Biomedical subjects

Ronald E Rose

Publications and source records attributed to Ronald E Rose.

5 recordsLinked to original sources

PubMed2006

Two-year assessment of entecavir resistance in Lamivudine-refractory hepatitis B virus patients reveals different clinical outcomes depending on the resistance substitutions present.

Entecavir (ETV) is a deoxyguanosine analog approved for use for the treatment of chronic infection with wild-type and lamivudine-resistant (LVDr) hepatitis B virus (HBV). In LVD-refractory patients, 1.0 mg ETV suppressed HBV DNA levels to below the level of detection by PCR (<300 copies/ml) in 21% and 34% of patients by Weeks 48 and 96, respectively. Prior studies showed that virologic rebound due to ETV resistance (ETVr) required preexisting LVDr HBV reverse transcriptase substitutions M204V and L180M plus additional changes at T184, S202, or M250. To monitor for resistance, available isolates from 192 ETV-treated patients were sequenced, with phenotyping performed for all isolates with all emerging substitutions, in addition to isolates from all patients experiencing virologic rebounds. The T184, S202, or M250 substitution was found in LVDr HBV at baseline in 6% of patients and emerged in isolates from another 11/187 (6%) and 12/151 (8%) ETV-treated patients by Weeks 48 and 96, respectively. However, use of a more sensitive PCR assay detected many of the emerging changes at baseline, suggesting that they originated during LVD therapy. Only a subset of the changes in ETVr isolates altered their susceptibilities, and virtually all isolates were significantly replication impaired in vitro. Consequently, only 2/187 (1%) patients experienced ETVr rebounds in year 1, with an additional 14/151 (9%) patients experiencing ETVr rebounds in year 2. Isolates from all 16 patients with rebounds were LVDr and harbored the T184 and/or S202 change. Seventeen other novel substitutions emerged during ETV therapy, but none reduced the susceptibility to ETV or resulted in a rebound. In summary, ETV was effective in LVD-refractory patients, with resistant sequences arising from a subset of patients harboring preexisting LVDr/ETVr variants and with approximately half of the patients experiencing a virologic rebound.

Antiviral Agents↗

PubMed2005

A dose-ranging study of the efficacy and tolerability of entecavir in Lamivudine-refractory chronic hepatitis B patients.

BACKGROUND & AIMS: Entecavir is a nucleoside analogue with potent in vitro activity against lamivudine-resistant hepatitis B virus (HBV). This randomized, dose-ranging, phase 2 study compared the efficacy and safety of entecavir with lamivudine in lamivudine-refractory patients. METHODS: Hepatitis B e antigen (HBeAg)-positive and -negative patients (n = 182), viremic despite lamivudine treatment for > or =24 weeks or having documented lamivudine resistance substitutions, were switched directly to entecavir (1.0, 0.5, or 0.1 mg daily) or continued on lamivudine (100 mg daily) for up to 76 weeks. RESULTS: At week 24, significantly more patients receiving entecavir 1.0 mg (79%) or 0.5 mg (51%) had undetectable HBV DNA levels by branched chain DNA assay compared with lamivudine (13%; P < .0001). Entecavir 1.0 mg was superior to entecavir 0.5 mg for this end point (P < .01). After 48 weeks, mean reductions in HBV DNA levels were 5.06, 4.46, and 2.85 log(10) copies/mL on entecavir 1.0, 0.5, and 0.1 mg, respectively, significantly higher than 1.37 log(10) copies/mL on lamivudine. Significantly higher proportions of patients achieved normalization of alanine aminotransferase levels on entecavir 1.0, 0.5, and 0.1 mg (68%, 59%, and 47%, respectively) than on lamivudine (6%). One virologic rebound due to resistance occurred (in the 0.5-mg group). CONCLUSIONS: In HBeAg-positive and HBeAg-negative lamivudine-refractory patients, treatment with entecavir 1.0 and 0.5 mg daily was well tolerated and resulted in significant reductions in HBV DNA levels and normalization of alanine aminotransferase levels. One milligram of entecavir was more effective than 0.5 mg in this population.

Adult↗

PubMed2005

Molecular basis for increased susceptibility of isolates with atazanavir resistance-conferring substitution I50L to other protease inhibitors.

Protease inhibitors (PIs) are highly effective drugs against the human immunodeficiency virus (HIV), yet long-term therapeutic use is limited by emergence of HIV type 1 (HIV-1) protease substitutions that confer cross-resistance to multiple protease inhibitor drugs. Atazanavir is a highly potent HIV protease inhibitor with a distinct resistance profile that includes effectiveness against most HIV-1 isolates resistant to one or two PIs. The signature resistance substitution for atazanavir is I50L, and it is frequently (53%) accompanied by a compensatory A71V substitution that helps restore viability and increases atazanavir resistance levels. We measured the binding affinities of wild-type (WT) and I50L/A71V HIV-1 proteases to atazanavir and other currently approved PIs (ritonavir, lopinavir, saquinavir, nelfinavir, indinavir, and amprenavir) by isothermal titration calorimetry. Remarkably, we find that all of the PIs have 2- to 10-fold increased affinities for I50L/A71V protease, except for atazanavir. The results are also manifested by thermal stability measures of affinity for WT and I50L/A71V proteases. Additional biophysical and enzyme kinetics experiments show I50L/A71V protease is a stable enzyme with catalytic activity that is slightly reduced (34%) relative to the WT. Computational modeling reveals that the unique resistance phenotype of I50L/A71V protease likely originates from bulky tert-butyl groups at P2 and P2' (specific to atazanavir) that sterically clash with methyl groups on residue L50. The results of this study provide a molecular understanding of the novel hypersusceptibility of atazanavir-resistant I50L/A71V-containing clinical isolates to other currently approved PIs.

Amino Acid Substitution↗

PubMed2005

Replication-competent chimeric hepatitis C virus subgenomic replicons.

OBJECTIVE: To utilize chimeric hepatitis C virus (HCV) replicons to select adaptive mutation(s) that allow replication of a genotype 1a replicon. METHODS: We used a genetic approach to gradually apply selective pressure by generating chimeric replicons through sequential replacement of nonstructural genes of a 1b replicon with genotype 1a sequences. RESULTS: A chimeric replicon containing a genotype 1a NS5A protein did not replicate in a transient assay, but could be used to establish stable cell lines using G418 selection. The cell lines contained a K1846T mutation in NS4B which functioned as an adaptive mutation that now allowed the chimera to replicate at levels similar to wild-type replicons. Similarly, replication of a 1a NS5A5B chimera was only observed after establishment of stable cell lines, even in the presence of the K1846T mutation. Sequence analysis of this cell line revealed an additional adaptive mutation of M1496L in NS3. Lastly, by including the K1846T mutation in a replicon that was entirely genotype 1a sequence, stable 1a cell lines could be established. CONCLUSION: These studies identify an NS4B adaptive mutation, K1846T, which allows establishment of a replication-competent 1a replicon and demonstrate the utility of this chimeric approach for establishing replicons for various HCV genotypes.

Amino Acid Substitution↗

PubMed2003

Biochemical and genetic characterizations of a novel human immunodeficiency virus type 1 inhibitor that blocks gp120-CD4 interactions.

BMS-378806 is a recently discovered small-molecule human immunodeficiency virus type 1 (HIV-1) attachment inhibitor with good antiviral activity and pharmacokinetic properties. Here, we demonstrate that the compound targets viral entry by inhibiting the binding of the HIV-1 envelope gp120 protein to cellular CD4 receptors via a specific and competitive mechanism. BMS-378806 binds directly to gp120 at a stoichiometry of approximately 1:1, with a binding affinity similar to that of soluble CD4. The potential BMS-378806 target site was localized to a specific region within the CD4 binding pocket of gp120 by using HIV-1 gp120 variants carrying either compound-selected resistant substitutions or gp120-CD4 contact site mutations. Mapping of resistance substitutions to the HIV-1 envelope, and the lack of compound activity against a CD4-independent viral infection confirm the gp120-CD4 interactions as the target in infected cells. BMS-378806 therefore serves as a prototype for this new class of antiretroviral agents and validates gp120 as a viable target for small-molecule inhibitors.

Animals↗