ADP-ribosylation of serum proteins: evaluation as a potential tumor marker

Serum samples from cancer patients revealed elevated levels of in vitro ADP-ribosylation through non-enzymic binding of ADP-ribose to free acceptor sites on serum proteins. Low concentrations of serum ADP-ribose caused by high NAD glycohydrolase activity together with elevated rates of ADP-ribose transport into erythrocytes appeared to account for under-saturation of the acceptor sites on serum proteins. ADP-ribosylation of serum proteins was assessed as an indicator of cancer disease, and an attempt was made to determine the correlation of ADP-ribosylation levels with carcinoembryonic antigen (CEA) values. Based on positive test results for all tumor patients and negative test results for all healthy controls, sensitivity and specificity of ADP-ribosylation as a tumor indicator were estimated as 67% and 95%, respectively. A close correlation appeared to exist with CEA (r = 0.67; P < 0.001). Similarly, the changes in the levels of ADP-ribosylation correlated with the changes in the levels of CEA during the clinical course (r = 0.58; P < 0.05).