School of Medical Sciences

PR104 and related dinitrobenzamide mustard prodrugs


A major emphasis in the Experimental Therapeutics Group is the clinical development of the hypoxia-activated prodrug PR-104, the first compound from the ETG to enter clinical trial (through Proacta, Inc). Our interests include a range of aspects of the mechanism of action and pharmacology of PR-104 that potentially impact on its use in humans. Allied projects focus on the use of PR-104 and similar dinitrobenzamide mustards (DNBM) for prodrug activating gene therapy (PAGT) in which the prodrug is activated by a microbial nitroreductase expressed in the tumour. The chemistry support for these projects is from Prof WA Denny, Dr Jeff Smaill and Graham Atwell in the ACSRC’s Medicinal Chemistry Group.

Our work has demonstrated that PR-104 is activated by endogenous nitroreductases in tumours through the metabolic pathway shown in the following figure. The key step is the reduction of the nitro group of the alcohol metabolite PR-104A to the corresponding hydroxylamine (PR-104H), which activates the nitrogen mustard moiety (red) resulting in intra-strand crosslinking of DNA and cytotoxicity.


Reduction of PR-104A to PR-104H is catalysed by endogenous “one-electron reductases” (eg, NADPH:cytochrome P450 oxidoreductase) via an oxygen-sensitive free radical intermediate, which makes this process selective for severely hypoxic cells. The active metabolites have sufficient stability to diffuse locally in tumour tissue, generating a “bystander effect” in which surrounding tumour cells are also killed. In parallel, PR-104A can also be activated by two-electron reduction in aerobic cells. We have recently identified the aerobic nitroreductase for PR-104A as aldo-keto reductase (AKR) 1C3, which has not previously been reported as a nitroreductase. Current preclinical and clinical studies are addressing whether, in addition to hypoxia, AKR1C3 can be exploited as a therapeutic target by PR-104.

Current research projects

Staff and students involved with this project

Funding sources

Health Research Council of New Zealand Programme Grant 08/103

Selected recent publications

Guise,C.P., Abbattista,M., Singleton,R.S., Holford,S.D., Connolly,J., Dachs,G.U., Fox,S.B., Pollock,R., Harvey,J., Guilford,P., Doñate,F., Wilson,W.R., Patterson,A.V. The bioreductive prodrug PR-104A is activated under aerobic conditions by human aldo-keto reductase 1C3. Cancer Res., in press

Gu, Y., Atwell, G.J. and Wilson,W.R. Metabolism and excretion of the novel bioreductive prodrug PR-104 in mice, rats, dogs and humans. Drug Metab. Dispos., in press doi:10.1124/dmd.109.030973

Jameson, M.B., Rischin, D., Pegram, M., Gutheil, J., Patterson, A.V., Denny, W.A. and Wilson, W.R. A phase I pharmacokinetic trial of PR-104, a nitrogen mustard prodrug activated by both hypoxia and aldo-ketoreductase 1C3, in patients with solid tumors. Cancer Chemother Pharmacol. Published online 10 Dec 09. DOI 10.1007/s00280-009-1188-1

Gu,Y. and Wilson, W.R. Rapid and sensitive ultra-high-pressure liquid chromatography-tandem mass spectrometry analysis of the novel anticancer agent PR-104 and its major metabolites in human plasma: Application to a pharmacokinetic study. J Chrom B, 877: 3181-3186, 2009

Gu, Y., Patterson, A.V., Atwell, G.J., Chernikova, S.B., Brown, J.M., Thompson, L.H. and Wilson, W.R. Roles of DNA repair and reductase activity in the cytotoxicity of the hypoxia-activated dinitrobenzamide mustard PR-104A. Mol. Cancer Ther. , 8: 1714-1723, 2009

Singleton, R.S., Guise, C.P., Ferry, D.M., Pullen, S.M., Dorie, M.J., Brown, J.M., Patterson, A.V. and Wilson, W.R. DNA crosslinks in human tumor cells exposed to the prodrug PR-104A: relationships to hypoxia, bioreductive metabolism and cytotoxicity. Cancer Res., 69: 3884-3891, 2009. doi:10.1158/0008-5472

Wilson, W.R., Hicks,K.O., Pruijn,F.B., Patterson,A.V. Targeting tumor hypoxia with prodrugs: challenges and opportunities. Am Assoc Cancer Res Educ Book 2008, 293-310

Atwell G.J., Yang, S., Pruijn, F.B., Pullen, S.M., Hogg, A., Patterson, A.V., Wilson, W.R. and Denny, W.A. Synthesis and structure-activity relationships for 2,4-dinitrobenzamide-5-mustards as prodrugs for the E. coli nfsB nitroreductase in gene therapy. J. Med. Chem., 50: 1197-1212, 2007

Wilson, W.R., Hicks, K.O., Pullen, S.M., Ferry, D.M., Helsby, N.A. and Patterson, A.V. Bystander effects of bioreductive drugs: potential for exploiting tumor hypoxia with dinitrobenzamide mustards. Rad. Res., 167: 625-636, 2007.

Patterson, A.V., Ferry, D.M., Edmunds, S.J., Gu, Y., Singleton, R.S., Patel, K., Pullen, S.M., Syddall, S.P., Hicks, K.O. Atwell, G.J., Yang, S., Denny, W.A. and Wilson, W.R. Mechanism of action and preclinical antitumor activity of the novel hypoxia-activated DNA crosslinking agent PR-104. Clinical Cancer Res., 13: 3922-3932, 2007

Hicks, K.O., Myint, H., Patterson, A.V., Pruijn, F.B., Siim, B.G., Patel, K., and Wilson. W.R. Oxygen dependence and extravascular transport of hypoxia-activated prodrugs: comparison of the dinitrobenzamide mustard PR-104A and tirapazamine. Int. J. Radiat. Oncol. Biol. Phys., 69: 560-571, 2007

Patel, K., Lewiston, D., Gu, Y., Hicks, K.O., and Wilson, W.R. Analysis of the hypoxia-activated dinitrobenzamide mustard phosphate pre-prodrug PR-104 and its alcohol metabolite PR-104A in plasma and tissues by liquid chromatography-mass spectrometry. J. Chromatog. B., 856: 302-311, 2007

Guise C.P., Wang A.T.W., Theil A., Bridewell D.J., Wilson W.R. and Patterson A.V. Identification of human reductases that activate the dinitrobenzamide mustard prodrug PR-104A: a role for cytochrome P450 reductase under hypoxia. Biochem. Pharmacol., 74: 810-820, 2007

Singleton, D.C., Li, D., Bai, S.Y., Syddall, S.P., Smaill, J.B., Shen, Y., Denny, W.A., Wilson, W.R. and Patterson, A.V. The nitroreductase prodrug SN 28343 enhances the potency of the systemically administered armed oncolytic adenovirus ONYX-411NTR. Cancer Gene Ther., 14: 953-967, 2007