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The Combi-Targeting Concept: In vitro and In vivo Fragmentation of a Stable Combi-Nitrosourea Engineered to Interact with the Epidermal Growth Factor Receptor while Remaining DNA Reactive

Authors' Affiliations: ¹ Cancer Drug Research Laboratory, Department of Medicine, McGill University Health Center/Royal Victoria Hospital; ² Sheldon Biotechnology Center, Department of Medicine, McGill University/Royal Victoria Hospital, Montreal, Quebec, Canada; and ³ Consumer and Clinical Radiation Protection Bureau, Health Canada, Ottawa, Ontario, Canada

Requests for reprints: Bertrand J. Jean-Claude, Cancer Drug Research Laboratory, Department of Medicine, Division of Medical Oncology, McGill University Health Center/Royal Victoria Hospital, 687 Pine Avenue West, Room M 7.15, Montreal, Quebec, Canada H3A 1A1. Phone: 514-934-1934, ext. 35841; Fax: 514-843-1475; E-mail: bertrandj.jean-claude{at}mcgill.ca.

Purpose: JDA58 (NSC 741282), a "combi-molecule" optimized in the context of the "combi-targeting concept," is a nitrosourea moiety tethered to an anilinoquinazoline. Here, we sought to show its binary epidermal growth factor receptor (EGFR)/DNA targeting property and to study its fragmentation in vitro and in vivo.

Experimental Design: The fragmentation of JDA58 was detected in cells in vitro and in vivo by fluorescence microscopy and tandem mass spectrometry. EGFR phosphorylation and DNA damage were determined by Western blotting and comet assay, respectively. Tumor data were examined for statistical significance using the Student's t test.

Results: JDA58 inhibited EGFR tyrosine kinase (IC₅₀, 0.2 µmol/L) and blocked EGFR phosphorylation in human DU145 prostate cancer cells. It induced significant levels of DNA damage in DU145 cells in vitro or in vivo and showed potent antiproliferative activity both in vitro and in a DU145 xenograft model. In cell-free medium, JDA58 was hydrolyzed to JDA35, a fluorescent amine that could be observed in tumor cells both in vitro and in vivo. In tumor cells in vitro or in vivo, or in plasma collected from mice, the denitrosated species JDA41 was the predominant metabolite. However, mass spectrometric analysis revealed detectable levels of the hydrolytic product JDA35 in tumor cells both in vitro and in vivo.

Conclusions: The results in toto suggest that growth inhibition in vitro and in vivo may be sustained by the intact combi-molecule plus JDA35 plus JDA41, three inhibitors of EGFR, and the concomitantly released DNA-damaging species. This leads to a model wherein a single molecule carries a complex multitargeted-multidrug combination.

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