ACTIBIND, an actin-binding fungal T₂-RNase with antiangiogenic and anticarcinogenic characteristics

BACKGROUND. ACTIBIND is an Aspergillus niger extracellular ribonuclease (T₂-ribonuclease [RNase]) that possesses actin-binding activity. In plants, ACTIBIND inhibits the elongation and alters the orientation of pollen tubes by interfering with the intracellular actin network. The question rose whether ACTIBIND can also affect mammalian cancer development. METHODS. Cell colony formation was performed in human colon (HT-29, Caco-2, RSB), breast (ZR-75-1), and ovarian (2780) cancer cells in the presence or absence of 1 μM ACTIBIND. In HT-29 and ZR-75-1 cells, the effect of ACTIBIND on cell migration was studied by microscopic observations and by invasion assay through Matrigel. Tube formation was assessed in human umbilical vein endothelial cells (HUVEC) in the presence of angiogenin or basic fibroblast growth factor (bFGF) (1 μg/mL each) following overnight incubation with 1 or 10 μM ACTIBIND. In an athymic mouse xenograft model, HT-29 cells were injected subcutaneously, followed by subcutaneous (0.4-8 mg/mouse/injection) or intraperitoneal (0.001-1 mg/mouse/injection) injections of ACTIBIND. In a rat dimethylhydrazine (DMH)-colorectal carcinogenesis model, ACTIBIND was released directly into the colon via osmotic micropumps (250 μg/rat/day) or given orally via microcapsules (1.6 mg/rat/day). Aberrant crypt foci, tumors in the distal colon, and tumor blood vessels were examined. RESULTS. ACTIBIND had an anticlonogenic effect unrelated to its ribonuclease activity. It also inhibited angiogenin-induced HUVEC tube formation in a dose-responsive manner. ACTIBIND was found to bind actin in vitro. It also bound to cancer cell surfaces, leading to disruption of the internal actin network and inhibiting cell motility and invasiveness through Matrigel-coated filters. In mice, ACTIBIND inhibited HT-29 xenograft tumor development, given either as a subcutaneous or intraperitoneal treatment. In rats, ACTIBIND exerted preventive and therapeutic effects on developing colonic tumors induced by DMH. It also reduced the degree of tumor observation. CONCLUSIONS. This study indicated that ACTIBIND is an effective antiangiogenic and anticarcinogenic factor.