DESIGN AND SYNTHESIS OF PROTEIN-PROTEIN INTERACTION MIMICS AS INHIBITORS OF PLASMODIUM FALCIPARUM CYSTEINE PROTEASE FALCIPAIN-2

Cysteine proteases play a significant role in the growth and the development of several human parasites such as Plasmodium, Leishmania, and Trypanosoma which affect more than 3.5 billion people worldwide. Falcipain-2 (FP-2) is an important cysteine protease of the human malaria parasite, P. falciparum (Pf), and is one of the most promising target for the development of new Pf inhibitors. FP-2 plays roles in haemoglobin degradation and merozoites egression at the asexual blood stages of Plasmodium development. Endogenous cysteine protease inhibitors have been described in a number of eukaryotic systems and they represent an important platform for new drug design. Cystatin and its homologues are natural inhibitors of Papain and others cysteine proteases, but the high molecular weight and the peptidic structure raise difficulties in their exploitation in the drug design process. In the present study, we designed a series of small peptides that mimic the protein-protein interaction between FP-2 and Chicken Egg White Cystatin and analyzed their effects on FP-2 activity. These peptide mimics were designed keeping in mind the distance of about 4-5 Å between the carbonyl of Pro11 or Val12 of cystatin. Three different linkers, γ-aminobutyrric acid (GABA), cis-4-aminocyclohexane carboxylic acid and a macrocycle formed by GABA and two cysteines joined by a disulfide bridge were used to link peptides. Some of these compounds showed considerable inhibition (≥50%) at 5 µM (Ki 2-7.5 µM). When these peptide mimics were tested against the mature parasite, they also produced morphological abnormalities especially in the food vacuole, similar to what have been observed with others cysteine protease inhibitors. We believe this approach could be an excellent starting point for the development of new cysteine protease inhibitors and in general for the development of new drugs against P. falciparum.