THOR Synthorx Inc

Synthorx, Inc. (NASDAQ: THOR), a clinical-stage biotechnology company developing optimized therapeutics for cancer and autoimmune disorders, today announced that preclinical data for immuno-oncology product candidate, THOR-707, will be presented at the upcoming European Society for Medical Oncology (ESMO) 2019 Congress in Barcelona, Spain, from September 27 through October 1, 2019.

Marcos E. Milla, Ph.D., chief scientific officer of Synthorx, will present preclinical data demonstrating the pharmacologic properties of drug candidate, THOR-707. THOR-707 is a recombinant interleukin-2 (IL-2) cytokine that is pegylated at one specific site, intended to block engagement of the high affinity IL-2 receptor alpha chain while retaining potency on the beta chain, thereby maintaining potent effector T cell anti-tumor activity while exhibiting a favorable safety profile.

The preclinical studies to be presented at ESMO 2019 reinforce THOR-707’s ability to induce CD8+ T cell tumor infiltration and anti-tumor efficacy in a dose-dependent manner.  Further, these preclinical data highlight the additive efficacy when a PD-1 checkpoint inhibitor is combined with THOR-707, resulting in the promotion of long-term survival and the rejection of tumor cells on re-challenge in two animal models.  Preclinical molecular profiling data will also be presented, demonstrating THOR-707’s induction of critical immunological mechanisms to elicit tumor infiltration and destruction, including expression markers of response.

“The preclinical evidence on THOR-707, including its favorable pharmacologic profile, durable anti-tumor effects and low risk of vascular leak syndrome, provide a strong rationale for moving into clinical development,” said Dr. Milla.

Synthorx is conducting HAMMER, a global Phase 1/2, first-in-human clinical trial of THOR-707 in adult subjects with advanced or metastatic solid tumors. The single agent and combination arms of the trial will evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics and anti-tumor activity of THOR-707 as a single agent and together with a checkpoint inhibitor. More information about the trial is available at https://clinicaltrials.gov/ct2/show/NCT04009681.

Details of the poster presentation are as follows. For the full abstract, visit the ESMO website.

THOR-707, a novel not-alpha IL-2, promotes all key immune system anti-tumoral actions of IL-2 without eliciting vascular leak syndrome (VLS)Presentation Number: 1225PPresenter: Marcos E. Milla, Ph.D., chief scientific officer, SynthorxSession Date: Monday, September 30th, 2019 Time: 12:00 – 13:00 CEST; 6:00 – 7:00 ETLocation: Poster Area (Hall 4), Fira Gran Via, Barcelona

A copy of the Synthorx poster will be available at the time of the presentation and archived in the Scientific Publications section of the company’s website.

About SynthorxSynthorx, Inc. is a clinical-stage biotechnology company focused on prolonging and improving the lives of people with cancer and autoimmune disorders. Synthorx’s proprietary, first-of-its-kind Expanded Genetic Alphabet platform technology expands the genetic code by adding a new DNA base pair and is designed to create optimized biologics, referred to as Synthorins. A Synthorin is a protein optimized through incorporation of novel amino acids encoded by the new DNA base pair that enables site-specific modifications, which enhance the pharmacological properties of these therapeutics. The company’s lead product candidate, THOR-707, a variant of IL-2, is in development in multiple tumor types as a single agent and in combination with an immune checkpoint inhibitor. The company was founded based on important discoveries by Dr. Floyd Romesberg and The Scripps Research Institute. Synthorx is headquartered in La Jolla, Calif. For more information, visit www.synthorx.com.

Forward-Looking Statements This press release contains forward-looking statements about Synthorx as that term is defined in Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Statements in this press release that are not purely historical are forward-looking statements. Such forward-looking statements include, among other things, preclinical data or plans underlying THOR-707 and the development of Synthorx’s product candidates. Actual results could differ from those projected in any forward-looking statements due to numerous factors. Such factors include, among others, risks associated with the process of discovering, developing and commercializing drugs that are safe and effective for use as human therapeutics and operating as a development stage company; Synthorx’s ability to develop, initiate or complete preclinical studies and clinical trials for, obtain approvals for and commercialize any of its product candidates; changes in Synthorx’s plans to develop and commercialize its product candidates; the potential for any clinical trials of THOR-707 or other product candidates to differ from preliminary or expected results; Synthorx’s ability to raise any additional funding it will need to continue to pursue its business and product development plans; regulatory developments in the United States and foreign countries; Synthorx’s reliance on key third parties, including contract manufacturers and contract research organizations; Synthorx’s ability to obtain and maintain intellectual property protection for its product candidates; the loss of key scientific or management personnel; competition in the industry in which Synthorx operates; and market conditions. These forward-looking statements are made as of the date of this press release, and Synthorx assumes no obligation to update the forward-looking statements, or to update the reasons why actual results could differ from those projected in the forward-looking statements. Investors should consult all of the information set forth herein and should also refer to the risk factor disclosure set forth in the documents the company files with the SEC available at www.sec.gov.

Investor Contacts: Enoch Kariuki, Pharm.D.Synthorx, Inc.ekariuki@synthorx.com 858-750-4750

Christina TartagliaStern Investor Relationschristina.tartaglia@sternir.com212-362-1200

Media Relations Contact:Lauren FishCanale Communicationslauren@canalecomm.com619-849-5386