PEGylation of a Peptide-Based Amphiphilic Delivery Agent and Influence on Protein Delivery to Cells

Design of thermo-responsive self-assembly of PEGylated fatty acids: Switching reversibly from tubes or vesicles to micelles at physiological temperature

HYPOTHESIS

The mixing of end-capped poly(ethylene glycol) (PEG) chains with 12-hydroxy stearic acid (12-HSA) molecules is a simple one-pot strategy to design thermo-responsive PEGylated self-assemblies of fatty acids with various morphology types at room temperature (multi-lamellar tubes or vesicles) that transit reversibly upon heating into small micelles around physiological temperature.

EXPERIMENTAL

4 types of 4k end-capped poly(ethylene glycol) (PEG) chains, capped respectively at one end or at both ends with either 12-HSA or stearic acid (SA), were mixed with 12-hydroxy stearic acid molecules, at a low constant ratio of end capped fatty acid moieties brought by the chains to that of free 12-HSA molecules. The detailed structure of the self-assemblies of mixtures was obtained using Small Angle Neutron Scattering with contrast variation at both 20 °C and 45 °C, and their temperature-dependent rheological behavior was characterized.

FINDINGS

For both types of mono-functionalized PEG, the chains insert homogenously in the multi-lamellar tubes formed by 12-HSA molecules. The mixtures of di-functionalized chains by 12-HSA with 12-HSA molecules produce PEGylated vesicles, since the change of packing parameter induced by insertion of the telechelic chains no longer allows the formation of tubes. Conversely, mixtures of di-functionalized chains by SA with 12-HSA molecules enable to keep multi-lamellar tubes, a specific behavior that likely comes from the fact that they only insert by one end within the 12-HSA bilayers. All systems transit reversibly into small PEGylated ellipsoidal micelles. The morphological transitions enable to tune the rheological properties of suspensions, that are gelled at low temperature and turn Newtonian liquid at around 37 °C.

In Vivo Interrogation of Cell-Penetrating Peptide Function: Accumulation in Tumors and the Potential as a Specific PET Probe

We aimed to evaluate the biodistribution and specificity of 68Ga-DOTA-TAT and RHO-TAT using MGC-803 and HT-29 tumor cells as well as tumor-xenografted nude mice and to demonstrate its application in positron emission tomography (PET) imaging. The in vitro evaluation of 68Ga-DOTA-TAT was assessed in MGC-803 and HT-29 cell lines, and the in vivo evaluation of 68Ga-DOTA-TAT was also performed in mice bearing MGC-803 or HT-29 tumors, respectively. Fluorescence microscopy was also employed to evaluate the specificity of RHO-TAT in vitro in MGC-803 and HT-29 cells as well as ex vivo in tumor slices of the corresponding tumor models. The in vivo imaging differences between 68Ga-DOTA-TAT and 18F-FDG in MGC-803 and HT-29 tumors were also studied. The biodistribution and micro-PET results demonstrated significant uptake of 68Ga-DOTA-TAT in non-FDG-avid MGC-803 tumors, whereas there was negligible uptake in FDG-avid HT-29 tumors. RHO-TAT showed superior fluorescence microscopy imaging effects in MGC-803 cells and tumor slices but not in HT-29 cells and tumor slices, which were consistent with the in vivo results. 68Ga-DOTA-TAT combined with 18F-FDG can be applied noninvasively in cancers with PET imaging for potential patient selection and stratification. We demonstrated a higher binding of 68Ga-DOTA-TAT and RHO-TAT to MGC-803 cells as well as to non-FDG-avid MGC-803 xenografted tumors and a lower binding to HT-29 cells and FDG-avid xenografted tumors. These results suggest that TAT has the potential to be a ligand for targeting certain tumors.

Peptide-based PET/CT imaging visualizes PD-L1-driven radioresistance in glioblastoma

Radioresistance remains a great challenge for radiotherapy in the treatment of glioblastoma (GBM). PD-L1 expression is a key contributor to radioresistance and immune escape in GBM. The lack of effective methods to monitor the change of PD-L1 during radiotherapy in patients limits timely intervention and management of the resistance. Here, we developed a novel peptide tracer [18F]AlF-NOTA-PCP2 for PET/CT to visualize the changes of PD-L1 expression in response to radiotherapy, revealing PD-L1-driven radioresistance in GBM. The [18F]AlF-NOTA-PCP2 demonstrated high specificity and binding affinity to PD-L1 in vitro. The uptake of [18F]AlF-NOTA-PCP2 on PET/CT showed a strong positive correlation with PD-L1 expression by immunohistochemistry (IHC) (R² = 0.861, P < 0.001) in GBM xenograft tumors. The radiotracer uptake in PD-L1-positive tumors significantly increased post-radiotherapy (21.25 ± 0.91 % vs. 25.12 ± 0.82 %, P = 0.008), aligning with the radioresistance observed in these tumors. In vitro studies revealed that PD-L1-driven radioresistance by enhancing DNA damage repair through upregulation of RAD51 after activation of the PI3K-Akt pathway in cells. Preliminary clinical application in a radiotherapy-treated GBM patient demonstrated the ability to monitor PD-L1 dynamics, supporting its potential for clinical translation. Collectively, this peptide-based small molecule PET/CT radiotracers offer a noninvasive, real-time, and quantitative method to dynamically visualize PD-L1-driven radioresistance in GBM. It could serve as a potential radiotracer for facilitating patient stratification, adjusting radiotherapy regimens, and guiding personalized immunotherapy strategies.

Enhancing peptide and PMO delivery to mouse airway epithelia by chemical conjugation with the amphiphilic peptide S10

Delivery of antisense oligonucleotides (ASOs) to airway epithelial cells is arduous due to the physiological barriers that protect the lungs and the endosomal entrapment phenomenon, which prevents ASOs from reaching their intracellular targets. Various delivery strategies involving peptide-, lipid-, and polymer-based carriers are being investigated, yet the challenge remains. S10 is a peptide-based delivery agent that enables the intracellular delivery of biomolecules such as GFP, CRISPR-associated nuclease ribonucleoprotein (RNP), base editor RNP, and a fluorescent peptide into lung cells after intranasal or intratracheal administrations to mice, ferrets, and rhesus monkeys. Herein, we demonstrate that covalently attaching S10 to a fluorescently labeled peptide or a functional splice-switching phosphorodiamidate morpholino oligomer improves their intracellular delivery to airway epithelia in mice after a single intranasal instillation. Data reveal a homogeneous delivery from the trachea to the distal region of the lungs, specifically into the cells lining the airway. Quantitative measurements further highlight that conjugation via a disulfide bond through a pegylated (PEG) linker was the most beneficial strategy compared with direct conjugation (without the PEG linker) or conjugation via a permanent thiol-maleimide bond. We believe that S10-based conjugation provides a great strategy to achieve intracellular delivery of peptides and ASOs with therapeutic properties in lungs.

Stability of a Multiresponsive Sulfonium Vinyl Sulfide Linker toward Nucleophilic/Radical Thiols, Reactive Nitrogen Species, and in Cells under Pro-inflammatory Stimulation

Chemical linkages that respond to biological stimuli are important for many pharmaceutical and biotechnological applications, making it relevant to explore new variants with different responsivity profiles. This work explores the responsiveness of a TAT peptide-based sulfonium vinyl sulfide probe that responds to nucleophilic thiols, radical thiol species (RTS), and reactive nitrogen species (RNS). Under model conditions, response to nucleophilic thiols was very slow (hours/days), though fast with down to molar equivalents of either RTS or RNS (minutes). These reactions led to the traceless release of a methionine-containing peptide in the first two cases and to a hydroxy nitration adduct in the third case. Despite the sensitive nature of the probe, it remained stable for at least ∼2 h in the presence of cells during TAT-mediated trafficking, even under pro-inflammatory stimulation. The thiol-responsiveness is intermediate to that observed for disulfide linkers and conventional cysteine-maleimide linkers, presenting opportunities for biotechnological applications.

[18F]AlF-NOTA-PCP2: a novel PET/CT tracer for enhanced PD-L1 heterogeneity imaging and comparative analysis with [18F]AlF-NOTA-WL12 in glioblastoma xenografts

PURPOSE

The unsatisfactory efficacy of PD-L1 antibodies in glioblastoma (GBM) is largely due to the temporal and spatial heterogeneity of PD-L1 expression. Molecular imaging can enhance understanding of the tumor immune microenvironment and guide immunotherapy. However, highly sensitive imaging agents capable of effectively visualizing PD-L1 heterogeneity are limited. This study introduces a novel PET tracer, offering improved imaging of PD-L1 heterogeneity in GBM xenografts, with a comparative analysis to [18F]AlF-NOTA-WL12.

METHODS

[18F]AlF-NOTA-PCP2 was synthesized with high purity and its affinity for PD-L1 was characterized using surface plasmon resonance (SPR) and cell binding assays. Its specificity for PD-L1 was evaluated both in vitro using various cell lines and in vivo with GBM xenograft models in NOD/SCID mice. PET/CT imaging was conducted to evaluate the tracer's biodistribution, pharmacokinetics, and ability to quantify tumoral spatial heterogeneity of PD-L1 expression. A focused comparative analysis between [18F]AlF-NOTA-PCP2 and [18F]AlF-NOTA-WL12 was conducted, examining binding affinity, biodistribution, pharmacokinetics, and imaging effectiveness in GBM xenografts. Additionally, human radiation dosimetry estimates compared the safety profiles of both tracers.

RESULTS

[18F]AlF-NOTA-PCP2 demonstrated high radiochemical purity (> 95%) and a strong affinity for PD-L1, comparable to [18F]AlF-NOTA-WL12. In vitro and in vivo studies confirmed its specificity for PD-L1, with increased uptake in PD-L1 expressing cells and tumors. Toxicological profiles indicated no significant abnormalities in serum biochemical indicators or major organ tissues. MicroPET/CT imaging showed [18F]AlF-NOTA-PCP2's effectiveness in visualizing PD-L1 expression levels and spatial heterogeneity in GBM xenografts. Comparative studies revealed [18F]AlF-NOTA-PCP2's improved pharmacokinetic properties, including higher tumor-to-blood ratios and lower nonspecific liver uptake, as well as reduced radiation exposure compared to [18F]AlF-NOTA-WL12.

CONCLUSION

[18F]AlF-NOTA-PCP2 distinguishes itself as an exceptionally sensitive PET/CT tracer, adept at non-invasively and accurately quantifying PD-L1 expression and its spatial heterogeneity in tumors, especially in GBM. Its favorable pharmacokinetic properties, safety profile, and high affinity for PD-L1 highlight its potential for enhancing the precision of cancer immunotherapy and guiding individualized treatment strategies. While promising, its clinical translation, especially in brain imaging, necessitates further validation in clinical trials.

Covalent conjugation and non-covalent complexation strategies for intracellular delivery of proteins using cell-penetrating peptides

Therapeutic proteins provided new opportunities for patients and high sales volumes. However, they are formulated for extracellular targets. The lipophilic barrier of the plasma membrane renders the vast array of intracellular targets out of reach. Peptide-based delivery systems, namely cell-penetrating peptides (CPPs), have few safety concerns, and low immunogenicity, with control over administered doses. This study investigates CPP-based protein delivery systems by classifying them into CPP-protein "covalent conjugation" and CPP: protein "non-covalent complexation" categories. Covalent conjugates ensure the proximity of the CPP to the cargo, which can improve cellular uptake and endosomal escape. We will discuss various aspects of covalent conjugates through non-cleavable (stable) or cleavable bonds. Non-cleavable CPP-protein conjugates are produced by recombinant DNA technology to express the complete fusion protein in a host cell or by chemical ligation of CPP and protein, which ensures stability during the delivery process. CPP-protein cleavable bonds are classified into pH-sensitive and redox-sensitive bonds, enzyme-cleavable bonds, and physical stimuli cleavable linkers (light radiation, ultrasonic waves, and thermo-responsive). We have highlighted the key characteristics of non-covalent complexes through electrostatic and hydrophobic interactions to preserve the conformational integrity of the CPP and cargo. CPP-mediated protein delivery by non-covalent complexation, such as zippers, CPP adaptor methods, and avidin-biotin technology, are featured. Conclusively, non-covalent complexation methods are appropriate when a high number of CPP or protein samples are to be screened. In contrast, when the high biological activity of the protein is critical in the intracellular compartment, conjugation protocols are preferred.

Therapeutic Peptides, Proteins and their Nanostructures for Drug Delivery and Precision Medicine

Peptide and protein nanostructures with tunable structural features, multifunctionality, biocompatibility and biomolecular recognition capacity enable development of efficient targeted drug delivery tools for precision medicine applications. In this review article, we present various techniques employed for the synthesis and self-assembly of peptides and proteins into nanostructures. We discuss design strategies utilized to enhance their stability, drug-loading capacity, and controlled release properties, in addition to the mechanisms by which peptide nanostructures interact with target cells, including receptor-mediated endocytosis and cell-penetrating capabilities. We also explore the potential of peptide and protein nanostructures for precision medicine, focusing on applications in personalized therapies and disease-specific targeting for diagnostics and therapeutics in diseases such as cancer.