Drug Development for Antiretroviral Therapies

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Drug Development for Antiretroviral Therapies 2001 (Hep DART 2001)

December 16-20, 2001, Maui, Hawaii   

By Mark Nelson, MD
Dr Nelson is Lead Clinician for HIV inpatient services at Chelsea & Westminster Hospital in London and Deputy Director of the Research Department at the hospital. He is also a Contributing Editor to HIV and Hepatitis.com.

Copyright 2002 by HIV and Hepatitis.com. All Rights Reserved.  
Editor's Note: Unless otherwise noted, all references are to Abstracts of Hep DART 2001. December 16-20, 2002, Maui, Hawaii.  

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The majority of antiviral research thus far has been performed on individuals infected with HIV.?However, it is clear that there are many more individuals infected with the hepatitis viruses compared with those with HIV.?Worldwide, 370 million individuals have hepatitis B virus (HBV) infection; 180 million are infected with hepatitis C virus (HCV) infection, compared with 30 million with HIV.?The deaths per year are similar between HBV and HIV at approximately one million a year, and around 250,000 individuals will die yearly due to complications from HCV. [Fig 1]
Hep DART 2001 Focus and Program Highlights

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Sponsored by Northwestern University Medical School, HEP DART 2001 assembled clinicians, researchers and basic scientists together to advance? knowledge of ongoing drug development processes in the treatment of hepatitis B and hepatitis C.

The conference program included sessions covering the following topics:

Pathogenesis and Immunology of the Hepatitis Viruses
Epidemiology and Emerging Viral Issues
Viral and Cell Dynamics Quasispecies and Quantitation of Hepatitis Viruses
Public Health and Outreach Efforts
Next Generation of Hepatitis Inhibitors
Cell Cultures and Animal Models for Hepatitis B and C
Impact of Drug Resistance
Optimizing Outcome of Therapeutics for Hepatitis Infections and Pediatric Issues
Therapeutic Modalities in Patients Co-Infected with Hepatitis and Other Viruses
Improved Therapeutic Modalities for Hepatitis Infections and Vaccines
Liver Damage, Fibrosis and Hepatocellular Carcinoma

[此贴子已经被作者于2003-9-30 8:59:42编辑过]

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As eradication of HBV is difficult, the goal of HBV treatment has been the suppression of viral replication with improvements in hepatic necroinflammatory disease and the reduction of long-term sequelae. Currently, there are only 2 approved treatments for hepatitis B: Intron-A (interferon alfa-2b) and Epivir-HBV (lamivudine, 3TC).

Epivir-HBV may also be of use in individuals with hepatic fibrosis with 67% of individuals showing improvement in fibrosis score when YMDD resistance has not developed, but only 40% where the YMDD resistant mutation is present. However 4% of individuals without the YMMD change developed further fibrosis, whilst 19% with the YMDD change had increases in their fibrosis score.

Two additional potentials uses of Epivir-HBV were discussed. Firstly, in the prevention of perinatal infection and secondly the possibility of using it to prevent nosocomial spread of HBV. [Abstract 037].

Mothers with high levels of HBV, despite standard hepatitis B immunoglobulin and vaccination of the child, may still transmit HBV in up to 25% of cases. A group from Rotterdam has presented data on three such mothers who were treated with Epivir-HBV from week 36 of pregnancy, followed by standard vaccination with hepatitis B immunoglobulin and hepatitis B vaccination of the infant. In the 3 infants at 12 months of follow up, none were HBsAg (hepatitis B surface antigen) positive compared with 4 out of 4 in a historical group.

Emergence of drug resistant virus in HBV-infected individuals treated with Epivir-HBV is well documented. This commonly occurs as a M552V/I mutation with resistance further enhanced by a further mutation at L528M in the hepatitis B viral polymerase. The 552 mutation is analogous to the M184V/I which occurs in HIV reverse transcriptase when it is exposed to this drug. Further mutations in the HBV polymerase are now described.

In one study [Abstract 032] 31 individuals with chronic HBV who completed at least 104 weeks of Epivir-HBV therapy were investigated. Resistant virus was detected in 7 of the individuals between 9 and 18 months of therapy. Of the 7 patients, 6 were HbeAg (hepatitis B e antigen) positive at baseline, and 4 had a double mutation consisting of RTM204V and RTL108M. Two had a RTM204I switch. In one patient two base substitutions at RTM204 leading to a methionine to serine change were detected as a novel DNA mutation at month 18. This new variant indicates new codon changes conferring Epivir-HBV resistance in vivo.

The gold standard therapy for HCV is interferon in combination with weight adjusted ribavirin. Individuals with genotype I should receive therapy for 48 weeks, however, interferon and ribavirin for genotype 2 and 4 showed similar viral response at both 24 and 48 weeks. Pegylated interferon appears more effective than interferon with improved compliance due to the once daily dosing and possible reductions in toxicity


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[此贴子已经被作者于2003-9-30 9:13:08编辑过]

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Although most acute infections with HCV are asymptomatic approximately 25% of individuals will develop symptoms, commonly flu-like with arthralgia and malaise and occasionally jaundice. The outcome of acute HCV infection is that approximately 80% will develop chronic infection with the remaining 20% making a spontaneous recovery. Of those individuals who go on to develop chronic infection, there is a high probability of developing hepatitis with possible progression to cirrhosis and hepatocellular carcinoma. Individuals who develop a symptomatic infection may be more likely to spontaneously recover, than those who remain asymptomatic. The treatment of those individuals who are found to have acute hepatitis C has been unclear.

Manns and colleagues [Abstract 050] reported the results of a German multicentre study of interferon for acute HCV infection. The premise behind treatment is that early control of viral replication will prevent depletion or loss of virus specific cytotoxic T cell responses, and also prevent diversification of HCV viral epitopes. In addition, the lessons learnt from HIV, would suggest that early treatment of infection may lead to sustained control of viral replication. 44 individuals were recruited to this study. They received 5 million units of Intron-A (interferon alfa-2b) daily for 4 weeks, and then 5 million units three times a week for 24 weeks.

Follow up to 48 weeks was reported. Of the 44 individuals, 21% were intravenous drugs users, 23% were infected sexually, 16% from medical procedures, and 32% from a needle stick injury. In 9% of individuals the source of hepatitis C was unknown 43% were male, and 68% of patients developed jaundice. The mean age was 36.7 years. HCV genotype 1 was the present in 61% of the patients. The viral load was 418,000IU/L at the time of initiation of therapy. Individuals were treated at a mean of 87 days post infection. Virological response at 24 weeks was 100% with a 98% response rate at 48 weeks. Treatment with interferon therefore was recommended by the authors for individuals with acute symptomatic hepatitis C infection. Although there was no control cohort, if compared with the results of another study from Bari in individuals with acute hepatitis C who were not treated, the natural course of infection showed that only 30% (12 of 40) of individuals spontaneously cleared 24 weeks post diagnosis.

The real problem at the present time is to try and find which individuals will spontaneously clear, and which ones will not. This treatment used interferon alone, but it should be noted that this was a potentially highly compliant group being made up of mainly non-IVDU individuals. A new study with pegylated interferon has commenced to try to examine whether there can be any better results although as the presenter pointed out this is difficult with 98% of individuals responding.

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Hepatitis GB (aka Hepatitis G)
It appears that the whole alphabet will soon be involved with new hepatitis viruses. Hepatitis A to E are well recognized, although hepatitis F appears to have been a false alarm. Hepatitis GB, which is synonymous with hepatitis G virus, was first isolated from a surgeon who developed hepatitis (with the initials GB in the 1950's). This agent is parentally transmitted and can result in a persistent infection. In controlled studies of transfusion and community acquired hepatitis, hepatitis G appears to have no specific association with clinical hepatitis and no influence on co-existent hepatitis C virus infection. Therefore this virus's designation as a hepatitis virus appears to be a misnomer. [Abstract 006]

In recent months there has been great excitement over the fact that individuals infected with HIV who remain chronically infected with hepatitis G, have an improved survival compared with those individuals who are hepatitis G antigen negative. Two studies have recently shown this and have shown not only an improved overall survival, but also a reduction in the development of AIDS, and survival in the post HAART era. The reasons why this is the case are unclear, although in vitro cells pre-infected with hepatitis G fail to support replication of HIV.

TTV
Another virus recently studied by Japanese investigators, TTV, is a small non-enveloped circular virus of the circoviridiae family. TTV is found in approximately 7 to 12% of blood donors, although it may be more prevalent in certain geographical areas, especially Japan. The clinical significance of this agent is unclear. The incidence of new TTV infection in cases of non- A-E hepatitis does not differ in incidence in transfused individuals who did not develop hepatitis compared with those that do. In addition, TTV has no impact on both severity and persistence of co-existent HCV infection. Therefore at present, there is no known disease association for TTV. [Abstract 006]

SENV
A sub virus of TTV, SENV, may be associated with hepatic disease. There are at least 8 members of the SENV family, with major variation between them (approximately a 25% difference in nucleotide sequence). SENV-H and SENV-D have shown a close association with post transfusion hepatitis, although both are found in low prevalence in volunteer donor populations (around 2%). In studies prospectively following patients having undergone open heart surgery, SENV was found in 30.1% of transfused individuals compared to only 3.1% of identically followed surgical patients who were not transfused. This was highly significant (p < 0.001). A positive donor could be identified in 70% of cases and donor recipient transmission was proven by sequence homology. SENV has also been found in a high proportion (up to 60% of individuals) with established parental exposure.

New SENV infections have been found in 92% of individuals with transfusion associated non A-E hepatitis compared to 24% of those who did not develop hepatitis. Clinical disease in such cases has been mild but 18% developed chronic hepatitis. The majority of individuals cleared this infection within one year. SENV has also been reported to occur as an acute co-infection in 41% of individuals developing hepatitis C, although the presence of this agent did not appear to affect the severity or persistence of hepatitis C.

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[Abstract 034]

The presence in some individuals of pre-core mutants is well described, with these individuals being HbeAg negative but continuing to have evidence of viral replication when tested by double-stranded DNA. The commonest mutation in the pre-core region to cause this is G1896A acting as a stop codon. Changes may also occur at codons 1762 and 1764 giving similar laboratory results. These pre-core mutants may be associated with differing immunological changes compared with standard HbeAg-positive chronic HBV with increased CD8+ T cell activity to hepatitis B epitopes. The major problem with pre-core mutants is definition of end of therapy.

A recent study of individuals with the pre-core mutant treated with standard doses of interferon showed at 12 months 25% had lost HBsAg, with 27% HBV DNA negative and 28% a normal ALT. A similar study with Epivir-HBV at 12 months in HBeAg negative individuals showed 70% had an HBV DNA below the level of detectability; however on stopping treatment a large percentage of these rebounded suggesting the importance of long-term therapy. However, it is known with extended therapy with Epivir-HBV that there is considerable development of resistance to Epivir-HBV and although initial benefits in histology have been shown, with the development of resistance there is an association with increased levels of DNA and worsening of liver histology.

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[Abstract 051]

Despite the advances associated with pegylated interferon in the treatment of hepatitis C there are still a large numbers of individuals who either do not respond to treatment or who have a viral relapse once therapy is discontinued. Various factors may be associated with this failure and it may be due to viral, drug, host or environmental factors. Factors so far identified have included a poor response in genotype 1, high initial HCV viral load, increasing age, male sex and the presence of fibrosis. In addition, in studies with interferon alone, but not interferon/ribavirin, African - American race has been a poor prognostic factor. Increasingly the importance of adherence has been realized and in one study with pegylated interferon adherence of less than 80% with therapy was associated with a reduction in efficacy.

HALT-C Study
The HALT-C study examines individuals who have failed treatment with interferon either alone or with ribavirin, and aims to examine reduction in progression of hepatitis to cirrhosis, hepatocellular carcinoma and liver failure, in individuals who receive pegylated interferon (Pegasys) and ribavirin.

To be eligible for the study, patients need to be HCV positive, have bridging fibrosis or cirrhosis present on liver biopsy and have been non respondent to at least 12 weeks of interferon therapy. Patients receive pegylated interferon and ribavirin and at week 20 a PCR is performed. If the PCR is negative patients continue therapy to 48 weeks, and if positive patients are randomized to cessation of therapy or maintenance therapy with pegylated interferon. So far 268 patients have been recruited with a mean age of 50. 72% are male and 88% Caucasian. Mean HCV viral load is 3.52 x 106 IU/mL, 84% of patients have genotype 1 and 41% are cirrhotic. 253 patients have reached week 20 with 15 patients having withdrawn. PCR is negative in 107 at 20 weeks (42.3% OT) Factors associated with poor response have been prior therapy with interferon and ribavirin compared with interferon alone, fibrosis and genotype non-2B/3A. 59 patients required dose reduction of interferon, ribavirin or both.

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[Abstract 056]

The major consequence of the continued inflammation secondary to viral hepatitis is the development of fibrosis. This seems to be secondary to stellate cell activation leading to production of type I collagen resulting in progressive accumulation of extra cellular matrix in the liver parenchyma. Approaches to therapy for fibrosis include removal of the fibrotic stimulus, inhibition of stellate cell activation, the treatment of the consequences of the stellate cell activation, and the induction of apoptosis of hepatic stellate cells.

The removal of the stimuli for hepatitis fibrosis has mixed results. In hepatitis B there is conflicting data over the ability of Epivir-HBV and interferon either alone or in combination to reduce fibrosis. However, in one study fibrosis worsened in only 2% of Epivir-HBV treated individuals versus 12% of a placebo group (p < 0.05). A recent trial of adefovir has demonstrated significant reduction of fibrosis progression versus placebo.

A meta analysis of several studies of interferon +/- ribavirin or pegylated interferon/ribavirin for hepatitis C showed fibrosis worsening in ranges from 23% in patients treated with interferon alone for 24 weeks to 8% in patients receiving optimized pegylated interferon/ribavirin. All regimens significantly reduced fibrosis progression rates in comparison to the rates before treatment. In addition a reversal of cirrhosis was observed in 75 of 153 patients with baseline cirrhosis. 6 factors were independently associated with the absence of significant fibrosis after treatment. These were baseline fibrosis stage, sustained viral response, age younger than 40, a low body mass index, no or minimal baseline activity and viral load lower than 3.5 million copies.

Hepatic stellate cell activation is associated with production of the cytokine TGF beta which inhibits intracellular matrix degradation and also activates hepatic stellate cells. Several TGF beta inhibitors have been isolated including comostat, mesylate, decorin and antibodies to both TGF beta and its receptor. These are presently being studied in animal models. As TGF beta is induced by the renin-angiotensin pathway, ACE II inhibitors have also been examined. These are known to reduce renal and cardiac fibrosis, and in animal models block hepatic fibrosis.

Another group of agents that may be useful are anti-oxidants which protect hepatocytes from damage and also inhibit Kupffer and stellate cell activation. These include vitamin E, respiritol, quercetine, and salymarin (which is the active ingredient in milk thistle) and TJ9 which is an herbal preparation from Japan. Studies with these agents have shown no effect in alcoholic cirrhosis although a pilot study with vitamin E showed improvement in fibrosis in hepatitis C infected individuals as did a pilot study with glyceyrizine. In a large recent cohort analysis no definite effect of these alternative therapies was shown.

Both gamma interferon and alpha interferon inhibit hepatic stellate cell activation. Gamma interferon has been shown to reduce fibrosis in animal models, and interferon alpha in multiple studies has shown a reduction of fibrosis in hepatitis C patients independent of virological response.

As activated hepatic cells have low levels of PPAR gamma; antagonists of PPAR gamma are also under study as are endothelium antagonists.

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[Abstract 058]

Hepatocellular carcinoma (HCC) is now the fourth commonest GI tumor found in the United States. It appears to be especially common in black males. The rise in HCC has been linked to an increased incidence of both hepatitis C and hepatitis B. HBsAg positivity has a relative risk of 63 for developing HCC, and in high prevalent areas hepatitis C is associated with 60% of hepatocellular carcinomas. The HCV core protein appears to play an important role. Although HCV is not integrated within the liver, the core protein appears to be involved in stimulating large amounts of regeneration and remodeling of the liver.

In HCV cirrhotics, the risk of development of HCC is 1-4% per year, although 43% of patients developing HCC will not have cirrhosis in the adjacent liver. Other risk factors for HCC include alcohol, metabolic diseases such as hemochromotosis and the use of estrogens and anabolic steroids.

Treatment and prognosis for HCC continues to remain poor. In those patients not receiving therapy, 1 year survival is 54% and 3 year survival only 28%. In patients who are able to undergo surgical resection, i.e., those patients with small lesions, prognosis improved to 81% at one year and 44% at 3 years. However, less than 5% of individuals are suitable for surgical techniques.

An alternative treatment is by ethanol injection which shows similar rates of prognosis (82% and 38%) as those undergoing surgical resection. Other local techniques would include local ablative therapies with agents such as TCA, and chemo-embolization and cryotherapy. The best survival is seen those individuals undergoing transplantation with survival rates of 84% and 74%. However, once more the number of patients suitable is small (those with a single tumor less than 5cm or three tumors each less than 3 cm in diameter).

Indications for Epivir-HBV and interferon treatment are HBeAg positive with a raised ALT and a positive HBV DNA, or in the pre-core mutant, which is HBeAg negative, raised ALT and positive HBV DNA. There appears to be an increased therapeutic response in individuals with higher ALT levels, and recent guidelines have suggested individuals who have an ALT less than 2 times normal should not receive treatment as they are much less likely to respond. Treatment with either interferon for between 12 and 24 weeks, or treatment with Epivir-HBV for 52 weeks both lead to a loss of HBeAg in approximately 1/3 of individuals, with normalization of ALT occurring at a much higher rate than in controls. Recent studies have suggested that a longer than standard four month treatment with interferon therapy may lead to significant increases in the number of individuals who respond. Epivir-HBV is the treatment of choice in individuals with decompensated cirrhosis where interferon may be associated with further decompensation, bacterial peritonitis and sepsis.

Whilst interferon has well known associated toxicity, the major drawback to therapy with Epivir-HBV is the development of resistance due to YMDD variants. These may occur in up to 66% of individuals at 4 years (see Fig. 2.) However, the emergence of YMDD variant does not always indicate the development of clinical antiviral resistance with some individuals continuing to sero-convert despite the development of resistance mutations.

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Recent guidelines suggest that treatment with Epivir-HBV should be stopped after seroconversion with loss of HBV DNA on two occasions at least 6 months apart. In individuals developing the YMDD variants the cessation of therapy should occur based on the clinical picture and increases in ALT and hepatitis B viral load.

[此贴子已经被作者于2003-9-30 9:00:51编辑过]

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Although there have been recent advances in the treatment of both hepatitis B and C new agents with increased efficacy and reduced toxicity are urgently needed. Several promising new agents were reported both in animal models and early clinical studies.

＊Hepatic C protease inhibitors
＊New analogues of ribavirin
＊Ribozymes
＊MCC478
＊L nucleoside analogues
＊Adefovir
＊Entecavir
＊Coviracil
＊Clevudine
＊ACH126443

[此贴子已经被作者于2003-9-30 9:01:25编辑过]