The goal of this study was to develop drugs that exclusively affect pathogenic dihydrofolate reductase (DHFR) without causing harm to the human counterpart. To achieve that goal, a well-known dihydrofolate reductase (DHFR) inhibitors, trimethoprim (TMP), methotrexate (MTX) and trimetrexate (TMQ), were modified, tested, and crystallized on Mycobacterium tuberculosis (Mtb) dihydrofolate reductase (DHFR), wild type and quadruple mutant Plasmodium falciparum (Pf) DHFR-thymidylate synthase (TS), Staphylococcus aureus DHFR, and human DHFR. We focused on the drug design to utilize the structural differences between the pathogenic DHFRs and the human DHFR; specifically, we focused on a pocket near the substrate binding site where Asp27 and Gln28 of Mtb DHFR, and Asp54 and Met55 of Pf DHFR-TS are located. The same site is closely packed in human DHFR. From the initial screening and designing process, C-8 benzyl-2,4-diaminoquinazoline TMQ analogs were found to have outstanding selectivity against Mtb and Pf DHFR. Co-crystal structures of C-8 benzyl TMQ analogs with Mtb and Pf DHFR showed that the flexibility of Gln28 in Mtb DHFR, and Met55 in Pf DHFR contributes to extra space and interaction with C-8 benzyl moiety. This flexibility, which is not available in the human DHFR, enables the TMQ analogs to bind exclusively to the pathogenic DHFRs. Our novel C-8 benzyl-2,4-diaminoquinazoline TMQ analogs exhibited great potency and selectivity toward pathogenic DHFRs. In addition, these C-8 benzyl-2,4-diaminoquinazoline TMQ analogs were potent on Staphylococcus aureus DHFR as well and we hypothesize based on our findings that our C-8 benzyl-2,4-diaminoquinazoline TMQ analogs have potential for selective, broad spectrum antimicrobials against whose DHFR share the common structural feature with Mtb or Pf DHFR, an acid residue and a flexible residue next to it.
- Sacchettini, James Professor