Abstract 908: Overexpression of nicotinamide N-methyltransferase confers gemcitabine resistance in bladder cancer
Authors: Martin Kelly A. , Sebastian Aimy , Hum Nicholas R. , Murugesh Deepa K. , Pan Chong-xian , Ma Ai-Hong , White Ralph W. de Vere , Loots Gabriela G. 
Published: August 2018

Bladder cancer is among the top ten most common cancers diagnosed, with about ~380,000 new cases and ~150,000 deaths per year reported worldwide. Platinum-based chemotherapy in combination with gemcitabine, a nucleoside analog, is a widely used treatment option for advanced bladder cancer. It has been shown that only ~50% of the patients with advanced bladder cancer respond to platinum-based therapy. Cancer cells often become non-responsive to therapy that once proved efficacious and are now drug resistant. Drug resistance represents a significant, ongoing challenge in eradicating cancer.

We have employed a patient-derived bladder cancer xenograft (PDX) platform to further investigate the molecular mechanisms that contribute to gemcitabine-induced drug resistance in advanced bladder cancer. Transcriptome profiling of passage 4 bladder cancer xenograft tumors from 2 gemcitabine sensitive PDX lines (BL0440 & BL0293) was performed using RNA sequencing (RNAseq) analysis, before and after a 21-day cisplatin/gemcitabine drug treatment regimen. Key regulatory pathways and genes contributing to drug resistant bladder cancer have been identified and validated by overexpression in a 5637 bladder cancer cell line.

RNA sequencing data has indicated significant differences between the transcriptional profiles of drug-sensitive and drug-resistant tumors. PDXs retained morphology and shared 92-97% of genetic alterations of parental cancer cells. We identified 106 genes &gt;1.5 fold up-regulated and 45 genes &gt;1.5 fold down-regulated in the drug resistant tumors compared to their drug sensitive counterparts. Of the genes that were significantly upregulated, two methyltransferase enzymes were further validated: Nicotinamide N-methyltransferase (NNMT) and methionine methyltransferase 1A (MAT1A). These genes were found to be contributors to gemcitabine-mediated drug resistance. 5637 cells overexpressing NNMT yielded a 200-fold increase in gemcitabine resistance relative to parental strain. In conclusion, chemoresistance to gemcitabine is associated with differential expression of genes and alteration of downstream signaling pathways. Upregulation of NNMT & MAT1A can potentially be used as novel biomarkers for subpopulations of drug resistant bladder cancer for which improved therapeutics can be developed. Future direction will likely include studies to elucidate exact molecular mechanisms by which cancer cells utilize methyltransferases to no longer respond to gemcitabine therapy.

This work was conducted under the auspices of the USDOE by LLNL (DE-AC52-07NA27344).

Citation Format: Kelly A. Martin, Aimy Sebastian, Nicholas R. Hum, Deepa K. Murugesh, Chong-xian Pan, Ai-Hong Ma, Ralph W. de Vere White, Gabriela G. Loots. Overexpression of nicotinamide N-methyltransferase confers gemcitabine resistance in bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 908.