Formulation and Comparative Characterization of SLNs and NLCs for Targeted Co-Delivery of Paclitaxel and Hydroxytyrosol Carboxylic Acid Esters Against Triple-Negative Breast Cancer

<b>Background:</b> The management of triple-negative breast cancer (TNBC) remains a therapeutic challenge due to the presence of multidrug resistance (MDR) and hypoxia-induced chemoresistance, both of which substantially reduce the efficacy of conventional chemotherapy. Although certain natural compounds have shown the ability to modulate these resistance mechanisms, their clinical application is hindered by poor solubility and limited bioavailability. Among such phenolic compounds, 7-hydroxytyrosol (HTyr)-a phenolic compound from olive oil and olive leaves-has been reported to modulate hypoxia-inducible factor-1 (HIF-1). <b>Methods:</b> In this study, we developed hyaluronic acid (HA)-decorated solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) for the targeted and synergistic co-delivery of paclitaxel (PTX) and hydroxytyrosol carboxylic acid esters (C_n-HTyrCA), precursors that share the antioxidant biphenolic moiety with HTyr. <b>Results:</b> Among the formulations tested, SLNs of trilaurin (TL) exhibited the highest entrapment efficiency (EE%), optimal average particle size, Zeta potential, and good colloidal stability. Of the synthesized C_n-HTyrCA derivatives, C₈- and C₁₀-HTyrCA showed superior loading capacity. In vitro release profiles indicated a sustained drug release pattern for both nanoparticles. HA decoration led to a marked increase in particle size and induced a shift in surface charge, confirming successful decoration and suggesting enhanced targeting potential via HA-CD44 interaction. Cytotoxicity assays conducted on MDA-MB-231 cells showed that PTX-loaded TL-SLNs exerted enhanced antitumor activity, particularly when HA-decorated, and a synergistic effect was observed upon co-administration with SLNs loaded with C₈-HTyrCA. <b>Conclusions:</b> Overall, our findings support the potential of SLN as a promising strategy to overcome key resistance mechanisms in TNBC, enabling reduced chemotherapeutic dosing and improving therapeutic outcomes.