PEG-farnesylthiosalicylate conjugate as a nanomicellar carrier for delivery of paclitaxel

S-trans, trans-farnesylthiosalicylic acid (FTS) is a synthetic small molecule that acts as a potent and especially nontoxic Ras antagonist. It inhibits both oncogenically activated Ras and growth factor receptor-mediated Ras activation, resulting in the inhibition of Ras-dependent tumor growth. In this work, an FTS conjugate with poly(ethylene glycol) (PEG) through a labile ester linkage, PEG_5K-FTS₂(L), was developed. PEG _5K-FTS₂ conjugate readily forms micelles in aqueous solutions with a critical micelle concentration of 0.68 μM, and hydrophobic drugs such as paclitaxel (PTX) could be effectively loaded into these particles. Both drug-free and PTX-loaded micelles were spherical in shape with a uniform size of 20-30 nm. The release of PTX from PTX-loaded PEG_5K-FTS ₂ micelles was significantly slower than that from Taxol formulation. In vitro cytotoxicity studies with several tumor cell lines showed that PEG_5K-FTS₂(L) was comparable to FTS in antitumor activity. Western immunoblotting showed that total Ras levels were downregulated in several cancer cell lines treated with FTS or PEG_5K-FTS ₂(L). The micellar formulation of PTX exhibited more in vitro cytotoxic activity against several tumor cell lines compared with free PTX, suggesting a possible synergistic effect between the carrier and the codelivered drug. The antitumor activity of the PTX loaded PEG_5K-FTS ₂(L) micelles in a syngeneic murine breast cancer model was found to be significantly higher than that of Taxol, which may be attributed to their preferential tumor accumulation and a possible synergistic effect between PEG_5K-FTS₂ carrier and loaded PTX.