I3IN-002 — the first small-molecule IGF2BP3 inhibitor with in vivo activity in an MLL-Af4 model
also called I3IN-002 · IGF2BP3 inhibitor 002
I3IN-002 is the first drug-like molecule made to block IGF2BP3 from gripping its target RNAs. It slowed leukaemia in mice carrying the MLL-Af4 fusion and was tolerated, which makes it a starting point rather than a medicine.
The same thing, for a scientist
I3IN-002 emerged from a biochemical screen followed by a cell-based counter screen for compounds inhibiting IGF2BP3-RNA interaction and leukaemic cell growth. It shows consistent growth inhibition, altered cell cycle and increased apoptosis across multiple leukaemia lines, is described by its authors as the most potent IGF2BP3 inhibitor reported to date, was tolerated in mice intraperitoneally, and showed potent anti-leukaemic activity in a **syngeneic transplantation model of MLL-Af4 leukaemia**. On-target activity is supported by disruption of in situ IGF2BP3-target mRNA binding, altered IGF2BP3-dependent gene expression, cell-free and cellular thermal shift assays and DARTS [E1]. It is the only chemical matter in this beat directed at an RNA-binding protein in the index fusion.
What the authors claim, and the two things the abstract does not say
The target-engagement package is unusually complete for a first-in-class RNA-binding-protein inhibitor: biochemical inhibition of protein-RNA interaction, a cellular counter screen, in situ binding disruption, downstream expression change, thermal shift in cell-free and cellular formats, and DARTS 1. That is more than most tool compounds in this space carry.
Two things the abstract does not state, and both matter here.
Paralogue selectivity. IGF2BP1, IGF2BP2 and IGF2BP3 share domain architecture and near-identical length. A compound that engages the RNA-binding surface of one plausibly engages all three, and this beat holds an open hypothesis that IGF2BP2 and IGF2BP3 buffer each other 2. Whether I3IN-002 is selective decides whether its MLL-Af4 activity supports or undercuts that hypothesis.
Potency and exposure. 'Most potent reported to date' is a statement about a small field. The abstract gives no IC50, no free-fraction exposure and no comparison to any other modality. This graph's standing rule applies: a best-reported affinity is a property of the most optimised compound in whichever series someone pursued, not a measure of tractability.
Why the target argument is stronger than the dependency data
The case for IGF2BP3 as a target does not rest on CRISPR, and should not be made to. Its Chronos mean is -0.137 with 1.6% of 1,208 lines depleted 3. It rests on the mouse genetics - Igf2bp3 deletion greatly attenuating MLL-Af4 disease with minimal impact on baseline haematopoiesis 4 - and on the oncofetal expression pattern the inhibitor paper invokes: cancer-specific expression, functional dispensability for normal development, an unleveraged pro-oncogenic function in mRNA homeostasis 1.
That is a coherent target rationale built entirely on expression and germline genetics with a contradicting dependency screen, which is an unusual position and should be stated as such rather than smoothed over. The experiment that would resolve it is in exp-igf2bp-degron-self-renewal-xenograft.
| target | gene-igf2bp3 |
|---|---|
| modality | small molecule (protein-RNA interaction inhibitor) |
| status | preclinical tool compound; described by its authors as paving the way for potent and selective inhibitors |
| route tested | intraperitoneal in mice |
| key open risk | paralogue selectivity, and the possibility that inhibiting IGF2BP3 raises KMT2A::AFF1 protein |
models
[ "multiple human leukaemia cell lines", "syngeneic transplantation model of MLL-Af4 leukaemia" ]
target engagement evidence
[ "in situ IGF2BP3-target mRNA binding disruption", "altered IGF2BP3-dependent gene expression", "cell-free and cellular thermal shift assay", "DARTS" ]
not reported in abstract
[ "IC50 or Kd", "paralogue selectivity against IGF2BP1 and IGF2BP2", "exposure, free fraction or oral bioavailability" ]
- Paralogue selectivity is unstated and is the first thing that determines whether this compound is what its title says.
- IGF2BP3 is reported to lower KMT2A::AFF1 protein abundance, so inhibiting it may raise fusion dose - a resistance mechanism built into the mechanism of action.
- IMP-family proteins are oncofetal and re-expressed across many cancers; normal-tissue expression has to be established before an inhibitor reaches an infant, and IGF2BP2 is abundant in healthy marrow.
- An amplifier of leukaemia-initiating-cell function is the target class least likely to show benefit on the bulk-response endpoints trials actually measure, so even a good molecule may fail on endpoint choice.
- Intraperitoneal tolerability in mice is the weakest safety evidence a compound can carry into a paediatric argument.
- Is I3IN-002 selective for IGF2BP3 over IGF2BP1 and IGF2BP2, and does the answer change what its MLL-Af4 activity means?
- Does I3IN-002 raise KMT2A::AFF1 protein abundance, as the reciprocal-transcript binding result would predict?
- What is its potency, and how does that compare to what would be needed at tolerable exposure in a child?
- E1moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
I3IN-002, identified through a biochemical screen and cell-based counter screen, inhibits IGF2BP3-RNA interaction, shows consistent growth inhibition, altered cell cycle and increased apoptosis in multiple leukaemia cell lines, is the most potent IGF2BP3 inhibitor reported to date, was tolerated in mice administered intraperitoneally, showed potent anti-leukaemic activity in a syngeneic transplantation model of MLL-Af4 leukaemia, and has on-target support from in situ binding disruption, altered IGF2BP3-dependent gene expression, cell-free and cellular thermal shift assays and DARTS.
A small molecule inhibitor of RNA-binding protein IGF2BP3 shows anti-leukemic activity · Jaiswal AK, et al. · Haematologica 2026What this evidence cannot show
Abstract read; full text not read. No IC50, exposure, free fraction or paralogue-selectivity data in the abstract. The authors themselves frame the compound as paving the way for potent and selective inhibitors rather than being one. Tolerability by intraperitoneal dosing in mice is not a safety statement for a paediatric patient.
Evidence that argues against this (2)
- The three IGF2BP paralogues share domain architecture and near-identical length (577, 599 and 579 aa), so an inhibitor of the RNA-binding surface may engage all three. If it does, the compound's MLL-Af4 activity is evidence about the family rather than about IGF2BP3, and the target attribution in the title is stronger than the data. UniProt Consortium 2026
- A separate laboratory reports IGF2BP3 binding both reciprocal t(4;11) fusion transcripts and REDUCING KMT2A::AFF1 protein abundance. Inhibiting IGF2BP3 would then be expected to raise fusion protein, which is the opposite of the intended direction and is not addressed anywhere in the inhibitor literature. Hanewald T et al. 2026
- E2moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
In B-ALL, MLL/AF4-positive disease over-expresses IGF2BP2 and IGF2BP3 together while IGF2BP1 marks ETV6/RUNX1, so paralogue selectivity is the first question any IGF2BP3 inhibitor raises in this disease.
Identification of characteristic IGF2BP expression patterns in distinct B-ALL entities · Stoskus M, et al. · Blood Cells Mol Dis 2011What this evidence cannot show
Transcript-level, 2011, single centre. Establishes co-expression, which is what makes selectivity consequential; it does not establish redundancy.
Evidence that argues against this (1)
- IGF2BP2 is high in healthy marrow and peripheral blood by the same assay. A non-selective pan-IMP inhibitor would therefore engage a protein that normal haematopoietic tissue expresses abundantly, which is a direct toxicity argument against the very non-selectivity that might make the compound work. Weng H et al. 2022
- E3moderate confidence 3 of 5: One strong study, or several smaller consistent ones.analysis
DepMap CRISPR (Chronos) gives IGF2BP3 a mean gene effect of -0.137 across 1,208 lines with 1.6% depleted below -0.5, and a B-lymphoid KMT2A-rearranged index-arm difference of -0.135 against 43 other leukaemia lines at the 16.3rd percentile of a 466-gene null.
The RNA layer in KMT2A-rearranged leukaemia lines: panel-wide selectivity scan and IGF2BP family co-dependency test · Oncofusion knowledge graph (internal analysis) 2026What this evidence cannot show
A dropout screen cannot see a requirement acting on leukaemia initiation or self-renewal, which is the phenotype the mouse genetics reports, so this row constrains the target argument rather than refuting it.
Evidence that argues against this (1)
- A compound showing in vivo anti-leukaemic activity in an MLL-Af4 model is a more direct test of the target than any dependency screen, and it went the other way. Either the screen is measuring the wrong thing or the compound is acting through something other than IGF2BP3. Jaiswal AK et al. 2026
- E4strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Igf2bp3 deletion significantly increases survival and greatly attenuates MLL-Af4-driven leukaemia in mice with minimal impact on baseline haematopoiesis, and MLL-Af4 leukaemia-initiating cells require Igf2bp3.
The RNA-binding protein IGF2BP3 is critical for MLL-AF4-mediated leukemogenesis · Tran TM, et al. · Leukemia 2022What this evidence cannot show
Abstract read; full text not read. Murine, chimeric construct, deletion before disease. The tolerability half is measured in an unstressed mouse.
Evidence that argues against this (1)
- Minimal impact on baseline haematopoiesis in an unstressed mouse is the condition under which this graph's menin work found nothing, with a long-term HSC defect appearing only under competitive transplantation. The compound's safety rationale inherits that weakness. Oncofusion knowledge graph (internal analysis) 2026
Disrupts IGF2BP3-target mRNA binding; thermal shift and DARTS support on-target activity
- treated by →KMT2A::AFF1 (MLL-AF4), t(4;11)(q21;q23)
Anti-leukaemic activity in a syngeneic MLL-Af4 transplantation model
Its unstated paralogue selectivity decides whether its activity supports or undercuts the redundancy hypothesis