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. 2015 Oct 1;75(19):4211-23.
doi: 10.1158/0008-5472.CAN-15-1107. Epub 2015 Aug 21.

Identification of P450 Oxidoreductase as a Major Determinant of Sensitivity to Hypoxia-Activated Prodrugs

Francis W Hunter  1 , Richard J Young  2 , Zvi Shalev  3 , Ravi N Vellanki  3 , Jingli Wang  1 , Yongchuan Gu  4 , Naveen Joshi  1 , Sreevalsan Sreebhavan  1 , Ilan Weinreb  3 , David P Goldstein  5 , Jason Moffat  6 , Troy Ketela  7 , Kevin R Brown  7 , Marianne Koritzinsky  8 , Benjamin Solomon  9 , Danny Rischin  10 , William R Wilson  1 , Bradly G Wouters  11
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Identification of P450 Oxidoreductase as a Major Determinant of Sensitivity to Hypoxia-Activated Prodrugs

Francis W Hunter et al. Cancer Res. .

Abstract

Hypoxia is a prevalent feature of many tumors contributing to disease progression and treatment resistance, and therefore constitutes an attractive therapeutic target. Several hypoxia-activated prodrugs (HAP) have been developed, including the phase III candidate TH-302 (evofosfamide) and the preclinical agent SN30000, which is an optimized analogue of the well-studied HAP tirapazamine. Experience with this therapeutic class highlights an urgent need to identify biomarkers of HAP sensitivity, including enzymes responsible for prodrug activation during hypoxia. Using genome-scale shRNA screens and a high-representation library enriched for oxidoreductases, we identified the flavoprotein P450 (cytochrome) oxidoreductase (POR) as the predominant determinant of sensitivity to SN30000 in three different genetic backgrounds. No other genes consistently modified SN30000 sensitivity, even within a POR-negative background. Knockdown or genetic knockout of POR reduced SN30000 reductive metabolism and clonogenic cell death and similarly reduced sensitivity to TH-302 under hypoxia. A retrospective evaluation of head and neck squamous cell carcinomas showed heterogeneous POR expression and suggested a possible relationship between human papillomavirus status and HAP sensitivity. Taken together, our study identifies POR as a potential predictive biomarker of HAP sensitivity that should be explored during the clinical development of SN30000, TH-302, and other hypoxia-directed agents.

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