ANTICANCER DRUGS FROM BCS CLASS II AND IV AND STRATEGIES FOR ENHANCING SOLUBILITY.

978-93-7143-560-4 183 Chapter - 13 ANTICANCER DRUGS FROM BCS CLASS II AND IV AND STRATEGIES FOR ENHANCING SOLUBILITY. Mr. Nitin B. Mahale Samarth College of Pharmacy, Belhe, Pune, Maharashtra, India. Mr. Ganesh J. Lamkhade Samarth Institute of Pharmacy, Belhe, Pune, Maharashtra, India. Mr. Ajay A. Bhagwat Samarth College of Pharmacy, Belhe, Pune, Maharashtra, India. Dr. Bipin R. Gandhi Samarth College of Pharmacy, Belhe, Pune, Maharashtra, India. Mr. Rohit R. Doke Jaihind College of Pharmacy, Vadgaon Sahani, Pune, Maharashtra, India. Corresponding author: Mr. Ajay A. Bhagwat Department of Pharmaceutics, Samarth College of Pharmacy, Belhe, Pune, Maharashtra, India. E-mail: bhagwataja[email protected] 1. Introduction Cancer remains one of the leading causes of morbidity and mortality worldwide, accounting for approximately 10 million deaths in 2023 according to the World Health Organization (1). Despite advances in cancer genomics, molecular diagnostics, and targeted therapies, poor aqueous solubility continues to be one of the major challenges in the ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 184 development and formulation of anticancer agents. Nearly 40% of currently marketed drugs and up to 60% of new chemical entities (NCEs) discovered through high-throughput screening exhibit poor water solubility, resulting in low oral bioavailability and variable therapeutic efficacy (2,3). Many anticancer drugs are lipophilic in nature, characterized by high molecular weight, aromaticity, and elevated log P values, which improve target binding but limit aqueous solubility (4,5). These physicochemical characteristics often lead to poor dissolution, erratic absorption, and unpredictable pharmacokinetic behavior (6). Consequently, therapeutic drug levels are difficult to achieve and maintain, necessitating higher doses that may increase systemic toxicity and adverse effects (7). Solubility is a critical determinant of a drug’s absorption and bioavailability, particularly for compounds classified under Biopharmaceutics Classification System (BCS) Class II and IV, where dissolution rate or solubility is the rate-limiting step in absorption (8). Therefore, improving the solubility and dissolution rate of poorly water-soluble anticancer drugs is essential to enhance bioavailability, therapeutic efficacy, and patient compliance (2,9). Traditional approaches such as particle size reduction, salt formation, and use of surfactants have been used to improve solubility; however, they often provide limited success with complex and highly hydrophobic molecules (10). Consequently, recent advancements in formulation technology—such as nanotechnologybased systems, solid dispersions, cyclodextrin complexation, cocrystallization, and self-emulsifying drug delivery systems (SEDDS)—have shown promising results in enhancing solubility and dissolution rates (11–15). These novel strategies not only improve physicochemical solubility but also contribute to controlled release, targeted delivery, and reduced systemic toxicity—addressing key limitations of conventional chemotherapy (16). Hence, a comprehensive understanding of solubility enhancement principles and technologies ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 185 is crucial for the successful development of modern anticancer drug formulations. Figure No.1: Anticancer drug and solubility 2. Approaches to Solubility Enhancement Enhancing the solubility of poorly water-soluble anticancer drugs is a crucial formulation challenge. Solubility improvement increases dissolution rate, absorption, and bioavailability, ultimately enhancing therapeutic efficacy and minimizing dose-related toxicity. Various conventional and advanced strategies have been developed to overcome solubility limitations depending on the drug’s physicochemical characteristics and route of administration (17,18). 2.1 Conventional Techniques 2.1.1 Particle Size Reduction Reducing particle size increases surface area, thereby improving dissolution rate as described by the Noyes–Whitney equation. Micronization, nanonization, and high-pressure homogenization are widely used for anticancer agents such as paclitaxel and docetaxel (19). However, nanoparticles may aggregate or undergo recrystallization during storage, affecting stability. ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 186 2.1.2 Salt Formation Salt formation is a simple and effective method for ionizable drugs. It enhances solubility by improving the drug’s ionization in aqueous media (20). Imatinib mesylate, for instance, exhibits higher solubility and better pharmacokinetic properties compared to its free base (21). However, this technique is unsuitable for non-ionizable compounds and may affect stability or cause irritation. 2.1.3 pH Adjustment and Buffering Adjusting pH to maintain the drug in its ionized form increases aqueous solubility, particularly in parenteral formulations (22). Buffer systems are often incorporated to stabilize the solution; however, physiological pH constraints limit their application. 2.1.4 Co-solvency Co-solvents such as ethanol, polyethylene glycol (PEG), propylene glycol, and glycerol reduce solvent polarity, allowing dissolution of hydrophobic drugs (23). The commercial paclitaxel formulation Taxol® employs Cremophor EL and ethanol as co-solvents to achieve solubilization (24). Nonetheless, co-solvents can cause irritation or toxicity upon administration and must be used cautiously. 2.1.5 Surfactant Solubilization Surfactants enhance solubility by forming micelles that encapsulate hydrophobic drug molecules. Common surfactants include Tween 80, Poloxamer 188, and Cremophor EL (25). This technique has been applied successfully in the formulation of several anticancer drugs, including docetaxel and paclitaxel. However, certain surfactants may cause hypersensitivity or neurotoxic effects. 2.2 Advanced and Novel Techniques 2.2.1 Cyclodextrin Complexation Cyclodextrins (CDs) are cyclic oligosaccharides that form inclusion complexes with hydrophobic drugs, improving solubility and stability ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 187 (10). β-Cyclodextrin complexes of anticancer agents such as camptothecin and docetaxel have demonstrated enhanced solubility and bioavailability. Cyclodextrin-based inclusion complexes are particularly attractive due to their biocompatibility and ease of preparation. 2.2.2 Solid Dispersions In solid dispersions, the drug is dispersed in a hydrophilic polymeric carrier (e.g., PVP, HPMC, PEG) in an amorphous or molecularly mixed form, which enhances wettability and reduces crystallinity (25). This technique has been successfully used for anticancer drugs like tamoxifen and gefitinib, improving both dissolution rate and oral absorption. 2.2.3 Nanotechnology-Based Systems Nanotechnology-based systems—such as liposomes, polymeric nanoparticles, solid lipid nanoparticles (SLNs), and nanostructured lipid carriers (NLCs)—enhance solubility, permeability, and targeted delivery (19). Liposomal doxorubicin (Doxil®) and albumin-bound paclitaxel (Abraxane®) are clinically approved examples that provide higher solubility and reduced toxicity. Table No.: 1 Anticancer Drugs Belonging to BCS Class II & IV with Solubility Enhancement Strategies Sr. No. BCS Class Drug Example Solubility Issue Solubility Enhancement Strategies 1 Class II Paclitaxel Poor aqueous solubility but high permeability Nanoformulations, lipid-based systems, cyclodextrin complexes, solid dispersions ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 188 2 Class II Docetaxel Low water solubility Polymeric micelles, nanoparticles, emulsions, inclusion complexes 3 Class II Erlotinib Poor water solubility Solid dispersion, pH adjustment, nanosuspensions 4 Class IV Imatinib Poor solubility & low permeability Salt formation, nanoparticles, bioenhancers 5 Class IV Dasatinib Very poor aqueous solubility Amorphous solid dispersions, lipid-based carriers 6 Class IV Topotecan Stability & solubility issues Prodrug approach, liposomes, pH modification 3. Future Trends and Perspectives The enhancement of anticancer drug solubility continues to be a critical area of research in pharmaceutical sciences. Although several traditional and modern formulation strategies have improved solubility and bioavailability, future innovations are expected to integrate nanotechnology, artificial intelligence (AI), and personalized medicine to design more effective and patient-specific therapies (26,27). One emerging trend is the development of smart nanocarrier systems that respond to physiological stimuli such as pH, temperature, redox potential, or enzymatic activity. These systems enable site-specific and controlled release of anticancer drugs, thereby improving therapeutic efficacy and minimizing systemic toxicity (28). For example, pH-sensitive liposomes and redox-responsive polymeric ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 189 nanoparticles are being designed to release drugs selectively within the tumor microenvironment. The application of computational modeling and AI-based algorithms is also transforming formulation design. Machine learning approaches can predict solubility, stability, and optimal excipient combinations, reducing experimental workload and accelerating drug development (29). Such in silico techniques are increasingly used to optimize solid dispersions, co-crystals, and nanosuspension formulations. Another promising direction is the use of biopolymer-based and hybrid delivery systems, which combine natural polymers, lipids, and inorganic nanomaterials to enhance solubility while maintaining biocompatibility. These multifunctional platforms can integrate diagnostic and therapeutic (theranostic) functions, enabling real-time monitoring of drug delivery and treatment response (30). Moreover, green formulation technologies, such as supercritical fluid processing and solvent-free manufacturing, are gaining importance due to their sustainability, scalability, and ability to produce stable, amorphous drug forms with improved solubility (31). 4. Analytical and Characterization Techniques Comprehensive analytical and characterization techniques are essential to evaluate the physicochemical properties, solubility improvement, and stability of anticancer drug formulations. These methods provide insights into particle size, crystallinity, molecular interactions, and dissolution behavior, which are critical for understanding the mechanisms behind solubility enhancement and ensuring product quality (32). 4.1 Spectroscopic Techniques 4.1.1 UV–Visible and FTIR Spectroscopy UV–Visible spectroscopy is widely employed to determine drug concentration, solubility, and dissolution rate. It provides a rapid and non-destructive quantification method for assessing solubility enhancement (33). ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 190 Fourier-transform infrared (FTIR) spectroscopy is used to identify possible interactions between the drug and excipients by detecting characteristic functional groups and hydrogen bonding patterns. This helps confirm the formation of complexes, solid dispersions, or cocrystals (34). 4.1.2 Nuclear Magnetic Resonance (NMR) Spectroscopy NMR spectroscopy provides detailed information on molecular structure and interaction patterns, particularly in inclusion complexes such as cyclodextrin–drug systems. It can confirm the presence and orientation of a drug molecule within the host cavity (34). 4.2 Thermal and Crystallinity Analysis 4.2.1 Differential Scanning Calorimetry (DSC) DSC is a powerful technique for evaluating the thermal behavior and crystallinity of drug formulations. A reduction or disappearance of the drug’s melting peak indicates transformation from crystalline to amorphous form, often associated with improved solubility (35). 4.2.2 X-Ray Diffraction (XRD) XRD analysis provides insight into the crystalline or amorphous nature of a formulation. Sharp peaks represent a crystalline structure, whereas diffused halos indicate amorphous character. This technique is crucial for confirming the physical state of solid dispersions or nanocrystalline formulations (35). 4.3 Microscopic and Particle Characterization 4.3.1 Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) SEM and TEM are used to observe surface morphology, particle size, and structural uniformity of nanoscale drug formulations. These tools help confirm successful particle size reduction and assess the shape and aggregation state of nanoparticles (36). ANTICANCER DRUGS ……… Mr. Nitin B. Mahale 191 4.3.2 Dynamic Light Scattering (DLS) DLS provides rapid and accurate measurement of particle size distribution and zeta potential, which are essential parameters for assessing stability and dispersion quality in nanocarrier-based formulations (36,37). 4.4 Dissolution and Solubility Studies Quantitative assessment of solubility enhancement is carried out through in vitro dissolution studies, which simulate physiological conditions. Data obtained help predict in vivo performance and guide formulation optimization (32,33,38). 5. Conclusion Poor aqueous solubility remains one of the most significant challenges in the development of effective anticancer drug formulations. Many chemotherapeutic and targeted agents exhibit hydrophobic characteristics, leading to poor dissolution, limited absorption, and reduced bioavailability. Consequently, solubility enhancement is not merely a formulation requirement but a crucial determinant of therapeutic success and patient safety. Conventional techniques such as particle size reduction, salt formation, co-solvency, and surfactant solubilization have provided practical yet limited solutions. However, the advent of advanced formulation strategies—including solid dispersions, cyclodextrin complexation, co-crystallization, self-emulsifying systems, and nanotechnologybased carriers—has revolutionized the ability to solubilize and deliver poorly soluble anticancer drugs with enhanced precision and efficacy. The integration of analytical and characterization tools such as FTIR, DSC, XRD, and electron microscopy provides critical insight into the physicochemical and structural transformations associated with solubility enhancement, ensuring product stability, reproducibility, and regulatory compliance. Looking forward, the future of solubility enhancement lies in multidisciplinary innovation, combining nanotechnology, artificial