guanosine-triphosphate and triciribine

The experimental antineoplastic agent triciribine (tricyclic nucleoside, TCN) is known to be activated to its phosphate TCN-P by adenosine kinase and to inhibit cell growth, purine nucleotide synthesis, and incorporation of amino acids into proteins. Our objective in this paper was to compare these effects in intact cells of a human cell line as a prerequisite to describing in a companion paper [Moore et al., Biochem. Pharmac. 38, 4045 (1989)] more detailed enzymic studies of their interrelationships. TCN treatment inhibited cloning of CCRF-CEM human leukemic lymphoblasts 50% at concentrations of 6, 30, and 90 microM with 8-day, 8-hr, and 2-hr exposures respectively. However, 6-20% of the cells survived exposure to 200 microM TCN for 24 hr. The intracellular formation of TCN-P from TCN was rapid, concentrative and essentially complete, but TCN-P did not exceed about 1.4 mM (1.4 nmol/10(6) cells) at 200 microM TCN. In cells exposed to 50 microM TCN for 1.25 to 24 hr, formate incorporation into ATP and GTP was inhibited the most rapidly and strongly; pools of ATP and GTP were decreased as much as 40% (as compared with controls); and incorporation of formate into RNA purines was inhibited as much as 65%. Incorporation of leucine into protein was more moderately inhibited up to 40%, apparently in proportion to the concentration of intracellular TCN-P, rather than of the TCN in the medium. These inhibitions occurred most rapidly during the first 2-4 hr and increased only gradually thereafter, whereas cloning ability was inhibited more slowly and uniformly over a longer time period. No one of these metabolic effects by itself showed a clear correlation with the loss of viability. The incorporation of formate into formylglycinamide ribotide (FGAR, when accumulated at a blockage by azaserine) was inhibited drastically by TCN. The rate of incorporation of hypoxanthine into ATP was increased by TCN, whereas incorporation into GTP was decreased. Thus, the principal sites of inhibition of purine synthesis by TCN-P were shown in these intact cells to be at a step prior to synthesis of FGAR in the de novo pathway and also at an additional site between IMP and GTP.

Topics: Adenosine Triphosphate; Antineoplastic Agents; Cell Survival; Formates; Glycine; Guanosine Triphosphate; Humans; Hypoxanthine; Hypoxanthines; Kinetics; Leukemia, Lymphoid; Lymphocytes; Phosphorylation; Protein Biosynthesis; Purines; Ribonucleosides; Ribonucleotides; RNA; Tumor Cells, Cultured