Downregulation of DNA repair proteins and increased DNA damage in hypoxic colon cancer cells is a therapeutically exploitable vulnerability.

Jennifer M J Jongen,Onno Kranenburg,Inne H M Borel Rinkes,Jamila Laoukili,Kari Trumpi,Susanne J Schenning-Van Schelven,Niek A Peters,Klaas M Govaert,Lizet M Van Der Waals

doi:10.18632/oncotarget.21145

Abstract

Surgical removal of colorectal cancer (CRC) liver metastases generates areas of tissue hypoxia. Hypoxia imposes a stem-like phenotype on residual tumor cells and promotes tumor recurrence. Moreover, in primary CRC, gene expression signatures reflecting hypoxia and a stem-like phenotype are highly expressed in the aggressive Consensus Molecular Subtype 4 (CMS4). Therapeutic strategies eliminating hypoxic stem-like cells may limit recurrence following resection of primary tumors or metastases.Here we show that expression of DNA repair genes is strongly suppressed in CMS4 and inversely correlated with hypoxia-inducible factor-1 alpha (HIF1α) and HIF-2α co-expression signatures. Tumors with high expression of HIF signatures and low expression of repair proteins showed the worst survival. In human tumors, expression of the repair proteins RAD51, KU70 and RIF1 was strongly suppressed in hypoxic peri-necrotic tumor areas. Experimentally induced hypoxia in patient derived colonospheres in vitro or in vivo (through vascular clamping) was sufficient to downregulate repair protein expression and caused DNA damage. Hypoxia-induced DNA damage was prevented by expressing the hydroperoxide-scavenging enzyme glutathione peroxidase-2 (GPx2), indicating that reactive oxygen species mediate hypoxia-induced DNA damage. Finally, the hypoxia-activated prodrug Tirapazamine greatly augmented DNA damage and reduced the fraction of stem-like (Aldefluorbright) tumor cells in vitro, and in vivo following vascular clamping.We conclude that decreased expression of DNA repair proteins and increased DNA damage in hypoxic tumor areas may be therapeutically exploited with hypoxia-activated prodrugs, and that such drugs reduce the fraction of Aldefluorbright (stem-like) tumor cells.

Highlights

Colorectal cancer (CRC) is the third most common cancer worldwide and a major cause of cancer-related mortality [1]
We have previously shown that expression of a gene signature comprising the genes most significantly coexpressed with hypoxia-inducible factor 2 (HIF2α) was strongly enriched in aggressive mesenchymal-type tumors [4], commonly referred to as Consensus Molecular Subtype 4 (CMS4)
We show that increased DNA damage, possibly caused by reduced repair protein expression, is a therapeutically exploitable feature of aggressive colon tumors

Summary

Introduction

Colorectal cancer (CRC) is the third most common cancer worldwide and a major cause of cancer-related mortality [1]. Treatment strategies that can limit disease recurrence following primary tumor resection or partial liver resection are not sufficiently effective. The development of such strategies should be based on an understanding of the pathways that drive metastasis and recurrence. CMS3 is characterized by high expression of genes regulating metabolic pathways and is enriched in tumors with activating mutations in the KRAS oncogene. CMS4 is characterized by atypical expression of genes reflecting a mesenchymal and a stem cell-like phenotype and has the highest propensity to form metastases [3]. We have recently shown that mesenchymal-type primary colon tumors express high levels of hypoxiarelated genes [4], which is in line with the observation that CMS4 is characterized by expression of angiogenesisstimulating genes [3]. Hypoxia is associated with more aggressive tumor phenotypes across different types of cancer (clear cell renal carcinoma, non-small cell lung carcinoma, neuroblastoma) [7]

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Conclusion