a few simple things can keep you sane when its hot for a run:
1) Pre-cool. A cold shower before you head out, or ice in a hat or your hands, drops/signals to your body that ur starting temperature is lower and buys you a few good miles before the heat catches up.
2) Drink before and during, and put something in your water.
You're sweating out salt, not just water, so a pinch (1/8 tsp or more) or any decent electrolyte mix keeps you from feeling weak halfway through.