The novel inhibitor BRM270 downregulates tumorigenesis by suppression of NF-κB signaling cascade in MDR-induced stem like cancer-initiating cells.

The nuclear factor κB (NF-κB) and interleukin-6 (IL-6) contribute to multidrug resistance (MDR) in tumor chemotherapy. The essential phenomenon of oncogenic activation of NF-κB in cancer-initiating cells showing MDR resulting from increased IL-6 expression is still unclear. Cancer stem cells (CSCs) have been the objective of intensive study. The aim of this study was to investigate the selective and potential efficacy of BRM270 against stem-like cancer-initiating cells (SLCICs) via the molecular mechanisms of its anticancer effects. Co-regulation of NF-κB and Cdk6 might be new arena to mitigate tumorigenesis. In the present study phyto-drug based approach provides a new avenue in understanding the amelioration and regulatory mechanisms in CSCs. In the present study, an in vivo tumor metastasis model of osteosarcoma was established by injecting Cal72 and SaOS-2 SLCICs into the right lower flank of nude mice. Later the development of tumor was analyzed by LICOR Biosciences (Pearl image analyzer). Significant suppression of activation of NF-κB and LPS-induced gene expression and apoptosis by BRM270 was confirmed by FACS, western blotting and qPCR. Further, both p65 and Cdk6 were significantly (P<0.05) overexpressed in BRM270 non-treated Cal72 SLCICs compared to treated group. BRM270 directly dephosphorylated RelA and selectively inhibited NF-κB transcriptional activity, resulting in decreased expression of interleukin-6, a cytokine implicated in cancer metastasis. BRM270-mediated cell shrinkage, pyknosis, karyorrhexis and programmed cell death (PCD) were observed by Hoechst 33342 staining while flow cytometry analysis showed significant (P<0.05) decrease in cell population from G0-G1 phases. These findings suggest that activation of the oncogenic Cdk6-NF-κB pathway, resulting from increased IL-6 expression, plays a central role in CD133 expressing SLCICs augmented MDR and neoplasia. This study proposes targeting of NF-κB, and Cdk6 with IL-6 as potential targets for PCD and treatment of chemotherapeutic resistance of CSCs to design novel therapies for their elimination.