§Zayed Bin Sultan Center for Health Sciences, United Arab Emirates University, PO. Box 15551 Al Ain, United Arab Emirates
Laboratory of Clinical Immunopathology, Research Institute of Fundamental and Clinical Immunology, 14 Yadrintsevskaya, 6300099 Novosibirsk, Russia
Novosibirsk State Medical University, 52, Krasny Prospect, 630091 Novosibirsk, Russia
*Corresponding and submitting author: n.saleh@uaeu.ac.ae (N.S.). Tel.: +971-(0)3-713-6138,eapashkina@niikim.ru (E.P.) Tel.:+7923-190-4706
ABSTRACT. The cellular uptake of drug carriers to the cytosol of a specific cell remains challenging, and a non-classical supramolecular strategy is motivated. Here, we select a model host-guest complex in which a diamino-viologen (VG) fluorescent tag was engulfed by cucurbit[8]uril (CB8) and covalently linked to alginate polysaccharides (ALG) as the modified drug vehicle. When adsorbed on the ALG surface, the encapsulation of VG was first confirmed utilizing FTIR and NMR spectroscopic methods. Solid optical measurements (DRS, PL, and TRPL) revealed emissive materials at around 650 nm and that CB8 enhanced the rigidity of the modified hydrogel. The molar composition of 2 to 1 for the complexation of VG to CB8 on the alginate surface and the thermal stabilities were also confirmed using TGA and DSC techniques. CB8 induced a dramatic decrease in the average size of the VGALG polysaccharides from 485 to 165 nm and a turnover in their charge from -19.8 to +14.4 mV. Flow cytometry with inhibitors of various endocytosis pathways was employed to track the cellular uptake across different blood cell types: human T-cell leukemia 1301 and peripheral blood mononuclear cells. Noticeably, complexation of VG to CB8 host on top of the sugar platform dramatically enhanced the internalization to 1301 cells (viz. from 1 to 99%) at a concentration of 1.8 mg/mL via caveolae-mediated endocytosis (CvME) because of the size reduction, turnover in the charge from negative to positive, and rigidity induction. These observations reveal a more profound understanding of the macrocyclic effects on drug delivery.
KEYWORDS: Cucurbiturils, alginates, viologen, time-resolved photoluminescence, cellular uptake, blood cancer cells.
INTRODUCTION
Optimizing drug-delivery methods to improve immunotherapeutic efficiency is often aided by different strategies that modulate cell or tissue targeting, controlled release, and the response of the drug to suitable triggers.[1]
Using a dynamic host-guest system, the supramolecular scientists set their goals by providing specific, tunable, and thermodynamically reversible bonds. This concept also led them to develop water-soluble nanocontainer-based drug delivery systems such as cucurbituril (CB)-based drug-delivery systems.[2] Nature is the primary inspiration for studying supramolecular chemistry in biorecognition, which includes multimolecular host-guest complexes formed by noncovalent interaction between suitable complementary guest molecules and nanocavity-based macrocyclic molecules known as molecular recognition.[3]
The reversible associations are highly selective and have been employed over several decades in generating supramolecular hydrogels such as polysaccharides-based hydrogels.[4,5] Generally, supramolecular hydrogels’ excellent elastic and mobility nature[6] offers superior performance in biomedical applications over chemically crosslinked. UV light-induced crosslinking or in situ crosslinking can irreversibly generate the latter. Yet, the resulting covalently crosslinked hydrogels are rigid and brittle and cannot be tuned. Due to several dynamic physical bonding and a shorter time for gelation formation, the supramolecular hydrogels gained unique properties such as excellent shear-thinning[7]elasticity,[8] mouldability, sol-gel switching,[9] capability for self-healing,[10] and control release of growth factors. The supramolecular hydrogels are known to have a well-defined stoichiometry, contiguous network, and high biocompatibility due to their high selectivity and supercilious binding strength.[11] The external environmental biochemical and physical variation can regulate the reversible association and dissociation of the host-guest supramolecular system.[12] Also, supramolecular hydrogels can be tailored for application in vivo due to their significant water content and biocompatibility.[13] Specifically, employing supramolecular hydrogels based on polysaccharides for biomedical applications utilizing CB macromolecules is not original.[5] It has also been described for various biological and clinical applications. For instance, biomedical researchers reported different designs using CB for crosslinking the supramolecular hydrogel based on various functional tags. Yet, the exact mechanism of cellular uptake by macrocycle-based hydrogels is to be explored.
Nowadays, treating and curing cancer is the world’s most pressing health-challenging task for clinical research. According to the WHO estimation, cancer death will increase globally by 80% by 2030.[14] On a global level, seven out of ten cancer deaths happened in Asia, Africa, Central and South America.[15] Leukemia is the most challenging treatment among all types of cancer. Clinical scientists are continuously working hard to prevent this grim projection. With care that aims to balance the effectiveness of treatment and the importance of quality of life, more patients than ever are living longer.
The nanocavity cucubit[n ]urils (CBn ) are more biocompatible than other water-soluble macrocyclic hosts because CBn is dexterity to functionalization.[16]The water-soluble macrocyclic molecules offer their hydrophobic cavity for encapsulating polar and non-polar guest molecules with a reasonable binding constant.[17] CBn is made from acid-catalyzed polymerization of glycoluril and formaldehyde to form macrocycles with different numbers of monomers unit.
The eight-monomer unit containing cucurbit[8]uril (CB8) forms a complex with viologen guests non-covalently.[18]The viologens are functional organic materials first discovered by Michaelis in 1932.[19] The viologens are the classic example of redox and electron-deficient compounds. Several viologen-based crystalline and amorphous photochromic materials have been synthesized for the last ten years, enabling photochemists to develop substantial multifunctional viologen-based photochromic materials.[20] To be effective, precise structural control of such materials is required. This, of course, puts a premium on the ability to control structural parameters during their tedious synthesis. However, the precise structural control of hydrogels is not easy. It requires the simultaneous adjustment of several parameters and/or possibly different processing techniques to achieve any size, charge, or rigidity.
Here, a supramolecular hydrogel as a drug delivery system is designed in which CB8-encapsulated viologen diamines salts (VG)[21] are covalently linked to the surface of alginate polysaccharides (ALG)[22] (Figure 1).