Design, synthesis, and structure-activity relationship study of novel plinabulin derivatives as anti-tumor agents based on the co-crystal structure

Plinabulin, a 2, 5-diketopiperazine-type tubulin inhibitor derived from marine natural products, is currently undergoing Phase III clinical trials for the treatment of non-small cell lung cancer (NSCLC) and chemotherapy-induced neutropenia (CIN). To obtain novel 2, 5-diketopiperazine derivatives with higher biological activity, we designed and synthesized two series of 37 plinabulin derivatives at the C-ring, based on the co-crystal structure of compound 1 and tubulin. Their structures were characterized using NMR and HRMS. All compounds were screened in vitro using the lung cancer cell line NCI-H460 using the MTT method, and the compounds with better activity were further screened in BxPC-3 and HT-29 cells. The compounds 16c (IC50 = 2.0, NCI-H460; IC50 = 1.2 nM, BxPC-3; IC50 = 1.97 nM, HT-29) and 26r (IC50 = 0.96, NCI-H460; IC50 = 0.66 nM, BxPC-3; IC50 = 0.61 nM, HT-29) had the best activity. The cytotoxic activity of compound 26r against various tumor cell lines occurred at less than 1 nM.

Design, synthesis and anti-tumor evaluation of plinabulin derivatives as potential agents targeting β-tubulin

Plinabulin is a promising microtubule destabilizing agent in phase 3 clinical stage for treating non-small cell lung cancer. However, the high toxicity and the poor water solubility of plinabulin limited its use and more plinabulin derivatives need to be explored. Here, two series of 29 plinabulin derivatives were designed, synthesized and evaluated for their anti-tumor effect against three types of cancer cell lines. Most of derivatives exerted obvious inhibition to the proliferation of the cell lines tested. Among them, compound 11c exerted stronger efficiency than plinabulin, and the reason might be the additional hydrogen bond between the nitrogen atom of the indole ring in compound 11c and Gln134 of β-tubulin. Immunofluorescence assay showed that compound 11c at 10 nM significantly disrupted tubulin structure. Compound 11c also significantly induced G2/M cell cycle arrest and apoptosis in dose dependent manner. These results suggest that compound 11c might be a potential candidate for cancer treatment as antimicrotubule agent.

Design, synthesis and biological evaluation of anti-pancreatic cancer activity of plinabulin derivatives based on the co-crystal structure

Based on the co-crystal structures of tubulin with plinabulin and Compound 1 (a derivative of plinabulin), a total of 18 novel plinabulin derivatives were designed and synthesized. Their biological activities were evaluated against human pancreatic cancer BxPC-3 cell lines. Two novel Compounds 13d and 13e exhibited potent activities with IC₅₀ at 1.56 and 1.72 nM, respectively. The tubulin polymerization assay indicated that these derivatives could inhibit microtubule polymerization. Furthermore, the interaction between tubulin and these compounds were elucidated by molecular docking. The binding modes of Compounds 13d and 13e were similar to the co-crystal structure of Compound 1. H-π interaction was observed between the aromatic hydrogen of thiophene moiety with Phe20, which could enhance their binding affinities.