Targeting Enox1 in tumor stroma increases the efficacy of fractionated radiotherapy

Abstract

The goal of this investigation was to clarify the question of whether targeting Enox1 in tumor stroma would synergistically enhance the survival of tumor-bearing mice treated with fractionated radiotherapy. Enox1, a NADH oxidase, is expressed in tumor vasculature and stroma. However, it is not expressed in many tumor types, including HT-29 colorectal carcinoma cells. Pharmacological inhibition of Enox1 in endothelial cells inhibited repair of DNA double strand breaks, as measured by γH2AX and 53BP1 foci formation, as well as neutral comet assays. For 4 consecutive days athymic mice bearing HT-29 hindlimb xenografts were injected with a small molecule inhibitor of Enox1 or solvent control. Tumors were then administered 2 Gy of x-rays. On day 5 tumors were administered a single ‘top-up’ fraction of 30 Gy, the purpose of which was to amplify intrinsic differences in the radiation fractionation regimen produced by Enox1 targeting. Pharmacological targeting of Enox1 resulted in 80% of the tumor-bearing mice surviving at 90 days compared to only 40% of tumor-bearing mice treated with solvent control. The increase in survival was not a consequence of reoxygenation, as measured by pimonidazole immunostaining. These results are interpreted to indicate that targeting of Enox1 in tumor stroma significantly enhances the effectiveness of 2 Gy fractionated radiotherapy and identifies Enox1 as a potential therapeutic target.

13q deletion is linked to an adverse phenotype and poor prognosis in prostate cancer

“…ENOX1 is a member of the ecto-nox family of NADH oxidases, which are involved in many cellular processes controlling cell growth and survival. 50 A recent study has shown that drugs targeting ENOX1 result in erroneous DNA double strand break repair, 51 That the difference in the prognosis of cancers with and without 13q deletion was relatively small (10%) even in our large set of more than 7300 analyzable cancers might explain the discrepant findings made in earlier studies employing LOH analysis to estimate the role of 13q deletions in 16-294 cancers. 24,25,27,[29][30][31][32][33]35,[37][38][39] While some studies reported higher rates of 13q loss with increased Gleason grade, 24 advanced tumor stage, 29,30,37,38 metastasis, 38 and patient outcome, 35 others could not reproduce such associations in their studies.…”

“…ENOX1 is a member of the ecto‐nox family of NADH oxidases, which are involved in many cellular processes controlling cell growth and survival . A recent study has shown that drugs targeting ENOX1 result in erroneous DNA double strand break repair, suggesting a role of ENOX1 deletion for development of genetic instability. Furthermore, it is well conceivable, that RB1 , located 4.5 megabases upstream of ENOX1 represents another relevant gene for 13q deleted prostate cancers as a co‐deletion of RB1 was seen in 98.6% of ENOX1 deleted cancers.…”

Identification of the Functions and Prognostic Values of RNA Binding Proteins in Bladder Cancer

“…Therefore, targeted inhibition of ENOX1 activity to inhibit tumor angiogenesis may be a feasible strategy for tumor control. Smith et al (2016) found that targeted inhibition of ENOX1 in tumor stroma improved radiotherapeutic efficacy in tumor patients. IGF2BP2 is a member of the insulin-like growth factor 2 mRNA-binding protein family, which are newly reported m6A "readers."…”