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Development of ß-Lapachone Prodrugs for Therapy Against Human Cancer Cells with Elevated NAD(P)H:Quinone Oxidoreductase 1 Levels

Authors' Affiliations: ¹ Laboratory of Molecular Stress Responses and Departments of ² Biochemistry, ³ Radiation Oncology, ⁴ Pharmacology, ⁵ Biomedical Engineering, and ⁶ Medicine, Case Western Reserve University; ⁷ Medical Research Service, Louis Stokes Veterans Affairs Medical Center, Cleveland, Ohio; ⁸ Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; and ⁹ Department of Molecular Imaging, M.D. Anderson University, Houston, Texas

Requests for reprints: David A. Boothman, Laboratory of Molecular Stress Responses, Department of Radiation Oncology and Pharmacology, Case Comprehensive Cancer Center, 2103 Cornell Avenue, WRB-3531 West, Cleveland, OH 44106-7285. Phone: 216-368-0840; Fax: 216-368-8919; E-mail: DAB30{at}case.edu.

ß-Lapachone, an o-naphthoquinone, induces a novel caspase- and p53-independent apoptotic pathway dependent on NAD(P)H:quinone oxidoreductase 1 (NQO1). NQO1 reduces ß-lapachone to an unstable hydroquinone that rapidly undergoes a two-step oxidation back to the parent compound, perpetuating a futile redox cycle. A deficiency or inhibition of NQO1 rendered cells resistant to ß-lapachone. Thus, ß-lapachone has great potential for the treatment of specific cancers with elevated NQO1 levels (e.g., breast, non–small cell lung, pancreatic, colon, and prostate cancers). We report the development of mono(arylimino) derivatives of ß-lapachone as potential prodrugs. These derivatives are relatively nontoxic and not substrates for NQO1 when initially diluted in water. In solution, however, they undergo hydrolytic conversion to ß-lapachone at rates dependent on the electron-withdrawing strength of their substituent groups and pH of the diluent. NQO1 enzyme assays, UV-visible spectrophotometry, high-performance liquid chromatography-electrospray ionization-mass spectrometry, and nuclear magnetic resonance analyses confirmed and monitored conversion of each derivative to ß-lapachone. Once converted, ß-lapachone derivatives caused NQO1-dependent, µ-calpain-mediated cell death in human cancer cells identical to that caused by ß-lapachone. Interestingly, coadministration of N-acetyl-L-cysteine, prevented derivative-induced cytotoxicity but did not affect ß-lapachone lethality. Nuclear magnetic resonance analyses indicated that prevention of ß-lapachone derivative cytotoxicity was the result of direct modification of these derivatives by N-acetyl-L-cysteine, preventing their conversion to ß-lapachone. The use of ß-lapachone mono(arylimino) prodrug derivatives, or more specifically a derivative converted in a tumor-specific manner (i.e., in the acidic local environment of the tumor tissue), should reduce normal tissue toxicity while eliciting tumor-selective cell killing by NQO1 bioactivation.

Key Words: ß-Lapachone derivatives • Apoptosis • Breast cancer • NQO1 (DT-diaphorase)

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