Novel Soluplus®—TPGS mixed micelles for encapsulation of paclitaxel with enhanced in vitro cytotoxicity on breast and ovarian cancer cell lines

• PTX was successfully encapsulated within Soluplus®:TPGS mixed micelles.
• The drug solubility in the mixed micelles was increased ∼38,000 times.
• Mixed micelles had better cytotoxic effect than PTX and single Soluplus® micelles.
• The presence of TPGS in the mixed micelles improved considerably the cellular uptake.

The aim of this work was to develop mixed micelles based on two biocompatible copolymers of polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol (Soluplus®) and D-α-tocopheryl polyethylene-glycol 1000 succinate (TPGS), to improve the aqueous solubility and the in vitro anti-tumor activity of paclitaxel (PTX). Pure and mixed nanomicelles were prepared by solvent evaporation method and characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Solubility of PTX was increased 60,000 and 38,000 times, when it was formulated in pure Soluplus® micelles and in mixed micelles (Soluplus®:TPGS; 4:1 ratio), respectively. The in vitro PTX release profile from micellar systems was characterized employing the dialysis membrane method where all drug-loaded formulations showed a sustained and slow release of PTX. In vitro assays were conducted on human cancer cell lines including ovarian cancer cells SKOV-3, breast cancer cells MCF-7 and triple negative breast cancer cells MDA-MB-231. Cytotoxicity studies showed that mixed micelles exhibited better antitumor activity compared to PTX solution against the three cell lines. Furthermore mixed micelles showed a significant increase on PTX cellular uptake in comparison with pure Soluplus® micelles and free drug in all cell lines assayed. More important, blank mixed micelles have shown cytotoxic activity due to the ability of TPGS to induce apoptosis in cancer cells. This effect was associated with the expression levels of cleaved-PARP, an apoptosis-related protein. On the basis of these results, the mixed micelles developed in this study might be a potential nano-drug delivery system for cancer chemotherapy.

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