Adewale Akinnuoye-Agbaje, Christian Slater and Holt McCallany have joined the cast of Walter Hill’s untitled action-thriller starring Sylvester Stallone.Pic is a Warner Bros. presentation, in association with Dark Castle Entertainment, IM Global and After Dark Films. Stallone stars as a New Orleans hitman who teams with a Gotham cop (Sung Kang, “Fast Five”) to take down the killers of their respective partners. Akinnuoye-Agbaje is set to play the main villain, a powerful attorney who’s trying to cover up his scam to exploit poor neighborhoods that have been ravaged by Hurricane Katrina. Slater will play a local handler who acts as a middleman, while McCallany will play a dirty cop who’s partners with Kang. Alessandro Camon (“The Messenger”) adapted the graphic novel “Bullet to the Head,” created by the singularly monikered Matz and Colin Wilson. WB will distribute in the U.S. under its ongoing arrangement with Dark Castle, whose Joel Silver and Andrew Rona are among the producers, who also include Alexandra Milchan of EMJAG Prods. Akinnuoye-Agbaje, best known for his small-screen turns on ABC’s “Lost” and HBO’s “Oz,” will soon be seen in Open Road Films’ actioner “Killer Elite” and Universal’s remake of “The Thing.” McCallany, who’s coming off strong notices for his work as an aging boxer on FX’s “Lights Out,” recently wrapped the lead in the indie sci-fi pic “White Space.” Slater next stars alongside Gary Oldman and Dane Cook in the indie crime pic “Guns, Girls and Gambling.” APA reps McCallany and Akinnuoye-Agbaje along with Mosaic and Kritzer Levine Wilkins Griffin Entertainment, respectively. Slater is repped by UTA and Untitled Entertainment.