BTX-A51, a multi-kinase inhibitor of CK1α and CDK9, has been approved for a Phase I clinical trial in relapsed or refractory AML.423,424 In 2019, the A51-based PROTAC PHM-A51 demonstrated potent degradation of CK1α and CDK9, along with anti-proliferative effects in AML and lymphoma cells at low nanomolar concentrations. The gene discussed is CDK9; the disease is acute myeloid leukemia.