Sirna Therapeutics Phase 1 Drug Candidate Highlighted on PBS NOVA scienceNow

Sirna Therapeutics Phase 1 Drug Candidate Highlighted on PBS NOVA scienceNow

Segment on Breaking Science Featured Therapeutic Potential of RNA Interference

SAN FRANCISCO and BOULDER, Colo., July 29 /PRNewswire-FirstCall/ -- Sirna Therapeutics, Inc. (NASDAQ:RNAI) announced today that its clinical drug candidate, Sirna-027, for age-related macular degeneration (AMD) was highlighted on the PBS (Public Broadcasting System) science program, NOVA scienceNow. One of Sirna's principal investigators, Peter Kaiser, M.D., of the Cole Eye Institute at the Cleveland Clinic together with the first patient to receive Sirna-027 spoke about their positive experience using Sirna-027 in the Phase 1 clinical trial. Dr. Kaiser stated, "[The patient's] vision has improved. It is a very promising result." The segment, which aired on July 26, 2005, examined the discovery, science and therapeutic potential of RNA interference (RNAi).

"We are extremely pleased that NOVA scienceNow dedicated a segment to RNA interference and the important therapeutic potential of this new area of medical science," stated Howard W. Robin, Sirna's President and Chief Executive Officer. "The segment provided a creative and informative educational platform for describing this exciting new field to the public. We hope that everyone has the opportunity to watch the program on the NOVA website and read the online articles."

In May 2005, Sirna reported the first human clinical data for an siRNA at the Association of Research in Vision and Ophthalmology (ARVO). Those interim Phase 1 results demonstrated Sirna-027 to be safe and well tolerated, with no systemic or local adverse events. All patients tested experienced visual acuity stabilization and almost half experienced improvement in their vision. The Sirna Phase 1 clinical trial for AMD is being conducted at four prestigious clinical centers including, The Cole Eye Institute at The Cleveland Clinic; the Wilmer Eye Institute, The Johns Hopkins University; the Joint Clinical Research Center, Harvard University, Massachusetts Eye and Ear Infirmary; and the Jules Stein Eye Institute, University of California Los Angeles.

The segment also addressed the potential use of siRNAs for the treatment of Huntington's Disease (HD). Currently, Sirna, in collaboration with Dr. Beverly Davidson at the University of Iowa and Targeted Genetics Corporation, is developing siRNAs for the treatment of this devastating disease. Studies by Dr. Davidson in animal models of HD have demonstrated that siRNAs targeting the messenger RNA for the mutant HD protein are able to attack the fundamental cause of HD and reduce the protein expression from the disease gene. These studies are the first to show that a therapy designed to inhibit HD protein production has a beneficial effect on the disease symptoms.

NOVA scienceNOW is a new series produced by NOVA and airs five times a year in the NOVA broadcast timeslot. Each magazine-style episode consists of several segments covering a wide variety of cutting-edge science topics and is hosted by veteran news reporter Robert Krulwich and reported by a team of correspondents in the field. The segment on RNA interference provided a background of the groundbreaking work in RNAi science and highlighted the potential for siRNAs to become an important therapeutic modality. Included in the segment was an excellent tutorial explaining RNAi. The tutorial, which was presented in the show and is also on the NOVA scienceNOW website, provides both a detailed scientific description of RNA interference as well as a "metaphor" explanation for the non-scientist.

To view the NOVA program please visit http://www.pbs.org/wgbh/nova/sciencenow/3210/02.html or www.sirna.com or to learn more about Sirna Therapeutics and the Company's programs and advancement in RNAi visit www.sirna.com.

About RNA interference

RNA interference (RNAi) is a natural, selective process for turning off genes. RNAi is triggered by short interfering RNA (siRNA) molecules that engage a group of cellular proteins, known as RISC (RNA induced silencing complex). The RISC guides the siRNA to its target messenger RNA (mRNA, the messenger between DNA and proteins) by complementary base pairing for the targeted break-up of the mRNA thus halting protein expression or viral replication. The RISC-siRNA-complex binds and cleaves multiple mRNA molecules in a catalytic fashion.

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, Huntington's Disease, diabetes and oncology. Sirna Therapeutics has presented interim Phase 1 clinical trial data for its most advanced compound, Sirna-027, a chemically optimized siRNA targeting the clinically validated vascular endothelial growth factor pathway to treat AMD. The results demonstrated Sirna-027 for AMD is safe and well tolerated and that visual acuity stabilized in 100 percent of patients treated with a trend demonstrating visual acuity improvement in approximately 50 percent of the patients. Sirna Therapeutics has collaborations with Eli Lilly and Company, Targeted Genetics, Archemix Corporation and Protiva Biotherapeutics. Sirna has a leading intellectual property portfolio in RNAi with 43 issued patents and over 250 pending applications worldwide. More information on Sirna Therapeutics is available on the Company's web site at http://www.sirna.com/.

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. Additional risks and uncertainties include 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 products, Sirna's need to obtain and protect intellectual property, risk of third-party patent infringement claims, Sirna's need to attract and retain qualified personnel, Sirna's need to engage collaborators, availability of materials for product manufacturing, the highly competitive nature of the pharmaceutical market, the limited trading volume and history of volatility of Sirna's common stock, Sirna's concentration of stock ownership, and risks from relocating Sirna headquarters. These and additional risk factors are identified in Sirna's Securities and Exchange Commission filings, including the 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.

Contacts:

Rebecca Galler Robison, Senior Director, Corporate Strategy of Sirna Therapeutics, Inc., +1-303-449-6500 or Zack Kubow of The Ruth Group, +1-646-536-7020

Source: Sirna Therapeutics, Inc.

CONTACT: Rebecca Galler Robison, Senior Director, Corporate Strategy of
Sirna Therapeutics, Inc., +1-303-449-6500; or Zack Kubow of The Ruth Group,
+1-646-536-7020, for Sirna Therapeutics, Inc.

Web site: http://www.pbs.org/wgbh/nova/sciencenow/3210/02.html

Web site: http://www.sirna.com/

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