RC-101,a Retrocyclin-1 Analogue with Enhanced Activity against Primary HIV Type 1 Isolates

Abstract

Rhesus macaques express three θ-defensins (RTDs 1–3), cyclic octadecapeptides with antiviral and lectin-like properties. Corresponding θ-defensin genes exist and are expressed in humans, but a signal sequence mutation prevents the formation of mature θ-defensin peptides. Retrocyclin-1 is a θ-defensin peptide whose precursor is encoded by human θ-defensin pseudogenes. It can protect human peripheral blood lymphocytes from infection by R5 and X4 strains of HIV-1, and provides a molecular template for designing novel antiviral agents. In this study, we used JC53-BL reporter cells to assess the activity of retrocyclin-1 (RC-100) and several analogues against primary HIV-1 isolates, including R5 and R5X4 strains of subtypes A–D, CRF-01_AE, and recombinants. Each analogue differed from retrocyclin-1 by a single amino acid substitution: Gly ↠ Tyr in RC-106, RC-115, and RC-116, and Arg ↠ Lys in RC-101. Although the modification in RC-101 was chemically conservative, this peptide was significantly more potent than retrocyclin-1 across the panel of primary isolates. We performed surface plasmon resonance binding studies, using recombinant gp120 and CD4 produced in insect cells. Although RC-100 and RC-101 bound gp120 LAV/IIIB with a K_d of 30–35 nM, they bound gp120 from CRF-01_AE strains (CM 235 and 93TH975.15) with K_d values of 200–750 nM. Overall, our findings suggest that clade-related differences in gp120 glycosylation impact the ability of retrocyclin-1 to bind this viral glycoprotein, and modulate the peptides' ability to prevent HIV-1 infection. The performance of RC-101 suggests that additional "engineering" could further enhance the antiviral properties of θ-defensins.