John McGuire

Research Overview:

This laboratory explores biochemical and molecular aspects: (1) of folic acid (folate) metabolism in tumor and normal tissues; (2) of the action of antifolates currently used in cancer chemotherapy and of experimental antifolates; and (3) of acquired and natural antifolate resistance. Novel antifolate drugs or therapeutic modalities involving folate metabolism are developed and characterized based on concepts derived from these studies.

Fundamental biochemical and molecular studies are designed to elucidate aspects of folate metabolism relevant to cancer therapeutics. Two areas are currently of greatest interest. One area is the potentiation of transport mediated by the reduced folate carrier (RFC) that occurs after exposure of cells to a natural nucleoside 5-amino-4-imidazolecarboxamide riboside (Z), which is a precursor of an intermediate in de novo purine synthesis. Elucidation of the mechanism of this potentiation should be relevant to use of antifolates such as methotrexate (MTX). A second area of interest is the synthesis, regulation, and function of poly(g-glutamyl) metabolites of folates and antifolates in proliferation and in resistance. Folylpolyglutamates are essential for normal folate metabolism and hence for cell viability. Thus, agents interfering with folylpolyglutamate synthesis and function may be therapeutically useful and could also be used as probes of their function. Folylpolyglutamate synthetase (FPGS) from a recombinant human source, from human tumor cell lines, and from normal murine intestinal epithelium is being characterized to provide a rational basis for design of selective FPGS inhibitors. Agents designed based on these studies are synthesized by collaborating chemists. Three classes of agents have been designed and synthesized to date: (1) direct FPGS inhibitors; (2) folate analogs that are nonsubstrates for FPGS; and (3) agents with enhanced ability to form short chain length polyglutamates. Biochemical and pharmacological properties of new agents are examined in detail and the results are used to refine the structures. The subcellular location of FPGS and factors regulating FPGS expression are also of interest. These studies should provide important information about the role of subcellular compartmentalization of folate metabolism.

Biochemical and molecular studies of drug sensitivity and resistance may lead to increased efficacy in clinical antifolate use. The mechanism of action of methotrexate (MTX) and other “classical” antifolates and their metabolism to poly(g-glutamates) are being explored in antifolate-sensitive and antifolate-resistant human tumor cell lines. These studies may identify factors relevant to natural and acquired MTX resistance as well as provide data allowing more judicious clinical use of these