Developing a novel therapeutic strategy for overcoming TKI resistance in ALL

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Nearly one-third of adult patients with acute lymphoblastic leukemia (ALL) are associated with the t(9;22) chromosomal translocation that forms the BCR-ABL oncogene. BCR-ABL induces B-cell acute lymphoblastic leukemia (B-ALL) directly or in acute blastic phase advanced from chronic phase myeloid leukemia. Compared to other types of B-ALL, BCR-ABL-positive B-ALL has a poor prognosis and is much less sensitive to tyrosine kinase inhibitors (TKIs) even in the absence of BCR-ABL kinase mutations, and the underlying mechanisms for this type of the TKI-resistance are largely unknown. We hypothesize that there must be critical downstream pathways whose activation by BCR-ABL is required for B-ALL development but cannot be completely shut down through inhibition of BCR-ABL kinase activity by TKIs, suggesting a BCR-ABL kinase-independent mechanism different from the TKI resistance induced by BCR- ABL kinase domain mutations. This novel idea is supported by our preliminary findings that arachidonate 15-lipoxygenase (Alox15) is upregulated by BCR-ABL and required for B-ALL development in mice but this Alox15 upregulation is not reversed by inhibiting BCR-ABL kinase activity with imatinib (a TKI). These preliminary findings link Alox15 to TKI resistance in B-ALL cells, providing a new strategy for overcoming TKI resistance in treating BCR-ABL-positive B-ALL and strategically other leukemias induced by oncogenic tyrosine kinases. We should mention that it is totally unknown about how the Alox15 pathway mediates TKI resistance in B-ALL, and a better understanding of this Alox15-mediated TKI resistant mechanism requires demonstration of an essential role of Alox15 in B-ALL induced by BCR-ABL and in-depth mechanistic studies that lead to a full understanding of Alox15-associated pathways and their contributions to B-ALL development. Without any doubt, these studies will help to develop a new therapeutic strategy for overcoming TKI resistance in treating BCR-ABL-positive B-ALL by targeting the Alox15 pathway. Specifically, by mainly taking a genetic approach using gene knockout mice and CRISPR-Cas9 technology, we will test our hypothesis by revealing the roles of Alox15 and its related pathways in B-ALL development and in the response of B-ALL cells to TKIs. If successful, the results will have a huge impact on our better understanding of disease mechanisms for B-ALL and help to identify novel targets in treating TKI-insensitive human B-ALL that still lacks effective therapies. The specific aims are: 1) To investigate the role of Alox15 lipid metabolites in promoting growth and inducing TKI resistance of B-ALL cells; 2) To study the roles of Alox15-regulated key partner genes in BCR-ABL-induced B-lymphoid transformation and resistance of leukemia cells to TKIs; and 3) To develop a therapeutic strategy for circumventing TKI resistance in human B-ALL by inhibiting the Alox15 pathway.