CHEK1 and neuroblastoma: The antitumor activity observed in MCL xenografts with the combination was stronger than the one observed in neuroblastoma xenografts treated with MK-1775 and the Chk1 inhibitor MK-8776, and comparable to what observed in colon cancer xenografts, where MK-1775 was used at much higher dose (50 mg/kg) [21, 22].