The treatment of chronic hepatitis B: Focus on adefovir-like antivirals

Moving Fast Toward Hepatitis B Virus Elimination

Currently, there are two safe and effective therapeutic strategies for chronic hepatitis B treatment, namely, nucleoside analogs and interferon alpha (pegylated or non-pegylated). These treatments can control viral replication and improve survival; however, they do not eliminate the virus and therefore require long-term continued therapy. In addition, there are significant concerns about virus rebound on discontinuation of therapy and the development of fibrosis and hepatocellular carcinoma despite therapy. Therefore, the search for new, more effective, and safer antiviral agents that can cure hepatitis B virus (HBV) continues. Anti-HBV drug discovery and development is fundamentally impacted by our current understanding of HBV replication, disease physiopathology, and persistence of HBV covalently closed circular DNA (cccDNA). Several HBV replication targets are the basis for novel anti-HBV drug development strategies. Many of them are already in clinical trial phase 1 or 2, while others with promising results are still in preclinical stages. As research intensifies, potential HBV curative therapies and modalities in the pipeline are now on the horizon.

Preemptive adefovir versus lamivudine for prevention of hepatitis B reactivation in chronic hepatitis B patients undergoing chemotherapy

BACKGROUND

This proof-of-concept study compared lamivudine (LAM) with a newer antiviral agent, adefovir dipivoxil (ADF), in preventing hepatitis B virus (HBV) reactivation in chronic HBV patients undergoing chemotherapy.

METHODS

Hepatitis B surface antigen (HBsAg) positive patients intended to undergo chemotherapy were randomized to receive either LAM 100 mg daily or ADF 10 mg daily. Anti-viral therapy was started 1 week prior to chemotherapy and until 6 months after completing chemotherapy. The primary outcome was HBV reactivation rate. All patients with viral breakthrough were screened for resistance mutations by direct sequencing.

RESULTS

Seventy treatment-naïve patients were consecutively randomized 1:1 to LAM or ADF. The median baseline HBV DNA levels were similar (LAM 3.36 vs. ADF 3.17 log10 copies/mL, p = 0.860). The median duration was 8.3 months on LAM and 10.6 months on ADF (p = 0.220). HBV reactivation was observed in 13/35 (37.1%) on LAM compared with 10/35 (28.6%) on ADF (p = 0.611). The median time to HBV reactivation was 4.6 and 8.1 months, on LAM and ADF respectively. Among these 13 patients, 8/13 (61.5%) on LAM had developed drug resistance mutations but none on ADF had developed drug resistance mutations to ADF (p = 0.003). Both drugs were well tolerated and no severe drug-related toxicities were reported.

CONCLUSION

In this randomized clinical study, adefovir and lamivudine demonstrated similar efficacy in preventing hepatitis B reactivation in HBsAg-positive patients undergoing chemotherapy. In patients whose hepatitis B reactivated, adefovir was associated with a lower resistance profile.

Mutation pattern of lamivudine resistance in relation to hepatitis B genotypes: hepatitis B genotypes differ in their lamivudine resistance associated mutation pattern

Little is known about differences between individual hepatitis B genotypes and mutation patterns associated with lamivudine resistance. This study analyses the lamivudine-associated mutation pattern in relation to the four major HBV genotypes A-D. The PubMed database was screened for keywords "HBV OR Hepatitis B," "YMDD," "genotype," and "lamivudine"; all identified publications published till June 2009 were analyzed for differences in mutation pattern. To confirm the literature-based findings the databases of two reference laboratories in Tübingen (Germany), and Melbourne (Australia) were analyzed. Twenty-nine studies were identified reporting 827 patients with known hepatitis B genotype who underwent lamivudine treatment and developed resistance mutations. The literature data revealed that genotype A favors the rtM204V mutation unlike the other major genotypes (P<0.001), which corresponds to a significant difference in the mutation pattern of genotypes endemic in Asian countries and those found in the rest of the world. These significant findings of the literature-review could be reproduced in the analysis of the databases from Tübingen and Melbourne. Furthermore, the rtL180M mutation is significantly connected to the rtM204V mutation in genotypes A, B, and C, respectively. It is concluded that there is proof that HBV genotypes differ in their mutation pattern of lamivudine resistance. Future studies will need to evaluate whether this will translate into genotype-specific differences in resistance emergence on either entecavir or telbivudine as these antivirals differ in their mutation profile, rtM204V for entecavir and rtM204I for telbivudine.

Regio- and enantioselective N-allylations of imidazole, benzimidazole, and purine heterocycles catalyzed by single-component metallacyclic iridium complexes

Highly regio- and enantioselective iridium-catalyzed N-allylations of benzimidazoles, imidazoles, and purines have been developed. N-Allylated benzimidazoles and imidazoles were isolated in high yields (up to 97%) with high branched-to-linear selectivity (up to 99:1) and enantioselectivity (up to 98% ee) from the reactions of benzimidazole and imidazole nucleophiles with unsymmetrical allylic carbonates in the presence of single component, ethylene-bound, metallacyclic iridium catalysts. N-Allylated purines were also obtained in high yields (up to 91%) with high N9/N7 selectivity (up to 96:4), high branched-to-linear selectivity (98:2), and high enantioselectivity (up to 98% ee) under similar conditions. The reactions encompass a range of benzimidazole, imidazole, and purine nucleophiles, as well as a variety of unsymmetrical aryl, heteroaryl, and aliphatic allylic carbonates. Competition experiments between common amine nucleophiles and the heterocyclic nitrogen nucleophiles studied in this work illustrate the effect of nucleophile pK(a) on the rate of iridium-catalyzed N-allylation reactions. Kinetic studies on the allylation of benzimidazole catalyzed by metallacyclic iridium-phosphoramidite complexes, in combination with studies on the deactivation of these catalysts in the presence of heterocyclic nucleophiles, provide insight into the effects of the structures of the phosphoramidite ligands on the stability of the metallacyclic catalysts. The data obtained from these studies have led to the development of N-allylations of benzimidazoles and imidazoles in the absence of an exogenous base.