Major advances have revolutionized the HCV antiviral treatment field, with interferon-free combinations of direct-acting antivirals (DAAs) resulting into success rates of > 90% for all HCV genotypes. Nevertheless, viral eradication at a global level stills remains challenging, stimulating the continued search for new affordable pan-genotypic drugs. To overcome selection of drug resistant variants, targeting host proteins can be an attractive mechanism of action. Alisporivir (Debio 025) is a potent pan-genotypic host-targeting antiviral agent, acting on cyclophilin A, which is necessary for HCV replication. The efficacy and safety of three different oral doses of alisporivir in combination with pegylated interferon-α2a given over a period of four weeks, was investigated in a randomized, double-blind and placebo-controlled phase IIa clinical trial, in 90 treatment-naïve subjects infected with chronic hepatitis C, wherefrom 58 HCV1b samples were selected for genetic sequencing purposes. Sequencing results were used to study the HCV genome for amino acid changes potentially related with selective pressure and resistance to alisporivir. By comparing baseline and on-treatment sequences, a large variation in proportion of amino acid changes was detected in all treatment arms. The NS5A variant D320E, which was previously identified during in vitro resistance selection and resulted in 3.6-fold reduced alisporivir susceptibility, emerged in two subjects in the alisporivir monotherapy arm. However, emergence of D320E appeared to be associated only with concurrent viral load rebound in one subject with 0.8 log10 IU/ml increase in HCV RNA. In general, for all datasets, low numbers of positions under positive selective pressure were observed, with no significant differences between naïve and treated sequences. Additionally, incomplete sequence information for some of the 22 patients and the low number of individuals per treatment arm, is limiting the power to assess the association of alisporivir or interferon treatment with the observed amino acid changes.

The anti-hepatitis C virus (HCV) effect and safety of three different oral doses of the cyclophilin inhibitor Debio 025 in combination with pegylated interferon-alpha 2a (PEG IFN-alpha 2a) were investigated in a multicenter, randomized, double-blind, placebo-controlled escalating dose-ranging phase 11 study in treatment-naive patients with chronic hepatitis C. Doses of 200, 600, and 1,000 mg/day Debio 025 in combination with PEG IFN-alpha 2a 180 mu g/week for 4 weeks were compared with monotherapy with either 1,000 mg/day Debio 025 or 180 mu g/week PEG IFN-alpha 2a. In patients with genotypes I and 4, the 600- and 1,000-mg combination treatments induced a continuous decay in viral load that reached -4.61 +/- 1.88 and -4.75 +/- 2.19 log(10) IU/mL at week 4, respectively. In patients with genotypes 2 and 3, HCV RNA levels at week 4 were reduced by - 5.91 +/- 1.11 and -5.89 +/- 0.43 log(10) IU/mL, respectively, with the same treatment regimens. Adverse events were comparable between treatment groups apart from a higher incidence of neutropenia associated with PEG IFN-alpha 2a and an increased incidence of isolated hyperbilirubinemia at the highest dose of Debio 025 (1,000 mg/day). Conclusion: These results confirm that Debio 025 has a potent activity and an additive effect on HCV RNA reduction in genotype I and 4 patients at 600 and 1,000 mg/day when combined with PEG IFN-alpha 2a. (HEPATOLOGY 2009;49:1460-1468.)

Debio 025 is a cyclophilin (Cyp) inhibitor without calcineurin-binding properties. The drug inhibits viral replication of genotype 1b and 2a replicons in nanomolar concentrations and shows an additive to synergistic antiviral effect with interferon, ribavirin, and specifically targeted antiviral therapy for hepatitis C (STAT-C) drugs. There is no cross-resistance with protease and polymerase inhibitors. In humans, Debio 025 has shown activity against genotypes 1, 2, 3, and 4, and displays an additive antiviral effect with pegylated interferon (peg-IFN)alpha 2a in genotype 1 and 4 patients. The most prominent side effect is reversible hyperbilirubinaemia caused by inhibition of biliary transporters. Debio 025 is a potent anti-HCV drug, with a novel mechanism of action and an efficacy profile that makes it an attractive candidate for combination with current and future HCV treatments.

Debio‐025 is an oral cyclophilin (Cyp) inhibitor with potent anti–hepatitis C virus activity in vitro. Its effect on viral load as well as its influence on intracellular Cyp levels was investigated in a randomized, double‐blind, placebo‐controlled study. Mean hepatitis C viral load decreased significantly by 3.6 log10 after a 14‐day oral treatment with 1200 mg twice daily (P < 0.0001) with an effect against the 3 genotypes (1, 3, and 4) represented in the study. In addition, the absence of viral rebound during treatment indicates that Debio‐025 has a high barrier for the selection of resistance. In Debio‐025–treated patients, cyclophilin B (CypB) levels in peripheral blood mononuclear cells decreased from 67 ± 6 (standard error) ng/mg protein (baseline) to 5 ± 1 ng/mg protein at day 15 (P < 0.01). Conclusion: Debio‐025 induced a strong drop in CypB levels, coinciding with the decrease in hepatitis C viral load. These are the first preliminary human data supporting the hypothesis that CypB may play an important role in hepatitis C virus replication and that Cyp inhibition is a valid target for the development of anti–hepatitis C drugs. (HEPATOLOGY 2008;47:817–826.)

Cyclophilins (Cyps) are proteins that are ubiquitously present with peptidyl-prolyl cis-trans isomerase activity and play an important role in de novo protein folding and in isomerization of native proteins in several cellular systems. There is growing evidence that indicates CypB is a positive modulator of the HCV RNA-dependent RNA polymerase in the replication complex. Early in vitro and animal data with selective Cyp inhibitors show a potent anti-HCV effect. This anti-HCV effect was confirmed in the first patient study with the selective Cyp inhibitor Debio-025. Preclinical data suggest that Cyp inhibitors may present a higher barrier to the selection of resistance than protease and polymerase inhibitors and that a combination of Cyp inhibitors with either of these drugs or interferon results in additive or synergistic anti-HCV activity. By interfering at the level of host-viral interaction, Cyp inhibition may open the way for a novel approach to anti-HCV treatment that could be complementary, not only to interferon-based treatment, but also to future treatments that directly target HCV replication enzymes such as protease and polymerase inhibitors.