EXPRESSION OF DEOXYCYTIDINE KINASE AND PHOSPHORYLATION OF 2-CHLORODEOXYADENOSINE IN HUMAN NORMAL AND TUMOR-CELLS AND TISSUES

Deoxycytidine kinase (dCK) activates several clinically important drug s, including the recently developed antileukaemic compound 2-chlorodeo xyadenosine (CdA). The distribution of dCK in cells and tissues has pr eviously been determined by activity measurements, which may be unreli able because of the presence of other enzymes with overlapping substra te specificities. Therefore we have measured dCK polypeptide levels in extracts of normal and malignant human peripheral blood mononuclear c ells, gastrointestinal tissues and sarcomas, using a specific immunobl otting technique, as well as the phosphorylation of CdA in the same ex tracts. High levels of dCK were found in all major subpopulations of n ormal mononuclear leucocytes (120 +/- 19 ng dCK\mg protein) and in B-c ell chronic lymphocytic leukaemia (81 +/- 30 ng/mg, n = 23). Hairy-cel l leukaemia contained lower levels (28 +/- 23 ng/mg, n = 7), as did th ree samples of T-cell chronic lymphocytic leukaemia (18 +/- 14 ng/mg). Phytohaemagglutinin stimulation of normal lymphocytes did not lead to any substantial increase in either dCK activity or protein expression (less than 2.5-fold). The human CEM wt T-lymphoblastoid cell line con tained 56 +/- 1 ng/dCK/mg protein, while in the CEM ddC50 and AraC8D m utants that lack dCK activity, no dCK polypeptide could be detected. I n colon adenocarcinomas, the dCK content was significantly higher (20 +/- 9 ng/mg, n = 20) than in normal colon mucosa (8 +/- 3.5 ng/mg, n = 19, P < 0.05). A similar pattern of dCK expression was found in gastr ic adenocarcinomas (21 +/- 13 ng/mg, n = 5) and normal stomach mucosa (6 +/- 5 ng/mg, n = 5, P < 0.15). One leiomyosarcoma and one extra-ske letal osteosarcoma showed dCK levels comparable with those found in no rmal lymphocytes (84 +/- 6 and 109 +/- 4 ng/mg, respectively), while o ther sarcoma samples contained lower levels, comparable to the gastroi ntestinal adenocarcinomas (20 +/- 7 ng/mg, n = 12). Thus, dCK is expre ssed constitutively and predominantly in lymphoid cells, but it is als o found in solid non-lymphoid tissues, with increased levels in malign ant cells. The phosphorylation of CdA in crude extracts showed a close correlation to the dCK polypeptide level.