Mechanism of action and preclinical antitumor activity of the novel hypoxia-activated DNA cross-linking agent PR-104.

Abstract

PURPOSE:

Hypoxia is a characteristic of solid tumors and a potentially important therapeutic target. Here, we characterize the mechanism of action and preclinical antitumor activity of a novel hypoxia-activated prodrug, the 3,5-dinitrobenzamide nitrogen mustard PR-104, which has recently entered clinical trials.

EXPERIMENTAL DESIGN:

Cytotoxicity in vitro was evaluated using 10 human tumor cell lines. SiHa cells were used to characterize metabolism under hypoxia, by liquid chromatography-mass spectrometry, and DNA damage by comet assay and gammaH2AX formation. Antitumor activity was evaluated in multiple xenograft models (PR-104 +/- radiation or chemotherapy) by clonogenic assay 18 h after treatment or by tumor growth delay.

RESULTS:

The phosphate ester "pre-prodrug" PR-104 was well tolerated in mice and converted rapidly to the corresponding prodrug PR-104A. The cytotoxicity of PR-104A was increased 10- to 100-fold by hypoxia in vitro. Reduction to the major intracellular metabolite, hydroxylamine PR-104H, resulted in DNA cross-linking selectively under hypoxia. Reaction of PR-104H with chloride ion gave lipophilic cytotoxic metabolites potentially able to provide bystander effects. In tumor excision assays, PR-104 provided greater killing of hypoxic (radioresistant) and aerobic cells in xenografts (HT29, SiHa, and H460) than tirapazamine or conventional mustards at equivalent host toxicity. PR-104 showed single-agent activity in six of eight xenograft models and greater than additive antitumor activity in combination with drugs likely to spare hypoxic cells (gemcitabine with Panc-01 pancreatic tumors and docetaxel with 22RV1 prostate tumors).

CONCLUSIONS:

PR-104 is a novel hypoxia-activated DNA cross-linking agent with marked activity against human tumor xenografts, both as monotherapy and combined with radiotherapy and chemotherapy.

• Authors: Adam V Patterson, Dianne M Ferry, Shelley J Edmunds, Yongchuan Gu, Rachelle S Singleton, Kashyap Patel, Susan M Pullen, Kevin O Hicks, Sophie P Syddall, Graham J Atwell, Shangjin Yang, William A Denny, William R Wilson
• Journal: Clinical cancer research : an official journal of the American Association for Cancer Research (Clin Cancer Res) Vol. 13 Issue 13 Pg. 3922-32 (Jul 01 2007) ISSN: 1078-0432 [Print] United States
• PMID: 17606726 (Publication Type: Journal Article)

Chemical References

• Antineoplastic Agents
• Cross-Linking Reagents
• Histones
• Nitrogen Mustard Compounds
• PR-104
• Phosphates
• gamma-H2AX protein, mouse
• DNA

Topics

• Animals
• Antineoplastic Agents (pharmacology)
• Cell Line, Tumor
• Comet Assay
• Cross-Linking Reagents (pharmacology)
• DNA (chemistry)
• DNA Damage
• Drug Screening Assays, Antitumor
• Histones (metabolism)
• Humans
• Hypoxia
• Mice
• Neoplasm Transplantation
• Neoplasms (drug therapy)
• Nitrogen Mustard Compounds (chemistry, pharmacology)
• Phosphates (pharmacology)