Peptides as Therapeutic Agents for Dengue Virus

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

Studies have shown that the E stem region was well conserved among Flaviviruses [including WNV, tick-borne encephalitis virus (TBE), YFV and JEV] [121, 136] . Therefore, an antiviral peptide targeting against one DENV serotype might possess the possibility to inhibit other DENV serotypes and closely related Flaviviruses. To further examine this hypothesis, investigated the antiviral potential of stem peptides derived from DENV-2 and WNV against DENV 1, 2, 3 and 4 [136] . The amino acid residues from 419-447 of the genome of each of the four DENV serotypes were synthesized along with a solubility tag (RGKGR). Results showed that DV2 419-447 remained the strongest inhibitor against all four dengue serotypes, followed by DV1 419-447 , DV3 419-447 and DV4 419-447 . Nonetheless, when stem peptides (residues 419-447) from related flaviviruses were tested against DENV infection, none of these peptides inhibited any of the DENV serotypes. This might be due to the variation in the seven residues located at the C-terminal which could have affected the non-specific interaction with the viral membrane rather than poor affinity against E protein, as WNV had nearly identical binding affinities for trimeric DV2 sE [136] . To further validate the observation, mutagenesis was performed, confirming that residues 442-444 were important in conferring the antiviral activity of the stem peptide whereby increased hydrophobicity would increase inhibitory strength [136] . On the other hand, a similar situation was observed by Hrobowski et al. (2005) , whereby the DN 59 peptide (peptide sequence corresponding to the pre-anchor stem of the E protein and highly conserved among flaviviruses) which was shown to inhibit DENV had also demonstrated cross-inhibitory activity against WNV (>99% inhibition with concentration of <25µM) [119] . Bai et al. (2007) found a peptide, P1, which was isolated from the murine brain cDNA phage display library by biopanning against the recombinant WNV E protein [137] . When P1 was tested against DENV-2, it inhibited ~99% DENV-2 at a concentration of 200 µM. Surface plasmon resonance (SPR) showed that P1 bound to the WNV E protein with a Kd of 6 µM. However, the specific binding site on E protein and the mode of action are unknown. Other peptides that blocked DENV infection by binding to the E proteins were DN57 opt and 1OAN1 [138] . In the study, a set of peptides were computationally designed based on the pre-entry dimeric E structure. Peptides DN57 and 1OAN1 specifically designed from the hinge of domain II and the first domain I/domain II connection, was shown to display IC50 of 8 and 7 µM, respectively [138] . Both peptides were shown to bind specifically (affinities ~1 µM) to the purified DENV-2 E protein. Images from cryoEM suggested that these peptides might have caused structural deformations to the DENV-2 surface, hence interfering the virus-host cell binding. Further study of peptide inhibitors 1OAN1 and DN59 has also revealed that both peptide inhibitors were able to inhibit the antibody dependent enhancement (ADE) effect in vitro with an IC50 of 3 µM and 6 µM, respectively [139] . In a recent study, Chew et al. (2015) identified a novel peptide, peptide gg-ww, by biopanning a randomised phage display peptide library against the purified DENV-2 viral particles [140] . Approximately 96% inhibition was achieved at the concentration of 250 µM and the data indicated that peptide gg-ww inhibited DENV-2 entry. On the other hand, s