A recombinant form of the endogenous chemokine platelet factor 4 with potential antiangiogenesis and antineoplastic activities. As a heparin-binding tetramer, iroplact inhibits growth factor-stimulated endothelial cell proliferation, migration, and angiogenesis; it has been shown that this agent inhibits fibroblast growth factor 2 (FGF2) angiogenic activity downstream from the FGF2 receptor. Its activity is antagonized by heparin. Recombinant platelet factor 4 may also directly inhibit the proliferation of some tumor cell types.