Company Will Provide New Interim Data for Pegzilarginase in Patients with Arginase 1 Deficiency

Preclinical Efficacy Data of AEB4104 - a New Enzyme Approach - for the treatment of Homocystinuria

Three-Conference Schedule Includes Five Abstract Acceptances Regarding Rare Genetic Disease and Cancer

AUSTIN, Texas, July 30, 2018 (GLOBE NEWSWIRE) -- Aeglea BioTherapeutics, Inc. (NASDAQ:AGLE), a clinical-stage biotechnology company that designs and develops innovative human enzyme therapeutics for patients with rare genetic diseases and cancer, today announced its schedule of medical conference presentations for the fall of 2018. The three-conference schedule includes five abstract acceptances on the Company’s latest data concerning the rare genetic disease Arginase 1 Deficiency (ARG1-D), uveal and cutaneous melanoma, and human-derived enzymatic approaches to treating the metabolic disorder homocystinuria.

“This has been an active and successful year for Aeglea,” said Anthony G. Quinn, M.B Ch.B, Ph.D., Aeglea’s president and chief executive officer. “We have a busy fall conference schedule during which we will provide important data updates from our clinical and preclinical programs. The repeat dose update from our ARG1-D trials builds on the initial data presented in April 2018 that demonstrated for the first time that rapid and sustained lowering of plasma arginine levels with pegzilarginase, our lead investigational therapy, was accompanied by clinically relevant treatment effects after only eight weeks of dosing. We look forward to providing new interim data from our rare genetic disease and cancer clinical trials with pegzilarginase in the third and fourth quarters of 2018.”

Conference Schedule

Event: Annual Symposium of the Society for the Study of Inborn Errors of Metabolism (SSIEM) Date: September 4-7, 2018 Location: Athens, Greece Title: Improvements in Arginase 1 Deficiency-related Disease Manifestations Following Plasma Arginine Reduction with Pegzilarginase

Event: American Society of Human Genetics (ASHG) Annual Meeting Date: October 16-20, 2018 Location: San Diego, CA Title: 1) Improvements in Arginase 1 Deficiency-related Disease Manifestations Following Plasma Arginine Reduction with Pegzilarginase (Early Phase 2 Results); 2) Clinical Features of Arginase 1 Deficiency: Review of Literature Case Series; 3) Improved Survival and Amelioration of Disease-Related Liver Pathology in a Mouse Model of Homocystinuria with a Novel Homocysteine Degrading Enzyme

Event: European Society for Medical Oncology (ESMO) 2018 Congress Date: October 19-23, 2018 Location: Munich, Germany Title: Initial Cohort Expansion Results of Sustained Arginine Depletion with Pegzilarginase in Melanoma Patients in a Phase 1 Advanced Solid Tumor Trial

Details regarding the date and time of each abstract will be announced before each conference.

About Pegzilarginase in Arginase 1 Deficiency Pegzilarginase is an enhanced human arginase that enzymatically degrades the amino acid arginine. Aeglea is developing pegzilarginase for the treatment of patients with Arginase 1 Deficiency, a debilitating urea cycle disorder caused by deficiency of a key arginine metabolizing enzyme that leads to severe and progressive hyperargininemia-related neurological abnormalities, hyperammonemia and early mortality. Pegzilarginase is intended for use as an enzyme replacement therapy in patients to reduce elevated blood arginine levels. The Company’s interim Phase 1/2 data demonstrated clinically relevant treatment effects and rapid and sustained lowering of plasma arginine in Arginase 1 Deficiency patients.

About Pegzilarginase in Cancer Pegzilarginase is an enhanced human arginase that enzymatically degrades the amino acid arginine. In some cancers, tumor cells stop producing specific amino acids and must acquire them from the blood, making the tumor cells susceptible to starvation through depletion of those amino acids. Aeglea is developing pegzilarginase to exploit vulnerabilities in some cancers that lead to an increased dependency on extracellular arginine. Pegzilarginase targets these arginine dependent cancers by depleting blood arginine levels to below the normal range. Preclinical data demonstrated that the resulting arginine starvation inhibits proliferation, induces cell death, increases turnover of cell components and promotes anti-tumor immune responses. The Company’s Phase 1 data in advanced solid tumors demonstrated that pegzilarginase was well tolerated at doses that produced marked and sustained reductions in blood arginine levels below the normal range.

About Aeglea BioTherapeutics Aeglea is a clinical-stage biotechnology company that designs and develops innovative human enzyme therapeutics for patients with rare genetic diseases and cancer. Aeglea is developing pegzilarginase, its lead investigational therapy, for the treatment of Arginase 1 Deficiency, as monotherapy in arginine-dependent cancers and in combination with an immune checkpoint inhibitor for small cell lung cancer. In addition, Aeglea has an active research pipeline of other human enzyme-based approaches in both therapeutic areas. For more information, please visit http://aegleabio.com.

Safe Harbor / Forward Looking Statements This press release contains "forward-looking" statements within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. Forward-looking statements can be identified by words such as: "anticipate," "intend," "plan," "goal," "seek," "believe," "project," "estimate," "expect," "strategy," "future," "likely," "may," "should," "will" and similar references to future periods. These statements are subject to numerous risks and uncertainties that could cause actual results to differ materially from what we expect. Examples of forward-looking statements include, among others, statements we make regarding our cash forecasts, the timing and success of our clinical trials and related data, the timing of announcements and updates relating to our clinical trials and related data, our ability to enroll patients into our clinical trials, success in our collaborations and the potential therapeutic benefits and economic value of our lead product candidate or other product candidates. Further information on potential risk factors that could affect our business and its financial results are detailed in our most recent Quarterly Report on Form 10-Q for the quarter ended March 31, 2018 filed with the Securities and Exchange Commission (SEC), and other reports as filed with the SEC. We undertake no obligation to publicly update any forward-looking statement, whether written or oral, that may be made from time to time, whether as a result of new information, future developments or otherwise.

Investor Contact: Charles N. York II Chief Financial Officer Aeglea BioTherapeutics investors@aegleabio.com

Media Contact: David Calusdian Sharon Merrill Associates AGLE@investorrelations.com