The original paper focused on NOTCH, a family of membrane-associated receptors that regulate cell fate, development, tissue renewal and cancer progression. In its canonical role, NOTCH signaling begins when a neighboring cell presents a ligand that binds the NOTCH receptor. This interaction triggers a sequence of proteolytic cleavages, ultimately releasing the NOTCH intracellular domain. That fragment can enter the nucleus and cooperate with transcriptional regulators to activate genes involved in proliferation, survival and cellular identity. Aberrant NOTCH activity has been implicated in several malignancies, including leukemias, breast cancer, brain tumors and other solid cancers. The retracted study proposed that NOTCH also has a direct mitochondrial role, extending the pathway beyond its well-known function in the nucleus.

Mitochondria are often described as the energy-producing structures of cells, but they also control metabolism, redox balance, calcium handling and programmed cell death. Cancer cells frequently reconfigure mitochondrial activity to survive hostile conditions, maintain rapid growth and resist therapy. Tumor-initiating cells, sometimes referred to as cancer stem-like cells, are a particularly important population because they can self-renew, generate diverse tumor cell types and contribute to relapse. The paper claimed that NOTCH could be redirected to mitochondria in these cells, where it might influence the organelle’s behavior and help preserve a tumor-initiating state. If validated, such a mechanism would have connected developmental signaling, mitochondrial biology and cancer persistence in a striking way.

Central to the reported mechanism was the interaction between TBC1D15 and FIS1. FIS1 is an outer mitochondrial membrane protein associated with mitochondrial dynamics, including the division of mitochondria into smaller units. TBC1D15 is a protein involved in membrane trafficking and has been linked to regulation of mitochondrial morphology through interactions with FIS1 and related cellular machinery. According to the retracted claim, this molecular pairing served as a route by which NOTCH localized to mitochondria. In technical terms, the proposed interaction would have placed a signaling protein traditionally studied at the plasma membrane and in the nucleus within a mitochondrial protein network, potentially allowing NOTCH to affect mitochondrial organization or signaling from inside the organelle’s immediate environment.

The study also described a stabilization mechanism involving an E3 ubiquitin ligase and CDK8. E3 ligases are enzymes that attach ubiquitin molecules to specific proteins, marking them for altered activity, transport or destruction by the proteasome. This system is one of the cell’s principal methods for controlling protein abundance. CDK8, or cyclin-dependent kinase 8, is a transcriptional regulator that functions as part of the Mediator complex and can influence gene expression programs associated with development and cancer. The paper proposed that blocking the recruitment of an E3 ligase and CDK8 to NOTCH prevented its degradation or inactivation, thereby stabilizing the protein and supporting a cellular reprogramming process linked to tumor initiation.

That proposed chain of events was potentially significant because it suggested that NOTCH could operate through two interconnected layers of control: a mitochondrial localization step and a protein-stabilization step. In principle, such a pathway might help explain how tumor-initiating cells maintain both metabolic flexibility and self-renewal capacity. It also raised the possibility that disrupting the TBC1D15-FIS1 interaction, altering mitochondrial recruitment or restoring NOTCH turnover could weaken cancer cells that depend on this state. However, these therapeutic implications relied entirely on the accuracy and reproducibility of the reported molecular interactions. Once a paper is retracted, those proposed connections must be regarded as unresolved rather than as a confirmed map of cancer biology.

A retraction is different from a routine correction. Corrections usually address limited errors that do not overturn the central conclusions of a study. Retraction, by contrast, signals that the publication should not be relied upon as part of the established scientific record. The citation supplied for this case identifies the publication as a “Retraction Note,” but it does not, by itself, provide the detailed reason or reasons for the decision. Without an official explanation specifying whether the issue involved data integrity, methodology, interpretation, authorship or another concern, it would be inappropriate to infer what went wrong. The responsible scientific position is therefore to distinguish clearly between the hypotheses described in the original title and results that have been independently confirmed.

The withdrawal is especially relevant in a field where molecular claims can rapidly influence laboratory priorities, drug-development strategies and public expectations about cancer treatments. A mechanism that appears to connect NOTCH, mitochondria and tumor-initiating cells may attract attention because it offers a single narrative linking several major areas of cancer research. Yet complex biological systems are vulnerable to experimental artifacts. Apparent protein interactions can be affected by overexpression, antibody specificity, cell-line differences, subcellular fraction contamination or conditions that do not reflect tumors in living organisms. Demonstrating mitochondrial localization, for example, generally requires complementary approaches such as high-resolution imaging, biochemical fractionation with appropriate purity controls and independent confirmation using endogenous proteins.

The retraction does not erase the importance of studying NOTCH signaling, mitochondrial dynamics or tumor-initiating cells. It does mean that the specific TBC1D15-FIS1 localization model and the proposed blockade of E3 ligase and CDK8 recruitment cannot currently serve as dependable foundations for new conclusions. Future research will need to establish whether any form of NOTCH-mediated mitochondrial regulation exists, whether it occurs in physiologically relevant cancer models and how it relates to protein degradation and transcriptional control. For now, the most accurate message is one of scientific caution: an intriguing mechanism linking a major developmental pathway to cancer-cell metabolism has been removed from the trusted literature, leaving the underlying question open for rigorous investigation.

Subject of Research: NOTCH signaling, mitochondrial localization, TBC1D15-FIS1 interaction, protein stabilization and tumor-initiating cells in cancer

Article Title: Retraction Note: NOTCH localizes to mitochondria through the TBC1D15-FIS1 interaction and is stabilized via blockade of E3 ligase and CDK8 recruitment to reprogram tumor-initiating cells.

Article References: Choi, H.Y., Zhu, Y., Zhao, X. et al. Retraction Note: NOTCH localizes to mitochondria through the TBC1D15-FIS1 interaction and is stabilized via blockade of E3 ligase and CDK8 recruitment to reprogram tumor-initiating cells. Exp Mol Med (2026). https://doi.org/10.1038/s12276-026-01834-9

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01834-9

Keywords: NOTCH signaling, mitochondria, TBC1D15, FIS1, E3 ligase, CDK8, tumor-initiating cells, cancer biology, retraction, molecular oncology

Notch signaling functions as a highly conserved cellular communication mechanism, orchestrating cell fate, proliferation, differentiation, and apoptosis. Dysregulation of this pathway is implicated in various malignancies, including hematologic cancers, breast, pancreatic, and lung carcinomas. Targeting Notch components thus presents a strategic avenue to disrupt oncogenic signaling cascades. However, the clinical translation of Notch inhibitors has been hindered by issues such as toxicity, off-target effects, and resistance mechanisms. This backdrop underscores the urgency for more selective, efficacious, and safe modulators — a niche that natural bioactive compounds are uniquely poised to fill.

This comprehensive review dissects the diverse classes of natural bioactive molecules that modulate Notch signaling. These include flavonoids, alkaloids, terpenoids, polyphenols, and others, each exhibiting distinct molecular interactions that either inhibit or fine-tune Notch receptor activation and downstream gene expression. The authors compile evidence demonstrating how such compounds impair ligand-receptor binding, inhibit γ-secretase-mediated receptor cleavage, or interfere with transcriptional partners such as CSL/RBPJ and mastermind-like proteins. The multifaceted mechanisms highlight the versatility and complexity of natural compounds as anticancer agents.

Among the flavonoid family, epigallocatechin gallate (EGCG), extracted predominantly from green tea leaves, emerges as a potent Notch pathway modulator. EGCG has been shown to reduce the expression of Notch1 and its targets, decreasing cancer stem cell populations and inducing apoptosis in breast and pancreatic tumor models. The nuanced molecular dynamics involve epigenetic regulation and oxidative stress modulation, contributing to a multifactorial attack on tumor survival pathways. What makes EGCG particularly promising is its favorable pharmacokinetics and low toxicity profile, reinforcing its translational potential.

Similarly, curcumin, a polyphenol derived from turmeric, demonstrates significant efficacy in disrupting Notch signaling in various cancer contexts. It modulates the pathway by downregulating Notch receptors and the associated downstream effectors Hes1 and Hey1, leading to diminished tumor growth and metastasis. Its ability to synergize with chemotherapeutic agents positions curcumin not only as a monotherapeutic candidate but also as an adjuvant that could sensitize resistant cancer cells, thereby overcoming a major hurdle in oncology.

The review also spotlights alkaloids such as berberine and sanguinarine, which impede Notch signaling at multiple levels. Berberine, traditionally used in Ayurvedic medicine, inhibits the Notch1 intracellular domain’s nuclear translocation, thwarting the transcriptional activation of oncogenes. These compounds trigger apoptosis, autophagy, and cell cycle arrest, highlighting their multitarget therapeutic profile. Moreover, their ability to modulate immune checkpoints through Notch crosstalk adds another layer to their anticancer prowess.

An intricate challenge that the article addresses is the targeted delivery and bioavailability of these natural bioactive compounds. Often, their clinical applicability is thwarted by poor solubility, rapid metabolism, and systemic clearance. The authors discuss cutting-edge nanotechnology-based delivery systems such as liposomes, polymeric nanoparticles, and exosome-mimetic vesicles engineered to enhance compound stability, cellular uptake, and selective tumor targeting. These bioengineering advances amplify the therapeutic index, mitigate side effects, and could revolutionize personalized cancer therapy.

From a molecular perspective, the Notch pathway’s complexity is reflected in its four receptors (Notch1-4) and five ligands (Jagged1/2 and Delta-like 1,3,4). Cancer types exhibit varied receptor-ligand expression patterns altering the pathway’s oncogenic or tumor-suppressive function contextually. The review delves into how natural compounds exhibit receptor-specific inhibition, which provides an elegant precision medicine approach. For example, suppressing Notch1 is critical in T-cell acute lymphoblastic leukemia, whereas targeting Notch3 holds promise in ovarian and lung cancers, emphasizing the need for compound specificity.

Furthermore, the article elucidates how resistance to current Notch inhibitors, such as γ-secretase inhibitors (GSIs), stems partly from pathway redundancy and compensatory signaling. Natural compounds, wielding polypharmacological effects, can simultaneously modulate convergent pathways like Wnt, Hedgehog, and PI3K/Akt, thereby thwarting adaptive resistance mechanisms. Such multimodal interference not only impedes tumor growth but also remodels the tumor microenvironment by modulating cancer-associated fibroblasts, immune cells, and angiogenesis through Notch-related axes.

Significantly, the immunomodulatory roles of Notch signaling are gaining recognition for their impact on cancer progression and therapy responsiveness. Natural bioactive compounds can fine-tune the immune landscape by influencing Notch-dependent differentiation of T-cell subsets, dendritic cells, and macrophages. This immunoregulatory capacity facilitates the reinvigoration of antitumor immunity while preventing immune evasion, a core challenge in immuno-oncology. The authors emphasize emerging data linking natural compound-mediated Notch modulation with augmented efficacy of immune checkpoint inhibitors.

Clinical translation remains a formidable challenge despite promising preclinical data. The review critically analyzes ongoing and forthcoming clinical trials harnessing natural compound-based Notch modulators, either as standalone therapies or in combination with existing regimens. These trials encompass diverse malignancies and are incorporating biomarker-driven patient stratification to enhance efficacy and minimize adverse effects. Such precision oncology trials will be instrumental in validating the translational impact of these natural modulators.

One cannot overlook the evolutionary rationale behind the efficacy of natural bioactive compounds. Their structural diversity and stereochemistry arise from millions of years of co-evolution with biological systems, inherently enabling these molecules to interact specifically and safely with complex signaling networks such as Notch. Unlike synthetic small molecules with limited target scopes, natural compounds provide a vast chemical space for drug discovery and optimizations tailored for cancer therapeutics.

The authors also acknowledge the challenges posed by the heterogeneity of natural extracts and the need for standardization in compound isolation, purity, and bioactivity assays. Advances in medicinal chemistry and computational modeling are envisaged to optimize leads derived from natural products, enhance target specificity, and improve pharmacodynamic properties. Integration with artificial intelligence-driven drug design could accelerate this process, paving the way for next-generation Notch-targeting agents.

In conclusion, this comprehensive synthesis of current knowledge positions natural bioactive compounds as cutting-edge modulators of the Notch signaling pathway, carving out a promising frontier in cancer therapy. By merging traditional wisdom with modern molecular oncology, these agents herald a new era of targeted, effective, and safer anticancer interventions. Continued interdisciplinary research promises to unlock the full therapeutic potential of natural molecules, ultimately transforming cancer treatment paradigms globally.

Subject of Research: Natural bioactive compounds as modulators of the Notch signaling pathway for cancer therapy.

Article Title: Natural bioactive compounds as notch signaling modulators: cutting-edge strategies for cancer therapy.

Article References:
Bouhenni, H., Zehravi, M., Reza, F. et al. Natural bioactive compounds as notch signaling modulators: cutting-edge strategies for cancer therapy. Med Oncol 42, 363 (2025). https://doi.org/10.1007/s12032-025-02792-4

Image Credits: AI Generated