Cyclopentenyl cytosine inhibits cytidine triphosphate synthetase in paediatric acute non-lymphocytic leukaemia: a promising target for chemotherapy

Cytidine triphosphate (CTP) synthetase is a key enzyme in the anabolic path ways of cytosine and uracil ribonucleotide metabolism. The enzyme catalyses the conversion of uridine triphosphate (UTP) into CTP, and has a high acti vity in various malignancies, which has led to the development of inhibitor s of CTP synthetase for therapeutic purposes. We studied both CTP synthetas e activity and ribonucleotide concentrations in leukaemic cells of 12 child ren suffering from acute non-lymphocytic leukaemia (ANLL), and performed in cubation experiments with cyclopentenyl cytosine (CPEC), a nucleoside analo gue that is capable of inhibiting CTP synthetase. The CTP synthetase activi ty in ANLL cells (5.1+/-2.3 nmol CTP/mg/h) was significantly higher compare d with granulocytes of healthy controls (0.6+/-0.4 nmol CTP/mg/h, P = 0.000 2), but was not different from the CTP synthetase activity in non-malignant CD34+ bone marrow cells (5.6+/-2.4 nmol CTP/mg/h). Major shifts were obser ved in the various ribonucleotide concentrations in ANLL cells compared wit h granulocytes: the absolute amount of ribonucleotides was increased with a substantial rise of the CTP (2.4 versus 0.4 pmol/mu g protein, P = 0.0007) and UTP (8.7 versus 1.6 pmol/mu g protein, P = 0.0007) concentrations in A NLL cells compared with granulocytes. Treatment of ANLL cells in vitro with CPEC induced a major depletion (77% with 2.5 mu M of CPEC) in the concentr ation of CTP, whilst the concentrations of the other ribonucleotides remain ed unchanged. Therefore, the high activity of CTP synthetase in acute non-l ymphocytic leukaemic cells can be inhibited by CPEC, which provides a key t o a new approach for the treatment of ANLL. (C) 2000 Elsevier Science Ltd. All rights reserved.