-Are you turning the correct direction? Non-driveside is righty-loosen.
-Use a better pedal wrench; something with more leverage and better 'bite'.
-Try allen socket and breaker bar on the backside of the spindle.
-Try shooting a little penetrant (like PB Blaster) into the threads from backside.
-Use a heat gun on the crank arm to try and expand it.
-Remove crankarm from bike, clamp in [plastic/protected] vice for even more leverage.

What pedal and what crank?