Turns out they did on both mice and primates.

Unfortunately the brain development data is unconvincing

And the side effect is only evaluated after the treatment:

Another potential concern, however, emerged about 1 month before Mei was treated: the final conclusions of a primate toxicology study conducted at PriMed. The company’s report, dated 17 February 2025, concluded all four monkeys that received the therapy, whether at low or high doses, developed moderate to severe liver damage.