Synthorx Inc. announced today the completion of a $63 million Series C financing, led by OrbiMed and joined by new investors, Medicxi and Osage University Partners, and existing investors, Avalon Ventures, RA Capital Management, and Correlation Ventures. In addition, Peter Thompson, M.D., private equity partner at OrbiMed, and Vickie Capps, an independent advisor with extensive financial and audit experience, will join the Synthorx board of directors. The proceeds of the financing will be used to advance the company's pipeline of Synthorin™ cytokines, including an IL-2 tuned specifically for activity on certain immune cells. Using the company's expanded genetic alphabet technology based on a breakthrough in synthetic biology, Synthorin cytokines are designed to selectively tune receptor pharmacology and extend half-life. These properties allow for efficacious immune system activation with convenient dosing schedules and without safety limitations to enhance the antitumor activity of leading immuno-oncology approaches, including checkpoint inhibitors, cancer vaccines, CAR-T therapies, and oncolytic viruses.

"The ability to activate tumor-fighting immune cells has been a tremendous breakthrough in curing cancer in some patients, but the rate of responses leading to long-term remission and overall survival is still limited. Combination therapies are needed that demonstrate improved efficacy but are safe and convenient for patients. IL-2 has proven activity but limited use due to safety issues," said Laura Shawver, Ph.D., president, CEO, and director of Synthorx. "Our investors immediately recognized the remarkable ability of our lead molecule, Synthorin IL-2, to deliver sustained cancer-killing activity without the safety liability through our unique ability to modify protein therapeutics for tuning receptor pharmacology and extending half-life."

"Since its discovery nearly 40 years ago, IL-2 is the most studied cytokine and potentially the most valuable molecule for boosting the efficacy of immuno-oncology therapies," said Marcos Milla, Ph.D., who was recently promoted to chief scientific officer of Synthorx. "To make the best IL-2 we have seen to date, the scientific team at Synthorx applied the company's expanded genetic alphabet technology to create specific receptor interactions with great precision that bias IL-2's activity to immune activation versus repression."

"We are impressed with the data for Synthorin IL-2 and how the Synthorx technology platform can specifically identify and select protein modifications that result in the desired therapeutic effect and pharmacokinetics. It is easy to see how this platform could be applied to a variety of protein therapeutics," said Dr. Thompson.

About OrbiMed

OrbiMed is a leading investment firm dedicated exclusively to the healthcare sector, with over $14 billion in assets under management. OrbiMed invests globally across the spectrum of healthcare companies, from venture capital start-ups to large multinational corporations, utilizing a range of private equity funds, public equity funds, royalty/credit funds and other investment vehicles. OrbiMed maintains its headquarters in New York City, with additional offices in San Francisco, Shanghai, Mumbai and Herzliya. OrbiMed seeks to be a capital provider of choice, with the flexibility to provide equity and debt capital solutions that are tailored to the unique needs of our portfolio companies. The firm's global team of over 80 professionals brings the resources and experience required to be an exceptional long-term partner in building world-class healthcare companies. For more information, please visit www.orbimed.com.

About Synthorx

Synthorx Inc. is a biotechnology company using synthetic biology to discover and develop novel protein therapeutics. Synthorx's expanded genetic alphabet platform has the unique ability to drive the site-specific incorporation of multiple synthetic amino acids into proteins thereby tuning receptor specificity important for improving efficacy and safety. In addition, their engineered organisms provide the ability to manufacture these improved proteins, called Synthorins, with the required fidelity and yield. The unique Synthorx platform expands the chemical and structural repertoire of protein therapeutics and uncovers new ways to modulate pharmacological properties of biologics, not possible with other technologies. The company was founded based on important discoveries in Dr. Floyd Romesberg's lab at The Scripps Research Institute in conjunction with Avalon Ventures, which housed Synthorx in its incubator, COI Pharmaceuticals, Inc. The company is headquartered in La Jolla, Calif.