Sierra Reports Late-Breaking Preclinical Data for SRA737 Presented at AACR 2019

- Late-breaking oral presentation reports profound, durable synergistic activity for immunotherapy combined with SRA737+LDG, its Chk1 inhibitor plus low dose gemcitabine (LDG), in small cell lung cancer models -

VANCOUVER, April 1, 2019 /PRNewswire/ - Sierra Oncology, Inc. (Nasdaq: SRRA), a clinical stage drug development company focused on advancing targeted therapeutics for the treatment of patients with significant unmet needs in hematology and oncology, announced that preclinical data for SRA737+LDG, its Chk1 inhibitor plus non-cytotoxic low dose gemcitabine (LDG), in combination with immunotherapy, are being reported today in a late-breaking oral presentation at the American Association of Cancer Research (AACR) Annual Meeting 2019 being held in Atlanta, Georgia.

"Given the limited response rates for anti-PD-L1 drugs in patients with small cell lung cancer (SCLC), better treatment options are sorely needed. Our data, showing durable tumor regressions when combining SRA737+LDG with anti-PD-L1 in a mouse model, warrant further clinical studies to investigate the potential of this approach as a strategy to improve outcomes in our patients," said senior researcher Lauren Averett Byers, M.D., Associate Professor of Thoracic/Head and Neck Medical Oncology at The University of Texas MD Anderson Cancer Center, Houston, Texas.

In the study, SRA737+LDG demonstrated significant anti-tumor activity when combined with anti-PD-L1 in a mouse model of SCLC, resulting in durable tumor regressions. These results were accompanied by an induction of anti-tumor cytotoxic T-cells and M1 macrophages and a corresponding reduction in several pro-tumorigenic cell types in the tumors of drug-treated animals.

"The unique replication stress-inducing properties of SRA737 as potentiated by non-cytotoxic low dose gemcitabine have been previously demonstrated to result in intrinsic anti-tumor activity in multiple preclinical models. These striking new data provide evidence for SRA737+LDG's activation of innate immune signaling and the establishment of an anti-tumor immune microenvironment that synergizes with immune checkpoint inhibitors," said Dr. Christian Hassig, Chief Scientific Officer, Sierra Oncology. "These findings provide a mechanistic basis for the growing body of evidence highlighting a synergistic interplay between replication stress and anti-tumor immune responses and afford a compelling rationale for evaluating SRA737+LDG with immunotherapy in the clinic." 

SRA737 AACR Late-Breaking Oral Presentation:
Date/Time: Monday, April 1st from 3:00 to 5:00 pm ET
Session: Minisymposium: Late-Breaking Research 2
Title: Combination treatment of the CHK1 inhibitor, SRA737, and low dose gemcitabine demonstrates profound synergy with anti-PD-L1 inducing durable tumor regressions and modulating the immune microenvironment in small cell lung cancer
Authors: Triparna Sen, Carminia M. Della Corte, Snezana Milutinovic, Lixia Diao, Robert J Cardnell, Ryan J. Hansen, Bryan Strouse, Michael P. Hedrick, Christian Hassig, Jing Wang, Lauren A Byers.
Location: Georgia World Congress Center, Room B404

Summary slides from this presentation will be made available on the company's website at www.sierraoncology.com

About SRA737+LDG
SRA737 is a potent, highly selective, orally bioavailable small molecule inhibitor of Checkpoint kinase 1 (Chk1), a key regulator of cell cycle progression and the DNA Damage Response (DDR). SRA737+LDG is a novel drug combination, where non-cytotoxic low dose gemcitabine acts as a potent inducer of replication stress that potentiates SRA737's anti-tumor activity.

Phase 1/2 clinical trials of SRA737 as monotherapy (NCT02797964) and in combination with low dose gemcitabine (NCT02797977) in multiple solid tumors (ovarian, prostate, non-small cell lung, squamous (head & neck, anal), colorectal, small cell lung, sarcoma, cervical, anogenital) are ongoing. Sierra has also prepared for a potential clinical study of SRA737 in combination with a PARP inhibitor.

Sierra Oncology retains the global commercialization rights to SRA737.

About Sierra Oncology
Sierra Oncology is a clinical stage drug development company advancing targeted therapeutics for the treatment of patients with unmet medical needs in hematology and oncology. Our lead drug candidate, momelotinib, is a potent, selective and orally-bioavailable JAK1, JAK2 and ACVR1 inhibitor that has been investigated in two completed Phase 3 trials for the treatment of myelofibrosis and has demonstrated a potentially differentiated therapeutic profile encompassing anemia-related benefits, as well as achieving substantive splenic volume reduction and constitutional symptom control.

Sierra is also advancing SRA737 and SRA141. SRA737 is a potent, highly selective, orally bioavailable small molecule inhibitor of Checkpoint kinase 1 (Chk1), a key regulator of cell cycle progression and the DNA Damage Response (DDR). SRA737 is currently being investigated in two Phase 1/2 clinical trials primarily focused on patients with ovarian cancer: SRA737-01, a monotherapy study, and SRA737-02, a drug combination study evaluating SRA737 potentiated by non-cytotoxic low dose gemcitabine. SRA141 is a potent, selective, orally bioavailable small molecule inhibitor of Cell division cycle 7 kinase (Cdc7). Cdc7 is a key regulator of DNA replication and is involved in the DDR network, making it a compelling emerging target for the potential treatment of a broad range of tumor types.

For more information, please 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 market and industry position, expectations from current data, anticipated clinical development activities and timing and potential benefits of Sierra Oncology's product candidates. 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 may be unable to successfully develop and commercialize product candidates, product candidates may not demonstrate safety and efficacy or otherwise produce positive results, Sierra Oncology may experience delays in the preclinical and anticipated clinical development of its product candidates, 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's cash resources may be insufficient to fund its current operating plans and it may be unable to raise additional capital when needed, Sierra Oncology may be unable to obtain and enforce intellectual property protection for its technologies and product candidates 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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