The rationale for the study rests on a well-documented clinical observation. A high prevalence of concurrent PIK3CA and CTNNB1 mutations has been reported among patients with endometrial cancer, yet the functional relationship between the two pathways these genes control has remained murky. PIK3CA drives the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) cascade, a growth-promoting network that has long attracted drug developers. CTNNB1, which encodes β-catenin itself, feeds into the Wnt pathway, a transcriptional program implicated in development and, when dysregulated, in numerous cancers. Whether these two axes cooperate to fuel tumor growth, or whether one could be exploited therapeutically against the other, was an open question.

To answer it, the team assembled a panel of eleven endometrial cancer cell lines and tested three mechanistically distinct inhibitors: ICG-001, which blocks the interaction between β-catenin and its transcriptional co-activator CBP; ipatasertib, an AKT inhibitor; and rapamycin, a classic mTOR inhibitor. The results were strikingly asymmetric. ICG-001, but not the PI3K/AKT/mTOR pathway inhibitors, exhibited potent antiproliferative activity specifically in the cells harboring both CTNNB1 and PIK3CA mutations. In other words, the very pathway combination that had seemed like an obvious target for dual blockade turned out to be most vulnerable to a single intervention on the Wnt side.

Transcriptomic profiling helped explain why. When the double-mutant cells were treated with ICG-001, a series of canonical β-catenin target genes were downregulated, confirming that the drug was doing what it was designed to do at the transcriptional level. But the more revealing finding was what appeared in their place: signature genes related to proteotoxic stress and proteostasis disruption were significantly enriched. Proteostasis, the cellular system that governs the synthesis, folding, and disposal of proteins, is a delicate balance. Its collapse is a recognized form of lethal stress in cancer cells, and the gene expression data suggested that ICG-001 was pushing the double-mutant cells precisely in that direction.

The mechanistic follow-up experiments painted a vivid picture of a cell in crisis. ICG-001 treatment induced de novo protein synthesis, meaning the cells began churning out new proteins at an accelerated rate. At the same time, the researchers observed autophagosome formation, detectable as accumulation of the lipidated form of the protein LC3B (LC3B-II), a hallmark of the cell’s attempt to digest and recycle its own contents. Endoplasmic reticulum expansion, another sign of protein-folding overload, was evident, along with the accumulation of ubiquitinated proteins, the molecular equivalent of garbage piling up faster than the cell’s disposal machinery can clear it. Together, these changes indicate severe proteostasis collapse, a state in which the cell’s protein economy fails catastrophically.

What makes this mechanism particularly compelling is the selectivity. The double-mutant cells appear to be running their protein production machinery close to capacity, perhaps because the combined PIK3CA and CTNNB1 mutations impose unusual demands on translation and folding. When ICG-001 disrupts β-catenin/CBP-dependent transcription, the resulting imbalance between protein synthesis and protein quality control becomes lethal specifically for cells with this genetic background, while sparing cells that lack the double mutation. This kind of synthetic vulnerability, where a drug exploits a weakness created by a specific combination of mutations, is the holy grail of precision oncology, because it promises efficacy with a built-in therapeutic window.

The in vitro findings translated into animal models. Daily administration of ICG-001 demonstrated robust antitumor efficacy in xenograft models of CTNNB1/PIK3CA double-mutant endometrial cancer, meaning tumors grown from the double-mutant cells in mice shrank or stopped growing under treatment. Critically, examination of the xenograft tissues revealed marked ubiquitin accumulation, mirroring the proteostasis collapse seen in cultured cells and confirming that the same mechanism operates in living tumors. This consistency between cell culture and animal data strengthens the case that the observed vulnerability is not an artifact of the laboratory dish but a genuine biological dependency of these tumors.

The study also carries a cautionary message for the alternative strategy. Inhibitors of the PI3K/AKT/mTOR pathway have been extensively developed and tested across many tumor types, with mixed results, and the finding that ipatasertib and rapamycin failed to show preferential activity against the double-mutant endometrial cancer cells suggests that simply attacking the PIK3CA-driven arm of the network may not be the right approach for this subset. The interplay between the two pathways, whatever its details, does not make the PI3K axis the Achilles’ heel. Instead, the data redirect attention toward β-catenin/CBP inhibition as the more productive point of attack.

For patients, the implications are significant but tempered by the usual caveats of preclinical research. ICG-001 is an experimental tool compound, and the path from xenograft efficacy to an approved medicine involves medicinal chemistry optimization, safety profiling, and clinical trials in appropriately selected patients. The study nonetheless establishes a clear biomarker strategy: tumors carrying both PIK3CA and CTNNB1 mutations, identifiable through routine genomic sequencing, would be the candidate population for β-catenin-targeted therapy. Given the high prevalence of this double-mutation pattern in endometrial cancer, the addressable patient group could be substantial, offering hope in a disease where advanced-stage options are currently limited largely to chemotherapy, hormone therapy, and, more recently, immunotherapy for a subset of tumors.

The work also adds to a growing appreciation of proteostasis as a therapeutic target in cancer. Drugs that overload the protein-folding and degradation machinery, such as proteasome inhibitors in multiple myeloma, have already proven that stressing this system can be clinically effective. The present study suggests that transcriptional modulation of β-catenin can trigger a similar collapse in a genetically defined solid tumor, extending the concept into gynecologic oncology. As the authors and their collaborators at the National Cancer Center and the University of Tokyo note, these preclinical findings collectively highlight the vulnerability of PIK3CA/CTNNB1 double-mutant endometrial cancers to β-catenin inhibition and establish β-catenin/CBP inhibitors as a promising targeted therapeutic strategy for this specific genetic subset. Clinical validation will take years, but the study provides the mechanistic foundation and the biomarker logic needed to begin that journey.

Subject of Research: Therapeutic potential of β-catenin inhibition in PIK3CA/CTNNB1 double-mutant endometrial cancer

Article Title: Potential of β-catenin inhibitors as a novel therapeutic strategy for PIK3CA/CTNNB1 double-mutant endometrial cancer

Article References: Nakao, T., Kamata, R., Saito, H., Yamamoto, G., Morita, T. Y., Kinoshita, K., Takahashi, Y., Mashima, C., Yamauchi, T., Sakae, Y., Kamii, M., Nakai, K., Hakozaki, Y., Nakajima, H., Harano, K., Naito, Y., Mukohara, T., & Ohashi, A. (2026). Potential of β-catenin inhibitors as a novel therapeutic strategy for PIK3CA/CTNNB1 double-mutant endometrial cancer. Cell Death Discovery. https://doi.org/10.1038/s41420-026-03321-6

Image Credits: AI Generated

DOI: 10.1038/s41420-026-03321-6

Keywords: endometrial cancer, β-catenin, CTNNB1, PIK3CA, Wnt signaling, ICG-001, proteostasis, targeted therapy, xenograft models, PI3K/AKT/mTOR, proteotoxic stress, precision oncology