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Arrowhead Presents New Clinical Data Demonstrating a Sustained Host Response in Hepatitis B Patients Following RNAi Therapy

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— Up to 5.0 log10 reduction in HBsAg observed; data presented at HEP
DART 2017 —

Arrowhead Pharmaceuticals, Inc. (NASDAQ:ARWR) presented new data from
the company's Phase 2 clinical study in patients that received multiple
doses of ARC-520, the company's prior generation RNAi-based clinical
candidate against chronic hepatitis B infection (HBV). A maximum
reduction from baseline in HBV surface antigen (HBsAg) of 5.0 log10 was
achieved seven months following the administration of the last dose of
ARC-520, with the lowest absolute level observed being just above the
lower limit of HBsAg quantitation. These data, presented at the 22nd
biennial HEP DART meeting held in Kona, Hawaii, from Dec. 3-7, indicate
that multiple doses of an RNAi-based therapy may lead to a host response
that is sustained after therapy is concluded.

Bruce D. Given, M.D., chief operating officer and head of R&D for
Arrowhead Pharmaceuticals, said: "We believe that achieving a functional
cure of chronic hepatitis B infection will require a sustained host
response, which is likely to be immune mediated. In our Phase 2 study of
ARC-520, multiple patients saw continued reductions in key HBV markers
long after ARC-520 treatment ceased. These data represent the first
clinical evidence that an RNAi-based approach can lead to the type of
favorable sustained host response that we have always believed is
possible. Achieving this result with ARC-520, which was not designed for
activity against HBV s-antigen produced by integrated DNA, provides us
with further confidence that our new RNAi-based compound, ARO-HBV, which
is designed to silence the production of all HBV gene products,
including transcripts derived from integrated DNA, has a good chance of
being a backbone therapy for combinations intended to cure chronic HBV."

In an oral presentation titled, "Looking Back to Move Forward -
Designing Next Gen RNAi for HBV," Dr. Given showed key evidence for the
first time that 2 of 3 (66.7%) HBV e-antigen (HBeAg) positive patients
and 2 of 5 (40%) HBeAg negative patients treated with an RNAi-based
therapy achieved a sustained host response off therapy. This was
characterized by continued reduction of multiple HBV viral markers,
including HBsAg, and coinciding with an increase in circulation of liver
enzyme alanine aminotransferase (ALT), indicative of host response. The
new data from Heparc-2001, the company's Phase 2 open-label extension
study of ARC-520 in combination with entecavir in 8 patients, follows
patients over 7 months after the last ARC-520 dose was administered,
which is the last time point currently available.

In the 4 patients that appeared to have a sustained host response,
observed reductions in HBsAg were 5.0, 3.1, 2.4, and 0.6 log10 from
baseline. In addition, these patients achieved absolute levels of HBsAg
of 58, 2.6, 0.36, and 0.051 IU/ml. The lower limit of quantitation for
this measurement of HBsAg is 0.05 IU/ml, below which would be deemed
seroclearance. These patients also achieved reductions in HBV DNA to
below the level of quantitation, and deep reductions in core-related
antigen (HBcrAg), and HBeAg, with many at or below their respective
lower limits of quantitation.

Dr. Given also presented select preclinical data on ARO-HBV, a new
therapy for patients with chronic HBV that utilizes the company's next
generation Targeted RNAi Molecule (TRiM™) platform. Notably, 3 doses of
ARO-HBV in wild type pHBV mice led to reductions in HBV DNA of 3.44
log10 and both HBsAg and HBeAg dropped below the lower limit of
quantitation (reductions of greater than 3.0 log10 and greater than 2.2
log10, respectively).

In addition, Arrowhead created a mutated pHBV mouse model that
eliminates the HBx trigger site to simulate HBV patients with high
levels of integrated HBV DNA relative to cccDNA. In this model, a single
dose of ARO-HBV led to a reduction in HBsAg of 2.95 log10. The duration
of effect was long, with a HBsAg reduction of approximately 2.0 log10
still observed 8 weeks after the dose.

ARO-HBV is designed to silence the production of all HBV gene products,
including transcripts derived from integrated DNA, with the goal of
getting to a level where patients' immune systems can reconstitute,
leading to a sustained host response and ultimately a functional cure.
Arrowhead's learnings from multiple clinical studies of prior generation
compounds, ARC-520 and ARC-521, and the extensive non-clinical research
completed in multiple species, including long-term treatment of
chimpanzees, have guided the rapid development of ARO-HBV. The results
presented with respect to ARC-520 are not necessarily predictive of
ARO-HBV results.

GLP-toxicology studies are being conducted and Arrowhead is
manufacturing the drug supply necessary to begin clinical studies of
ARO-HBV. The company anticipates filing a Clinical Trial Application by
the second quarter of 2018.

Slides from Dr. Given's presentation may be accessed on the Events
and Presentations
page under the Investors section of the Arrowhead
website.

About Arrowhead Pharmaceuticals

Arrowhead Pharmaceuticals develops medicines that treat intractable
diseases by silencing the genes that cause them. Using a broad portfolio
of RNA chemistries and efficient modes of delivery, Arrowhead therapies
trigger the RNA interference mechanism to induce rapid, deep, and
durable knockdown of target genes. RNA interference, or RNAi, is a
mechanism present in living cells that inhibits the expression of a
specific gene, thereby affecting the production of a specific protein.
Arrowhead's RNAi-based therapeutics leverage this natural pathway of
gene silencing.

For more information, please visit www.arrowheadpharma.com,
or follow us on Twitter @ArrowheadPharma.
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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 the safety and efficacy of our product
candidates, the duration and impact of regulatory delays in our clinical
programs, 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. Our 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.

Source: Arrowhead Pharmaceuticals, Inc.

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