Hepatitis C therapy: other players in the game

Hepatitis C therapy in non-genotype 1 patients: the near future

Worldwide, 50-70 million subjects are infected with an hepatitis C virus (HCV) genotype 2, 3, 4, 5 or 6. In these patients, the combination of PEG-INF-α and ribavirin remains the currently approved standard-of-care treatment. The identification of different potential therapeutic targets in the HCV life cycle has led to the development of both direct antiviral agents (DAAs) and reagents targeting host functions essential for viral replication. DAAs comprise so far first-generation, second-wave and second-generation NS3/4A protease inhibitors (PIs), nucleos(t)ide (NIs) and non-nucleoside inhibitors of the NS5B RNA polymerase and NS5A complex inhibitors. The main host-protein-directed antiviral agents are cyclophilin inhibitors and silibinin. Whereas the launch of first-generation PIs was a major landmark in the management of genotype 1 (GT-1)-infected patients, these drugs are inactive in most non-GT-1-infected patients. Several of these and other drugs have now reached phase II and even phase III clinical stage development. The purpose of this article is to provide an overview of the clinical results recently reported for the treatment for non-GT-1 HCV infection with a focus on the most promising new compounds and combinations.

Chronic hepatitis C: treatments of the future

The launch of first-generation protease inhibitors (PIs) was a major step forward in hepatitis C virus (HCV) treatment. However, this major advance has, up to now, only been applicable to genotype-1 patients. Second-wave and second-generation PIs appear to achieve higher antiviral potency, with pan-genotype activities, fewer side-effects and potential activity against PI-resistant mutation by second-generation PIs, through more convenient daily administration. Other direct-acting antivirals (DAAs) include NS5B inhibitors such as nucleoside/nucleotide inhibitors (NIs) and non-nucleoside inhibitors (NNIs). NIs have similar efficacy across all genotypes and present with the highest barrier to resistance of all DAAs to date. PSI-7977, a pyrimidine nucleotide analogue, also has highly potent antiviral activity across all HCV genotypes. In combination with ribavirin in an interferon-free regimen, it can achieve a 100% sustained viral response (SVR) rate in genotype 2/3 treatment-naïve patients. In association with pegylated interferon and ribavirin (PR), it achieves an SVR of 91% in genotype-1 naïve patients. NNIs in association with PR appear to be less potent, but they may nonetheless play a key role in many of the combination trials including either PIs or NIs. NS5A inhibitors also exhibit highly potent antiviral activity. Evaluation of their activity in combination with PIs demonstrated for the first time that an interferon-free regimen can cure genotype-1b null-responder patients. Furthermore, quadruple therapy with PR can achieve a 100% SVR in genotype-1 null-responder patients. Other players in the field, such as cyclophilin inhibitors and therapeutic vaccines, may have a role in combination with DAAs. The near future of HCV treatment looks promising. However, whether or not DAA combinations will lead to an interferon-free regimen for all patients remains an open question.