Acute Myeloid Leukaemia (AML) is the predominant acute leukaemia in the Western world. Current treatment has not substantially changed in the past two decades and is dependent on chemotherapy and allogeneic haematopoietic stem cell transplantation. Poor prognosis AML frequently harbour Mixed Lineage Leukaemia (MLL) translocations. Subsequent fusion of MLL with a partner gene results in a chimeric oncogene expressing an MLL-fusion protein (MLL-FP), able to recruit critical transcriptional regulatory factors, epigenetic enzymes and large regulatory transcription complexes. Inhibition of cyclin dependent kinase 9 (CDK9), critical to transcriptional elongation, has been demonstrated to be effective against MLL-driven AML in part by down regulation of Myeloid Cell Leukaemia 1 (MCL-1). Genetic deletion studies have further established MCL-1 dependency in this malignancy. Based on the importance of MCL-1 for MLL-driven AML survival, we hypothesised that direct targeting of MCL-1 by the novel small molecule BH3 mimetic AZ-MCL1 would potently activate intrinsic apoptosis in murine and human MLL-driven AML models, with therapeutic benefits.
To establish the activity of AZ-MCL1, viability assays using relevant murine and human models of MLL-driven AML were used to assess leukaemia responses to the compound. A further mechanistic understanding and selectivity of AZ-MCL1 was achieved through analysis of biochemical and biological hallmarks of apoptosis, in addition to transcriptional expression and retroviral transduction studies using MCL-1 and its pro-survival homologs. Moreover, comprehensive proteomic analysis in silico of Homo sapiens and Mus musculus MCL-1 and its functional domains was performed to gain an insight into the applicability of murine systems for AZ-MCL1 assessment. Based on our findings in vitro and in silico, the therapeutic potency of AZMCL1was evaluated using clinically relevant murine syngeneic and xenograft models of MLL driven AML.
These studies demonstrate that AZ-MCL1 activates the intrinsic apoptotic pathway in human and murine MLL-driven cell lines with differential potency in vitro. Importantly for the first time, AZ-MCL1 was shown to be effective against a human MLL-driven AML, MV4;11, in vivo. These promising pre-clinical data provide evidence that direct antagonism of MCL-1 by AZ-MCL1 has potential for clinical evaluation and putatively offers a novel strategy to treat, particularly high-risk MLL-driven, AML.