AbstractsBiology & Animal Science

KIT inhibition with dasatinib represents a promising approach to targeted therapy in t(8;21) acute myeloid leukemia (AML) and clinical trials are currently evaluating its clinical relevance. However, data on continuous long-term dasatinib exposure of AML cells are limited and the potential effects on KIT inhibition and dasatinib sensitivity are unexplored. Treatment-related resistance ultimately limits clinical efficacy of tyrosine kinase inhibitors (TKI), which could similarly apply to dasatinib in t(8;21) AML. In this study, we used the dasatinib-sensitive KITmut t(8;21) AML cell line Kasumi-1 to model, in a confined and control- lable way, molecular effects upon continuous dasatinib treatment. Long-term dasatinib exposure at clinically relevant levels resulted in markedly decreased drug-sensitivity of KITmut t(8;21) AML cells. Notably, all dasatinib-resistant clones lacked secondary KIT-mutations. Instead, persistent growth correlated with alterations in KIT expression levelsdthat is, either KIT overexpression with maintained downstream signaling or KIT downregulation with concomitant activation of alternate pathways. Although KIT overexpression was associated with retained receptor activity and STAT3 activation, KIT downregulation correlated with decreased STAT3 levels and increased ERK-signaling. Importantly, brief discontinuation of dasatinib restored dasatinib-sensitivity associated with reversal of signaling signatures similar to treatment-naive, dasatinib-sensitive cells. The observed desensitization of KITmut t(8;21) AML cells upon continuous dasatinib exposure suggests that therapy-related acquisition of resistance could pose significant limitations on therapeutic efficiency. Notably, we identified TKI-resistant states of transient nature that correlate with alterations in KIT expression and can be reversed upon brief inhibitor withdrawal. These findings indicate that discontinu- ing treatment maintains dasatinib sensitivity in KITmut AML cells.