Chaetocin Exhibits Anti-Leukemia Activity Against Chronic Myeloid Leukemia Stem Cells
Bibliographic record
Abstract
Abstract Abstract 1667 Treatment of chronic myeloid leukemia (CML) patients with tyrosine kinase inhibitors (TKIs) targeting BCR-ABL kinase results in a dramatic reduction in proliferating BCR-ABL expressing leukemia cells. However, these agents do not eliminate the CML stem cell population, indicating that inhibiting BCR-ABL kinase activity alone is not sufficient to eradicate the disease, and implicating TKI-insensitive CML stem cells in relapse. Thus, there is great interest in identifying new therapeutic agents that can be combined with TKIs to eliminate TKI-insensitive CML stem cells that are not fully addicted to BCR-ABL. Chaetocin, a mycotoxin that inhibits histone methyltransferase SUV39H1, exhibits anticancer properties against myeloma and AML cells. To investigate a potential role for chaetocin in CML treatment, we first compared its cytotoxic effects with those of imatinib on TonB210, a murine hematopoietic cell line with doxycycline-inducible BCR-ABL expression that is dependent on BCR-ABL for survival and proliferation in the absence of exogenous IL-3. As expected, imatinib treatment produced cytotoxic effects in TonB210 cells induced to express BCR-ABL, but not in uninduced TonB210 cells, as assessed by trypan blue viability assays and Annexin V expression by flow cytometry. In contrast, chaetocin, displayed significant cytotoxicity against both TonB210 cells induced to express BCR-ABL and uninduced TonB210 cells. We then used a standard murine retroviral transduction system that models CML blast crisis (BC-CML) to study chaetocin effects on BCR-ABL expressing cells highly enriched for leukemia initiating potential. Purified LIN-, Sca-1+, CD117+ cells (LSKs) were isolated from the bone marrow of C57BL6/J mice and retrovirally-transduced with BCR-ABL-GFP and Nup98/HoxA9-YFP then injected intravenously into recipient C57BL6/J mice. All animals developed leukemia within 21 days characterized by leukocytosis and extensive infiltration of bone marrow and spleen with leukemic blasts. LSKs expressing both BCR-ABL-GFP and Nup98/HoxA9-YFP (GFP+/YFP+ LSKs) were purified from the spleens or bone marrows of leukemic mice and cultured for 48 hrs in chaetocin across a range of concentrations (0 – 400 nM). Chaetocin exhibited cytotoxic effects against GFP+/YFP+ LSKs as assessed by trypan blue, Annexin V, and colony forming assays. Chaetocin effects on CML stem cell self-renewal in vivo were assessed by performing secondary transplantation assays and limiting dilution analysis (LDA). GFP+/YFP+ LSKs were purified from primary CML mice and transplanted into secondary recipients following in vitro exposure to IC50 concentrations of chaetocin and/or imatinib. Survival after transplantation and LSC frequency were compared in four treatment cohorts: Group 1 (untreated control), Group 2 (chaetocin), Group 3 (imatinib) and Group 4 (chaetocin + imatinib). Compared to untreated mice, survival was significantly prolonged in mice treated with imatinib alone and the survival benefit of imatinib was enhanced by co-treatment with chaetocin. LDA showed both chaetocin and imatinib treatment alone decreased LSC frequency (1 in 10,143 in chaetocin treated, and 1 in 95,782 in imatinib treated vs. 1 in 4,036 in untreated control) but that the combination of chaetocin and imatinib treatment resulted in a dramatic decrease in LSC frequency (1 in 293,628 in chaetocin + imatinib treatment vs. 1 in 4036 in untreated control). Chaetocin, imatinib, and chaetocin + imatinib treatment of normal murine hematopoietic stem cells resulted in only minimal cytotoxicity as assessed by trypan blue, Annexin V, and colony forming assays. Our findings suggest that chaetocin, or chaetocin-related compounds, might serve to complement TKI therapy in the treatment of CML. Disclosures: No relevant conflicts of interest to declare.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".