They need to do multi decade testing on people that take only that sweetner at various rates, with a control group that don't use any artificial sweetners, to reach a valid inference on how splenda damages human tissues.

Although in vitro testing is a start to cause enough concern to do advanced testing as mentioned above.

The study didn't expose these chemicals directly to DNA, the chemicals were exposed to digestive tract cells. FYI DNA is in the nucleus of the cells.