy tissues. Aptamer-drug conjugate is one of the attractive alternatives in this field. ApDCs are a class of agents which utilize the high specificity of aptamers (a single-stranded DNA or RNA oligonucleotide with a high affinity for a target molecule) combined with the therapeutic potential of cytotoxic drugs. It results in the selective drug delivery into neoplastic cells. This review provides an overview of the recent development of new strategies utilizing ApDCs as next generation targeted cancer therapeutics (aiming to obtain improved therapeutic responses and to minimize off-target toxicities), which represent the main power over classical chemotherapeutics. Subsequent studies will seek to optimize the design of ApDCs and broaden their therapeutic use beyond cancer therapy. With the progress of research, ApDCs are predicted to have a greater role for the treatment of cancer in the future. Keywords: Aptamers; Aptamer-Drug Conjugates (ApDCs); Targeted Therapy; Cancer; Drug Delivery 1. Introduction Targeted cancer therapies aim to eliminate cancer cells while reducing detrimental effects on adjacent healthy tissues, establishing themselves as a crucial approach in oncology [1,2]. Molecular targeted therapy has revolutionized cancer treatment due to better therapeutic responses and less systemic toxicity [3]. Conventional therapies such as chemotherapy are frequently not specific enough, and cause general toxicity with reduced therapeutic effectiveness [4]. Chemotherapy is directed to retard cell growth and multiplication, but also causes toxic effects due to its effect on normal cells. Chemotoxicity is linked to systemic damage of DNA and inflammation in normal cells [5]. In this sense, to cope with these drawbacks, innovative approaches with high precision of delivery toward tumor cells are being studied and aptamer-drug conjugates are strongly considered as one of the most promising strategy [6,7]. Aptamers, which are often called “chemical antibodies,” are single-stranded DNA or RNA oligonucleotides that have high affinity and specificity for binding with a selected target molecule [8–12]. Apart from typical antibodies, aptamers have several advantages over antibodies, such as their small size, higher chemical stability, easy synthesis, low immunogenicity, penetration into tissues more quickly, and capacity to target a broader range of biomolecules, including those which are not accessible to antibody targeting. ApDCs exploit the distinctive attributes of aptamers to facilitate the direct delivery of cytotoxic agents to neoplastic cells [13,14].Through the association with aptamers, such conjugates may selectively concentrate in the targeted region of cancer cells, augmenting pharmacological efficacy while minimizing unintended adverse reactions [15]. By this targeted delivery system, there's a great potential for enhancing the efficacy of oncologic interventions and reducing the side effects usually associated with traditional therapeutic modalities [15]. World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 260 The effectiveness of ApDCs therapy is based on the selective recognition and binding of aptamer to its cognate target residing on the cancer cell surface and it is a consequence of a complex mechanism of action [16]. This selective activity is based on the “lock-and-key” mechanism where the special three-dimensional structure of the aptamer matches the three-dimensional structure of the target molecule such as protein or cell surface receptor overexpressed exclusively in cancer cells [17,18]. Conjointly, as the driving forces determining a strong and specific interaction, the binding forces are mainly manifested through electrostatic interactions, hydrogen bonds, hydrophobic interactions, π−π stacking effect and van der Waals interactions [19,20]. Once bound the ApDCs are internalized by receptor-mediated endocytosis, a process in which it is surrounded by the cell membrane to form a vesicle which assists the molecule in crossing the membrane and entering the cell along a transcellular pathway [21–23]. The internalizing mechanism mediated by ApDCs greatly minimizes systemic toxicity and off-target effects [24,25]. Recent preclinical and clinical research concerning ApDC has demonstrated significant promise for these conjugates. Numerous ApDCs have demonstrated effectiveness against several cancer types-including breast cancer, lung cancer, and leukemia [26–28]. Such findings indicated that ApDCs specifically target cancer cells, inhibit tumor growth, and prolong survival in animal model [29]. Moreover, aptamers can be easily altered and functionalized for designing custom ApDCs with specific features [30]. However, there are a number of issues that still need to be overcome before ApDCs can truly materialize [31] The primary challenge is the in-vivo stability of aptamers, particularly that of RNA-aptamers, which are easily cleaved by nucleases [32]. To address this challenge, researchers are investigating multiple approaches to enhance aptamer stability, including chemical modifications and usage of nuclease-resistant aptamer analogs [33,34]. Apart from its potential use in cancer treatment, ApDCs are also promising candidates for diagnostic, imaging, and drug delivery in other diseases [35]. Through their capacity to identify and quantify particular biomarkers within biological specimens, aptamers enhance the prospects for early disease identification and the advancement of personalized medical approaches. This review seeks to summarize the new and developing approaches using ApDCs as the next generation of targeted cancer therapeutics designed to enhance treatment response and decrease off-target toxicities relative to traditional approaches. Future studies are going to focus on solving problems in ApDCs development, improving its design and implementation, and expanding their uses beyond cancer treatment. ApDCs are anticipated to become increasingly important in combating cancer as research advances. 2. Mechanism Aptamer-Drug Conjugates (ApDCs) are a novel and extremely promising platform for targeted cancer therapy in which the high targeting specificity of aptamers is coupled with the strong therapeutic activities of a cytotoxic drug [15]. This is achieved through a sophisticated mechanism involving target recognition and binding, drug release triggered by specific stimuli, and several advantages over traditional antibody-drug conjugates (ADCs) [7,15]. 2.1. Target Recognition and Binding Aptamers, also known as “chemical antibodies,” are short single-stranded DNA or RNA oligonucleotides that exhibit extraordinary characteristics that enable them to bind to their target with high affinity and specificity [9].This specificity is based on a “lock-and-key” principle that the unique three-dimensional structure of the aptamer precisely complements the three-dimensional structure of the target molecule (cell surface receptors or proteins overexpressed in cancer cells, etc.) [17,18]. This covalent binding is further supported by electrostatic interactions, hydrogen bonding, hydrophobic interactions, and van der Waals forces to strengthen a stable and specific binding [15]. This sophisticated recognition capability enables ApDCs to preferentially accumulate within the tumor microenvironment, thereby specifically targeting neoplastic cells and delivering their therapeutic agents, all while sparing adjacent healthy tissues [15]. Several Potent aptamers have also been developed against a broad number of cancer-relevant targets such as AXL, CD133, EGFRvIII, PDGFR-α, PDGFR-β, indicating the versatility of aptamers in the treatment of cancer [37].The high specificity of aptamers surpasses that of antibodies, facilitating a reduction of side effects by avoiding off-target binding [15]. Firstly, the aptamer component, a short single-stranded oligonucleotide, selectively binds to the cell surface receptors or proteins expressed on cancer cells [13,37]. These aptamers, ranging from 20 to 100 nucleotides in length are usually selected through Systematic Evolution of Ligands by Exponential Enrichment (SELEX) [14,38]. This screening process guarantees that the aptamers are high affinity and specificity for the target molecules, such as protein, peptide or cellular structure relevant for cancer cells [38]. The aptamer recognizes its target and starts receptor-mediated World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 261 endocytosis, leading to the internalization of ApDC into the target cell, which is a determining factor to transfer the drug payload in the intracellular compartment where it is able to produce its therapeutic action. The specificity of this internalization process is a major asset of ApDCs, limiting off-target effects and lowering systemic toxicities [23]. Figure 1 Target Binding of Aptamer via Conformational change 2.2. Drug Release Mechanisms After binding, the ApDC is internalized inside the cell through receptor-mediated endocytosis where the cell membrane envelops the bound ApDC and forms a vesicle that carries the ApDC into the cell cytoplasm [23,39]. ApDCs have the advantage of precise internalization with few off-target effects and less systemic toxicity [23]. Following internalization of the ApDC, the release of its cytotoxic counterpart (payload) in the cell is the next step for the ApDCs to exert cytotoxic effects. After being released, the drug interferes with critical cellular pathways in the targeted cancer cells, which in turn leads to the death of the cell [40]. These effects are driven by the drugs used for the composition of the ApDCs, of which the most employed payloads are either conventional chemotherapeutics, like doxorubicin or paclitaxel, or novel targeted treatments, for example kinase inhibitors, or drugs inducing DNA lesions [40,41]. This unique biodistribution allows for a high local drug concentration and potentially diminishes the overall dosage required, which may enhance therapeutic effectiveness[42]. Figure 2 Receptor-mediated endocytosis of cytotoxic drugs. Aptamer-drug conjugates attach to their specific receptor and enter the cell through receptor-mediated endocytosis. Inside the lysosome, the drug is detached from the aptamer, released, and subsequently transported to the nucleus World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 262 Several ingenious mechanisms have been developed to achieve this, including enzymatic cleavage, pH sensitivity, and photo-triggered systems, ensuring that the drug is released at the right time and place to maximize its therapeutic effect [43]. Enzymatic cleavage is one such mechanism, exploiting the unique biochemical environment of tumors [44]. Tumors frequently display overexpression of certain enzymes, including lysosomal cathepsin B protease and matrix metalloproteinases (MMPs) [45,46]. ApDCs can be designed with linkers that are specifically cleaved by these enzymes, triggering drug release within the tumor microenvironment [17]. For example, gemcitabine, a common chemotherapeutic, has been conjugated to aptamers via a dendrimer structure and enzymatically cleavable linkers, allowing for controlled intracellular drug release upon cleavage by lysosomal cathepsin B protease [47]. This localization strategy improves the therapeutic index of the drug by enriching it in the tumor itself and minimizing exposure to healthy tissue, which can mitigate many of the side effects that typically arise from conventional chemotherapy [13]. The improved pharmacokinetics and biodistribution of ApDCs, compared to free drugs, can lead to better tumor penetration and retention, known as the enhanced permeability and retention (EPR) effect, resulting in prolonged exposure of cancer cells to the therapeutic agent and potentially improving treatment outcomes [13]. pH-sensitive linkers are yet another option for controlled drug release [48]. Tumor tissues are frequently more acidic because of altered metabolism [49]. Different linkers can be utilized for designing the ApDCs that are stable at physiological pH, but become unstable and cleavable in an acidic tumor microenvironment, thus leading to drug release [48]. To enhance the drug release profiles associated with ApDCs, acid-labile linkers including the hydrazone, amide, imine, cis-acotinyl, oxime, ketal and acetal linkers have been employed [48]. Photo-triggered systems offer a high degree of spatial and temporal control over drug release [50]. These systems utilize light to activate the release of the drug from the ApDC [51]. Upon reaching the tumor site, the ApDC is exposed to light of a specific wavelength, which cleaves a light-sensitive linker and releases the drug. This method enables direct targeting of drug delivery to the tumor site, which is expected to reduce off-target effects [52]. The light-triggering mechanisms can involve changing the hydrophobicity of a nanocarrier constituent, introducing local defects within a nanocarrier, or bond cleavage. 3. Comparison with Antibody-Drug Conjugates ApDCs have a large number of advantages relative to antibody-drug conjugates or other targeted therapies. Aptamers are smaller in size than antibodies, which contributes to enhanced tissue penetration and accumulation in tumors [17,53]. They also exhibit lower immunogenicity, which minimizes immune-related side effects. Moreover, there is more control over production and modification of aptamers than there is over antibodies since aptamers are chemically synthesized [7,54]. Such benefits offer ApDCs, a potential alternative to ADCs for an effective therapy for cancer. 3.1. Comparison between Aptamers and Antibodies Table 1 In-Depth Comparison of Aptamers and Antibodies: Analyzing Nature, Size, Stability, and Functional Characteristics. Characteristic Aptamers Antibodies Nature Nucleic acid ligands (DNA/RNA-based) Protein-based molecules Size Small (~10–30 kDa, ~2 nm) Large (~150–170 kDa, ~15 nm) Molecular Weight ~6–30 kDa ~150–180 kDa Target Wide range, including small molecules, non-immunogenic compounds Mostly immune-related proteins Affinity High High Specificity High High Synthesis Simple (chemical synthesis, SELEX process) Complex (in vivo production using animal models) World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 263 Stability Stable at room temperature, denaturation is reversible Sensitive to temperature, requires refrigeration; denaturation is irreversible Modification Easily modified at both 5’ and 3’ ends Limited modifications, may affect function Storage Term Long Relatively short Development Time Short (~1–3 months) Long (~4–6 months) Production Time Several weeks (~1–3 months) Several months (~4–6 months) Generation Time Few hours to months Several months In Vivo Half-life Short (~20 min) Long (~one month) Cost Low High Nuclease Degradation Sensitive Resistant Minimum Target Size ≥60 Daltons ≥600 Daltons Manufacturing Process Chemical synthesis (animal-free) In vivo (cell culture, requires immune response) Batch Consistency High Variable (depends on biological system) Immunogenicity Low (non-toxic, non-immunogenic) High Optimal Working Concentration ~5 to 10 times lower than antibodies in some applications Varies by application Secondary Structure Hairpin, stem-loop, G-quadruplex α-helix and β-fold Penetration Ability Can infiltrate tissues and cells Limited penetration Scalability Easy to scale up (chemical synthesis) Difficult to scale (biological production) Targeting Toxic Compounds Possible Difficult due to immune response Long-term Availability Sequence is digitally stored and chemically synthesized when needed Requires frozen cell stocks for production Target Potential Can bind very small, non-immunogenic, and toxic targets Requires an immune response, limiting target options Production Cost Lower cost, as aptamers are chemically synthesized Expensive due to complex in vivo processes Development Process Selected in vitro via SELEX, including positive and negative selection Requires immune response and animal models Optimal Working Concentration ~5 to 10 times lower than antibodies in some applications Varies widely by application World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 264 Figure 3 Structural comparison of aptamers and antibodies with protein binding 4. Recent Advances in ApDCs for Cancer Therapy Aptamer-drug conjugates represent a promising approach for targeted cancer therapy, providing benefits over traditional chemotherapy by directly delivering cytotoxic drugs to tumor locations, thereby reducing off-target effects [6,55]. Recent advances in aptamer development, conjugation strategies, and drug delivery systems have propelled ApDCs to the forefront of cancer research. 4.1. Specific ApDCs and Their Applications A certain number of ApDCs have been successful in preclinical and clinical trials [3]. For instance, studies have investigated the fabrication of ApDCs such as P19-dFdCMP, P19-5FdUMP, sgc8c-Dox and NucA-PTX [43,56,57]. Aptamer with chemotherapy drugs is a new approach for the targeted drug delivery to tumor cells, resulting in a higher targeting specificity, efficacy and therapeutic ratio [13]. The sgc8c aptamer with high binding affinity towards protein tyrosine kinase 7 (PTK-7) is applicable to drug delivery systems [58]. The sgc8c-Dox conjugate can prevent the nonspecific uptake of Dox, reducing cytotoxicity in non-targeted cells [59]. NucA-PTX has targeting effect to the tumor, PTX is localized in tumor and as soon as being taken up by cells, the dipeptide bond linker of NucA-PTX would be cleaved by cathepsin to release PTX [17,60]. 4.2. Novel Aptamer Targets Novel aptamer targets for cancer therapy have also been discovered [61,62]. Such as, nucleolin is a cell surface protein, it makes an ideal carrier for drug internalization, facilitating drug trafficking carrying relevant aptamers that bind to nucleolin [17,63]. Other potential targets are PSMA, HER2 and VEGF which are in progress for development of new ApDCs [64,65]. The aptamer–antibody conjugates induce the T cell response and leads to the destruction of cancer cells effectively [13]. 4.3. Improved Drug Delivery Systems Improved drug delivery systems that incorporate aptamers have further enhanced the therapeutic potential of ApDCs [66]. Plenty of aptamer-based targeted drug delivery systems, including aptamer-drug conjugation and aptamer-nano materials, have been established [14,67,68]. Advanced systems ensure the greatest degree of drug delivery efficiency, lowered toxicity and therapeutic effectiveness [69]. Expands on the application of bioconjugates of nanomaterials and aptamers to advance the development of promising cancer therapy methods [55,67]. In the following table, the discoveries of Aptamer-Drug Conjugates (ApDCs) as a promising targeted cancer treatment have been summarized recently, listing their specificity, therapeutic effectiveness and clinical translation. World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 265 Table 2 Recent Developments in Aptamer-Drug Conjugates (ApDCs) for Targeted Cancer Therapy Aptamer Target Drug Payload Cancer Type Study Findings Reference Sgc8c-Dox Protein Tyrosine Kinase 7 (PTK7) Doxorubicin Leukemia Enhanced drug uptake in cancer cells, reduced off-target toxicity. [65] AS1411Gem Nucleolin Gemcitabine Pancreatic Cancer Increased tumor accumulation, improved cytotoxic effects. [56] PSMA-AptPTX Prostate-Specific Membrane Antigen (PSMA) Paclitaxel Prostate Cancer Selective drug delivery, inhibition of tumor growth. [64] A10-3-Dox PSMA Doxorubicin Prostate Cancer Enhanced tumor penetration, improved survival rates. [17] EpCAMApt-Dox Epithelial Cell Adhesion Molecule (EpCAM) Doxorubicin Breast Cancer Targeted drug release, higher cytotoxicity in tumor cells. [39] NucAPTX Nucleolin Paclitaxel Lung and Breast Cancer Enzyme-triggered drug release, improved therapeutic index. [17] 5. Benefits of Aptamer-Drug Conjugates in Cancer Therapy Aptamer-drug conjugates exhibit a number of advantages over traditional chemotherapy and antibody-drug conjugates for cancer therapy. These advantages are owed to the intrinsic features of aptamers as targeting agents. 5.1. Enhanced Specificity and Reduced Off-Target Effects The high affinity and specificity of aptamers allow ApDCs to specifically bind to cancer cells, minimizing the toxicities of the cytotoxic drug to healthy tissues [26,70]. This approach results in significantly less off-target effects and toxicities with the greatest advantage of increased safety profile in the treatment of cancer [71]. Comparing to classical chemotherapeutic drug-based therapies, ApDCs provide better specificity and therapeutic advantages. This small size is around 15–20 fold smaller than that of antibodies, allowing for a better tissue penetration and higher accumulation within the tumor, increasing the targeted delivery of drugs [6,29]. 5.2. Lower Immunogenicity Compared to Antibodies The risk of inducing an immune response with ApDCs is less than with antibodies thus minimizing adverse effects and enhancing tolerability of the treatment [13,72]. The non-immunogenic nature of aptamers is crucial for ApDCs, particularly when repeated administrations are necessary, as it minimizes the development of neutralizing antibodies that could compromise treatment efficacy [26]. Preclinical and clinical trials suggest that oligonucleotides do not typically induce the development of neutralizing antibodies [73], and aptamers can shield viruses from these antibodies, allowing efficient delivery to tumor cells [74]. 5.3. Potential for Multifunctional Systems Aptamers can be conveniently modified and conjugated with many types of agents, including imaging and therapeutic moieties [17]. This adaptability allows for the creation of multifunctional ApDCs that integrate diagnostic imaging with targeted therapy in a single agent [75,76]. For instance, an innovative approach involves combining chemotherapy and immunotherapy through ApDCs labeled on bacteria, enhancing drug delivery and overcoming the tumor microenvironment's barriers [26]. These systems allow the real-time tracking of the delivery of drugs and the response to the treatment [61], which facilitates personalized medicine and the optimization of therapeutic outcomes [26]. World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 266 6. Challenges in ApDC Development 6.1. Limitations of Conventional Anticancer Drug Delivery Most anticancer agents lack specificity for cancerous cells, resulting in toxicity of surrounding healthy tissues and thus requiring lower doses for effective therapy [77]. Moreover, the upsurge of drug-resistant cells necessitates more selective treatments. Early approaches aimed at targeted drug delivery, relied on ligands based on polyunsaturated fatty acids, folic acid, hyaluronic acid and oligopeptides [77,78]. so as to overcome the limitations of each, including unclear tumortargeting mechanism, poor performance in conjugates of small size [78] and susceptibility to enzymatic degradation in circulation, they have thus limited application in vivo. However, unmodified aptamers are quickly degraded or lose their ability to specifically bind to the target, so we have modified aptamers as promising targeting agents to improve their stability in biological environments. SELEX to develop aptamers is a complicated workflow that usually relies on optimization [77,79] and has yet to meet the dual challenge of developing highly specific and highaffinity binding molecules. Therefore, aptamer-small molecule conjugates require efficient conjugation strategies to act as both carriers and ligands, whereas proper functionalization of aptamer-nanomaterial conjugates with nanoparticles is needed for effective targeting of these drugs. 6.2. Challenges in Developing Stable Aptamers for Therapeutic Use The development of clinically relevant aptamer-drug conjugates (ApDCs) is challenged by several issues. Aptamers, especially RNA-based aptamers, are prone to quick digestion by nucleases in physiological environment, a key problem is their stability in vivo [80]. These properties lead to short in vivo half-lives, which are typically less than 10 minutes [81], significantly limiting their therapeutic efficacy considerably. Various strategies have been developed for the stabilization of aptamers. Chemical modifications help to increase the resistance to nuclease degradation without a significant loss of target affinity [80]. TH2 leading to certain cytokines upregulating antibody production whilst others downregulate it such as TH1, B-cells undergo isotype switching which can lead to them producing IgG or IgM, however, if IgG is produced, conjugation occurs where the drug gets bound to a polymer, it can be a polymer like polyethylene glycol (PEG), this increases the molecular weight of the drug making it too large to be filtered through the kidneys, therefore increasing its half-life/circulation longevity. The inherent stability of aptamers can also be improved by optimizing their secondary structure [80]. 6.3. Optimization of Conjugation Chemistry for Effective Drug Delivery Another key issue is the optimization of the conjugation chemistry for drug loading efficiency. Manufacturing aptamers, they use the same sequences, so the conjugation process should retain aptamer affinity to effectively bind the target which is achieved through careful selection of conjugation sites and linkers [82]. Additionally, maintaining a balanced drug-to-aptamer ratio is crucial for uniform therapeutic outcome, thus homogeneous drug-to-aptamer ratio (DAR) preparations are highly favored [80]. These site-specific conjugation approaches provide more control over the properties of the ApDCs (e.g. stability and binding to the target), thereby enhancing their therapeutic potential [83]. 6.4. Scalability and Manufacturing Challenges in Clinical Applications Ultimately, challenges remain in ApDCs scalability and manufacture for clinical applications. Demonstrated high reproducibility is a prerequisite in large-scale aptamer synthesis that translates directly to the clinical setting by ensuring the quality and purity necessary for clinical use [80,82]. Addressing these issues is essential to move ApDCs from bench-based discovery to effective clinical agents. 7. Future Perspectives Although aptamer-drug conjugates have some shortcoming, they also offer great potential for targeted cancer treatment and continued research is progressing closer to an exciting future in this space. Furthermore, Increased interest in enhancing aptamer selection, mainly in enhancing SELEX approaches, is expected to generate more aptamers targeting cancer biomarkers with high specificity and affinity [84]. There are several significant domains that will influence ApDCs’ trajectories. 7.1. Combination Therapies ApDCs are a very promising approach with the potential to synergize with other treatment modalities. ApDCs have an exquisite specificity for their targets and the dual combination of ApDCs with immunotherapy could additionally enhance anti-tumor immune responses, whereas the dual combination of ApDCs with radiotherapy could improve World Journal of Biology Pharmacy and Health Sciences, 2025, 22(02), 259-276 267 tumor targeting while reducing off-target effects [6,84]. Other treatments involve the combination synthesize of above aptamers that are discussed in a chemotherapy study in cancer therapy. The high off-target effects of many chemotherapeutic agents limit how much can be administered due to adverse side effects in healthy tissues and what is considered the maximum tolerated dosage for conventional chemotherapy. The selective delivery of chemotherapeutics to cancer tissues holds potential to solve these complications [15]. Aptamers with Immunotherapies: The aptamers binding to the immune checkpoints including PD-L1, CTLA-4 etc., can be designed as either agonists (enhancing immunity) or antagonists (blocking the inhibitory signal) [85]. Combining with immune checkpoint inhibitors based on antibodies could achieve an even stronger and persistent immune response. Aptamers may be used for directly transporting checkpoint inhibitors of immune the system or other immune inflammatory agents to the tumor microenvironment to activate the local immune system and reduce systemic adverse reactions. Aptamer-mediated delivery of STING (stimulator of interferon genes) agonists to stimulate innate immunity in tumors, together with PD-1/PD-L1 blockade for enhanced adaptive immunity [86,87]. More studies are needed to investigate ideal combinations and administration options for further improving therapeutic efficacy [84]. 7.2. Aptamer Selection and modification Aptamer selection and modification technologies are advancing to improve the ApDCs performance and their clinical translatability [84]. Developing novel aptamers that have high-affinity and specificity for cancer-specific targets is essential [84]. SELEX, a Darwinian evolution-based screening method, is used for aptamer selection, where highaffinity and specific aptamers are enriched through iterative cycles of binding, separation, and amplification. SELEX starts with a pool of random oligonucleotide sequences that are incubated with a target, and the best binding sequences are retained for amplification in subsequent rounds. Advanced techniques, including CellSELEX and In Vivo SELEX, increase the specificity through direct selection of aptamers against target cells or within living organisms and are especially useful in identifying biomarkers and targeting diseases [88]. Although, Aptamer modifications improve binding affinity with Chemical modifications at sugar unit, nucleobase, or backbone for nuclease biostability, renal clearance as well as degradation. This problem was addressed by modifications of the 3′ terminus of the oligonucleotide such as 3′-Biotin and 3′-inverted thymidine, which showed a statistically significant improvement of the nuclease resistance, whereas 3′-inverted thymidine provides a major stability since the half-life of an affinity-enhanced aptamers can reach up to 72 hours in serum. 5′-Cholesterol and lipid-modified extend time circulation via reduced renal filtration, with cholesterol-conjugated aptamers showing ninefold longer half-life in plasma than their unmodified counterparts [88]. Additionally, novel modification strategies to improve their stability, cell uptake, and drug delivery efficiency will be essential in optimizing ApDCs design [89]. 7.3. 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Email id: nosibkhan[email protected] Md Inzamam Ul Haque School of Pharmaceutical Sciences, Zhengzhou University, Henan, China. Email id: inzamam1[email protected]