Pre-clinical activity of PR-104 as monotherapy and in combination with sorafenib in hepatocellular carcinoma

Abstract

PR-104 is a clinical stage bioreductive prodrug that is converted in vivo to its cognate alcohol, PR-104A. This dinitrobenzamide mustard is reduced to activated DNA cross-linking metabolites (hydroxylamine PR-104H and amine PR-104M) under hypoxia by one-electron reductases and independently of hypoxia by the 2-electron reductase aldo-keto reductase 1C3 (AKR1C3). High expression of AKR1C3, along with extensive hypoxia, suggested the potential of PR-104 for treatment of hepatocellular carcinoma (HCC). However, a phase IB trial with sorafenib demonstrated significant toxicity that was ascribed in part to reduced PR-104A clearance, likely reflecting compromised glucuronidation in patients with advanced HCC. Here, we evaluate the activity of PR-104 in HCC xenografts (HepG2, PLC/PRF/5, SNU-398, Hep3B) in mice, which do not significantly glucuronidate PR-104A. Cell line differences in sensitivity to PR-104A in vitro under aerobic conditions could be accounted for by differences in both expression of AKR1C3 (high in HepG2 and PLC/PRF/5) and sensitivity to the major active metabolite PR-104H, to which PLC/PRF/5 was relatively resistant, while hypoxic selectivity of PR-104A cytotoxicity and reductive metabolism was greatest in the low-AKR1C3 SNU-398 and Hep3B lines. Expression of AKR1C3 in HepG2 and PLC/PRF/5 xenografts was in the range seen in 21 human HCC specimens. PR-104 monotherapy elicited significant reductions in growth of Hep3B and HepG2 xenografts, and the combination with sorafenib was significantly active in all 4 xenograft models. The results suggest that better-tolerated analogs of PR-104, without a glucuronidation liability, may have the potential to exploit AKR1C3 and/or hypoxia in HCC in humans.

Keywords:

• AKR1C3
• Hypoxia
• hypoxia-activated prodrugs
• hepatocellular carcinoma
• nitrogen mustards
• PR-104
• sorafenib

Disclosure of Potential Conflicts of Interest

AVP and WRW are inventors on patents related to PR-104.

Acknowledgments

We thank Chenbo Wu, Jie Li and Dr Kevin Sun for assistance with the xenograft model assays.

Funding

This study was funded by the Health Research Council of New Zealand (grant 111103).