Abstract
Dihydrofolate reductase (DHFR) , beause of its essential role in DNA synthesis, has been targeted for the treatment of a wide variety of human diseases including cancer, autoimmune and infectious diseases. Methotrexate (MTX), a tight binding inhibitor of DHFR is one of the most widely used drugs in cancer treatment, and is especially effective in the treatment of acute lymphocytic leukemia, non-Hodgkin's lymphoma, and osteosarcoma. Limitations to its use in cancer include natural resistance and acquired resistance due to decreased cellular uptake and decreased retention due to impaired polyglutamylate formation and toxicity at higher doses. Here we describe a novel mechanism to induce DHFR degradation through cofactor depletion in neoplastic cells by inhibition of NAD kinase, the only enzyme responsible for generating NADP, which is rapidly converted to NADPH by dehydrogenases/reductases. We identified an inhibitor of NAD kinase, thionicotinamide adenine dinucleotide phosphate (NADPS) that led to accelerated degradation of DHFR and to inhibition of cancer cell growth. Importantly, combination treatment of NADPS with MTX displayed significant synergy in a metastatic colon cancer cell line and was effective in a MTX-transport resistant leukemic cell line. We suggest that NAD kinase is a valid target for further inhibitor development for cancer treatment.
- Proteasome-mediated protein degradation
- Oxidation/reduction
- Ubiquitination
- Molecular dynamics
- Structure-activity relationships and modeling
- Regulation of gene expression
- Regulation - physiological
- Structure/function/mechanism
- Nucleoside/Nucleotide derivatives
- Resistance
- Received May 23, 2012.
- Revision received November 7, 2012.
- Accepted November 8, 2012.
- The American Society for Pharmacology and Experimental Therapeutics