Abstract
Conventional treatment with taxanes (docetaxel-DTX or cabazi-taxel-CBZ) increases the survival rates of patients with aggressive metastatic castration-resistant prostate cancer (mCRPC); however, most patients acquire resistance to taxanes. The andrographolide analog, 19-tert-butyldiphenylsilyl-8,7-epoxy andrographolide (3A.1), has shown anticancer activity against various cancers. In this study, we investigated the effect of 3A.1 alone and in combination with DTX/CBZ against mCRPC and their mechanism of action. Exposure to 3A.1 alone exhibited a dose-and time-dependent antitumor activ-ity in mCRPC. Chou-Talalay's combination index (CI) values of all 3A.1 1 TX combinations were less than 0.5, indicating synergism. Co-treatment of 3A.1 with TX reduced the required dose of DTX and CBZ (P < 0.05). Caspase assay (apoptosis) results concurred with in vitro cytotoxicity data. RNA sequencing (RNAseq), followed by ingenuity pathway analysis (IPA), identified that upregulation of heat-shock proteins (Hsp70, Hsp40, Hsp27, and Hsp90) and downregulation of MAT2A as the key player for 3A.1 response. Furthermore, the top treatment-induced differentially expressed genes (DEGs) belong to DNA damage, cell migration, hypoxia, autophagy (MMP1, MMP9, HIF-1a, Bag-3, H2AX, HMOX1, PSRC1), and cancer progression pathways. Most importantly, top downregulated DEG MAT2A has earlier been shown to be involved in cell migration and invasion. Furthermore, using in sil-ico analysis on the Cancer Genome Atlas (TCGA) database, this study found that MAT2A and highly co-expressed (r > 0.7) genes, TRA2B and SF1, were associated with worse Gleason score and nodal metastasis status in prostate adenocarcinoma patients (PRAD-TCGA). Immunoblotting, comet, and migration assays corroborated these findings. These results suggest that 3A.1 may be useful in increasing the anticancer efficacy of tax-anes to treat aggressive PCa. SIGNIFICANCE STATEMENT The andrographolide analogue, 19-tert-butyldiphenylsilyl-8,7-epoxy andrographolide (3A.1), showed anticancer activity against meta-static castration-resistant and neuroendocrine variant prostate can-cers (mCRPC/NEPC). Additionally, 3A.1 exhibited synergistic anti-cancer effect in combination with standard chemotherapy drugs docetaxel and cabazitaxel in mCRPC/NEPC. Post-treatment gene expression studies revealed that heat shock proteins (Hsp70, Hsp40, Hsp27, and Hsp90) and MAT2A are important in the mech-anism of 3A.1 action and drug response. Furthermore, DNA dam-age, cell migration, hypoxia, and autophagy were crucial pathways for the anticancer activity of 3A.1.