The stakes are considerable. Arachnid venom peptides are attracting intense interest as candidates for human therapeutics, agricultural bioinsecticides and agents that target vectors of human disease such as ticks and mosquitoes. Their typical molecular targets read like a catalogue of druggable biology: voltage-gated sodium, calcium and potassium channels, ligand-gated ion channels, glutamate receptors and transient receptor potential channels, many of them concentrated in the central nervous system and neuromuscular junctions. Yet a peptide can only reach such targets if it can get past the barriers in between. Understanding membrane permeation is therefore not a technical footnote; it is a prerequisite for translating venom chemistry into medicines and pesticides.

The review first examines the general machinery of cell-penetrating peptides, or CPPs, which cross membranes either by endocytosis, in which the cell engulfs them into vesicles, or by direct permeation through the lipid bilayer. Most CPPs are rich in positively charged residues, particularly arginine and lysine. The guanidinium group of arginine and the amine group of lysine interact with negatively charged membrane surfaces and can help form hydrophobic alpha-helical structures within the bilayer. Once inside endosomes, cationic CPPs exploit their high content of basic amino acids to perturb endosomal pH and escape before being degraded in lysosomes. A second class, the amphipathic peptides, translocate by forming multi-peptide complexes with hydrophobic faces pointing outward and hydrophilic faces inward, sliding through the membrane as a group.

Strikingly, the authors catalogue eight arachnid CPPs from four spider and four scorpion species, six of them cationic and two amphipathic. Among those with characterized mechanisms are latarcin 1 and lycosin-1, both from spiders, whose entry is significantly reduced by cold temperature and endocytosis inhibitors, hallmarks of energy-dependent uptake. The amphipathic peptide LETX-VI, isolated from the eggs of the black widow spider Latrodectus tredecimguttatus, penetrates PC12 cell membranes via endocytosis using the vesicular membrane protein synaptotagmin 1 as a receptor, ultimately promoting dopamine release. Other candidates remain mechanistically mysterious, including LVTX-8, which permeates cancer cell membranes and activates the mitochondrial death pathway, and the scorpion toxins imperatoxin A, maurocalcine and hadrucalcin, all of which must reach the intracellular faces of ryanodine receptors in the endoplasmic reticulum to exert their effects.

Perhaps the most remarkable case is the wasabi receptor toxin WaTx from the Australian scorpion Urodacus manicatus. Despite being amphipathic with a low content of cationic residues, WaTx appears to enter cells by passive diffusion, crossing the membrane without any transporter or endocytic machinery to reach its intracellular binding site on TRPA1 channels. The example underscores that arachnids have evolved more than one solution to the membrane problem. The authors also note that all four known scorpion CPPs are believed to possess cell-penetrating properties because their receptor and channel binding sites sit inside the cell, an indirect but compelling inference from their pharmacology.

Beyond single cells, the review turns to the vertebrate blood-brain barrier, the three-layered fortress of endothelial cells, basement membrane and astrocytic glia limitans that shields the central nervous system. The numbers cited are sobering: only about 2 percent of lipophilic small molecules can cross the barrier, nearly 98 percent of small molecules under 500 daltons fail without delivery systems, and essentially 100 percent of large molecules, including peptides, are excluded. Yet five arachnid peptides have been reported to breach it. Chlorotoxin from the deathstalker scorpion Leiurus quinquestriatus crosses the barrier in tumor-bearing mice and specifically enters glioma cells by clathrin-mediated endocytosis, binding Annexin-2 and matrix metalloproteinase-2, and its safety in human tumor therapy has already been tested in clinical trials. HsTX1[R14A] from the scorpion Heterometrus spinnifer, a selective blocker of the KV1.3 channel linked to Alzheimer’s and Parkinson’s disease, penetrates the mouse brain under neuroinflammatory conditions when tight junctions are disrupted, suggesting a route to treating secondary neuroinflammation.

On the agricultural side, the insect midgut is the critical gate for oral insecticidal activity. Venoms are injected by stinging, so there was no evolutionary pressure to make them orally active, yet eight arachnid venom peptides have now shown oral toxicity against arthropods, implying they can survive the harsh, alkaline midgut environment and cross its epithelium. Transport may occur transcellularly through endocytosis or pore formation, or paracellularly through septate junctions, the invertebrate analogues of tight junctions, through which peptides up to about 5 kilodaltons are thought to pass. The commercial bioinsecticide Spear-T, containing GS-omega/kappa-HXTX-Hv1a from the Blue Mountains funnel-web spider Hadronyche versuta, is designed as a contact spray presumed to enter insects through their respiratory system, with the mesothoracic spiracles offering the fastest route to the central nervous system.

When it comes to physico-chemical signatures, the review delivers a genuinely surprising observation. Although arginine dominates most cationic cell-penetrating peptides outside arachnids, venom CPPs and membrane-crossing arachnid peptides preferentially deploy lysine, which predominates in 18 of the 23 membrane-crossing peptides analysed. One explanation offered is that while arginine-rich peptides are absorbed more efficiently during endocytosis, lysine-rich peptides are more potent at causing liposome leakage, potentially easing their escape into the hemolymph. Lysine substitutions have also been shown to enhance the activity of scorpion antimicrobial venom peptides, hinting at a broader functional role. Compounding the picture, the disulfide-rich inhibitor cystine knot motif, or knottin, grants venom peptides extraordinary thermal and chemical stability, allowing them to survive serum enzymes and the midgut, although several linear, unknotted peptides cross barriers too, possibly relying on pore-forming amphipathic helices.

For peptides with no inherent permeating ability, the review surveys an expanding toolkit of delivery strategies. Poly-lysine and poly-arginine tags can shepherd cargo across cell membranes. Midgut penetration can be boosted by fusion to carrier proteins such as snowdrop lectin, which accumulates in insect hemolymph after oral ingestion, or by co-delivery with insect-specific entomopathogens like Beauveria and Metarhizium fungi or luteoviruses and baculoviruses, whose phyletic selectivity limits off-target effects. Co-application with pore-forming Cry toxins from Bacillus thuringiensis, already deployed in genetically modified crops worldwide, can open the gut lining to venom peptides, while nanoformulations and virus-like particles stripped of genetic material offer safer vehicles. For brain delivery, cationized albumin, the transferrin receptor antibody OX26, liposomes and established CPPs such as TAT provide routes across the blood-brain barrier.

The authors close with a vision in which dissecting these permeation mechanisms benefits both venom biology and applied pharmacology. Conserved features between vertebrate and invertebrate barriers, such as ATP-binding cassette transporters mediating efflux in both, suggest that insect BBB models could reduce the need for vertebrate experiments and accelerate screening of bioinsecticide candidates. Understanding how barrier composition differs between taxa may likewise enable the engineering of drugs and insecticides with sharper selectivity, sparing beneficial organisms. Much remains unresolved, including why lysine outperforms arginine in arachnid peptides and whether in vitro permeation findings hold up in the presence of proteases, renal clearance and off-target binding. But the message is clear: the wall between a promising peptide and its target is no longer assumed to be impassable, and some of nature’s oldest chemical weapons are teaching us how to open the gate.

Subject of Research: Membrane-permeating arachnid venom peptides and their mechanisms for crossing biological barriers

Article Title: Thou shalt not pass – arachnid venom peptides interacting with biological membranes

Article References: Wang, Y., Guo, S., Jee, K. F., & Herzig, V. (2024). Thou shalt not pass – arachnid venom peptides interacting with biological membranes. Frontiers in Arachnid Science, 3, Article 1490313. https://doi.org/10.3389/frchs.2024.1490313

Image Credits: AI Generated

DOI: 10.3389/frchs.2024.1490313

Keywords: arachnid venom, cell-penetrating peptides, blood-brain barrier, insect midgut, bioinsecticides, drug delivery, spider venom, scorpion venom, lipid bilayer, knottins, chlorotoxin, lysine-rich peptides

The researchers built two small libraries of cell-penetrating peptides composed of alternating arginine and tryptophan residues. Arginine carries a positive charge and binds the negatively charged RNA backbone, while tryptophan is hydrophobic and helps the carrier interact with the lipid bilayer of the cell membrane. Each peptide contained a constant five alternating tryptophan-arginine units, either in linear form or as a cyclic ring, attached through a lysine linker to an increasing number of additional linear arginine-tryptophan units. This produced five linear peptides, designated L1 through L5, and five hybrid cyclic/linear peptides, designated C1 through C5, allowing the team to compare the effect of cyclization and of increasing molecular weight within a consistent chemical framework.

The first surprise came from binding measurements. The team mixed each peptide with scrambled siRNA in saline across fourteen nitrogen-to-phosphate (N/P) ratios and quantified binding with a SYBR Green II dye-exclusion assay, calculating the ratio needed for fifty percent binding, known as BR50. The values ranged from 1.21 to 2.08, considerably tighter than the BR50 values above 2.7 typically seen with the group’s earlier peptide carriers. As expected, adding more arginine residues lowered BR50, and the hybrid cyclic peptides generally bound more strongly than their linear counterparts, with statistically significant differences for the L2/C2 and L3/C3 pairs. On paper, this looked like excellent carrier performance: strong binding means good encapsulation and protection from degrading enzymes.

But strong binding has a dark side. When the researchers measured the size and surface charge of the peptide/siRNA complexes, they found hydrodynamic diameters of roughly 98 to 115 nanometers at an N/P ratio of 10, squarely within the 50 to 200 nanometer range considered useful for cancer applications and the enhanced permeation and retention effect. Zeta potentials turned positive at N/P ratios of 10 and above, and the hybrid peptides C2, C4, and C5 showed significantly higher positive charges than their linear counterparts, likely because cyclization makes the peptide more rigid and redistributes its charge. Everything about the particles suggested they should enter cells efficiently.

And enter cells they did. In three breast cancer cell lines, including the triple-negative lines MDA-MB-231 and MDA-MB-468 and the HER2-positive AU 565, flow cytometry with fluorescently labeled siRNA showed that several linear peptides, particularly L1 and L3, achieved internalization comparable to or better than Lipofectamine, a commercial transfection reagent. Confocal microscopy confirmed that the fluorescent signal sat inside the cells, not merely stuck to their surfaces. Yet when the team tested whether this uptake translated into actual gene silencing, targeting the STAT3 protein in MDA-MB-231 cells, the answer was a resounding no. Lipofectamine reduced STAT3 expression to about 61 percent of baseline, but the lead peptide L1 left STAT3 essentially untouched, at 92.5 percent expression.

The explanation lay in the serum stability experiments. When peptide/siRNA complexes were exposed to fetal bovine serum for 24 hours and then treated with heparin, a polyanion normally capable of displacing siRNA from carriers, most complexes refused to release their cargo. The siRNA bands barely moved through the gel, staying trapped in the loading wells, and even raising the heparin concentration from 1.4 to 4 milligrams per liter did not help. Only L1 and, to a lesser extent, L2 showed partial release. This was direct evidence that the peptides gripped siRNA so tightly that neither heparin in the lab nor the cytoplasm inside the cell could pry the cargo loose. The siRNA was being delivered into cells and then effectively imprisoned there, vulnerable to degradation before it could reach the RNA-induced silencing complex.

The solution was to add a third component: Trans-Booster, a commercially available negatively charged transfection aid developed in Hasan Uludag’s laboratory and supplied by RJH Biosciences. When mixed into the peptide/siRNA complexes at a 1:2 siRNA-to-Trans-Booster weight ratio, the polyanion reduced binding affinity, lowered zeta potentials at lower N/P ratios, and, crucially, restored the free siRNA band in the release assays for complexes that had previously shown no release at all. The functional consequences were striking. With Trans-Booster added at 2, 4, and 8 micrograms per milliliter, STAT3 expression in MDA-MB-231 cells dropped to approximately 82, 45, and 41 percent of untreated levels, respectively. In a quantitative GFP-silencing assay in engineered MDA-231 cells, L1 combined with Trans-Booster left only 23.7 percent of the GFP signal remaining, essentially matching Lipofectamine’s 23.6 percent, while the peptides alone left 90 to 96 percent of the signal intact.

The team then asked whether the same principle applied to CRISPR/Cas9 delivery, a far more demanding cargo because the ribonucleoprotein must reach the nucleus. Using fluorescently labeled tracrRNA in HEK-293 cells, they found that the linear peptide L3 at 25 micromolar achieved the highest uptake among the peptides, though the commercial reagent CRISPRMAX still outperformed all peptide formulations. When the peptides were used to deliver RNPs targeting the housekeeping gene HPRT, none of the tested peptides alone produced the two diagnostic cleavage bands detected by the T7 endonuclease assay. But in the groups that included Trans-Booster, faint cleavage bands appeared, most noticeably for L3 and C3, providing the first hint that charge modulation could extend beyond siRNA to genome editing cargo.

The toxicity profile offered additional reassurance. Across all three breast cancer cell lines, the peptide/siRNA complexes were significantly milder than Lipofectamine, which reduced viability in AU 565 cells to 42 percent under the manufacturer’s recommended conditions. The worst peptide complex, C3 in MDA-MB-231 cells, still left 80 percent viability even at the highest N/P ratio of 80. The authors also noted interesting structure-activity nuances: increasing arginine content did not monotonically improve uptake, and in some cell lines the lower N/P ratio of 20 outperformed 40, possibly because excess free peptide disrupts complex organization or because higher tryptophan content promotes compact peptide conformations that bury the very arginine residues needed for cargo binding.

The broader message is that intermediate, tunable binding affinity, not maximal affinity, is the design target for nucleic acid carriers. The finding aligns with reports from other groups, including work showing that excessively tight siRNA binding impairs the in vivo antitumor efficacy of polyplexes, and with the observation that some cell-penetrating peptides require heparin concentrations as high as 4 milligrams per milliliter for complete cargo release. At the same time, the literature contains opposing examples in which ultra-high-affinity RNA-binding proteins enhanced cytosolic delivery, underscoring that the optimum is system-dependent. The authors acknowledge that their study was conducted entirely in vitro, that direct mechanistic evidence of the intracellular release event is still lacking, and that techniques such as isothermal titration calorimetry, circular dichroism spectroscopy, and cryo-electron microscopy will be needed to fully characterize the carrier/cargo interaction. Still, the design principle they establish, that a polyanionic additive can convert a binding-locked carrier into a functional one, offers a practical and generalizable lever for the next generation of peptide-based gene delivery systems.

Subject of Research: Charge modulation of peptide/nucleic acid complexes: an anionic additive enhances gene silencing and CRISPR/Cas9 editing by promoting intracellular nucleic acid release

Article Title: Charge modulation of peptide/nucleic acid complexes: an anionic additive enhances gene silencing and CRISPR/Cas9 editing by promoting intracellular nucleic acid release

Article References: Alhazza, A., Shoushtari, S. K., Uludag, H., Parang, K., & Aliabadi, H. M. (2026). Charge modulation of peptide/nucleic acid complexes: an anionic additive enhances gene silencing and CRISPR/Cas9 editing by promoting intracellular nucleic acid release. Frontiers in Nanotechnology, 8, Article 1925723. https://doi.org/10.3389/fnano.2026.1925723

Image Credits: AI Generated

DOI: 10.3389/fnano.2026.1925723

Keywords: siRNA delivery, CRISPR/Cas9, cell-penetrating peptides, gene silencing, nanomedicine, charge modulation, Trans-Booster, STAT3, breast cancer, nucleic acid release, polyanionic additive, drug delivery

The problem the authors set out to solve is one that anyone who has worked in peptide informatics will recognize immediately. Over the past two decades, the community has built curated databases for cell-penetrating peptides, anticancer peptides, antimicrobial peptides, neuropeptides, toxin peptides and many other functional classes. Each resource encodes genuine expert knowledge, but the knowledge is locked in silos. A researcher asking a simple question — does this sequence cross cell membranes, and is it toxic to cancer cells, and does it serve any other function? — would need to consult multiple databases, reconcile conflicting labels, and contend with inconsistent definitions of what counts as a positive example. The team behind Pep2Net, led by researchers at Hunan University with collaborators at Central South University, the University of Electronic Science and Technology of China and Shenzhen University of Advanced Technology, argues that this fragmentation has become one of the main bottlenecks for computational peptide design.

Their first answer is Pep2Net-DB, an ontology-inspired knowledge base that unifies the 52 peptide resources into a single, coherent structure. The word ontology-inspired is doing real work here: rather than simply dumping datasets into one table, the developers organized peptide types and their attributes according to structured relationships, so that a sequence annotated in one database as a cell-penetrating peptide and in another as an anticancer agent can be understood in a common conceptual framework. Label standardization, one of the keywords the authors attach to the paper, is central to this effort. Without shared definitions, a machine-learning model trained on merged data would learn noise rather than biology; with standardized labels, the merged corpus becomes a training resource far larger and more diverse than any single source database.

The second component, Pep2Net-XAtt, is the predictive engine. It is a multi-task model, meaning that instead of training a separate classifier for each peptide property, one network learns to predict several properties simultaneously. Multi-task learning has a well-established rationale in machine learning: tasks that share underlying structure can regularize one another, and a single model exposed to many labels can pick up generalizable features that a single-task model would miss. For peptides this is particularly apt, because the same physicochemical principles — charge, hydrophobicity, amphipathicity, conformational propensity — govern multiple functional behaviors at once.

What distinguishes Pep2Net-XAtt technically is how it fuses two very different kinds of information. On one side are embeddings from a protein language model, a neural network trained on massive corpora of natural protein sequences that learns to represent amino acid context in dense numerical vectors. These embeddings capture subtle evolutionary and structural patterns that no hand-crafted feature list can encode. On the other side are physicochemical descriptors, the classic quantitative measurements — molecular weight, isoelectric point, hydrophobic moment, charge distribution — that peptide chemists have relied on for decades. Previous models typically treated these two representations separately or simply concatenated them, which the authors argue fails to capture the interactions between semantic sequence context and chemical properties.

Pep2Net-XAtt solves the fusion problem with cross-attention and low-rank bilinear pooling. Cross-attention, the mechanism made famous by transformer architectures, allows one representation to selectively focus on relevant parts of another: the physicochemical descriptor vector can attend to specific positions in the language-model embedding, and vice versa, so that the model learns which chemical features matter in which sequence contexts. Low-rank bilinear pooling then compresses the pairwise interactions between the two representations into a tractable form, multiplying the expressiveness of simple concatenation without the combinatorial explosion that full bilinear interaction would require. The combination lets the network model multiplicative, context-dependent relationships — for instance, how a positive charge at one end of a peptide changes its meaning depending on the hydrophobic pattern along the rest of the chain.

According to the study, this architecture achieves state-of-the-art performance on three prediction tasks: identifying cell-penetrating peptides, predicting anticancer toxicity, and recognizing multi-functional peptides that carry several biological activities simultaneously. The multi-functional task is arguably the most important, because the most therapeutically interesting peptides are rarely one-trick molecules. A candidate drug that crosses cell membranes, kills tumor cells and modulates an immune pathway is exactly the kind of compound that fragmented single-task databases and single-task models systematically overlook. Supplementary material accompanying the paper reports extensive benchmarking, including comparisons with baseline methods, class-wise performance analyses, sequence-length and ensemble robustness checks, and interpretability analyses probing what the model actually learned.

The practical delivery vehicle is Pep2Net Web, a browser-based platform that lets researchers submit sequences and receive multi-task predictions without installing anything. For experimental groups without computational infrastructure, this lowers the barrier substantially: a medicinal chemist screening a panel of candidate peptides can upload them and get functional annotations back in a single pass. The authors position the platform as a tool for large-scale peptide characterization as well as targeted design, and the open-access publication under a Creative Commons license means the underlying data and methods are freely inspectable.

Looking at the bigger picture, Pep2Net arrives at a moment when peptide therapeutics are enjoying a genuine renaissance. GLP-1 receptor agonists have reshaped the treatment of diabetes and obesity, antimicrobial peptides are being pursued as answers to antibiotic resistance, and cell-penetrating peptides are explored as delivery vehicles for cargo that cannot cross membranes on its own. The bottleneck in all these areas is the same: synthesizing and testing peptides is expensive, and the search space of possible sequences is astronomically large. Reliable computational filters that rank candidates before they ever reach the bench can save enormous time and cost, but only if those filters are trained on comprehensive, well-labeled data and can evaluate the full functional profile of a molecule rather than one property at a time.

There are, of course, the usual caveats that accompany any machine-learning advance in biology. Benchmark performance does not guarantee performance on genuinely novel sequence families, and experimental validation remains the final arbiter of any predicted function. The exploratory graph-based structural modeling noted in the supplementary information suggests the authors themselves see structural representation as a frontier for future work. Still, the conceptual contribution is clear and considerable. By unifying 52 scattered resources into one ontology-grounded knowledge base and pairing it with a fusion architecture that finally lets semantic sequence understanding and physicochemical chemistry talk to each other inside a single multi-task model, Pep2Net offers the peptide community something it has lacked: a shared foundation. If the field adopts it, the era in which every peptide property required its own database, its own model and its own paper may finally be drawing to a close.

Subject of Research: An integrated peptide knowledge base and cross-attention deep-learning model for multi-task prediction of peptide functions

Article Title: Pep2Net: an integrated peptide knowledge base and cross-attention model for multi-task prediction of peptides

Article References: Zheng, B., Yuan, J., Wang, Y., Cao, D., Zou, Q., Chen, H., & Fu, X. (2026). Pep2Net: an integrated peptide knowledge base and cross-attention model for multi-task prediction of peptides. Genome Biology. https://doi.org/10.1186/s13059-026-04270-0

Image Credits: AI Generated

DOI: 10.1186/s13059-026-04270-0

Keywords: peptides, Pep2Net, knowledge base, cross-attention, multi-task learning, protein language models, low-rank bilinear pooling, cell-penetrating peptides, anticancer peptides, multi-functional peptides, database integration, peptide design

The delivery strategy is disarmingly simple. Preformed high-fidelity Cas9-ribonucleoproteins are mixed with a molar excess of the peptide in a buffer containing the crowding reagent PEG-PVA, which encourages complexation. The cationic peptide electrostatically binds the negatively charged guide RNA within the RNP, forming nanoparticles that cells take up through a route involving class A scavenger receptors. Ornithine residues built into the peptide’s sequence shield it from degradation by serum proteases. Gel shift assays confirmed that even the lowest peptide ratios immobilized the RNPs, and transmission electron microscopy revealed substantially enlarged nanoparticles at a 1:100 molar ratio compared with RNPs alone. Confocal microscopy using red-fluorescent Cas9 showed punctate intracellular signal within one hour, consistent with endosomal entrapment, followed by diffuse cytoplasmic and nuclear fluorescence by 24 hours.

Optimization began with a titration of Cas9-RNP concentrations, from 10 to 17 nanomolar, against peptide molar ratios spanning 1:50 to 1:200. Higher doses drove editing rates up to roughly 75 percent in fibroblasts and 70 percent in keratinocytes but devastated viability, dropping to as low as 9 percent at the most aggressive condition in keratinocytes. The sweet spot emerged at 10 nanomolar Cas9-RNP with a 1:100 peptide ratio, which preserved about 90 percent viability in fibroblasts and 86 percent in keratinocytes, compared with 74 and 66 percent respectively for electroporation. Although electroporation edited a larger fraction of surviving cells, the superior survival of peptide-treated cultures yielded comparable total numbers of edited cells.

Gene expression profiling added a biological argument for gentleness. Using droplet digital PCR 24 hours after editing, the team found that electroporation upregulated CDKN1A, a marker of cell cycle arrest, while suppressing BUB1, a master regulator of mitotic spindle assembly, in fibroblasts. Most strikingly, electroporated fibroblasts showed elevated TGFB1 expression, a hallmark of fibroblast activation and differentiation into myofibroblasts. Because TGF-beta1 is a major driver of fibrosis and squamous cell carcinoma progression in recessive dystrophic epidermolysis bullosa, seeding engineered skin grafts with electrically stressed, myofibroblast-prone cells could undermine clinical outcomes. Peptide delivery perturbed these pathways to a noticeably smaller extent.

A single amino acid proved consequential. Adding one C-terminal lysine to PepFect14 produced PF14-K, which delivered a consistent, roughly 10 percent improvement in editing across three guide RNAs compared with the parent peptide. Structural analysis offered a possible explanation: circular dichroism spectroscopy showed slightly elevated alpha-helical content in PF14-K, and dynamic light scattering revealed larger RNP-peptide particles, around 130 nanometers versus 90 nanometers for the original peptide, with similar polydispersity. The longer, positively charged lysine side chain may strengthen interaction with the RNP’s negatively charged surface. By contrast, a variant in which the N-terminal stearic acid was replaced by oleic acid lost activity across all tested guides, consistent with the idea that the saturated fatty acid’s straight tail promotes tight hydrophobic packing that stabilizes the nanoparticles, while oleic acid’s double-bond kink disrupts it.

Solvent and serum conditions also mattered. Dissolving the peptide in 90 percent ethanol with 10 percent DMSO, rather than water, yielded subtle but reproducible editing gains, echoing prior observations that this solvent combination better solubilizes both the charged and hydrophobic faces of amphipathic peptides and discourages formation of large micellar aggregates. Despite the peptide’s ornithine-stabilized serum resistance, transfection in serum-free medium improved editing by 15 to 20 percent, with two of three guide RNAs reaching statistical significance. Under fully optimized conditions, PF14-K routinely achieved 70 to 75 percent editing in primary fibroblasts and 50 to 60 percent in keratinocytes, at viability exceeding 80 to 90 percent, versus roughly 70 percent for electroporated cultures.

The therapeutic applications were tested directly in patient-derived cells. For recessive dystrophic epidermolysis bullosa, which stems from COL7A1 mutations, the team used dual Cas9-RNPs to excise mutation-bearing exons and restore the reading frame. In patient keratinocytes carrying a heterozygous single-base deletion within exon 31, PF14-K achieved deletion efficiencies up to 58.4 percent by Nanopore amplicon sequencing, and up to 67.8 percent in patient fibroblasts. Electroporation reached 85 to 90 percent but at the cost of viability averaging just 50.7 percent in patient fibroblasts and 63.3 percent in patient keratinocytes, cells already fragile and slow-growing. Flow cytometry confirmed restoration of COL7 protein in up to 61 percent of peptide-edited keratinocytes. Because 20 to 35 percent editing is considered sufficient for therapeutic benefit in epidermolysis bullosa, the peptide-edited cell populations, being both sufficiently corrected and substantially healthier, could represent a superior graft product.

The most technically demanding result was precise homology-directed repair. Using short single-stranded repair templates co-delivered with the RNPs, the researchers corrected a prevalent nonsense mutation in LAMB3, c.1903C>T, which underlies junctional epidermolysis bullosa. In primary patient keratinocytes, the baseline 3:1:100 molar ratio of template to RNP to peptide achieved 14 percent mutation correction. Raising the peptide ratio to 3:1:150 lifted silent marker incorporation to 48 percent, and adding small-molecule inhibitors of the DNA repair enzymes polymerase theta and DNA-PK pushed precise correction to 37 percent by CRISPResso2 analysis, with electroporation reaching up to 51 percent, or 65 percent with inhibitors, but again with lower viability. Notably, the authors state this is the first demonstration of HDR-mediated repair of a pathogenic mutation, or exon skipping, in primary human cells using a non-viral cell-penetrating peptide strategy; earlier peptide HDR efforts were confined to transfection-permissible cell lines, reporter constructs, or safe-harbor loci.

Caveats remain. The AZD7648 DNA-PK inhibitor used in the dual-inhibition scheme has been linked to large-scale genomic alterations in other contexts, so genome-wide off-target assessment will be essential, even though pairing it with a polymerase theta inhibitor has been shown to mitigate genotoxicity. The gene expression analysis covered only a small panel of markers, and three-dimensional skin models will be needed to test whether PF14-K can deliver editors into intact tissue; prior work showed the parent peptide can deliver miRNA via subcutaneous injection in mice, an encouraging precedent. Still, the mix-and-incubate approach requires nothing more exotic than a commercially synthesized peptide and preformed RNPs, sidestepping the packaging limits and insertional risks of viral vectors, the specialized hardware and cytotoxicity of electroporation, and the microfluidics and mRNA-manufacturing burden of lipid nanoparticles. With base and prime editors increasingly bypassing the need for DNA templates altogether, the researchers argue that PF14-K and its successors could extend non-viral genome editing to a broad range of hard-to-transfect primary cells, and perhaps one day, directly to the skin itself.

Subject of Research: Non-viral CRISPR/Cas9 delivery into primary human skin cells using a PepFect14 cell-penetrating peptide analog for genome editing and repair of epidermolysis bullosa mutations

Article Title: A PepFect14 analog improves non‐viral CRISPR delivery in primary human cells to facilitate genome editing and repair

Article References: du Rand, A., Masterson, C., Verdon, D., Siow, A., Loef, E., Dunbar, R., Kingston, R., Harris, P., & Sheppard, H. (2026). A PepFect14 analog improves non‐viral CRISPR delivery in primary human cells to facilitate genome editing and repair. Bioengineering & Translational Medicine, Article e70172. https://doi.org/10.1002/btm2.70172

Image Credits: AI Generated

DOI: 10.1002/btm2.70172

Keywords: CRISPR, Cas9 ribonucleoproteins, cell-penetrating peptides, PepFect14, PF14-K, epidermolysis bullosa, COL7A1, LAMB3, homology-directed repair, gene therapy, keratinocytes, non-viral delivery