(STML) Presentation of SL-401 Preclinical Efficacy Data in Multiple Myeloma

NEW YORK, May 20, 2014  — Stemline Therapeutics, Inc. (Nasdaq:STML) announced today that data demonstrating SL-401 efficacy in multiple myeloma (MM) preclinical models will be presented at the American Society of Clinical Oncology (ASCO) Annual Meeting being held May 30-June 3, 2014 in Chicago, IL.

In collaboration with Stemline, experiments conducted at the Dana-Farber Cancer Institute, Boston, MA, by Drs. Dharminder Chauhan and Kenneth Anderson and their MM research team demonstrated that Stemline’s clinical candidate SL-401 significantly decreased the viability of malignant cells by targeting neighboring plasmacytoid dendritic cells (pDCs) in the tumor microenvironment of the bone marrow. The researchers have previously shown that pDCs, which express the IL-3R, the target of Stemline’s SL-401, promote MM growth, potentially via IL-3/IL-3R signaling. SL-401’s novel activity against MM occurs at extremely low (picomolar) concentrations that are readily achievable in patients. Based on these results and prior data, SL-401 appears to have both direct (anti-MM) and indirect (anti-pDC) activity in this disease.

The Dana-Farber researchers also demonstrated that SL-401 was active against MM cells obtained from patients resistant to standard agents used to treat MM including bortezomib (Velcade®), dexamethasone, and lenalidomide (Revlimid®). Additionally, SL-401 demonstrated synergistic activity against MM cells when combined with bortezomib, melphalan, lenalidomide, or pomalidomide (Pomalyst®). Finally, SL-401 was also found to inhibit the formation of osteoclasts, which are the bone marrow cells responsible for bone loss, fractures, and significant morbidity in MM patients. SL-401 also stabilized the formation of bone-strengthening bone marrow cells called osteoblasts.

Eric K. Rowinsky, M.D., Chief Medical Officer and Head of Research and Development at Stemline Therapeutics, noted, “Although many agents for multiple myeloma have emerged over the last decade, these therapies ultimately fail. In such situations, new agents with unique mechanisms of action, like SL-401, have provided additional improvement in patient outcomes.” He added, “We look forward to building on these extraordinary results with SL-401 in MM which will serve as a foundation for its clinical development in this malignancy.”

About SL-401

SL-401 is a novel targeted therapy directed to the interleukin-3 receptor (IL-3R), a target present on tumor bulk and cancer stem cells (CSCs) of multiple hematologic cancer indications. SL-401 has demonstrated clinical activity in several indications, including blastic plasmacytoid dendritic cell neoplasm (BPDCN), acute myeloid leukemia (AML), and myelodysplastic syndrome (MDS), as well as preclinical activity in multiple myeloma (MM), chronic myeloid leukemia (CML), rare IL-3R+ cancers such as chronic eosinophilic leukemia, and certain lymphoid leukemias and lymphomas.

Details on the presentation are as follows:

Effect of a novel agent SL-401, targeting Interleukin-3 Receptor (IL-3R) on plasmacytoid dendritic cell (pDC)-induced myeloma cell growth and osteolytic bone disease
Lead Author: Dharminder Chauhan, Ph.D., Dana-Farber Cancer Institute
Authors: Dharminder Chauhan, Arghya Ray, Deepika Das Sharma, Vincent Macri, Christopher Brooks, Paul Richardson, Eric Rowinsky, and Kenneth C. Anderson
Abstract: #8599
Date and Time: Monday, June 2, 2014 – 1:15 to 5:00 PM CT
Location: S Hall A2
Poster Board: #286

A copy of the above referenced abstracts can be viewed online through the ASCO website at www.asco.org.

About Stemline Therapeutics

Stemline Therapeutics, Inc. is a clinical-stage biopharmaceutical company developing novel oncology therapeutics that target both cancer stem cells (CSCs) and tumor bulk in a variety of cancer types. Stemline is currently developing two clinical-stage product candidates, SL-401 and SL-701. SL-401 is a targeted therapy directed to the interleukin-3 receptor (IL-3R). SL-401 has demonstrated single-agent activity, including durable complete responses (CRs), in a Phase 1/2 trial in several indications including blastic plasmacytoid dendritic cell neoplasm (BPDCN) and relapsed or refractory acute myeloid leukemia (AML). SL-401 is being advanced into programs in BPDCN and other rare IL-3R+ malignancies, as well as additional hematologic cancers including AML and myeloma. SL-701 is an enhanced immunotherapy that activates the immune system to attack tumors. An earlier version of this therapy demonstrated single-agent activity, including durable CRs and partial responses (PRs), in Phase 1/2 trials in advanced adult and pediatric brain cancers. SL-701 is being advanced into trials of adults with glioblastoma multiforme (GBM) at first recurrence, and children with non-brainstem and brainstem glioma. For more information about Stemline Therapeutics, visit www.stemline.com.

Forward-Looking Statements

Some of the statements included in this press release may be forward-looking statements that involve a number of risks and uncertainties. For those statements, we claim the protection of the safe harbor for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995. The factors that could cause our actual results to differ materially are identified from time to time in our reports filed with the Securities and Exchange Commission. Any forward-looking statements set forth in this press release speak only as of the date of this press release. We do not intend to update any of these forward-looking statements to reflect events or circumstances that occur after the date hereof.

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