Transport and Phosphorylation Kinetics of Zidovudine in the Chinese Population: Implications for Individualized Antiretroviral Therapy

Background and Purpose Zidovudine (AZT), a nucleoside reverse transcriptase inhibitor, exerts its antiviral effect through intracellular conversion to AZT-triphosphate(AZT-TP), with therapeutic efficacy and toxicity closely linked to intracellular AZT-TP levels rather than plasma AZT concentrations. However, research on AZT transport and phosphorylation in the Chinese population is scarce, and the relationship between transporter/kinase protein expression and AZT intracellular metabolism remains unclear. This study aimed to characterize the cellular transport and phosphorylation kinetics of AZT in Chinese individuals, develop a pharmacokinetic model linking plasma AZT to intracellular AZT-TP, and explore the impact of transporter expression, to support personalized antiretroviral therapy. Experimental Approach In vitro experiments used Molt-4 and HUVEC cells. Cytotoxicity was assessed via CCK-8 assay. Concentration-dependent studies incubated cells with 0–200 μM AZT for 12 hours, while time-course studies exposed cells to 100 μM AZT for 0.5–36 hours, quantifying intracellular AZT and metabolites via HPLC-MS/MS. In vivo, six healthy Chinese volunteers received a single 600 mg oral AZT dose, with blood samples collected over 10 hours to measure plasma AZT and intracellular metabolites in peripheral blood mononuclear cells (PBMCs). A two-compartment pharmacokinetic model was developed, and ABC transporter expression was quantified using HPLC-MS/MS. Key Results In vitro, AZT showed negligible cytotoxicity at 50 μM for 36 hours. Intracellular AZT, zidovudine monophosphate (AZT-MP), zidovudine diphosphat (AZT-DP), and zidovudine triphosphate (AZT-TP) increased linearly with extracellular AZT (0–200 μM), with time-course studies showing rapid initial accumulation followed by plateauing, and cell-type differences in kinetics. In vivo, plasma AZT had a Tmax of 0.62 ± 0.20 hours and T1/2 of 1.95 ± 0.20 hours. Intracellular AZT-TP in PBMCs exhibited marked inter-individual variability. The pharmacokinetic model parameters differed from non-Chinese cohorts. ABCB1 and ABCG2 expression strongly correlated with AZT efflux, while ABCC1 did not. Conclusion and Implications This study clarifies AZT's transport and phosphorylation kinetics in Chinese subjects, showing that intracellular AZT-TP levels, linked to efficacy and toxicity, are influenced by plasma concentrations, transporter/kinase activity, and protein expression. The findings highlight the role of ABCB1 and ABCG2 in AZT efflux and support the need for individualized dosing based on intracellular metabolite levels and transporter expression, advancing personalized antiretroviral therapy in the Chinese population.