Production of human alpha 1-antichymotrypsin-like protein by a human malignant melanoma transplanted into nude mice.

A tissue culture line of a human malignant melanoma, SEKI, induced cachexia in nude mice (BALB/c-nu/nu) (Kondo et al., Cancer Res., 41: 2912-2916, 1981). During the investigation of the cause of the cachexia, the melanoma was found to produce a protein immunologically identical to human alpha 1-antichymotrypsin (alpha 1-Ach). Tissues of the SEKI melanoma contained the protein immunologically equivalent to 0.29 +/- 0.11 (S.D.) mg of human alpha 1-Ach per g of wet tissue, while the other six human malignant tumors transplanted into nude mice did not contain a detectable amount of it. In the serum of nude mice bearing the melanoma, this protein appeared soon after the tumor growth occurred and gradually increased up to the level equivalent to 5 mg of human alpha 1-Ach per dl. Removal of the tumor resulted in a rapid decrease of the protein in the serum to an undetectable level within 1 day. This problem was never detected in the serum of nude mice bearing the other 27 human malignant tumors or controls. Purification of this protein was carried out by the column chromatography using DE-52, Blue-Sepharose, and SP-Sephadex. The elution patterns were the same as those of alpha 1-Ach in human serum, and the molecular weight of the protein was estimated as 69,000 by Sephadex G-100 column chromatography and 65,000 by polyacrylamide gel electrophoresis with sodium dodecyl sulfate. This purified protein, however, did not exhibit inhibitory activity against chymotrypsin. These results show that this melanoma produced a protein immunologically identical and physicochemically very similar to human alpha 1-Ach. This melanoma-nude mouse system may provide a useful model for investigating the synthesis of human alpha 1-Ach and analysis of its physiological roles.