Antiviral effects of milk proteins: Acylation results in polyanionic compounds with potent activity against human immunodeficiency virus types 1 and 2 in vitro

A number of native and modified milk proteins from bovine or human sources were analyzed for their inhibitory effects on human immunodeficiency virus type 1 (HIV-1) and HIV-2 in vitro in an MT4 cell test system, The proteins investigated were lactoferrin, alpha-lactalbumin, beta-lactoglobulin A, and beta-lactoglobulin B. By acylation of the amino function of the lysine residues in the proteins, using anhydrides of succinic acid or cis-aconitic acid, protein derivatives were obtained that all showed a strong antiviral activity against human immunodeficiency virus type 1 and/or 2. The in vitro IC50 values of the aconitylated proteins were in the concentration range of 0.3 to 3 nM. Succinylation or aconitylation of alpha-lactalbumin and beta-lactoglobulin A/B also produced strong anti-HIV-2 activity with IC50 values on the order 500 to 3000 nM. All compounds showed virtually no cytotoxicity at the concentration used. Peptide-scanning studies indicated that the native lactoferrin as well as the charged modified proteins strongly bind to the V3 loop of the gp120 envelope protein, with K-d values in the same concentration range as the above-mentioned IC50. Therefore, shielding of this domain, resulting in inhibition of virus-cell fusion and entry of the virus into MT4 cells, may be the likely underlying mechanism of antiviral action.