Sierra Oncology to Report Favorable Dose Intensity Data and Long-Term Safety Data for Momelotinib at the 25th European Hematology Association (EHA) Congress

- Momelotinib's demonstrable anemia benefit and low myelosuppressive potential facilitate sustained dose intensity and prolonged clinical activity -

- Long-term safety profile reinforces lack of emergent or cumulative toxicity with extended daily momelotinib administration -

VANCOUVER, May 14, 2020 /PRNewswire/ - Sierra Oncology, Inc. (SRRA), a late-stage drug development company focused on the registration and commercialization of momelotinib, a JAK1, JAK2 & ACVR1 inhibitor with a potentially differentiated therapeutic profile for the treatment of myelofibrosis, today announced that Dose Intensity and Long-Term Safety data for momelotinib will be presented in two posters at the 25(th) European Hematology Association (EHA) Virtual Congress taking place from June 11-21, 2020.

"In these new analyses of data from the previously completed Phase 3 SIMPLIFY studies, momelotinib displayed favorable long-term efficacy, safety and tolerability consistent with its differentiated pharmacological and clinical profile. These data reinforce the remarkable durability of momelotinib treatment, which was achieved while maintaining sustained active and well tolerated dose intensity," said Dr. Barbara Klencke, Chief Development Officer of Sierra Oncology. "Specifically, momelotinib showed an absence of significant rates of high-grade hematological and other toxicities, which reinforce the compound's potential to safely and effectively address the unmet needs of patients with intermediate/high risk myelofibrosis. Importantly, no new safety signals or evidence of cumulative toxicity were observed during extended momelotinib daily dosing."

"Momelotinib's demonstrable anemia benefits facilitate sustained dose intensity and prolonged clinical activity across the continuum of JAK inhibitor naïve and previously JAK inhibitor treated myelofibrosis patients. These properties are in stark contrast to ruxolitinib, where progressive dose reductions due to induced or exacerbated myelosuppression are common, resulting in markedly diminished dose intensity compared to momelotinib," said Dr. Mark Kowalski, Chief Medical Officer of Sierra Oncology. "Critically, patients who subsequently switched from ruxolitinib treatment to momelotinib achieved an immediate and sustained improvement in both hemoglobin and platelets, and generally went on to receive full-dose momelotinib over an extended period, affirming momelotinib's potential to successfully treat myelofibrosis patients with JAKi-induced hematological toxicity."

The long-term safety data and dose intensity data to be reported at EHA draw from the extensive clinical dataset available for momelotinib from the two previously conducted SIMPLIFY Phase 3 studies and their subsequent ongoing extended treatment periods. The SIMPLIFY-1 trial was conducted in JAKi-naïve myelofibrosis patients (n=432) randomized 1:1 to momelotinib or ruxolitinib. SIMPLIFY-2 was conducted in prior ruxolitinib-treated myelofibrosis patients with hematological toxicity (n=156) randomized 2:1 to momelotinib or best available therapy (consisting of ruxolitinib in 88% of patients). Patients randomized to ruxolitinib in SIMPLIFY-1 and best available therapy in SIMPLIFY-2 were eligible to cross-over to momelotinib at the end of the 24-week randomized treatment period in both studies, subsequently receiving momelotinib for an extended treatment period.

Sierra is currently enrolling patients in the MOMENTUM clinical trial for patients with myelofibrosis. The randomized double-blind global Phase 3 trial is designed to confirm the efficacy of momelotinib on myelofibrosis symptoms, transfusion independence and splenomegaly, as compared to danazol. The trial is targeting enrollment of 180 myelofibrosis patients who are symptomatic, anemic and have been treated previously with a JAK inhibitor. The Primary Endpoint of the trial is the Total Symptom Score (TSS) response rate of momelotinib compared to danazol at Week 24 (99% power; 2-sided alpha of 0.05). Data from MOMENTUM, along with data from more than 820 myelofibrosis patients previously treated with momelotinib in prior clinical studies, will form the basis of the global registration strategy for momelotinib.

About the EHA Posters
Title: Long term Safety of Momelotinib in JAKi Naïve and Previously JAKi Treated Intermediate/High Risk Myelofibrosis Patients
Lead Author: Prof. Claire Harrison, Guy's and St. Thomas' NHS Foundation Trust, London, United Kingdom
Session Title: Myeloproliferative neoplasms - Clinical
Poster No.: EP1113

Title: Momelotinib Dose-Intensity is Maintained in JAKi Naïve and Previously JAKi Treated Intermediate/High Risk Myelofibrosis Patients
Lead Author: Dr. Vikas Gupta, Princess Margaret Cancer Centre, Toronto, ON, Canada
Session Title: Myeloproliferative neoplasms - Clinical
Poster No.: EP1103

The accepted abstracts are now available online on the EHA conference websites at

Both e-posters will be made available through the on-demand Virtual Congress platform and at as of Friday, June 12, 08:30 CEST.

About Sierra Oncology
Sierra Oncology is a late stage drug development company focused on achieving the successful registration and commercialization of momelotinib, a potent, selective and orally-bioavailable JAK1, JAK2 & ACVR1 inhibitor with a targeted mechanism of action that enables it to address all three key drivers of myelofibrosis. Momelotinib's differentiated therapeutic profile encompasses robust constitutional symptom improvements, a range of meaningful anemia benefits, including eliminating or reducing the need for frequent blood transfusions, and comparable spleen control to ruxolitinib. More than 1,200 subjects have received momelotinib since clinical studies began in 2009, including more than 820 patients treated for myelofibrosis.

Sierra has launched MOMENTUM, a randomized double-blind Phase 3 clinical trial designed to enroll 180 myelofibrosis patients who are symptomatic and anemic, and who have been treated previously with a JAK inhibitor. The U.S. Food and Drug Administration has granted Fast Track designation to momelotinib. Momelotinib is protected by patents anticipated to provide potential exclusivity to 2040 in the United States and Europe (inclusive of potential Patent Term Extension or Supplementary Protection Certificate).

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Cautionary Note on Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the "safe harbor" provisions of the Private Securities Litigation Reform Act of 1995, including, but not limited to, statements regarding Sierra Oncology's expectations from current data, anticipated clinical development activities, and potential benefits of momelotinib. All statements other than statements of historical fact are statements that could be deemed forward-looking statements. These statements are based on management's current expectations and beliefs and are subject to a number of risks, uncertainties and assumptions that could cause actual results to differ materially from those described in the forward-looking statements. Such forward-looking statements are subject to risks and uncertainties, including, among others, the risk that Sierra Oncology's cash resources may be insufficient to fund its current operating plans and it may be unable to raise additional capital when needed, the risk that disruptions and impacts of COVID-19 will be significant and lengthy, Sierra Oncology may be unable to successfully develop and commercialize momelotinib, momelotinib may not demonstrate safety and efficacy or otherwise produce positive results, Sierra Oncology may experience delays in the clinical development of momelotinib, Sierra Oncology may be unable to acquire additional assets to build a pipeline of additional product candidates, Sierra Oncology's third-party manufacturers may cause its supply of materials to become limited or interrupted or fail to be of satisfactory quantity or quality, Sierra Oncology may be unable to obtain and enforce intellectual property protection for its technologies and momelotinib and the other factors described under the heading "Risk Factors" set forth in Sierra Oncology's filings with the Securities and Exchange Commission from time to time. Sierra Oncology undertakes no obligation to update the forward-looking statements contained herein or to reflect events or circumstances occurring after the date hereof, other than as may be required by applicable law.

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