Structure-Based Design and Synthesis of N‑Substituted 3‑Amino-β-Carboline Derivatives as Potent αβ-Tubulin Degradation Agents

So far, relatively few small molecules have been reported to promote tubulin degradation. Our previous studies have found that compound 2, a noncovalent colchicine-site ligand, was capable of promoting αβ-tubulin degradation. To further improve its antiproliferative activity, 66 derivatives or analogues of 2 were designed and synthesized based on 2-tubulin cocrystal structure. Among them, 12b displayed nanomolar potency against a variety of tumor cells, including paclitaxel- and adriamycin-resistant cell lines. 12b binds to the colchicine site and promotes αβ-tubulin degradation in a concentration-dependent manner via the ubiquitin–proteasome pathway. The X-ray crystal structure revealed that 12b binds in a similar manner as 2, but there is a slight conformation change of the B ring, which resulted in better interaction of 12b with surrounding residues. 12b effectively suppressed tumor growth at an i.v. dose of 40 mg/kg (3 times a week) on both A2780S (paclitaxel-sensitive) and A2780T (paclitaxel-resistant) ovarian xenograft models, with respective TGIs of 92.42 and 79.75% without obvious side effects, supporting its potential utility as a tumor-therapeutic compound.