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This study aims to compare the mucus permeating and mucoadhesive properties of three generations of thiolated cyclodextrins (CDs). Free thiol groups of thiolated γ-CDs (CD-SH) were S-protected with 2-mercaptonicotinic acid (MNA), leading to a second generation of thiolated CDs (CD-SS-MNA) and with 2 kDa polyethylene glycol (PEG) bearing a terminal thiol group leading to a third generation of thiolated CDs (CD-SS-PEG). The structure of these thiolated CDs was confirmed and characterized by FT-IR, 1H NMR and colorimetric assays. Thiolated CDs were evaluated regarding viscosity, mucus diffusion, and mucoadhesion. The viscosity of the mixture of CD-SH, CD-SS-MNA, or CD-SS-PEG with mucus increased up to 11-, 16-, and 14.1-fold compared to unmodified CD within 3 hours, respectively. Mucus diffusion increased in the following rank order: unprotected CD-SH < CD-SS-MNA < CD-SS-PEG. The residence time of CD-SH, CD-SS-MNA, and CD-SS-PEG on porcine intestine was up to 9.6-, 12.55-, and 11.2-fold prolonged compared to native CD, respectively. According to these results, S-protection of thiolated CDs can be a promising approach to improve their mucus permeating and mucoadhesive properties. Three generations of thiolated cyclodextrins (CDs) with different types of thiol ligands have been synthesized to improve mucus interaction. 1st generation of thiolated CDs was synthesized by converting hydroxyl groups into thiols by reaction with Thiourea. For 2nd generation, free thiol groups were S-protected by reaction with 2-mercaptonicotinic acid (MNA), resulting in high reactive disulfide bonds. For 3rd generation, terminally thiolated short PEG chains (2 kDa) were used for S-protection of thiolated CDs. Mucus penetrating properties were found to be increased as follows: 1st generation < 2nd generation < 3rd generation. Furthermore, mucoadhesive properties were improved in the following rank order: 1st generation < 3rd generation < 2nd generation. This study suggests that the S-protection of thiolated CDs can enhance mucus penetrating and mucoadhesive properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrophobic ion pairing is a promising strategy to raise the lipophilic character of therapeutic peptides and proteins. In past studies, docusate, an all-purpose surfactant with a dialkyl sulfosuccinate structure, showed highest potential as hydrophobic counterion. Being originally not purposed for hydrophobic ion pairing, it is likely still far away from the perfect counterion. Thus, within this study, docusate analogues with various linear and branched alkyl residues were synthesized to derive systematic insights into which hydrophobic tail is most advantageous for hydrophobic ion pairing, as well as to identify lead counterions that form complexes with superior hydrophobicity. The successful synthesis of the target compounds was confirmed by FT-IR, 1H-NMR, and 13C-NMR. In a screening with the model protein hemoglobin, monostearyl sulfosuccinate, dioleyl sulfosuccinate, and bis(isotridecyl) sulfosuccinate were identified as lead counterions. Their potential was further evaluated with the peptides and proteins vancomycin, insulin, and horseradish peroxidase. Dioleyl sulfosuccinate and bis(isotridecyl) sulfosuccinate significantly increased the hydrophobicity of the tested peptides and proteins determined as logP or lipophilicity determined as solubility in 1-octanol, respectively, in comparison to the gold standard docusate. Dioleyl sulfosuccinate provided an up to 8.3-fold higher partition coefficient and up to 26.5-fold higher solubility in 1-octanol than docusate, whereas bis(isotridecyl) sulfosuccinate resulted in an up to 6.7-fold improvement in the partition coefficient and up to 44.0-fold higher solubility in 1-octanol. The conjugation of highly lipophilic alkyl tails to the polar sulfosuccinate head group allows the design of promising counterions for hydrophobic ion pairing. Hydrophobic ion pairing enables efficient incorporation of hydrophilic molecules into lipid-based formulations by forming complexes with hydrophobic counterions. Docusate, a sulfosuccinate with two branched alkyl tails, has shown highest potential as anionic hydrophobic counterion. As it was originally not purposed for hydrophobic ion pairing, its structure is likely still far away from the perfect counterion. To improve its properties, analogues of docusate with various alkyl tails were synthesized in the present study. The investigation of different alkyl residues allowed to derive systematic insights into which tail structures are most favorable for hydrophobic ion pairing. Moreover, the lead counterions dioleyl sulfosuccinate and bis(isotridecyl) sulfosuccinate bearing highly lipophilic alkyl tails provided a significant improvement in the hydrophobicity of the resulting complexes. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent decades, three generations of thiomers have been developed with the main purpose of obtaining enhanced interactions with mucosal tissues. Therefore, many different types of thiolated ligands have been generated and attached to polymeric backbones. The aim of this study was to synthesize all three generations of thiomers and to directly compare their properties regarding mucus penetration and mucoadhesion. Starting from pectin, the unprotected thiomer pectin-cysteine (Pec-Cys), the preactivated S-protected thiomer pectin-cysteine-mercaptonicotinic acid (Pec-Cys-MNA) and the less reactive S-protected thiomer pectin-cysteine-glutathione (Pec-Cys-GSH) were synthesized and characterised by FT-IR, NMR, and colorimetric studies. The polymers were evaluated regarding their cytotoxicity, swelling behaviour, viscosity after mixing with mucus, mucus diffusion, penetration into mucosa, and mucoadhesion. The amount of the three ligands (Cys, Cys-MNA and Cys-GSH) bound to the polymer was determined to be in the range of 193-196 µmol/g. All polymers showed no cytotoxicity. Viscosity of the mixture of Pec-Cys-MNA and Pec-Cys-GSH with mucus increased 21.5- and 26.7-fold, respectively, compared to the unmodified polymer within 3 hours. Swelling, mucoadhesion, interpenetration and mucus diffusion were increased in the following rank order: Pec-Cys < Pec-Cys-MNA < Pec-Cys-GSH. Results of mucoadhesion study indicated a 7.4 and 8.1-fold increase of Pec-Cys-MNA and Pec-Cys-GSH, respectively, compared to the unmodified polymer. As the less reactive S-protected thiomer exhibited higher mucoadhesive properties than the other thiomers, this study provides evidence for the superior mucoadhesion of 3rd generation thiomers. Three generations of thiolated polymers have been developed bearing different types of thiol ligands with the main purpose of enhancing mucus interactions. In this study, all generations were synthesized on the polymeric backbone of pectin for the first time to directly compare their mucus penetrating and mucoadhesive properties. 1st generation exhibited covalently bound L-cysteine moieties. For 2nd generation, thiols of cysteines were S-protected with 2-mercaptonicotinic acid (MNA), resulting in high reactive disulfide bonds. 3rd generation was synthesized by a thiol/disulfide exchange of glutathione with MNA, producing a less reactive disulfide bond. Mucus penetrating and mucoadhesive properties were found to be increased as follows: 1st generation < 2nd generation < 3rd generation. According to these results, the thiomer of 3rd generation represents a promising excipient with strong mucoadhesion. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] This study aims to design chemically crosslinked thiolated cyclodextrin-based hydrogels and to evaluate their mucoadhesive properties via mucosal residence time studies on porcine small intestinal mucosa and on porcine buccal mucosa. Free thiol groups of heptakis(6-deoxy-6-thio)-β-cyclodextrin (β-CD-SH) were S-protected with 2-mercaptoethanesulfonic acid (MESNA) followed by crosslinking with citric acid. Cytotoxicity was assessed by hemolysis as well as resazurin assay. Hydrogels were characterized by their rheological and mucoadhesive properties. Ritonavir was employed as model drug for in vitro release studies from these hydrogels. The structure of S-protected β-CD-SH was confirmed by IR and 1H NMR spectroscopy. Degree of thiolation was 390 ± 7 µmol/g. Hydrogels based on native β-CD showed hemolysis of 12.5 ± 2.5 % and 13.6 ± 2.7 % within 1 and 3 h, whereas hemolysis of just 3.5 ± 2.8 % and 3.9 ± 3.0 % was observed for the S-protected thiolated CD hydrogels, respectively. Both native and S-protected thiolated hydrogels showed minor cytotoxicity on Caco-2 cells. Rheological investigations of S-protected thiolated β-CD-based hydrogel (16.2 % m/v) showed an up to 13-fold increase in viscosity in contrast to the corresponding native β-CD-based hydrogel. Mucosal residence time studies showed that thiolated β-CD-based hydrogel is removed to a 16.6- and 2.4-fold lower extent from porcine small intestinal mucosa and porcine buccal mucosa in comparision to the native β-CD-based hydrogel, respectively. Furthermore, a sustained release of ritonavir from S-protected thiolated β-CD-based hydrogels was observed. Because of their comparatively high mucoadhesive and release-controlling properties, S-protected thiolated β-CD-based hydrogels might be promising systems for mucosal drug delivery. [ABSTRACT FROM AUTHOR]

Cyclodextrins (CD) and derivatives are functional excipients that can improve the bioavailability of numerous drugs. Because of their drug solubility improving properties they are used in many pharmaceutical products. Furthermore, the stability of small molecular drugs can be improved by the incorporation in CDs and an unpleasant taste and smell can be masked. In addition to well-established CD derivatives including hydroxypropyl-β-CD, hydroxypropyl-γ-CD, methylated- β-CD and sulfobutylated- β-CD, there are promising new derivatives in development. In particular, CD-based polyrotaxanes exhibiting cellular uptake enhancing properties, CD-polymer conjugates providing sustained drug release, enhanced cellular uptake, and mucoadhesive properties, and thiolated CDs showing mucoadhesive, in situ gelling, as well as permeation and cellular uptake enhancing properties will likely result in innovative new drug delivery systems. Relevant clinical trials showed various new applications of CDs such as the formation of CD-based nanoparticles, stabilizing properties for protein drugs or the development of ready-to-use injection systems. Advanced products are making use of various benefical properties of CDs at the same time. Within this review we provide an overview on these recent developments and take an outlook on how this class of excipients will further shape the landscape of drug delivery. [Display omitted] [ABSTRACT FROM AUTHOR]

In consequence of some unique properties, such as nanophase separation, biocompatibility and mechanical stability, amphiphilic polymer conetworks (APCNs) have received significant attention in recent years. APCNs are composed of hydrophilic and hydrophobic polymer chains connected with covalent bonds. The unique properties of APCNs make them suitable for many specialized applications. Although APCNs were widely investigated and described in the literature, this is the first study on the swelling behavior of these materials in the solutions of physiologically relevant salts. Homopolymer polyelectrolyte hydrogels are known to suffer phase transition like rapid gel collapse at a certain salt concentration in the solutions of bi- or multivalent metal salts. Systematic swelling investigation of poly(methacrylic acid)- l- polyisobutylene (PMAA- l -PIB) conetwork series in CaCl 2 salt solutions led to unexpected findings. Our results indicate that these polyelectrolyte APCNs do not behave the same way in salt solutions as the homopolymer hydrogels, i.e. APCNs do not suffer gel collapse, the change of the swelling degree remains continuous with increasing salt concentration. The gel contraction was reversible by changing the solute to NaOH solution, i.e. the gels returned to their original volume by reswelling. This non-collapsing swelling means that the presence of hydrophobic polymer segments as cross-linkers in amphiphilic polyelectrolyte gels radically change the swelling behavior of such materials, which become substantially different from that of homopolymer polyelectrolyte gels. [ABSTRACT FROM AUTHOR]

Oral delivery is one of the most advantageous routes for drug administration, but due to the short gastrointestinal (GI) residence time, the systemic uptake of poorly absorbed drugs is too low to reach the desired therapeutic effect. In order to prolong the GI residence time of orally given drugs, we synthesized per-thiolated β-cyclodextrin (CD) as mucoadhesive drug carrier. Due to thiolation, the mucoadhesive properties of CD on porcine intestinal mucosa were increased 2-fold. In vivo studies showed 4 h after oral administration, a 19.4-fold, 2.1- fold, and 4.5-fold higher quantity of per-thiolated β-CD vs. unmodified β-CD in the stomach, duodenum/jejunum, and the ileum of rat model, respectively. Eight hours after oral administration, still, 60 % of per-thiolated CD, but no native CD remained in the GI tract. These results provide evidence that due to thiolation of β-CD, GI-residence time can be essentially prolonged. [Display omitted] [ABSTRACT FROM AUTHOR]

Monomers from renewable resources, such as terpenes, recently came into the focus of interest of polymer chemists. This work describes the first reversible addition fragmentation chain transfer (RAFT) polymerization of myrcene, a simple monoterpene, with 2-ethylsulfanylthiocarbonylsulfanyl-propionic acid ethyl ester chain transfer agent (CTA), in bulk. The polymerizations showed pseudo first order kinetics and the molar masses of the produced polymers increased linearly with the conversion, while the dispersities (Ð) were in the range of 1.1–1.4. Chain extension studies using the preliminary synthesized polymyrcene as macroCTA in the polymerization of styrene resulting in block-copolymer with low Ð. The copolymer formation confirmed the trithiocarbonate chain ends of the used polymer. These results clearly confirm the controlled nature of the polymerization for the selected system. The microstructure of the polymer was also investigated. Low glass transition temperatures of the produced polyterpenes (≈−60 °C) were determined by differential scanning calorimetric measurements that clearly indicate the dominance of the 1,4 polymyrcene structure. The microstructure was quantified by NMR spectroscopy validating a composition of the polymer at least 96% 1,4 units, with the coexistence of cis and trans isomers. These results confirm the controlled nature not only in terms of dispersity, functionality and molar mass, but also of microstructure of the RAFT polymerized monoterpene with the applied CTA. [ABSTRACT FROM AUTHOR]

• Radical polymerization of isobutylene in water was developed using cyclodextrin solubilizer. • Copolymerization of isobutylene with polar monomer acrylamide was accomplished. • Reversible addition-fragmentation chain transfer polymerization of isobutylene was achieved for the first time. • Green and mild conditions are used to prepare polyisobutylene and its new copolymers with polar monomers. The synthesis of a linear polyisobutylene is achieved for the first time by free radical polymerization. The reaction was performed in environmentally friendly conditions, i.e., in an aqueous medium using cyclodextrin solubilizer, around room temperature. This mild and straightforward radical polymerization resulted in a predominantly linear polymer with low dispersity. Isobutylene was also copolymerized with acrylamide via this cyclodextrin assisted aqueous free-radical polymerization, leading to new poly(isobutylene- co -acrylamide) amphiphilic copolymers. The feed composition of copolymerization had a huge effect on the composition and, therefore, the resulting copolymer's solubility. Reversible addition-fragmentation chain transfer radical polymerization (RAFT) of isobutylene was also carried out using a PEG-based symmetrical macro chain transfer agent. Poly(PEG- b -isobutylene- b -PEG) block-copolymer was formed in this one-pot reaction. This novel polymerization method for isobutylene opens new, environmentally benign routes to produce novel copolymers for various applications. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effect of thiolated α-cyclodextrin (α-CD-SH) on the cellular uptake of its payload. For this purpose, α-CD was thiolated using phosphorous pentasulfide. Thiolated α-CD was characterized by FT-IR and 1H NMR spectroscopy, differential scanning calorimetry (DSC), and powder X-ray diffractometry (PXRD). Cytotoxicity of α-CD-SH was evaluated on Caco-2, HEK 293, and MC3T3 cells. Dilauryl fluorescein (DLF) and coumarin-6 (Cou) serving as surrogates for a pharmaceutical payload were incorporated in α-CD-SH, and cellular uptake was analyzed by flow cytometry and confocal microscopy. Endosomal escape was investigated by confocal microscopy and hemolysis assay. Results showed no cytotoxic effect within 3 h, while dose-dependent cytotoxicity was observed within 24 h. The cellular uptake of DLF and Cou was up to 20- and 11-fold enhanced by α-CD-SH compared to native α-CD, respectively. Furthermore, α-CD-SH provided an endosomal escape. According to these results, α-CD-SH is a promising carrier to shuttle drugs into the cytoplasm of target cells. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] This study aimed to evaluate the cellular uptake of nanostructured lipid carriers (NLCs) decorated with polyphosphate coated linear and loop cell-penetrating peptides (CPPs). Linear-CPPs and loop-CPPs were synthesized via ring-opening polymerization and anchored on the surface NLCs, followed by coating with polyphosphate (PP). These nanocarriers (NCs) were characterized in terms of particle size, polydispersity index (PDI), and zeta potential. Cell viability and hemolysis, as well as enzyme-induced charge conversion via phosphate cleavage by free and membrane-bound intestinal alkaline phosphatase (IAP) were investigated. Cellular uptake studies by Caco-2 and HEK cells were quantitatively analyzed by flow cytometry and visualized by confocal microscopy. A shift in charge from positive to negative was obtained for both linear- and loop-CPPs-NLCs by coating with PP. PP-linear-CPPs-NLCs and PP-loop-CPPs-NLCs exhibited a particle size < 270 nm and a PDI of approximately 0.3. They had a minor effect on cell viability and caused in a concentration of 0.1 % (m/v) around 10 % hemolysis within 24 h. IAP triggered the cleavage and release of monophosphate from the surface of NLCs causing charge conversion from –22.2 mV to + 5.3 mV (Δ27.5 mV) for PP-linear-CPPs-NLCs and from −19.2 mV to + 11.9 mV (Δ31.1 mV) for PP-loop-CPPs-NLCs. Inhibition of alkaline phosphatase activity on Caco-2 and HEK cells confirmed the involvement of this enzyme in charge conversion. PP-linear-CPPs-NLCs showed on Caco-2 cells a higher uptake than PP-loop-CPPs-NLCs, whereas on HEK cells uptake of both types of NLCs was on the same level. The results of cellular uptake were confirmed visually by confocal microscopy. CPPs-NLCs coated with polyphosphate are a promising approach to overcome the polycationic dilemma and to enhance cellular uptake. [ABSTRACT FROM AUTHOR]

Overcoming P-glycoprotein (P-gp)-mediated efflux poses a significant challenge for the pharmaceutical industry. This study investigates the potential of thiolated β-cyclodextrins (β-CD-SHs) as inhibitors of P-gp-mediated efflux in Caco-2 cells. Through a series of transport assays, intracellular accumulation, and efflux of the P-gp substrates Rhodamine 123 (Rh123) and Calcein-AM with and without co-administration of β-CD-SHs were assessed. The results revealed that the cellular uptake of Rh123 and Calcein-AM were enhanced up to 7- and 3-fold, compared to the control, respectively. In efflux studies an up to 2.5-fold reduction of the Rh123 efflux was reached compared the control, indicating a substantial decrease of Rh123 efflux by β-CD-SHs. Furthermore, it was observed that β-CD-SHs led to a decrease in the reactivity of fluorescence-labeled anti-P-gp, suggesting additional effects on the conformation of P-gp. Overall, this study demonstrates the potential of β-CD-SHs as effective modulator of P-gp-mediated drug efflux in Caco-2 cells. [Display omitted] [ABSTRACT FROM AUTHOR]

To prepare new polycationic pullulan derivatives exhibiting highly mucoadhesive and sustained drug release properties. Hydroxy groups of pullulan were activated with mesyl chloride followed by conjugation with low-molecular weight polyamines. Pullulan-tris(2-aminoethyl)amine (Pul-TAEA) and pullulan-polyethyleneimine (Pul-PEI) were evaluated regarding swelling behaviour, mucoadhesive properties and potential to control drug release. Pul-TAEA and Pul-PEI exhibited excellent swelling properties at pH 6.8 showing 240- and 370-fold increase in weight. Compared to unmodified pullulan, Pul-TAEA and Pul-PEI displayed 5- and 13.3-fold increased dynamic viscosity in mucus. Mucoadhesion studies of Pul-TAEA and Pul-PEI on intestinal mucosa showed a 6- and 37.8-fold increase in tensile strength, and a 72- and 120-fold increase in mucoadhesion time compared to unmodified pullulan, respectively. Due to additional ionic interactions between cationic groups on polyaminated pullulans and an anionic model drug, a sustained drug release was achieved. Polyaminated pullulans are promising novel mucoadhesive excipients for mucosal drug delivery. [Display omitted] [ABSTRACT FROM AUTHOR]