A new ADP-ribosyltransferase in human serum: significance in cancer

A novel ADP-ribosyltransferase (ADPRT) is reported from sera of both healthy human subjects (n = 25) and patients with colorectal tumors (n = 12) and breast cancer (n = 55). In sera of healthy controls (n = 25) the average ADPRT values were 250 +/- 56 picokatal/liter. ADPRT serum activities in metastatic cancer patients (n = 47) were three times higher (p less than 0.01) than in normal controls. A tumor origin of the serum ADPRT can be inferred from the statistical correlation (R = 0.74) between tumor and serum levels. The radiometric test procedure (CV 20-25%) is critically validated and kinetic properties of serum ADPRT have been studied, showing a competitive inhibition by nicotinamide, benzamide and 3-aminobenzamide. The kinetic parameters of serum ADPRT resemble those reported for nuclear ADPRT, thus indicating that serum ADPRT activity could be due to a nuclear enzyme released from the tumor cells.