Developing Supramolecular Metallogel Derived from Pd2L4 Cage Molecule for Delivering an Anti-Cancer Drug to Melanoma Cell B16-F10.

Supramolecular gels are an important class of materials that are promising for its wide range of applications including drug delivery. While supramolecular gels are intrinsically porous because of the 3D nano-matrix (gel matrix) that is being formed due to supramolecular self-assembly process involving the gelator molecules during gelation, additional nanopores can be introduced to the overall gel if the gelator molecule itself holds molecular cavity such as metal-organic-cage (MOC) molecules. A MOC having the molecular formula [(Pd2L24).4NO3].3H2O.2DMF.MeOH (Pd-cage) (L2=5-Azido-N,N'-di-pyridin-3-yl-isophthalamide) was successfully synthesized and characterized by FT-IR, 1H NMR, ESI-MS and single crystal X-ray diffraction. Stimuli-reversible supramolecular metallogel PdG could easily be formed from Pd-cage in DMSO/water mixture. The molecular cage of Pd-cage was demonstrated to be available for loading an anti-cancer drug namely doxorubicin (DOX). Subsequently, DOX was also loaded within PdG and delivered to melanoma cell line B16-F10 displaying significant anti-cancer activity as revealed by both MTT and scratch assay. Rheoreversibility of PdG and its ability to load and deliver DOX to cancer cells clearly raised hope for developing this metallogel further as topical anticancer gel.

An injectable supramolecular hydrogel as a self-drug-delivery system for local chemoimmunotherapy against melanoma.

Skin-cancer melanoma caused 57k death in 2020. Some of the available therapies are: topical application of a gel loaded with an anti-skin cancer drug and intravenous injection of immune cytokines; however, both the approaches have drawbacks such as inefficient internalization of the drug in cancer cells and a short half-life with severe side effects, respectively. Interestingly, we observed for the first time that a subcutaneously implanted hydrogel designed and synthesized by coordinating NSAIDs and 5-AP with Zn(II) can effectively combat melanoma cell (B16-F10)-induced tumors in C57BL/6 mice. Both in vitro and in vivo results show that it can effectively reduce PGE2 expression, consequently upregulating IFN-γ and IL-12 that eventually engage M1-macrophages for activating T cells (CD8+), triggering apoptosis. This unique all-in-one self-drug-delivery approach, wherein the hydrogel implant is made from the drug molecules itself providing both chemotherapy and immunotherapy in combating deadly melanoma, highlights the supramolecular chemistry-based bottom-up approach in cancer therapy.

Designing a vehicle-free anti-bacterial topical hydrogel from Fmoc-diphenylalanine.

A supramolecular synthon-based salt formation strategy has been employed to afford an anti-bacterial topical hydrogel from Fmoc-diphenylalanine (FmocFF). The nontrivial steps (pH/solvent switch along with heat-cool protocol) required for making the hydrogel from FmocFF were successfully avoided following this strategy.

Nitrile-Containing Terpyridyl Zn(II)-Coordination Polymer-Based Metallogelators Displaying Helical Structures: Synthesis, Structures, and "Druglike" Action against B16-F10 Melanoma Cells.

An attempt has been made to develop a self-drug-delivery system against melanoma from a series of metallogelators derived from coordination polymers. Thus, a series of coordination polymers (CP1-CP6) derived from a nitrile-containing terpyridyl ligand (L) and transition metal salts (Cu(I)/Zn(II)) have been synthesized and thoroughly characterized by a number of physicochemical techniques including single crystal X-ray diffraction. Reactions of the ingredients of the coordination polymers guided by their single crystal structures produced four metallogels (CPG2-CPG5) which were characterized by dynamic rheology and TEM. The metallogelator CPG3 turned out to be the best suited for further studies as revealed from MTT assay against melanoma (B16-F10) and macrophage (RAW 264.7) cells. Various experiments (scratch, cell cycle, nuclear condensation, annexin V-FITC/PI, mitochondrial membrane potential, Ho-efflux assays) not only supported the "druglike" action against melanoma B16-F10 cells but also suggested that the mechanism of cancer cell death was via mitochondrial membrane potential depolarization-driven apoptosis. Because melanoma B16-F10 is a model cell line for human skin cancer, the metallogel CPG3 may, therefore, be further developed for such treatment.

Designing coordination polymers as multi-drug-self-delivery systems for tuberculosis and cancer therapy: in vitro viability and in vivo toxicity assessment.

A proof of concept for designing multi-drug-delivery systems suitable for self-drug-delivery is disclosed. Simple coordination chemistry was employed to anchor two kinds of drugs namely isoniazid (IZ - anti-tuberculosis), various non-steroidal-anti-inflammatory-drugs (NSAIDs) namely ibuprofen-IBU, fenoprofen-FEN, naproxen-NAP, diclofenac-DIC and mefenamic acid-MEF and Zn(NO3)2 to synthesize a series of 1D coordination polymers namely IZIBU, IZFEN, IZNAP, IZDIC and IZMEF which were structurally characterized by single crystal X-ray diffraction (SXRD). The coordination polymers wherein both types of drugs were anchored to Zn(II) metal centers could easily be ground to nano-sized particles suitable for biological studies by hand grinding in a mortar and pestle. Zone inhibition studies revealed that all the coordination polymers possessed antibacterial properties against Gram positive, Gram negative and mycobacteria namely Mycobacterium tuberculosis (M.tb). Detailed studies carried out on IZDIC employing flow cytometry and confocal microscopy under various staining conditions established that such antibacterial activity was due to the generation of reactive oxygen species (ROS) such as nitric oxide (NO) and also inhibition of mycolic acid leading to incomplete cell wall formation. It was also established that IZDIC could indeed inhibit the growth of M.tb within a mouse macrophage host cell namely RAW 264.7 thereby simulating the treatment of Tuberculosis (TB) under in vitro conditions. Scratch assay and cell cycle analysis on a human lung cancer cell line (A549) revealed its anti-cancer property, thereby indicating its potential as a multi-drug-delivery system. In vivo toxicity assessment (serum parameters, histopathology, and haemolysis) carried out on BALB/c mice showed that IZDIC was safe up to a concentration of 100 mg kg-1. Finally, a reasonably high yield in bulk synthesis, stability under high temperature and humid conditions, tabletability and, slow and sustained release of the drug component of IZDIC suggested its suitability in real-life applications as multi-drug-delivery systems.

Multi-NSAID-based Zn(II) coordination complex-derived metallogelators/metallogels as plausible multi-drug self-delivery systems.

Metallogelators/metallogels derived from a series of multi-NSAID-based Zn(II)-coordination complexes displaying anti-cancer and anti-bacterial properties were designed based on a structural rationale as plausible multi-drug self-delivery systems.

Anchoring Drugs to a Zinc(II) Coordination Polymer Network: Exploiting Structural Rationale toward the Design of Metallogels for Drug-Delivery Applications.

A new series of coordination polymers (CPs) were synthesized and crystallographically characterized by single-crystal X-ray diffraction with the aim of developing drug-delivery systems via metallogel formation. Structural rationale was employed to design such coordination-polymer-based metallogels. As many as nine CPs were obtained by reacting two bis(pyridyl)urea ligands, namely, 1,3-dipyridin-3-ylurea (3U) and 1,3-dipyridin-4-ylurea (4U), and the sodium salt of various nonsteroidal antiinflammatory drugs, namely, ibuprofen (IBU), naproxen (NAP), fenoprofen (FEN), diclofenac (DIC), meclofenamic acid (MEC), mefenamic acid (MEF), and Zn(NO3)2. All of the CPs displayed 1D polymeric chains that were self-assembled through various hydrogen-bonding interactions involving the urea N-H and carboxylate O atoms and, in a few cases, lattice-occluded water molecules. The reacting components of the CPs produced five metallogels in dimethyl sulfoxide/water. The gels were characterized by rheology and transmission electron microscopy. Three selected metallogelators, namely, 3UMEFg, 3UNAPg, and 3UMECg, showed in vitro anticancer, cell imaging, and multidrug delivery for antibacterial applications, respectively. The shear-thinning properties of 3UMECg (rheoreversibility and injectability) make it a potential candidate for plausible topical application.

Designing Metallogelators Derived from NSAID-based Zn(II) Coordination Complexes for Drug-Delivery Applications.

A crystal engineering approach has been invoked to design a new series of eight Zn(II) coordination complexes derived from various non-steroidal anti-inflammatory drugs (NSAIDs), namely diclofenac (DIC), ibuprofen (IBU), naproxen (NAP), flufenamic acid (FLU) and meclofenamic acid (MEC), and two co-ligands, namely N-phenyl-3-pyridylamide (3-Py) and N-phenyl-4-pyridylamide (4-Py), and Zn(NO3 )2 as potential supramolecular gelators. Half of the coordination complexes thus synthesized were able to form aqueous gels (MG-3-PyMEC, MG-3-PyDIC, MG-4-PyNAP and MG-4-PyMEC). Single-crystal structures of all eight complexes revealed that they possessed a gelation-inducing 1D hydrogen-bonded network including amide…amide synthon in some cases, which supported strongly the design principles based on which these complexes were synthesized. Interestingly, one such metallogelator complex, namely 3-PyMEC, showed an intriguing anticancer property against a human breast cancer cell line (MDA-MB-231), as revealed by both MTT and cell migration assays.

Cu(II)-Metallacryptands Self-Assembled to Vesicular Aggregates Capable of Encapsulating and Transporting an Anticancer Drug Inside Cancer Cells.

Crystallographically characterized M2 L4 type cationic Cu(II)-metallacryptands [MC(X)] derived from a series of bis-pyridyl-bis-urea ligands (LX ; X = O, S, C) are self-assembled to single-layered vesicular aggregates in DMSO, DMSO/water, and DMSO/DMEM (biological media). One such vesicle is MC(O)-vesicle that is demonstrated to be able to load and release (pH responsive) an anticancer drug, namely doxorubicin hydrochloride (DOX). DOX-loaded MC(O)-vesicle is also successfully transported within MDA-MB-231 cells-a highly aggressive human breast cancer cell line. Such self-assembling behavior to form vesicular aggregates by metallacryptands (MCs) is hitherto unknown.

Design and Synthesis of ZnII -Coordination Polymers Anchored with NSAIDs: Metallovesicle Formation and Multi-drug Delivery.

A series of coordination polymers synthesized from a bis-pyridyl linker, namely 4,4'-azopyridine (L), selected non-steroidal-anti-inflammatory drugs (NSAIDs), namely diclofenac (Dic), ibuprofen (Ibu), flurbiprofen (Flu), mefenamic acid (Mefe), and naproxen (Nap), and Zn(NO3 )2 were characterized by single crystal X-ray diffraction. One of the coordination polymers, namely CP3 derived from Flu, was able to form metallovesicles in DMSO, DMSO/H2 O and DMSO/DMEM (biological media) as revealed by TEM, AFM and DLS. Metallovesicle formation by CP3 was further supported by loading a fluorescent dye, namely calcein, as well as an anti-cancer drug, doxorubicin hydrochloride (DOX), as revealed by UV-vis and emission spectra, and fluorescence microscopy. DOX-loaded metallovesicles of CP3 (DOX@CP3-vesicle) could be delivered in vitro to a highly aggressive human breast cancer cell line, namely MDA-MB-231, as revealed by MTT and cell migration assays, and also cell imaging performed under laser scanning confocal microscope (LSCM). Thus, a proof of concept for developing a multi-drug delivery system derived from a metallovesicle for delivering an anti-cancer drug to cancer cells is demonstrated for the first time.

An easy access to topical gels of an anti-cancer prodrug (5-fluorouracil acetic acid) for self-drug-delivery applications.

An easy access to topical gels (both hydro- and organogels) derived from an anti-cancer prodrug namely 5-fluorouracil acetic acid (5-FuA) achieved by exploiting a simple salt formation strategy is reported for the first time. Nearly 85% of the salts synthesized were gelators. Single crystal structures of some of the gelator salts revealed an intriguing hydrogen bonding network including double stranded 1D chains stabilized through uracil-uracil complementary interactions and the crystal structures of the gelator salts corroborated well with the hypothesis based on which the gelators were designed. Studies indicated that both the hydrogel and the methyl salicylate gel of the gelator salt FuA-15 were suitable for self-drug-delivery application.

Self-Assembly of Spherical Organic Molecules to Form Hollow Vesicular Structures in Water for Encapsulation of an Anticancer Drug and Its Release.

Developing hierarchical supramolecular structures is important for better understanding of various biological functions and possibly generating new materials for biomedical applications. Herein, we report the first examples of functional vesicles derived from cationic spherical organic molecules (C1 -C3 ) which were readily synthesized by reacting a C3 -symmetric tris-benzimmidazole derivative (possessing a 1,3,5-ethyl substituted aromatic core) with 1,3,5-substituted tris-bromomethyl benzene derivatives. Vesicle formation by C1 -C3 was probed by high-resolution microscopy (TEM and AFM), dynamic light scattering (DLS) and fluorescence microscopic imaging of calcein-loaded vesicles. One of the vesicles [Vesicle(C3 )] displayed the ability to load the anticancer drug doxorubicin (DOX). The drug was subsequently released from DOX@Vesicle(C3 ) in a stimuli-responsive manner in presence of the well-known vesicle destroyer Triton X-100, as revealed by in vitro cell migration assay carried out on a highly aggressive human breast cancer cell line (MDA-MB-231).

Supramolecular Gels Derived from Simple Organic Salts of Flufenamic Acid: Design, Synthesis, Structures, and Plausible Biomedical Application.

Following supramolecular synthon rationale in the context of crystal engineering, a nonsteroidal-anti-inflammatory-drug (NSAID), namely flufenamic acid (FA) and its ß-alanine monopeptide derivative (FM), were converted to a series of primary ammonium monocarboxylate (PAM) salts. Majority of the PAM salts (∼90%) showed gelation with various solvents including water and methyl salicylate (important solvents in topical gel formulation). Structure-property correlation studies based on single-crystal X-ray diffraction (SXRD) and powder X-ray diffraction (PXRD) data provided intriguing insights into the structure of the gel network. Furthermore, one of the gelator salts (S7) displayed anticancer activity on a highly aggressive human breast cancer cell line (MDA-MB-231) ,as revealed by MTT, PEG2, and cell migration assays.

Rational Approach Towards Designing Metallogels From a Urea-Functionalized Pyridyl Dicarboxylate: Anti-inflammatory, Anticancer, and Drug Delivery.

A structural rationale was adopted to design a series of metallogels from a newly synthesized urea-functionalized dicarboxylate ligand, namely, 5-[3-(pyridin-3-yl)ureido]isophthalic acid (PUIA), that produces metallogels upon reaction with various metal salts (CuII , ZnII , CoII , CdII , and NiII salts) at room temperature. The gels were characterized by dynamic rheology and transmission electron microscopy (TEM). The existence of a coordination bond in the gel state was probed by FTIR and 1 H NMR spectroscopy in a ZnII metallogel (i.e., MG2). Single crystals isolated from the reaction mixture of PUIA and CoII or CdII salts characterized by X-ray diffraction revealed lattice inclusion of solvent molecules, which was in agreement with the hypothesis based on which the metallogels were designed. MG2 displayed anti-inflammatory response (prostaglandin E2 assay) in the macrophage cell line (RAW 264.7) and anticancer properties (cell migration assay) on a highly aggressive human breast cancer cell line (MDA-MB-231). The MG2 metallogel matrix could also be used to load and release (pH responsive) the anticancer drug doxorubicin. Fluorescence imaging of MDA-MB-231 cells treated with MG2 revealed that it was successfully internalized.

Rationally Developed Metallogelators Derived from Pyridyl Derivatives of NSAIDs Displaying Anti-Inflammatory and Anticancer Activities.

Metal-ligand coordination involving hydrogen-bond-functionalized ligands was employed rationally to get an easy access to a series of metallogelators derived from 3-pyridyl derivatives of nonsteroidal anti-inflammatory drugs [e.g., ibuprofen, sulindac, and flurbiprofen designated as 3-pyIBU, 3-pySUL, and 3-pyFLR, respectively] and biogenic metal centers [Zn(II), Cu(II), Mn(II), and Ag(I)]. A total of 13 metallogels (MG1-MG13) were obtained by allowing the ligands and the metal salts to react in dimethyl sulfoxide (DMSO)/water at room temperature. A slightly different solvent system (DMSO/water/MeOH) afforded four crystalline coordination complexes of 3-pyIBU, namely, [{Cu(3-pyIBU)4(DMSO)2}(NO3)2] (CC1), [{Ag(3-pyIBU)2}(BF4)] (CC2), [{Ag(3-pyIBU)2}(ClO4)] (CC3), and [{Cu(3-pyIBU)4(CH3OH)2}(OTf)] (CC4), which were fully characterized by single-crystal X-ray diffraction. However, none of these coordination complexes produced metallogels-the results corroborated well with the rationale, based on which the metallogelators were obtained. Two selected metallogels (MG3 and MG9) could be leached out from the corresponding metallogels to the bulk solvent to the extent of 51 and 59%, respectively after 24 h of incubation at 37 °C, indicating their plausible use in topical application. Moreover, one of the selected metallogelators, i.e., MG9, displayed anti-inflammatory response and was able to inhibit the migration of highly aggressive human breast cancer cells MDA-MB-231, suggesting its plausible use as anticancer agent.

Exploring Orthogonal Hydrogen Bonding towards Designing Organic-Salt-Based Supramolecular Gelators: Synthesis, Structures, and Anticancer Properties.

A series of primary ammonium monocarboxylate (PAM) salts derived from ß-alanine derivatives of pyrene and naphthalene acetic acid, along with the parent acids, were explored to probe the plausible role of orthogonal hydrogen bonding resulting from amide⋅⋅⋅amide and PAM synthons on gelation. Single-crystal X-ray diffraction (SXRD) studies were performed on two parent acids and five PAM salts in the series. The data revealed that orthogonal hydrogen bonding played an important role in gelation. Structure-property correlation based on SXRD and powder X-ray diffraction data also supported the working hypothesis upon which these gelators were designed. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and cell migration assay on a highly aggressive human breast cancer cell line, MDA-MB-231, revealed that one of the PAM salts in the series, namely, PAA.B2, displayed anticancer properties, and internalization of the gelator salt in the same cell line was confirmed by cell imaging.

Simple Organic Salts Having a Naphthalenediimide (NDI) Core Display Multifunctional Properties: Gelation, Anticancer and Semiconducting Properties.

Following a supramolecular synthon rationale, a dicarboxylic acid derivative having a naphthalenediimide (NDI) core, namely, bis-N-carboxymethyl naphthalenediimide (NDI-G), was reacted with n-alkyl amines with varying alkyl chain lengths to generate a new series of primary ammonium dicarboxylate (PAD) salts. The majority of the salts (≈85 %) were found to gel various polar solvents. The gels were characterized by dynamic rheology and high-resolution electron microscopy. Single-crystal and powder X-ray diffraction analyses were used to study the supramolecular synthon present in one of the gelator salts (i.e., S8). Charge-transfer (CT)-induced gelation with donor molecules such as anthracene methanol (Ant) and pyrene (Py) was also possible with S8. The CT complex (S8.Ant) displayed anticancer activity as probed by cell migration assay on the highly aggresive breast cancer cell line MDA-MB-231. The DMSO gel of S8.Ant also displayed semiconducting behavior. To the best of our knowledge, simple organic salts with an NDI core that display such mulitifunctional properties are hitherto unknown.

Rationally Developed Organic Salts of Tolfenamic Acid and Its ß-Alanine Derivatives for Dual Purposes as an Anti-Inflammatory Topical Gel and Anticancer Agent.

A new series of primary ammonium monocarboxylate (PAM) salts of a nonsteroidal anti-inflammatory drug (NSAID), namely, tolfenamic acid (TA), and its ß-alanine derivatives were generated. Nearly 67 % of the salts in the series showed gelling abilities with various solvents, including water (biogenic solvent) and methyl salicylate (typically used for topical gel formulations). Gels were characterized by rheology, electron microscopy, and so forth. Structure-property correlations based on single-crystal and powder XRD data of several gelator and nongelator salts revealed intriguing insights. Studies (in vitro) on an aggressive human breast cancer cell line (MDA-MB-231) with the l-tyrosine methyl ester salt of TA (S7) revealed that the hydrogelator salt was more effective at killing cancer cells than the mother drug TA (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay); displayed better anti-inflammatory activity compared with that of TA (prostaglandin E2 assay); could be internalized within the cancer cells, as revealed by fluorescence microscopy; and inhibited effectively migration of the cancer cells. Thus, the easily accessible ambidextrous gelator salt S7 can be used for two purposes: as an anti-inflammatory topical gel and as an anticancer agent.

Hand-Ground Nanoscale ZnII -Based Coordination Polymers Derived from NSAIDs: Cell Migration Inhibition of Human Breast Cancer Cells.

Increased levels of intracellular prostaglandin E2 (PGE2 ) have been linked with the unregulated cancer cell migration that often leads to metastasis. Non-steroidal anti-inflammatory drugs (NSAIDs) are known inhibitors of cyclooxygenase (COX) enzymes, which are responsible for the increased PGE2 concentration in inflamed as well as cancer cells. Here, we demonstrate that NSAID-derived ZnII -based coordination polymers are able to inhibit cell migration of human breast cancer cells. Various NSAIDs were anchored to a series of 1D ZnII coordination polymers through carboxylate-Zn coordination, and these structures were fully characterized by single-crystal X-ray diffraction. Hand grinding in a pestle and mortar resulted in the first reported example of nanoscale coordination polymers that were suitable for biological studies. Two such hand-ground nanoscale coordination polymers NCP1 a and NCP2 a, which contained naproxen (a well-studied NSAID), were successfully internalized by the human breast cancer cells MDA-MB-231, as was evident from cellular imaging by using a fluorescence microscope. They were able to kill the cancer cells (MTT assay) more efficiently than the corresponding mother drug naproxen, and most importantly, they significantly inhibited cancer cell migration thereby displaying anticancer activity.

Multifunctional single-layered vesicles derived from Cu(ii)-metal-organic-polyhedra.

Cu(ii) metal-organic-polyhedra (MOP) derived from a tris-pyridyl ligand gave stable single-layered vesicles capable of encapsulating an anti-cancer drug (doxorubicin - DOX) and its pH responsive release. While encapsulation of DOX was further confirmed by MTT assay and cellular imaging, α-chymotrypsin inhibition assay corroborated well with the single crystal structures of the MOP. The MOP derived vesicles reported herein not only represent the rare examples of such hierarchical architectures derived from MOP but also provide the first example of multifunctional organic-inorganic synthetic bio-membranes.