[Allogeneic stem cell transplantation in the management of acute myeloid leukemia]

Small-molecule inhibition of BRD4 as a new potent approach to eliminate leukemic stem- and progenitor cells in acute myeloid leukemia AML

Acute myeloid leukemia (AML) is a life-threatening stem cell disease characterized by uncontrolled proliferation and accumulation of myeloblasts. Using an advanced RNAi screen-approach in an AML mouse model we have recently identified the epigenetic ‘reader’ BRD4 as a promising target in AML. In the current study, we asked whether inhibition of BRD4 by a small-molecule inhibitor, JQ1, leads to growth-inhibition and apoptosis in primary human AML stem- and progenitor cells. Primary cell samples were obtained from 37 patients with freshly diagnosed AML (n=23) or refractory AML (n=14). BRD4 was found to be expressed at the mRNA and protein level in unfractionated AML cells as well as in highly enriched CD34⁺/CD38⁻ and CD34⁺/CD38⁺ stem- and progenitor cells in all patients examined. In unfractionated leukemic cells, submicromolar concentrations of JQ1 induced major growth-inhibitory effects (IC₅₀ 0.05-0.5 μM) in most samples, including cells derived from relapsed or refractory patients. In addition, JQ1 was found to induce apoptosis in CD34⁺/CD38⁻ and CD34⁺/CD38⁺ stem- and progenitor cells in all donors examined as evidenced by combined surface/Annexin-V staining. Moreover, we were able to show that JQ1 synergizes with ARA-C in inducing growth inhibition in AML cells. Together, the BRD4-targeting drug JQ1 exerts major anti-leukemic effects in a broad range of human AML subtypes, including relapsed and refractory patients and all relevant stem- and progenitor cell compartments, including CD34⁺/CD38⁻ and CD34⁺/CD38⁺ AML cells. These results characterize BRD4-inhibition as a promising new therapeutic approach in AML which should be further investigated in clinical trials.

Evaluation of in vivo antineoplastic effects of rapamycin in patients with chemotherapy-refractory AML

BACKGROUND

The mammalian target of rapamycin (mTOR) has recently been identified as a potential target in acute myeloid leukemia (AML).

METHODS

We treated 5 patients with chemotherapy-refractory AML with the mTOR-inhibitor rapamycin at 2mg per os daily for 14 days, with dose adjustment allowed to reach a target serum rapamycin concentration of 10-20 ng/mL. Four of five patients received additional hydroxyurea at constant dose during treatment with rapamycin.

RESULTS

Two patients achieved a leukocyte response, in one of them, a prolonged response was seen. In the other patients, blast counts remained stable or increased during rapamycin therapy. We did not observe severe hematologic or non-hematologic side effects of rapamycin.

CONCLUSION

Rapamycin at 2mg per day acts mildly cytoreductive in a subgroup of patients with refractory AML. Higher doses and drug combinations may be required to obtain long lasting anti-leukemic effects in these patients.