** Akeso 9926.HK falls 7.5 to HK$145.2; set for biggest one-day pct drop since August 7

** Stock hits lowest since August 4; set for fourth straight session of decline

** Antibody drugs developer and manufacturer to sell 23.55 mln shares, or 2.56% of enlarged share capital, to third party investors via share placement, raising HK$3.52 bln ($450.6 mln) for R&D, infra building, products commercialisation

** Issue price of HK$149.54 represents 4.75% discount to Wednesday's close

** Key shareholders Xia Yu, Li Baiyong planning to sell 3 mln existing shares at same price to third party investors

** YTD, stock surges ~148%

($1 = HK$7.8113)

(Reporting by Donny Kwok)

((donny.kwok@thomsonreuters.com))