Two thoughts for Panther...

-Try canned mackeral. It stinks to high heaven, which might stimulate his appetite. I did this once with my RB girl Quasar when she stopped eating.

-When she continued to have appetite problems, the vet gave her a steroid shot and gave her steroid pills that I then put in her food. Her appetite was amazing after the first shot. People laughed at my "bodybuilding" kitty, but it saved her life.

I don't know if this helps, but I wish you and Panther the best and send you my prayers.