A distinctive
glycopeptide, which acts as an acceptor for a
cancer-associated
galactosyltransferase, has been detected in sera and effusions of patients with extensive
carcinoma.
Cancer-associated galactosyltransferase acceptor (CAGA) purified from human malignant effusions was tested for its effects on cell growth in vitro and in vivo. Addition of the
glycopeptide to the media of cells growing in tissue culture significantly inhibited the attachment and growth of transformed cells but had minimal effect on nontransformed cells. Transformed hamster cells (BHKpy, BHKpygiv, Nilpy) and human malignant cells (BT-20 human breast, pancreatic and colonic
carcinoma cells) were killed by the addition of as little as 0.5 microgram of acceptor (per ml of medium); whereas nontransformed counterparts did not show a significant change in growth or morphology. In vivo studies showed that the acceptor inhibited development and progression of
tumors in hamsters inoculated with tumorigenic BHKpy cells and in nude mice inoculated with human
carcinoma cells. Growth of
tumors was inhibited 69--94% in animals given 20 micrograms of acceptor subcutaneously and 39--67% when acceptor was given intraperitoneally at the time of
tumor cell inoculation. Administration of the acceptor after the development of palpable
tumor (congruent to 0.5 cm) caused a 60--85% reduction in growth rate and, in some cases, actual reduction in size and disappearance of palpable
tumor. These studies demonstrate that a
galactosyltransferase glycopeptide acceptor purified from human malignant effusions produces selective inhibition of transformed cell growth in animal and tissue culture systems.