Synthesis and Evaluation of GnRHa-paclitaxel Tumor-targeting Conjugates†

Abstract

Tumor targeting can be achieved by combining a chemotherapeutic agent with a targeting moiety,which recognizes tumor-specific or highly expressed receptors on cancer cells. GnRH receptor is over-expressed on various tumor cells but is barely expressed in healthy visceral organs which makes it possible to use GnRH analogues( GnRHa) as the targeting moieties to deliver cytotoxic agents. Two conjugates were synthesized by incorporating paclitaxel( PTX) into GnRH analogue which was synthesized in the solid phase,the conjugation of PTX with GnRH analogs was performed by thio-ether bond and disulfide bond as a linker. The purity of the conjugates was analyzed by high performance liquid chromatography( HPLC) and the structures of the conjugates were confirmed by high resolution mass spectrum( HRMS). The resulting conjugates 1 and 2both preserved the cytotoxic activity of PTX and also retained the high binding affinity of the peptide hormone portion of the conjugates. The high affinity indicated that the conjugates might be specifically delivered to tumor tissues or cells via endocytosis mediated by GnRH receptor. The results showed that more than 50%prototypes of conjugate 1 remained with incubating in human serum for 24 h which indicating a favorable stability.