Arrowhead Subsidiary Reports Non-Viral, Systemic Inhibition of Tumor Growth in Animals with siRNA

PASADENA, Calif.--(BUSINESS WIRE)--April 21, 2005--Arrowhead Research Corporation (NASDAQ:ARWR) (NASDAQ:ARWRW) announced today that preclinical data on proprietary siRNA technology being developed by Calando Pharmaceuticals, Inc., a subsidiary of Arrowhead, has been released. The data shows that treatment with siRNA formulations using Calando's proprietary technology resulted strong tumor inhibition with no detectable immune response.

"siRNA technology represents a new generation of specific treatments for cancer and many other diseases," said R. Bruce Stewart, President of Arrowhead Research. "The great promise of this technology lies in the ability to treat disease with targeted therapeutics and minimal side effects."

“The great promise of this technology lies in the ability to treat disease with targeted therapeutics and minimal side effects.”

Calando's technology uses a proprietary cyclodextrin polymer that self-assembles with siRNA and transferrin, a naturally occurring protein that normally delivers iron to cells. The cyclodextrin molecule protects the RNAi from degradation as it makes its way to the tumor site and prevents immune response to the siRNA. Once at the tumor site, the transferrin molecule binds to the tumor cells, which have a larger number of transferrin receptors, causing the siRNA-polymer nano-particle to be taken up by the cell.

The data shows strong inhibition of tumor growth in mice injected with disseminated Ewing Sarcoma cancer. The Calando technology did not result in any detectable immune response or other abnormalities. Other delivery mechanisms for siRNA are based on viral and lipid membrane vehicles that have been problematic due to the interferon response they trigger, resulting death of normal cells.

Siwen Hu-Lieskovan, MD, PhD, of Children's Hospital Los Angeles (CHLA), presented the findings on behalf of the laboratories of Dr. Mark Davis of Chemical Engineering at Caltech and Dr. Timothy Triche at CHLA in a mini-symposium at the American Association of Cancer Research Annual Meeting in Anaheim, Calif.

About Arrowhead Research Corporation

Arrowhead Research is a development-stage nanotechnology company structured to bring together a diverse and innovative mix of technologies, rights to a broad suite of intellectual property, and some of the most respected minds in this dynamic field. There are three strategic components to Arrowhead's business model:

-- The Commercialization Program: Arrowhead forms or acquires majority-owned subsidiary companies pursuing products based on nanotechnology in high-growth technology markets.

-- The Research Program: Arrowhead funds nanoscience research at universities in exchange for exclusive rights to license the technology.

-- The Patent Toolbox: Arrowhead acquires, licenses, and sublicenses intellectual property in nanotechnology. To date, Arrowhead has licensed

Arrowhead Research operates four majority-owned subsidiary companies:

-- Aonex Technologies, Inc., developing and commercializing proprietary semiconductor nanomaterial technology.

-- Insert Therapeutics, Inc., developing and commercializing a proprietary nanoscale drug delivery system.

-- Nanotechnica, Inc., developing a variety of proprietary nanoscale devices and systems, including laboratory on a chip.

-- Calando, Inc. is developing nanostructures for delivery and therapeutic use of RNA interference.

Arrowhead is funding three research and development efforts in nanotechnology at the California Institute of Technology.

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