Hmmmm... "Как волка ни корми, он все в лес смотрит" With the help of google-sensei and my moderate understanding of Russian, I'd say "As the wolf eats, he looks into the woods." HOWEVER, I'm not entirely certain about the use of ни in the first part, so I might be wrong.
A leopard cannot change its spots.
Lit.: No matter how good you feed the wolf, it still looks into the forest.