If your horse is conditioned for it, if there'll be water and shade available, and the if the humidity is low--yes, you can ride.
Here's a good rule of thumb someone posted at my old forum:
Add heat and humidity together.
If the total is below 120 ride in your usual way.
If the total is 120-180, take some care (shade, water, maybe a sponge to sponge him off at streams, ride more slowly)
If the total is above 180--do not ride.
So...70 degrees, 30% humidity = 100, no worries
70 degrees, 80% humidity = 150, ride with care
(this is actually what it was like one day early in the summer--and frankly, I'm never riding in 80% humidity again, ever!)
90 degrees, 90% humidity = 180, don't ride.
So 110 degrees with humidity of between 10 and 50%, you could ride with care.
Ride before 8 am or after 7 pm, that helps, too.