Self-recovering dual cross-linked hydrogels based on bioorthogonal click chemistry and ionic interactions.

The biocompatible, injectable and high water-swollen nature of hydrogels makes them a popular candidate to imitate the extracellular matrix (ECM) for tissue engineering both in vitro and in vivo. However, commonly used covalently cross-linked hydrogels, despite their stability and tunability, are elastic and deteriorate as bulk material degrades which would impair proper cell function. To improve these deficiencies, here, we present a self-recovering cross-linked hydrogel formed instantaneously with functionalized poly(ethylene glycol) as a basis. We combine covalent cross-links introduced via a strain-promoted azide-alkyne cycloaddition (SPAAC) click reaction and non-covalent links between phosphonate groups and calcium ions. By adjusting the ratios of non-covalent and covalent cross-links, we synthesized these dual cross-linked (DC) hydrogels that displayed storage moduli below ∼2000 Pa and relaxation times from seconds to minutes. The gels recovered to 41-96% of their initial mechanical properties after two subsequent strain failures. Cryo-scanning electron microscopy revealed that DC hydrogels containing approximately equal amounts of covalent and non-covalent cross-links displayed phase separation. Finally, we functionalized the DC hydrogels by incorporating an integrin binding motif, RGDS, to provide a biocompatible environment for human mesenchymal stem cells (HMSCs) by facilitating adhesion inside the gel network. Inside these DC gels HSMCs displayed a viability up to 73% after five days of cell culture.

Soft PEG-Hydrogels with Independently Tunable Stiffness and RGDS-Content for Cell Adhesion Studies.

Poly(ethylene)glycol (PEG)-based hydrogels are often used as matrix material for cell culturing. An efficient method to prepare soft PEG gels is by cross-linking via copper-free strain-promoted azide-alkyne cycloaddition (SPAAC). Here, the effect of polymer density and RGDS-content on hydrogel formation and cell adhesion was studied, by varying the total polymer content (10, 20 and 30 mg · mL(-1) ) and the amount of RGDS moieties (0-100%) independently of each other. Rheology studies confirmed the soft nature of the hydrogels (G' = 25-2 298 Pa). HOS cells are able to adhere well to all RGDS-containing gels. Interestingly, both HeLa cells and NIH 3T3 fibroblasts showed substantial adherence to 10 and 20 mg · mL(-1) gels, but with increased hydrogel stiffness (30 mg · mL(-1) ), their cellular adhesion decreased significantly.

Strain-promoted oxidation-controlled cyclooctyne-1,2-quinone cycloaddition (SPOCQ) for fast and activatable protein conjugation.

A main challenge in the area of bioconjugation is to devise reactions that are both activatable and fast. Here, we introduce a temporally controlled reaction between cyclooctynes and 1,2-quinones, induced by facile oxidation of 1,2-catechols. This so-called strain-promoted oxidation-controlled cyclooctyne-1,2-quinone cycloaddition (SPOCQ) shows a remarkably high reaction rate when performed with bicyclononyne (BCN), outcompeting the well-known cycloaddition of azides and BCN by 3 orders of magnitude, thereby allowing a new level of orthogonality in protein conjugation.

A fast and activatable cross-linking strategy for hydrogel formation.

Strain-promoted oxidation-controlled cyclo-octyne-1,2-quinone cycloaddition (SPOCQ) is a fast and activatable cross-linking strategy for hydrogel formation. Gelation is induced by oxidation, which is performed both chemically using sodium periodate and enzymatically using mushroom tyrosinase. Due to the fast reaction kinetics, SPOCQ-formed hydrogels can be functionalized in one-pot with an azido-containing moiety using SPAAC cross-linking.

Broad-spectrum antimalarial activity of peptido sulfonyl fluorides, a new class of proteasome inhibitors.

Despite declining numbers of cases and deaths, malaria remains a major public health problem in many parts of the world. Today, case management relies heavily on a single class of antimalarial compounds: artemisinins. Hence, development of resistance against artemisinins may destroy current malaria control strategies. Beyond malaria control are elimination and eradication programs that will require drugs with good activity against acute infection but also with preventive and transmission-blocking properties. Consequently, new antimalarials are needed not only to ensure malaria control but also for elimination and eradication efforts. In this study, we introduce peptido sulfonyl fluorides (PSF) as a new class of compounds with antiplasmodial activity. We show that PSF target the plasmodial proteasome and act on all asexual stages of the intraerythrocytic cycle and on gametocytes. PSF showed activities at concentrations as low as 20 nM against multidrug-resistant and chloroquine-sensitive Plasmodium falciparum laboratory strains and clinical isolates from Gabon. Structural requirements for activity were identified, and cytotoxicity in human HeLa or HEK 293 cells was low. The lead PSF PW28 suppressed growth of Plasmodium berghei in vivo but showed signs of toxicity in mice. Considering their modular structure and broad spectrum of activity against different stages of the plasmodial life cycle, proteasome inhibitors based on PSF have a great potential for further development as preclinical candidate compounds with improved species-specific activity and less toxicity.

Physicochemical properties and applications of poly(lactic-co-glycolic acid) for use in bone regeneration.

Poly(lactic-co-glycolic acid) (PLGA) is the most often used synthetic polymer within the field of bone regeneration owing to its biocompatibility and biodegradability. As a consequence, a large number of medical devices comprising PLGA have been approved for clinical use in humans by the American Food and Drug Administration. As compared with the homopolymers of lactic acid poly(lactic acid) and poly(glycolic acid), the co-polymer PLGA is much more versatile with regard to the control over degradation rate. As a material for bone regeneration, the use of PLGA has been extensively studied for application and is included as either scaffolds, coatings, fibers, or micro- and nanospheres to meet various clinical requirements.

Peptido sulfonyl fluorides as new powerful proteasome inhibitors.

A new class of potent proteasome inhibitors is described, of which the members contain an amino acid inspired sulfonyl fluoride as the electrophilic trap. In total, 24 peptido sulfonyl fluoride inhibitors have been designed and synthesized, which were inspired by the backbone sequences of the proteasome inhibitors bortezomib, epoxomicin, and Cbz-Leu(3)-aldehyde. Nine of them were very potent proteasome inhibitors, the best of which had an IC(50) of 7 nM. A number of the peptido sulfonyl fluoride inhibitors were found to be highly selective for the ß5 proteasome subunit.

Synthesis and biological evaluation of novel irreversible serine protease inhibitors using amino acid based sulfonyl fluorides as an electrophilic trap.

We have designed and synthesized novel irreversible serine protease inhibitors containing aliphatic sulfonyl fluorides as an electrophilic trap. These substituted taurine sulfonyl fluorides derived from taurine or protected amino acids were conveniently synthesized from ß-aminoethanesulfonyl chlorides using KF/18-crown-6 or from ß-aminoethanesulfonates using DAST. Their potency of irreversible inhibition of serine proteases is described in different enzyme assays using chymotrypsin leading to binding affinities up to 22 µM.