A long time ago someone told me about a sci-fi book that was off the beaten path about a group of scientists living underground in a post apocalyptic world that has been all but destroyed by aliens. The aliens are experimenting with the scientists. One has been made into a primate. Another scientist was homosexual but hormonally altered into a heterosexual. Do you have any idea what book I am talking about?
This is actually a very famous science fiction short story called “I Have No Mouth and I Must Scream” by Harlan Ellison. Your friend misremembered one detail: it was a superintelligent supercomputer that destroyed the world and experimented horribly on the last surviving humans, not aliens. “Experiment” isn’t the right word; it kept them alive to be the targets of the computer’s cruel sadism. It doesn’t have a happy ending.
John Byrne did an incredibly good comic adaptation of it in 1994, in Dream Corridor. Pick it up if you can get it. Also, there was a really good video game adaptation during the DOS days that I recommend getting at Good Old Games. As of yet, though, there has been no film version.