September 11, 2008

Calando Pharmaceuticals Phase II Clinical Study Opens to Patient Enrollment

Calando Pharmaceuticals, Inc., a majority owned subsidiary of Arrowhead Research Corporation (NASDAQ:ARWR), announced today that it has initiated a Phase II clinical trial in the United States evaluating the safety and efficacy of its drug candidate, IT-101 in patients with platinum-sensitive ovarian cancer. The study is open for enrollment.

Previous work with IT-101 suggests that twice monthly "maintenance doses" of IT-101 given after the patient's standard chemotherapy may have minimal side effects, allowing for improved quality of life, and improved progression free survival. This Phase 2 study is designed to determine if IT-101 treatment initiated after a standard 2nd line course of platinum chemotherapy in patients who have stable disease, a partial response, or a complete response can delay disease progression.

The study is expected to enroll 150 patients in the United States and is co-led by Jonathan S. Berek MD, MMS, Professor and Chair, Department of Obstetrics and Gynecology, Stanford University School of Medicine and the Stanford Cancer Center and Franco Muggia, MD, Anne Murnick Cogan and David H. Cogan Professor of Oncology, Director of the Division of Medical Oncology at NYU Medical Center, and Associate Director for Clinical Research. A team of experts from Dana Farber, Sloan Kettering, Columbia University, and M.D. Anderson comprise the Data Safety Monitoring Committee.

IT-101, a conjugate of camptothecin and Insert's proprietary cyclodextrin polymer nanoparticle, Cyclosert(TM), has demonstrated a highly favorable toxicity profile and pharmacokinetic characteristics.

About Calando Pharmaceuticals Inc.

Calando Pharmaceuticals Inc. (, a majority-owned subsidiary of Arrowhead Research Corporation (NASDAQ:ARWR), is a biopharmaceuticals company using proprietary technologies developed at Caltech to create targeted siRNA-based therapeutics and small molecule nanoparticle drug conjugates. Calando uses its innovative Cyclosert(TM) and RONDEL(TM) nanoparticle systems to solve the long-standing obstacle of effective delivery and targeting for oligonucleotide and small molecule therapeutics.

Calando's Cyclosert(TM) technology uses cyclodextrins as building blocks to create an entirely new class of biocompatible materials - linear cyclodextrin-containing polymers that are non-toxic and non-immunogenic at therapeutic doses. The Company leverages Cyclosert(TM) to design, develop and commercialize drug-delivery-enhanced small-molecule therapeutics. IT-101 is Calando's lead small molecule Cyclosert conjugate, which recently completed a phase I study in solid tumors at City of Hope Comprehensive Cancer Center.

Calando's RONDEL(TM) technology involves the use of cyclodextrin-containing polymers that form the foundation for its two-part siRNA delivery system. The first component is a linear, cyclodextrin-containing polycation that, when mixed with small interfering RNA (siRNA), binds to the anionic "backbone" of the siRNA. The polymer and siRNA self-assemble into nanoparticles smaller than 100 nm in diameter that fully protect the siRNA from nuclease degradation in serum. The siRNA delivery system has been designed to allow for intravenous injection. Upon delivery to the target cell, the targeting ligand binds to membrane receptors on the cell surface and the RNA-containing nanoparticle is taken into the cell by endocytosis. There, chemistry built into the polymer functions to unpackage the siRNA from the delivery vehicle. Based upon this breakthrough in siRNA delivery enabled by the RONDEL(TM) system, the promise of using siRNA in new systemic therapies may finally be realized.

Forward-Looking Statements

This news release and any oral statements made with respect to the information contained in this news release, contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Such forward-looking statements include statements which express plans, anticipation, intent, contingency, goals, targets, future development and are otherwise not statements of historical fact. These statements are based on Calando's management current expectations and are subject to risks and uncertainties that could cause actual results or developments to be materially different from historical results or from any future results expressed or implied by such forward-looking statements. Factors that may cause actual results or developments to differ materially include, among others: the risk that CALAA-01 or IT-101 may appear promising in early research and clinical trials but may not demonstrate safety and/or efficacy in larger-scale or later stage clinical trials, the risks that the regulatory approvals may not be obtained, the risks associated with dependence upon key personnel, the risks associated with reliance on collaborative partners and others for further clinical trials, development, manufacturing and commercialization of our product candidates; the cost, delays and uncertainties associated with our scientific research, product development, clinical trials and regulatory approval process; our history of operating losses since our inception; competition; litigation; and risks associated with our ability to protect our intellectual property. You are cautioned not to place undue reliance on any forward-looking statements, any of which could turn out to be wrong due to inaccurate assumptions, unknown risks or uncertainties or other risk factors.