INVESTORS
Sierra to Report Preclinical Data Demonstrating SRA737 Synergy with PARPi at the AACR 2018 Annual Meeting

- Data reinforce the potential clinical utility of combination therapy -

VANCOUVER, Feb. 21, 2018 /CNW/ - Sierra Oncology, Inc. (Nasdaq: SRRA), a clinical stage drug development company focused on advancing next generation DNA Damage Response (DDR) therapeutics for the treatment of patients with cancer, today announced it has been accepted to present preclinical data demonstrating that its Chk1 inhibitor, SRA737, synergizes with niraparib, a poly ADP-ribose inhibitor (PARPi), in a poster at the American Association of Cancer Research (AACR) Annual Meeting 2018 being held in Chicago, Illinois from April 14-18.

"There is a strong biological rationale for synergy between SRA737 and PARP inhibition, which is further validated by these data. Notably, this combination was effective in homologous repair proficient tumor cell lines where PARP inhibitors are substantially less active in the clinical setting," said Dr. Christian Hassig, Chief Scientific Officer of Sierra Oncology. "Sierra is designing a potential clinical study to evaluate SRA737 in combination with a PARP inhibitor, including evaluation in comparable patient populations."

Poster Title: The Chk1 inhibitor, SRA737, synergizes with niraparib to kill cancer cells via multiple cell death pathways
Session Category: Experimental and Molecular Therapeutics
Session Title: Cell Cycle, Drug Resistance, and Combinations
Session Date and Time: Monday Apr 16, 2018 8:00 AM - 12:00 PM
Location: McCormick Place South, Exhibit Hall A, Poster Section 37
Poster Board Number: 11
Permanent Abstract Number: 1853

The Poster will be available April 16, 2018 on the company's website at www.sierraoncology.com.

About Sierra Oncology
Sierra Oncology is a clinical stage drug development company advancing next generation DNA Damage Response (DDR) therapeutics for the treatment of patients with cancer. Our lead drug candidate, SRA737, is a potent, highly selective, orally bioavailable small molecule inhibitor of Checkpoint kinase 1 (Chk1), currently being investigated in two Phase 1 clinical trials in patients with advanced cancer. Sierra Oncology is also advancing SRA141, a potent, selective, orally bioavailable small molecule inhibitor of Cell division cycle 7 kinase (Cdc7) undergoing preclinical development. 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 expectations from current data, anticipated clinical development 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, SRA737 and SRA141 are at early stages of development and may not demonstrate safety and efficacy or otherwise produce positive results, Sierra Oncology may experience delays in the preclinical and anticipated clinical development of SRA737 or SRA141, 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.

SOURCE Sierra Oncology

For further information: James Smith, Vice President of Corporate Affairs, Sierra Oncology, 604.558.6536, investors@sierraoncology.com