The inhibition mechanism of the uptake of lamivudine via human organic anion transporter 1 by Stellera chamaejasme L. extracts

Stellera chamaejasme L. is a traditional Chinese medicine with a long history to treat stubborn skin ulcer, and it also has antiviral and antitumor effects. Neochamaejasmine B (NCB), Neochamaejasmine A (NCA) and Chamaechromone (CMC) are the major components in dried roots of Stellera chamaejasme L.. Our studies suggested that NCB, NCA and CMC are inhibitors of Organic anion transporter 1 (OAT1). OAT1 is encoded by solute carrier family 22 member 6 gene (SLC22A6) in humans and plays a critical role in the organic anion drug uptake and excretion in the kidney. Lamivudine is the typical substrate of OAT1 and is frequently used in combination with other antiviral drugs in clinical antiviral treatments. The aim of this study is to investigate the interaction and its mechanism between these bi-flavone components in Stellera chamaejasme L. and lamivudine via OAT1 both in vitro and in vivo. In vitro, the uptake studies in Madin-Darby canine kidney (MDCK) cells overexpressing OAT1 suggested that NCB inhibited the uptake of 6-CFL and lamivudine.Similar results were obtained for NCA and CMC. NCB was a noncompetitive and competitive inhibitor interaction with OAT1. IC₅₀ values of NCB, NCA and CMC for inhibiting OAT1-mediated lamivudine transport were 2.46, 8.35 and 0.61 μmol·L^-1, respectively. In vivo, the pharmacokinetic results of lamivudine in rats showed that the mean area under the plasma concentration-time curve (AUC_0-∞) and maximal plasma concentration (C_max) of lamivudine after co-administration is increased 2.94-fold and 1.87-fold, respectively, compared to lamivudine administration alone. The results of interactions between lamivudine and these bi-flavone components in Stellera chamaejasme L. extracts via OAT1 in vivo are consistent with studies in vitro. The inhibition of OAT1-mediated uptake of lamivudine by NCB, NCA and CMC is the possible mechanism for Stellera chamaejasme L. extracts improving the oral bioavailability of lamivudine in rats.

Persistence of Multidrug-Resistant HIV-1 without Antiretroviral Treatment 2 Years after Sexual Transmission

Objectives

To understand the virological mechanisms of 2-year persistence of multidrug-resistant virus without selective antiretroviral pressure in HIV-1-infected patients.

Patients and Methods

Two patients were contaminated recently by their HIV-1-infected partners, who had received, before the transmission, all available antiretroviral drugs and who exhibited a severe therapeutic failure. The resistance mutations analysis was performed by clonal sequencing of 1.2 kb of pol gene in plasma of index and sources patients. Sequencing of HIV-1 DNA was performed in PBMCs of index patients.

Results

Genotypic testing performed in index patients at time of seroconversion showed resistance mutations to three classes of drugs. All mutations were linked on the same viral genome and all quasispecies carried all mutations. No wild-type virus was detected. The same results were found in source patients and showed that all mutations were transmitted. In the index patients, all mutations persisted over 2 years without antiretroviral treatment. Moreover, the resistance mutations were all archived in the cellular reservoir. Viral load and CD4 count of index patients remained unchanged during 2 years of follow-up.

Discussion

Only multidrug-resistant viruses were detected in the source patients and could be transmitted in index patients. In the latter, an expansion of predominant multidrug-resistant quasispecies and the ‘archival’ of all mutations were observed. These results explain the persistence of mutations and suggest that it is highly difficult to return to a wild-type viral population, sensitive to an antiretroviral treatment. The treatment of index patients is limited and the major risk is the transmission of these multidrug-resistant viruses. This work was presented in part in the XII International HIV Drug Resistance Workshop, Los Cabos, Mexico, June 2003; and in the 2nd IAS Conference on HIV Pathogenesis & Treatment, Paris, France, July 2003.

K65R with and without S68: A New Resistance Profile in Vivo Detected in Most Patients Failing Abacavir, Didanosine and Stavudine

Antiretroviral treatment with three nucleoside reverse transcriptase inhibitors (NRTIs) is widely used, but the combination of abacavir, didanosine and stavudine has never been investigated.

We describe the surprising and consistent genotypic and phenotypic outcome in patients failing this combination. As part of a Danish multicentre study, 60 antiretroviral-naive patients were randomized to treatment with abacavir, didanosine and stavudine. Failure was defined as one HIV-1 RNA >400 copies/ml. Genotyping was performed using TrueGene™ HIV-1 assay (Visible Genetics, London, UK). Phenotypic susceptibilities were determined with the Virco Antivirogram assay.

Eight patients failed treatment with a median viral load of 2.980 copies/ml (range 478-5.950).

At baseline, five patients were wild-type. Three patients harboured nucleoside excision mutations (NEMs), but phenotypic susceptibilities were within normal range.

All five patients with wild-type virus developed K65R and four of these patients also acquired the S68G mutation. Phenotypic susceptibility decreased towards abacavir (median 8.9-fold) and didanosine (median 3.2-fold), while susceptibility towards stavudine was unchanged (median 0.8-fold). Susceptibility towards lamivudine and tenofovir decreased median 14.2- and 4.0-fold, respectively. In two patients with baseline resistance mutations, further accumulation of NEMs and V75T or L74V was observed. One patient developed Q151M.

Failure of a triple NRTI regimen is possible and frequent with only the K65R mutation. Under adequate selection pressure K65R can easily emerge in vivo and may compromise several future treatment options including newer NRTIs. The unexpected high incidence of S68G suggests a functional role of this mutation in viruses harbouring K65R.