Blueprint Medicines to Present Preclinical Data at 2015 ASH Annual Meeting Demonstrating Anti-tumor Activity of BLU-285 in a Model of Acute Myeloid Leukemia

CAMBRIDGE, Mass., Nov. 12, 2015 /PRNewswire/ -- Blueprint Medicines (NASDAQ: BPMC) today announced that it will present new preclinical data demonstrating the potential utility of BLU-285 in a subset of patients with acute myeloid leukemia (AML) characterized by a mutation in KIT Exon 17 during an oral presentation at the 2015 American Society of Hematology (ASH) Annual Meeting and Exposition being held December 5-8 in Orlando, Fla.

KIT Exon 17 mutations have been identified as drivers in multiple diseases, and the presence of these mutations greatly reduces the effective treatment options available to patients. BLU-285 is a potent and highly selective inhibitor of KIT Exon 17 and PDGFRα D842V mutants, which are drivers of disease in patients with gastrointestinal stromal tumors (GIST) and systemic mastocytosis (SM).

Blueprint Medicines is enrolling patients in a dose-escalation, Phase 1 clinical trial of BLU-285 for the treatment of unresectable, treatment-resistant GIST. Additionally, the U.S. Food and Drug Administration in September accepted Blueprint Medicines' Investigational New Drug application to begin a Phase 1 clinical trial of BLU-285 for the treatment of advanced SM, and Blueprint Medicines is in the process of initiating clinical sites for this trial.

In AML, a subset of patients with the t(8;21) translocation and an additional KIT Exon 17 mutation are at increased risk of recurrence compared to those without it, creating a strong need for new therapies to address their form of the disease.

In preclinical results to be presented by Blueprint Medicines at ASH, BLU-285 showed potent inhibition of KIT activity in an AML cell line with the N822K mutation in Exon 17, including reduced phosphorylation, downstream signaling and cellular proliferation. BLU-285 administration in a xenograft model harboring AML cells driven by the KIT Exon 17 mutation resulted in a reduction of disease burden compared to cytarabine-treated animals. All BLU-285-dosed mice showed tumor regression, and several showed complete disease clearance.

"We are encouraged by these preclinical results, which further strengthen our belief that BLU-285 may play an important role in multiple hematologic and solid tumor malignancies," said Andy Boral, M.D., Ph.D., Senior Vice President of Clinical Development. "We continue to advance our clinical programs for BLU-285 while also exploring new therapeutic areas where targeting the KIT Exon 17 mutation may bring substantial clinical benefit."

ASH presentation details:

About the Phase 1 Clinical Trials for BLU-285

The Phase 1 clinical trial for BLU-285 for the treatment of unresectable, treatment-resistant GIST will evaluate the safety and tolerability of BLU-285 in multiple ascending doses with the goal of establishing a maximum tolerated dose (MTD) or a recommended dose if the MTD is not achieved. Blueprint Medicines expects to enroll approximately 60 patients in this clinical trial at multiple sites in the United States, European Union and Asia. All patients will be tested retrospectively for both KIT Exon 17 and PDGFRα D842V mutational status. Once the MTD is reached, or a recommended dose is established, Blueprint Medicines will open expansion cohorts for genomically selected patients. Secondary objectives include assessing response rate by Response Evaluation Criteria In Solid Tumors (RECIST) criteria commonly used to measure clinical responses in solid tumors, the pharmacokinetics of BLU-285 and allelic burden using circulating tumor DNA.

The planned Phase 1 clinical trial for BLU-285 for the treatment of advanced SM will evaluate the safety and tolerability of BLU-285 in multiple ascending doses with the goal of establishing an MTD or a recommended dose if the MTD is not achieved. Blueprint Medicines expects to enroll approximately 60 patients in this clinical trial at multiple sites in the United States and European Union. All patients will be tested retrospectively for KIT D816V mutational status. Once the MTD is reached, or a recommended dose is established, Blueprint Medicines will open expansion cohorts for specific subtypes of SM. Secondary objectives include assessment of the pharmacokinetic profile of BLU-285, assessment of response rate by the International Working Group Myeloproliferative Neoplasms Research and Treatment criteria, changes in KIT D816V mutant allele fractions in bone marrow and circulating tumor DNA, and changes in patient reported outcomes.

About Blueprint Medicines

Blueprint Medicines is developing a new generation of highly selective and potent kinase medicines to improve the lives of patients with genomically defined diseases. The Company's approach is rooted in a deep understanding of the genetic blueprint of cancer and other diseases driven by the abnormal activation of kinases. Blueprint Medicines is advancing three programs in clinical development for subsets of patients with gastrointestinal stromal tumors, hepatocellular carcinoma and systemic mastocytosis, as well as multiple programs in research and preclinical development. For more information, please visit www.blueprintmedicines.com.

Cautionary Note Regarding Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including, without limitation, statements regarding the potential for BLU-285 to provide clinical benefit to patients and Blueprint Medicines' preclinical and clinical plans or programs. The words "may," "will," "could," "would," "should," "expect," "plan," "anticipate," "intend," "believe," "estimate," "predict," "project," "potential," "continue," "target" and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Any forward-looking statements in this press release are based on management's current expectations and beliefs and are subject to a number of risks, uncertainties and important factors that may cause actual events or results to differ materially from those expressed or implied by any forward-looking statements contained in this press release, including, without limitation, risks and uncertainties related to the delay of any current or planned clinical trials or the development of Blueprint Medicines' drug product candidates, including BLU-285 and BLU-554; Blueprint Medicines' advancement of multiple early-stage efforts, including its RET program; Blueprint Medicines' ability to successfully demonstrate the efficacy and safety of its drug product candidates; the preclinical and clinical results for Blueprint Medicines' drug product candidates, which may not support further development of such drug product candidates; and actions of regulatory agencies, which may affect the initiation, timing and progress of clinical trials. These and other risks and uncertainties are described in greater detail in the section entitled "Risk Factors" in Blueprint Medicines' Quarterly Report on Form 10-Q for the quarter ended September 30, 2015, as filed with the Securities and Exchange Commission (SEC) on November 9, 2015, and other filings that Blueprint Medicines may make with the SEC in the future. Any forward-looking statements contained in this press release represent Blueprint Medicines' views only as of the date hereof and should not be relied upon as representing its views as of any subsequent date. Blueprint Medicines explicitly disclaims any obligation to update any forward-looking statements.

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