Arrowhead Pharmaceuticals Presents Late-Breaking Clinical Data on ARO-AAT at Liver Meeting® 2018

• Three monthly doses of 300 mg ARO-AAT led to reductions in serum
  alpha-1 antitrypsin to below the level of quantitation in 100% of
  subjects
• Reductions were sustained for greater than 14 weeks indicating that
  quarterly or less frequent dosing appears feasible
• Single and multiple doses of ARO-AAT appear to be well-tolerated at
  all doses tested

PASADENA, Calif.–(BUSINESS WIRE)–Nov. 9, 2018–
Arrowhead Pharmaceuticals Inc. (NASDAQ: ARWR) today announced clinical
data from a Phase 1 study of ARO-AAT, the company’s second generation
subcutaneously administered RNA interference (RNAi) therapeutic being
developed as a treatment for a rare genetic liver disease associated
with alpha-1 antitrypsin (AAT) deficiency, will be presented in a
late-breaking poster at The Liver Meeting®, the Annual Meeting of the
American Association for the Study of Liver Disease (AASLD), being held
in San Francisco.

In the AROAAT1001 study, 45 normal healthy volunteers (NHV) received a
single dose of ARO-AAT (n=16), three monthly doses of ARO-AAT (n=12), or
placebo (n=17). Key data presented include the following:

• ARO-AAT at single- and multiple-doses produced robust and consistent
  reductions in serum AAT levels
  • Single-doses of 200 and 300 mg resulted in greater than 91% serum
    AAT reduction, with 3 of 4 subjects having concentrations below
    the level of quantitation (BLQ)
  • In 200 and 300 mg single-dose cohorts, an average serum AAT
    reduction of greater than 90% was sustained for 6 weeks
  • In the multiple-dose cohorts of 200 and 300 mg, for subjects
    receiving all 3 doses, an average of greater than 90% reduction in
    serum AAT was sustained for longer than 14 weeks
  • The maximum NADIR reduction is 94%
• Monthly serum AAT follow up is ongoing with 9 of 10 subjects at BLQ in
  the multiple-dose cohorts, including 100% of subjects from the 300 mg
  cohort
• Duration of response indicates that quarterly or less frequent dosing
  appears feasible
• ARO-AAT has been well tolerated at all doses tested (up to 300 mg)
  given three times every 28 days
  • The most common adverse events (AE) were upper respiratory tract
    infection (39%) and headache (32%)

“The ARO-AAT data being presented at The Liver Meeting demonstrate the
power of our Targeted RNAi Molecule (TRiM^TM) platform, which
is the basis of our growing pipeline of RNAi therapeutics targeting a
diverse range of diseases,” said Bruce Given, M.D., Arrowhead’s chief
operating officer and head of R&D. “These data indicate that ARO-AAT can
produce robust and consistent reductions in the liver production of the
AAT protein. In addition, the duration of response indicates that a
dosing interval of once a quarter or even less frequent is feasible. Our
next step is to initiate a Phase 2 study to evaluate whether this
reduction can, over time, have an impact on the progressive liver
disease in alpha-1 patients, whose only treatment option currently is
liver transplant.”

Poster Details:

A Phase 1 Single and Multiple Dose-Escalating Study to Evaluate the
Safety, Tolerability, Pharmacokinetics and Effect of ARO-AAT on Serum
Alpha-1 Antitrypsin levels in Normal Adult Volunteers

• Publication Number: LB-9
• Session: Late-Breaking Poster Session
• Session Date and Time: November 12, 2018 from 8:00 a.m. to 5:30 p.m. PT
• Location: Moscone Center North/South Building, Hall C
• Authors: Dr. Christian Schwabe, et al.

A copy of the poster may be accessed on the Events
and Presentations page under the Investors section of the Arrowhead
website.

ARO-AAT is designed to silence the production of the misfolded Z-AAT
protein with the intent to:

• Prevent accumulation of the disease-causing protein in the liver
• Allow for clearance of the accumulated protein
• Prevent repeated cycles of cellular damage
• Reverse fibrosis associated with prior damage

About AROAAT1001

AROAAT1001 (NCT03362242)
is a Phase 1 randomized, double-blind, placebo controlled
single-ascending dose (SAD) and multiple-ascending dose (MAD) study to
evaluate the safety, tolerability, pharmacokinetics, and effect of
subcutaneous doses of ARO-AAT on serum alpha-1 antitrypsin levels in
healthy adult volunteers. The SAD portion of the study included four
cohorts at dose levels of 35, 100, 200, and 300 mg and the MAD portion
of the study included three cohorts at dose levels of 100, 200, and 300
mg. Additional cohorts were planned at a dose of 400 mg, but were deemed
unnecessary based on observed activity at lower doses. AROAAT1001
enrolled 45 healthy volunteers.

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.

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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
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success of our scientific studies, our ability to successfully develop
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Source: Arrowhead Pharmaceuticals, Inc.

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Source: Arrowhead Pharmaceuticals Inc.

Arrowhead Pharmaceuticals, Inc.
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ir@arrowheadpharma.com
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