Barbara Fox is the new CEO of Rheos Medicines. She was most recently chief executive of Tilos Therapeutics, which was acquired by Merck (NYSE: MRK) earlier this year. Fox succeeds interim Rheos CEO Abbie Celniker, a partner at Third Rock Ventures. Celniker will remain chair of the Rheos board of directors. Cambridge, MA-based Rheos emerged last year with $60 million in Series A financing to develop drugs that target cellular metabolism as a way to treat disease.