Cell-Penetrating Peptide Examples: A Cited List From the Published Literature

Cell-penetrating peptides, often shortened to CPPs, are short amino acid sequences studied because they can carry much larger molecules across the plasma membrane of cells. Reviews of the field describe them as delivery vehicles for cargo that would otherwise be excluded by the membrane, including proteins, nucleic acids and nanoparticles (PMID 28209404). The formal definition, including what counts as a CPP and what does not, is covered separately in the cell-penetrating peptide glossary entry, so this page focuses on the named examples that appear most often in published work.

This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about your own health. Nothing here describes how any substance should be used in a person, and no amounts, schedules or regimens are provided.

How the Examples Below Are Organised

Published reviews generally sort CPPs by the chemistry of their sequences rather than by what they carry. A common grouping separates strongly positively charged (cationic) sequences, amphipathic sequences that combine charged and water-repelling faces, and largely hydrophobic sequences, with the mode of membrane interaction differing between these groups (PMID 34193708). A second common axis is origin: some sequences were identified inside naturally occurring proteins, while others were designed or assembled synthetically (PMID 29039455).

The table lists the examples that recur across the cited reviews. The "main published use" column summarises what the cited source describes as the research application, not an approved indication.

Table: Frequently Cited Cell-Penetrating Peptides

Notes on the Best-Known Entries

TAT

TAT is the sequence most often used as a reference point in CPP work. The 2017 review of CPPs from basic research to clinics placed TAT among the peptides that opened the field and discussed the translation of CPP-based constructs toward clinical settings (PMID 28209404). A separate review focused on genome function modification described CPPs including TAT as vehicles used to deliver molecules that act on gene expression and genome editing machinery inside cells (PMID 29039455).

Penetratin

Penetratin derives from a transcription factor domain and is frequently paired with TAT in comparative work. In ocular delivery research, reviewers reported that CPPs have been examined as a way to move drugs across the barriers of the eye, an application area where short cationic peptides including penetratin-type sequences feature (PMID 29913221).

Polyarginine

Arginine repeats are the clearest demonstration that the guanidinium group, rather than a specific natural protein sequence, drives much of the uptake behaviour of cationic CPPs. Work on peptides that target biomembranes described how charge, helicity and amphipathicity shape the way such sequences associate with and cross lipid bilayers (PMID 34193708). Reviews of CPP and nanoparticle hybrids reported arginine-rich ligands as a common strategy for increasing uptake of liposomes and polymeric particles (PMID 30634689).

What the Cargo Literature Reports

The practical interest in CPPs comes from the cargo problem. Large, charged or fragile molecules do not cross membranes well on their own, and researchers have tested peptide carriers against that limitation in several distinct areas.

• Nucleic acids. A 2019 review of therapeutic mRNA delivery technologies surveyed the carrier systems under investigation, including peptide-based approaches, and reported that delivery remains a central obstacle for mRNA therapeutics (PMID 30846391).
• Genome function tools. Reviewers described CPPs as carriers used in studies that modify genome function, including the intracellular delivery of effector molecules and editing components (PMID 29039455).
• Nanoparticles. A review of CPP and nanoparticle combinations reported that attaching penetrating sequences to particle surfaces has been used to improve cellular entry of the whole construct (PMID 30634689).
• Intracellular bacteria. Researchers reviewing antimicrobial and cell-penetrating peptides reported that bacteria surviving inside host cells are difficult for conventional antibacterials to reach, which motivated interest in membrane-crossing peptides (PMID 33614528).
• Ocular delivery. A state-of-the-art review examined CPPs for drug delivery to the eye and discussed the barriers that limit conventional formulations (PMID 29913221).
• Oral routes. A review of chemically modified peptides and proteins described the critical considerations for oral delivery, where enzymatic degradation and epithelial barriers constrain what peptide constructs can achieve (PMID 27358754).

Research Tools Versus Clinical Status

Most of the sequences in the table above are laboratory reagents used to study membrane crossing, cargo delivery and intracellular targeting. The 2017 review that traced CPPs from basic research toward the clinic discussed the gap between laboratory performance and clinical development, noting that translation has been slower than early enthusiasm suggested (PMID 28209404). Clinical status therefore varies by construct rather than by peptide family, and a sequence being widely used in cell culture says nothing about whether any product containing it has been evaluated or authorised in people.

In the infectious disease space, researchers writing on the design of improved active peptides reported that stability, selectivity and manufacturing cost are recurring hurdles for moving peptide candidates forward (PMID 29330093). In oncology, the review of cancer targeting peptides described targeting sequences as a strategy intended to concentrate payloads in tumour tissue, which is a research objective rather than a demonstrated clinical outcome for any particular sequence (PMID 30877335).

Limitations and Safety Signals: What Studies Report

Reviews of the field have been consistent about the weaknesses of peptide carriers. The 2017 clinical translation review reported that limited selectivity between cell types and entrapment of cargo inside endosomes are major constraints on CPP performance (PMID 28209404). Work on biomembrane-targeting peptides described how the same membrane interactions that allow entry can also perturb lipid bilayers, which is why sequence design attempts to balance uptake against membrane damage (PMID 34193708).

Stability is a second theme. The review of chemically modified peptides for oral delivery reported that proteolytic degradation and poor permeability limit peptide bioavailability, prompting chemical modification strategies (PMID 27358754). Reviewers of peptide design for infectious disease similarly reported that natural sequences often require engineering to resist degradation and to reduce unwanted activity against host cells (PMID 29330093). For nucleic acid cargo specifically, the mRNA delivery review reported that carrier systems must protect the payload and release it in the cytoplasm, a two-step requirement that many systems satisfy only partially (PMID 30846391).

None of the cited sources establishes a safety profile for any of these peptides in people outside controlled research settings, and none of the material above should be read as a suggestion that any sequence be used by an individual.

Reading the List Critically

1. Names are not standardised. The same sequence can appear under several labels and with different length variants across papers, which the CPP review literature reflects (PMID 29039455).
2. Uptake depends on context. Cell type, cargo, concentration and measurement method all influence what a study observes, and reviewers of CPP-based delivery techniques emphasised that mechanism remains debated (PMID 29680237).
3. Origin does not predict behaviour. Naturally derived and fully synthetic sequences appear throughout the field, and plant-derived membrane-active peptides are studied as design templates in their own right (PMID 24092498).

Related Reading

• Cell-penetrating peptide: glossary definition
• What is a signal peptide?
• Polypeptide examples

References

• Cell-Penetrating Peptides: From Basic Research to Clinics (Trends in Pharmacological Sciences, 2017)
• Delivering the Messenger: Advances in Technologies for Therapeutic mRNA Delivery (Molecular Therapy, 2019)
• Cancer targeting peptides (Cellular and Molecular Life Sciences, 2019)
• Antimicrobial Peptides and Cell-Penetrating Peptides for Treating Intracellular Bacterial Infections (Frontiers in Cellular and Infection Microbiology, 2020)
• Plant antimicrobial peptides (Folia Microbiologica, 2014)
• Cell-penetrating peptides and their utility in genome function modifications (International Journal of Molecular Medicine, 2017)
• Smart Cell-Penetrating Peptide-Based Techniques for Intracellular Delivery of Therapeutic Macromolecules (Advances in Protein Chemistry and Structural Biology, 2018)
• Combination of Cell-Penetrating Peptides with Nanoparticles for Therapeutic Application: A Review (Biomolecules, 2019)
• Chemically modified peptides and proteins, critical considerations for oral delivery (Tissue Barriers, 2016)
• Functional Peptides That Target Biomembranes: Design and Modes of Action (Chemical and Pharmaceutical Bulletin, 2021)
• Cell penetrating peptides in ocular drug delivery: State of the art (Journal of Controlled Release, 2018)
• Designing improved active peptides for therapeutic approaches against infectious diseases (Biotechnology Advances, 2018)