Most of HIV-1 infections are acquired through sexual contact. In the absence of a preventive vaccine, the development of topical microbicides that can block infection at the mucosal tissues is needed. Dermaseptin S4 (DS4) is an antimicrobial peptide derived from amphibian skin, which displays a broad spectrum of activity against bacteria, yeast, filamentous fungi, and herpes simplex virus type 1. We show here that DS4 inhibits cell-free and cell-associated HIV-1 infection of P4-CCR5 indicator cells and human primary T lymphocytes. The peptide is effective against R5 and X4 primary isolates and laboratory-adapted strains of HIV-1. Its activity is directed against HIV-1 particles by disrupting the virion integrity. Increasing the number of DS4-positive charges reduced cytotoxicity without affecting the antiviral activity. The modified DS4 inhibited HIV-1 capture by dendritic cells and subsequent transmission to CD4(+) T cells, as well as HIV-1 binding on HEC-1 endometrial cells and transcytosis through a tight epithelial monolayer.

The in vitro antiviral activity of dermaseptins (S1-S5) against herpes simplex virus type 1 (HSV1) was investigated. These peptides were incubated with the virus and its target cells under various conditions, and their effects were examined by the cytopathic effect inhibition assay or by reduction in virus yield in Hep-2 cell cultures as well as by direct immunofluorescence. Dermaseptin S4 displayed the strongest antiviral effect against HSV1, at micromolar doses. Experiments including acyclovir as a reference antiviral agent were performed to investigate the mode of action of this dermaseptin. In contrast to acyclovir, dermaseptin S4 showed its inhibitory effect only when applied to the virus before, or during virus adsorption to the target cells. This suggested that the activity of this dermaseptin was exerted at a very early stage of the viral multiplication cycle, most likely at the virus-cell interface.

Over the last 20 years, natural peptides playing a key role in defense mechanisms and innate immunity have been isolated from unicellular organisms. Amphibian skin secretes dermaseptins, 24-34 amino acids in length that have a wide antimicrobial spectrum incorporating yeast, fungi, protozoa, bacteria and enveloped viruses. The anti-rabies virus (RABV) activity of dermaseptins S3 (30aa) and S4 (28aa) from Phyllomedusa sauvagei has been investigated, and further dissected its molecular basis by comparing punctual mutation or deletion of S4 analogues. The results showed that: (1) S4 is more active than S3 against RABV infection, 89% versus 38% inhibition at 7.5 μM; (2) the 5 NH2-aa of S4 are crucial for its inhibitory potential (S4 lost any inhibition) but the COOH terminus stabilizes the inhibitory potential (S4 showed only 23% inhibition at 7.5 μM); (3) there is a correlation between viral inhibition and dermaseptin cytotoxicity, which remains however moderated for BSR cells (≤12% at 10 μM). A single mutation in position 4 (S4) slightly reduced cytotoxicity while keeping its antiviral activity, 97% at 7.5 μM. S4 and S4 showed an antiviral activity in vitro when provided 1 h after infection. In vivo experiments in mice by intramuscular injection of non-toxic doses of dermaseptin S4 1 h post-infection by a lethal dose of RABV at the same site allowed more than 50% improvement in mice survival. This study highlights the potential interest of dermaseptins as non-expansive alternatives to rabies immunoglobulins for the treatment of rabies that continues to claim about 60,000 human lives per year worldwide, almost exclusively in developing countries.

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