The actress replaced Aishwarya Rai Bachchan in the lead role after the latter announced she was pregnant in June.
Bhandarkar told Hindustan Times: "Heroine is basically a journey in a heroine's life in the contemporary world.
"It's going to portray how an actress reaches the top and how her life goes through ups and downs. There are lot of catharsis and traumas shown in the film.
"Kareena is a great star and we even discussed a lot of films but nothing materialised. But Heroine is a great script and a great story. I am sure it will be a landmark cinema in Kareena's career."
He added that production is "on track" and the film would be completed in spring next year.
In July, Kapoor described the film as being specially created for her, despite initially turning it down because of the controversial content.