α-Tocopherol succinate loaded nano-strutted lipid carriers improves antitumor activity of doxorubicin in breast cancer models in vivo

Combination-based chemotherapies have been the standard treatment for multiple solid tumors since the 1960s. Combined therapies where both agents have toxicity results in dose-limiting effects. alpha-tocopherol succinate (TS) is an analogue of vitamin E that exhibits antitumor properties in the absence of toxicity. Hence, its combination with a frontline chemotherapy, doxorubicin (DOX) is an alternative to increase antitumor efficacy. Therefore, the aim of this work was to evaluate the antitumor activity of nanostructed lipid carriers (NLC) loaded with TS and DOX. The NLC-TS-DOX were prepared, characterized and radiolabeled with technetium-99m. Cytotoxicity studies were performed in vitro, using two breast cancer cell lines, MDA-MB-231 and 4T1. Biodistribution and antitumor activity were evaluated in 4T1 tumor-bearing mice. The results showed that NLC-TS-DOX had a small diameter (85 nm) and a long blood clearance (T-1/2 beta = 1107.71 min) that consequently resulted in a higher tumor uptake compared to contralateral muscle for up to 48 h. Drug combination studies in MDA-MB-231 and 4T1 cells showed a combination index below 0.8 at ED50-90 for both cell lines. Interestingly, a high synergism was found at ED90 Antitumor activity showed a better control of tumor growth for animals treated with NLC-STDOX. The small particle size, along with the EPR effect and the controlled release of DOX from the particle, associated with the synergic combination between TS and DOX led to an increase of the antitumor efficacy. Therefore, NLC-TS-DOX can be considered a plausible alternative to improve antitumor efficacy in DOX therapeutic regimens.