DOT1L808 - a 5 nM DOT1L degrader that cleared an orthotopic leukaemia and still works after menin inhibitors fail
also called DOT1L808 · DOT1L PROTAC DOT1L808
This is a molecule that does not block DOT1L but destroys it, tagging it for the cell's own disposal machinery. In mice with leukaemia it cleared the disease completely, and its sister compound still killed cells that had already become resistant to menin inhibitors.
The same thing, for a scientist
DOT1L808 is a PROTAC degrader of DOT1L reported in 2026 with a **DC50 of 5 nM**, developed on the explicit premise that DOT1L's non-enzymatic functions cannot be blocked by an active-site inhibitor and that pinometostat's limited clinical efficacy reflects that [E1]. Its companion compound **DOT1L705** (DC50 0.33 microM) shows viability effects highly dependent on MLL-rearranged status and **retains activity against menin-inhibitor-resistant cells**; DOT1L808 achieved **complete tumour regression in an orthotopic leukaemia model without overt toxicity** [E1]. Read against this graph's holdings, the compound is the first agent that could distinguish a refuted target from a wrong modality - but the two headline claims sit on **different compounds**, no haematological-toxicity comparison against a catalytic inhibitor at matched target coverage has been reported, and adult marrow is known to require DOT1L's catalytic activity, which a degrader removes along with everything else [E2]. This is preclinical chemical biology, not a clinical candidate, and this field has already had one DOT1L agent with excellent mouse data produce 2 complete remissions in 51 adults [E3].
What is new here that pinometostat could not do
Two things, and only two 1:
- It removes the protein. Every separation-of-function experiment that exists says DOT1L contributes to cell fate and to transcription elongation through activities that survive catalytic inactivation (
mechanism-dot1l-catalysis-independent-function). A degrader is the only reported modality that reaches those. - It works after menin inhibitors. Retained activity in menin-inhibitor-resistant cells is the most consequential sentence in the paper for this project, because the graph's central therapeutic bet is the menin interface and resistance to it is now documented. A DOT1L degrader is a candidate second line that does not run through the same interface.
What is not new: MLL-rearrangement-dependent killing and mouse efficacy. Pinometostat had both.
The safety question this compound makes sharper, not softer
Acute Dot1l inactivation in adult mouse marrow reduces myeloid progenitors within 7 days and then depletes long-term HSCs, and in rescue experiments wild-type and PPI-deficient DOT1L restore sustained haematopoiesis while an enzymatically inactive DOT1L does not 2. So adult blood needs the catalytic activity.
A degrader removes the catalytic activity and the scaffold. On that biology the prediction is that a DOT1L degrader is at least as myelosuppressive as a catalytic inhibitor and plausibly more so. 'Without overt toxicity' in a short orthotopic mouse experiment does not test that, and pinometostat's own safety profile in humans was clean - so a preclinical safety claim here has very little discriminating power.
The experiment that matters is a matched-exposure comparison of degrader and catalytic inhibitor with marrow readouts, which is written as exp-dot1l-degrader-vs-inhibitor-matched-exposure.
| target | gene-dot1l |
|---|---|
| modality | PROTAC degrader |
| status | preclinical chemical-biology tool, first reported 2026; no IND, no trial registered |
| dc50 NM | 5 |
| in vivo | complete tumour regression in an orthotopic leukaemia model without overt toxicity (single report) |
| e3 ligase | not stated in the abstract |
| why this entry exists | it is the first agent that could distinguish 'DOT1L is a refuted target' from 'pinometostat was the wrong modality' |
companion compound
{
"name": "DOT1L705",
"dc50_uM": 0.33,
"properties": [
"MLL-r-dependent viability effect",
"active in menin-inhibitor-resistant cells"
]
}trials
[]
key ae
[ "none reported; myelosuppression is the predicted class risk because adult marrow requires DOT1L catalytic activity" ]
resistance
[ "E3 ligase loss or downregulation (generic PROTAC liability)", "any resistance route that does not run through DOT1L, including the adaptive transcriptional rewiring documented for DOT1L inhibition in KMT2A-rearranged ALL" ]
- Adult haematopoiesis requires DOT1L's enzymatic activity, so a degrader removes exactly the function normal marrow needs - the therapeutic index that made the catalytic inhibitor safe may not survive the change of modality.
- PROTACs lose activity when the recruited E3 ligase is lost or downregulated, a resistance route that a small-molecule active-site inhibitor does not have and that would not be detected by any H3K79 pharmacodynamic assay.
- If DOT1L's leukaemic contribution is largely catalytic after all, a degrader buys nothing over pinometostat except a worse safety profile and a harder pharmacology.
- By what route were the menin-inhibitor-resistant cells resistant? Cross-resistance to a DOT1L degrader would mean something very different after a MEN1 binding-site mutation than after a lineage switch or a MEN1-independent programme.
- Is a DOT1L degrader more myelosuppressive than a catalytic inhibitor at matched target coverage? Nothing published addresses this and the separation-of-function data predict that it is.
- Does degradation work in KMT2A::AFF1, the commonest infant fusion, which reaches DOT1L neither through AF9/ENL AHD nor through AF10? The abstract reports MLL-r dependence without naming partners.
- E1weak confidence 2 of 5: Preliminary, small, indirect, or not yet peer reviewed.paper
DOT1L-targeting PROTACs DOT1L705 and DOT1L808 are potent and selective DOT1L degraders with DC50 values of 0.33 micromolar and 5 nanomolar respectively; DOT1L705's effect on cell viability is highly dependent on the MLL-rearranged status of leukaemia cell lines and it retains activity against menin-inhibitor-resistant cells; DOT1L808 achieved complete tumour regression in an orthotopic leukaemia model without overt toxicity. The programme's stated rationale is that non-enzymatic DOT1L functions cannot be blocked by enzymatic inhibitors such as pinometostat, which showed limited clinical efficacy.
Development of DOT1L-Targeted Protein Degraders for Treating MLL-r Leukemia. · Quan S, Unno K, Gupta DG, et al. · J Med Chem 2026What this evidence cannot show
Abstract read from the eutils record; full text not read. Published 2026, single report, not independently replicated. The MLL-r dependence and the menin-inhibitor-resistance result are attributed to DOT1L705 and the in vivo regression to DOT1L808, so no one compound carries both. The E3 ligase, linker, selectivity panel and pharmacokinetics are not stated in the abstract, and 'menin inhibitor-resistant cells' is not defined there - resistance route matters, since a MEN1 binding-site mutation and a lineage switch would predict very different cross-resistance. Lowered to weak on 2026-09-19: the Q18b sweep established that the menin-resistance route asserted here is undefined in the source and unrecoverable from any deposition.
Evidence that argues against this (1)
- Preclinical regression has already failed once for this target: a catalytic DOT1L inhibitor with 80 pM potency and clean preclinical efficacy produced 2 complete remissions in 51 adults, both in a single genotype. Mouse efficacy for a DOT1L agent therefore carries less evidential weight in this disease than it would for a target with no clinical history. Stein EM et al. 2018
- E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Acute Dot1l inactivation in adult mouse bone marrow reduces myeloid progenitor numbers within 7 days and subsequently depletes long-term haematopoietic stem cells; wild-type and PPI-deficient DOT1L mutants, but not an enzymatically inactive mutant, rescue sustained haematopoiesis.
Elucidating the Importance of DOT1L Recruitment in MLL-AF9 Leukemia and Hematopoiesis. · Grigsby SM, Friedman A, Chase J, et al. · Cancers (Basel) 2021What this evidence cannot show
Abstract read from the eutils record; full text not read. Mouse marrow with genetic inactivation - complete and irreversible - whereas a degrader gives partial, reversible, dose-dependent protein loss, so the severity does not transfer directly. Rescue constructs are expressed against an endogenous background at unstated levels.
Evidence that argues against this (1)
- Pharmacological inhibition of DOT1L with EPZ-5676 in vivo minimally affected mouse erythropoiesis, and the pinometostat adult trial had a clean safety profile with the maximum tolerated dose never reached. Genetic ablation may therefore substantially overstate the haematological cost of a drug-like degree of protein loss. Malcom CA et al. 2021
- E3established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
Pinometostat, an SAM-competitive DOT1L inhibitor, reduced H3K79 methylation in patients and produced 2 complete remissions among 51 adults with acute leukaemia.
The DOT1L inhibitor pinometostat reduces H3K79 methylation and has modest clinical activity in adult acute leukemia. · Stein EM, Garcia-Manero G, Rizzieri DA, et al. · Blood 2018What this evidence cannot show
Abstract read from the eutils record; full text not read. The maximum tolerated dose was never reached, so the comparison this entry makes between a degrader and 'what a catalytic inhibitor achieved' is a comparison against an exposure that was never maximised.
Evidence that argues against this (1)
- Both complete remissions were in t(11;19)/KMT2A::MLLT1. A genotype-restricted two-patient signal is not the same as a flat negative, and a degrader programme that does not stratify by fusion partner may repeat the trial's main design weakness rather than its pharmacology. Daigle SR et al. 2013
PROTAC degradation, DC50 5 nM
its entire rationale is the function a catalytic inhibitor cannot reach
- related to →Pinometostat (EPZ-5676) — the DOT1L inhibitor, and the most instructive failure in this field
the successor modality; retains activity where menin inhibitors fail
companion compound active in menin-inhibitor-resistant cells
adult marrow needs the catalytic activity a degrader removes
degrader versus catalytic inhibitor at matched time-integrated target coverage
the resistance route behind this drug's central claim is undefined and unrecoverable