The problem with all potential senolytic drugs is cancer. Looking at all the animal models (and spontaneous human mutations) where senescence is reduced there is a corresponding increase in cancer. We really can't do much about ageing until we can cure or prevent cancer.
That would only be the case in the models where senescence is blocked completely.
If instead for a short time killing some fraction of all currently existing senescent cells, the effect on cancer risk should be a reduction, due to decreased inflammatory signaling from those cells. The senescent cells that are hanging around at any given moment in time aren't helping you in any way; they're not reducing the risk of cancer. If there are enough of them, they are in fact increasing the risk of cancer due to messing with the surrounding environment. If those senescent cells ever actually helped, then that help was applied at the time the cell became senescent - and shortly thereafter it became a liability that should be destroyed.
There are emerging exceptions to that view, such as adaptive senescence in the immune system and possibly in support cells in the brain, but fortunately both of those should be largely moot points for the early senolytic therapies, and don't seem to be obstacles in old mice.
