** Canadian drug developer's U.S.-listed stock down as much as 22.4 pct at $2.15; biggest intraday pct loss in 5 months
** Stock is 3rd biggest pct loser on Nasdaq
** Toronto-listed shares down 20.5 pct at C$2.94
** Says FDA requests additional info about clinical hold, placed on early-stage trial of its cancer drug in November
** More than 270,000 shares traded, 4.9x 30-day moving avg.
** Up to Wednesday's close, U.S. stock had risen 9.6 pct YTD