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. Guerciolini.

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

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 release.

Sirna Therapeutics, Inc.