Shares of Aerpio Pharmaceuticals Inc. plummeted 71% toward a record low in active trade Monday, after the biopharmaceutical company said a phase 2b study of its treatment for diabetic retinopathy failed to meet its primary endpoint of improvement over placebo. The stock was the biggest decliner listed on major U.S. exchanges, with volume reaching 5.5 million shares, or about 22 times the full-day average. Meanwhile, the company said the trial of its lead candidate AKB-9778 was found did to be safe and well tolerated and showed some encouraging in some secondary endpoints. "While we are disappointed in the primary endpoint results of this study, we are nevertheless encouraged by the fact that several other promising findings observed in our prior 3-month Phase 2a trial have been prospectively confirmed in this 1-year trial," said Chief Executive Stephen Hoffman. The company said it plans to provide an update on the status of AKB-9778 after a full analysis. The stock has now lost 37% over the past 3 months while the iShares Nasdaq Biotechology ETF has gained 16% and the S&P 500 has tacked on 11%.