The purpose of this study was to investigate the mechanism of acquired cellular resistance to AZT, a mechanism that has been described as a potential source of drug resistance in addition to viral mutations. To study this phenomenon the kinetics parameters of thymidine kinase (TK) activity have been defined in CEMazt, a cell line previously selected for resistance to AZT, in comparison with the parental AZT-sensitive CEM cells. The results revealed that the value of the maximum velocity (V(max)) of TK activity for deoxythymidine (dThd) phosphorylation is decreased in CEMazt as compared to the wild-type cell line (V(max): CEM = 105.3 ± 17.6 nmol/hr/mg of protein; CEMazt = 0.3 ± 0.02 nmol/hr/mg of protein; p <0.001). Furthermore, the enzyme affinity versus dThd is lower in CEMazt as compared to CEM (K(m): CEM = 0.9 ± 0.2 μM; CEMazt = 1.6 ± 0.2 μM; p <0.01). Consequently phosphorylation efficiency, expressed as the ratio between V(max) and K(m), is also reduced in CEMazt (p <0.001). To evaluate whether such a phenomenon may also occur in patients, ex vivo experiments were carried out by using PBMCs from HIV-infected patients, treated or not treated with AZT. The results (mean values from 10 patients for each group) indicate that a prolonged treatment (>6 months) with AZT may modify the enzymatic kinetics of TK, leading to a significant reduction in the phosphorylation efficiency of the enzyme (4.07 ± 1.7 in treated patients versus 13.5 ± 1.7 in untreated patients; p <0.001). These results indicate that AZT treatment can also induce a defect in TK activity in patients.
|Number of pages||6|
|Journal||AIDS Research and Human Retroviruses|
|Publication status||Published - Feb 10 1996|
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