Proteostasis Therapeutics Inc. PTI, +4.84% shares rose 14.2% in premarket trade Wednesday after the company said it won't proceed with an equity offering due to "market conditions." The decision followed the company's stock being shorted by Kerrisdale Capital, betting that the stock would fall, and which caused shares to tank 26.2% on Tuesday. Proteostasis had previously planned to offer 9 million shares in a public offering announced on March 19. "The company believes that current market conditions are not conducive for an offering on terms that would be in the best interest of its current stockholders," Proteostasis said in a statement. Proteostasis previously got an orphan drug designation from the Food and Drug Administration for its cystic fibrosis drug. But Kerrisdale Capital questioned the achievement, saying that company shares have "run up on unimportant breakthrough-therapy designation, but the underlying clinical data is terrible. The drug is a dud." Proteostasis shares have risen 1.8% over the last three months, compared with a 1.2% rise in the S&P 500 SPX, +0.11%