Pyrazole-linked quinoline hydrazone derivatives: Design, synthesis, antimicrobial and antiproliferative activity via dihydrofolate reductase inhibition

Dihydrofolate reductase (DHFR) is an essential biological macromolecule that serves as a multi-therapeutic target. Its selective inhibition leads to effective anticancer or antimicrobial outcomes. The present study investigated the antimicrobial and antiproliferative activities of pyrazole-linked quinoline hydrazone derivatives ( 11a-11r ) through the inhibition of DHFR enzyme. Among the screened derivatives, 11r showed excellent antibacterial activity (MIC = 3.12 µg/mL) in comparison to the standard drug Ofloxacin (MIC = 6.25 µg/mL) against Escherichia coli and P. aeruginosa . Compound 11r also showed significant inhibitory activity (MIC = 100 µg/ mL) in comparison to the standard drug Ciprofloxacin (MIC = 50 µg/mL) against Methicillin-resistant S. aureus (MRSA). This compound also exhibited good anticancer activity (IC 50 = 1.26 µM) against HCT-116 colon cancer cells and profound selectivity. Compound 11r showed potent DHFR inhibitory activity (IC 50 = 0.326 µM), outperforming Trimethoprim (IC 50 = 15.33 µM) and approaching Methotrexate (IC 50 = 0.164 µM). Density Functional Theory (DFT) analysis indicated that 11r is relatively softer and more reactive with higher charge-transfer ability (ΔE = 2.182 eV), which makes it a more likely candidate to interact with the targeted site. In-vivo Oral acute toxicity study showed that compound 11r was non-toxic (LD 50 > 2000 mg/Kg) and did not indicate signs of adverse reaction during the study period. These findings suggested that 11r may be a lead molecule in the discovery of antibacterial and anticancer agents via targeting the DHFR enzyme.