Microbicides, which are compounds ideally characterized by low toxicity and high activity against human immunodeficiency virus type 1 (HIV-1), are urgently needed as a means to reduce or eliminate the risk of heterosexual HIV-1 transmission. In collaboration with Novaflux Biosciences, we are studying a unique family of compounds as candidate microbicidal agents. Polybiguanides are polymeric, polycationic molecules comprised of biguanide subunits connected by hydrocarbon chains. We have demonstrated that polyethylene hexamethylene biguanide (PEHMB), which is a member of the polybiguanide family, is characterized by low cytotoxicity, minimal in vivo toxicity, and the ability to inhibit HIV-1 infection of susceptible cell types. We have also shown that this compound can provide persistent protection against HIV-1 challenge. Based in preliminary experiments in which CXCR4 and CCR5 cell-surface presentation were disturbed by exposure to PEHMB, we postulate that the antiviral activity of this molecule involves changes in co-receptor presentation that are detrimental to events that support HIV-1 binding and entry. Our current studies are focused on defining the mechanism(s) of action of PEHMB and determining the impact of PEHMB on co-receptor-mediated signal transduction. These studies will provide valuable information relevant to the safety and efficacy of polybiguanide-based microbicides.