This is possible, but it would be very noisy and using an external amplifier for high gains is recommended. The maximum gain in a PGA is 48, with 3 dB point at 80 kHz. Cascading 3 results in gain of 110,592. They would have to be AC coupled from one to the next, or the offset voltage would make the gain useless.
For AC Coupling: Either the output of one stage can be routed to a pin and then fed back by unsing external capacitors or signal can be routed to SC BLOCK configured as PGA or unity gain buffer to provide AC coupling.