Medscape Gastroenterology
The Next Wave of Agents for Treatment of Hepatitis C
William F. Balistreri, MD
November 21, 2013
For several years, the recommended standard of care for patients with chronic hepatitis C virus (HCV) infection consisted of a combination of pegylated interferon (PEG-IFN) and ribavirin (RBV). On the basis of understanding of the biology of the virus and identification of proteins involved in HCV replication came the development of agents that inhibited the HCV protease and polymerase enzymes.
A few years ago, the US Food and Drug Administration (FDA) approved 2 direct-acting antiviral agents for the treatment of HCV genotype 1: the NS3 protease inhibitors telaprevir and boceprevir. The American Association for the Study of Liver Diseases guidelines[1] were updated to recommend triple therapy consisting of one of these protease inhibitors given in combination with PEG-IFN and RBV. This recommendation was based on results of clinical trials of this combination, which showed significantly improved sustained virologic response (SVR) rates. Although this triple therapy is generally well tolerated, troublesome side effects occur in many patients. The good news is that the guidelines may once again be revised thanks to the emergence of the next wave of direct-acting antivirals.
Simeprevir and Sofosbuvir
Simeprevir is a potent, once-daily oral investigational NS3/4A protease inhibitor that was shown to be effective when coadministered with standard therapy (PEG-IFN and RBV) for treatment of HCV genotype 1 infection both in treatment-naive patients and in patients who did not respond to standard therapy.[2-10]
Primary efficacy and safety data from clinical trials of simeprevir in patients with genotype 1 chronic HCV infection were in part responsible for the recommended FDA approval of this agent on October 24, 2013. The FDA's Antiviral Drugs Advisory Committee recommendation was unanimous, commenting that the available data overwhelmingly supported approval of the simeprevir, PEG-IFN, and RBV combination for HCV genotype 1 infection in treatment-naive patients and in those who had relapse after previous therapy. The committee reviewed safety and efficacy data from a series of double-blind, placebo-controlled trials -- phase 3 studies of treatment-naive patients and patients with previous relapse, and a phase 2b study involving patients with previous relapse and nonresponders.
For example, simeprevir (TMC435) administered once daily in combination with PEG-IFN and RBV was associated with SVR 12 weeks after the end of treatment (SVR12) in approximately 80% of treatment-experienced (relapsed) genotype 1 chronic hepatitis C patients. The SVR12 rate was less than 40% in patients receiving placebo plus PEG-IFN and RBV. Treatment failure rates and relapse rates were lower in simeprevir recipients than placebo recipients.
Simeprevir was shown to be generally safe and well tolerated, even among patients with advanced liver fibrosis. The most common adverse events were fatigue, headache, and influenza-like illness.
The FDA Advisory Committee did, however, further recommend that patients be screened for the commonly occurring Q80K mutation because simeprevir was found to be less effective in the presence of this mutation. They also recommended that the label should indicate that sunburn is a common side effect. More information about the simeprevir clinical trials can be found at ClinicalTrials.gov.
Soon to follow was the recommended FDA approval of sofosbuvir, a nucleotide analog that inhibits NS5B-directed HCV replication; this agent has also been shown to be highly effective. Sofosbuvir in combination with standard therapy was associated with SVR12 rates of 90% compared with 58% in placebo-treated patients.[11,12]
Both agents will be indicated for treatment of patients with HCV genotype 1, but only in combination with PEG-IFN and RBV. These drugs represent an advance in management -- they promise to be capable of inducing high SVR rates with 1 pill per day, shorter duration of therapy, better tolerability, and no resistance development. The 1-pill-daily regimen simplifies the treatment strategy; however, the cost and side effects are likely to remain high.
A Glimpse of the Future in HCV Treatment
There is an even higher degree of optimism, however, because recent studies may usher in the next wave of treatment strategies for HCV infection. In my opinion, the goal for treatment in terms of efficacy, safety, and tolerability is an IFN-free regimen. Simeprevir is being studied in phase 2 IFN-free trials with and without RBV and in combination with a host of other agents that act synergistically to inhibit HCV replication, and which include all oral regimens. For example, studies in progress suggest that high SVRs can be achieved in patients treated with simeprevir and sofosbuvir together, with and without RBV.
I will end by offering a glimpse of the future. Currently under evaluation in clinical studies are second-generation protease inhibitors and small-molecule drugs that inhibit other viral enzymes. Drug cocktails that target multiple HCV enzymes simultaneously may ultimately become the standard of treatment, as in the current strategy for the management of infection with HIV.
The bottom line is that these exciting advances in antiviral therapy will lead to significant improvements in response rates with reduced adverse effects. These advantages may lower the threshold for HCV treatment for both patients and physicians.
It is important to note, though, that at present only a minority of HCV-infected patients may benefit because of multiple barriers that have been identified and that impede delivery of therapy. A major issue is inadequate case-finding, an obstacle that could be overcome by widespread screening. The Centers for Disease Control and Prevention recently advised enhanced testing; their guidelines state that many persons who test positive for hepatitis C do not receive the necessary follow-up to determine whether they require medical care. Therefore, enhanced efforts to improve awareness, education, and specialist availability are needed.
The high prevalence of HCV infection worldwide should also stimulate expanded efforts in primary prevention, including vaccine development. Perhaps we can soon wave good-bye to HCV!
http://www.medscape.com/viewarticle/814701_3
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