Synergy Pharmaceuticals has entered into a definitive merger agreement, to acquire Callisto Pharmaceuticals. At closing, Callisto stockholders will own approximately 38.3% of the combined company, and Synergy stockholders will own approximately 61.7%. The transaction, subject to regulatory approvals and certain other conditions, is expected to close by the end of October.   Callisto is a biopharma company focused on the development of drugs to treat GI disorders and diseases. Callisto’s drug can...