INVESTORS
Sierra Oncology to Present at the DNA Damage Response Therapeutics Summit

- "Addressing Intrinsic & Acquired PARP Inhibitor Resistance Through Chk1 Inhibition" scheduled for 9:00 am ET on January 30 in Boston -

VANCOUVER, Jan. 23, 2019 /CNW/ - 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, today announced that its Chief Scientific Officer, Dr. Christian Hassig, will present "Addressing Intrinsic & Acquired PARP Inhibitor (PARPi) Resistance Through Chk1 Inhibition" at the DNA Damage Response (DDR) Therapeutics Summit in Boston, MA. The presentation is scheduled for 9:00 am Eastern Time (ET) on January 30, 2019.

"Targeting components of the DDR machinery that regulate replication stress, such as Chk1, represents an attractive therapeutic strategy to address both intrinsic and acquired PARPi resistance," noted Dr. Hassig. "For example, CCNE1-driven tumors, frequently found in high grade serous ovarian, breast and endometrial cancers, are associated with high replication stress and are generally insensitive to PARPi therapy. We have demonstrated that our Chk1 inhibitor, SRA737, plus low dose gemcitabine is highly effective in CCNE1-amplified preclinical models, where low-dose gemcitabine induces an additional exogenous form of replication stress further enhancing sensitivity to Chk1 inhibition. Moreover, PARPi acquired resistance is driven, in part, through increased replication fork stabilization and partial recovery of homologous recombination repair, two processes regulated by Chk1. As such, our preclinical results suggest that combining PARPi with SRA737 may prove effective in treating this significant emerging clinical issue."

Sierra Oncology is a key sponsor of the DNA Damage Response Therapeutics Summit, which will gather leading stakeholders from across drug development over two days to discuss how to advance the therapeutic potential of targeting DNA repair pathways.

Inducement Grants Under Nasdaq Listing Rule 5635(c)(4)

Sierra also announced that on January 21, 2019 the Compensation Committee of Sierra Oncology's Board of Directors granted non-qualified stock options to purchase an aggregate of 141,000 shares of its common stock to 5 new employees under Sierra Oncology's 2018 Equity Inducement Plan.

The 2018 Equity Inducement Plan is used exclusively for the grant of equity awards to individuals who were not previously an employee or non-employee director of Sierra (or following a bona fide period of non-employment), as an inducement material to such individual's entering into employment with Sierra, pursuant to Rule 5635(c)(4) of the Nasdaq Listing Rules.

The options have an exercise price of $1.41 per share, which is equal to the closing price of Sierra's common stock on January 22, 2018, the first day on which markets are open following the date of grant. Each option will vest and become exercisable as to 25% of the shares on the first anniversary of the recipient's start date, and then will vest and become exercisable as to the remaining 75% of the shares in 36 equal monthly installments following the first anniversary, in each case, subject to each such employee's continued employment with Sierra on such vesting dates. The options are subject to the terms and conditions of Sierra's 2018 Equity Inducement Plan, and the terms and conditions of the stock option agreement covering the grant.

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 spleen 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 low dose gemcitabine. Sierra has also prepared for a potential clinical study of SRA737 in combination with a PARP inhibitor. 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.

SOURCE Sierra Oncology

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