Distinct In Vitro Effects of Liposomal and Nanostructured Lipid Nanoformulations with Entrapped Acidic and Neutral Doxorubicin on B16-F10 Melanoma and Walker 256 Carcinoma Cells

<b>Background:</b> Liposomes and, more recently, structured nanolipid particles have demonstrated effectiveness as carriers for delivering hydrophilic or lipophilic anticancer agents, enhancing their biocompatibility, bioavailability, and sustained release to target cells. <b>Objective:</b> Herein, four doxorubicin formulations-comprising either the acidic or neutral form-were encapsulated into liposomes (Lipo) or nanostructured lipid carriers (NLCs) and characterized in terms of size, entrapment efficiency, morphology, and effects on two cancer cell lines (melanoma B16-F10 and breast carcinoma Walker 256 cells). <b>Methods and Results:</b> While liposomal formulations containing acidic doxorubicin displayed IC₅₀ values ranging from 1.33 to 0.37 µM, NLC-based formulations, particularly NLC-Doxo@Ac, demonstrated enhanced cytotoxicity with IC₅₀ values as low as 0.58 µM. Neutral Doxorubicin demonstrated lower cytotoxicity in both the nanoformulations and cell lines. Differences were also observed in their internalization patterns, cell-cycle impact, and apoptotic/necrotic effects. Compared to liposomes, NLCs exhibited distinct internalization patterns and induced stronger cell-cycle arrest and necrosis, especially in melanoma cells. Notably, NLC-Doxo@Ac outperformed liposomal counterparts in melanoma cells, while liposomal formulations showed slightly higher efficacy in Walker cells. Early and late apoptosis were more pronounced in Walker cells, whereas necrosis was more prominent in melanoma B16-F10 cells, particularly with the nanolipid formulations. <b>Conclusions:</b> These results correlated positively with cell-cycle measurements, highlighting the potential of NLCs as an alternative to liposomes for the delivery of neutral or acidic doxorubicin, particularly in tumor types that respond poorly to conventional formulations.