Reductive metabolism of the dinitrobenzamide mustard anticancer prodrug PR-104 in mice.
OBJECTIVE
PR-104, a bioreductive prodrug in clinical trial, is a phosphate ester which is rapidly metabolized to the corresponding alcohol PR-104A. This dinitrobenzamide mustard is activated by reduction to hydroxylamine (PR-104H) and amine (PR-104M) metabolites selectively in hypoxic cells, and also independently of hypoxia by aldo-keto reductase (AKR) 1C3 in some tumors. Here, we evaluate reductive metabolism of PR-104A in mice and its significance for host toxicity.


METHODS
The pharmacokinetics of PR-104, PR-104A and its reduced metabolites were investigated in plasma and tissues of mice (with and without SiHa or H460 tumor xenografts) and effects of potential oxidoreductase inhibitors were evaluated.


RESULTS
Pharmacokinetic studies identified extensive non-tumor reduction of PR-104A to the 5-amine PR-104H (identity of which was confirmed by chemical synthesis), especially in liver. However, high concentrations of PR-104H in tumors that suggested intra-tumor activation is also significant. The tissue distribution of PR-104M/H was broadly consistent with the target organ toxicities of PR-104 (bone marrow, intestines and liver). Surprisingly, hepatic nitroreduction was not enhanced when the liver was made more hypoxic by hepatic artery ligation or breathing of 10% oxygen. A screen of non-steroidal anti-inflammatory drugs identified naproxen as an effective AKR1C3 inhibitor in human tumor cell cultures and xenografts, suggesting its potential use to ameliorate PR-104 toxicity in patients. However, neither naproxen nor the pan-CYP inhibitor 1-aminobenzotriazole inhibited normal tissue reduction of PR-104A in mice.


CONCLUSIONS
PR-104 is extensively reduced in mouse tissues, apparently via oxygen-independent two-electron reduction, with a tissue distribution that broadly reflects toxicity.
Gu
Yongchuan
Y
Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand.
Guise
Christopher P
CP
Patel
Kashyap
K
Abbattista
Maria R
MR
Li
Jie
J
Lie
Jie
J
Sun
Xueying
X
Atwell
Graham J
GJ
Boyd
Maruta
M
Patterson
Adam V
AV
Wilson
William R
WR
D015096:3-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D000074425:Aldo-Keto Reductase Family 1 Member C3; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics* / Q000633:toxicity; D045744:Cell Line, Tumor; D004583:Electrons; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D006911:Hydroxyprostaglandin Dehydrogenases / Q000378:metabolism*; D008175:Lung Neoplasms / Q000188:drug therapy / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D009588:Nitrogen Mustard Compounds / Q000493:pharmacokinetics* / Q000633:toxicity; D010084:Oxidation-Reduction; D011355:Prodrugs; D014018:Tissue Distribution; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy / Q000473:pathology; D023041:Xenograft Model Antitumor Assays
D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D009588:Nitrogen Mustard Compounds; C522381:PR-104; C524170:PR-104A; D011355:Prodrugs; D015096:3-Hydroxysteroid Dehydrogenases; D006911:Hydroxyprostaglandin Dehydrogenases; C487341:AKR1C3 protein, human; D000074425:Aldo-Keto Reductase Family 1 Member C3