Computational and Experimental Validation of Methotrexate as Staphylococcal - DHFR inhibitor

Dihydrofolate reductase (DHFR) is an enzyme that reduces dihydrofolate to tetrahydrofolate for the denovo synthesis of purines. DHFR is a well-established and classic drug target used in cancer therapy. Several drugs like Methotrexate (MTX), Trimethoprim, Pemetrexed, Pyrimethamine, etc. are known inhibitors of DHFR and presently used to treat cancer patients. Staphylococcus is a major human pathogen and the causative agent of numerous hospital and community-acquired infections. In the present investigation, DHFR of Staphylococcus aureus (PDB Id: 2W9G) was subjected to molecular docking to evaluate whether the anti-cancer drugs, MTX and Pemetrexed strongly bind to the former. The results of molecular docking indicated that MTX and Pemetrexed strongly interact with Staphylococcal DHFR with the binding energy of -8.3kcal/mol and -9.0kcal/mol respectively. To validate the in silicostudies, the antimicrobial property of MTX and pemetrexed was evaluated in clinical strains of S. arlettae and S.sciuriin vitro and the results indicated that MTX but not pemetrexed possessed antimicrobial activity. But the similar antimicrobial effect of the abovementioned drugs was not found in gram-negative bacteria Pseudomonas aeruginosa (ATCC 27853), and E. coli (ATCC 25922). The Minimal Inhibitory Concentration (MIC) of MTX was found to be higher than 2mg/ml for both strains. Even though the MIC values of MTX are high, we propose that structural modification of MTX or its combination with conventional antibiotics may lead to the discovery of the new potential antimicrobial drug.