Abstract 1355: A novel andrographolide analogue (3A.1) synergizes with Taxane derivatives in aggressive metastatic prostate cancers through upregulation of heatshock proteins and downregulation of MAT2A-mediated cell migration and invasion
Authors: Ghosh Taraswi Mitra , Kansom Teeratas , Mazumder Suman , Davis Joshua , Alnaim Ahmed , Bird Aedan , Opanasopit P , Mitra Amit K. , Arnold Robert 
Published: July 2021

BACKGROUND: Prostate cancer (PCa) is the 2nd leading cause of non-cutaneous cancer deaths among men in the USA with many progressing to aggressive metastatic castration resistant PCa (mCRPC; PCa unresponsive to androgen deprivation). Conventional treatment with taxanes (TX; docetaxel (DTX) or cabazitaxel (CBZ)) increases survival rates only slightly. 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 and CBZ against models of aggressive PCa.

METHODS: Androgen receptor negative (AR-ve) mCRPC cell lines were treated with CBZ, DTX and 3A.1 as single-agent or combination over a broad concentration range, and in vitro cytotoxicity was determined. Chou-Talalay's combination index (CI) theorem was used to determine synergism and predicted dose reduction of taxanes. Post-treatment effect of single-agent and combination regimens on gene expression profile (GEP) was assessed using mRNA sequencing. Differentially expressed genes (DEGs) and molecular pathways involved in 3A.1 mechanism of action and drug synergy were identified using DESeq2, edgeR and Ingenuity pathway analysis (IPA). Protein expression of top DE genes was confirmed by immunoblotting. Cell cycle analysis, scratch/wound healing, and COMET assays were used to functionally validate the top treatment-associated genes.

RESULTS: Exposure to 3A.1 alone exhibited a dose- and time-dependent antitumor activity in mCRPC. CI values of all 3A.1+ TX combinations were less than 0.5, indicating synergism. Co-treatment of 3A.1 with TX reduced the required dose of DTX by 9.5 to 18-folds (p&lt;0.05), and CBZ by 3 to 14-folds (p&lt;0.05). Our caspase 3/7 assay (apoptosis) results agreed with in vitro cytotoxicity data. RNAseq followed by IPA analysis identified that the top treatment-induced DEGs belong to cell migration, growth, apoptosis (MMP1, HSPB1, PSRC1), protein ubiquitination (HNRNPH2, HSPA1A/HSPA1B), and DNA repair (H2BC4, 11) pathways, along with cancer progression. Most importantly, our top downregulated DEG was MAT2A which has earlier been shown to be involved in cell migration and invasion. Our analysis using Immunoblotting, COMET, and Wound healing/Scratch (cell migration) assays corroborated with these findings. Finally, using in silico analysis on the TCGA (The Cancer Genome Atlas) database, we found that MAT2A and highly co-expressed (r&gt;0.7) genes, TRA2B and SF1, were associated with worser Gleason score and nodal metastasis status in prostate adenocarcinoma patients (PRAD-TCGA).

CONCLUSION: These results suggest that 3A.1 may be useful in increasing the anticancer efficacy of taxanes to treat aggressive prostate cancer.

Citation Format: Taraswi Mitra Ghosh, Teeratas Kansom, Suman Mazumder, Joshua Davis, Ahmed Alnaim, Aedan Bird, P Opanasopit, Amit K. Mitra, Robert Arnold. A novel andrographolide analogue (3A.1) synergizes with Taxane derivatives in aggressive metastatic prostate cancers through upregulation of heatshock proteins and downregulation of MAT2A-mediated cell migration and invasion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1355.