Discovery of new non-pyrimidine scaffolds as DHFR inhibitors by fragment-based screening.

In various malaria-endemic regions, the appearance of resistance has precluded the use of pyrimidine-based antifolate drugs. Here, a three-step fragment screening was used to identify new non-pyrimidine dihydrofolate reductase (DHFR) inhibitors. Starting from a 1163-fragment commercial library, a two-step differential scanning fluorimetry screen identified 75 primary fragment hits. Subsequent enzyme inhibition assay identified 11 fragments displaying IC in the 28-695 μM range and selectivity for DHFR. In addition to the known pyrimidine, three new anti-DHFR chemotypes were identified. Fragments from each chemotype were successfully co-crystallized with DHFR, revealing a binding in the active site, in the vicinity of catalytic residues, which was confirmed by molecular docking on all fragment hits. Finally, comparison with similar non-hit fragments provides preliminary input on available growth vectors for future drug development.