Dual Inhibition of FLT3 and AXL by Gilteritinib Overcomes Hematopoietic Niche-Driven Resistance Mechanisms in FLT3-ITD Acute Myeloid Leukemia.

PURPOSE: AXL has been shown to play a pivotal role in the selective response of FLT3-ITD acute myeloid leukemia (AML) cells to FLT3 tyrosine kinase inhibitors (TKI), particularly within the bone marrow microenvironment. EXPERIMENTAL DESIGN: Herein, we compared the effect of dual FLT3/AXL-TKI gilteritinib with quizartinib through in vitro models mimicking hematopoietic niche conditions, ex vivo in primary AML blasts, and in vivo with dosing regimens allowing plasma concentration close to those used in clinical trials. RESULTS: We observed that gilteritinib maintained a stronger proapoptotic effect in hypoxia and coculture with bone marrow stromal cells compared with quizartinib, linked to a dose-dependent inhibition of AXL phosphorylation. In vivo, use of the MV4-11 cell line with hematopoietic engraftment demonstrated that gilteritinib was more effective than quizartinib at targeting leukemic cells in bone marrow. Finally, FLT3-ITD AML patient-derived xenografts revealed that this effect was particularly reproducible in FLT3-ITD AML with high allelic ratio in primary and secondary xenograft. Moreover, gilteritinib and quizartinib displayed close toxicity profile on normal murine hematopoiesis, particularly at steady state. CONCLUSIONS: Overall, these findings suggest that gilteritinib as a single agent, compared with quizartinib, is more likely to reach leukemic cells in their protective microenvironment, particularly AML clones highly dependent on FLT3-ITD signaling.

Verteporfin targeting YAP1/TAZ-TEAD transcriptional activity inhibits the tumorigenic properties of gastric cancer stem cells.

Gastric carcinomas (GC) are heterogeneous tumors, composed of a subpopulation of cluster of differentiation-44 (CD44)+ tumorigenic and chemoresistant cancer stem cells (CSC). YAP1 and TAZ oncoproteins (Y/T) interact with TEA domain family member 1 (TEAD) transcription factors to promote cell survival and proliferation in multiple tissues. Their activity and role in GC remain unclear. This work aimed to analyze Y/T-TEAD activity and molecular signature in gastric CSC, and to assess the effect of verteporfin, a Food and Drug Administration-approved drug preventing Y/T-TEAD interaction, on gastric CSC tumorigenic properties. Y/T-TEAD molecular signature was investigated using bioinformatical (KmPlot database), transcriptomic and immunostaining analyses in patient-derived GC and cell lines. Verteporfin effects on Y/T-TEAD transcriptional activity, CSC proliferation and tumorigenic properties were evaluated using in vitro tumorsphere assays and mouse models of patient-derived GC xenografts. High expressions of YAP1, TAZ, TEAD1, TEAD4 and their target genes were associated with low overall survival in nonmetastatic human GC patients (n = 444). This Y/T-TEAD molecular signature was enriched in CD44+ patient-derived GC cells and in cells resistant to conventional chemotherapy. Verteporfin treatment inhibited Y/T-TEAD transcriptional activity, cell proliferation and CD44 expression, and decreased the pool of tumorsphere-forming CD44+ /aldehyde dehydrogenase (ALDH)high gastric CSC. Finally, verteporfin treatment inhibited GC tumor growth in vivo; the residual tumor cells exhibited reduced expressions of CD44 and ALDH1, and more importantly, they were unable to initiate new tumorspheres in vitro. All these data demonstrate that Y/T-TEAD activity controls gastric CSC tumorigenic properties. The repositioning of verteporfin targeting YAP1/TAZ-TEAD activity could be a promising CSC-based strategy for the treatment of GC.

Targeting Tyrosine Kinases in Acute Myeloid Leukemia: Why, Who and How?

Acute myeloid leukemia (AML) is a myeloid malignancy carrying a heterogeneous molecular panel of mutations participating in the blockade of differentiation and the increased proliferation of myeloid hematopoietic stem and progenitor cells. The historical "3 + 7" treatment (cytarabine and daunorubicin) is currently challenged by new therapeutic strategies, including drugs depending on the molecular landscape of AML. This panel of mutations makes it possible to combine some of these new treatments with conventional chemotherapy. For example, the FLT3 receptor is overexpressed or mutated in 80% or 30% of AML, respectively. Such anomalies have led to the development of targeted therapies using tyrosine kinase inhibitors (TKIs). In this review, we document the history of TKI targeting, FLT3 and several other tyrosine kinases involved in dysregulated signaling pathways.