Arrowhead's ARC-520 Leads to Consistent Immune Reactivation in Chimpanzees with Chronic Hepatitis B Infection

PASADENA, Calif.--(BUSINESS WIRE)-- Arrowhead Research Corporation (NASDAQ: ARWR), a biopharmaceutical company developing targeted RNAi therapeutics, presented data at HEP DART 2015 showing that in chronically HBV-infected chimpanzees treated with ARC-520 in combination with nucleoside analogs, 7 of 9 (78%) exhibited signs of immune reactivation, which is likely a necessary step for achieving a functional cure of chronic HBV. One chimpanzee also exhibited an on-treatment therapeutic ALT flare and sustained virologic improvements 31 weeks off all treatment. ARC-520 is currently being studied in multiple Phase 2b global clinical trials.

"The hepatitis B virus causes infected cells to produce several proteins that suppress the host immune system, and, therefore, enable chronic viral infection by removing immune control. Our goal with ARC-520 is to reduce expression of those proteins and thereby enable reconstitution of the immune system. We now have shown that ARC-520 can do that, and not just in 1 or 2 infected chimps, but in 7 of the 9 chimps we treated, and this is a big deal," said Christopher Anzalone, Ph.D., Arrowhead president and CEO. "ARC-520 deeply reduces HBV proteins and we believe the elevations in T-cell responsive serum cytokines observed in this study represent a strong proof of principle that ARC-520 can begin the process of immune reconstitution that many believe can lead to functional cure. These data are particularly encouraging when combined with our recent human data. Our Phase 2a clinical trial, which we reported at AASLD last month, showed that ARC-520 can dramatically reduce s-antigen, e-antigen, and core-related antigen in humans after a single dose. During the ongoing Phase 2b clinical trials, we are studying ARC-520 as monotherapy as well as in combination with other agents with the goal of identifying a regimen that leads to consistent functional cures."

Christine Wooddell, Ph.D., director of liver targeting for Arrowhead, presented poster number 152 titled, "Sustained reduction of HBV DNA, RNA and proteins, and HBeAg seroconversion in a chronically HBV-infected chimpanzee treated with nucleoside analog/ARC-520 combination therapy."

In this presentation, Dr. Wooddell and co-authors show that 7 of 9 chimps, HBeAg positive and negative, exhibited indications of an immune response during ARC-520 treatment, as evidenced by elevations in T-cell responsive serum cytokines. Chimp Manetta exhibited deep decreases in HBV DNA, RNA and viral proteins during ARC-520/NUC treatment. The sustained induction of CXCL9 in Manetta was associated with a therapeutic ALT flare (218 U/L) followed by HBeAg seroconversion. Sustained virologic improvements were still observed 31 weeks after all treatment was removed. At this final time point, serum HBV DNA was 5 log₁₀ lower, HBsAg was 1.7 log₁₀ lower, and liver HBV RNA was 99% lower than pre-study.

HBV suppresses the immune system to allow chronic HBV infection. Interferon gamma (IFN-γ) is a key antiviral cytokine critical to innate and adaptive immune responses. IFN-γ produced by natural killer cells and natural killer T cells induces the chemokines CXCL9 and CXCL10 to mediate a T-cell response. An elevation of CXCL9 in the chimps studied is a promising sign of immune system reactivation.

8 out of 9 chimps exhibited episodes of serum cytokine CXCL9 elevation. For 7 chimps these occurred during ARC-520 treatment and in one chimp (Tattoo) these coincided with seroclearance of HBeAg that began prior to study.

To reduce viral replication prior to treatment with ARC-520, chimps were treated for 8-24 weeks with entecavir or in one case (chimp Michele) with entecavir and tenofovir. Following the NUC lead-in period, animals were administered ARC-520 intravenously at 4-week intervals (q4w). Dose levels were 2, 3, or 4 mg/kg ARC-520, along with maintenance doses of entecavir or entecavir and tenofovir. All 9 chimpanzees responded to ARC-520 with HBsAg reductions of 0.5 - 2.7 log₁₀ at nadir, the greater reductions being in HBeAg positive chimps. HBsAg levels in all chimps continued to decrease with repeat dosing. Chimps were monitored for up to 31 weeks off all treatment.

Copies of presentation materials can be accessed by visiting the Events section of the company's website at http://ir.arrowheadresearch.com/events.cfm.

About ARC-520

Arrowhead's RNAi-based candidate ARC-520 is being investigated in the treatment of chronic HBV infection. The small interfering RNAs (siRNAs) in ARC-520 intervene at the mRNA level, upstream of the reverse transcription process where current standard of care nucleotide and nucleoside analogues act. Arrowhead is investigating ARC-520 specifically to determine if it can be used to achieve a functional cure, which is an immune clearant state characterized by hepatitis B s-antigen negative serum with or without seroconversion. Arrowhead is conducting Phase 2b multiple dose and combination studies in chronic HBV patients. Approximately 350-400 million people worldwide are chronically infected with the hepatitis B virus, which can lead to cirrhosis of the liver and is responsible for 80% of primary liver cancers globally.

About Arrowhead Research Corporation

Arrowhead Research Corporation is a biopharmaceutical company developing targeted RNAi therapeutics. The company is leveraging its proprietary Dynamic Polyconjugate^™ delivery platform to develop targeted drugs based on the RNA interference mechanism that efficiently silences disease-causing genes. Arrowhead's pipeline includes ARC-520 and ARC-521 for chronic hepatitis B virus, ARC-AAT for liver disease associated with alpha-1 antitrypsin deficiency, ARC-F12 for hereditary angioedema and thromboembolic diseases, and ARC-HIF2 for renal cell carcinoma.

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Safe Harbor Statement under the Private Securities Litigation Reform Act:

This news release contains forward-looking statements within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995. These statements are based upon our current expectations and speak only as of the date hereof. Our actual results may differ materially and adversely from those expressed in any forward-looking statements as a result of various factors and uncertainties, including our ability to finance our operations, the future success of our scientific studies, our ability to successfully develop drug candidates, the timing for starting and completing clinical trials, rapid technological change in our markets, and the enforcement of our intellectual property rights. Arrowhead Research Corporation's most recent Annual Report on Form 10-K and subsequent Quarterly Reports on Form 10-Q discuss some of the important risk factors that may affect our business, results of operations and financial condition. We assume no obligation to update or revise forward-looking statements to reflect new events or circumstances.

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Source: Arrowhead Research Corporation

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