** Sienna Biopharmaceuticals SNNA.O drops >20 pct
premarket as drug developer raises $20 mln
** Prices 8 mln shares at $2.50, a 16 pct discount to
stock's Tues close urn:newsml:reuters.com:*:nGNXb9cRyR
** Offering represents about half of co's free float and
more than 30 days worth of stock's trading volume
** Co to use net proceeds to fund advancement of SNA-120
Phase 3 clinical trials for treatment of psoriasis, per offering
prospectus
** SNNA's stock among biggest pct losers before the bell
** Stock tumbled nearly 40 pct on Dec 3 after SNA-120 failed
to meet main goal in a mid-stage study, with co saying would
start late-stage trial in latter half of 2019 urn:newsml:reuters.com:*:nL4N1Y84M2
** Stock up 29 pct YTD, though has lost 80 pct of its value
over past 12 mths
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