Xanthus Presents Preclinical Data Demonstrating Potent Symadex Activity in Leukemia Cells.

- Presentation at the American Society of Hematology Meeting -

CAMBRIDGE, Mass. -- Xanthus Pharmaceuticals, Inc., a privately-held oncology drug development company, today announced the presentation of data from preclinical studies in which Symadex[TM] (C-1311) demonstrated potent in vitro and in vivo activity against leukemia cells. The presentation was made in a poster session at the American Society of Hematology 48th Annual Meeting and Exposition in Orlando, Florida.

Researchers from Xanthus and the Medical University of South Carolina, Charleston, previously identified Symadex as a potent and selective inhibitor of the FLT3 receptor tyrosine kinase, in addition to its topoisomerase II activity. In the preclinical studies being discussed here, Symadex was examined in acute myeloid and lymphoid leukemia cell lines and was found to be active, especially in those expressing FLT3. This finding was further supported by data observed from in vivo studies. The data was presented on Sunday, December 10th in the Leukemias: Biology, Cytogenetics, and Molecular Markers in Diagnosis and Prognosis: AML session in a poster titled, "Imidazoacridinones are Bifunctional Targeting Agents Active in Leukemia Cells."

"These new data provide further support for our strategy to initiate a leukemia-focused clinical development program for Symadex," stated Robert L. Capizzi, M.D., Chief Medical Officer at Xanthus. "The dual function of Symadex may be the reason why we saw more potent activity in the FLT3 expressing cell lines, suggesting that Symadex or other novel imidazoacridinones in our portfolio may be useful for a variety of hematological malignancies and other tumor types."

About Symadex[TM]

Symadex (formerly C-1311) is the lead compound in clinical development from a new series of agents, the imidazoacridinones, and in vitro have shown it to be a potent and selective FLT3 receptor tyrosine kinase inhibitor. Symadex is currently in Phase 2 clinical trials in oncology. Xanthus is also exploring the use of Symadex for the treatment of a number of autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis, where early preclinical data has shown encouraging signs of activity. Xanthus licensed intellectual property related to Symadex from BTG International, Ltd.

About Xanthus Pharmaceuticals, Inc.

Xanthus Pharmaceuticals, Inc. is developing a portfolio of novel, clinical-stage, small-molecule oncology candidates through a management team whose accomplished track record encompasses all aspects of drug development, from discovery through regulatory approval and commercialization. The Company is applying its expertise both to advance its current pipeline and expand it into indications of unmet medical need beyond oncology.

Xanthus is headquartered in Cambridge, Massachusetts with an additional facility in Montreal, Quebec. More information is available at www.xanthus.com.

This press release contains forward-looking statements concerning Xanthus that involve a number of risks and uncertainties. For this purpose, any statements contained herein that are not statements of historical fact may be deemed to be forward-looking statements. Without limiting the foregoing, the words, "believes," "anticipates," "plans," "expects," "estimates," "intends," "should," "could," "will," "may," and similar expressions are intended to identify forward-looking statements. There are a number of important factors that could cause Xanthus' actual results to differ materially from those indicated by such forward-looking statements, including risks as to whether results obtained in early clinical studies or in preclinical studies such as the studies referred to above will be indicative of results obtained in future clinical trials or warrant additional trials; whether products based on Xanthus' technology will advance through the clinical trial process and receive approval from the United States Food and Drug Administration or equivalent foreign regulatory agencies; whether the company will have the cash resources to develop and commercialize its products; and whether the patent and patent applications owned or licensed by Xanthus will protect the Company's technology and prevent others from infringing it. Xanthus disclaims any intention or obligation to update any forward-looking statements.