Abstract 3670: Matrix metalloproteinase 9 has a novel tumor suppressive role in inflammation associated colorectal cancer by modulating intrinsic tumor microenvironment

Colitis associated cancer (CAC) is a deadly complication of inflammatory bowel disease, and a subtype of colon cancer. CAC malignancy progresses through enhanced DNA damage. Observance of microsatellite instability and chromosomal instability in non-cancer related inflammatory conditions, supports the fact that inflammation could contribute to genomic destabilization by generating reactive oxygen nitrogen species, producing double strand breaks leading to DNA damage. Thus chronic colitis can induce DNA damage and modulate DNA repair systems- components of the intrinsic pathway to modulate tumor microenvironment. Matrix metalloproteinases (MMPs) are the most prominent family of proteinases associated with almost all the junctures of inflammation and tumorigenesis. They mediate inflammation, tissue remodeling, invasion, metastasis and tumor growth. Among the 24 known human MMPs, MMP9 is very unique as it is undetectable in normal tissues but highly expressed in inflamed or ulcerated tissues. We have observed that MMP9 has a protective role in CAC, which is exclusive and contrary to its traditional role of a facilitator in acute inflammation and sporadic colon cancer. In this study we explore the molecular mechanism by which MMP9 prevents DNA damage by activating tumor suppressors and DNA repair pathways in CAC. We generated transgenic mice overexpressing MMP9 in intestinal epithelium (TgM9) and to mimic human CAC, 3 cycles of 3% DSS (dextran sodium sulfate, a colonic inflammation inducer) for 5 days, followed by two weeks of recovery was used for in vivo model. Stably-transfected HCT116 cells with/without p-EGFP-MMP9 plasmid were used for in vitro experiments. We have observed that in CAC, TgM9 mice had significantly decreased tumor incidence and dysplastic lesions and a lower histological score compared to their WT littermates. TgM9 mice exhibited increased apoptosis, protein expressions of active-Notch1, p19ARF, p53, p21WAF1/Cip1, caspase-3 and cyclinE in CAC compared to WTs. HCT116-cells overexpressing MMP9 indicated decreased cell proliferation. FACS analysis indicated S-phase cell-cycle arrest and WB analysis of phosphorylated gamma-H2AX expressions indicated less DSBs compared to vector. HCT116 cells overexpressing MMP9 indicated increased expression of MDC1 and mis-match repair proteins MLH1. Our study highlights two novel findings i) MMP9 being a secretory protein activates transcellular protein Notch1 which translocates to nucleus and activates wildtype p53 via ARF and ii) MMP9 suppresses DNA double strand breaks by activating MMR gene- MLH1 and removing the damaged cells by apoptosis and or cell cycle arrest. Our study highlights the paradox of using MMP9 inhibitors in current therapies to treat CAC patients, implying that MMP9 expression might be a natural/ biological way to suppress inflammation associated ulceration. Citation Format: Lewins Walter, Adani Pujada, Sayeed Mohammadian, Agnieszka Bialkowska, Vincent Yang, Pallavi Garg. Matrix metalloproteinase 9 has a novel tumor suppressive role in inflammation associated colorectal cancer by modulating intrinsic tumor microenvironment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3670.