In vivo targeted delivery of antibodies into cancer cells with pH-responsive cell-penetrating poly(disulfide)s

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.

Organ/Cell-Selective Intracellular Delivery of Biologics via N-Acetylated Galactosamine-Functionalized Polydisulfide Conjugates

Biologics, including proteins and antisense oligonucleotides (ASOs), face significant challenges when it comes to achieving intracellular delivery within specific organs or cells through systemic administrations. In this study, we present a novel approach for delivering proteins and ASOs to liver cells, both in vitro and in vivo, using conjugates that tether N-acetylated galactosamine (GalNAc)-functionalized, cell-penetrating polydisulfides (PDSs). The method involves the thiol-bearing cargo-mediated ring-opening polymerization of GalNAc-functionalized lipoamide monomers through the so-called aggregation-induced polymerization, leading to the formation of site-specific protein/ASO-PDS conjugates with narrow dispersity. The hepatocyte-selective intracellular delivery of the conjugates arises from a combination of factors, including first GalNAc binding with ASGPR receptors on liver cells, leading to cell immobilization, and the subsequent thiol-disulfide exchange occurring on the cell surface, promoting internalization. Our findings emphasize the critical role of the close proximity of the PDS backbone to the cell surface, as it governs the success of thiol-disulfide exchange and, consequently, cell penetration. These conjugates hold tremendous potential in overcoming the various biological barriers encountered during systemic and cell-specific delivery of biomacromolecular cargos, opening up new avenues for the diagnosis and treatment of a range of liver-targeting diseases.

Advances in cell-penetrating poly(disulfide)s for intracellular delivery of therapeutics

Efficient intracellular delivery is essential for most therapeutic agents; however, existing delivery vectors face a dilemma between efficiency and toxicity, and always encounter the challenge of endolysosomal trapping. The cell-penetrating poly(disulfide) (CPD) is an effective tool for intracellular delivery, as it is taken up through thiol-mediated cellular uptake, thus avoiding endolysosomal entrapment and ensuring efficient cytosolic availability. Upon cellular uptake, CPD undergoes reductive depolymerization by glutathione inside cells and has minimal cytotoxicity. This review summarizes CPD's chemical synthesis approaches, cellular uptake mechanism, and recent advances in the intracellular delivery of proteins, antibodies, nucleic acids, and other nanoparticles. Overall, CPD is a promising candidate carrier for efficient intracellular delivery.

The Dawn of a New Era: Targeting the "Undruggables" with Antibody-Based Therapeutics

The high selectivity and affinity of antibodies toward their antigens have made them a highly valuable tool in disease therapy, diagnosis, and basic research. A plethora of chemical and genetic approaches have been devised to make antibodies accessible to more "undruggable" targets and equipped with new functions of illustrating or regulating biological processes more precisely. In this Review, in addition to introducing how naked antibodies and various antibody conjugates (such as antibody-drug conjugates, antibody-oligonucleotide conjugates, antibody-enzyme conjugates, etc.) work in therapeutic applications, special attention has been paid to how chemistry tools have helped to optimize the therapeutic outcome (i.e., with enhanced efficacy and reduced side effects) or facilitate the multifunctionalization of antibodies, with a focus on emerging fields such as targeted protein degradation, real-time live-cell imaging, catalytic labeling or decaging with spatiotemporal control as well as the engagement of antibodies inside cells. With advances in modern chemistry and biotechnology, well-designed antibodies and their derivatives via size miniaturization or multifunctionalization together with efficient delivery systems have emerged, which have gradually improved our understanding of important biological processes and paved the way to pursue novel targets for potential treatments of various diseases.

pH-triggered cancer-targeting polymers: From extracellular accumulation to intracellular release

Stimuli-responsive polymers are promising to achieve targeted delivery, improved stability during circulation, and controlled release of therapeutic and diagnostic agents. Among them, pH-responsive polymeric nanocarriers have attracted significant attention as pH varies in different body fluids (e.g., stomach, intestine, and colon) and intracellular organelles (e.g., endosome, lysosome, and mitochondria) to maintain homeostasis, while distinctive pH changes are also found in certain pathological states. For example, the extracellular environment of the tumor is acidic, which can be employed to drive selective delivery. During the internalization process, since most nanocarriers enter cells upon endocytosis where a drop of pH from 6.5 to 5.0 can occur from endosome to lysosome, pH-sensitive groups have been developed for enhanced cargo release. In this review, both non-covalent and covalent interactions responsive to pH changes are introduced, with a focus on the structure-property relationship and their applications in cancer targeting and endosomal escape.

Controllable Disulfide Exchange Polymerization of Polyguanidine for Effective Biomedical Applications by Thiol-Mediated Uptake

New preparation methods of vectors are the key to developing the next generation of biomacromolecule delivery systems. In this study, a controllable disulfide exchange polymerization was established to obtain low-toxicity and efficient bioreducible polyguanidines (mPEG₂₂₅ -b-PSS_n , n=13, 26, 39, 75, 105) by regulating the concentration of activated nucleophiles and reaction time under mild reaction conditions. The relationship between the degrees of polymerization and biocompatibility was studied to identify the optimal polyguanidine mPEG₂₂₅ -b-PSS₂₆ . Such polyguanidine exhibited good in vitro performance in delivering different functional nucleic acids. The impressive therapeutic effects of mPEG₂₂₅ -b-PSS₂₆ were further verified in the 4T1 tumor-bearing mice as well as the mice with full-thickness skin defects. Controllable disulfide exchange polymerization provides an attractive strategy for the construction of new biomacromolecule delivery systems.