The Combination of ATRA and Dasatinib for Differentiation Therapy in Acute Myeloid Leukemias with IDH Mutations

Acute myeloid leukemia (AML) is characterized by the accumulation of malignant blasts with impaired differentiation programs due to recurrent mutations, amongst which IDH mutations occur in 15% of AML patients. Here, we show both in vitro as well as in a xenografted mouse model,

that clinically achievable doses of ATRA are sufficient to achieve a terminal granulocytic differentiation in primary AML samples and in AML cell lines harboring IDH1-R132H mutation. There is no effect at this concentration on the WT controls. This is associated with reduction of both proliferation and colony formation, and further leads to apoptosis, thereby improving overall survival of mutant xenografted mice.

We further showed, through transcriptomic and western blot analysis, that specific ATRA sensitivity is due to overexpression and activation of C/EBPα in the presence of IDH1-R132H mutation. This primes blasts into myeloid differentiation.

Moreover, IDH1 R132H mutation also reduces LYN activation, and thus, also sensitizes to clinically achievable doses of dasatinib, a LYN inhibitor. As ATRA induces a brief LYN activation, which transiently reduces ATRA activity, its combination with dasatinib synergistically increases differentiation. In vivo, the combination of ATRA and dasatinib reduces tumor growth of mutant xenografted mice.

The combination ATRA and dasatinib might also be considered for other IDH mutations that produce 2-hydroxyglutarate, since treatment with the mutant-specific oncometabolite (eg. 2-hydroxyglutarate) sensitizes AML cells to ATRA and dasatinib-induced differentiation.

Finally, ATRA also reduces BCL2 expression specifically in the presence of IDH1 R132H mutation. Since it has been shown that IDH mutations increase BCL2 dependence in leukemic cells, our results identified a subgroup of patients that is likely to respond to pharmacologic concentrations of ATRA.

To conclude, our data provide the preclinical rationale for investigating the use of the combination ATRA and dasatinib in a subgroup of patients who carry IDH1 R132H mutation, in clinical trials. The addition of a BCL2 inhibitor such as ABT-199 would also be considered.