Peptides as Therapeutic Agents for Dengue Virus

Chew, Miaw-Fang; Poh, Keat-Seong; Poh, Chit-Laa

Tambunan and Alamudi (2010) designed several cyclopentapeptides based on the substrate specificity for the NS2B-NS3 protease and a cyclopentapeptide, CKRKC, was found to be the best candidate with the estimated free binding energy of -8.39 kcal/mol and Ki of 0.707 μM [173] . Nonetheless, the cyclopentapeptide was designed in silico, further in vitro and cell-based experiments were required to further exploit the inhibitory potential of the peptide against DENV. Similarly, Velmurugan et al. (2014) found a hexapeptide with the highest binding energy of -80.4 kcal/mol against the NS2B-NS3 protease, but further investigation is required to verify its antiviral potential via in vitro studies [174] . In another study, a natural peptide library composed of conotoxins (a mixture of peptide neurotoxins produced by cone snails) was used to screen against the DENV NS2B-NS3 protease [175] . A 13-mer cyclic peptide inhibitor, MrIA (derived from Conus marmoreus), was shown to possess a Ki value of 9 µM. Mutagenesis study further revealed that the inhibitory activity was mainly mediated by a disulphide bond loop with a Lys residue at the active site. As the NS2B-NS3 protease was previously shown to have a preference for Ser at the P' position, further optimization was carried out. By changing the Leu to Ser, the resultant peptide 7 (P7) and peptide 9 (P9) were shown to have stronger inhibitory activities with improved Ki values of 1.4 µM and 2.2 µM, respectively. Nonetheless, stability assays showed that about half of the inhibitory activity of P7 was lost after 2.5h, while only ~25% inhibitory activity of P9 was lost after incubating with protease for 2.5h. Although P9 had a higher Ki value of 2.2 µM as compared to P7 (1.4 µM), the stability of P9 to withstand protease degradation and its efficient cell permeability in BHK-21 and Vero cells had shown that P9 is a better drug candidate. Rothan et al. (2012a and 2012b) identified two antiviral peptides, namely protegrin-1 and retrocyclin-1 against DENV NS2B-NS3 protease [176, 177] . It was previously shown that protegrin-1, a cationic cyclic peptide, possessed broad antimicrobial properties against different microorganisms [178] . In addition to having good binding affinity (Ki value of 5.85 μM) against the DENV NS2B-NS3 protease, protegrin-1 was able to inhibit DENV replication in Rhesus monkey kidney (MK2) cells with an IC50 of 11.7 μM [176] . On the contrary, retrocyclin-1, a circular cationic peptide, was shown to inhibit the NS2B-NS3 protease at an IC50 of 21.4 μM [177] . Results indicated that retrocyclin-1 worked best when incubated with DENV-2 during simultaneous treatment, giving 85% reduction in viral replication after 75 hours. These findings suggest that both protegrin-1 and retrocyclin-1 are feasible candidates to be potential therapeutic drugs for dengue treatment.