Purification, physicochemical characterization, and antitumor activity of a cancer-associated human serum protein that is increased by treatment with schizophyllan, an antitumor polysaccharide.

Abstract

A serum protein was purified from normal human sera by several steps of purification, and tentatively designated as cancer-associated serum protein (CAP-135), since the content of the protein was remarkably decreased in cancer patients. The purified CAP-135 has an approximate molecular weight of 135,000 daltons, and is composed of three subunits of 78,000, 34,500 and 24,800 daltons. CAP-135 showed an isoelectric point of pH 5.5-5.8 and contained a small amount (1.38%) of neutral sugar. CAP-135 is assumed to be modified complement C3 on the basis that it reacted only with anticomplement C3 in immunodiffusion assay, and one of its subunits had a molecular weight similar to that of the beta-chain of human complement C3. The ip injection of CAP-135 apparently inhibited the growth of sarcoma-180 implanted into the groin of Jc1:ICR female mice. The present results indicate that CAP-135 may be of diagnostic value.