15Cancer research: from folate antagonism to molecular targets
Section snippets
Dihydrofolate reductase and methotrexate
During the second and third year of my haematology fellowship with Clement A. Finch at the University of Washington, I was fortunate to work with Frank Huennekens, an assistant professor of biochemistry, who had initiated a programme to work out the enzymology of folate enzymes. The year before I joined the lab, in 1958, 10 years after MTX was introduced in the clinic, the mechanism of the action of MTX as a potent inhibitor of dihydrofolate reductase (DHFR) was established in a landmark paper
Methotrexate and beyond
At Yale, my colleagues and I initiated studies of high-dose MTX and leucovorin rescue for the treatment of head and neck cancer and diffuse large cell lymphoma [4], [5]. New anti-tumour agents, including trimetrexate and carboxypetidase G2(glucarpidase), were discovered [6]. Compared with methotrexate, trimetrexate is a quinazoline and lacks the terminal glutamate moiety (Fig. 1). Trimetrexate also has the property of being able to enter cells without the folate carriers needed by methotrexate.
Methotrexate resistance
While on sabbatical with Robert Schimke at the Stanford University, we discovered DHFR gene amplification as a mechanism of methotrexate resistance [15]. This discovery was remarkable because, at that time, it was believed that DNA was stable, and the concept of somatic cells generating additional gene copies was novel. Subsequently, it has been shown that resistance to other tight binding enzyme inhibitors could also be attributed to gene amplification.
At the Memorial Sloan-Kettering Cancer
Drug resistance genes
Mutations and overexpressed target proteins, due to gene amplification or other mechanisms, can confer resistance to drugs. Using this knowledge, others and we have conducted studies to determine the feasibility of protecting normal haematopoietic precursors from chemotherapy by transfer of drug resistance genes via retroviral constructs into marrow stem cells (reviewed by Budak-Alpdogan et al [17].). The rationale behind this approach is that tumours develop resistance to chemotherapy while
Translational regulation of DHFR
Our early studies showed that DHFR levels (bound tightly to MTX) increase within hours in both normal leucocytes and acute leukaemia cells after treatment with MTX. As MTX slowly dissociates from the enzyme, cells that survive treatment synthesise tetrahydrofolate and continue to proliferate. Our work[24] and the studies of Chu et al [25]. have shown that DHFR translation is inhibited by binding of the DHFR protein to its cognate mRNA. Translation inhibition due to DHFR enzyme is relieved by
Conclusions
Probably more is known about the mechanism of action of antifolates than any other class of drugs. Folate antagonists have been useful for the treatment of many diseases, ranging from bacterial infections, malaria, autoimmune disease and cancer. Knowledge of their mechanism of action continues to grow, giving rise to new antifolates and new uses of these drugs. To paraphrase the late George Hitchings, “understanding the mechanism of action of a drug can open many doors.”
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2020, Chemico-Biological InteractionsHuman dihydrofolate reductase is a substrate of protein kinase CK2α
2019, Biochemical and Biophysical Research CommunicationsCitation Excerpt :The low level of S145 phosphorylation may indicate that the reaction was unspecific or required additional factors to effectively occur. Considering all important roles of DHFR, the protein has been an object of extensive structural, kinetic, and pharmacological studies as a molecular target in numerous chemotherapies (reviewed e.g. Refs. [17–20]). However, relatively little research is devoted to the role of posttranslational modifications of this important enzyme.
Loss of ALDH1L1 folate enzyme confers a selective metabolic advantage for tumor progression
2019, Chemico-Biological InteractionsCitation Excerpt :Since that time, the antifolate methotrexate (MTX) has been used for the treatment of leukemia as well as other cancers [8], and over the years new antifolate drugs have been developed [9,10]. MTX is a very specific inhibitor of dihydrofolate reductase (DHFR) [11], one of the key enzymes in folate metabolism, which is responsible for the incorporation of folic acid (dietary sources) and dihydrofolate (the second product in the TMP biosynthesis pathway) into the reduced folate pool [1]. Other enzymes in folate pathways bring one-carbon groups into the folate pool, oxidize/reduce folate-bound groups, or use them in biosynthetic reactions [1].