All PI3K isoforms - α, β, γ and δ - are expressed in all the MCL cell lines tested... copanlisib is more potent in targeting MCL cells in vitro with IC50 at a nanomolar range. Copanlisib at low dosage of 6 mg/kg/2d significantly inhibited in vivo tumor growth of an ibrutinib-venetoclax dual-resistant PDX model...Volasertib at low dosage of 10 mg/kg/week diminished in vivo tumor growth of the ibrutinib-venetoclax dual-resistant PDX model.