Synthesis of folic conjugated LR octapeptide

Ovarian cancer is the fifth cause of death from cancer and the most common cause of death from gynecologic cancer in women of all ages in the Western world. The standard first-line treatment is a combination of paclitaxel and carboplatin or carboplatin alone, but drug resistance events or disease progression boost the research for the discovery of novel anticancer molecules. Recently, Costi and co-workers identified a small peptide called LR (primary sequence: LSCQLYQR) able to inhibit human Thymidylate Synthase (TS) activity . Tested in vitro, LR was able to inhibits the intracellular TS enzyme in ovarian cancer cells and was also able to reduces cellular growth at low micromolar concentration in both cisplatin-sensitive and -resistant cells. In addition, in 90% of human ovarian carcinomas the folate receptor (FR) was found over-expressed. This receptor would be employed for the selective delivery of anticancer agents. On these basis we synthesized a selective N-terminal  conjugated folate-LR peptide. As reported in literature , selective folate  conjugation is required for a fruitful folate/FR recognition. The tentative to introduce a folate unit in N-terminal position of LR peptide by solid phase peptide synthesis failed. Thus, the folic acid was chemoselectively added in solution to the LR peptide previously synthesized in solid phase. With this synthetic strategy we were able to obtain both  and  conjugated folic-LR isomers. Biological activity of compound 5 is under investigation. Preliminary results showed that 5 derivative decreased cell growth of both cisplatin-sensitive and –resistant human ovarian cancer cell lines (2008, C13*, A2780 and A2780/CP) only if protected from degradation in the cell medium by a liposomal delivery system or by protease inhibitors.