Long-term AZT Exposure Alters the Metabolic Capacity of Cultured Human Lymphoblastoid Cells

Abstract

The antiretroviral efficacy of 3′-azido-3′-deoxythymidine (AZT) is dependent upon intracellular mono-, di-, and triphosphorylation and incorporation into DNA in place of thymidine. Thymidine kinase 1 (TK-1) catalyzes the first step of this pathway. MOLT-3, human lymphoblastoid cells, were exposed to AZT continuously for 14 passages (P1–P14) and cultured for an additional 14 passages (P15–P28) without AZT. Progressive and irreversible depletion of the enzymatically active form of the TK-1 24-kDa monomer with loss of active protein was demonstrated during P1–P5 of AZT exposure. From P15 to P28, both the 24- and the 48-kDa forms of TK-1 were undetectable and a tetrameric 96-kDa form was present. AZT-DNA incorporation was observed with values of 150, 133, and 108 molecules of AZT/106 nucleotides at the 10μM plasma-equivalent AZT dose at P1, P5, and P14, respectively. An exposure-related increase in the frequency of micronuclei (MN) was observed in cells exposed to either 10 or 800μM AZT during P1–P14. Analysis of the cell cycle profile revealed an accumulation of S-phase cells and a decrease in G1-phase cells during exposure to 800μM AZT for 14 passages. When MOLT-3 cells were grown in AZT-free media (P15–P29), there was a reduction in AZT-DNA incorporation and MN formation; however, TK-1 depletion and the persistence of S-phase delay were unchanged. These data suggest that in addition to known mutagenic mechanisms, cells may become resistant to AZT partially through inactivation of TK-1 and through modulation of cell cycle components.

AZT and emodin exhibit synergistic growth-inhibitory effects on K562/ADM cells by inducing S phase cell cycle arrest and suppressing MDR1 mRNA/p-gp protein expression

“…Cell cycle abnormalities induced by AZT have been previously observed in human HL60 (Roskrow & Wickramasinghe, 1990), Jurkat (Wu et al, 2004), Hela (Olivero et al, 2005) and lymphoblastoid cells (Olivero et al, 2010). Our results showed that the combination of AZT and emodin caused an accumulation of K562/ADM cells in S phase, which is consistent with Oliver's findings (Olivero et al, 2010).…”

“…Our results showed that the combination of AZT and emodin caused an accumulation of K562/ADM cells in S phase, which is consistent with Oliver's findings (Olivero et al, 2010). These results suggest that the regulation of cell cycle progression may be an important factor in the inhibition of cell growth in K562/ADM cells.…”

<i>In vitro</i> evidence of baicalein’s inhibition of the metabolism of zidovudine (AZT)

“…The inhibition of herbal components liquiritigenin and isoliquiritigenin towards the metabolism of hypnotic agent propofol limited the co-utilization of these two herbal components and propofol 13 . The dose beyond the efficient concentration of AZT can induce the genotoxicity and minimum cell death 14 . AZT has a narrow therapeutic index, and slight alteration of AZT concentration will exceed the minimal toxicity concentration of AZT.…”

Differential gene expression in human hepatocyte cell lines exposed to the antiretroviral agent zidovudine

“…Our data indicate that the expression of TK1 gene and protein as well as its enzymatic activity is inhibited in THLE2 cells and elevated in HepG2 cells following AZT treatment. The suppression of TK1 results in a decreased activation of AZT, and consequently, decreased AZT incorporation into DNA (Fang and Beland 2009; Olivero et al 2010). Importantly, it remains to be established whether the observed induction of TK1 expression may lead to an increase in the intracellular concentration of AZT 5′-triphosphate.…”