§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).