Surface-Modified Lyotropic Crystalline Nanoconstructs Bearing Doxorubicin and Buparvaquone Target Sigma Receptors through pH-Sensitive Charge Conversion to Improve Breast Cancer Therapy

In the current study, we aimed to develop lyotropic crystalline nanoconstructs (LCNs) based on poly(l-glutamic acid) (PLG) with a two-tier strategy. The first objective was to confer pH-responsive charge conversion properties to facilitate the delivery of both doxorubicin (DOX) and buparvaquone (BPQ) in combination (B + D@LCNs) to harness their synergistic effects. The second goal was to achieve targeted delivery to sigma receptors within the tumor tissues. To achieve this, we designed a pH-responsive charge conversion system using a polymer consisting of poly(ethylenimine), poly(l-lysine), and poly(l-glutamic acid) (PLG), which was then covalently coupled with methoxybenzamide (MBA) for potential sigma receptor targeting. The resulting B + D@LCNs were further modified by surface functionalization with PLG–MBA to confer both sigma receptor targeting and pH-responsive charge conversion properties. Our observations indicated that at physiological pH 7.4, P/B + D-MBA@LCNs exhibited a negative charge, while under acidic conditions (pH 5.5, characteristic of the tumor microenvironment), they acquired a positive charge. The particle size of P/B + D-MBA@LCNs was determined to be 168.23 ± 2.66 nm at pH 7.4 and 201.23 ± 1.46 nm at pH 5.5. The crystalline structure of the LCNs was confirmed through small-angle X-ray scattering (SAXS) diffraction patterns. Receptor-mediated endocytosis, facilitated by P/B + D-MBA@LCNs, was confirmed using confocal laser scanning microscopy and flow cytometry. The P/B + D-MBA@LCNs formulation demonstrated a higher rate of G2/M phase arrest (55.20%) compared to free B + D (37.50%) and induced mitochondrial depolarization (59.39%) to a greater extent than P/B + D@LCNs (45.66%). Pharmacokinetic analysis revealed significantly improved area under the curve (AUC) values for both DOX and BPQ when administered as P/B + D-MBA@LCNs, along with enhanced tumor localization. Tumor regression studies exhibited a substantial reduction in tumor size, with P/B + D-MBA@LCNs leading to 3.2- and 1.27-fold reductions compared to B + D and nontargeted P/B + D@LCNs groups, respectively. In summary, this two-tier strategy demonstrates substantial promise for the delivery of a drug combination through the prototype formulation. It offers a potential chemotherapeutic option by minimizing toxic effects on healthy cells while maximizing therapeutic efficacy.