Activity of and effect of subcutaneous treatment with the broad-spectrum antiviral lectin griffithsin in two laboratory rodent models

Abstract

Griffithsin (GRFT) is a red-alga-derived lectin that binds the terminal mannose residues of N-linked glycans found on the surface of human immunodeficiency virus type 1 (HIV-1), HIV-2, and other enveloped viruses, including hepatitis C virus (HCV), severe acute respiratory syndrome coronavirus (SARS-CoV), and Ebola virus. GRFT displays no human T-cell mitogenic activity and does not induce production of proinflammatory cytokines in treated human cell lines. However, despite the growing evidence showing the broad-spectrum nanomolar or better antiviral activity of GRFT, no study has reported a comprehensive assessment of GRFT safety as a potential systemic antiviral treatment. The results presented in this work show that minimal toxicity was induced by a range of single and repeated daily subcutaneous doses of GRFT in two rodent species, although we noted treatment-associated increases in spleen and liver mass suggestive of an antidrug immune response. The drug is systemically distributed, accumulating to high levels in the serum and plasma after subcutaneous delivery. Further, we showed that serum from GRFT-treated animals retained antiviral activity against HIV-1-enveloped pseudoviruses in a cell-based neutralization assay. Overall, our data presented here show that GRFT accumulates to relevant therapeutic concentrations which are tolerated with minimal toxicity. These studies support further development of GRFT as a systemic antiviral therapeutic agent against enveloped viruses, although deimmunizing the molecule may be necessary if it is to be used in long-term treatment of chronic viral infections.

FIG 1

Griffithsin concentrations in plasma and serum samples. Data were obtained from mouse plasma after a single high-dose administration of 50 mg/kg GRFT (A) and a chronic daily administration of 10 mg/kg GRFT (B) and from guinea pig serum after 10 daily administrations of 10 mg/kg GRFT (C). PBS was administered to control animals, and bars indicate mean group concentrations.

FIG 2

Antiviral activity of samples collected from GRFT-treated animals. (A) For HIV-1 env, pseudovirus neutralization activity was assessed for mouse plasma after a single high-dose administration of 50 mg/kg GRFT and is expressed as ID₅₀. (B) The ID₅₀ values were obtained for samples from guinea pigs and mice chronically treated with 10 mg/kg GRFT. Control animals were treated with PBS bars indicate mean group concentrations. Statistical significance (P < 0.05; 1-way ANOVA) is indicated by asterisks (*).

FIG 3

Quantitation of GRFT in mouse organs. Pooled protein samples were extracted from kidneys, livers, and spleens after a chronic subcutaneous administration of GRFT or PBS, and GRFT was detected using gp120 binding ELISA.

FIG 4

Guinea pig body weight gain as an indicator of overall health. Body weights were measured on experimental day 1 and on the termination day (day 11 or day 15). Statistical significance (P < 0.05) is indicated by asterisks (*).

FIG 5

Effect of GRFT on guinea pig organ weights. Liver (A), kidney (B), and spleen (C) weights were measured relative to body weight at sacrifice.

FIG 6

Serum chemistry data for guinea pigs after chronic treatment with GRFT. Levels of serum albumin (A), alkaline phosphatase (B), and amylase (C) were obtained from GRFT- or PBS-treated animals at sacrifice. Bars indicate mean group concentrations.

FIG 7

Hemagglutination activity of GRFT. A wide range of GRFT concentrations (5 μg/ml equals 391 nM) was used to examine GRFT's potential hemagglutination activity on erythrocytes from multiple species, including sheep (A), guinea pig (B), human (C), and mouse (D). PHA (5 μg/ml) and PBS were used as positive and negative controls, respectively.