Serum alkaline deoxyribonuclease activity, a sensitive marker for the therapeutic monitoring of cancer patients: methodological aspects.

Alkaline deoxyribonuclease (DNase) is present in human circulating serum but its physiological role and signification of its variations are still largely unknown. The present report demonstrates that between 37 degrees C and 50 degrees C, as measured in the presence of 0.25 mmol/l Ca2+ and 5 mmol/l Mg2+, serum alkaline DNase activity increases, in most sera, reaching a level far higher than expected from thermal activation. This observation is thought to be due to the thermal inactivation of a serum inhibitor of the enzyme, which limits its usefulness as a therapeutic marker. By measuring serum alkaline DNase activity at 50 degrees C, the authors have developed a clinical test which has been successfully applied to the therapeutic monitoring of patients with various types of cancers.