Oncofusion

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Experimentmoderate confidence 3 of 5: One strong study, or several smaller consistent ones.Q3b-dot1l-h3k79

Measure all three H3K79 states on a real scale, across a dose series and after a menin inhibitor - the measurement this whole field has been doing by proxy

also called state-resolved ICeChIP dose series · H3K79me1/2/3 calibrated ChIP in KMT2A-rearranged cells · residual H3K79me2 after menin inhibition

Nobody has measured the three versions of the H3K79 tag separately, on an absolute scale, in this leukaemia. Doing so across a range of drug doses would answer whether a DOT1L drug leaves a partial tag behind, and whether a menin drug removes only half of it - two predictions the project's central ideas rest on.

The same thing, for a scientist

Every H3K79 measurement this beat found, including the pharmacodynamic endpoint of the pinometostat trial, is a **relative** measurement with a state-specific antibody. The states co-occur on one residue because the enzyme is distributive [E1], so antibody cross-reactivity is not a small correction, and the only calibrated measurement in this disease - ICeChIP in the non-canonical-pathway study - found H3K4me3 **rising** and H3K27me3 **falling** at the same loci where H3K79me2 fell [E2], which is precisely the situation in which relative scaling misleads. **Design.** In a KMT2A::MLLT3 and a KMT2A::AFF1 line, run calibrated internal-standard ChIP-seq for H3K79me1, me2 and me3 separately across (a) a **10-point pinometostat dose series** spanning the FLT3 and HOXA9 regimes, (b) a **time series over five cell divisions** at fixed saturating exposure, and (c) **menin inhibition to full target engagement, with and without MLLT10 knockout**. **Three questions answered at once.** Does partial DOT1L inhibition leave me1 behind or go to zero (`mark-h3k79me1`)? Do the state ratios move together, as distributive kinetics predict, or do loci hold ratios, as the zoning model predicts (`mechanism-h3k79-nonprocessive-deposition`)? And is residual H3K79me2 after menin inhibition MLLT10-dependent, as the two-unit model predicts [E3]? Cost tier: medium. Timeline: 6-12 months.

Go deeper
Why calibration is the design, not a refinement

Internal-standard calibrated ChIP spikes in semisynthetic nucleosomes carrying defined modifications and defined barcodes, so the recovered signal can be expressed as a fraction of nucleosomes carrying the mark rather than as a fold-enrichment. Three things become possible that are not possible otherwise:

  1. Cross-reactivity is measured rather than assumed. Spike-ins for me1, me2 and me3 reveal directly how much of an 'me2' signal is me1 or me3. For a residue whose states co-occur, this is the difference between a result and an artefact.
  2. Absolute occupancy makes doses comparable across experiments. 'H3K79me2 reduced by 60%' means something only with a denominator.
  3. Marks moving in opposite directions can be interpreted. The published ICeChIP result - H3K4me3 up, H3K27me3 down, H3K79me2 down at the same loci 2 - would look like a normalisation artefact in a relative assay.

This matters beyond the experiment. If the dose series shows that a conventional ChIP over-reports depletion, then every pharmacodynamic claim about DOT1L inhibitors, including the trial's, is on an unknown scale, and that is a finding in itself.

The three sub-experiments and what each settles

(a) Dose series, 10 points, single time point. Plot absolute occupancy of each state at fusion-target gene bodies, at KEE enhancers and genome-wide. Read off whether the me2-to-me1 boundary is crossed before or after the HOXA9/MEIS1 collapse, and whether the FLT3 regime coincides with a partial or a complete depletion. Settles: what state a clinically achievable exposure actually leaves behind.

(b) Time series, saturating exposure, five divisions. With no eraser, loss should track histone replacement 4. Measure clearance half-life per locus and correlate with nucleosome turnover at the same loci. Settles: the clearance clock - the number of divisions a schedule has to cover, and whether the broad HOXA domains are the slowest to clear.

(c) Menin inhibition, with and without MLLT10. Full target engagement, then measure residual H3K79me2 at fusion targets and genome-wide; repeat in MLLT10 knockout. Settles: whether the two-unit partition 3 holds at endogenous loci in a human leukaemia line, and whether it holds in KMT2A::AFF1, where it has never been shown.

Sub-experiment (c) is the highest-value and the cheapest, because it is one drug, two genotypes and one readout.

Facts and figures
designCalibrated internal-standard ChIP-seq (ICeChIP) for H3K79me1, H3K79me2 and H3K79me3 separately in a KMT2A::MLLT3 and a KMT2A::AFF1 line, across three arms: (a) a 10-point pinometostat dose series spanning the FLT3 and HOXA9/MEIS1 regimes at a fixed time point; (b) a time series over five cell divisions at fixed saturating exposure, with nucleosome turnover measured at the same loci; (c) menin inhibition to full target engagement, with and without MLLT10 knockout.
readoutabsolute fraction of nucleosomes carrying each methylation state, at fusion-target gene bodies, at H3K79me2/3 enhancer elements (KEEs) and genome-wide; per-locus clearance half-life in arm (b); MLLT10-dependence of the residual fraction in arm (c)
controlsspike-in semisynthetic nucleosomes for all three states to quantify antibody cross-reactivity directly; a KMT2A-germline leukaemia line; DOT1L knockout as the zero-methylation floor; vehicle time-matched controls at every division
cost tiermed
timeline6-12 months
cheapest high value armarm (c) - one drug, two genotypes, one readout
secondary finding if it worksif conventional ChIP over-reports depletion relative to calibrated ChIP, every published DOT1L pharmacodynamic claim including the trial's is on an unknown scale
tests hypotheses
[
  "hyp-menin-inhibition-spares-endogenous-h3k79-unit",
  "hyp-pinometostat-wrong-modality"
]
questions settled
[
  "whether partial DOT1L inhibition leaves H3K79me1 behind or reaches zero",
  "whether state ratios move together (distributive/redundancy) or loci hold ratios (zoning)",
  "the clearance clock in cell divisions, per locus class",
  "whether residual H3K79me2 after menin inhibition is MLLT10-dependent, and whether the partition holds in KMT2A::AFF1"
]
How this could bite us back
  • Spike-in nucleosomes do not sit in the same chromatin context as endogenous ones, so calibration is better than relative scaling and is not absolute truth - and the contexts where the difference is largest are the compacted broad domains this experiment most wants to measure.
  • If the answer is that state ratios simply track total flux, the experiment confirms that the three-state granularity this beat introduced adds little, which is a real possible outcome and is why the hypothesis it tests is held as speculative.
Still open
  1. Are semisynthetic nucleosome standards for all three H3K79 methylation states commercially available, or would they have to be made? The whole design depends on them.
  2. How is 'full target engagement' defined for a menin inhibitor in arm (c)? Without an independent measure of menin occupancy, a small residual H3K79me2 is indistinguishable from incomplete dosing.
  3. Can nucleosome turnover be measured at the same loci in the same cells, or does it require a separate system whose turnover rates may not transfer?
Every source behind this entry (4)
  1. E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    Dot1 introduces multiple methyl groups by a non-processive mechanism, so the H3K79 methylation states cannot be generated independently and co-occur, and the authors note that multiple methylation is expected to limit regulation by putative demethylases or binding proteins.

    Nonprocessive methylation by Dot1 leads to functional redundancy of histone H3K79 methylation states. · Frederiks F, Tzouros M, Oudgenoeg G, et al. · Nat Struct Mol Biol 2008
    PMID 18511943DOI
    What this evidence cannot show

    Abstract read from the eutils record; full text not read. Yeast. Cited as the reason state-specific antibody cross-reactivity is a first-order problem on this residue rather than a routine caveat.

    Evidence that argues against this (1)
    • If the zoning model is right and loci are dominated by single states, then cross-reactivity is a smaller problem than the co-occurrence argument implies - and the experiment would then be testing a premise that is already false. The design is agnostic between the models, which is the point, but the motivation is not. Park NH et al. 2026
  2. E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    By ICeChIP-seq in MLL-rearranged leukaemia cells, H3K79me2 is markedly depleted at pinometostat-downregulated and MLL-fusion target genes with paradoxical increases of H3K4me3 and loss of H3K27me3; low pinometostat concentrations act through FLT3 downregulation rather than through HOXA9 and MEIS1.

    PMID 34263728DOI
    What this evidence cannot show

    Abstract read from the eutils record; full text not read. This is the only calibrated H3K79 measurement this beat's reading found in this disease, and it reports H3K79me2 alone - not the three states side by side, which is the gap this experiment fills. Cell lines; 'some MLL-rearranged leukemias' without a denominator.

    Evidence that argues against this (1)
    • Calibrated ChIP has its own failure modes: spike-in nucleosomes do not experience the same chromatin context as endogenous ones, and recovery can differ between a naked semisynthetic nucleosome and one inside a compacted domain. Calibration reduces the scale problem without eliminating it, and a broad HOXA domain is exactly the context where the difference would be largest. Sharma P et al. 2022
  3. E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    CRISPR-ChIP partitions H3K79 methylation into an oncogenic DOT1L complex directed by the MLL fusion in a menin-dependent manner and a separate endogenous DOT1L complex directed by MLLT10, which predicts a measurable MLLT10-dependent residue of H3K79me2 after menin inhibition.

    CRISPR-ChIP reveals selective regulation of H3K79me2 by Menin in MLL leukemia. · Gilan O, Talarmain L, Bell CC, et al. · Nat Struct Mol Biol 2023
    PMID 37679565DOI
    What this evidence cannot show

    Abstract read from the eutils record; full text not read. The pooled screen is reporter-based, but the partition is not reporter-only: GSE192555 holds genome-wide H3K79me2 ChIP-seq for six arms plus FLAG-MLLAF9 occupancy, so the partition is supported at endogenous loci as well. **The fusion is now resolved and it is not the index fusion: murine MLL-AF9.** It is not named in the abstract, and the full text is unreachable, but the study's GEO depositions name it per sample. In GSE192555 all eight H3K79me2 ChIP-seq samples are Mus musculus with `cell type: MLLAF9`, including both DOT1L-KO guides, both MLLT10-KO guides and **the menin-inhibitor arm** (GSM5751590). GSE192561 is 24/24 murine. Across all 65 samples in the three series, **none mentions AFF1, AF4 or any AFF-family gene**. The human arm is K562 — a CML line with no KMT2A rearrangement — carrying H3K4me3, Pol II, and five H3K79me2 samples used as a mouse/human library-mix species-spike normalisation under a DOT1L inhibitor, not as a fusion system. So this result reaches KMT2A::AFF1 only by import across fusion, species and lineage at once. Verified by the coordinator directly against the GEO SOFT records on 2026-09-19. Originally recorded as reporter-only with an unnamed fusion - which is why sub-experiment (c) is specified to run in both a KMT2A::MLLT3 and a KMT2A::AFF1 line.

    Evidence that argues against this (2)
    • Menin inhibition displaces the fusion from chromatin, so any locus-specific loss of H3K79me2 after menin inhibition could follow from the fusion leaving rather than from menin regulating a DOT1L complex. The MLLT10 knockout arm is what discriminates, and if the residue is MLLT10-independent the experiment returns an uninterpretable middle result. Neville D et al. 2026
    • The fusion behind this result is murine MLL-AF9, not KMT2A::AFF1 — established from the study's own GEO depositions, since the full text is unreachable. Every H3K79me2 sample in GSE192555 is Mus musculus, cell type MLLAF9, and no sample in any of the three series mentions an AFF-family gene. The menin-dependence of the oncogenic unit, which is the part this graph leans on hardest, was measured in mouse myeloid MLL-AF9 cells. KMT2A::AFF1 engages DOT1L through a different architecture — AFF1 carries neither the AHD that MLLT3 and MLLT1 use nor the AF10 OM-LZ — so the partition may not transfer, and `hyp-index-fusion-h3k79-is-entirely-endogenous` is the sharper alternative. NCBI Gene Expression Omnibus 2022
  4. E4strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper

    H3K79 methylation has a single writer and no known demethylase, and the valency of H3K79 methylation is determined by nucleosome turnover rates, with propagation across the genome predicted by turnover simulations.

    Nucleosome Turnover Regulates Histone Methylation Patterns over the Genome. · Chory EJ, Calarco JP, Hathaway NA, et al. · Mol Cell 2019
    PMID 30472189DOI
    What this evidence cannot show

    Abstract read from the eutils record; full text not read. PubMed types the record as a Meta-Analysis in part. Chemical-induced proximity is an artificial recruitment regime. Cited here to justify the time-series arm's design - measuring clearance against nucleosome turnover at the same loci - rather than for a quantitative prediction.

    Evidence that argues against this (1)
    • If a claimed H3K79 demethylase such as KDM2B is real, clearance would not track nucleosome turnover and the time-series arm would return a rate the turnover model cannot explain. That would be an informative failure, but the experiment as designed would not immediately identify the cause. Kang JY et al. 2018
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