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Published on: October 17, 2025
Imipramine blue sensitively and selectively targets FLT3-ITD positive acute myeloid leukemia cells
Jonathan Metts1,2, Heath L Bradley1,2, Zhengqi Wang1,2
1Department of Pediatrics, Division of Hem/Onc/BMT, Emory University, Atlanta, GA, USA.
Abstract:
Aberrant cytokine signaling initiated from mutant receptor tyrosine kinases (RTKs) provides critical growth and survival signals in high risk acute myeloid leukemia (AML). Inhibitors to FLT3 have already been tested in clinical trials, however, drug resistance limits clinical efficacy. Mutant receptor tyrosine kinases are mislocalized in the endoplasmic reticulum (ER) of AML and play an important role in the non-canonical activation of signal transducer and activator of transcription 5 (STAT5). Here, we have tested a potent new drug called imipramine blue (IB), which is a chimeric molecule with a dual mechanism of action. At 200-300 nM concentrations, IB is a potent inhibitor of STAT5 through liberation of endogenous phosphatase activity following NADPH oxidase (NOX) inhibition. However, at 75-150 nM concentrations, IB was highly effective at killing mutant FLT3-driven AML cells through a similar mechanism as thapsigargin (TG), involving increased cytosolic calcium. IB also potently inhibited survival of primary human FLT3/ITD+ AML cells compared to FLT3/ITDneg cells and spared normal umbilical cord blood cells. Therefore, IB functions through a mechanism involving vulnerability to dysregulated calcium metabolism and the combination of fusing a lipophilic amine to a NOX inhibiting dye shows promise for further pre-clinical development for targeting high risk AML.
Insights
A novel drug, imipramine blue (IB), effectively targets high-risk acute myeloid leukemia (AML) by inhibiting STAT5 and disrupting calcium metabolism in FLT3-mutated cells. IB shows promise for pre-clinical development against AML.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Aberrant cytokine signaling from mutant receptor tyrosine kinases (RTKs) drives high-risk acute myeloid leukemia (AML).
- FLT3 inhibitors face drug resistance, limiting clinical efficacy.
- Mutant RTKs in AML mislocalize to the endoplasmic reticulum (ER), activating Signal Transducer and Activator of Transcription 5 (STAT5).
Purpose of the Study:
- To evaluate the efficacy of imipramine blue (IB), a novel chimeric drug, against FLT3-mutated AML.
- To elucidate the dual mechanism of action of IB in AML cells.
Main Methods:
- Testing imipramine blue (IB) on FLT3-mutated AML cell lines and primary human cells.
- Assessing IB's effects on STAT5 inhibition, NADPH oxidase (NOX) activity, and cytosolic calcium levels.
- Comparing IB's efficacy against FLT3/ITD+ and FLT3/ITD- AML cells, and normal cells.
Main Results:
- IB potently inhibits STAT5 at 200-300 nM via NOX inhibition and phosphatase activity.
- IB effectively kills FLT3-driven AML cells at 75-150 nM by increasing cytosolic calcium, similar to thapsigargin (TG).
- IB significantly inhibits primary FLT3/ITD+ AML cells while sparing normal cells.
Conclusions:
- IB exhibits a dual mechanism of action, targeting both STAT5 and calcium metabolism in AML.
- IB's efficacy against high-risk AML, particularly FLT3-mutated types, highlights its therapeutic potential.
- The combination of a lipophilic amine and a NOX inhibiting dye in IB offers a promising strategy for AML treatment development.
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