Design, Synthesis, and Biological Evaluations of Tumor-Targeting Dual-Warhead Conjugates for a Taxoid–Camptothecin Combination Chemotherapy

Novel tumor-targeting dual-warhead conjugates, 2 (DW-1) and 3 (DW-2), which consist of a next-generation taxoid, 1 (SB-T-1214), and camptothecin as two warheads, self-immolative disulfide linkers for drug release, biotin as the tumor-targeting moiety, and 1,3,5-triazine as the tripod splitter module, were designed and synthesized. The potency of 2 was evaluated against MX-1, MCF-7, ID8, L1210FR (BR+, biotin receptor overexpressed) and WI38 (BR-, normal) cell lines in the absence and presence of glutathione (GSH), which is an endogenous thiol that triggers drug release inside the cancer cells. With the GSH and resuspension protocol, 2 exhibited IC50 values of 3.22-9.80 nM against all BR+ cancer cell lines, and 705 nM against WI38. Thus, there was a two orders of magnitude higher selectivity to cancer cells. Also, a clear cooperative effect was observed for the taxoid-camptothecin combination when two drugs were delivered to the cancer cells specifically in the form of a dual-warhead conjugate.