ROLE OF DEPHOSPHORYLATION IN ACCUMULATION OF 1-BETA-D-ARABINOFURANOSYLCYTOSINE 5'-TRIPHOSPHATE IN HUMAN LYMPHOBLASTIC CELL-LINES WITH REFERENCE TO THEIR DRUG SENSITIVITY

  • 1 January 1982
    • journal article
    • research article
    • Vol. 42  (7) , 2846-2851
Abstract
After a 3-day exposure to 0.1 .mu.M 1-.beta.-D-arabinofuranosylcyotosine (ara-C) in culture, growth was inhibited to 5.6% in MOLT-4F, 25% in Raji and 91% in Daudi cells compared with control. Growth inhibition was more profound when exposure time was extended up to 7 days. Inhibition of DNA synthesis varied with sensitivity to ara-C. Plateau levels of intracellular 1-.beta.-D-arabinofuranosylcytosine 5''-triphosphate (ara-CTP) were 35.5, 13.4 and 3.6 nmol/109 cells exposed to 0.1 .mu.M ara-C in MOLT-4F, Raji and Daudi cells, respectively, corresponding to the sensitivity to ara-C. The nucleotide levels at the plateau, however, did not correspond to the initial levels of the ara-CTP or to the calculated rate of ara-CTP synthesis, which decreased from Raji to MOLT-4F to Daudi cells. ara-C deamination had negligible effect on the differential accumulation of ara-CTP. ara-CTP degradation due to dephosphorylation was marked in Raji and Daudi cells but slight in MOLT-4F cells. The half-life of intracellualr ara-CTP was 204, 26.4 and 31.1 min in MOLT-4F, Raji and Daudi cells, respectively. The ara-CTP level was considered to be maintained bimodally by synthesis and degradation of the nucleotide. The Raji and Daudi cells exposed to 0.1 .mu.M ara-C in the presence of 1 mM hydroxyurea, the plateau levels of ara-CTP increased 3-fold through inhibition of the nucleotide degradation. Thus, not only ara-C phoshorylation but also subsequent ara-CTP dephosphorylation was important in the accumulation and maintenance of ara-CTP and in the sensitivity to ara-C.