A photoinduced pH jump applied to drug release from cucurbit[7]uril

Phototriggered release of amine from a cucurbituril macrocycle

Amines are released from a cucurbituril macrocycle by photoinduced pH jump and modulation of the competitiveness of a fluorescent guest.

A supramolecular keypad lock

The reversible photoswitching between an anthracene derivative and its [4+4] dimer, using the template effect of the CB8 macrocycle, was demonstrated. This example of supramolecular chemistry in water was harnessed to demonstrate the operation of a keypad lock device that is driven by means of light and chemicals as inputs.

Supramolecular interaction between a hydrophilic coumarin dye and macrocyclic hosts: spectroscopic and calorimetric study

The photophysics of a hydrophilic molecule, 7-(diethylamino)-coumarin-3-carboxylic acid (7-DCCA), was studied in the presence of two macrocycles, (2-hydroxypropyl)-γ-cyclodextrin and cucurbit[7]uril. We have used steady-state absorption, fluorescence, and time-resolved fluorescence emission spectroscopy; Fourier transform infrared (FTIR) spectroscopy; (1)H NMR spectroscopy; and isothermal titration calorimetry (ITC) to confirm the supramolecular host-guest complex formation. The spectral properties of 7-DCCA were modulated in the presence of both macrocycles. It was assigned that 7-DCCA forms a 1:2 complex with (2-hydroxypropyl)-γ-cyclodextrin and cucurbit[7]uril. The large modulation of the emission properties of 7-DCCA in the presence of the macrocycles indicates the formation of supramolecular complexes. A significant shift in the bond vibration frequencies in the FTIR studies showed encapsulation of the dyes in the hydrophobic cavity of the macrocycles. This is further substantiated by the (1)H NMR studies, in which the upfield and downfield shifts of the protons were observed in both the aliphatic and aromatic region in the presence of macrocycles. The time-resolved anisotropy measurements further reinforce the conception of host-guest supramolecular complex formation because, in both cases, the rotational relaxation time increases significantly compared to that in water. A deeper understanding between the differences in interaction of an anionic molecule with cucurbit[7]uril and (2-hydroxypropyl)-γ-cyclodextrin will be achieved through this work. From the ITC measurement, we have formulated the forces due to complex formation.

Dynamic disordering of liposomal cocktails and the spatio-temporal favorable release of cargoes to circumvent drug resistance

Multidrug resistance (MDR) has been a major impediment to the success of cancer chemotherapy. Extensive efforts have been devoted to the development of drug delivery systems using nanotechnology to reverse MDR in cancer. However, the spontaneous release of drug payloads was always a slow process, which leads to the low intracellular drug concentration resulting in consequent drug insensitivity. To circumvent this limitation, we described a liposomal cocktail (LMDHV) constructed by a pH-responsive molecule (i.e., malachite green carbinol base (MG)) and liposome conjugated with Her-2 antibody for codelivery of doxorubicin (DOX) and verapamil (VER) to suppress drug resistance in Her-2 positive breast cancer. MG inserted in the bilayer as pH responders greatly contributed to the destabilization of the vesicle membrane in low pH, followed by the rapid release of the payloads. LMDHV showed 6-fold reversal efficiency in DOX resistant breast cancer owing to the efficient tumor targeting delivery and rapid burst release of drug intracellularly. Compared to tumor inhibition ratio of treated groups by free DOX (32.4 ± 7.4%), our designed kinetically favorable drug release system exhibited significantly (P < 0.01) enhanced tumor inhibition ratio up to 83.9 ± 12.5%, which is attributed to the remarkably increased drug concentration in cells. The spatio-temporal favorable release of drugs resulted in synergistic inhibition of tumor growth in xenografts. We envision that this new type of liposomal cocktail might be potentially utilized to circumvent drug resistance in the future.

Topical cream-based dosage forms of the macrocyclic drug delivery vehicle cucurbit[6]uril

The macrocycle family of molecules called cucurbit[n]urils are potential drug delivery vehicles as they are able to form host-guest complexes with many different classes of drugs. This study aimed to examine the utility of Cucurbit[6]uril (CB[6]) in topical cream-based formulations for either localised treatment or for transdermal delivery. Cucurbit[6]uril was formulated into both buffered cream aqueous- and oily cream-based dosage forms. The solid state interaction of CB[6] with other excipients was studied by differential scanning calorimetry and the macrocycle's transdermal permeability was determined using rat skin. Significant solid state interactions were observed between CB[6] and the other dosage form excipients. At concentrations up to 32% w/w the buffered aqueous cream maintained its normal consistency and could be effectively applied to skin, but the oily cream was too stiff and is not suitable as a dosage form. Cucurbit[6]uril does not permeate through skin; as such, the results imply that cucurbituril-based topical creams may potentially only have applications for localised skin treatment and not for transdermal drug delivery.

Molecular structural transformation regulated dynamic disordering of supramolecular vesicles as pH-responsive drug release systems

The spontaneous release of drug payloads in the whole body always results in the compromised drug bioavailability and ultimate therapeutic efficacy. To achieve enhanced therapeutic efficacy and reduced side effects, pH-responsive targeted drug delivery systems have been studied due to their enhanced tumor accumulation and controllable maximum drug release feature. The present study described a co-assembly constructed by a pH responsive molecule (i.e., malachite green carbinol base (MG)) and liposome for highly efficient doxorubicin (DOX) release in tumor cells (MG-DOX⊂L). The structural transformation of MG effectively regulates the drug release profile in acidic environment. The pH-responsive sensitivity of co-assembly can be fine-tuned by altering the mixing ratios of building blocks with pH responders (i.e., MG molecules). MG-DOX⊂L was beneficial for the DOX release at pH5.0 and showed a higher cytotoxicity in KB cells owing to the pH-responsive drug release in acidic organelles following endocytosis pathway. In vivo tumor targetability and growth inhibition were evaluated in KB cell-xenografted nude mice. We have demonstrated that effective tumor growth inhibition in vivo is attributed to the synergistic contributions from highly efficient cellular entry and responsive intracellular release of DOX from MG-DOX⊂L.

The strategic use of supramolecular pK(a) shifts to enhance the bioavailability of drugs

Macrocyclic hosts of the cyclodextrin, sulfonatocalixarene, and cucurbituril type can be employed as discrete supramolecular drug delivery systems, thereby complementing existing supramolecular drug formulation strategies based on polymers, hydrogels, liposomes, and related microheterogeneous systems. Cucurbiturils, in particular, stand out in that they do not only provide a hydrophobic cavity to encapsulate the drug in the form of a host-guest complex, but in that they possess cation-receptor properties, which favor the encapsulation of protonated drugs over their unprotonated forms, resulting in pronounced pK(a) shifts up to 5 units. These pK(a) shifts can be rationally exploited to activate prodrug molecules, to stabilize the active form of drug molecules, to enhance their solubility, and to increase their degree of ionization, factors which can jointly serve to enhance the bioavailability of drugs, particularly weakly basic ones. Additionally, macrocycles can serve to increase the chemical stability of drugs by protecting them against reactions with nucleophiles (e.g., thiols) and electrophiles, by increasing their photostability, and by causing a higher thermal stability in the solid state. Detailed examples of the different effects of macrocyclic encapsulation of drugs and the associated pK(a) shifts are provided and discussed. Other important considerations, namely a potential lowering of the bioactivity of drugs by macrocyclic complexation, interferences of the macrocycles with biocatalytic processes, the toxicity of the macrocyclic host molecules, and problems and opportunities related to a targeted release and the rate of release of the drug from the host-guest complexes are critically evaluated.