Isolation and Characterization of a Novel Cytolytic Factor in Purple Fluid of the Sea Hare, Aplysia kurodai

A novel cytolytic factor, aplysianin P, which induces tumor lysis, was purified to apparent homogeneity from the purple fluid of the sea hare Aplysia kurodai. Purified aplysianin P was a single Mr60,000 polypeptide. This factor was half-maximally active at 3-25 ng protein/ml and lysed all the tumor cells tested but did not lyse normal WBC or RBC. Aplysianin P was labile on treatments with heat, low pH, urea, and periodate, but not with Pronase. The factor completely inhibited the syntheses of DNA, RNA, and protein by tumor cells within 2 h and caused their complete cytolysis within 18 h. Tumor lysis by aplysianin P was inhibited by N-acetylneuraminic acid, suggesting that recognition of the sugar moiety is a key step in the cytolysis induced by aplysianin P. The factor also prolonged the survival of mice bearing syngeneic MM46 ascites. It did not resemble previously isolated antineoplastic glycoproteins from the eggs (aplysianin E) or albumen gland (aplysianin A) of A. kurodai in terms of molecular size, antigenicity, or amino acid composition. These results suggest that aplysianin P found in an invertebrate, the sea hare, is a new antitumor factor.