Synthesis of Rapamycin Derivatives Containing the Triazole Moiety Used as Potential mTOR-Targeted Anticancer Agents

Rapamycin, a potent antifungal antibiotic, was approved as immunosuppressant, and lately its derivatives have been developed into mTOR targeting anticancer drugs. Structure modification was performed at the C-42 position of rapamycin, and a novel series of rapamycin triazole hybrids (4a-d, 5a-e, 8a-e, and 9a-e) was facilely synthesized via Huisgen's reaction. The anticancer activity of these compounds was evaluated against the Caski, H1299, MGC-803, and H460 human cancer cell lines. Some of the derivatives (8a-e, 9a-e) appeared to have stronger activity than that of rapamycin; however, 4a-d and 5a-e failed to show potential anticancer activity. Compound 9e with a (2,4-dichlorophenylamino)methyl moiety on the triazole ring was the most active anticancer compound, which showed IC50 values of 6.05 (Caski), 7.89 (H1299), 25.88 (MGC-803), and 8.60 μM (H460). In addition, research on the mechanism showed that 9e was able to cause cell morphological changes and to induce apoptosis in the Caski cell line. Most importantly, 9e can decrease the phosphorylation of mTOR and of its downstream key proteins, S6 and P70S6K1, indicating that 9e can effectively inhibit the mTOR signaling pathway. Thus, it may have the potential to become a new mTOR inhibitor against various cancers.