Don't put the whole bag into water if it has an interlining of cardboard!
I clean my old Kate Spades very vigorously, they are worthless if left as they were so I go for broke. I try the dishwashing suds on a sponge then on a brush. If no improvement, I then put straight dishwashing soap on the stain and scrub. Rinse well without soaking the bag which will ruin the cardboard interlining! Use a hand held hair dryer to check your progress. If the dishwashing soap doesn't work I *will* get out the big guns, Resolve. That will remove grease. It will also fade cotton canvas. I now have a faded red canvas and leather
Kate Spade Sam. Fine by me, it hasn't the awful built up grime from daily use it came with. Used the Resolve with the disgusting lining of a boarskin and multistripe Leonore with melted candy in the pocket.
What about the Tide pen? I haven't bought one, have heard rave reviews.