Exploring rifamycin cytotoxic potential through targeted liposomal formulations

Drug repositioning is an alternative in the search for treatment of different ailments, including cancer. In this scenario, various antibiotics molecules might be promising due to their antiproliferative activity. This study aims to explore rifamycin, a well-know antibiotic that inhibit bacterial RNA synthesis, as a potential cytotoxic agent. For this, liposomes were chosen as nanocarriers for rifamycin delivery, once they can incorporate diverse drugs and be conjugated with antibodies aiming a tumor-targeted effect. Rifamycin- loaded liposomes (Rf-Lp) were produced by thin film formation, achieving particle size of 140 nm with PDI below 0.2. Rf-Lp presented physical and chemical stability for at least 21 days when stored at 4 °C and prevented rifamycin precipitation in physiological-like conditions (PBS at 37 °C). Blank and rifamycin-loaded liposomes presented a low hemolytic potential (hemolytic activity below 6% in all concentrations tested), confirming their biocompatibility for systemic drug delivery. Cytotoxic activity of rifamycin, in solution or encapsulated, was proven against a panel with six different tumor cells, and Rf-Lp showed greater activity in spheroids model, indicating that liposomal formulation may increase rifamycin penetration in a more complex environment. The monoclonal antibody 2C5 (mAb 2C5), that specifically binds to nucleosomes on tumor cell surfaces, was conjugated with Rf-Lp and significantly improved rifamycin cytotoxic activity in U87 and A549 cell lines specially after short exposition periods (15 to 120 min), suggesting that active targeting with mAb 2C5 improves cellular uptake and formulation efficacy. In conclusion, besides improving rifamycin stability and sustained release, liposome encapsulation proved to be a promising strategy, allowing functionalization with antibodies such as 2C5 to further enhance its targeted therapeutic potential.