The original research, conducted by Zhu and colleagues, examined dendrobine in larval zebrafish subjected to high-glucose conditions, a widely used short-term model of early diabetic retinopathy. The team combined several complementary techniques: imaging of the retinal vasculature, histological examination of retinal tissue, behavioral testing, assays of oxidative stress, and transcriptomic analysis of gene expression. Together, these approaches suggested that dendrobine attenuated a range of abnormalities induced by short-term high-glucose exposure, including the enlargement of retinal vessels that characterizes the earliest stages of the disease. At a concentration of 40 milligrams per liter, the compound appeared to reduce both vascular changes and whole-body glucose levels in the larvae, prompting the authors to propose dendrobine as a candidate therapeutic agent.

Chen’s central criticism concerns the timing of treatment, a detail that may sound technical but carries enormous clinical weight. In the original study, dendrobine and glucose were administered concurrently, from three to six days post-fertilization, meaning the compound was present in the larvae from the very moment hyperglycemic stress began. Dendrobine was never introduced after a retinal abnormality had already been established. The experiment, Chen argues, therefore answers a prevention question rather than a treatment question: it shows that dendrobine can limit injury while high-glucose stress is being induced, but it says nothing about whether the compound can reverse damage that already exists.

This distinction matters because diabetic retinopathy in human patients is almost never caught at the moment metabolic stress begins. By the time most people are diagnosed and treated, vascular and neural changes in the retina have already taken hold. A compound that reduces retinal injury when present from the onset of metabolic stress may not retain the same efficacy once those structural changes are established. Chen points out that the 130 millimolar glucose larval model used in the study was originally developed as a short-term model of early hyperglycemia-related retinal vascular change, and that subsequent work in the field has consistently distinguished such short-term larval immersion models from longer-duration diabetic models designed to study more established retinal complications. The results, in other words, support a protective effect during acute exposure but do not yet demonstrate therapeutic efficacy against established disease.

Chen also notes a second design gap: the study included no dendrobine-only group under normal glucose conditions. This omission is significant because several outcomes interpreted as rescue, including developmental and transcriptomic changes, could plausibly have been influenced by direct effects of dendrobine on normal larval development. Without knowing how the compound behaves in healthy larvae, it is difficult to attribute every observed improvement to protection against glucose injury. Chen proposes that a delayed-treatment design would address both concerns at once: researchers could first document vascular or structural retinal abnormalities after glucose exposure, then initiate dendrobine treatment while maintaining hyperglycemic conditions. Such an approach would more closely mirror the question faced in clinical practice, namely whether a drug can improve retinal injury that is already present rather than prevent it from developing.

The second major issue raised in the letter involves disentangling local retinal effects from systemic glucose lowering. Because dendrobine at 40 milligrams per liter reduced both retinal vessel enlargement and whole-body glucose levels, and because most major outcomes were assessed at the same six-day time point, it remains unclear whether the retinal benefit was a direct effect on eye tissue or simply a downstream consequence of reduced blood sugar. The original authors suggested that retinal improvement might occur before major systemic metabolic change, implying a local retinal mechanism, but as Chen observes, no serial measurements or glucose-matched comparisons were performed to establish that temporal sequence. To their credit, the authors acknowledged that systemic metabolic effects could not be separated from direct retinal actions, but Chen argues that the field needs more: retina-specific assays, direct measurements of retinal dendrobine exposure, or comparisons between experimental groups with similar systemic glucose levels would all help determine whether the compound acts on the retina independently of its glucose-lowering properties.

The third and perhaps most methodologically intricate criticism concerns the transcriptomic data. RNA sequencing in the original study was performed on whole larvae rather than isolated retinal tissue, yet the enriched biological pathways were subsequently linked to retinal protection. Chen emphasizes that whole-organism bulk transcriptomic data cannot identify which tissue or cell type is responsible for differential gene expression without additional spatial or cell-resolved information, a limitation increasingly recognized in the genomics community. Signals arising from the gut, liver, kidney, or other glucose-responsive organs could dominate the expression profile, masking or mimicking retinal-specific changes.

Compounding this concern is a statistical question. Chen notes that neither the main methods section nor the supplementary text of the original study specifies whether the reported transcriptome-wide P values were adjusted for multiple testing. This matters because false-discovery control is a standard requirement when thousands of genes are tested simultaneously; without such correction, apparent pathway enrichments can arise by chance. The quantitative reverse transcription PCR experiments in the original paper do support the direction of expression changes in selected genes, but validating a handful of genes does not establish that the implicated pathways causally mediate the retinal phenotype. At this stage, Chen concludes, the transcriptomic findings are better suited to generating candidate pathways than to identifying what the original authors called precise molecular targets. Retina-specific transcriptomic profiling and functional perturbation of the proposed pathways, such as genetic or pharmacological manipulation in larvae, would provide firmer mechanistic support.

The exchange arrives at a moment of growing interest in natural products as sources of anti-diabetic and neuroprotective compounds. Dendrobine, extracted from Dendrobium orchids long used in traditional medicine, has attracted attention for its reported anti-inflammatory and antioxidant properties, and zebrafish have become a favored platform for early-stage drug screening because their transparent larvae allow direct visualization of developing blood vessels. The high-glucose immersion model offers speed and scale that rodent models cannot match, letting researchers survey vascular changes within days rather than months. Yet the same convenience creates interpretive traps, as this letter makes clear: short exposure windows, whole-organism measurements, and concurrent treatment designs can each blur the line between protection and treatment, between a retinal effect and a systemic one.

None of this diminishes the value of the original work, and Chen is explicit on that point. The study provides useful evidence that dendrobine modifies retinal and systemic responses during acute high-glucose exposure in zebrafish larvae, and the multi-modal approach, spanning imaging, histology, behavior, oxidative stress assays, and transcriptomics, offers a template for how such screens should be conducted. What the letter demands is precision in interpretation: determining whether dendrobine can treat established retinal injury, separating local retinal effects from systemic glucose lowering, and validating the proposed pathways within retinal tissue itself. For the millions of people worldwide at risk of vision loss from diabetic retinopathy, the difference between a preventive compound and a therapeutic one is not academic. It defines the clinical trials that must eventually be run, the patients who could benefit, and the stage of disease at which any new drug must prove itself. This careful critique, published open access in the Journal of Translational Medicine, is a reminder that in translational science, the rigor of interpretation matters as much as the rigor of the experiment.

Subject of Research: Evaluation of dendrobine's protective effects in a zebrafish model of diabetic retinopathy

Article Title: Letter to the Editor regarding “Functions of dendrobine in a zebrafish model of diabetic retinopathy”

Article References: Letter to the Editor regarding “Functions of dendrobine in a zebrafish model of diabetic retinopathy”. (n.d.). https://doi.org/10.1186/s12967-026-08991-5

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08991-5

Keywords: dendrobine, diabetic retinopathy, zebrafish, high glucose, retinal vasculature, transcriptomics, oxidative stress, glucose lowering, letter to the editor, translational medicine, drug screening, hyperglycemia

The scale of the problem the review addresses is enormous. In 2020 alone, gastrointestinal cancers accounted for more than 4.8 million new cases and 3.4 million deaths worldwide. Colorectal cancer ranks as the third most commonly diagnosed cancer globally, with gastric, hepatic, and esophageal cancers following in fifth, sixth, and seventh places respectively. Pancreatic cancer, though only twelfth in incidence, is seventh in mortality, a grim reflection of its aggressive biology and late detection. Even when early-stage tumors can be surgically resected with curative intent, five-year relapse rates remain high, and neoadjuvant or adjuvant chemotherapy and radiotherapy deliver only modest long-term survival gains. The authors argue that this persistent therapeutic ceiling makes the search for actionable molecular drivers a matter of urgency rather than academic curiosity.

At the heart of that search sits the PI3K/AKT/mTOR cascade, a signaling highway that connects growth factor receptors on the cell surface to the core machinery of cell growth, metabolism, survival, and proliferation. When extracellular signals activate receptor tyrosine kinases such as EGFR or HER2, phosphoinositide 3-kinase generates lipid second messengers that recruit AKT to the membrane, where it is phosphorylated and activated. AKT then relays signals to mTOR, a kinase existing in two functionally distinct complexes, mTORC1 and mTORC2, that together regulate protein synthesis, autophagy, lipid metabolism, and angiogenesis. The review emphasizes that this axis governs chemotherapy resistance, metastatic dissemination, cell survival, metabolic reprogramming, and tumor growth, while also shaping the tumor microenvironment through the promotion of angiogenesis and inflammatory immune cell infiltration.

Dysregulation of this pathway is strikingly common across gastrointestinal malignancies. Somatic mutations in PIK3CA, the gene encoding the p110alpha catalytic subunit of PI3K, were first identified at high frequency in human cancers by Samuels and colleagues in a landmark 2004 Science paper, and subsequent studies confirmed their prevalence in gastric and colon tumors. In esophageal squamous cell carcinoma, PIK3CA mutations have been associated with worse patient outcomes. In gastric cancer, the pathway is frequently activated not only through PIK3CA mutation but also through loss of the negative regulator PTEN, HER2 amplification, and epigenetic mechanisms including long non-coding RNAs and microRNAs that modulate pathway components. In hepatocellular carcinoma, members of the PI3K/AKT/mTOR pathway and eukaryotic translation initiation factors have been proposed as novel biomarkers, while in pancreatic cancer, intrinsic PI3Kalpha activity has been shown to accelerate metastasis and rewire the macrophage composition of the tumor microenvironment.

The mechanistic detail matters because it explains why the pathway is such an attractive drug target. mTORC1, acting through its downstream effectors p70S6K and 4E-BP1, controls the translational landscape of the cell, steering cancer initiation and metastasis by selectively boosting the synthesis of mRNAs encoding growth and survival proteins. AKT phosphorylation of downstream targets suppresses apoptosis and promotes glucose uptake and glycolysis, feeding the metabolic appetite of rapidly dividing tumors. PI3K signaling also drives the expression of vascular endothelial growth factor and proangiogenic cytokines such as interleukin-8, linking pathway activation directly to the blood supply that tumors need to expand. Blocking any node in this cascade should, in principle, starve the cancer of multiple survival advantages simultaneously.

Preclinical evidence reviewed by the authors bears this out across nearly every gastrointestinal tumor type. In gastric cancer models, the natural compounds apigenin, deltonin, pectolinarigenin, and the coral-derived sinulariolide all induced apoptosis, autophagy, or cell cycle arrest by suppressing PI3K/AKT/mTOR signaling, with deltonin additionally sensitizing cells to cisplatin. The dual PI3K/mTOR inhibitor NVP-BEZ235 augmented the efficacy of fluorouracil in gastric cancer cells and enhanced chemotherapy and antiangiogenic responses in pancreatic cancer models. In pancreatic cancer stem cells, rottlerin triggered autophagy leading to apoptotic death through pathway inhibition. Everolimus, the mTORC1 inhibitor known as RAD001, inhibited tumor growth in hepatocellular carcinoma xenografts, while the novel inhibitor W922 prevented colorectal cancer growth through autophagy regulation. Dual targeting of the MAP kinase and PI3K/mTOR pathways showed synergistic effects in preclinical colorectal cancer models, and the p70S6K/AKT dual inhibitor DIACC3010 proved efficacious in gastric cancer models both alone and in combination with trastuzumab.

Translating this laboratory promise into clinical benefit has proven far harder. The phase III GRANITE-1 trial tested everolimus against placebo in previously treated advanced gastric cancer and failed to meet its survival endpoint, despite earlier phase II activity. A SWOG phase II study of the allosteric AKT inhibitor MK-2206 as second-line therapy for advanced gastric and gastroesophageal junction cancer likewise yielded disappointing results. In metastatic colorectal cancer, a phase II study of everolimus in patients previously treated with bevacizumab-, fluoropyrimidine-, oxaliplatin-, and irinotecan-based regimens showed limited benefit. Everolimus in gemcitabine-refractory metastatic pancreatic cancer and temsirolimus combined with sorafenib in advanced hepatocellular carcinoma produced similarly modest outcomes. Phase II studies of the AKT inhibitor ipatasertib added to mFOLFOX6 in gastric cancer, and of copanlisib combined with gemcitabine and cisplatin in advanced biliary tract cancers, underscored both the interest in the strategy and the difficulty of demonstrating clear gains.

The review identifies toxicity as a principal culprit in these clinical setbacks, and the class effects are rooted in the pathway’s normal physiology. Because PI3K/AKT/mTOR signaling is central to glucose homeostasis, lipid metabolism, and cell survival in healthy tissues, its inhibition produces hyperglycemia, diarrhea, hepatotoxicity, neuropsychiatric effects, mucositis, skin rash, and metabolic complications. Meta-analyses of everolimus trials documented substantial rates of stomatitis, and studies of temsirolimus confirmed frequent rash and mucosal injury. Hyperglycemic complications on phase I trials of PI3K-AKT-mTOR inhibitors have been systematically characterized, and preclinical work suggests PI3K/AKT inhibitors can aggravate death receptor-mediated hepatocyte apoptosis and liver injury, a particular concern in patients with underlying liver disease. These toxicities constrain dosing, force interruptions, and erode the therapeutic window that the drugs need to exert meaningful antitumor effects.

The authors also highlight a second, equally fundamental barrier: the lack of molecular stratification. Early trials enrolled unselected patients, mixing tumors whose pathway activation was driven by PIK3CA mutation with those in which the pathway was activated downstream, upstream, or not at all. Without biomarkers to identify which tumors are genuinely addicted to the axis, inhibitors were tested in populations diluted with patients unlikely to respond, diluting signal and inviting failure. The reviewers argue that refined personalization, guided by genomic and epigenetic profiling of pathway alterations, is essential, and they point to the growing recognition of crosstalk between microRNAs and the pathway as a potential source of predictive biomarkers. They further contend that combination strategies, pairing pathway inhibitors with chemotherapy, antiangiogenic agents, MAPK inhibitors, autophagy blockers such as chloroquine, or trastuzumab in HER2-positive disease, represent the most credible route to overcoming the feedback loops and parallel survival pathways that allow tumors to evade single-agent blockade.

The review’s conclusions land at a moment of renewed interest in the pathway across oncology, with lessons learned in breast cancer, where PI3K inhibitors have achieved regulatory success, informing expectations for gastrointestinal disease. The authors, writing from the Student Research Committee and research institutes of Kashan University of Medical Sciences with collaborators in Tabriz, acknowledge that no datasets were generated or analyzed in the study and that it received no specific grant funding. Their synthesis ultimately delivers a dual verdict: the PI3K/AKT/mTOR axis is indisputably a central driver of gastrointestinal cancer progression, metastasis, and therapy resistance, and preclinical studies consistently show that its inhibition reduces tumor growth, induces cell death, and boosts chemosensitivity. Whether that promise finally reaches patients, they conclude, will depend on biomarker-driven trial designs, smarter combinations, and toxicity management strategies that respect the pathway’s indispensable role in healthy physiology as much as its corrupting influence in cancer.

Subject of Research: Targeting the PI3K/AKT/mTOR signaling pathway in gastrointestinal cancers

Article Title: Targeting the PI3K/AKT/mTOR pathway in gastrointestinal cancers: a comprehensive review of mechanisms, preclinical evidence, and clinical challenges

Article References: Kaikavoosnejad, F., Haddad Kashani, H., Dizaji Asl, K., Mazloumi, Z., Keyhani, A., Ashraf Moosavi, S. S., Verdi, M., & Rafat, A. (2026). Targeting the PI3K/AKT/mTOR pathway in gastrointestinal cancers: a comprehensive review of mechanisms, preclinical evidence, and clinical challenges. Medical Oncology, 43(10), Article 256. https://doi.org/10.1007/s12032-026-03374-8

Image Credits: AI Generated

DOI: 10.1007/s12032-026-03374-8

Keywords: PI3K/AKT/mTOR pathway, gastrointestinal cancers, targeted therapy, colorectal cancer, gastric cancer, hepatocellular carcinoma, pancreatic cancer, mTOR inhibitors, drug resistance, hyperglycemia, biomarkers, combination therapy