LS-007, an inhibitor of cyclin-dependent kinase 9 (CDK9), exhibits potential antitumor activity against chronic lymphocytic leukemia and ovarian cancer, but its effect on melanoma and tumor microenvironment (TME) has not been reported yet. This study aimed to investigate the role of LS-007 in B16F10 melanoma and relevant mechanisms. LS-007 significantly inhibited viability and induced apoptosis of B16F10 cells in a dose-dependent manner, which were accompanied with the increased ratio of Bax to Bcl-2 and decreased Mcl-1 mRNA level. Western blot analysis showed that LS-007 increased the expression of cleaved caspase-3 and poly ADP-ribose polymerase (PARP). Furthermore, flow cytometry analysis and qRT-PCR results showed that LS-007 treatment resulted in cell cycle arrest by changing cell cycle-related gene expression. Notably, in vivo evaluation showed that LS-007 significantly decreased the weight and volume of tumor and the expression of Ki67, promoted the expression of iNOS and inhibited the expression of CD206, suggesting that LS-007 might inhibit tumor growth by suppressing polarization of macrophages into tumor-associated macrophages (TAMs) in the TME. The increase in M1/M2 treated with LS-007 detected by flow cytometry hinted that macrophages were polarized towards an antitumor phenotype. In addition, LS-007 induced higher apoptotic rate of B16F10 cells when co-cultured B16F10 with BMDMs. LS-007 has inhibitory effects on B16F10 cells in vivo and in vitro via inducing apoptosis, cell cycle arrest, and changing macrophage function in the TME.
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