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HBV rtI233V Polymerase Variant Remains Sensitive to Adefovir
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Reported by Jules Levin
EASL, April 11-15, 2007, Barcelona, Spain
Maria Curtis, Yuao Zhu, Katyna Borroto-Esoda
Biology Department, Gilead Sciences, Inc., USA
Comprehensive resistance surveillance has identified the rtA181V and rtN236T mutations in HBV polymerase as adefovir-associated resistance mutations .
The rtI233V mutation was recently reported to cause decreased in vitro susceptibility and primary ADV treatment failure.
AUTHOR CONCLUSIONS
All four patients with rtI233V responded to ADV therapy with a median decrease in HBV DNA of 4.0 log10 at the end of treatment, regardless of genotype or the concurrent LAM-R mutations.
No patient was found to develop the rtI233V mutation following therapy with ADV.
Patient isolates as well as laboratory virus with the rtI233V mutation remained susceptible to adefovir in vitro; less than 2-fold change in EC50 compared to wild type.
Clinical results along with the associated in vitro phenotypic results demonstrate that the HBV rtI233V polymerase variant remains sensitive to ADV therapy and that it is not associated with resistance to adefovir .
STUDY OBJECTIVE:
To retrospectively evaluate the prevalence of rtI233V mutation at baseline, and whether it emerged during treatment .
To evaluate the effect of the rtI233V mutation in HBV polymerase on the clinical response to ADV treatment .
To evaluate the effect of the rtI233V mutation on HBV susceptibility to adefovir in vitro.
PATIENTS & METHODS
998 patients with chronic HBV infection from 4 adefovir clinical studies were included in thr evaluation. Genotypic data were available from 853 patients enrolled in these four phase II and III ADV clinical trials and were evaluated for the prevalence of the rtI233V mutation:
--Study GS-438; placebo controlled phase III randomized trial in patients with HBeAg negative chronic Hepatitis B
--Study GS-437; placebo controlled phase III randomized trial in patients with HBeAg positive chronic Hepatitis B
-- Study GS-435; open-label phase III study in lamivudine-resistant chronic hepatitis B patients either pre- or post-liver transplantation
-- Study 412 (extension phase); phase II dose range finding study in HBeAg positive and HBeAg negative patients
Response to ADV therapy was determined by measuring changes in serum HBV DNA using the Roche AmplicorTM PCR assay (LLQ = 1000 copies/mL).
Phenotypic analyses
-- Full-length HBV clinical isolates obtained from patients with the rtI233V mutation and laboratory HBV strain (genotype D) containing the rtI233V created by site directed mutagenesis
-- Transient transfection of plasmid HBV DNA (patient derived and laboratory strain) into HepG2 cells followed by treatment with adefovir for 7 days
-- Quantification of intracellular HBV DNA using Southern Blot
RESULTS
HBV carrying the rtI233V variant was identified in 4 out of 853 (0.45%) patient baseline samples
-- Patient A, rtI233V, HBeAg+, genotype C
-- Patient B, rtI233V, HBeAg+, genotype C
-- Patient C, rtI233V/I, HBeAg-, genotype D
-- Patient D, rtL180M+M204V+I233V, HBeAg-, genotype D
All 4 patients responded to ADV therapy (median HBV DNA reduction 4.0 log10 copies/mL at the end of treatment), and 3 of them achieved undetectable HBV DNA.
None of the 853 patients was found to develop the rtI233V mutation while on ADV therapy.
Susceptibility to Adefovir In Vitro
PCR products were successfully obtained from three of the four patients with rtI233V at baseline. Phenotypic evaluation of these samples demonstrated that all three isolates remained susceptible to inhibition by adefovir as demonstrated by a 0.4 to 0.6-fold change in EC50 values compared to the wild-type control. Likewise, a lab isolate containing the rtI233V substitution remained susceptible to inhibition by adefovir with a 0.7-fold change in EC50 compared to the parent lab strain.
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