– Submission seeks approval of momelotinib for the treatment of myelofibrosis –

Sierra Oncology, Inc. (NASDAQ: SRRA), a late-stage biopharmaceutical company on a mission to deliver transformative therapies for rare cancers, today announced the company has submitted a New Drug Application (NDA) to the US Food and Drug Administration (FDA) for momelotinib, an ACVR1 / ALK2, JAK1 and JAK2 inhibitor in development for the treatment of myelofibrosis.

“Today is truly momentous for everyone at Sierra Oncology and the patients we serve. This team designed a targeted study to address the highest unmet need and delivered incredible results in the midst of a pandemic. We are thrilled to submit this NDA on behalf of myelofibrosis patients and look forward to working with the FDA over the coming months,” said Stephen Dilly, MBBS, PhD, President and Chief Executive Officer of Sierra Oncology. “We are immensely grateful to the patients and investigators who participated in momelotinib trials over the years, making it possible to achieve this milestone.”

The NDA submission is based on the results from several Phase 2 and Phase 3 studies, including the recently completed MOMENTUM study. As with all new drug applications, the company expects the FDA to respond as to whether this submission is accepted within 60 days. Assuming the submission is accepted and a subsequent approval is granted, commercial launch of momelotinib is anticipated in 2023.

About the Pivotal MOMENTUM Clinical Trial

MOMENTUM is a global, randomized, double-blind Phase 3 clinical trial of momelotinib versus danazol in patients with myelofibrosis who were symptomatic and anemic, and had been previously treated with an FDA-approved JAK inhibitor. The study was designed to evaluate the safety and efficacy of momelotinib for the treatment and reduction of the key hallmarks of disease: symptoms, blood transfusions (due to anemia) and splenomegaly (enlarged spleen). Results from the MOMENTUM study were presented at the 2022 Annual Meeting of the American Society of Clinical Oncology.

The primary endpoint of the study is Total Symptom Score (TSS) reduction of >50% over the 28 days immediately prior to the end of Week 24 compared to baseline TSS, using the Myelofibrosis Symptom Assessment Form (MFSAF). Secondary endpoints included Transfusion Independence (TI) rate for >12 weeks immediately prior to the end of Week 24 with Hgb levels ≥ 8 g/dL, and Splenic Response Rate (SRR) based on splenic volume reduction of >35% at Week 24. The study enrolled 195 patients based on a planned 180 patients across 21 countries.

Danazol was selected as the treatment comparator given its use to ameliorate anemia in patients with myelofibrosis, as recommended by National Comprehensive Cancer Network (NCCN) and European Society of Medical Oncology (ESMO) guidelines. Patients were randomized 2:1 (MMB n = 130 and DAN n = 65) to receive either momelotinib or danazol. After 24 weeks of treatment, patients on danazol were allowed to crossover to receive momelotinib. Early cross-over to momelotinib was available for confirmed symptomatic splenic progression.

About Momelotinib

Momelotinib is a potent, selective and orally bioavailable ACVR1 / ALK2, JAK1, JAK2 inhibitor under investigation for the treatment of myelofibrosis in symptomatic, anemic patients previously treated with an approved JAK inhibitor. More than 1,200 subjects have received momelotinib since clinical studies began in 2009, including approximately 1,000 patients treated for myelofibrosis, several of whom remain on treatment for over 12 years. Momelotinib is the first and only JAK inhibitor to demonstrate positive data for all key hallmarks of the disease—symptoms, splenic response and anemia.

About Myelofibrosis

Myelofibrosis is a rare blood cancer that results from dysregulated JAK-STAT signaling and is characterized by constitutional symptoms, splenomegaly (enlarged spleen) and progressive anemia. From prior studies with momelotinib, we know approximately half of myelofibrosis patients are moderately to severely anemic when eligible for JAK inhibitor treatment. Furthermore, currently approved JAK inhibitors only address symptoms and splenomegaly and are myelosuppressive. This can lead to worsening anemia, resulting in dose reductions that potentially reduce treatment effect.

About Sierra Oncology

Sierra Oncology is a late-stage biopharmaceutical company on a mission to deliver targeted therapies that treat rare forms of cancer. We harness our deep scientific expertise to identify compounds that target the root cause of disease to advance targeted therapies with assets on the leading edge of cancer biology. Our team takes an evidence-based approach to understand the limitations of current treatments and explore new ways to change the cancer treatment paradigm. Together we are transforming promise into patient impact.

For more information, visit www.SierraOncology.com.

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 regarding the potential and future success of momelotinib, statements by Sierra Oncology’s President and Chief Executive Officer, the timing of the FDA’s response to Sierra Oncology’s NDA, the possibility of an approval of momelotinib and the timing of a commercial launch 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 uncertainties associated with the regulatory approval process, the risk that Sierra Oncology may be unable to successfully commercialize momelotinib, 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.

SOURCE: Sierra Oncology

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