Shares of Acer Therapeutics Inc. (NASDAQ:ACER) fell 78.6% to $4.12 Tuesday after the FDA issued a complete response letter (CRL)calling for the company to conduct an "adequate and well-controlled trial" to determine whether the orphan-designated beta-blocker Edsivo (celiprolol) reduces the risk of clinical events in patients with vascular Ehlers-Danlos syndrome (vEDS), an inherited connective tissue disorder.