Authors: Breton Roussel, Nadine Johnson-Farley, John E. Kerrigan, Kathleen W. Scotto, Debabrata Banerjee, Krzysztof Felczak, Krzysztof W. Pankiewicz, Murugesan Gounder, HongXia Lin, Emine Ercikan Abali and Joseph R. Bertino

Breton Roussel

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

Nadine Johnson-Farley

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

John E. Kerrigan

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

Kathleen W. Scotto

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

Debabrata Banerjee

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

Krzysztof Felczak

The Center for Drug Design; University of Minnesota; Minneapolis, MN USA

Krzysztof W. Pankiewicz

The Center for Drug Design; University of Minnesota; Minneapolis, MN USA

Murugesan Gounder

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

HongXia Lin

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

Emine Ercikan Abali

Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

Joseph R. Bertino

Corresponding author: bertinoj@umdnj.edu
Departments of Medicine, Biochemistry and Pharmacology; Robert Wood Johnson Medical School; New Brunswick, NJ USA

Abstract:
Dihydrofolate reductase (DHFR) is an essential enzyme involved in de novo purine and thymidine biosynthesis. For several decades, selective inhibition of DHFR has proven to be a potent therapeutic approach in the treatment of various cancers including acute lymphoblastic leukemia, non-Hodgkin’s lymphoma, osteogenic sarcoma, carcinoma of the breast, and head and neck cancer. Therapeutic success with DHFR inhibitor methotrexate (MTX) has been compromised in the clinic, which limits the success of MTX treatment by both acquired and intrinsic resistance mechanisms. We report that benzamide riboside (BR), via anabolism to benzamide adenine dinucleotide (BAD) known to potently inhibit inosine monophosphate dehydrogenase (IMPDH), also inhibits cell growth through a mechanism involving downregulation of DHFR protein. Evidence to support this second site of action of BR includes the finding that CCRF-CEM/R human T-cell lymphoblasic leukemia cells, resistant to MTX as a consequence of gene amplification and overexpression of DHFR, are more resistant to BR than are parental cells. Studies of the mechanism by which BR lowers DHFR showed that BR, through its metabolite BAD, reduced NADP and NADPH cellular levels by inhibiting nicotinamide adenine dinucleotide kinase (NADK). As consequence of the lack of NADPH, DHFR was shown to be destabilized. We suggest that, inhibition of NADK is a new approach to downregulate DHFR and to inhibit cell growth.

Received: May 10, 2012; Accepted: August 8, 2012; Published Online: September 6, 2012

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