Paclitaxel-Loaded Folate-Coated pH-Sensitive Liposomes Enhance Cellular Uptake and Antitumor Activity

Paclitaxel (PTX) is a microtubule-stabilizing agent widely used to treat breast cancer. Nevertheless, the low solubility of the drug and the side effects of commercial formulations available limit its clinical use. In this way, our group recently described the preparation of PTX-loaded folate-coated long-circulating and pH-sensitive liposomes (SpHL-folate-PTX). Therefore, a proof-of-concept study was designed in order to demonstrate the feasibility of SpHL-folate-PTX against breast tumor cell line MDA-MB-231. Cellular uptake of the liposomes and PTX was evaluated. Apoptosis and cell cycle were analyzed by flow cytometry. In vivo antitumor activity was carried out in MDA-MB-231 tumor-bearing BALB/c nude mice. Cellular uptake assay showed a high cell delivery of PTX by SpHL-folate-PTX, which leads to superior cytotoxicity and activation of apoptosis pathways. The SpHL-folate-PTX treatment induces an expressive increase of cells in the G0/G1 phase compared to free PTX and SpHL-PTX (without folate). In vivo studies showed a significant reduction in the tumor growth and a lower uptake of a radiopharmaceutical in the scintigraphic images for the SpHL-folate-PTX group, suggesting its higher efficacy compared with free PTX and SpHL-PTX. Histomorphometric analyses demonstrated an increase in necrosis and inflammation areas in animals treated with SpHL-folate-PTX. A decrease in the proliferative cells and a higher percentage of apoptotic cells were observed by immunohistochemical analyses after the treatment with SpHL-folate-PTX. Therefore, the data confirmed the potential of SpHL-folate-PTX as an alternative antitumor therapy, especially for breast cancer.