EVIDENCE OF IN-VITRO DEVELOPMENT OF DRUG-RESISTANCE TO AZIDOTHYMIDINEIN T-LYMPHOCYTIC LEUKEMIA-CELL LINES (JURKAT E6-1 AZT-100) AND IN PEDIATRIC-PATIENTS WITH HIV-1 INFECTION/
Vi. Avramis et al., EVIDENCE OF IN-VITRO DEVELOPMENT OF DRUG-RESISTANCE TO AZIDOTHYMIDINEIN T-LYMPHOCYTIC LEUKEMIA-CELL LINES (JURKAT E6-1 AZT-100) AND IN PEDIATRIC-PATIENTS WITH HIV-1 INFECTION/, Journal of acquired immune deficiency syndromes, 6(12), 1993, pp. 1287-1296
Clinical reports indicate that the development of drug resistance to A
ZT after chronic administration is common. In order to study this phen
omenon, the T-cell line Jurkat E6-1 was treated continuously in vitro
with low, gradually increased, concentrations of azidothymidine (AZT).
Initially, 1 muM AZT significantly retarded the cell line from reachi
ng confluence. However, after 10 weeks the T-cell line was able to gro
w in 10 muM AZT without any evidence of growth inhibition. Subsequentl
y, cell isolates could grow continuously in the presence of 20, 50, an
d 100 muM AZT without growth inhibition. These T-cell lines (Jurkat E6
-1/AZT-10, Jurkat E6-1/AZT-20, Jurkat E6-1/AZT-50, and Jurkat E6-1/AZT
-100) were tested for AZT anabolism using purified [H-3]AZT, and the r
esults were compared to the wild-type untreated Jurkat E6-1 cell line.
Similar intracellular AZT anabolites concentrations were determined i
n all cell lines. However, a four- to sixfold lower cellular concentra
tion of mono-, di-, and triphosphate anabolites of AZT was determined
in the Jurkat E6-1/AZT-10 cell line after 1 muM AZT incubation and 6.5
-fold lower after 10 muM AZT treatment. In general, a five- to sixfold
reduction in the phosphorylation rates were estimated in the AZT resi
stant T-cell line. Pharmacology studies of [H-3]AZT in the Jurkat E6-1
/AZT-100 cell line showed a much lower level of activation of the pro-
drug (28-fold), due to lack of thymidine kinase (TK) activity when com
pared to the Jurkat E6-1/AZT-10 T-cell line. A similar level of resist
ance was obtained at the thymidylate (dTMP) kinase level. Concurrently
an additional mode of resistance (407-fold) was seen on the incorpora
tion of the AZT triphosphate anabolite (AZTTP) into cellular DNA. The
formation of this cell line in a period of less-than-or-equal-to 4 mon
ths coincides with the evidence of the clinical development of ''resis
tance'' to AZT in patients who receive the drug continuously. In addit
ion, these T-cell lines have been infected with HIV, and studies on th
e development of collaterally sensitive regimens are under way.