The biopharmaceutical problems begin with the molecule itself. Tamoxifen is a synthetic nonsteroidal selective estrogen receptor modulator, classified as a Biopharmaceutical Classification System Class II drug, meaning low solubility combined with high permeability makes dissolution the rate-limiting step for absorption. Its log P value sits between six and seven, confirming extreme lipophilicity, while a tertiary amine group with a pKa of roughly 8.8 to 9.0 gives it pH-dependent solubility behavior. Its intrinsic aqueous solubility measures approximately 1.60 × 10⁻² mM. Even the clinically used citrate salt, which improves solubility relative to the free base, cannot fully escape dissolution-limited bioavailability. A stable crystal lattice further reduces thermodynamic solubility compared with amorphous forms, and conventional fixes such as micronization or salt modification often prove insufficient to optimize both solubility and release control.

Compounding these physicochemical headaches is a pharmacogenetic one. Tamoxifen’s most potent active metabolites, endoxifen and 4-hydroxytamoxifen, are formed through hepatic biotransformation that depends substantially on CYP2D6 activity, which partially explains why patients respond so differently to identical doses. The review is explicit on this point: nanoformulation should not be regarded as a strategy that inherently bypasses CYP2D6-dependent metabolic activation. Tamoxifen itself retains antiestrogenic and antiproliferative activity, so enhanced cellular uptake and intracellular exposure to the parent drug may themselves contribute to the increased antiproliferative effects observed in laboratory studies. Prolonged therapy also carries risks, including endometrial carcinoma and thromboembolic complications, making any delivery innovation subject to a careful benefit-risk assessment.

Nanotechnology offers several mechanisms that directly address these constraints. Reducing particle size to the nanoscale increases specific surface area and thins the diffusion layer, accelerating dissolution according to the Noyes-Whitney equation, while increased particle curvature can raise saturation solubility through the Kelvin effect. Controlled release becomes possible by tuning carrier characteristics such as molecular weight, degree of crystallinity, hydrophilic-lipophilic balance, and cross-linking density; in polymer nanoparticles, release typically reflects a combination of diffusion and matrix erosion. Tumor accumulation can occur passively through the enhanced permeability and retention effect, exploiting disrupted tumor vasculature and poor lymphatic drainage, and actively through surface ligands such as antibodies, peptides, sugars, or vitamins that bind receptors overexpressed on cancer cells. Encapsulation can also prolong circulation time, reduce premature biotransformation, and enable theranostic functions that combine therapy with real-time diagnostic monitoring.

Chitosan enters this picture as an unusual candidate. It is a linear cationic polysaccharide obtained by deacetylating chitin, the structural biopolymer found in crustacean exoskeletons, insects, and fungal cell walls, with industrial production typically drawing on waste from fish processing. Its backbone consists of β-(1→4)-linked D-glucosamine and N-acetyl-D-glucosamine units, and the ratio between them, described by the degree of deacetylation, drives significant heterogeneity in commercial and laboratory forms. Primary amino groups at the C-2 position become protonated at acidic pH, giving chitosan its unique cationic character among natural polysaccharides and explaining its pH-dependent solubility in weak organic acids. This feature underlies mucoadhesion, electrostatic interactions with biological membranes, and the ability to form polymer complexes and nanostructures, while the reactive amine and hydroxyl groups make it exceptionally flexible for chemical modification.

Native chitosan, however, carries real limitations for a drug like tamoxifen. Its solubility is limited and highly pH-dependent, so deprotonation under neutral and slightly alkaline conditions leads to aggregation and unpredictable release. Batch-to-batch variability in molecular weight and degree of deacetylation complicates standardization and regulatory evaluation. Non-functionalized chitosan offers limited control over drug loading, and in the absence of specific polymer-drug interactions, pronounced burst release is common. Upon systemic administration, nonspecific electrostatic interactions with plasma proteins and cell membranes can trigger rapid clearance or off-target accumulation. Most critically for tamoxifen, the predominantly hydrophilic polymer lacks distinct hydrophobic domains, so lipophilic drugs distribute unevenly within the matrix, yielding lower encapsulation efficiency and less stable delivery systems.

Chemical modification changes this calculus dramatically. In one widely cited study, researchers covalently conjugated chitosan with stearic acid to form an amphiphilic copolymer capable of self-assembling into polymeric micelles. Confirmed by FT-IR and NMR spectroscopy, the system demonstrated increased tamoxifen loading, controlled release, and significantly enhanced cytotoxicity against MCF-7 breast cancer cells compared with the free drug. In vivo pharmacokinetic studies showed a significant increase in the area under the concentration-time curve, prolonged half-life, and reduced clearance. Encapsulation efficiency exceeded 90 percent, attributed to hydrophobic interactions between stearic acid chains and the drug, supplemented by hydrogen bonds and van der Waals forces that retain the active substance within the micellar structure.

Graft polymerization offers a second powerful strategy. Chitosan-modified PLGA micelles containing tamoxifen achieved an entrapment efficiency of 89.78 ± 7.31 percent and a drug loading of 45 ± 4.24 percent, quantitative evidence that covalent hybrid modification improves tamoxifen incorporation. The same system exhibited a lower IC₅₀ than free drug and higher dermokinetic parameters in epidermis and dermis. Oleic acid-grafted carboxymethylated chitosan demonstrates that combining hydrophilic and hydrophobic functionalization produces amphiphilic micellar systems suited to hydrophobic antitumor agents. Recent Quality by Design work on polycaprolactone-chitosan hybrid nanocomposites yielded an optimized tamoxifen formulation with roughly 47 percent entrapment efficiency and a biphasic release profile, though biological evaluation remained limited to in vitro models against MCF-7 and 4T1 cells.

Surface engineering provides an alternative that leaves the chitosan backbone untouched. A direct comparison between uncoated and alginate-coated chitosan nanoparticles revealed that alginate increases particle size and flips surface charge from positive to negative while generally reducing encapsulation efficiency. The trade-off comes in release control: initial tamoxifen release under acidic conditions dropped from approximately 10 to 18 percent for uncoated nanoparticles to just 2 to 3 percent after alginate coating, followed by a more controlled pH-dependent profile. This suggests the alginate layer is particularly advantageous for oral administration, where protecting the carrier in the gastric environment and releasing drug in the intestine are desirable. In a separate hybrid approach, tamoxifen was completely released from unmodified porous silicon within six hours, whereas a chitosan/silica xerogel coating prolonged complete release to approximately seven days, showing that complementary material properties within a delivery architecture can provide substantially greater control than individual components.

Production method matters as much as chemistry. Ionotropic gelation, based on electrostatic interactions between protonated chitosan and multivalent anions such as tripolyphosphate, is simple and organic-solvent-free but often yields lower encapsulation efficiency for highly lipophilic molecules like tamoxifen. Particle size depends on chitosan concentration, molecular weight, TPP levels, pH, and mixing speed, with more vigorous blending producing smaller particles through rapid nucleus formation and limited aggregation. Self-assembly of amphiphilic derivatives forms micelle-like structures whose properties depend on degree of modification, concentration, and environmental conditions. Emulsion techniques, nanospray drying, and polyelectrolyte complexation with anionic polymers such as gellan gum round out the toolkit, with the latter producing biocompatible nanocapsules that showed increased cytotoxicity against MCF-7 cells compared with free drug.

Release kinetics from these systems typically follows a biphasic profile: an initial burst from surface-localized drug, then sustained diffusion-controlled release describable by Higuchi and Korsmeyer-Peppas models. The Korsmeyer-Peppas exponent n distinguishes Fickian diffusion from non-Fickian transport, and non-Fickian behavior is frequently observed in amphiphilic chitosan systems, reflecting combined diffusion and polymer relaxation. Modified derivatives with increased hydrophobicity show stronger drug retention, reducing burst release by stabilizing lipophilic molecules within hydrophobic cores. PEGylation of chitosan can prolong circulation and reduce recognition by the reticuloendothelial system, though the strategy carries the accelerated blood clearance effect from anti-PEG antibodies and the so-called PEG dilemma, where the hydrophilic coating limits cellular uptake and intracellular delivery.

In vitro evidence consistently shows that chitosan-based nanoparticles improve cellular uptake and antiproliferative effect, with increased cytotoxicity in MCF-7 lines attributed to greater intracellular accumulation. In vivo, polymeric nanocarriers appear to improve tissue distribution and tumor exposure. Combining tamoxifen with phloretin-loaded chitosan nanoparticles in DMBA-induced breast cancer mouse models produced synergistic anti-inflammatory and antiproliferative effects, including reductions in IL-6 and cyclin D1, improved histopathology, and increased tumor-cell apoptosis, though the specific contribution of the chitosan carrier itself was not isolated against blank nanoparticles. Hyaluronic acid-coated chitosan nanoparticles achieved 55 percent encapsulation efficiency for tamoxifen, adding another targeting dimension.

The review’s most sobering conclusion concerns the evidence base itself. Hydrophobic and amphiphilic modifications, particularly fatty acid-conjugated and graft-polymer systems, currently provide the most direct experimental support, while carboxymethylated, thiolated, and PEGylated derivatives are supported predominantly by studies with other hydrophobic drugs. Differences in nanoparticle composition, preparation methods, drug-to-polymer ratios, release conditions, and biological models preclude reliable quantitative comparison across studies, so apparent superiority of any strategy cannot yet be established. A gap also separates formulation optimization from clinical trials, since physicochemical advantages do not necessarily translate into improved therapeutic efficacy. Future work must systematically evaluate cellular uptake, pharmacokinetics, biodistribution, tumor accumulation, and antitumor efficacy in vivo, establishing rational structure-performance relationships. Modified chitosan nanocarriers represent a promising but underexplored platform for tamoxifen, and their development requires coordinated efforts across pharmaceutical technology, nanomedicine, and clinical pharmacology.

Subject of Research: Technological approaches to tamoxifen nanoformulation: emphasis on modified chitosan-based nanoparticles: a review

Article Title: Technological approaches to tamoxifen nanoformulation: emphasis on modified chitosan-based nanoparticles: a review

Article References: Argilashki, D. (2026). Technological approaches to tamoxifen nanoformulation: emphasis on modified chitosan-based nanoparticles: a review. Pharmacia, 73, Article e206326. https://doi.org/10.3897/pharmacia.73.e206326

Image Credits: AI Generated

DOI: 10.3897/pharmacia.73.e206326

Keywords: Technological, approaches, tamoxifen, nanoformulation, emphasis, modified, chitosan-based, nanoparticles, review, scientific research