Optimized peptide based inhibitors targeting the dihydrofolate reductase pathway in cancer.

We report the first peptide based hDHFR inhibitors designed on the basis of structural analysis of dihydrofolate reductase (DHFR). A set of peptides were rationally designed and synthesized using solid phase peptide synthesis and characterized using nuclear magnetic resonance and enzyme immunoassays. The best candidate among them, a tetrapeptide, was chosen based on molecular mechanics calculations and evaluated in human lung adenocarcinoma cell line A549. It showed a significant reduction of cell proliferation and an IC(50) of 82 µM was obtained. The interaction of the peptide with DHFR was supported by isothermal calorimetric experiments revealing a dissociation constant K(d) of 0.7 µM and ΔG of -34 ± 1 kJ mol(-1). Conjugation with carboxylated polystyrene nanoparticles improved further its growth inhibitory effects. Taken together, this opens up new avenues to design, develop and deliver biocompatible peptide based anti-cancer agents.