Purification and characterization of tumor invasion-inhibiting factors.

Tumor invasion-inhibiting factors were purified from bovine liver using an in vitro system for estimating the tumor invasion ability. The acid-ethanol extract of liver was subjected to ultrafiltration (Amicon PM10 membrane), and the fraction corresponding to the molecular weight range below 10,000 was further fractionated by ion-exchange (DEAE-Toyopearl), gel filtration (Bio-Gel P6), and reverse-phase (C18) chromatographies. Two types of active polypeptides with molecular weights of about 5,000 and 2,000 were purified and named IIF-1 and IIF-2, respectively. Both peptides inhibited tumor invasion with half-maximum concentrations of 2-6 ng/ml in vitro. The amino acid compositions of both peptides were determined.