Pirtobrutinib (LOXO-305), a highly selective and non-covalent next generation BTK inhibitor, inhibits diverse BTK C481 substitution mutations. Pirtobrutinib causes regression of BTK-dependent lymphoma tumors in mouse xenograft models. Pirtobrutinib is also more than 300-fold selective for BTK versus 370 other kinases tested and shows no significant inhibition of non-kinase off-targets at 1 μM.In Vitro: Pirtobrutinib potently inhibits both wild-type BTK and BTK C481S-mediated kinase activity with nanomolar potency. Pirtobrutinib inhibits WT BTK (Y223) autophosphorylation with an IC50 of 3.68 nM. Pirtobrutinib inhibits BTK C481S Y223, C481T Y223, and C481R Y223 autophosphorylation with IC50s of 8.45, 7.23, and 11.73 nM, respectively.