Abstract 2675: MMP9 modulates ROS levels and DNA repair pathway to maintain genomic stability in colitis associated cancer

Introduction: Chronic inflammation predisposes tissues to oncogenic, and in the colon this condition is termed as colitis associated cancer (CAC). CAC is the inflammation-dysplasia-carcinoma pathway which is significantly different compared to the adenoma-carcinoma pathway of sporadic colon cancer (CRC). In CAC, chronic inflammation causes accumulation of reactive oxygen species (ROS) resulting in DNA damage that nurtures tumor microenvironment and accelerates cancer cell growth. Gut microbiota is important in regulating ROS levels, and DNA repair pathways are critical in restoring the genomic instability. Matrix Metalloproteinases (MMPs) are a family of zinc dependent endopeptidases which mediate inflammation, tissue remodeling, and tumorigenesis. MMP9 is the most unique MMP because it is undetectable in healthy tissue but highly upregulated during inflammation and cancer. We have previously shown that MMP9 plays a protective role in CAC which is opposite to its conventional role of mediator in acute inflammation and cancer. Aim: In this study, we examined that if MMP9 acts as a tumor suppressor by modulating gut microbiota and mismatch repair (MMR) genes to reinstate genomic stability in CAC. Methods: We used C57/B6 transgenic MMP9 mice which can express MMP9 under villin promoter (TgM9) and their wild type (WT) littermates. CAC was induced by azoxymethane (AOM) and dextran sodium sulfate (DSS, inflammation inducer) to assess the microbiota population. As a proof of principal model, we used MMP9 small interfering RNA (siRNA) encoded within nanoparticles and gavaged WT mice to inhibit MMP9 in colonic epithelium. Results: QPCR data showed that mRNA levels of total microbiota population were more among TgM9 mice compared to WTs in CAC. QPCR analysis also indicated increased mRNA levels for the phylum Bacteroidetes sp., Akkermansia muciniphila but decreased mRNA levels for the phylum Firmicutes sp. TgM9 mice had lower levels of ROS compared to WTs in CAC. WB data showed decrease in protein expressions of γH2AX and MDC1 while an increase in protein expressions of MLH1 and pCNA compared to WTs in CAC. WT mice treated with MMP9 siRNA loaded nanoparticles showed worsened CAC condition compared to WT mice given scrambled siRNA loaded nanoparticles as reflected by significant bodyweight loss and higher clinical score. We also observed that WT mice treated with MMP9 siRNA loaded nanoparticles showed increase in protein expression of γH2AX while decrease in MLH1 protein levels compared to control group. Conclusion: Our study has two clinically relevant outcomes that MMP9 expression in CAC: i) promotes the beneficial microbiota population and controls the ROS production, ii) restores the DNA damage via activation of the MMR pathway. This implies the contradiction of the use of targeted MMP9 inhibitors in CAC treatment therapies by showing that MMP9 expression may be a natural way to suppress CAC. Citation Format: Lewins Walter, Adani Pujada, Brandon Canup, Hamed Laroui, Pallavi Garg. MMP9 modulates ROS levels and DNA repair pathway to maintain genomic stability in colitis associated cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2675. doi:10.1158/1538-7445.AM2017-2675