PMC8514815_01
Schematic representation showing timeline of treatment course and clinical information. FLAI-5, fludarabine-cytarabine-idarubicin; Allo-SCT, allogeneic stem cell transplantation; WBC, white blood cells; Hb, hemoglobin; PLTs, platelets.
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After transplant, she remained in complete remission until the last follow-up.  Figure 1  summarizes relevant clinical course and diagnostic results.
Sanger sequencing chromatogram showing the FLT3 deletion identified in the BM at diagnosis. TMD, transmernbrane domain; JMD, juxtamembrane domain; TKD, tyrosine kinase domain.
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The mutation was confirmed by Sanger sequencing ( Figure 2 ) and mutant-to-wild-type allelic ratio (AR) was obtained through PCR-electrophoresis and fragment analysis (FLT3-ITD-AR=1.1).
Western blot analysis of FLT-3 expression and of its down-stream signalling pathway. (A) Analysis of patient cells at two different time points (Dx: diagnosis with FLT3 carrying the c.1770_1784del15; CR: complete remission with wt FLT3). (B) Analysis of 5 AML patients with wt FLT3 along with 5 patients carrying FLT3-ITD, used as control of FLT3 downstream signalling. BM, bone marrow; PBL, peripheral blood.
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Figure 3A , we observed that the deletion in the JM domain resulted in the constitutive activation of FLT3, with the sample at diagnosis showing increased levels of phosphorylated FLT3 and of its downstream signalling molecules. Five AML patients with wild-type (wt) FLT-3 and 5 AML patients carrying canonical FLT3-ITD mutations (with an AR ranging from 0.8 to 1.5) were used as control for protein expression levels of FLT3 downstream signalling molecules ( Figure 3B ).
Effects of increasing doses of midostaurin on the clonogenic capacity of primary BM and PBL cells carrying the reported FLT3 deletion (c.1770_1784del15; p.Phe590_Arg595delinsLeu).
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Midostaurin induced a dose-dependent reduction in colony formation with an LD50 of 100nM, suggesting that the newly reported mutation is sensitive to midostaurin inhibition ( Figure 4 ).