Atiprimod Active in Mouse Model of Multiple Myeloma

Callisto Pharmaceuticals, Inc. (AMEX: KAL), today announced that Atiprimod inhibits growth of tumors in a cutting-edge animal model of human multiple myeloma. Dana-Farber researchers developed the unique animal model to improve their ability to study the drug's effectiveness as a potential new therapy.

The article which appeared in the July issue of the American Society of Hematology's journal Blood, Volume 106, Number 2, pp.713-716 (2005), and is entitled, "A clinically relevant SCID-hu in vivo model of human multiple myeloma," was authored by a team of scientists at Dana-Farber Cancer Institute and Callisto Pharmaceuticals, Inc.

"The Dana-Farber research team is well known for their pioneering research and clinical activities in the field of multiple myeloma," said Dr. Gary S. Jacob, Chief Executive Officer of Callisto Pharmaceuticals. "Their present paper describes an elegant mouse model of the human disease, and demonstrates that Atiprimod inhibits growth of MM tumors in this model. What's more, this work demonstrates that Atiprimod can target human MM cells in the human bone marrow microenvironment."

Multiple myeloma can be treated with drug therapies. However, a significant number of multiple myeloma patients stop responding to existing drugs; Atiprimod is being developed as a novel alternative treatment option for these so-called relapsed patients.

The manuscript described a novel in vivo MM model developed by engrafting a human MM cell line into severe combined immunodeficiency (SCID) mice previously given implants of a human fetal bone chip. Researchers from Dana-Farber monitored growth of these IL-6 dependent human MM cells by measuring the level of soluble human IL-6 receptor in mouse serum and by fluorescence imaging of host animals.

Atiprimod is currently being evaluated in a Phase I/IIa clinical trial in relapsed or refractory multiple myeloma patients at four clinical sites in the United States -- the Dana-Farber Cancer Institute (Boston, MA), the M.D. Anderson Cancer Center (Houston, TX), the St. Vincent's Comprehensive Cancer Center (New York, NY) and the Roswell Park Cancer Institute (Buffalo, NY).

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company focused on the development of drugs to treat cancer and osteolytic bone disease. Callisto has two lead drugs in clinical development, Annamycin to treat relapsed leukemia, and Atiprimod to treat relapsed multiple myeloma. Callisto's second drug, Atiprimod, is in a Phase I/IIa clinical trial in relapsed multiple myeloma patients, and is a small-molecule, orally available drug with antiproliferative and antiangiogenic activity. Callisto has exclusive worldwide licenses from AnorMED Inc. and M.D. Anderson Cancer Center to develop, manufacture, use and sell Atiprimod and Annamycin, respectively. For investor-specific information about Callisto, including recent news and stock price data, please visit http://www.trilogy-capital.com/tcp/callisto/