Plexxikon and Roche Enter Second Partnership to Develop PLX5568 for Polycystic Kidney Disease

Plexxikon Inc. and Roche (SWX:ROG), today announced that they have entered into an agreement to develop and commercialize a second novel kinase inhibitor, PLX5568. The main focus of this partnership will be the development of this small molecule inhibitor of Raf kinase as an oral therapeutic treatment for polycystic kidney disease (PKD). There is currently no registered treatment for PKD which affects over 600,000 patients in the U.S and is the most common life-threatening genetic disease.

This agreement with Plexxikon in PKD is consistent with the overall mission of Roche to address diseases with significant unmet medical need. Plexxikon is evaluating PLX5568 in an ongoing Phase 1 human clinical trial.

"PLX5568 is yet another first-in-class compound from Plexxikon that further highlights our platform’s capability to develop highly selective kinase inhibitors. We hope PLX5568 will significantly delay the loss of kidney function due to this debilitating disease, leading to improved quality of life for patients,” stated K. Peter Hirth, Ph.D., chief executive officer of Plexxikon. "We are pleased to announce our second collaboration with Roche, building on the foundation of an excellent and continuing partnership centered on our oncology program and lead product candidate, PLX4032.”

"We are enthusiastic about collaborating with Plexxikon on this program. We have built a strong relationship through our partnership on PLX4032. Together, we will advance PLX5568 to help patients suffering from PKD,” said Dan Zabrowski, Global Head of Pharma Partnering at Roche. "Plexxikon has demonstrated excellent capabilities in discovery and early development necessary to bring forward novel and differentiated product candidates in a variety of indications. These capabilities have driven our interest in a second collaboration with Plexxikon.”

Terms of Second Roche-Plexxikon Collaboration

Under the terms of the agreement, Roche will have a worldwide, exclusive license to develop and commercialize PLX5568, in addition to certain other selective Raf inhibitors resulting from the partnership. In exchange, Roche will pay Plexxikon $60 million as an upfront payment. Plexxikon could also receive approximately $275 million in payments over the term of the partnership based on the successful completion of a series of milestones for PKD. In addition, Plexxikon will be eligible to receive further payments based on the successful achievement of milestones for other compounds and indications. Separately, Plexxikon will receive royalties for any sales related to products under the collaboration. Plexxikon retains an option to co-promote PLX5568 or any other product resulting from the collaboration for any non-PKD indication in the United States.

Plexxikon will be responsible for any discovery and early development through completion of Phase 1 clinical trials, including the completion of the Phase 1 clinical trial currently being conducted for PLX5568. The partners will co-develop any products under the collaboration through commercialization, with clinical development to transition to Roche with the start of Phase 2 clinical trials. Also under the new agreement, the partners may develop additional selective Raf inhibitors for other human diseases.

About PLX5568

Plexxikon is currently engaged in a Phase 1 study of PLX5568 in healthy volunteers designed to evaluate the safety and tolerability of the drug candidate as well as to gain insight into its pharmacokinetic profile. To date, this drug candidate has been well tolerated, and once daily dosing has achieved the target exposures for efficacy for both PKD and pain. Following the successful completion of the Phase 1 trial and chronic toxicology studies, a Phase 2 clinical trial in PKD patients will be initiated in 2009.

PLX5568 is a very selective and potent inhibitor of Raf kinase, a critical mediator of PKD pathology. PLX5568 has demonstrated impressive efficacy in orthologous models of both genetic forms of PKD, resulting in decreased cyst size and improved kidney function. Non-clinical GLP toxicology studies including doses up to 2000 mg/kg per day over a period of 28 days have revealed no dose limiting toxicity, confirming the expected safety profile of the drug. The data gathered so far suggest that the selectivity of PLX5568 for its target could translate into a very favorable therapeutic index.

The kinase family represents over 500 potential drug targets for a broad range of chronic diseases. The capability to make highly selective kinase inhibitors has created the opportunity for the development of many new targeted drugs with exceptional safety profiles.

PKD is a genetic disease in which cysts form in the kidneys, causing them to become progressively enlarged, ultimately leading to loss of kidney function in most patients. Currently, there are no treatments for this disease, and patients may eventually require kidney transplantation or dialysis. PKD presents a major unmet need worldwide.

Plexxikon has also conducted preclinical efficacy studies in multiple models of pain, including acute, inflammatory and neuropathic pain. Preclinical research indicates that PLX5568 may be a non-opioid agent, with opiate-like efficacy. The efficacy shown in these models provides support for testing this compound’s therapeutic benefit in pain in human clinical trials which Plexxikon and Roche may also explore under the new agreement.

About Roche

Headquartered in Basel, Switzerland, Roche is one of the world’s leading research-focused healthcare groups in the fields of pharmaceuticals and diagnostics. As the world’s biggest biotech company and an innovator of products and services for the early detection, prevention, diagnosis and treatment of diseases, the Group contributes on a broad range of fronts to improving people’s health and quality of life. Roche is the world leader in in-vitro diagnostics and drugs for cancer and transplantation, and is a market leader in virology. It is also active in other major therapeutic areas such as autoimmune diseases, inflammatory and metabolic disorders and diseases of the central nervous system. In 2007 sales by the Pharmaceuticals Division totalled 36.8 billion Swiss francs, and the Diagnostics Division posted sales of 9.3 billion francs. Roche has R&D agreements and strategic alliances with numerous partners, including majority ownership interests in Genentech and Chugai, and invested over 8 billion Swiss francs in R&D in 2007. Worldwide, the Group employs about 80,000 people. Additional information is available on the Internet at www.roche.com.

About Plexxikon

A proprietary Scaffold-Based Drug Discovery™ platform has enabled Plexxikon’s position as a leader in structure-guided discovery and development of novel first-in-class small molecule pharmaceuticals to treat human disease. The company has discovered a portfolio of clinical and preclinical stage compounds in multiple disease areas addressing significant unmet needs in several therapeutic categories. The company’s clinical stage programs include PLX204 for the treatment of diabetes, PLX4032 for the treatment of melanoma and colorectal cancer and PLX5568 for the treatment of pain and PKD. Among the company’s preclinical development programs, candidates are being developed for the treatment of rheumatoid arthritis, multiple sclerosis and other autoimmune diseases, again with highly specific kinase inhibitors. Plexxikon is targeting an IND in early 2009 for its first-in-class oral DMARD for rheumatoid arthritis and other autoimmune diseases. For more information, please visit www.plexxikon.com.

Forward-Looking Statements

This press release contains forward-looking statements. Such forward-looking statements, include, among others, those relating to the successful development, approval and launch of a product from PLX5568; the potential receipt by Plexxikon of substantial payments by successfully fulfilling certain development and commercial milestones for multiple indications and/or multiple compounds and successful launch of a product in the U.S. and other countries; that PLX5568 will be successfully developed and approved as a product which may be sold to the public; that Plexxikon will receive royalties from sales of this product, if successfully launched and that this product, if developed, could represent a significant step forward in treating patients. These statements are based on current expectations of future events. Forward-looking statements are not guarantees of performance. If underlying assumptions prove inaccurate or unknown risks or uncertainties materialize, actual results could vary materially from expectations and projections.

These forward looking statements are subject to numerous risks and uncertainties. These risks and uncertainties include but are not limited to, general industry conditions and competition; obtaining U.S. and other countries regulatory approvals; health care changes in the U.S. and other countries; unexpected outcomes; product efficacy or safety concerns; product manufacturing issues; successful marketing of the product if developed; superior products being brought to market; loss of key employees; government reimbursement issues; economic conditions; technological advances and patents attained by competitors; manufacturing and supply disruptions; challenges inherent in new product development, including obtaining regulatory approvals; challenges to patents by competitors or allegations that the product infringes the patents of third parties; U.S. and other countries health care reforms; governmental laws and regulations; product liability claims or litigation risks; governmental investigations; and trends toward health care cost containment. These risks and uncertainties also include the risks that clinical trials may not proceed as planned due to technical, scientific, or patient enrollment issues, or disagreements with regulatory authorities over trial design or other matters; that the scale and scope of future clinical and nonclinical studies may change and will be determined in significant part by data collected in ongoing and future trials; that further clinical studies may not reflect the results obtained in early clinical and nonclinical studies; that ongoing nonclinical studies, including toxicology studies, will yield currently unanticipated negative outcomes that could adversely affect planned clinical trials; that results from the clinical trials will be insufficient to support additional phase programs without additional trials and consequent delay in the timetable for potential approval; and that any potential product may not achieve sales sufficient to earn the royalties referenced above. The foregoing list sets forth many, but not all, of the factors that could impact upon the ability to achieve results described in any forward-looking statements. It is not possible to predict or identify all such factors and should not consider this list to be a complete statement of all potential risks and uncertainties. Neither company assumes any obligation to update any forward-looking statements as a result of new information or future events or developments.