BCR-ABL1+ B progenitor acute lymphoblastic leukemia (Ph+ B-ALL) is an aggressive disease that frequently responds poorly to currently available therapies. Alterations in IKZF1, which encodes the lymphoid transcription factor Ikaros, are present in over 80% of Ph+ ALL and are associated with a stem cell–like phenotype, aberrant adhesion molecule expression and signaling, leukemic cell adhesion to the bone marrow stem cell niche, and poor outcome. Here, we show that FAK1 is upregulated in Ph+ B-ALL with further overexpression in IKZF1-altered cells and that the FAK inhibitor VS-4718 potently inhibits aberrant FAK signaling and leukemic cell adhesion, potentiating responsiveness to tyrosine kinase inhibitors, inducing cure in vivo. Thus, targeting FAK with VS-4718 is an attractive approach to overcome the deleterious effects of FAK overexpression in Ph+ B-ALL, particularly in abrogating the adhesive phenotype induced by Ikaros alterations, and warrants evaluation in clinical trials for Ph+ B-ALL, regardless of IKZF1 status.

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Abstract. Interferon regulatory factor (IRF) 1 and its functional antagonist IRF2 were originally discovered as transcription factors that regulate the interferon-ß gene. Control of cell growth has led to the definition of IRF1 as a tumour suppressor gene and IRF2 as an oncogene. Clinically, approximately 70% of cases of acute myeloid leukaemia demonstrate dysregulated expression of IRF1 and/or IRF2. Our previous studies have shown that human leukaemic TF-1 cells exhibit abnormally high expression of both IRF1 and IRF2, the latter acting to abrogate IRF1 tumour suppression, making these cells ideal for analysis of down-regulation of IRF2 expression. A novel G418 screening protocol was developed and used for identifying effective siRNA that targets IRF2 (siIRF2). Using optimized siIRF2 in leukaemic TF-1 cells, IRF2 was downregulated by approximately 70% at both mRNA and protein levels. Phenotypically, this resulted in growth inhibition associated with G 2 /M arrest as well as induction of polyploidy, differentiation and apoptosis. In contrast to these results, siIRF2 targeting did not affect normal haematopoietic stem/progenitor cell growth. These results indicate the potential utility of IRF2 inhibition as a therapeutic approach to cancer.

Infants with KMT2A-rearranged B-cell acute lymphoblastic leukemia (ALL) have a dismal prognosis. Survival outcomes have remained static in recent decades despite treatment intensification and novel therapies are urgently required. KMT2A-rearranged infant ALL cells are characterized by an abundance of promoter hypermethylation and exhibit high BCL-2 expression, highlighting potential for therapeutic targeting. Here, we show that hypomethylating agents exhibit in vitro additivity when combined with most conventional chemotherapeutic agents. However, in a subset of samples an antagonistic effect was seen between several agents. This was most evident when hypomethylating agents were combined with methotrexate, with upregulation of ATP-binding cassette transporters identified as a potential mechanism. Single agent treatment with azacitidine and decitabine significantly prolonged in vivo survival in KMT2A-rearranged infant ALL xenografts. Treatment of KMT2A-rearranged infant ALL cell lines with azacitidine and decitabine led to differential genome-wide DNA methylation, changes in gene expression and thermal proteome profiling revealed the target protein-binding landscape of these agents. The selective BCL-2 inhibitor, venetoclax, exhibited in vitro additivity in combination with hypomethylating or conventional chemotherapeutic agents. The addition of venetoclax to azacitidine resulted in a significant in vivo survival advantage indicating the therapeutic potential of this combination to improve outcome for infants with KMT2A-rearranged ALL.