Stemline Expands its Oncology Pipeline with Acquisition of Clinically Active Compound Directed to “Cancer Stem Cell" Target

NEW YORK, March 7, 2007/ -- Stemline Therapeutics, Inc. today announced that it has in-licensed the exclusive worldwide rights to SL-401, a clinically active oncology compound directed at a key “cancer stem cell" target. SL-401 has demonstrated single agent anti-tumor activity in a multi-center Phase I dose escalation study conducted at Duke University, the British Columbia Cancer Agency, and the Scott & White Cancer Research Institute/Texas A&M Health Science Center College of Medicine, the licensor. Thirty adult patients with relapsed, refractory, or poor risk acute myeloid leukemia (AML) were treated with escalating doses of SL-401 without dose limiting toxicity. Anti-tumor activity has been observed, including 1 durable complete response (CR) in a patient refractory to standard chemotherapy, 2 partial responses (PR), and 3 minor responses (MR).

SL-401 targets the interleukin-3 receptor (IL-3R) and has been shown to impair the ability of cancer stem cells to form tumors. IL-3R is over-expressed on multiple hematological cancers. Importantly, in AML, IL-3R is over-expressed on both leukemia blasts as well as leukemia cancer stem cells. Cancer stem cells comprise a unique subpopulation of neoplastic cells within tumors that is highly malignant and resistant to standard treatment. Cancer stem cells are believed to be a major contributor to treatment failure, relapse, and death from malignancy.

Dr. David Rizzieri of Duke University Medical Center, a leader in the field of hematological cancers and investigator on the Phase I trial, commented, "SL-401 is an exciting new compound with a novel mechanism of action and clear signs of clinical activity. SL-401 constitutes the first concerted clinical effort to target leukemia stem cells. We look forward to completing the Phase I study and to working closely with Stemline to advance SL-401 into future trials."

"This in-licensing represents a significant milestone for the company and adds to our portfolio of compounds directed at IL-3R and other important cancer stem cell targets," said Ivan Bergstein, M.D., CEO of Stemline Therapeutics. He added, “With clinical signs of activity at tolerable doses, including a complete responder, we are gearing up to advance SL-401 into Phase II trials."

About Stemline Therapeutics, Inc. Stemline Therapeutics, Inc. is a clinical stage biotechnology company developing novel oncology compounds directed to “cancer stem cell" targets. Stemline’s lead compound, SL-401, targets the interleukin-3 receptor present on multiple hematological cancers including leukemia and leukemia cancer stem cells. SL-401 has demonstrated single agent anti-tumor activity at tolerable doses in a multi-center Phase I human trial. Behind its lead, Stemline is developing a pipeline of small molecule and biologic compounds directed at additional cancer stem cell targets of a variety of solid and hematological cancers. Stemline has also built a robust discovery platform called “StemScreen®" which the Company has utilized to identify multiple compounds that target and impair cancer stem cells. For more information, please visit the Company’s updated website at www.stemline.com.