Acer Therapeutics Inc., formerly Opexa Therapeutics, Inc., is a pharmaceutical company. The Company is engaged in acquires, develops and intends to commercialize therapies for patients with serious rare diseases with critical unmet medical need. Its late-stage clinical pipeline includes Edsivo (celiprolol) and ACER-001. The Company is developing Edsivo for the treatment of vascular Ehlers-Danlos Syndrome (vEDS) in the United States. The Company is developing ACER-001, a pharmacologic treatment option for the treatment of Maple Syrup Urine Disease (MSUD). ACER-001 is an immediate-release formulation of sodium phenylbutyrate (NaPB) developed using a microencapsulation process. The Company is also developing ACER-001 for the treatment of Urea Cycle Disorders (UCD).