THYMIDINE KINASE IN MALIGNANT-MELANOMA

Thymidine kinase (EC 2.7.1.21) is an enzyme supporting DNA synthesis u nder conditions of increased cell proliferation. Although it has prove d to be a useful marker for various malignant diseases, it has not bee n tested in malignant melanoma. Thymidine kinase activity was measured by means of a radioenzymic assay in two classical animal models of me lanoma disease - B16 and Cloudman S91 melanoma-bearing mice. Tumour ce ll proliferation was assessed histochemically by measuring the express ion of proliferating cell nuclear antigen (PCNA). Tumour cytosolic spe cific thymidine kinase activity was found to be higher in less pigment ed Cloudman S91 melanoma than in differentiated, ie pigmented B16 mela noma, relative to the proliferative activity of the two tumours. Serum thymidine kinase levels were increased in melanoma-bearing animals of both types compared with healthy mice; this also reflected the effica cy of the therapy: cyclophosphamide-treated B16 melanoma-bearing mice in which the tumour development was slowed down had significantly lowe r serum enzyme levels in comparison with the non-treated group and the same levels compared with control, healthy mice. Our results suggest that serum thymidine kinase levels might be used as a marker to follow the effect of melanoma therapy.