Entecavir: a new nucleoside analog for the treatment of chronic hepatitis B infection

BACKGROUND

Chronic hepatitis B infection carries considerable risk for the development of cirrhosis and hepatocellular carcinoma. Treatment options are increasing but are limited to interferon alfa-2b, pegylated interferon alfa-2a, lamivudine, adefovir dipivoxil, and entecavir. Entecavir, a nucleoside analog, is the newest oral antiviral approved in the United States for treatment of chronic hepatitis B.

OBJECTIVE

To review the available data for entecavir regarding its pharmacology, pharmacokinetics, safety, efficacy, and clinical use.

METHODS

A MEDLINE, EMBASE, and Cochrane search of the English-language literature from January 1997-May 2006 was performed. Preapproval studies provided by the manufacturer and abstracts from recent scientific meetings on infectious disease and hepatology were also reviewed.

RESULTS

Three phase III clinical trials representing more than 1600 subjects established the superior efficacy and equivalent safety of entecavir compared with lamivudine for treating patients who are hepatitis B early antigen (HBeAg) positive, HBeAg negative, or refractory to lamivudine. Entecavir resistance has not occurred in nucleoside-naïve patients but may develop in those who already possess lamivudine resistance mutations.

CONCLUSION

Trial results, along with previously published response rates for adefovir dipivoxil and interferon monotherapy, make entecavir the preferred first-line treatment option for patients with chronic hepatitis B who are nucleoside naïve, HBeAg positive or negative, and have compensated liver disease. Both entecavir and adefovir dipivoxil maintain activity against hepatitis B virus in patients with chronic hepatitis B who are refractory to lamivudine, and both agents are reasonable first-line treatment options. Longer trials involving nucleoside-naïve, lamivudine-refractory patients are needed to determine entecavir's optimal treatment duration, long-term safety, and durability of response, including rate of resistance.

Defining the opportunity for pharmacogenetic intervention in primary care

Pharmacogenetics (PG), the study of human genome function and its effects on drug response, represents an exciting approach for reducing adverse drug events and increasing therapeutic efficacy. However, there is no clear information of the potential impact of PG in the primary care setting. Therefore, a study was conducted to determine the frequency of use of medications under PG influence, including 16 PG adverse drug reaction (ADR)-associated medications, in the primary care setting. Patients and methods: A cohort of 607 consecutive patients was accrued over a 3-month period from three primary care practices. Patients were asked to answer a verbal survey of demographics and medication use during the past 12 months. The survey specifically evaluated 16 drugs known to commonly cause ADRs and undergo metabolism by polymorphic enzymes. Patients also disclosed information on all other medication use in the last year. Medication use was verified by chart review. The primary outcome was the frequency of medication use. Results: Among the 16 ADR-associated medications, patients used analgesics (88.5%), antihypertensives (14.3%) and antidepressants (9.6%) most commonly. Overall, 28.6% of patients took more than one of the PG ADR-associated medications. Neither gender nor race appeared to influence the frequency of use of these medications (p = 0.5 and p = 0.08, respectively). Patients taking one or more of the drugs were older (p < 0.001). More patients seen for a chronic visit took one or more of the ADR-associated drugs than patients seen for an acute visit (35.8 versus 18.5%, p < 0.001). Discussion: This is the first attempt to describe the potential role of pharmacogenetics in the primary care setting. The findings indicate that at least one in four primary care patients take at least one medication that commonly causes adverse drug reactions due to genetic variability in drug metabolism, indicating that there is a potential role of pharmacogenomics in primary care. Nearly every patient was on a medication with putative PG association. Conclusions: Studies of the ability of PG should not be limited to medical subspecialties, as there is a great potential impact of PG on the primary care setting.

A candidate prostate cancer susceptibility gene at chromosome 17p

It is difficult to identify genes that predispose to prostate cancer due to late age at diagnosis, presence of phenocopies within high-risk pedigrees and genetic complexity. A genome-wide scan of large, high-risk pedigrees from Utah has provided evidence for linkage to a locus on chromosome 17p. We carried out positional cloning and mutation screening within the refined interval, identifying a gene, ELAC2, harboring mutations (including a frameshift and a nonconservative missense change) that segregate with prostate cancer in two pedigrees. In addition, two common missense variants in the gene are associated with the occurrence of prostate cancer. ELAC2 is a member of an uncharacterized gene family predicted to encode a metal-dependent hydrolase domain that is conserved among eukaryotes, archaebacteria and eubacteria. The gene product bears amino acid sequence similarity to two better understood protein families, namely the PSO2 (SNM1) DNA interstrand crosslink repair proteins and the 73-kD subunit of mRNA 3' end cleavage and polyadenylation specificity factor (CPSF73).

BRG1, a component of the SWI-SNF complex, is mutated in multiple human tumor cell lines

Human BRG1 is a component of the evolutionarily conserved SWI-SNF chromatin remodeling complex. BRG1 has been implicated in growth control through its interaction with the tumor suppressor pRb and may consequently serve as a negative regulator of proliferation. Postulating that BRG1 may itself be a tumor suppressor gene, we screened a panel of tumor cell lines to determine whether the gene is targeted for mutation. We report that the COOH-terminal region of BRG1 is homozygously deleted in two carcinoma cell lines, prostate TSU-Pr1 and lung A-427. In addition, biallelic inactivations of BRG1 were observed in four other cell lines derived from carcinomas of the breast, lung, pancreas, and prostate; their mutations in BRG1 included three frameshift lesions and one nonsense lesion. Point mutations were also discovered in a number of other cell lines, however in most cases any effect of these mutations on BRG1 function remains to be established. A variety of different mutations within BRG1, in several cell lines, suggest that BRG1 may be targeted for disruption in human tumors. Significantly, reintroduction of BRG1 into cells lacking BRG1 expression was sufficient to reverse their transformed phenotype inducing growth arrest and a flattened morphology. These data strongly support the model that BRG1 may function as a tumor suppressor and strengthen the hypothesis that the regulation of gene expression through chromatin remodeling is critical for cancer progression. It will be important to confirm these observations in primary tumors.