Eleven Biotherapeutics Inc., a Cambridge biopharmaceutical company, said Tuesday that it has secured $20 million dollars in Series A equity financing, expanding the total Series A investment to $45 million. New investor, JAFCO Co. Ltd., a Tokyo-based private equity firm, joined the Series A financing with a $10 million investment; $10 million was also received from commitments from existing investors, Third Rock Ventures and Flagship Ventures. Third Rock and Flagship helped found Eleven Biotherapeutics in 2010.