Hepatitis B Virus Program

Transcription

1 Hepatitis B Virus Program Abstract Hepatitis B is a viral hepatitis representing a major global health problem. According to the World Health Organization (WHO), some 360 million people, or 5% of the world s population, suffer from chronic hepatitis B and are therefore at risk of cirrhosis, decompensated cirrhosis, end-stage liver disease, hepatocellular carcinoma and death. Despite this threat to global health, the chronic hepatitis B patient population still has substantial unmet medical needs that must be addressed for effective treatment and control of the disease. Current treatment regimens, based on interferons and antivirals, are not reliably effective in eradicating infection in chronically infected patients; are often rendered ineffective by the emergence of resistant strains of the virus; and suffer from problematic dosing schedules and debilitating side effects that negatively impact patient compliance. Arrowhead researchers have shown that small interfering RNA (sirna) therapeutics have the capacity to knockdown production of all hepatitis B genes and thereby significantly decrease the number of infectious viral particles and viral antigens. This reduction in viral and antigen load is designed to permit the immune system to mount an effective response to chronic hepatitis B infection resulting in virological suppression, biochemical remission, histological improvement and prevention of complications. Arrowhead Research Corporation has combined its advanced expertise in RNAi with its proprietary Dynamic PolyConjugate (or DPC ) sirna delivery technology to develop a novel therapy for the effective treatment of HBV in patients without the liabilities associated with current treatment options. Arrowhead s DPC/siRNA candidates have generated strong data in a number of in vitro and in vivo preclinical studies including those involving transgenic and nontransgenic mouse models of hepatitis B disease. 1

2 Hepatitis B Biology Hepatitis B Virus (HBV) Hepatitis B virus is a small, enveloped DNA virus that belongs to the family Hepadnaviridae. Eight genotypes (A-H) with distinct geographic distribution have been identified. Genotypes A and D are most common in Europe, whereas genotypes B and C are most common in China and Southeast Asia. In the developing world, HBV transmission most commonly occurs by perinatal means from mother to child. In the developed world, the disease is mainly transmited via unprotected sexual contact, blood transfusion and injectable drug use. Infection with HBV occurs in phases that can run the gamut from a silent, acute phase that is resolved by the immune system to a persistent chronic stage of infection that often requires life-long therapy. HBV infection occurs primarily in hepatocytes and is non-cytopathic. In chronic hepatits B, it is the long-term infection that causes hepatic inflammation leading to acute and chronic hepatic dysfunction including acute hepatic failure, cirrhosis and hepatocellular carcinoma. The likelihood of becoming chronically infected is highest if the virus is acquired in infancy and decreases with age at the time of infection. The various HBV genotypes also appear to have differing impacts on the natural course of HBV infection and the development of negative sequelae (Stein LL, Loomba, R. Drug targets in hepatitis B virus infection. Infect. Disord Drug Targets. 2009:9(2): ). Virus Life Cycle Following attachment to the hepatocyte membrane, the virus enters the cell by a mechanism that is not well understood. After uncoating and release in the cytoplasm, the nucleocapsid is transported to the nucleus where the partially double-stranded viral relaxed circular DNA (rcdna) is repaired by both cellular and viral enzymes. Ultimately, covalent ligation of both DNA strands of the rcdna forms covalently closed circular DNA (cccdna). Viral cccdna is a replicative intermediate of HBV and is crucial for the persistence of HBV infection, serving as the template for viral genomic RNA as well as mrna synthesis. The viral DNA contains four major open reading frames: Precore/core gene nucleocapsid protein and the secreted, non-structural, precore protein, and the hepatitis B envelope antigen (HBeAg); 2

3 Polymerase gene containing reverse transcriptase, RNase H and terminal protein domains; PreS1/L-, Pre2S/M- and Surface/S-gene three envelope proteins; and X gene coding for the regulatory X-protein (Urban S, Schulze A, Dandri M, Petersen J. The replication cycle of hepatitis B virus. J Hepatol. 2010;52(2): ). DNA-containing nucleocapsids are formed in the cytoplasm and can be re-imported into the nucleus to form additional cccdna, or enveloped for secretion via the endoplasmic reticulum. The envelope proteins are secreted by the cell either as small, non-infectious subviral spherical or filamentous particles (SVPs) or as infectious virions (Dane particles). SVPs are usually produced in a 1,000 to 1,000,000-fold excess over DNA-containing virions. Natural History of Chronic Hepatitis B Chronic hepatitis B is a dynamic and complex disease. The European Association for the Study of Liver Disease (EASL) has divided it into the following five phases which are not necessarily sequential in nature: Immune Tolerant Phase this first phase is more frequent and prolonged in perinatally-infected patients or those infected in the early years of life. It is characterized by HBeAg positivity, high levels of HBV replication, normal or low levels of aminotransferases, and mild or no liver involvement. Patients in this stage are highly contagious because of the high levels of viremia. Immune Reactive Phase this phase may occur after several years of immune tolerance and is more frequently observed in patients infected during adulthood. It is characterized by HBeAg positivity, a lower level of HBV replication, increased or fluctuating levels of aminotransferases, and a greater degree of liver involvement than in the Immune Tolerant phase. Inactive HBV Carrier State this phase may follow seroconversion from HBeAg positive to anti-hbe antibody positive. It is characterized by very low or undetectable serum HBV DNA levels and normal aminotransferases. This state is associated with a favorable long-term outcome with a very low risk of cirrhosis or hepatocellular carcinoma in the majority of patients. HBeAg-negative Chronic Hepatitis B this phase may follow HBeAg seroconversion during the immune reactive phase and represents a later stage in the natural history of chronic hepatitis B. It is characterized by periodic reactivation with a pattern of fluctuating levels of HBV DNA and aminotransferases and active hepatitis. Although 3

4 patients in this phase are HBeAg negative, they harbor HBV variants with mutations in the precore and/or basal core promoter regions and so are unable to express or express only low levels of HBeAg. In contrast to patients who have truly seroconverted from HBeAg to anti-hbe antibodies and who have a good prognosis, these patients have active liver disease, with a high risk of progression to advanced hepatic fibrosis, cirrhosis and subsequent complications such as decompensated cirrhosis and hepatocellular carcinoma. Hepatitis B surface antigen (HBsAg)-negative Phase low levels of HBV replication may still occur in the liver after loss of HBsAg. HBsAg loss is associated with improvement in outcome with a lowered risk of cirrhosis, decompensation and hepatocellular carcinoma. Immunosuppression can lead to reactivation in these patients (EASL Clinical Practice Guidelines: management of chronic hepatitis B. J Hepatol. 2009;50(2): ). Diagnosis of HBV Serological tests that measure the levels of certain hepatitis B antigens and antibodies can confirm hepatitis B infection and differentiate acute from chronic infection. The three most commonly used Hepatitis B antigens used in these tests are - HBsAg, the core antigen (HBcAg) and HBeAg. The presence of HBsAg in the blood indicates that an individual is currently infected with the virus. HBsAg appears an average of four weeks after initial exposure to the virus. Individuals who recover from acute hepatitis B infections clear the blood of HBsAg within approximately four months after the onset of symptoms. These individuals develop antibodies to HBsAg (anti-hbs). Anti-HBs provide complete immunity to subsequent hepatitis B viral infection. Similarly, individuals who are successfully vaccinated against hepatitis B produce anti-hbs. Patients who fail to clear the virus during an acute episode develop chronic hepatitis B. The diagnosis of chronic hepatitis B is made when the HBsAg is present in the blood for at least six months. In chronic hepatitis B, HBsAg can be detected for many years, and anti-hbs do not appear. As alluded to above (Natural History of Chronic Hepatitis B Infection), chronic hepatitis B can present as HBeAg positive or HBeAg negative depending on the length of the chronic infection. HBeAg positive patients are generally in the early phase of chronic infection and are infected with the so called wild-type HBV. The HBeAg negative cases are caused by replication of a naturally occurring HBV variant with nucleotide substitutions in the precore and/or basal core promoter regions of the genome and represents a later phase of chronic infection. The HBeAg- 4

5 negative population has been increasing over the last 10 to 15 years due to the aging of the chronic hepatitis B population. In many regions, including Europe, it represents the majority of the cases (EASL Clinical Practice Guidelines: management of chronic hepatitis B. J Hepatol. 2009;50(2): ). Hepatitis B Market Epidemiology Chronic hepatitis B is a global health problem, with over 360 million carriers worldwide. Of these, approximately 500,000 to 1,000,000 die annually from cirrhosis, decompensated cirrhosis, end-stage liver disease, and hepatocellular carcinoma. Although chronic hepatitis B is often characterized as a disease that predominantly affects the developing world, it s treatment and prophylaxis still exacts a significant toll on the healthcare budgets of major pharmaceutical markets. For example, in the United States alone, there are 1.25 million individuals living with chronic hepatitis B and over 60,000 new cases annually. Costs associated with large infected populations within the developing world have the potential to negatively affect those maturing economies as well as the broader world economy in the coming decades. Datamonitor estimates that China alone will have over 63 million prevalent cases of hepatitis B in 2020 (Epidemiology: Hepatitis B in China; March 2011). This is a group that is larger than the entire population of the United Kingdom today. Needless to say, national budgets and healthcare systems will struggle to withstand the burden placed upon them by such vast numbers of untreated or poorly-treated chronic hepatitis B patients progressing into the final stages of infection. New and effective treatments are needed to limit the human and economic damage associated with large-scale infection. Current HBV Treatment Options and Market The introduction of prophylactic hepatitis B vaccines into childhood vaccination schedules has been a key element in the developing world s success in driving down infection rates. However, despite this success, the relative ease of population movement and migration are changing the prevalence and incidence of the disease in many regions of the developed world meaning that 5

6 substantial healthcare resources will continue to be required for control of the global burden of the disease. This fact has exposed the inadequacies of current treatment options and spurred the search for novel, more effective therapies and therapeutic strategies. The currently approved therapies consisting of interferon therapy and a growing set of antivirals composed of nucleotide and nucleoside analogues (collectively, NUCs), while potentially providing long term viral load suppression, are, unfortunately, only associated with low rates of complete cure. Interferon alpha has been used extensively in the treatment of chronic hepatitis B. It is available in both pegylated (peginf) and non-pegylated forms. peginf has a longer half-life than its nonpegylated counterpart, allowing it to be dosed once, instead of three times weekly. Administration of both forms of interferon is accomplished via subcutaneous injection and associated with significant side effects including influenza-type symptoms (fatigue, myalgias, and fever), cytopenia, depression, anxiety, irritability, and autoimmune disorders. Interferon treatment is of a finite duration (48 weeks), does not give rise to resistance (in contrast to NUCs, see below), and results in a higher rate of anti-hbe and anti- HBs seroconversion (although patients with HBV genotypes A and B show a better treatment response than patients with genotype C and D). In addition, it is primarily indicated for patients who are otherwise healthy since administration to decompensated patients can lead to fulminant hepatitis. NUCs are orally administered drugs that have a potent antiviral effect. Although treatment with NUCs is generally well tolerated, it can very often be of life-long duration, is associated with resistance (including cross resistance in some instances), and gives rise to lower anti-hbe and anti-hbs seroconversion than interferon treatment. Currently, five NUCs are available to treat hepatitis B: Zefflix/Epivir-HBV (lamivudine, GlaxoSmithKline); Hespera (adefovir dipivoxil, Gilead); Baraclude (entecavir, Bristol Myers-Squibb); Tyzeka/Sebivo (telbivudine, Novartis/Idenix); and Viread (tenofovir, Gilead). In randomized controlled clinical trials, HBeAg-positive patients showed a generally better virological response (undetectable HBV DNA) at one year following treatment with NUCs versus interferon. However, the rates of HBeAg seroconversion were around 30% after interferon treatment versus approximately 20% for NUCs (HBeAg seroconversion rates are further negatively impacted if resistance occurs). In HBeAg-negative patients, virological response at one year is higher after treatment with interferons or NUCs. However, albeit at a low rate (3%), 6

7 only interferon treatment was associated with loss of HBsAg after one year (EASL Clinical Practice Guidelines: management of chronic hepatitis B. J Hepatol. 2009;50(2): ). Datamonitor reported that, in 2009, combined sales for small molecule antivirals and interferon for the treatment of hepatitis B reached $1 B in the seven major pharmaceutical markets alone (US, Japan, France, Germany, Italy, Spain and UK). The small molecule antivirals dominated the market claiming a 97% market share. The 2009 sales represented a CAGR of 37.5% in the period 2005 to Datamonitor estimated that it expected sales of antivirals alone to grow to $1.4 B by 2014 (Datamonitor. Forecast Insight: Hepatitis B Baraclude and Viread set to thrive in the face of limited competition. July 2010). Interestingly, the size of the market for chronic hepatitis B therapeutics in China is expected to triple by 2019 from its reported value of $227 M in Small molecule antivirals dominated the market in 2009 with sales of $200.1 M. However, it is predicted that the growth of the market will be fuelled by new, expensive drugs such as peginf and the latest NUCs such as entecavir and tenofovir as well as anticipated new launches (Datamonitor. Commercial Insight: Hepatitis B in China. April 2011). If China is used as a bellwether for the developing world, it can be assumed that the market for chronic hepatitis B therapeutics will enjoy healthy growth into the foreseeable future as the developing nations, realizing the pressing need to address this potentially devastating healthcare crisis, promote investment in safer, more effective therapies. The inadequacy of current treatment approaches will focus drug development on therapies that interfere with the virus lifecycle and its complex relationship with the host immune system. Unmet Medical Need in HBV Therapy Although the number of therapies for chronic hepatitis B has increased significantly over the past decade, several unmet medical needs remain to be addressed: There is still no therapy that reliably cures the disease in chronically infected patients. The best outcome for most patients is the establishment of a stable carrier state that requires treatment lasting several years or a lifetime. Furthermore, responses to therapy are not durable, with patients experiencing relapse of disease even after long term treatment. A therapy that would lead to a persisting eradication of HBV from chronically infected patients is therefore the single most crucial unmet medical need and represents a huge commercial opportunity. 7

8 An increasing number of patients stop responding to antiviral hepatitis B therapies due to the emergence of mutations in the virus genome. This is a particular problem for long-term treatment. The development of new antivirals that target different components of the virus has had success in battling resistance but is not a viable longterm strategy as the number of resistant strains of the virus increases. Candidate therapies that concentrate on other mechanisms of action will be required in order to overcome this problem. Current hepatitis B pharmacotherapy is of a long duration, has inconvenient dosing schedule and is associated with significant debilitating side effects. Patients on interferons must endure injections once or three time weekly and patients on antivirals must take pills daily for at least one year. Moreover, side effects range from malaise to depression, that sometimes can result in suicide. For these reasons, there is therefore an opportunity for a therapy of limited duration with an acceptable side effect profile that generates a high rate of clinical cure based on HBV surface antigen serum conversion. The goal of treatment is the improvement of the quality of life and survival of patients by preventing the progression of chronic hepatitis B to cirrhosis, decompensated cirrhosis, endstage liver disease, hepatocellular carcinoma and death. It seems that HBV cannot be completely eradicated due to the persistence of cccdna in the nucleus of infected hepatocytes. Indeed, it has been theorized that the clinical resolution of CHB does not require complete eradication but merely control of replication by the host immune system (Levrero, et.al. Control of cccdna function in hepatitis B virus infection. J Hepatol. 2009;51(3): ). Among new issues and unmet needs identified by EASL, it recommended that new strategies be aimed at therapies designed to enhance loss of HBeAg and HBsAg and subsequent seroconversion. 8

9 Arrowhead Hepatitis B Therapeutic Arrowhead HBV Product Opportunity The large target market population, the impending global health care crisis engendered by hundreds of millions of patients progressing into end-stages of the disease, and the inadequacies of current approaches to treatment make it critical that new strategies to treat chronic hepatitis B be pursued. Of the many emerging novel antiviral treatment modalities currently being considered for chronic hepatitis B, RNAi is one of the most promising. HBV is susceptible to RNAi because it replicates via an RNA intermediate and, to date, a number of studies have described an antiviral effect of RNAi against HBV in vitro and in vivo (Stein LL, Loomba R. Drug targets in hepatitis B virus infection. Infect. Disord Drug Targets. 2009;9(2): ). Recently a Phase I safety study of NUC B1000, a plasmid DNA construct designed to produce four sirna molecules, showed that the treatment was safe and well tolerated. NUC B100 was designed to specifically reduce the viral antigen load in addition to viral titer (Gish RG, Satishchandran C, Young M, Pachuk C. RNA interference and its potential applications to chronic HBV treatment: results of a Phase I safety and tolerability study. Antivir Ther. 2011;16(4):547-54). Rationale sirna Design An RNAi therapeutic has the unique ability to significantly reduce the amount of circulating viral antigens (Lau, Khokhar et al. 2000; Papatheodoridis, Dimou et al. 2002; Romano, McCallus et al. 2006). A reduction of viral antigens is considered crucial to effective therapy because it is the expression of viral proteins that is the primary cause of liver disease from HBV infection (Chisari and Ferrari 1995). An individual infected with HBV can produce in the liver and secrete into the blood as many as infectious HBsAg-containing viral DNA particles per milliliter of serum and a vast excess of HBsAg-containing particles that do not include the infectious DNA. Leaders in the field of HBV therapeutics hypothesize that the function of this large excess of particles that do not contain HBV DNA may be to absorb antibodies that would otherwise neutralize the virus, and that potent reduction of HBV antigens would allow the patient s immune system to clear the infection (Ganem and Prince 2004). Even chronically 9

10 infected patients produce antibodies to HBV proteins (Webster, Reignat et al. 2004). RNAi can be used to target multiple components of HBV production in addition to the pregenomic RNA that would be reverse transcribed to generate the viral DNA. All HBV genes are encoded within open reading frames that overlap. As a result, a single sirna can target the mrnas that produce HBsAg proteins, the viral polymerase, the core protein that forms the capsid, and the HBeAg. The most favorable outcome in chronic HBV infection is HBsAg seroconversion, whereby elimination of HBsAg by the immune system is accompanied by a robust antibody response to this antigen. DPC DPC technology is Arrowhead s proprietary polymer-based approach to the safe and efficacious delivery of sirna delivery. It is fundamentally different from current sirna delivery systems that are based on liposomes or lipid nanoparticles. The platform provides for more efficient delivery of sirna to tissues; is amenable to linkage to targeting ligands and enjoys a relatively straightforward, cost effective manufacturing scheme. Arrowhead has developed a DPC formulation and, to date, has demonstrated its safety in non-glp single and multiple dose toxicology studies in animals. Also, it has utilized DPC to deliver sirna therapeutics to hepatocytes in non-human primates with up to 99% knockdown of the target gene. 10

11 Efficacy of Candidate DPC /sirnas in Nontransgenic and Transgenic Models of HBV Disease To test the efficacy of Arrowhead s DPC technology for delivery of anti-hbv sirnas, a nontransgenic mouse model of chronic HBV infection of the liver was established. These mice produce HBsAg and HBV viral particles that are secreted into the blood. The mice were then given a single injection of 1.5 mg/kg DPC with 0.2 mg/kg sirna that targeted HBV. One week later, HBsAg levels in the serum were reduced by 90% (A) and the amount of HBV DNA in the blood was reduced by 94% (B). A B DPC s containing sirna targeting HBV were also shown to be highly effective against a transgenic mouse model of chronic HBV infection (C). Transgenic HBV mice were given a single injection of 2 mg/kg DPC with 0.5 mg/kg HBV sirna. Four days later, the level of 2.1 kilobase messenger RNA that codes for HBsAg was knocked down by 89%. C 11

12 Next Steps Additional preclinical efficacy data have been generated and will be disseminated over the course of the next 12 months via publication in peer-reviewed scientific journals and public presentation at scientific forums. As a prelude to successful clinical development and commercialization, Arrowhead has secured a license granting it the exclusive right to develop, manufacture and commercialize sirna therapeutics against the HBV genome to treat HBV from Alynylam Pharmaceuticals Inc. IND-enabling studies are ongoing and Arrowhead is engaging clinical experts and thought leaders in the field to design the most suitable clinical development program. 12