Charlize Theron next movie could be "American Express," an indie movie. The Oscar winner could star in and produce the film, according to The Wrap. Theron will produce "American Express" through her Denver & Delilah banner. Denver & Delilah also recently optioned Susannah Cahalan's best-selling book "Brain On Fire: My Month Of Madness" which will star Dakota Fanning.

"American Express" plot details are currently kept under wraps. "The Square" filmmaker Nash Edgerton is attached to direct the film.

Theron, who won an Oscar for "Monster," next stars in Seth MacFarlane's comedy "A Million Ways to Die in the West." She will also be seen in "Dark Places," also starring Chloe Moretz and Christina Hendricks. Theron is also signed to star with Javier Bardem in Sean Penn's African romance "The Last Face."

Theron will host "Saturday Night Live" for the second time this weekend on May 10 with musical guest The Black Keys. The actress is currently promoting her film "A Million Ways to Die in the West."

"Brain on Fire: My Month of Madness" is a 2012 New York Times Bestselling autobiographical book by Susannah Cahalan. The book was first published on November 13, 2012 through Free Press in hardback. The book details Cahalan's struggle with a rare autoimmune disease, anti-NMDA receptor encephalitis. At age 24, Calahan woke up in the hospital with no memory of the events of the previous month, during which time she had violent episodes and delusions.

Dakota Fanning, who recently played the role of Jane Volturi in 'Twilight' series, will be portraying the book's author in the movie which depicts the young woman's terrifying descent into madness.

Movie rights to Cahalan's bestselling book were recently bought by Charlize Theron's production company Denver & Delilah. The "Prometheus" actress will also portray a supporting role in the upcoming true-story drama film.