Optimization of Peptides That Target Human Thymidylate Synthase to Inhibit Ovarian Cancer Cell Growth

Thymidylate synthase (TS) is a target for pemetrexed and the prodrug 5-fluorouracil (5-FU) that inhibit the
protein by binding at its active site. Prolonged administration of these drugs causes TS overexpression, leading to drug resistance.
The peptide lead, LR (LSCQLYQR), allosterically stabilizes the inactive form of the protein and inhibits ovarian cancer (OC)
cell growth with stable TS and decreased dihydrofolate reductase (DHFR) expression. To improve TS inhibition and the
anticancer effect, we have developed 35 peptides by modifying the lead. The D-glutamine-modified peptide displayed the best
inhibition of cisplatin-sensitive and -resistant OC cell growth, was more active than LR and 5-FU, and showed a TS/DHFR
expression pattern similar to LR. Circular dichroism spectroscopy and molecular dynamics studies provided a molecular-level
rationale for the differences in structural preferences and the enzyme inhibitory activities. By combining target inhibition studies
and the modulation pattern of associated proteins, this work avenues a concept to develop more specific inhibitors of OC cell
growth and drug leads.