Discovery of novel thiophene[3,2-d]pyrimidine-based tubulin inhibitors with enhanced antitumor efficacy for combined use with anti-pd-l1 immunotherapy in melanoma.

Herein, we designed and synthesized a series of novel 2-methylthieno [3,2-d]pyrimidine analogues as tubulin inhibitors with antiproliferative activities at low nanomolar levels. Among them, compound DPP-21 displayed the most potent anti-proliferative activity against six cancer cell lines with an average IC ₅₀ of ∼6.23 nM, better than that of colchicine (IC ₅₀  = 9.26 nM). DPP-21 exerted its anti-cancer activity by suppressing the polymerization of tubulin with an IC ₅₀ of 2.4 μM. Furthermore, the crystal structure of DPP-21 in complex with tubulin was solved by X-ray crystallography to 2.94 Å resolution, confirming the direct binding of DPP-21 to the colchicine site. Moreover, DPP-21 arrested the cell cycle in the G2/M phase of mitosis, subsequently inducing tumor cell apoptosis. Additionally, DPP-21 was able to effectively inhibit the migration of cancer cells. Besides, DPP-21 exhibited significant in vivo anti-tumor efficacy in a B16-F10 melanoma tumor model with a TGI of 63.3 % (7 mg/kg) by intraperitoneal (i.p.) injection. Notably, the combination of DPP-21 with NP-19 (a PD-L1-targeting small molecule inhibitor reported by our group before) demonstrated enhanced anti-cancer efficacy in vivo. These results suggest that DPP-21 is a promising lead compound deserving further investigation as a potential anti-cancer agent.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jianjun chen reports a relationship with Southern Medical University that includes: non-financial support. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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