Comparative Study of Fisetin-Loaded Poloxamer 407 and Poloxamer 188 Mixed Micelles as Nanocarrier Systems

Fisetin (FIS) is a bioactive flavonoid with antioxidant, anti-inflammatory, and anticancer activity, but its poor aqueous solubility and high lipophilicity limit its therapeutic use. In this study, three-component FIS-loaded mixed micelles based on Poloxamer 407 (P407) or Poloxamer 188 (P188), sodium deoxycholate, and Kolliphor HS15 or Kolliphor ELP were developed and comparatively evaluated. The formulations were prepared by the thin-film hydration method and characterized in terms of physicochemical properties, storage stability, solid-state properties, and in vitro biological activity. All freshly prepared formulations formed nanosized systems with high encapsulation efficiency. Although P188-based micelles showed smaller initial particle sizes, P407-based systems exhibited superior stability after lyophilization and rehydration. Formulations containing Kolliphor ELP showed the most favorable stability profile over 28 days of storage. FT-IR, TG, DSC, and XRPD analyses confirmed successful incorporation of FIS into the polymeric matrix and transformation of the drug into an amorphous or molecularly dispersed state. In vitro studies demonstrated that micellar encapsulation enhanced the cytotoxic activity of FIS against MICH-2 melanoma cells compared with the free compound, while P407-based systems showed a more favorable safety profile toward MRC-5 fibroblasts. These findings indicate that P407-based mixed micelles, particularly those containing Kolliphor ELP, may serve as promising nanocarriers for improving FIS delivery with potential relevance for dermal and anticancer applications.