A new class of uncharged synthetic molecules entered cells more efficiently than a leading cell-penetrating peptide while avoiding the charge-related problems that have limited CPP drug delivery.
Outperformed R9 CPPNoncharged oligoTEAs entered cells more efficiently than the widely used R9 cell-penetrating peptide while maintaining lower toxicity
What the researchers found
Researchers discovered a new class of noncharged cell-penetrating oligoTEAs (CPOTs) that entered cells extensively and rapidly across multiple cell lines with low toxicity. These synthetic oligomers outperformed R9 — a widely used nine-arginine cell-penetrating peptide — in cellular uptake efficiency.
Unlike traditional cationic cell-penetrating peptides that rely on positive charges (which cause unwanted biological interactions and rapid degradation), CPOTs achieve cell entry through a charge-independent mechanism. This makes them more stable in serum and better candidates for delivering water-soluble drugs inside cells.
Why it matters
Cell-penetrating peptides (CPPs) have been studied for decades as drug delivery tools, but their positive charge causes problems — they interact nonspecifically with biological molecules, trigger unwanted immune responses, and are quickly degraded by enzymes. This discovery of noncharged alternatives that outperform traditional CPPs addresses these fundamental limitations and could unlock more practical intracellular drug delivery systems for therapeutics that need to reach targets inside cells.
The numbers in context
Outperformed R9 CPP in uptake · Low cytotoxicity · Multiple cell lines tested · Noncharged design · Sequence-defined architecture
How the study worked
Researchers synthesized a library of noncharged sequence-defined oligoTEAs and screened their cell-penetrating ability across different cell lines. Cellular uptake was quantified using fluorescence measurements and compared head-to-head against R9 peptide (a standard CPP). Cytotoxicity was assessed to ensure safety. The mechanism of entry and delivery efficiency for hydrophilic small molecules were characterized.
Who was studied
In vitro cell culture studies using multiple human cell lines including HeLa cells
What this study cannot tell us
All experiments were conducted in vitro using cell lines, which may not predict in vivo performance. The study focused on small-molecule cargo delivery — whether CPOTs can deliver larger payloads like proteins or nucleic acids was not demonstrated. Long-term stability, biodistribution, and safety in animals remain untested. The comparison was against R9 alone; performance against other advanced CPPs was not assessed.
How to read the evidence
This is a preclinical in vitro discovery study demonstrating a new class of cell-penetrating molecules. The comparison against R9 peptide provides a useful benchmark, but all work is in cell culture with no in vivo data.
When this study was published
Published in 2018, this study introduced CPOTs as a new delivery platform. Subsequent research may have further developed this approach or compared it against more advanced CPP variants.
The bigger picture
The field of intracellular drug delivery has been heavily invested in cationic cell-penetrating peptides for over two decades, despite their well-known limitations. This work challenges the assumption that positive charge is necessary for cell entry, potentially opening a new chapter in drug delivery science. If CPOTs prove effective in vivo, they could complement or replace traditional CPPs for delivering a wide range of therapeutics to intracellular targets.
Questions still open
- Can CPOTs deliver larger cargo like proteins or nucleic acids as effectively as small molecules?
- How do CPOTs perform in vivo — do they maintain their cell-penetrating advantage in blood and tissues?
- What is the specific mechanism by which noncharged molecules cross cell membranes?
Common questions
Why is getting drugs inside cells so difficult?
How can something without a charge get inside a cell?
Read the original research
Intracellular Delivery via Noncharged Sequence-Defined Cell-Penetrating Oligomers.
Bioconjugate chemistry, 29(8), 2628-2635
Citation
Phan, Ngoc N; Li, Connie; Alabi, Christopher A. (2018). Intracellular Delivery via Noncharged Sequence-Defined Cell-Penetrating Oligomers.. Bioconjugate chemistry, 29(8), 2628-2635. https://doi.org/10.1021/acs.bioconjchem.8b00336