- The nucleoside analog, 3’-azido-3’-deoxythymidine (Zidovudine, AZT), is a major component in the first-line therapy for HIV-1 infection worldwide.
- HIV-1 infected patients treated long-term with AZT often become resistant, and different mechanisms have been proposed.
- Two possible mechanisms are silencing/reducing activity of the thymidine kinase 1 (TK1) enzyme, the first step in metabolism of AZT, by:
(1) an increase in 5-methyl-cytosine (5-meC) methylation, or by
(2) TK1 dimerization.
- Human T lymphoblast MOLT-3 cells, cultured for several passages in AZT (P3-P5), developed drug resistance via TK1 activity. Resistance was accompanied by TK1 dimerization (1,2). However, MOLT-3 cells had very high baseline 5-meC levels and therefore could not be evaluated for changes due to AZT exposure.
- Here, human ovarian cancer BT-20 cells, exposed to 100 μM AZT, were examined for TK1 resistance by 5-meC methylation in the promoter of the TK1 gene, and by Western Blot of the TK1 protein, at passages 0, 3 and 5.
- Our study indicates that dimerization of TK1 may be responsible for the observed resistance to AZT.
