On August 22 1987, Madonna’s Who’s That Girl single (from the soundtrack album of the same name) went to number-one on the US Billboard Hot 100.
Regarding the development of the music for the film, Madonna explained:
“I had some very specific ideas in mind, music that would stand on its own as well as support and enhance what was happening on screen and the only way to make that a reality was to have a hand in writing the tunes myself. The songs aren’t necessarily about Nikki [her character name in the movie] or written to be sung by someone like her, but there’s a spirit to this music that captures both what the film and the characters are about, I think.”
Today In Madonna History 