Speaking to Digital Spy, Shankman discussed the difficulties of transferring Ages, which he acknowledged is a "much darker" show than his previous outing.
In the Broadway original, Tom Cruise's rock legend Stacee Jaxx is far less likeable - his stage incarnation has an affair with the underage Sherrie (played here by Julianne Hough) and is ultimately charged with statutory rape.
Shankman explained: "Not only does he do that, he has sex with her immediately, in the bathroom of the club, and then has her fired!
"So he's awful, she's a bit of a slut, and in the movie I wanted somebody to root for. You couldn't root for those people."
Rock of Ages is showing in cinemas now.
> 'Rock of Ages' Julianne Hough, Diego Boneta interview - video