Xanthus Presents Updated Xanafide Phase 2 Data Showing Durable Complete Remissions in Secondary AML

06-02-2008

Follow-up Results of Phase 2 Study Presented at ASCO

Xanthus Pharmaceuticals, Inc. today announced the presentation of updated results based on follow-up data as of December 2007 from the Company’s completed Phase 2 study of Xanafide® in combination with cytarabine (ara-C) in patients with secondary acute myeloid leukemia. The presentation was made by Harry P. Erba, M.D., Ph.D., Associate Professor of Internal Medicine at the University of Michigan Health System, at the 44th Annual Meeting of the American Society of Clinical Oncology (ASCO). Xanafide is a DNA intercalator that induces apoptotic signaling by blocking TopoII binding to DNA, and is now in a randomized Phase 3 registration trial under a special protocol assessment (SPA) agreement with the US Food and Drug Association (FDA) for the treatment of secondary AML.

“Patients with secondary AML have a very poor prognosis. In this Phase 2 multi-center study, most patients were older than age 60 and almost half had leukemic blast karyotypes associated with an unfavorable outcome. Despite these adverse prognostic characteristics, a 38.6% complete remission rate was observed and an additional 3.4% of patients showed CRi, with a median duration of complete remission (CR) of greater than ten months. Despite the elderly age of the patient population, 43% of the patients were still in CR at one year," said Dr. Erba. "These results indicate that Xanafide and ara-C may be a promising alternative for patients with secondary AML, especially those with poor prognosis characteristics such as unfavorable blast karyotype, expression of multi-drug resistance, and older age.”

The reported findings confirm the preliminary complete remission rate results reported in June 2007. Similar complete remission rates were observed in the overall population, as well as in poor risk subsets of secondary AML, including older patients, patients with treatment-related AML, and patients who previously received treatment for their prior myelodysplastic syndrome (MDS).

The Phase 2 trial of Xanafide evaluated 88 patients with secondary AML (patients with antecedent MDS or prior exposure to leukemogenic therapy). Patients received a daily dose of Xanafide for five days in combination with a standard dose of ara-C as a continuous infusion for seven days. The mean duration for patient follow-up was 208 days. The primary endpoint for this study was the rate of complete remission with or without complete hematopoietic recovery (CR).

The Phase 2 follow-up results were presented in a poster session titled, “Amonafide + ara-C in secondary acute myeloid leukemia (sAML): Consistent efficacy in poor risk populations” on Monday, June 2, 2008 from 2:00pm until 6:00pm.

“The activity of Xanafide in poor-risk AML may reflect its ability to avoid the multidrug resistance efflux pumps, P-glycoprotein and related proteins, that prevent drug accumulation in leukemia cells and affect typical standard of care drugs used to treat AML,” stated Robert L. Capizzi, M.D., Xanthus’ Chief Medical Officer. “We independently examined the leukemia cells from 15 patients who participated in the Phase 2 trial, and found that the leukemia cells retained significantly greater Xanafide compared to daunorubicin. Daunorubicin was prevented from accumulating in the leukemia cells due to an excess of P-glycoprotein in the cell, an efflux mechanism that does not affect Xanafide. This provides a mechanism for the encouraging clinical activity of Xanafide seen in the Phase 2 trial.”

More information about the correlation between the lack of Pgp effect with treatment outcome are presented in the ASCO abstract ID: 13536 (www.asco.org), titled, “Blast cells from patients treated for secondary AML (sAML) show less P-glycoprotein (Pgp) – mediated efflux of amonafide compared to daunorubicin: implications for therapy”.

About Xanafide® and Secondary AML

Xanafide is a DNA intercalator that induces apoptotic signaling by blocking TopoII binding to DNA. This is different from the action of classical TopoII inhibitors, which induce apoptosis by causing extensive DNA damage. A further distinctive feature of Xanafide is its ability to evade PgP and related transporters responsible for multi-drug resistance. Xanafide is being developed for the treatment of secondary acute myeloid leukemia and related disorders. Secondary AML patients have had either antecedent myelodysplastic syndrome or prior exposure to leukemogenic therapy and represent a poor prognosis population. In both Phase 1 and Phase 2 studies conducted in patients with poor-risk AML, amonafide exhibited promising clinical activity in patients with secondary AML. Xanafide is currently in a Phase 3 clinical trial under a SPA agreement with the 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. The Company is applying its expertise to advance its current pipeline to address significant unmet medical need 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.

Contacts
MacDougall Biomedical Communications, Inc.
Kari Watson, 781-235-3060
kwatson@macbiocom.com
or
Xanthus Pharmaceuticals, Inc.
Lisa Terry, 617-225-0522, x 105
lisa.terry@xanthus.com