Sierra Oncology Successfully Transfers Sponsorship of SRA737 Clinical Trials

- Company plans to study synthetic lethality in genetically-defined patient cohorts -
- Preclinical research underway studying DDR and immuno-oncology combinations -

VANCOUVER, Jan. 9, 2017 /PRNewswire/ - 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 that it has successfully transferred sponsorship of the two ongoing Phase 1 clinical trials evaluating its Checkpoint kinase 1 (Chk1) inhibitor, SRA737, from the Cancer Research UK Centre for Drug Development to the company. In accordance with the license agreement for SRA737, a $2.0 million fee is due to CRT Pioneer Fund LP for the achievement of this milestone.

"SRA737 targets Chk1, a key cell cycle checkpoint and central regulator of the DDR network, an exciting emerging target in oncology that has broad clinical and commercial potential," said Dr. Nick Glover, President and CEO of Sierra Oncology. "We are pleased to announce that the formal transfer of sponsorship to Sierra Oncology of these two actively recruiting clinical trials was completed as planned and ahead of schedule. Our goal is to provide an update from these studies within twelve months that will further inform our development strategy."

Professor Paul Workman, Chief Executive and President of The Institute of Cancer Research, London, added, "Working with Sierra Oncology, we have made very promising progress with these studies. I'm confident that SRA737 – which was discovered here at the ICR – is in excellent hands for the future. Sierra is developing a sophisticated strategy for advancing SRA737 and we look forward to continuing to collaborate in taking this agent forward together for the benefit of cancer patients."

In September 2016, Sierra Oncology licensed the exclusive worldwide rights to SRA737, a highly selective, orally available, small molecule inhibitor of Chk1. SRA737 was discovered and initially developed by scientists in the Cancer Research UK Cancer Therapeutics Unit at The Institute of Cancer Research (ICR) in collaboration with Sareum Holdings plc (LSE AIM: SAR), with funding provided by Cancer Research UK, the ICR and Sareum. SRA737 is being investigated in two recently initiated Phase 1 clinical trials in patients with advanced solid tumors: a monotherapy trial and a trial of SRA737 in combination with chemotherapy. (ClinicalTrials.gov identifiers: NCT02797964 and NCT02797977).

"Working with the ICR and The Royal Marsden NHS Foundation Trust, we are charting an expanded and optimized development plan for SRA737. In particular, we are keen to evaluate SRA737's potential to induce synthetic lethality as monotherapy in certain genetically-defined patient cohorts, while also exploring its potentiating effects in combination with chemotherapy," added Dr. Barbara Klencke, Chief Development Officer of Sierra Oncology. "Concurrently we are also conducting preclinical research evaluating SRA737 in combination with other DDR agents including PARP inhibitors and our proprietary Cdc7 inhibitor, SRA141, as well as with immuno-oncology therapeutics. Results of this research, expected in late 2017, will guide a potential next wave of clinical development for our asset, possibly further broadening its therapeutic utility."

About Sierra Oncology
Sierra Oncology is a clinical stage drug development company advancing next generation DDR therapeutics for the treatment of patients with cancer. Our lead drug candidate, SRA737, is a highly selective, orally bioavailable small molecule inhibitor of Checkpoint kinase 1 (Chk1), a key cell cycle checkpoint and central regulator of the DNA Damage Response (DDR) network. In cancer cells, replication stress induced by oncogenes (e.g., MYC and RAS) combined with loss of function in tumor suppressors (e.g., p53 and ATM) results in persistent DNA damage and genomic instability. Targeted inhibition of the remaining components of the DDR network such as by SRA737 may be synthetically lethal to cancer cells and have utility as a monotherapy in a range of tumor indications. Chk1 is also believed to facilitate tumor cell resistance to chemotherapy or radiation-induced DNA damage and the combination of SRA737 with these standards-of-care may provide synergistic anti-tumor activity. SRA737 is currently being investigated in two Phase 1 clinical trials in patients with advanced cancer.

Sierra Oncology is also advancing SRA141, a potent, selective and orally bioavailable small molecule inhibitor of the Cdc7 kinase undergoing preclinical development. Cdc7 is a key regulator of both DNA replication and the DDR network, making it a compelling emerging target for the potential treatment of a broad range of tumor types.

Sierra Oncology retains the global commercialization rights to both SRA737 and SRA141. 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 anticipated clinical development activities, timing and results of data from clinical development and research, and the 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