Indesign GREP: find everything before a matching sequence

Couldn't exactly find the answer in other threads. Here's what I'm trying to accomplish:

In the below example I want to apply a GREP style by finding only the title of the artwork. In this case, only the information before the comma on the first line.

My Beautiful Painting #3, 1999.
Oil on canvas
25 x 25cm
Gift of the artist.

I think this needs to be done via the "positive lookbehind" match function, but I can't seem to figure out the syntax.