Sirna Therapeutics Reports Final Results From Phase 1 Study On Its RNAi-Based Therapeutic For Age-Related Macular Degeneration

Sirna Therapeutics,
Inc. (Nasdaq: RNAI), a leading RNAi-based therapeutics company, reported
the final results from its recently completed Phase 1 trial for Sirna-027,
a novel therapeutic for age-related macular degeneration (AMD). Single
ascending doses of Sirna-027 were safe and well tolerated, and all 26
patients (100%) showed visual acuity stabilization eight weeks after a
single injection. In addition, at the same time point, five of 26 patients
(19%) experienced clinically significant improvement in visual acuity,
indicated by an increase of at least three lines on an eye chart.

Three months after a single injection, 24 of 26 patients (92%) showed
visual acuity stabilization, with four of 26 patients (15%) experiencing
clinically significant improvement in visual acuity; only two of 26
patients (8%) experienced a reduction in visual acuity of three lines or
more. Importantly, a decrease in foveal thickness was observed in some
patient groups, which is an indication of biological activity of Sirna-027.

“This is the first demonstration of biological activity of a chemically
optimized siRNA in humans,” said Sirna Chief Medical Officer Roberto
Guerciolini, M.D. “These data represent an important milestone toward the
demonstration of the potential therapeutic benefit of Sirna-027 and the
clinical validation of RNAi as a therapeutic modality.”

The potential for a long-lasting effect on visual acuity after a single
dose of Sirna-027 could be due to the unique catalytic mechanism of short
interfering RNA (siRNA), and could make this compound amenable to a more
favorable dosing regimen than other approved products.

“Less frequent dosing in this devastating disease should greatly
improve patient convenience, compliance, and quality of life,” said Dr.

The Phase 1 study evaluated the safety, tolerability, and biological
effect of single-ascending doses of Sirna-027 in patients with AMD. A total
of 26 patients with active disease were enrolled to receive a single
intravitreal injection of Sirna-027 ranging from 100-1,600 micrograms.

In September 2005, Sirna and Allergan, Inc., a global leader in eye
care, established a Strategic Alliance in eye diseases which includes
Sirna-027 for AMD. Under the terms of the Agreement, Allergan assumed all
developmental and commercialization costs for Sirna-027. Sirna and Allergan
expect to initiate the Phase 2 trial during the second half of 2006.

About Sirna Therapeutics

Sirna Therapeutics is a clinical-stage biotechnology company developing
RNAi-based therapies for serious diseases and conditions, including age-
related macular degeneration (AMD), hepatitis B and C, dermatology, asthma,
respiratory syncytial virus (RSV), Huntington’s disease, diabetes and
oncology. Sirna Therapeutics completed its Phase 1 clinical trial for
Sirna- 027 in AMD in 2005 and with its strategic partner, Allergan, Inc.,
will move Sirna-027 into Phase 2 clinical trials in the second half of
2006. Sirna has selected a clinical compound for hepatitis C virus,
Sirna-034, which the Company plans to bring into Phase 1 clinical trials by
the end of 2006. Sirna has established an exclusive multi-year strategic
alliance with GlaxoSmithKline for the development of siRNA compounds for
the treatment of respiratory diseases. Sirna has a leading intellectual
property portfolio in RNAi covering over 250 mammalian gene and viral
targets and over 200 issued or pending patents covering other major aspects
of RNAi technology, including the microRNA technology. More information on
Sirna Therapeutics is available on the Company’s web site at sirna.

Safe Harbor Statement

Statements in this press release which are not strictly historical are
“forward-looking” statements which should be considered as subject to many
risks and uncertainties. For example, most drug candidates do not become
approved drugs. The development of Sirna-027 and Sirna-034 as well as
Sirna’s other programs are still at a relatively early stage. All of these
programs, and Sirna’s ability to obtain milestone and royalty payments for
them, are subject to significant risks and unknowns, are highly contingent
upon future successes, and require significant funding. In addition, patent
applications may not result in issued patents, and issued patents may not
be enforceable or could be invalidated. Other risks and uncertainties
include, among others, Sirna’s early stage of development and short
operating history, Sirna’s history and expectation of losses and need to
raise capital, Sirna’s need to obtain clinical validation and regulatory
approval for Sirna-027, Sirna-034 and Sirna’s other product candidates, any
of which could have negative results, Sirna’s need to engage collaborators,
Sirna’s need to obtain and protect intellectual property, and the risk of
third-party patent infringement claims. These and additional risk factors
are identified in Sirna’s Securities and Exchange Commission filings,
including Forms 10-K and 10-Q and in other SEC filings. Sirna undertakes no
obligation to revise or update any forward- looking statements in order to
reflect events or circumstances that may arise after the date of this

Sirna Therapeutics, Inc.