Avidity Biosciences slides on planned $500 mln stock offering

** Shares of Avidity Biosciences RNA.O down 18.1% to $38 post-market as it seeks equity raise

** San Diego, California-based firm announces $500 mln stock offering

** Co plans to use net offering proceeds to advance its three late-stage clinical programs, to progress R&D associated with its Antibody Oligonucleotide Conjugates platform, among other uses

** Leerink, JP Morgan, TD Cowen, Cantor and Wells Fargo are joint bookrunners

** Early Weds, co said its experimental drug, Del-zota, for a form of Duchenne muscular dystrophy showed that patients improved on key movement tests in early-mid-stage trial

** RNA shares ended session on Weds down 0.5% at $46.40, up ~60% YTD

** With ~128.7 mln shares outstanding, it has roughly $6 bln market cap

** All 18 analysts are bullish on the stock with $66.50 median PT, per LSEG