| Purpose: Silibinin, is a natural compound, which has shown anticancer activity in various
malignancies. In this study, we evaluated the anticancer effects of silibinin in B16-F10 melanoma cells and
developed a novel thermoresponsive hydrogel for local delivery of this compound. Method: A
thermoresponsive hydrogel loaded with silibinin was prepared using triblock copolymers of poly[(α-benzyl
carboxylate--caprolactone)-co-(α-carboxyl--caprolactone)]ran-b-PEG-b-[(α-benzyl carboxylate--caprolactone)
-co-(α-carboxyl--caprolactone)]ran (PCBCL-b-PEG-b-PCBCL), namely PolyGelTM, and compared with a
Pluronic F-127 formulation of silibinin. Sol-gel transition temperature of hydrogels was measured by inverse
flow method and modulated differential scanning calorimetry (MDSC). Silibinin loading efficiency was
measured by HPLC. The MTT and clonogenic assays were used to assess the cytotoxicity and anti-proliferative
effects of silibinin on B16-F10 melanoma cells. Flow cytotmetry was used to quantify the induced level of
apoptosis and measure the intracellular level of activated STAT3 (pSTAT3) following silibinin treatment in
B16.F10 cells. The effects of silibinin on the activation of oncogenic proteins were also evaluated by western
blot. Results: Silibinin inhibited cell proliferation (IC50 = 67 μM), provoked cell cycle arrest, induced apoptosis,
suppressed key oncogenic pathways (i.e STAT3 and MEK/ERK), and enhanced the cytotoxic effects of
doxorubicin in B16-F10 cells. Both PolyGelTM and Pluronic F-127 hydrogels were effective in loading silibinin.
A lower drug release pattern within 24h, fitting first- order release kinetics, was observed for the release of
silibinin from both gels compared to free drug. PolyGelTM demonstrated enhanced percutaneous absorption of
silibinin through increasing mouse skin intracellular lipid fluidity as documented by DSC of skin following
PolyGelTM use. Silibinin loaded in PolyGel TM inhibited the growth of B16-F10 cells (IC50 = 30 μM) and
effectively suppressed pSTAT3 activity in B16-F10 cells at 10 μM. Conclusion: Our results imply a great
potential for PolyGel TM formulations of silibinin for local treatment of malignant melanoma |