In general the uptake of selleck screening library nucleobases e.g. [3H]-Ade (adenine), [3H]-Gua (guanine), [3H]-Ura (uracil), and [3H]-Hx (hypoxanthine) was low (< 1%) as compared selleck compound with that of [3H]-dT (thymidine) (> 7%). Dipyridamole strongly inhibited the uptake and incorporation of [3H]-Hx and [3H]-Gua into DNA and RNA but had no effect on uptake and metabolism of all other nucleobases and [3H]-dT, suggesting that dipyridamole is a specific inhibitor of purine transport. Similar to dipyridamole, 6-TG also strongly inhibited the uptake and incorporation of [3H]-Hx and [3H]-Gua into DNA and RNA but had no effect on any other nucleobases and dT. Pyrimidine nucleoside analogs, TFT, 5FdU
(5-fluorodeoxyuridine) and dFdC, inhibited the uptake and incorporation of all nucleobases. However, [3H]-dT uptake was stimulated (2-fold) by TFT and 5FdU but inhibited by dFdC, and the percentage of radioactivity found in DNA was similar to that of
control in all cases (Table 2). These results indicate that there are distinct transporters selleck chemicals for purines and pyrimidines and that metabolic rate determines the extent of uptake. Table 2 Inhibition of tritium labelled natural nucleoside and nucleobase uptake and metabolism by selected analogs* [3H]-dT [3H]-Ura [3H]-Hx [3H]-Gua [3H]-Ade Total uptake Incorporation Total uptake Incorporation Total uptake Incorporation Total uptake Incorporation Total uptake Incorporation None 7.6±0.5 97.5±0.5 0.20±0.003 40±5 0.050± 0.001 62±7 0.9±0.05 56±3 0.62±0.1 44±1 Dipyridamole 7.2±1.1 97.0±1.3 0.20±0.003 38±6 0.008± 0.001 44±3 0.09±0.002 56±6 0.67±0.1 47±1 6-TG 7.9±0.6 97.4±0.7 0.21±0.003 39±8 0.005 ± 0.0004 43±6 0.080±0.002 67±3 0.66±0.1 46±3 TFT 18.2±0.6 97.4±0.5 0.11±0.002 27±0.2 0.011± 0.001 67±1 0.19±0.02 85±4 0.43±0.01 48±2 5FdU 14.7±0.2
96.0±0.5 0.087±0.003 19±7 0.006± 0.001 76±4 0.16±0.03 87±3 0.36±0.1 42±2 dFdC 5.2±0.4 96.7±1.1 0.12±0.001 26±6 0.009±0.0002 67±7 0.10±0.02 90±6 0.41±0.08 39±8 *Total uptake: percentage of radioactivity recovered in the cells divided by total radioactivity added to the growth medium. Incorporation: percentage of radioactivity in the acid insoluble fraction divided by total radioactivity recovered in the cells. Up-regulation of Mpn TK activity by TFT To understand why TFT and 5FdU stimulated Metalloexopeptidase [3H]-dT uptake, Mpn wild type cells were incubated with various concentrations of TFT in the presence of [3H]-dT. Total proteins were extracted from these cultures and used to determine the TK and TS activity. Total uptake of [3H]-dT increased in a concentration dependent manner while the percentage of [3H]-dT found in DNA was similar. TK activity increased also as the concentration of TFT increases and with 10 μM TFT the TK activity was ~ 3 times of the activity found in the controls.