Mn(II) Promoted Divergent-Convergent Domino Reaction Giving Dinuclear Tetrasubstituted Pyrrole Complex.

Domino reaction of benzo[d]thiazole-2-methylamine (S1) has been developed in the presence of MnCl2 ⋅ 4H2O, leading to tetrasubstituted pyrrole coordinated dinuclear Mn(II) complex 1 ([MnClP]2, P-=2,3,4,5-tetrakis(benzo[d]thiazol-2-yl)pyrrol-1-ide). The reaction process has been studied by assigning a series of intermediates based on time-dependent mass spectrometry, control experiments, crystallography, and density functional theory (DFT) theoretical calculation. A plausible mechanism involving an unprecedented divergent-convergent domino sequence has been proposed. Compound S1 could be activated by MnCl2 ⋅ 4H2O via coordination, which divergently produces two intermediates imine II (1-(benzo[d]thiazol-2-yl)-N-(benzo[d]thiazol-2-ylmethyl)methanimine) and alkene C (1,2-bis(benzo[d]thiazol-2-yl)ethene) through oxidative self-condensation and free radical coupling followed by elimination, respectively. They could then react with each other convergently via formal [3+2] cycloaddition to give deprotonated tetrasubstituted pyrrole coordinated intermediate [MnClP] after aromatization. Dimerization of [MnClP] produces the final product 1. Three C-C bonds and one C-N bond are formed through this six-step domino sequence. The corresponding organic skeleton (HP: 2,2',2'',2'''-(1H-pyrrole-2,3,4,5-tetrayl)tetrakis(benzo[d]thiazole)) has been obtained from 1 and shows a higher fluorescent quantum yield (52 %) than the reported 3,4-diphenyl substituted analogue 2,2'-(3,4-diphenyl-1H-pyrrole-2,5-diyl)bis(benzo[d]thiazole) (DPB) (42 %).

Dual-modified nanoparticles overcome sequential absorption barriers for oral insulin delivery.

The efficacy of oral insulin drug delivery is seriously hampered by multiple gastrointestinal barriers, especially transepithelial barriers, including apical endocytosis, lysosomal degradation, cytosolic diffusion and basolateral exocytosis. In this study, a functional nanoparticle (PG-FAPEP) with dual-modification was constructed to sequentially address these important absorption obstacles for improved oral insulin delivery. The dual surface decorations folate and charge-convertible tripeptide endowed PG-FAPEP with the ability to target the apical and basolateral sides of enterocytes, respectively. After fast diffusion across the mucus layer, PG-FAPEP could be efficiently internalized into epithelial cells via a folate receptor-mediated pathway and subsequently became positively charged in acidic lysosomes due to the surface tripeptide, triggering the proton sponge effect to escape lysosomes. When entering the cytosolic medium, PG-FAPEP was converted to neutral charge again, attenuating intracellular adhesion, and gained improved motility toward the basolateral side. Finally, the tripeptide helped PG-FAPEP recognize the proton-coupled oligopeptide transporter (PHT1) in the basolateral membrane, boosting intact exocytosis across intestinal epithelial cells. The in vivo studies further verified that PG-FAPEP could traverse the intestinal epithelium by folate receptor-mediated endocytosis, lysosomal escape, and PHT1-mediated exocytosis, exhibiting a high oral insulin bioavailability of 14.3% and a prolonged hypoglycemic effect. This formulation addresses multiple absorption barriers on demand with a simple dual-modification strategy. Therefore, these features allow PG-FAPEP to unleash the potential of oral macromolecule delivery.

Ligand-switchable nanoparticles resembling viral surface for sequential drug delivery and improved oral insulin therapy.

Mutual interference between surface ligands on multifunctional nanoparticles remains a significant obstacle to achieving optimal drug-delivery efficacy. Here, we develop ligand-switchable nanoparticles which resemble viral unique surfaces, enabling them to fully display diverse functions. The nanoparticles are modified with a pH-responsive stretchable cell-penetrating peptide (Pep) and a liver-targeting moiety (Gal) (Pep/Gal-PNPs). Once orally administered, the acidic environments trigger the extension of Pep from surface in a virus-like manner, enabling Pep/Gal-PNPs to traverse intestinal barriers efficiently. Subsequently, Gal is exposed by Pep folding at physiological pH, thereby allowing the specific targeting of Pep/Gal-PNPs to the liver. As a proof-of-concept, insulin-loaded Pep/Gal-PNPs are fabricated which exhibit effective intestinal absorption and excellent hepatic deposition of insulin. Crucially, Pep/Gal-PNPs increase hepatic glycogen production by 7.2-fold, contributing to the maintenance of glucose homeostasis for effective diabetes management. Overall, this study provides a promising approach to achieving full potential of diverse ligands on multifunctional nanoparticles.

The upregulated intestinal folate transporters direct the uptake of ligand-modified nanoparticles for enhanced oral insulin delivery.

Transporters are traditionally considered to transport small molecules rather than large-sized nanoparticles due to their small pores. In this study, we demonstrate that the upregulated intestinal transporter (PCFT), which reaches a maximum of 12.3-fold expression in the intestinal epithelial cells of diabetic rats, mediates the uptake of the folic acid-grafted nanoparticles (FNP). Specifically, the upregulated PCFT could exert its function to mediate the endocytosis of FNP and efficiently stimulate the traverse of FNP across enterocytes by the lysosome-evading pathway, Golgi-targeting pathway and basolateral exocytosis, featuring a high oral insulin bioavailability of 14.4% in the diabetic rats. Conversely, in cells with relatively low PCFT expression, the positive surface charge contributes to the cellular uptake of FNP, and FNP are mainly degraded in the lysosomes. Overall, we emphasize that the upregulated intestinal transporters could direct the uptake of ligand-modified nanoparticles by mediating the endocytosis and intracellular trafficking of ligand-modified nanoparticles via the transporter-mediated pathway. This study may also theoretically provide insightful guidelines for the rational design of transporter-targeted nanoparticles to achieve efficient drug delivery in diverse diseases.

Rapid transport of germ-mimetic nanoparticles with dual conformational polyethylene glycol chains in biological tissues.

Polyethylene glycols (PEGs) can improve the diffusivity of nanoparticles (NPs) in biological hydrogels, while extended PEG chains severely impede cellular uptake of NPs. Inspired by invasive germs with flagellum-driven mucus-penetrating and fimbriae-mediated epithelium-adhering abilities, we developed germ-mimetic NPs (GMNPs) to overcome multiple barriers in mucosal and tumor tissues. In vitro studies and computational simulations revealed that the tip-specific extended PEG chains on GMNP functioned similarly to flagella, facilitating GMNP diffusion (up to 83.0-fold faster than their counterparts). Meanwhile, the packed PEG chains on the bodies of GMNP mediated strong adhesive interactions with cells similarly to the fimbriae, preserving cellular uptake efficiency. The in vivo results proved the superior tumor permeability and improved oral bioavailability provided by the GMNP (21.9-fold over administration of crystalline drugs). These findings offer useful guidelines for the rational design of NPs by manipulating surface polymer conformation to realize multiple functions and to enhance delivery efficacy.

Overcoming Poor Tabletability of Bulky Absorption Enhancers by Spray Drying Technology.

Absorption enhancers are often a major component of solid oral peptide formulations as compared to the active pharmaceutical ingredient and excipients. This commonly results in poor tabletability that is hard to mitigate in direct compaction by addition of small amounts of excipients. To improve the tabletability of bulky absorption enhancers, the model absorption enhancers, sodium cholate and deoxycholic acid, were co-spray-dried with hydroxypropyl methylcellulose E5, where the percentage of absorption enhancers was not lower than 90% (w/w). The physicochemical properties of the resulting powders were assessed by laser diffraction, scanning electron microscopy, X-ray powder diffraction, thermogravimetric analysis, and differential scanning calorimetry. The powders were compressed into tablets, and the tabletability was evaluated. Co-spray drying with 10% of hydroxypropyl methylcellulose significantly improved the tabletability of the both absorption enhancers. Moreover, it was demonstrated that small particle size and amorphous state rather than high moisture content contributed to the improved tabletability of the spray-dried powders. The study suggests that spray drying technology can be promising to overcome the poor tabletability of oral peptide formulation consisting of large amounts of absorption enhancers.

Protein Corona Liposomes Achieve Efficient Oral Insulin Delivery by Overcoming Mucus and Epithelial Barriers.

Oral delivery of peptide/protein drugs has attracted worldwide attention due to its good patient compliance and convenience of administration. Orally administered nanocarriers always encounter the rigorous defenses of the gastrointestinal tract, which mainly consist of mucus and epithelium barriers. However, diametrically opposite surface properties of nanocarriers are required for good mucus penetration and high epithelial uptake. Here, bovine serum albumin (BSA) is adsorbed to cationic liposomes (CLs) to form protein corona liposomes (PcCLs). The aim of using PcCLs is to conquer the mucus and epithelium barriers, eventually improving the oral bioavailability of insulin. Investigations using in vitro and in vivo experiments show that the uptake amounts and transepithelial permeability of PcCLs are 3.24- and 7.91-fold higher than that of free insulin, respectively. Further study of the behavior of PcCLs implies that BSA corona can be shed from PcCLs as they cross the mucus layer, which results in the exposure of CLs to improve the transepithelial transport. Intrajejunal administration of PcCLs in type I diabetic rats produces a remarkable hypoglycemic effect and increases the oral bioavailability up to 11.9%. All of these results imply that PcCLs may provide a new insight into the method for oral insulin delivery by overcoming the multiple barriers.

Rapid transport of deformation-tuned nanoparticles across biological hydrogels and cellular barriers.

To optimally penetrate biological hydrogels such as mucus and the tumor interstitial matrix, nanoparticles (NPs) require physicochemical properties that would typically preclude cellular uptake, resulting in inefficient drug delivery. Here, we demonstrate that (poly(lactic-co-glycolic acid) (PLGA) core)-(lipid shell) NPs with moderate rigidity display enhanced diffusivity through mucus compared with some synthetic mucus penetration particles (MPPs), achieving a mucosal and tumor penetrating capability superior to that of both their soft and hard counterparts. Orally administered semi-elastic NPs efficiently overcome multiple intestinal barriers, and result in increased bioavailability of doxorubicin (Dox) (up to 8 fold) compared to Dox solution. Molecular dynamics simulations and super-resolution microscopy reveal that the semi-elastic NPs deform into ellipsoids, which enables rotation-facilitated penetration. In contrast, rigid NPs cannot deform, and overly soft NPs are impeded by interactions with the hydrogel network. Modifying particle rigidity may improve the efficacy of NP-based drugs, and can be applicable to other barriers.