TLDR
- A 2018 study in the Journal of Controlled Release investigated CB5005, a synthetic cell-penetrating peptide designed to also inhibit NF-κB signaling.
- Researchers attached CB5005 to PEGylated liposomes carrying the chemotherapy drug doxorubicin.
- In U87 glioma cells, CB5005-modified liposomes increased cellular uptake, improved penetration into three-dimensional tumor spheroids, and helped deliver doxorubicin into the nucleus.
- The modified liposomes reduced the doxorubicin IC50 in U87 cells from about 2.006 μM to 0.342 μM, an approximately sixfold difference in that specific cell assay.
- In mice with intracranial glioblastoma models, median survival was 33.5 days with CB5005-modified doxorubicin liposomes compared with 28.5 days for ordinary doxorubicin liposomes and 25 days for saline.
- These were preclinical experiments involving cultured cells and mice. They do not demonstrate that CB5005 is an effective glioblastoma treatment in humans.
- Later preclinical research has continued to investigate CB5005 as a drug-delivery and nuclear-penetrating peptide, but the research reviewed here has not established it as a clinically validated therapy.
A useful peptide does not necessarily need to perform only one biological task.
That idea was central to a 2018 study published in the Journal of Controlled Release. Researchers investigated a synthetic peptide called CB5005 that was designed to combine two potentially useful properties: it could help cargo cross cellular barriers, and it could interfere with the NF-κB signaling pathway.
Rather than studying CB5005 only as an isolated peptide, the researchers attached it to the surface of PEGylated liposomes carrying doxorubicin. Their goal was ambitious. They wanted the peptide to help the drug-delivery system reach glioma tissue, penetrate tumor cells, transport doxorubicin toward the nucleus, and simultaneously reduce a signaling pathway associated with cancer-cell survival and chemotherapy resistance.
The results were promising enough to make CB5005 an interesting example of how peptides can be used as functional components of experimental drug-delivery systems.
But the study was conducted in cell models and mice. Understanding what it showed requires keeping that limitation in view.
Why Glioblastoma Is Such a Difficult Drug-Delivery Problem
Glioblastoma is one of the most difficult cancers to treat.
Modern treatment for newly diagnosed glioblastoma generally combines maximal safe surgical removal with radiation and temozolomide-based chemotherapy. Despite decades of research, outcomes remain poor.
Part of the problem is the biology of the tumor itself.
Glioblastoma is highly infiltrative. Tumor cells can extend into surrounding brain tissue, making complete surgical removal difficult. Different regions of the same tumor can also contain biologically different cell populations.
Then there is the physical problem of delivering drugs into the brain.
The blood-brain barrier, or BBB, tightly regulates movement of substances from the bloodstream into brain tissue. Glioblastoma can disrupt portions of this barrier, but drug delivery remains inconsistent. The related blood-tumor barrier can further limit how much of a systemically administered therapy reaches all regions of a tumor.
These delivery barriers remain major research problems in 2026.
And they explain why researchers are interested in peptides that can help move therapeutic cargo through biological membranes.
What Is CB5005?
CB5005 is a synthetic peptide designed to combine cell penetration with inhibition of NF-κB signaling.
The peptide used in the 2018 study had the sequence:
KLKLALALALAVQRKRQKLMPC
The researchers described it as containing functional regions associated with membrane penetration and an NF-κB nuclear localization sequence.
This design was not created from scratch for the 2018 liposome study.
Earlier work from some of the same researchers had investigated CB5005 as a free peptide. In a 2016 study, CB5005 entered brain endothelial and U87 glioma cells, accumulated in their nuclei, penetrated glioma spheroids, and distributed to brain and tumor tissue in mouse experiments.
That previous research also suggested that CB5005 could interfere with nuclear translocation of NF-κB and act synergistically with doxorubicin in preclinical glioma models.
The 2018 paper took the next step.
Instead of simply administering CB5005 alongside doxorubicin, the researchers used the peptide as part of the drug carrier itself.
Why NF-κB Was Part of the Strategy
NF-κB stands for nuclear factor kappa-light-chain-enhancer of activated B cells.
It is not one single protein. NF-κB refers to a family of transcription factors involved in processes such as:
- inflammation
- immune responses
- cell survival
- proliferation
- stress responses
- cytokine production
In resting cells, NF-κB proteins are often retained outside the nucleus through interactions with inhibitory proteins.
When the pathway is activated, NF-κB can move into the nucleus and regulate gene expression.
That is normal biology.
But abnormal or persistent NF-κB signaling is also associated with several cancers. Depending on the tumor and biological context, NF-κB activity can contribute to survival signaling, inflammation, treatment resistance, and other processes that support tumor progression.
The 2018 researchers reported constitutive NF-κB activation in the U87 glioma cells used for their experiments.
CB5005 was designed to interfere with the nuclear localization process.
The researchers found that sufficiently high concentrations of CB5005 reduced the amount of the NF-κB-related p50 protein detected in U87 cell nuclei.
That gave the peptide its second proposed function.
It was not merely intended to carry something into a cell.
It was also intended to alter a cancer-related signaling pathway.
Why Combine CB5005 With Liposomes?
Liposomes are microscopic vesicles composed largely of lipid bilayers.
Their structure makes them useful experimental and pharmaceutical drug carriers because they can encapsulate drugs and alter how those drugs circulate and distribute.
PEGylation adds polyethylene glycol chains to the liposome surface.
PEG can help reduce rapid recognition and removal of liposomes from circulation, although PEGylation introduces its own biological and formulation considerations.
The 2018 researchers created doxorubicin-loaded PEGylated liposomes and attached CB5005 to the surface.
The resulting formulation was called:
CB5005-LS/DOX
They compared it with similar liposomes containing doxorubicin but without CB5005:
LS/DOX
This comparison was important.
It allowed the researchers to ask whether adding the peptide changed the behavior of an otherwise similar liposomal carrier.
What Did the CB5005 Liposomes Look Like?
The peptide-modified doxorubicin liposomes had an average particle size of approximately:
111.7 ± 0.23 nanometers
The unmodified doxorubicin liposomes were slightly smaller at approximately:
105.7 ± 0.35 nanometers
The CB5005 formulation had a polydispersity index of approximately 0.150 and a zeta potential of roughly -4.94 mV.
One interesting tradeoff appeared in drug encapsulation.
The researchers reported approximately:
90.8% doxorubicin encapsulation efficiency for LS/DOX
compared with:
70.0% for CB5005-LS/DOX
So peptide modification did not improve every formulation characteristic.
The CB5005 system carried a lower percentage of encapsulated doxorubicin under the conditions reported in the study.
Its proposed advantage was instead what happened after the liposomes encountered cells and tumors.
CB5005 Dramatically Increased Cellular Uptake in the Model
The researchers first studied whether peptide modification helped the liposomes enter glioma cells.
Fluorescent molecules were used to make uptake easier to measure.
At one of the lower concentrations tested, 0.01 μM, more than 99% of cells were reported as fluorescence-positive after exposure to CB5005-modified liposomes.
Under the same conditions, fewer than 1% were fluorescence-positive with the unmodified liposomes or free fluorescent compound.
That is a large experimental difference.
It suggested that CB5005 fundamentally changed how the liposomal particles interacted with U87 glioma cells.
The result also fit the original design of CB5005 as a cell-penetrating peptide.
The Liposomes Also Penetrated Three-Dimensional Tumor Spheroids
Two-dimensional cell culture is useful, but it does not reproduce many of the physical characteristics of a solid tumor.
Researchers therefore also used tumor spheroids.
These are three-dimensional collections of tumor cells that provide a more challenging penetration environment than cells grown as a flat layer.
CB5005-modified fluorescent liposomes produced substantially stronger fluorescence throughout the U87 tumor spheroids than either free fluorescent material or unmodified liposomes.
The researchers interpreted this as evidence that CB5005 improved penetration into the three-dimensional tumor model.
This is important because reaching the outside of a tumor is not the same thing as penetrating deeply through tumor tissue.
Drug distribution within a solid tumor can be uneven.
A delivery system that concentrates only near blood vessels or around the tumor surface may leave other tumor cells insufficiently exposed.
CB5005 Helped Deliver Doxorubicin Toward the Cell Nucleus
Doxorubicin works largely through interactions involving DNA and topoisomerase II.
Getting doxorubicin into a cell is therefore only part of the delivery problem.
Intracellular localization matters too.
The researchers used microscopy to follow doxorubicin fluorescence.
CB5005-modified liposomes produced stronger intracellular and nuclear localization than ordinary doxorubicin liposomes.
This fits with the structure of CB5005.
The peptide was designed not only for membrane penetration but also for movement toward the nucleus.
That gave the system a layered delivery strategy:
bloodstream → tumor → cell → nucleus
Each level represents a different biological barrier.
The Cell-Killing Difference Was Substantial
The researchers next measured cytotoxicity against U87 glioma cells.
A common way to compare cytotoxicity is through the IC50, which is the concentration associated with 50% inhibition in the particular assay being used.
The reported IC50 values were approximately:
CB5005-LS/DOX: 0.342 μM
LS/DOX: 2.006 μM
That is nearly a sixfold difference.
In other words, much less doxorubicin was required in the CB5005-modified formulation to produce the same level of inhibition in that U87 assay.
The paper’s abstract described the modified liposomes as increasing glioma-cell killing efficiency by more than fivefold compared with unmodified doxorubicin liposomes.
This was one of the study’s strongest findings.
But IC50 values should always be interpreted within their experimental context.
They do not translate directly into human doses or clinical effectiveness.
The Researchers Then Tested Distribution in Mice
Cell experiments cannot determine whether a drug-delivery system survives circulation or reaches a tumor inside an organism.
The research team therefore moved into mouse models.
Fluorescently labeled CB5005-modified liposomes were given intravenously.
Imaging suggested that CB5005 modification increased delivery to the brain and accumulation within tumor tissue compared with unmodified liposomes.
The researchers examined several models, including intracranial glioblastoma-bearing nude mice.
This was particularly relevant because intracranial tumors introduce some of the anatomical barriers that do not exist in a subcutaneous tumor model.
The peptide-modified liposomes again showed increased tumor-associated fluorescence.
What Happened to Survival in the Mouse Glioblastoma Model?
The most clinically intuitive endpoint in the study was survival.
Median survival in the intracranial glioblastoma-bearing mice was reported as approximately:
- 33.5 days with CB5005-LS/DOX
- 28.5 days with LS/DOX
- 27.5 days with free doxorubicin
- 27 days with CB5005 liposomes without doxorubicin
- 25 days with saline
The difference between CB5005-LS/DOX and the control groups was statistically significant in the study.
The result supported the researchers’ central hypothesis.
Adding CB5005 appeared to do more than change an imaging signal.
It improved therapeutic performance in their animal model.
Still, the absolute interpretation needs restraint.
These were mice carrying experimentally produced tumors, not patients with naturally occurring human glioblastoma.
Why the Dual-Function Design Is Scientifically Interesting
The most interesting part of the study may not be any one numerical result.
It is the design philosophy.
CB5005 was intended to perform two different jobs.
Function 1: Improve Delivery
The peptide helped the liposome:
- associate with cells;
- penetrate cells;
- move through tumor spheroids;
- accumulate in brain tumor models;
- increase nuclear delivery of doxorubicin.
Function 2: Modify Tumor Signaling
CB5005 was also intended to interfere with NF-κB nuclear signaling.
That potentially attacks a second problem: cellular pathways associated with survival and chemotherapy resistance.
Instead of treating the carrier as biologically passive, the researchers designed part of the carrier to have biological activity of its own.
That concept continues to appear in peptide-based drug-delivery research today.
Why NF-κB Inhibition Is More Complicated Than It Sounds
It would be easy to summarize the paper as:
NF-κB is bad in cancer, so blocking NF-κB is good.
Biology is not that simple.
NF-κB is a fundamental signaling system involved in normal:
- immune defense
- inflammatory responses
- tissue homeostasis
- cell survival
- development
A 2025 review in Cellular & Molecular Immunology emphasized this problem. Systemically and indiscriminately suppressing NF-κB can compromise normal immune responses and potentially increase susceptibility to infection.
That creates an important argument for targeted delivery.
If NF-κB inhibition is useful primarily inside certain tumor cells, a system that concentrates the inhibitor at the tumor could theoretically be preferable to widespread inhibition.
Whether CB5005 achieves enough specificity and safety to accomplish that in humans remains unanswered.
Cell-Penetrating Peptides Have Their Own Targeting Problem
Cell-penetrating peptides can be very good at entering cells.
That can also be their weakness.
If a peptide efficiently enters many different kinds of cells, it may lack the specificity needed for systemic therapy.
The earlier CB5005 research was partly motivated by this problem.
The investigators reported preferential brain and glioma accumulation in their mouse models, but animal biodistribution does not establish human tumor specificity.
Modern reviews of cell-penetrating peptides still list selectivity, stability, pharmacokinetics, toxicity, and efficient in vivo targeting among the challenges that need to be solved before many CPP systems can become clinical therapies.
So cell penetration and tumor targeting should not be treated as synonymous.
What Happened to CB5005 Research After This Study?
The idea did not disappear after 2018.
A 2020 study applied CB5005 to another liposomal chemotherapy system.
Researchers attached CB5005 to irinotecan-loaded liposomes and studied the system against non-small-cell lung cancer.
Again, the peptide increased cellular uptake and reduced nuclear NF-κB-related p50 levels.
In mouse xenograft experiments, CB5005 modification improved the antitumor performance of the irinotecan formulation.
A 2022 study took a different approach.
Researchers incorporated CB5005 into a more complicated experimental nanocomposite designed to improve nuclear delivery of doxorubicin in multidrug-resistant breast cancer models.
These studies support the broader concept that CB5005 can function as part of different drug-delivery architectures.
But they remain preclinical research.
What the 2018 Study Did Not Establish
This distinction is essential.
The study did not establish that CB5005:
- treats glioblastoma in humans;
- improves survival in human patients;
- is safe for human administration;
- can be administered repeatedly without toxicity;
- has an established clinical dose;
- reliably crosses the human blood-brain barrier;
- provides adequate tumor specificity in humans;
- is superior to current glioblastoma therapy.
It was not a clinical trial.
The experiments used U87 glioma cells, tumor spheroids, and mouse models, including nude mice.
Nude mice are immunodeficient, which makes human tumor xenograft research possible but also means the model cannot reproduce a normal human immune system.
That becomes especially relevant when studying a signaling pathway as deeply connected to immunity as NF-κB.
U87 Cells Are Useful, but Glioblastoma Is Far More Complex
Another important limitation is the tumor model.
U87 cells have been used extensively in glioma research.
But a long-established cell line does not reproduce the molecular heterogeneity of human glioblastoma.
Modern glioblastoma research increasingly uses:
- patient-derived tumor cells
- glioma stem-cell models
- organoids
- genetically defined models
- patient-derived xenografts
- immunocompetent models where appropriate
Modern classification has also changed.
Under current WHO criteria, the term glioblastoma is specifically associated with IDH-wildtype diffuse astrocytic tumors meeting defined histological or molecular criteria.
That level of molecular stratification was not the focus of the 2018 CB5005 study.
The paper is best understood as proof-of-concept drug-delivery research rather than evidence applicable to every modern glioblastoma subtype.
Doxorubicin Is Also Important Context
Doxorubicin is a well-established chemotherapy drug for several cancers.
It is not part of the routine standard systemic treatment for newly diagnosed glioblastoma.
One reason is limited penetration into the central nervous system.
That makes it useful experimentally for testing whether a delivery technology can change brain exposure.
But showing that CB5005 improves delivery of doxorubicin in mice does not automatically establish that doxorubicin is the optimal payload for future human glioblastoma therapy.
The broader platform concept may ultimately matter more than the particular drug used in this experiment.
A peptide delivery system could potentially be paired with other therapeutic cargoes if future research supported doing so.
Peptide-Based Glioblastoma Delivery Is Still an Active Research Area
The broader scientific idea behind the CB5005 paper remains highly relevant.
A 2025 review in the Journal of Controlled Release specifically examined peptide-based approaches for glioblastoma, including peptides used as therapeutic molecules, targeting agents, and delivery vehicles.
Researchers continue to investigate ways of using peptides to:
- cross or bypass the blood-brain barrier;
- bind receptors expressed at the BBB;
- target glioblastoma cells;
- penetrate tumor tissue;
- carry drugs;
- alter tumor-associated immune cells;
- deliver nucleic acids or other therapeutic molecules.
Peptide stability and bioavailability remain major barriers to clinical translation.
So the 2018 CB5005 study fits into an area of research that is still very active rather than being an isolated experiment from a discarded field.
Why This Study Still Matters
The CB5005 paper is useful because it demonstrates several principles of modern peptide research in one experiment.
First, peptides can be designed as functional molecular tools, not only as standalone therapeutic compounds.
Second, drug delivery has multiple levels.
Reaching the brain is not enough.
A system may also need to:
- reach the tumor;
- leave the tumor vasculature;
- penetrate tumor tissue;
- enter the target cell;
- escape intracellular compartments;
- reach the correct organelle or molecular target.
Third, the carrier itself can potentially contribute biologically to therapy.
CB5005 was designed to help transport the liposome while also modifying NF-κB signaling.
That multifunctional approach is increasingly common in experimental nanomedicine and peptide engineering.
The Most Accurate Interpretation of the Research
The 2018 results are promising.
They are also early.
CB5005-modified liposomes performed better than comparable unmodified doxorubicin liposomes across several preclinical measurements.
The peptide increased cellular uptake.
It improved penetration into U87 spheroids.
It increased nuclear localization of doxorubicin.
It lowered the IC50 of liposomal doxorubicin in U87 cells by almost sixfold.
And it extended median survival in an intracranial mouse glioblastoma model from 28.5 days with ordinary doxorubicin liposomes to 33.5 days with CB5005-modified liposomes.
Those are meaningful experimental findings.
What they demonstrate is that CB5005 was a promising multifunctional drug-delivery component in the particular models studied.
They do not demonstrate that CB5005 is an effective human glioblastoma treatment.
That next step requires a much larger chain of evidence involving pharmacology, toxicology, manufacturing, biodistribution, tumor specificity, appropriate animal models, and ultimately controlled human clinical trials.
That distinction is not a criticism of the study.
It is how preclinical research is supposed to work.
The experiment provided a reason to keep investigating.
It did not provide the final answer.
FAQs
What Is CB5005?
CB5005 is a synthetic peptide designed to combine cell-penetrating properties with interference in NF-κB nuclear signaling. It has been studied as both an experimental peptide and a component of drug-delivery systems.
What Was CB5005 Used for in the 2018 Study?
Researchers attached CB5005 to PEGylated liposomes containing doxorubicin. The peptide was intended to improve glioma penetration and cellular uptake while also inhibiting NF-κB signaling.
Did CB5005 Cross the Blood-Brain Barrier?
The researchers observed increased brain and intracranial tumor-associated fluorescence after intravenous administration of CB5005-modified liposomes in mice. That supports brain delivery in the animal models used, but it does not establish equivalent penetration across the human blood-brain barrier.
Did CB5005 Make Doxorubicin More Effective?
In U87 glioma cells, CB5005-modified doxorubicin liposomes had an IC50 of about 0.342 μM compared with approximately 2.006 μM for unmodified doxorubicin liposomes. The modified formulation also increased survival in the study’s intracranial mouse tumor model.
What Is NF-κB?
NF-κB is a family of transcription factors involved in inflammation, immune responses, cell survival, and numerous other biological processes. Abnormal NF-κB activity is associated with several cancers and can contribute to treatment resistance in some contexts.
Is CB5005 an Approved Glioblastoma Treatment?
No. The research discussed here is preclinical. The 2018 study used cells and mice, not human patients.
Has CB5005 Been Studied Since 2018?
Yes. Later preclinical work has investigated CB5005-modified liposomal irinotecan in lung cancer models and CB5005-assisted nuclear drug delivery in experimental breast cancer systems.
Does This Research Show That Peptides Can Treat Brain Cancer?
The study shows that a peptide can be engineered to alter drug delivery and biological signaling in experimental glioma models. It does not establish that CB5005 or peptide-based delivery in general is clinically effective against human glioblastoma.
References
- Zhang Y, Zhang L, Hu Y, Jiang K, Li Z, Lin YZ, Wei G, Lu W. Cell-permeable NF-κB inhibitor-conjugated liposomes for treatment of glioma. Journal of Controlled Release. 2018;289:102-113. ScienceDirect | PubMed
- Zhang L, Zhang Y, Tai L, et al. Functionalized cell nucleus-penetrating peptide combined with doxorubicin for synergistic treatment of glioma. Acta Biomaterialia. 2016;42:90-101. PubMed
- Hu Y, et al. Treatment of Lung Cancer by Peptide-Modified Liposomal Irinotecan Endowed with Tumor Penetration and NF-κB Inhibitory Activities. Molecular Pharmaceutics. 2020;17:3685-3695. PubMed | ACS Publications
- Liu Y, Zhou Z, Li P, et al. Combating multidrug resistance and metastasis of breast cancer by endoplasmic reticulum stress and cell-nucleus penetration enhanced immunochemotherapy. Theranostics. 2022. Full text at PubMed Central
- Mao H, Zhao X, Sun SC. NF-κB in inflammation and cancer. Cellular & Molecular Immunology. 2025;22:811-839. Nature
- Yang D, Liu B, Sha H. Advances and prospects of cell-penetrating peptides in tumor immunotherapy. Scientific Reports. 2025;15:3392. Nature
- Moreno-Vega LM, et al. Cancer-Targeting Applications of Cell-Penetrating Peptides. International Journal of Molecular Sciences. 2025;26:2. Full text at PubMed Central
- Peptide-based strategies for glioblastoma therapy: From small molecular drugs to delivery vehicles. Journal of Controlled Release. 2025;385:114023. PubMed | ScienceDirect
- Combination of cell-penetrating peptides with nanomaterials for the potential therapeutics of central nervous system disorders: a review. Journal of Nanobiotechnology. 2021. PubMed | Springer Nature
- Glioblastoma in adults: A Society for Neuro-Oncology and European Society of Neuro-Oncology consensus review on current management and future directions. Full text at PubMed Central