In Silico Study Probes Potential Inhibitors of Human Dihydrofolate Reductase for Cancer Therapeutics

Dihydrofolate reductase (DHFR) is an essential cellular enzyme and thereby catalyzes thereduction of dihydrofolate to tetrahydrofolate (THF). In cancer medication, inhibition of humanDHFR (hDHFR) remains a promising strategy, as it depletes THF and slows DNA synthesis and cellproliferation. In the current study, ligand-based pharmacophore modeling identified and evaluatedthe critical chemical features of hDHFR inhibitors. A pharmacophore model (Hypo1) was generatedfrom known inhibitors of DHFR with a correlation coefficient (0.94), root mean square (RMS)deviation (0.99), and total cost value (125.28). Hypo1 was comprised of four chemical features,including two hydrogen bond donors (HDB), one hydrogen bond acceptor (HBA), and onehydrophobic (HYP). Hypo1 was validated using Fischer's randomization, test set, and decoy setvalidations, employed as a 3D query in a virtual screening at Maybridge, Chembridge, Asinex,National Cancer Institute (NCI), and Zinc databases. Hypo1-retrieved compounds were filtered byan absorption, distribution, metabolism, excretion, and toxicity (ADMET) assessment test andLipinski's rule of five, where the drug-like hit compounds were identified. The hit compounds weredocked in the active site of hDHFR and compounds with Goldfitness score was greater than 44.67(docking score for the reference compound), clustering analysis, and hydrogen bond interactionswere identified. Furthermore, molecular dynamics (MD) simulation identified three compounds asthe best inhibitors of hDHFR with the lowest root mean square deviation (1.2 Å to 1.8 Å), hydrogenbond interactions with hDHFR, and low binding free energy (-127 kJ/mol to -178 kJ/mol). Finally,the toxicity prediction by computer (TOPKAT) affirmed the safety of the novel inhibitors of hDHFRin human body. Overall, we recommend novel hit compounds of hDHFR for cancer and rheumatoidarthritis chemotherapeutics.

Asymmetric synthesis of (S)-ethyl-4-chloro-3-hydroxy butanoate using a Saccharomyces cerevisiae reductase: enantioselectivity and enzyme-substrate docking studies

Ethyl (S)-4-chloro-3-hydroxy butanoate (ECHB) is a building block for the synthesis of hypercholesterolemia drugs. In this study, various microbial reductases have been cloned and expressed in Escherichia coli. Their reductase activities toward ethyl-4-chloro oxobutanoate (ECOB) have been assayed. Amidst them, Baker's yeast YDL124W, YOR120W, and YOL151W reductases showed high activities. YDL124W produced (S)-ECHB exclusively, whereas YOR120W and YOL151W made (R)-form alcohol. The homology models and docking models with ECOB and NADPH elucidated their substrate specificities and enantioselectivities. A glucose dehydrogenase-coupling reaction was used as NADPH recycling system to perform continuously the reduction reaction. Recombinant E. coli cell co-expressing YDL124W and Bacillus subtilis glucose dehydrogenase produced (S)-ECHB exclusively.

Identification of amino acids required for the functional up-regulation of human dihydrofolate reductase protein in response to antifolate Treatment

Human dihydrofolate reductase (DHFR) protein levels rapidly increase upon exposure to methotrexate, a potent inhibitor of this enzyme. A model to explain this increase proposes that DHFR inhibits its own translation by binding to its cognate mRNA and that methotrexate disrupts the DHFR protein-mRNA complex allowing its translation to resume. In the present study, Chinese hamster ovary cells lacking DHFR were transfected with wild type and mutants of human DHFR to identify amino acids that are essential for increases in DHFR in response to methotrexate. Glu-30, Leu-22, and Ser-118 were involved in the up-regulation of DHFR protein levels by methotrexate and certain other antifolates. Cells transfected with E30A, L22R, and S118A mutants that did not respond to methotrexate up-regulation had higher basal levels of DHFR, consistent with the model, i.e. lack of feedback regulation of these enzymes. Although cells containing the S118A mutant enzyme had higher levels of DHFR and had catalytic activity similar to that of wild type DHFR, they had the same sensitivity to the cytotoxicity of methotrexate, as were cells with wild type DHFR. This finding provides evidence that the adaptive up-regulation of DHFR by methotrexate contributes to the decreased sensitivity to this drug. Based on these observations, a new model is proposed whereby DHFR exists in two conformations, one bound to DHFR mRNA and the other bound to NADPH. The mutants that are not up-regulated by methotrexate are unable to bind their cognate mRNA.