Inhibition of the Mitochondrial Protein Import Machinery Is Selectively Cytotoxic to Acute Myeloid Leukemia (AML) Cells and Stem Cells
Bibliographic record
Abstract
Abstract A subset of AML and stem cells have increased mitochondrial stress and increased expression of mitochondrial proteases that degrade misfolded mitochondrial proteins. Given the recent findings of the interplay between mitochondrial homeostasis and mitochondrial protein import, we hypothesized that AML cells have an increased reliance on mitochondrial protein import as a compensatory mechanism for increased mitochondrial stress. To test this hypothesis, we measured expression levels of key mitochondrial protein import genes in publicly available datasets (GSE30377, GSE42414 and GSE 24759) and demonstrated their up regulation in a subset of AML cells over normal hematopoietic cells. Increased expression occurred across the spectrum of molecular mutations and cytogenetic abnormalities. Moreover, expression levels of mitochondrial protein import genes were enriched in functionally defined AML stem cells over bulk cells. To assess the impact of inhibiting mitochondrial protein import in AML, we knocked down the outer mitochondrial membrane import channel TOM40, the inner membrane import channel Tim23 and the oxidase ALR, that folds proteins through a disulfide relay system in the mitochondrial inner membrane space and is a rate limiting step for the import of a subset of mitochondrial proteins. Knockdown of these targets in OCI-AML2, TEX and U937 leukemia cells with shRNA reduced growth and viability of AML cells. Knockdown of ALR targeted the leukemia initiating cells as it abrogated engraftment of TEX leukemia cells into immune deficient mice (shRNA ALR = 5.481 +/- 0.9 % engraftment vs shRNA control= 29.44 +/- 5.4 % engraftment; p =0.0004) . Mechanistically, knockdown of mitochondrial import genes reduced levels of nuclear (ATP5A, SDHB and NDUFB8), but not mitochondrial (CoxII) encoded proteins of the OXPHOS chain. This in turn led to decreased basal oxygen consumption in leukemic cells. As a chemical approach to investigate the impact of inhibiting mitochondrial protein import in AML and normal cells, we tested the effects of MitoBloCK-6 and related analogues that selectively inhibit ALR in zebrafish, hESCs and yeast models. MitoBloCK-6 and related analogues killed leukemia cell lines (OCI-AML2, TEX, Jurkat and NB4) with an IC50of 5-10 µM. At these concentrations, MitoBloCK-6 decreased levels of nuclear (ATP5A, SDHB and NDUFB8), but not mitochondrial encoded (CoxII) proteins of the OXPHOS chain. Demonstrating the functional importance of changes in mitochondrial metabolism by these compounds, rho zero 143B rhabdomyosarcoma cells that lack mitochondrial DNA and rely solely on glycolysis were resistant to MitoBloCK-6. Finally, we tested the effects of MitoBloCK-6 on primary AML and normal cells. Treatment with MitoBloCK-6 (2 µM) inhibited clonogenic growth of (4 of 5) primary AML > 64% but produced <3% loss of clonogenic growth in normal hematopoietic cells. Finally, in an OCI-AML2 xenograft model, systemic administration of MitoBloCK-6 reduced tumor growth > 50% of control without toxicity. Thus, we have demonstrated that AML cells have a unique reliance on mitochondrial protein import and inhibition of this pathway may be a new therapeutic strategy to selectively target a subset of AML and AML stem cells. Disclosures Schimmer: Novartis: Honoraria.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".