Correlation of serum, tumor, and liver serum glycoprotein: N-acetylneuraminic acid transferase activity with growth of the R3230AC mammary tumor in rats and relationship of the serum activity to tumor burden.

The observation that the activity of sialyltransferase (EC 2.4.99.1; serum glycoprotein:N-acetylneuraminic acid transferase) is often elevated in the serum of cancer patients necessitates an elucidation of the interrelationships of this serum enzyme with host tissues. Accordingly, the activity of this enzyme in serum, tumor, and liver was determined at various times after implantation of the R3230AC mammary carcinoma into Fischer rats. Results from samples obtained at numerous, sequential time points demonstrated that significant elevations in serum sialyltransferase enzyme activity occurred only in animals bearing large tumor burdens, i.e., greater than 20 g, or in animals with tumors present for longer than 21 days. In these tumor-bearing rats, the activity of sialyltransferase increased in liver tissue at 21 to 25 days concurrently with the increase in serum enzyme activity, suggesting that the liver may be a potential source of the serum enzyme. Sialyltransferase activity in tumor tissue was quite variable; the activity increased one week after tumor implantation and remained at the same level thereafter. When tumors were excised, the activity of the serum enzyme returned to control values within four days after surgery, suggesting that the half-life of serum sialyltransferase was two days. Serum enzyme levels were again elevated upon regrowth of the tumor. These results show that the serum sialyltransferase alters its activity in conjunction with changes in tumor burden.