With the IPO window open, Aptinyx and Iterum look to get out before it closes. : Two Chicago startup drug companies are taking advantage of an increasingly bullish IPO market. Aptinyx, the follow-up to a Northwestern University spinout that sold for $1.7 billion three years ago, plans to go public. Iterum Therapeutics, a Dublin, Ireland-based company that's run from Chicago by CEO Corey Fishman, says it's raising $80 million in an IPO that will close next week.