Figure 9. Schematic representation of blood cellular uptake of
VGALG and VGCB8ALG hydrogels. Chemical structures of VG, ALG, and CB8
are also shown. The 2:1 binary complex of CB8 with the viologen dimers
is not shown for simplicity.
As described in the introduction, employing supramolecular hydrogels
based on polysaccharides for biomedical applications and utilizing
cucurbituril macromolecules is not original and has received significant
attention. It has also been described for various biological and
clinical applications. Hydrogels are themselves a widely researched
field of (bio)materials. They have been enormously reported, and the
field is not novel.[12] For example, hydrogel drug
delivery has already implemented the host-guest association between
cucurbit[7]uril (CB7) and cisplatin.[35]Nonetheless, elucidating the effects of macromolecules on the mechanism
of cellular uptake is still motivated.
The biocompatibility and low toxicity have been confirmed for the
modified ALG in the present work. The translation of the unmodified ALG
has already been explored in literature.[36] The
research concluded the significant role of size. Three different
size-dependent mechanisms for cellular uptake were suggested. Oleoyl ALG
ester nanoparticles whose sizes are 50, 120, or 730 nm enter the colon
cancer cells via Clathrin-Mediated Endocytosis (CME), CvME, or
micropinocytosis, respectively.[36] From Figure 4,
the CB8-modified ALG has a size that is 165 nm compared to 1540 nm for
the undecorated ALG. The uptake mechanism was confirmed to be CvME which
agrees with the literature. In another account, the authors highlighted
the effect of charges on the uptake of nanoparticles. Because the lung
cancer cell’s surface has a negative charge, cationic cerium oxide
nanoparticles[37] were better internalized than
neutrally or negatively charged ones, such as the cellular
internalization of polyplexes, lipoplexes, and lipopolyplexes into a
myoblast cell line.[38] From Figure 4, the
modified VGCB8ALG has a positive charge (viz. +14.4 mV) compared to the
negatively charged VGALG (-19.8 mV) and thus was better internalized
into leukemia cancer in agreement with those reports. The rigidity
factor was demonstrated to modulate the type of cellular uptake, in
which rigid nanoparticles of N ,N -diethyl acrylamide, and
2-hydroxyethyl methacrylate cross-linked with N ,N ′-methylene-bis-acrylamide were better internalized to RAW 264.7
murine macrophage cells compared to soft
nanoparticles.[39] From Figure S5 in the
Supporting Information, adding CB8 renders the modified hydrogels more
rigid than VGALG. Thus, the increase in endocytosis is unsurprising. The
exciting point remains the straightforward elucidation of how CB8 has
modulated the cellular uptake, which can be further utilized for other
clinical applications in the future.
Collectively these data unfold the factors that biomedical researchers
need to consider (among others) to get more efficient drug delivery
systems in cancer therapy that involves a macromolecular system or other
drug vehicles. Although, nowadays, the field of application, material
type, and drug loading need to be precisely selected and extensively
studied, we envisage that the successful modulation of cellular
internalization upon the addition of CB8 on VGALG must have a wide
impact in the broader research field and benefits similar cellular
studies performed on other macrocycle-based biomaterials for other
biomedical applications. The technology is patentable, which would then
be of interest to international pharmaceutical companies for commercial
development.
CONCLUSION
The present work offers a supramolecular strategy to modulate the
cellular uptake and intracellular processing of drug delivery systems,
paving the way for a more remarkable improvement in the development of
drug therapeutics of alginates in cancer therapy. We showed that
supramolecular encapsulation is the key required for the efficient
delivery of a model drug system via CvME, as manifested in the
substantial decrease in the size of the alginate hydrogels. The
employment of a supramolecular approach to modify drug carriers is not
new. Still, the results here confirm a distinct, unique modulation of
the intracellular processing of alginate carriers, unfolding a thorough
understanding of the macrocyclic effects on drug delivery compared to
previous reports.
Supplementary Information The online version contains
supplementary material available at XXXXXX .
Author Contributions
F.C.; optical data (UV, PL, TRPL) acquisition and analysis and writing
the initial draft, V. P.; material characterization by FTIR, DLS, TGA,
DSC, and NMR, P.L.; data analysis, M.B., A.A., O.B., M.B., and E.P.;
clinical studies and contribute to manuscript writing, N.S. created the
idea, conceptualization, supervision, and final manuscript writing. All
authors have approved the final version of the manuscript.
Funding Sources
This study was supported by Grant 12R113 from UAE University.
Data availability: All relevant data are within the paper.