Cambridge-based Infinity ­Pharmaceuticals Inc. said that its 5.7 million-share offering priced flat with Wednesday’s close of $26.33, as it seeks to raise funds for research and ­development costs, potential acquisitions and other purposes, Dow Jones reported. Infinity’s shares had climbed to their highest level in a decade on Tuesday after the company ­reported positive results from an early clinical trial of its drug IPI-145 as a treatment for blood cancers.