Hitting the same axis at two points was predicted to be sub-additive; the one published test found synergy in all four KMT2A-rearranged lines
also called enitociclib plus MI-463 · CDK9 inhibitor menin inhibitor combination
If a menin inhibitor and a CDK9 inhibitor both block the same chain of events, blocking it twice should add little. The one experiment that tested this in KMT2A-rearranged leukaemia cells found the opposite: the two drugs together did more than the sum of their parts in every cell line tried.
The same thing, for a scientist
The reasoning that predicts sub-additivity is sound on its face: menin inhibitors displace the fusion from chromatin and CDK9 inhibitors block the kinase the fusion recruits, so the two act at successive steps of one pathway. Sharma and colleagues tested it. Enitociclib (formerly BAY 1251152 / VIP-152) combined with the menin-KMT2A inhibitor MI-463 gave **Chou-Talalay combination index values below 1 in all four KMT2A-rearranged lines tested** - MV4-11, THP-1, KOPN-8 and INL2 - with strong synergy across all concentrations in INL2 and KOPN-8 and at higher concentrations in MV4-11 and THP-1, and the combination reduced HOXA9 protein by approximately 75-85% at 24 hours against DMSO [E1]. The authors' proposed explanation is that the two drugs act on **different outputs**: MI-463 lowers HOXA9 while enitociclib lowers c-MYC and MCL-1, whose short half-lives make them the first casualties of any CDK9 block [E1]. That is a coherent reason for synergy between agents that look like they share a pathway, and it is the mechanistic point this entry exists to record. Two caveats are load-bearing. MI-463 is a tool compound, not revumenib, ziftomenib or bleximenib, so **no clinical menin inhibitor has been tested in combination with a CDK9 inhibitor in any published study** [E2]. And the same paper reports dose-dependent killing of healthy-donor PBMCs and CD34+ cells [E1].
What was actually done
| element | detail |
|---|---|
| CDK9 inhibitor | enitociclib (BAY 1251152 / VIP-152), from Selleckchem |
| Menin inhibitor | MI-463, a tool compound |
| KMT2A-rearranged lines | MV4-11, THP-1, KOPN-8, INL2 |
| KMT2A wild-type comparators | SUP-B15, AML-193 (two lines only) |
| Normal controls | healthy-donor PBMCs and bone-marrow CD34+ cells |
| Combination design | varying enitociclib against a fixed IC25 of MI-463, 72 h |
| Synergy metric | Chou-Talalay combination index, CompuSyn v1.0 |
| Result | CI < 1 in all four KMT2A-rearranged lines; HOXA9 protein down ~75-85% at 24 h |
The individual CI values appear only in a figure panel (Fig 5B) that this reader could not read, so no number beyond 'CI < 1' is quoted here. The paper reports MV4-11 CI values of 0.9 with doxorubicin and 0.5 with prednisolone for comparison, which gives a sense of the scale the authors are working at 1.
Why the naive prediction failed, and what that implies for the reservoir question
The prediction of sub-additivity assumes the two drugs converge on one output. They do not. Menin inhibition removes the fusion from its target loci and lowers HOXA9; CDK9 inhibition lowers c-MYC and MCL-1 globally by starving short-lived transcripts. A cell can survive one and not the other, so the combination is closer to hitting two pathways than one pathway twice 1.
For this beat the implication is specific. The synergy does not require the reservoir to be involved at all. It is fully explained by two different downstream outputs, and nothing in the paper measures free versus sequestered P-TEFb. So this result answers the brief's question - is the combination sub-additive? no, it is synergistic - without bearing on whether KMT2A-rearranged cells have an altered 7SK partition. Those remain separate questions and hyp-kmt2a-aff1-shifts-the-free-versus-sequestered-ptefb-balance is still open.
The bounded absence around it
On 2026-09-20, "menin inhibitor"[tiab] AND (CDK9[tiab] OR "CDK9 inhibitor"[tiab]) returned zero records, and a broad query naming revumenib, SNDX-5613, VTP-50469, ziftomenib, KO-539, MI-3454, bleximenib and the phrases 'menin inhibitor'/'menin inhibition' against CDK9, alvocidib, flavopiridol, AZD4573, dinaciclib, atuveciclib and KB-0742 returned exactly one record - this one 2. There is no in vivo combination study, no patient-derived xenograft, no trial. A single in vitro paper with two sponsor-employed authors is the entire evidence base.
| mechanism class | pharmacological interaction |
|---|---|
| drug a | enitociclib (BAY 1251152 / VIP-152), CDK9 inhibitor |
| drug b | MI-463, menin-KMT2A inhibitor (tool compound) |
| synergy metric | Chou-Talalay combination index (CompuSyn v1.0), CI<1 = synergy |
| result | CI<1 in 4/4 KMT2A-rearranged lines; HOXA9 protein down ~75-85% at 24 h |
| proposed basis | non-overlapping outputs - MI-463 lowers HOXA9, enitociclib lowers MYC and MCL-1 |
| reservoir involvement | none measured; free versus sequestered P-TEFb was not assayed |
| clinical menin inhibitor tested | false |
| in vivo | false |
cell lines index
[ "MV4-11", "THP-1", "KOPN-8", "INL2" ]
cell lines comparator
[ "SUP-B15", "AML-193" ]
normal controls
[ "healthy-donor PBMCs", "healthy-donor bone-marrow CD34+ cells" ]
related entries
[ "gene-cdk9", "target-cdk9-inhibition-kmt2a-r", "drug-revumenib", "drug-venetoclax" ]
- Enitociclib killed healthy-donor PBMCs and CD34+ cells dose-dependently. A synergistic combination is also a combination whose marrow toxicity may be synergistic, and that was not measured.
- A CDK9 inhibitor's activity here runs through MCL-1 and MYC turnover. A blast that raises BCL-2, stabilises MYC, or is already venetoclax-exposed changes the arithmetic.
- Menin inhibitors already cause differentiation syndrome and QTc prolongation; adding a transcriptional CDK inhibitor to a differentiating blast population is a schedule problem as much as a potency problem.
- The only supporting study has two authors employed by the CDK9 inhibitor's sponsor and no independent replication.
- MI-463 is not a clinical compound. Transferring a tool-compound combination index to revumenib assumes pharmacodynamic equivalence that nobody has shown.
- Does a clinical menin inhibitor - revumenib, ziftomenib or bleximenib - synergise with a CDK9 inhibitor? No published study has tested one.
- Does the synergy hold in vivo, and at what cost to normal marrow? There is no animal experiment.
- Is the synergy KMT2A-dependent, or would it appear in any MYC- and MCL-1-dependent leukaemia? Two wild-type lines cannot answer this.
- E1established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
Enitociclib synergised with the menin-KMT2A inhibitor MI-463 by Chou-Talalay combination index in all four KMT2A-rearranged cell lines tested (MV4-11, THP-1, KOPN-8, INL2), with strong synergy at all concentrations in INL2 and KOPN-8 and at higher concentrations in MV4-11 and THP-1; the combination reduced HOXA9 protein by approximately 75-85% at 24 hours, and enitociclib alone lowered MYC and MCL-1, reduced bone-marrow-stroma-mediated survival support, and also potentiated venetoclax and prednisolone.
Targeting CDK9 inhibits the growth of KMT2A-rearranged infant leukemia and demonstrates synergy with menin inhibition. · Sharma R, Zhang C, Shah R, Frigault MM, Johnson AJ, Mangum DS, Maese LD, Lacayo NJ, Narendran A · Blood Neoplasia 2025What this evidence cannot show
In vitro only, no animal experiment. Four KMT2A-rearranged lines against two KMT2A-wild-type lines. MI-463 is a tool menin inhibitor, not a clinical one. Enitociclib was dosed against a fixed IC25 of MI-463 rather than in a full matrix. Two authors are employees of Vincerx Pharma, the enitociclib sponsor. The individual CI values are in a figure this reader could not read. INL2's specific KMT2A partner is not stated in the main text.
Evidence that argues against this (1)
- The same paper shows enitociclib reduces viability of healthy-donor PBMCs and CD34+ cells dose-dependently, so the selectivity claim rests on a two-line wild-type comparator rather than on a demonstrated normal-marrow window. Sharma R et al. 2025
- E2moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
A PubMed query on 2026-09-20 combining revumenib, SNDX-5613, VTP-50469, ziftomenib, KO-539, MI-3454, bleximenib and the phrases 'menin inhibitor' and 'menin inhibition' against CDK9, alvocidib, flavopiridol, AZD4573, dinaciclib, atuveciclib and KB-0742 returned exactly one record, the Sharma study; the narrower query 'menin inhibitor'[tiab] AND (CDK9[tiab] OR 'CDK9 inhibitor'[tiab]) returned zero.
Targeting CDK9 inhibits the growth of KMT2A-rearranged infant leukemia and demonstrates synergy with menin inhibition. · Sharma R, Zhang C, Shah R, Frigault MM, Johnson AJ, Mangum DS, Maese LD, Lacayo NJ, Narendran A · Blood Neoplasia 2025What this evidence cannot show
A counted absence bounded by the drug names searched. It would miss a paper using only a compound code this beat did not enumerate, a paper framing the combination as 'menin-MLL inhibitor plus transcriptional CDK inhibitor' without naming CDK9, or an unindexed conference abstract. The query translation was read and contained no [UID] rewriting.
Evidence that argues against this (1)
- The 2024-2025 menin-inhibitor combination literature is largely in abstract form and this project has documented that a conference abstract is frequently unreachable from PubMed, so the true number of untested-or-unreported combinations is unknown. Sharma R et al. 2025
its low-scoring claim describes this project's own PubMed query terms rather than the paper's contents
its two claims on one paper are the internal control: -0.069 for the query claim, +0.372 for the finding
enitociclib, CDK9 inhibitor arm of the combination
MI-463, tool menin inhibitor arm of the combination
- treated by →KMT2A-rearranged acute lymphoblastic leukaemia
CI<1 in four KMT2A-rearranged lines in vitro; no clinical menin inhibitor tested
a combination result the existing target dossier predates
one record in the entire menin-inhibitor x CDK9-inhibitor query space