Infection by hepatitis C virus (“HCV”) is a compelling human medical problem and is now recognized as the causative agent for most cases of non-A, non-B hepatitis.
The hepatitis C virus is thought to infect chronically 3% of the world's population [A. Alberti et al., “Natural History of Hepatitis C,” J. Hepatology, 31 (Suppl. 1), pp. 17-24 (1999)]. In the United States alone the infection rate is 1.8% or 3.9 million people [M. J. Alter, “Hepatitis C Virus Infection in the United States,” J. Hepatology, 31 (Suppl. 1), pp. 88-91 (1999)]. Of all patients infected over 70% develop chronic infection. Chronic infection is a major cause cirrhosis and hepatocellular carcinoma. [D. Lavanchy, “Global Surveillance and Control of Hepatitis C,” J. Viral Hepatitis, 6, pp. 35-47 (1999)]
While interferon-α therapy and more recently interferon-ribavirin combination therapy have been available for the treatment of hepatitis C infection sustained response rates tend to be low (<50%) and side effects tend to be severe [M. A. Walker, “Hepatitis C Virus: an Overview of Current Approaches and Progress,” DDT, 4, pp. 518-529 (1999); and D. Moradpour et al., “Current and Evolving Therapies for Hepatitis C,” Eur. J. Gastroenterol. Hepatol., 11, pp. 1199-1202 (1999)]. There is a clear need for more effective and better tolerated therapies
The HCV genome encodes a polyprotein of 3010-3033 amino acids [Q.-L. Choo, et al., “Genetic Organization and Diversity of the Hepatitis C Virus”, Proc. Natl. Acad. Sci. USA, 88, pp. 2451-2455 (1991); N. Kato et al., “Molecular Cloning of the Human Hepatitis C Virus Genome From Japanese Patients with Non-A, Non-B Hepatitis”, Proc. Natl. Acad. Sci. USA, 87, pp. 9524-9528 (1990); A. Takamizawa et al., “Structure and Organization of the Hepatitis C Virus Genome Isolated From Human Carriers”, J. Virol., 65, pp. 1105-1113 (1991)]. The HCV nonstructural (NS) proteins are presumed to provide the essential catalytic machinery for viral replication. The NS proteins are derived by proteolytic cleavage of the polyprotein [R. Bartenschlager et al., “Nonstructural Protein 3 of the Hepatitis C Virus Encodes a Serine-Type Proteinase Required for Cleavage at the NS3/4 and NS4/5 Junctions”, J. Virol., 67, pp. 3835-3844 (1993); A. Grakoui et al. “Characterization of the Hepatitis C Virus-Encoded Serine Proteinase: Determination of Proteinase-Dependent Polyprotein Cleavage Sites”, J. Virol., 67, pp. 2832-2843 (1993); A. Grakoui et al., Expression and Identification of Hepatitis C Virus Polyprotein Cleavage Products”, J. Virol., 67, pp. 1385-1395 (1993); L. Tomei et al., “NS3 is a serine protease required for processing of hepatitis C virus polyprotein”, J. Virol., 67, pp. 4017-4026 (1993)].
The HCV NS protein 3 (NS3) contains a serine protease activity that helps process the majority of the viral enzymes, and is thus considered essential for viral replication and infectivity. It is known that mutations in the yellow fever virus NS3 protease decreases viral infectivity [T. J. Chambers et al., “Evidence that the N-terminal Domain of Nonstructural Protein NS3 From Yellow Fever Virus is a Serine Protease Responsible for Site-Specific Cleavages in the Viral Polyprotein”, Proc. Natl. Acad. Sci. USA, 87, pp. 8898-8902 (1990)]. The first 181 amino acids of NS3 (residues 1027-1207 of the viral polyprotein) have been shown to contain the serine protease domain of NS3 that processes all four downstream sites of the HCV polyprotein [C. Lin et al., “Hepatitis C Virus NS3 Serine Proteinase: Trans-Cleavage Requirements and Processing Kinetics”, J. Virol., 68, pp. 8147-8157 (1994)]
The HCV NS3 serine protease and its associated cofactor, NS4A, helps process all of the viral enzymes, and is thus considered essential for viral replication. This processing appears to be analogous to that carried out by the human immunodeficiency virus aspartyl protease, which is also involved in viral enzyme processing HIV protease inhibitors, which inhibit viral protein processing are potent antiviral agents in man, indicating that interrupting this stage of the viral life cycle results in therapeutically active agents. Consequently it is an attractive target for drug discovery.
Several potential HCV protease inhibitors have been described. PCT publications WO 00/09558, WO 00/09543, WO 99/64442, WO 99/07733, WO 99/07734, WO 99/50230 and WO 98/17679 each describe potential HCV NS3 protease inhibitors. Unfortunately, none of those inhibitors has yet begun clinical trials and there are no serine protease inhibitors available currently as anti-HCV agents.
Furthermore, the current understanding of HCV has not led to any other satisfactory anti-HCV agents or treatments. The only established therapy for HCV disease is interferon treatment. However, interferons have significant side effects [H. L. A. Janssen et al., “Suicide Associated with Alfa-Interferon Therapy for Chronic Viral Hepatitis,” J. Hepatol., 21, pp. 241-243 (1994); P. F. Renault et al., “Side effects of alpha interferon”, Seminars in Liver Disease 9, pp. 273-277. (1989)] and induce long term remission in only a fraction (˜25%) of cases [O. Weiland, “Interferon Therapy in Chronic Hepatitis C Virus Infection”, FEMS Microbiol. Rev., 14, PP. 279-288 (1994)]. Moreover, the prospects for effective anti-HCV vaccines remain uncertain.
Thus, there is a need for more effective anti-HCV therapies. Such inhibitors would have therapeutic potential as protease inhibitors, particularly as serine protease inhibitors, and more particularly as HCV NS3 protease inhibitors. Specifically, such compounds may be useful as antiviral agents, particularly as anti-HCV agents.