PRO 2000 is a polyanionic compound under development as a topical antimicrobial gel for the potential prevention of HIV-1 transmission. It has been shown that PRO 2000 binds to HIV-1 gp120 and interferes with virus attachment to and/or fusion with CD4(+) T cells. Here, we demonstrate that PRO 2000 interacts not only with viral gp120 but also with CD4 and CXCR4 receptors on the cell surface. Minor or no effects were noticed on DC-SIGN and on CCR5. PRO 2000 dose-dependently inhibited the interaction of CXCL12 with the CXCR4 receptor as demonstrated with CXCL12(AF647)-labeled binding, CXCL12-induced calcium signaling, CXCR4 internalization and chemotaxic assays. These CXCR4 antagonistic properties of PRO 2000 are a potential additional mechanism of action that could explain the observation that PRO 2000 is described to be more active against X4 viruses than R5 viruses. The cellular activation potential and inflammatory properties of PRO 2000 were also examined in PBMCs. PRO 2000 had minor effects on the expression level of several cellular activation markers and enhanced the production of a small number of cytokines/chemokines, as determined by the Bio-Plex human cytokine 27-plex assay system. PRO 2000 showed less mitogenic and stimulatory activity than cyanovirin-N, but careful monitoring for potential side-effects is still advised.