Sa1911 Mitochondrial Alterations in Early Colon Carcinogenesis: Evidence for Warburg Effect in the Initiation of Colorectal Cancer (CRC) Carcinogenesis

Abstract

Background: There is emerging realization of the central role of metabolism in carcinogenesis with the Warburg effect (preferential utilization of glycolysis in normoxic environment) (e.g. Weinberg, Cell 2012). We have previously noted an increase in microvascular blood supply in the predysplastic colonic mucosa (field carcinogenesis) (Gut 2005, Gastro 2008, Clin Cancer Res 2009, Cancer Prev Res 2010) which may reflect altered metabolism, however molecular determinants remain unexplored. The role of mitochondria in CRC is well established in frank tumors with dysfunction reflected by increased fission leading to less efficient oxidative phosphorylation, enabling shunting of precursors for cell growth. However, the presence of mitochondrial dysfunction and Warburg effect in early colon carcinogenesis has yet been explored. Therefore, we chose to investigate potential mitochondrial changes in the pre-malignant colon. Methods: To investigate mitochondrial changes we incorporated both human and animal studies: For human studies we obtained biopsies from endoscopically normal rectal muscosa from 80 patients undergoing screening colonoscopies. Samples were processed for gDNA and RNA isolation. Real Time PCRwas conducted to assess mitochondrial mass, OPA-1, UCP2, and PKM2 expression. For animal experiments we utilized the Polypopsis in Rat Colon (Pirc) rat, which possesses an APC truncation, consistent with the initiating factor in ~80% of sporadic CRCs. 7 Pirc rats with age-matched controls were euthanized after 24 wks of age. Colons were excised from these animals to obtain colonic gDNA and RNA. Real Time PCR was conducted to assess mitochondrial mass, OPA-1 and UCP2 expression. Results: In patient biopsies, mitochondrial mass was shown to be upregulated with adenomal presence (~72% increase, p=0.05). Pirc rats were also shown to possess a 63.6% induction of mitochondrial mass (p=0.03). OPA-1 expression was upregulated in both patients with adenomas as well as Pirc rats (49%, p=0.05 and 67%, p<0.03 respectively). Induction of UCP2 was detected in patients with adenomas (99%, p<0.04) and in Pircs (101%, p=0.05). Interestingly, patients with lesions had a 80% increase in PKM2 (p=0.002), suggestive of a Warburg effect in early colon carcinogenesis. Conclusions: We demonstrate for the first time, that in the predysplastic mucosa there is profound metabolic alterations consistent with a Warburg effect. Specifically, we noted increased mitochondria mass (fission) which suppresses oxidative phosphorylation. Aside from structural alterations, electron transport system is further inhibited by overexpression of UCP2. Biologically, this provides insight into early metabolic events in colon carcinogenesis. Clinically, these insights may enable novel biomarkers for early detection and also a myriad of potentially druggable targets for chemoprevention.