Xanthus' Xanafide Bypasses Multi-Drug Resistance Proteins in Acute Myeloid Leukemia

CAMBRIDGE, Mass.--(BUSINESS WIRE)--Dec 10, 2007 - Xanthus Pharmaceuticals, Inc. today announced results from an independent study of Xanafide(R) (amonafide malate) in multi-drug resistant (MDR) leukemia and myeloma cell lines and in pre-treatment marrow samples from patients with secondary acute myeloid leukemia (s-AML). The study, presented on December 9th at the 2007 American Society of Hematology Annual Meeting in Atlanta, GA, demonstrated that the uptake, efflux and cytotoxicity of Xanafide in this study were unaffected by MDR proteins expressed in AML cells, and s-AML cells in particular, while other topoisomerase II inhibitors evaluated in this study were affected by the expression of these proteins. Increased levels of these proteins are a common cause of multi-drug resistance of AML cells to currently used treatments, so this study indicates that Xanafide may not be subject to this mode of drug resistance. Xanafide's ability to overcome resistance in s-AML cells may explain the encouraging complete remission rates previously observed in Phase 1 and Phase 2 trials of Xanafide in AML.

A team of researchers from the University of Maryland Greenebaum Cancer Center and Roswell Park Cancer Institute, led by Dr. Maria Baer, investigated the transport and cytotoxicity of Xanafide and its active metabolite N-acetyl amonafide in leukemia and myeloma cell lines that over-express the MDR-associated proteins P-glycoprotein (Pgp), multi-drug resistance protein-1 (MRP-1) and breast cancer resistance protein (BCRP). Xanafide was also studied in pre-treatment marrow samples from s-AML patients that expressed these proteins. These results were compared to those of classical topoisomerase II inhibitors doxorubicin, daunorubicin, idarubicin, mitoxantrone and etoposide.

The researchers observed that in this study the uptake, efflux and cytotoxicity of Xanafide did not differ in drug-resistant cell lines that over-expressed the MDR-related proteins when compared to non-resistant cell lines. The Company believes Xanafide's ability to maintain its AML cell uptake, as well as its cytotoxicity, in these cell types indicates that it may better reach therapeutic concentrations and maintain potency when compared to other drugs in its class.

"This study confirms our prior findings that Xanafide is unaffected by common multi-drug resistance proteins, and we're pleased that these results offer additional supporting data for Xanafide's potential as a new treatment for AML and other blood-borne cancers that suffer from poor treatment response rates due to resistance," said Richard T. Dean, Ph.D., Chief Executive Officer of Xanthus. "Xanafide is currently in a Phase 3 trial under an SPA with the FDA, and we are hopeful that it will eventually become a much-needed option for patients facing this poor prognosis."

"The results of this in vitro study are encouraging and add to a growing body of literature supporting the potential therapeutic activity of Xanafide in the treatment of AML," said Dr. Maria Baer, lead investigator in the study and Director of the Hematologic Malignancies Program at the University of Maryland Greenebaum Cancer Center. "Current treatment options for patients with secondary AML yield generally poor results and if Xanafide meets continued success in its Phase 3 study and is approved by the FDA, it would be a much needed and welcome addition to the treatment armamentarium."

These results were discussed in a presentation by Dr. Baer and colleagues entitled "Amonafide L-Malate Bypasses Multidrug Resistance Proteins in Secondary Acute Myeloid Leukemia."

About Xanafide(R) and Secondary AML

Xanafide (amonafide malate) is an ATP-independent topoisomerase II inhibitor that the Company is developing for the treatment of secondary acute myeloid leukemia (AML) and related disorders. Secondary AML patients have had either antecedent myelodysplastic syndrome or prior exposure to leukemogenic therapy and represent a poor prognosis population. While AML has approved treatments, no therapies are approved by FDA specifically for patients with secondary AML. In both Phase 1 and Phase 2 studies conducted in patients with poor-risk AML, amonafide exhibited particularly promising clinical activity in patients with secondary AML and the candidate does not appear to be susceptible to multi-drug resistance. Xanafide is currently in a Phase 3 clinical trial under a special protocol assessment (SPA) agreement with the U.S. Food and Drug Administration (FDA). Xanafide has also been granted Orphan Drug designation by the FDA for use in the treatment of AML.

About Xanthus Pharmaceuticals, Inc.

Xanthus Pharmaceuticals, Inc. is developing a portfolio of novel, clinical-stage, small-molecule therapeutic candidates through a management team whose accomplished track record encompasses all aspects of drug development, from discovery through regulatory approval and commercialization. Xanthus is applying its expertise to advance its current pipeline to address significant unmet medical needs in oncology and autoimmune diseases.

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.

Contact

For Xanthus Pharmaceuticals, Inc.
MacDougall Biomedical Communications, Inc.
Sarah Cavanaugh, 508-647-0209
scavanaugh@macbiocom.com
or
Xanthus Pharmaceuticals, Inc.
Lisa Terry, 617-225-0522, x 105
lisa.terry@xanthus.com

Posted: December 2007

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