Intraparticular drug transfer results in high level of raltegravir (RAL) activity
H. Walter, K. Tennert, C. Paatz, S. Wittmann
Institute of Virology, Erlangen, Germany
Raltegravir has proven to be a powerful compound. Recently, once daily dosage was comparably active to twice daily dosage of RAL despite that the drug's half life is 10 hours and the plasma Cmin is 10‑fold higher than the in vitro inhibitory concentration (IC50) only. Also the recently described slopes of drug dose response curves did not reveal high potency for strang transfer inhibitors. In this study, we examined if the high affinity of RAL may contribute to the high clinical response rates.
293T cells were transfected with HIV-1-NL4-3-DNA, and different concentrations of RAL (0-1µM), the coreceptor antagonist AMD3100, and saquinavir were added, respectively. After 48 hours, viruses were spun down and resuspended in drug-free media. Viral infectivity (TCID50) was determined by infecting CEMx-174 cells. The IC50 of RAL virions was determined in comparison to infections in the presence of RAL. The decrease of infectivity of the drug-preincubated viruses was correlated with the RAL concentration and given as fold-decrease in comparison to the uninhibited controls.
As expected, saquinavir was fully active when added during transfection, and AMD3100 was not. Viruses generated in the presence of RAL, but infected in the absence of the drug, were clearly less infective. The TCID50 of viruses generated in the presence of 1µM RAL was diminished from 30 to 120-fold in comparison to viruses generated in the absence of RAL (SQV 30 to 80-fold).
RAL seems to be active when the drug is present during the generation of virions. The effect may be caused by the high drug affinity avoiding the drug's release from the preintegration complex. Since the time from viral budding to integration is 8-12h, RAL activity may exhibit a second peak, which is rather independent of drug plasma levels and may contribute to the drug potency relatively independent from plasma levels.
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