Dicerna Announces Dosing of First Patient in Phase 1 Clinical Trial of DCR-HBVS for the Treatment of Chronic Hepatitis B Virus

— Clinical Proof-of-Concept Data Expected in Fourth Quarter of 2019 —

CAMBRIDGE, Mass.–(BUSINESS WIRE)–Dicerna
Pharmaceuticals, Inc. (Nasdaq: DRNA) (the “Company” or “Dicerna”), a
leading developer of investigational ribonucleic acid interference
(RNAi) therapeutics, today announced the dosing of the first patient in
its Phase 1 clinical trial of DCR-HBVS, the Company’s investigational
GalXC^TM-based therapy for the treatment of chronic hepatitis
B virus (HBV) infection in adults. The Company anticipates human
proof-of-concept data from the Phase 1 trial, which is known as
DCR-HBVS-101, in the fourth quarter of 2019. In January 2019, Dicerna
announced the dosing of the first human volunteer in this Phase 1 study.

“Dosing of the first patient in the DCR-HBVS-101 trial signals a major
step toward our ultimate goal of developing a viable therapeutic option
for patients with chronic hepatitis B virus, a serious liver infection
that can result in advanced liver disease or liver cancer if not treated
effectively,” said Ralf Rosskamp, M.D., chief medical officer of
Dicerna. “Based upon our encouraging preclinical data with DCR-HBVS and
our initial experience with the healthy volunteers who are enrolled in
this trial, we are optimistic about the clinical potential of RNA
interference as an innovative approach to effectively treat chronic
hepatitis B virus infection.”

The DCR-HBVS-101 clinical trial is a Phase 1, randomized,
placebo-controlled study designed to evaluate the safety and
tolerability of DCR-HBVS in healthy volunteers (HVs) and in patients
with non-cirrhotic chronic HBV infection. Secondary objectives are to
characterize the pharmacokinetic profile of DCR-HBVS and to evaluate
preliminary pharmacodynamics and antiviral efficacy on plasma levels of
hepatitis B surface antigen (HBsAg) and HBV DNA in blood.

DCR-HBVS is comprised of a single GalXC molecule that targets HBV
messenger RNAs within the HBsAg gene sequence region. Preclinical
studies with a standard mouse model of HBV infection showed DCR-HBVS led
to greater than 99% reduction in circulating HBsAg, suggesting a level
of HBsAg suppression (both in magnitude and duration of suppression)
that may be greater than that achieved from targeting within the X gene
sequence region.

“Given the encouraging inhibitory activity of DCR-HBVS in animal
studies, its favorable preclinical safety profile, and the lack of major
safety signals among healthy volunteers dosed thus far in the
DCR-HBVS-101 trial, we eagerly anticipate the results from patients with
chronic hepatitis B who are treated with DCR-HBVS,” said Man-Fung Yuen,
D.Sc., M.D., Ph.D., Professor of Medicine and Chair of Gastroenterology
and Hepatology at the University of Hong Kong. “Unlike other therapeutic
approaches to treating chronic HBV infection, DCR-HBVS leverages the
power of RNA interference to silence multiple viral genes in addition to
the S antigen, potentially reducing HBsAg to very low levels, which
could allow the patient’s own immune system to generate an effective
immune response. With its long-acting mechanism, DCR-HBVS may help
patients with chronic HBV infection achieve a functional cure.”

DCR-HBVS-101 Trial Design

The DCR-HBVS-101 clinical trial is divided into three phases or groups:

• In Group A, 30 HVs are to receive a single ascending-dose of DCR-HBVS
  (0.1, 1.5, 3, 6, or 12 mg/kg) or placebo, with a four-week follow-up
  period.
• Group B is a single-dose arm in which eight participants with HBV who
  are naïve to nucleoside analog therapy will receive a 3 mg/kg dose of
  DCR-HBVS or placebo; these participants will be followed for at least
  12 weeks. The Company expects to initiate Group B dosing in the third
  quarter of 2019, in parallel with Group C at the 3 mg/kg dose level.
• Group C is a multiple ascending dose arm in which DCR-HBVS (1.5, 3, or
  6 mg/kg) or placebo will be administered to 18 participants with HBV
  who are already being treated with nucleoside analogs, with a
  treatment and follow-up period of 16 weeks or more. The first
  participant dosed was from this group, at a dose of 1.5 mg/kg.

Study participants in Groups B and C, in whom HBsAg will have dropped by
more than 1 log10 IU/mL below baseline at their last scheduled study
visit, will continue to be followed until their HBsAg level is less than
1 log10 IU/mL below the baseline value.

For more information about the DCR-HBVS-101 clinical trial, please visit www.clinicaltrials.gov
and use the identifier NCT03772249.

About Chronic Hepatitis B Virus (HBV) Infection

Hepatitis B virus (HBV) is the world’s most common serious liver
infection, with more than 292 million patients chronically infected,
according to an estimate by the World Health Organization. Chronic HBV
infection, a condition characterized by the presence of the HBV surface
antigen (HBsAg) for six months or more, claims approximately 780,000
lives annually; an estimated 650,000 of these deaths are caused by
cirrhosis and liver cancer as a result of chronic hepatitis B, and
130,000 of these deaths result from complications associated with acute
disease.¹

About DCR-HBVS

DCR-HBVS is an investigational drug in development for the treatment of
chronic hepatitis B virus (HBV) infection. Current therapies for HBV,
such as nucleoside analogs and pegylated interferon, aim to suppress the
virus; however, although these treatments can provide long-term viral
suppression if taken continuously, they rarely lead to a long-term
functional cure, as measured by the clearance of HBV surface antigen
(HBsAg) and sustained HBV deoxyribonucleic acid (DNA) suppression in
patient plasma or blood. By contrast, DCR-HBVS targets HBV messenger RNA
(mRNA) and leads to greater than 99% reduction in circulating HBsAg, as
observed in mouse models of HBV infection. Those data suggest that
DCR-HBVS may induce long-term clearance of intrahepatic and serum HBsAg.

About Dicerna Pharmaceuticals, Inc.

Dicerna Pharmaceuticals, Inc., is a biopharmaceutical company focused on
the discovery and development of innovative, subcutaneously delivered
RNAi-based therapeutics for the treatment of diseases involving the
liver, including rare diseases, chronic liver diseases, cardiovascular
diseases, and viral infectious diseases. Dicerna is leveraging its
proprietary GalXC™ RNAi technology platform to build a broad pipeline in
these core therapeutic areas, focusing on target genes where connections
between target gene and diseases are well understood and documented.
Dicerna intends to discover, develop and commercialize novel
therapeutics either on its own or in collaboration with pharmaceutical
partners. Dicerna has strategic collaborations with Boehringer
Ingelheim, Eli Lilly and Company and Alexion Pharmaceuticals. For more
information, please visit www.dicerna.com.

Cautionary Note on Forward-Looking Statements

This press release includes forward-looking statements. Such
forward-looking statements are subject to risks and uncertainties that
could cause actual results to differ materially from those expressed or
implied in such statements. Examples of forward-looking statements
include, among others, statements we make regarding: (i) the enrollment
and successful screening of patients in the Phase 1 clinical trial of
DCR-HBVS; (ii) the expectation of human proof-of-concept data from the
Phase 1 trial in the fourth quarter of 2019; (iii) the therapeutic and
commercial potential of the GalXC™ platform, including DCR-HBVS; (iv)
research and development plans and timelines related to GalXC, including
DCR-HBVS; and (v) the potential of our technology and drug candidates in
our research and development pipeline. The process by which an early
stage investigational therapy such as DCR-HBVS and an early stage
platform such as GalXC could potentially lead to an approved product is
long and subject to highly significant risks. Applicable risks and
uncertainties include those relating to our clinical research and other
risks identified under the heading “Risk Factors” included in our most
recent Form 10-Q filing and in other future filings with the Securities
and Exchange Commission (SEC). These risks and uncertainties include,
among others, the cost, timing and results of preclinical studies and
clinical trials and other development activities; the unpredictability
of the duration and results of regulatory review of New Drug
Applications (NDAs) and Investigational NDAs; market acceptance for
approved products and innovative therapeutic treatments; competition;
the possible impairment of, inability to obtain and/or costs of
obtaining intellectual property rights; possible safety or efficacy
concerns, general business, financial and accounting risks; and, the
risks associated with litigation. The forward-looking statements
contained in this press release reflect Dicerna’s current views with
respect to future events, and Dicerna does not undertake and
specifically disclaims any obligation to update any forward-looking
statements.

Contacts

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