The retraction of this study underscores how the peer-review process, while rigorous, is not infallible. When the original paper appeared in September 2020, it joined a growing body of literature examining whether compounds derived from plants could be repurposed as anticancer therapeutics. The idea that a common ornamental plant might harbor molecules capable of attacking one of the most lethal human cancers captured considerable attention. Glioblastoma, the aggressive brain tumor at the center of the research, has long frustrated oncologists, with median survival for patients typically measured in months despite surgery, radiation, and chemotherapy. Any claim of a compound that could suppress glioblastoma growth while also targeting the signaling pathways thought to drive tumor recurrence was therefore met with significant interest from researchers seeking new options for a disease with remarkably few approved treatments.

Supercritical carbon dioxide extraction, the technique used to produce the botanical drug in the study, is a method worth understanding in its own right. Unlike conventional solvent-based extraction, supercritical CO2 extraction uses carbon dioxide held at a temperature and pressure where it behaves as both a liquid and a gas, allowing it to dissolve compounds from plant material with high efficiency. When the pressure is released, the carbon dioxide simply evaporates, leaving behind a concentrated extract free of residual solvent contamination. This property has made the technique especially attractive for preparing botanical drugs intended for human use, since it aligns with the purity expectations of regulatory agencies. Oleander extracts prepared this way had previously been the subject of early-phase clinical investigation, which lent the retracted study an air of translational relevance beyond basic laboratory science.

The biological rationale behind the research also merited attention. The Akt/mTOR signaling pathway is a central regulator of cell growth, proliferation, and survival, and it is frequently hyperactivated in glioblastoma. Drugs that inhibit components of this pathway have been explored extensively, though single-agent mTOR inhibitors have generally produced disappointing results in clinical trials for brain tumors, partly because of the pathway’s redundancy and the blood-brain barrier’s exclusion of many compounds. A plant-derived extract that appeared to suppress this axis offered a potentially different approach, since complex botanical mixtures contain multiple bioactive constituents that may act on several targets simultaneously. The reported effects on glioma stem-like cells added further significance, as these slow-dividing cell populations are widely believed to contribute to treatment resistance and tumor recurrence after standard therapy.

The way this retraction came about reflects broader changes in how scientific integrity issues are identified and addressed. The notice specifically credits Sholto David, an independent researcher who has become known for systematically examining published figures in cancer biology papers and alerting journals to potential problems. This form of post-publication peer review has grown increasingly influential in recent years. Sophisticated image analysis tools and public forums allow researchers unaffiliated with a paper to scrutinize western blots, microscopy panels, and other graphical data for signs of duplication, splicing, or manipulation. What once might have escaped notice indefinitely can now be flagged within days or weeks of publication, placing pressure on journals to investigate and resolve concerns transparently.

The handling of the investigation followed a sequence that has become fairly standard among major publishers. Following publication, concerns were raised about the integrity of the images in the published figures. The journal then contacted the authors and requested the underlying raw data or a satisfactory explanation. When neither was provided, the editors concluded that they could no longer have confidence in the findings. This step is critical: raw data serves as the foundation upon which published conclusions rest, and its absence prevents any independent verification of whether the reported results were genuine, erroneous, or fabricated. In cases where authors promptly supply original data files that resolve the questions raised, papers may be corrected rather than retracted. The inability or unwillingness to produce such data almost invariably leads to the more severe outcome.

Retraction notices serve several purposes within the scientific ecosystem. They formally detach an author’s name from claims that can no longer be trusted, they warn other researchers against building future work on unreliable results, and they create a permanent public record of the concerns. Databases maintained by the research community track retractions across the scientific literature, and indexed articles are typically flagged so that readers encountering the original paper will be alerted to its retracted status. Notably, a retraction is not always an accusation of deliberate misconduct. Errors can arise from honest mistakes, poor laboratory record-keeping, or inadequate oversight of collaborators. However, when authors cannot produce raw data to resolve legitimate questions, the distinction between error and misconduct becomes less important than the practical reality that the findings cannot be trusted.

For the field of botanical drug research, the episode carries particular weight. Natural product oncology occupies a delicate position in science. On one hand, many of the most effective anticancer drugs in clinical use derive from plants, and there is genuine biochemical logic to screening plant extracts for activity against cancer cells. On the other hand, the field has historically attracted exaggerated claims and treatments promoted to vulnerable patients without adequate evidence. Oleander in particular has been marketed in various unregulated forms as an alternative cancer remedy despite limited clinical evidence of benefit and known toxicity concerns, as the plant contains cardiac glycosides that can be dangerous at sufficient doses. Rigorous, well-documented research is essential for separating genuine therapeutic potential from unsubstantiated hope, and retractions of flawed studies make that task harder by muddying the evidentiary record.

The six-year interval between the original publication and the retraction notice may seem lengthy, but it is not unusual. Investigations of potential image integrity problems involve correspondence among editors, authors, institutional officials, and sometimes external experts. Authors must be given opportunities to respond, institutions may conduct their own inquiries, and publishers typically require approval from senior editorial leadership before issuing a formal notice. In this case, the retraction was approved by the Chief Editors of Frontiers in Pharmacology together with the Chief Executive Editor of Frontiers, and the authors received communication about the decision and an opportunity to respond, with that exchange recorded by the publisher. These procedural safeguards exist to ensure fairness, even though they extend the timeline considerably.

For patients and clinicians who may have encountered the original findings, the retraction is a clear signal that the reported results should no longer be relied upon. Claims that a botanical extract inhibited glioblastoma growth, reduced Akt/mTOR activity, and modulated stem-like cell properties cannot be considered established science following this decision. Individuals considering oleander-based products for cancer treatment should be aware that this study’s conclusions have been withdrawn, that no robust clinical evidence supports such use, and that oleander preparations carry real risks of toxicity. Patients facing glioblastoma are best served by discussing evidence-based treatment options with their oncology teams rather than pursuing remedies based on research that has since been invalidated.

The episode also illustrates why the reproducibility of scientific findings depends so heavily on data transparency. Journals and funding agencies have increasingly required authors to deposit raw data, share reagents, and document their methods in sufficient detail for independent replication. When raw data exists and is available, disputed results can often be resolved quickly, either confirming the original findings or revealing honest analytical errors. When it does not, the scientific community is left with results that cannot be verified, and the safest course is to remove them from the literature. The fact that the editors here cite the lack of raw data as central to their decision highlights how data availability has become a cornerstone of research integrity rather than an optional courtesy.

Finally, the retraction demonstrates the collective nature of scientific self-correction. A vigilant outside reader, a journal willing to investigate, editorial leadership willing to act, and a formal notice that permanently documents the outcome all played roles in the process. Science advances not only through new discoveries but through the deliberate removal of findings that fail to withstand scrutiny. While each retraction represents a disappointment, the system that identifies and publicizes them is functioning as intended, protecting the reliability of the published record on which future research and, ultimately, patient care depend.

Subject of Research: Retraction of a 2020 Frontiers in Pharmacology study on the botanical drug PBI-05204 for glioblastoma

Article Title: Retraction: The botanical drug PBI-05204, a supercritical CO2 extract of Nerium oleander, inhibits growth of human glioblastoma, reduces Akt/mTOR activities, and modulates GSC cell-renewal properties

Article References: Frontiers Editorial Office (2026). Retraction: The botanical drug PBI-05204, a supercritical CO2 extract of Nerium oleander, inhibits growth of human glioblastoma, reduces Akt/mTOR activities, and modulates GSC cell-renewal properties. Frontiers in Pharmacology, 17, Article 2021904. https://doi.org/10.3389/fphar.2026.2021904

Image Credits: AI Generated

DOI: 10.3389/fphar.2026.2021904

Keywords: PBI-05204, Nerium oleander, glioblastoma, retraction, research integrity, Frontiers in Pharmacology, image manipulation, Akt/mTOR pathway, glioma stem cells, botanical drug, supercritical CO2 extract, raw data

The research team, led by Mohamed T. Selim and Nashaat N. Mahmoud of the Botany and Microbiology Department, took a deliberately comparative approach. Rather than examining a single plant part or a single solvent, they prepared extracts of dried stems, leaves, and flowers using five solvents spanning a wide range of polarity: petroleum ether, ethyl acetate, acetone, methanol, and water. This polarity gradient matters because different classes of plant metabolites dissolve preferentially in solvents of different chemical character. Non-polar solvents such as petroleum ether tend to pull out lipids, waxes, and steroids, while highly polar water and methanol extract sugars, glycosides, tannins, and other hydrophilic compounds. By running the full spectrum, the researchers could determine exactly where the plant’s chemical treasure is concentrated.

Before any extraction began, the team characterized the proximate composition of each plant part, and the results revealed striking differences. The flowers carried the highest moisture content at 9.40 percent, while the stems were unusually mineral-rich, showing an ash content of 18.58 percent that exceeded both leaves and flowers. The flowers also proved to be the most nutritionally dense tissue, with a lipid content of 4.33 percent, a carbohydrate content of 66.16 percent, and a crude protein content of 15.29 percent. These baseline measurements are more than academic bookkeeping; they help determine which plant part is worth processing for which purpose, since a tissue dominated by carbohydrates will behave very differently in extraction and formulation than one rich in lipids or minerals.

When it came to extraction efficiency, solvent choice dominated the outcome. Water extracts delivered the highest percentage yield across the plant parts, followed by methanol, acetone, ethyl acetate, and finally petroleum ether. Among the plant tissues, leaves produced the maximum extract yield, with flowers and stems trailing behind. This pattern is chemically intuitive: oleander tissues are loaded with polar glycosides and phenolic compounds that dissolve readily in water and methanol but remain locked away from non-polar solvents. For anyone hoping to industrialize the process, the message is clear: the cheapest and greenest solvent, plain water, is also the most productive one, an encouraging alignment of economic and environmental incentives.

The phytochemical screening painted a detailed portrait of the plant’s defensive arsenal. Across the different parts, the researchers detected alkaloids, flavonoids, tannins, glycosides, steroids, coumarins, quinones, phenols, cardiac glycosides, and terpenoids, the full roster of secondary metabolites that plants typically deploy against microbes and herbivores. Two classes were conspicuously absent: saponins and anthraquinones were not found in any part of the plant. Anthocyanins, the pigments responsible for red and purple coloration, appeared exclusively in the flowers and were completely absent from stems and leaves. This tissue-specific distribution underscores a key principle of natural product chemistry: a plant is not a uniform bag of chemicals but a mosaic of specialized tissues, each with its own metabolic profile.

Quantitative assays sharpened that picture considerably. The acetone extract of the flowers emerged as the phytochemical powerhouse, registering the greatest levels of total phenols at 157.12 milligrams of gallic acid equivalents per gram, total flavonoids at 187.43 milligrams of quercetin equivalents per gram, and tannins at 89.93 milligrams of tannic acid equivalents per gram. At the opposite extreme, the petroleum ether extract of stems contained the lowest amounts of all three, at just 5.45, 6.43, and 3.45 milligrams per gram respectively. The roughly thirtyfold spread between these extremes illustrates how dramatically solvent polarity and plant tissue interact to determine the composition of an extract, and why screening studies of this kind are essential before any product development can begin.

The antimicrobial testing then put these chemical inventories to work. Using the agar well diffusion method, a standard technique in which extract-loaded wells are cut into plates seeded with microorganisms and zones of inhibited growth are measured, the team challenged six strains. The panel included Gram-positive bacteria Staphylococcus aureus ATCC 6538 and Bacillus subtilis ATCC 6633, Gram-negative bacteria Pseudomonas aeruginosa ATCC 9027, Salmonella Typhimurium ATCC 14028, and Escherichia coli ATCC 11229, and the unicellular fungal pathogen Candida albicans ATCC 10231. The extracts showed the ability to inhibit representatives of all these groups, a breadth of activity that spans both major bacterial membrane architectures as well as a eukaryotic pathogen responsible for serious infections in immunocompromised patients.

That broad-spectrum activity is significant in the context of the global antimicrobial resistance crisis. Gram-negative bacteria such as Pseudomonas aeruginosa and E. coli are wrapped in an outer membrane that excludes many conventional antibiotics and makes new drug development notoriously difficult, which is why the World Health Organization has flagged carbapenem-resistant Pseudomonas among its priority pathogens. Plant phenolics, tannins, and flavonoids are known to attack microbial cells through multiple mechanisms simultaneously, including membrane disruption, enzyme inhibition, and interference with quorum sensing, and this multi-target action makes resistance harder to evolve. The oleander extracts’ activity against both Gram-positive and Gram-negative organisms, along with Candida, suggests a complex mixture whose components complement one another rather than a single narrow-spectrum compound.

The study also carries a sustainability angle that fits squarely within the green chemistry movement. Oleander is fast-growing, drought-tolerant, and widely cultivated as an ornamental, which means substantial biomass is already generated through routine pruning in parks and along roadsides. Converting that low-value biomass into standardized bioactive extracts would require no dedicated agricultural land, and the finding that water, the greenest solvent of the five tested, gives the highest yields strengthens the environmental case further. The researchers note that the collection of plant material complied with WHO guidelines for the assessment of herbal medicines, and the work was conducted at the Faculty of Science of Al-Azhar University in Cairo with open access funding provided through Egypt’s Science, Technology and Innovation Funding Authority and the Egyptian Knowledge Bank.

Important caveats remain before oleander extracts could ever reach a pharmacy shelf or a food-preservation line. The plant’s cardiac glycosides, including the compounds known as oleandrin and nerine referenced in the study, are potently toxic to humans and animals, so any practical application would demand rigorous fractionation, toxicity testing, and dosage control to separate antimicrobial benefit from systemic danger. The current work was conducted in vitro, meaning the results demonstrate inhibition on agar plates rather than efficacy in living organisms, and standardization of extract composition would be essential given the natural variability of plant chemistry. Still, as a foundational map of where oleander’s bioactive chemistry lives, which solvents unlock it, and which microbes it can suppress, the study provides a credible starting point. It transforms a familiar poisonous shrub from a hazard into a candidate feedstock for the search for new natural antimicrobials at a moment when such candidates are urgently needed.

Subject of Research: Phytochemical composition and antimicrobial activity of Nerium oleander extracts obtained with different solvents

Article Title: Green extraction routes for conversion of Nerium oleander L. biomass into bioactive agents: phytochemical insights and antimicrobial promise

Article References: Selim, M. T., & Mahmoud, N. N. (2026). Green extraction routes for conversion of Nerium oleander L. biomass into bioactive agents: phytochemical insights and antimicrobial promise. BMC Complementary Medicine and Therapies, 26(1), Article 288. https://doi.org/10.1186/s12906-026-05594-x

Image Credits: AI Generated

DOI: 10.1186/s12906-026-05594-x

Keywords: Nerium oleander, phytochemistry, green extraction, antimicrobial activity, natural products, phenolics, flavonoids, cardiac glycosides, antimicrobial resistance, plant biomass, solvent extraction, Candida albicans