Tiazofurin (TR) is anabolized intracellularly to an analogue of NAD, tiazole-4-carboxamide adenine dinucleotide (TAD), which is a potent inhibitor of IMP dehydrogenase (IMPDH). Inhibition of IMPDH results in reduced synthesis of guanylates, including GTP and dGTP. TR has shown good responses in Phase I/II trials in patients with end stage leukemia, but repeated treatment with TR is required to maintain remission, leading to development of resistance. To eliminate this problem, new inhibitors of IMPDH were synthesized. Benzamide riboside (BR) shows potent cytotoxicity against murine and human tumor cells in culture and antitumor activity in mice bearing L1210 leukemia. BR demonstrates a similar mechanism of action to TR, wherein it is converted to benzamide adenine dinucleotide (BAD), an analogue of NAD, and tumor cells form more BAD than TAD. In order to illustrate the usefulness of BR for future clinical trials in patients with acute myeloid leukemia (AML), the present study directly compared the activity of TR and BR in AML cells. Peripheral blood samples were obtained from AML patients, diluted with RPMI 1640 cell growth medium, carefully layered over Histopaque and centrifuged at 400 g for 20 minutes. Leukemic cells in the interface layer were separated and washed with growth medium containing 10% fetal bovine serum. To develop a test to determine the sensitivity and selectivity of leukemic cells to BR or TR, the cells were incubated at 37°C with 5 to 20 μM [3H]TR or [3H]BR for periods between 0.5 and 12 hours. After treatment, cells were centrifuged, extracted with 10% trichloroacetic acid and analyzed by high pressure liquid chromatography (HPLC). BAD concentration exceeded TAD concentration at all time points and was 11-fold higher than TAD concentration within 6 hours. Although 10 μM TR produced no significant reduction in cellular GTP pools, 10 μM BR caused up to 50% reduction compared to controls. In conclusion, leukemic cells from AML patients demonstrate selective sensitivity to BR over TR. This study should form the basis for phase I/II trials of BR in patients with end stage leukemia.
|Original language||English (US)|
|Journal||Journal of Investigative Medicine|
|State||Published - Feb 1999|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)