Biomarker Displacement Activation: A General Host–Guest Strategy for Targeted Phototheranostics in Vivo

Host-Guest Chemistry in Supramolecular Theranostics

Macrocyclic hosts, such as cyclodextrins, calixarenes, cucurbiturils, and pillararenes, exhibit unparalleled advantages in disease diagnosis and therapy over the past years by fully taking advantage of their host-guest molecular recognitions. The dynamic nature of the non-covalent interactions and selective host-guest complexation endow the resultant nanomaterials with intriguing properties, holding promising potentials in theranostic fields. Interestingly, the differences in microenvironment between the abnormal and normal cells/tissues can be employed as the stimuli to modulate the host-guest interactions, realizing the purpose of precise diagnosis and specific delivery of drugs to lesion sites. In this review, we summarize the progress of supramolecular theranostics on the basis of host-guest chemistry benefiting from their fantastic topological structures and outstanding supramolecular chemistry. These state-of-the-art examples provide new methodologies to overcome the obstacles faced by the traditional theranostic systems, promoting their clinical translations.

Multistimuli-Responsive and Photocontrolled Supramolecular Luminescent Gels Constructed by Anthracene-Bridged Bis(dibenzo-24-crown-8) with Secondary Ammonium Salt Polymer

A novel multistimuli-responsive and photcontrolled supramolecular luminescent gel is fabricated from anthracene-bridged bis(dibenzo-24-crown-8) (1) and secondary ammonium salt-functionalized graft polymer (3). X-ray crystallographic analysis reveals that the dibenzo-24-crown-8 (DB24C8) ring is located at the opposite site of 1, which will greatly hinder the mutual intermolecular π-π stacking between anthracene groups. By taking advantage of the controllable binding of 1 with 3, the unique gel-sol transition could occur under different temperatures, pH, and competitive guest bindings. Benefiting from the photo-oxygenation of anthracene, the luminescence behavior of the supramolecular gel could be switched off and on under UV light (365 nm) and heating treatment, which provides a new approach for constructing photocontrolled supramolecular luminescent gel.

Reversible Shielding between Dual Ligands for Enhanced Tumor Accumulation of ZnPc-Loaded Micelles

Herein, we report a ligand-reversible-shielding strategy based on the mutual shielding of dual ligands tethered to the surface of nanoparticles. To exemplify this concept, phenylboronic acid-functionalized poly(ethylene glycol)- b-poly(ε-caprolactone) (PBA-PEG-PCL) and galactose-functionalized diblock polymer (Gal-PEG-PCL) were mixed to form dual-ligand micelles (PBA/Gal). PBA and Gal residues could form a complex at pH 7.4 and mutually shield their targeting function. At pH 6.8, the binding affinity between PBA and Gal weakened, and PBA preferred to bind with the sialic acid residues on the tumor cell surface rather than to Gal on the micellar surface; furthermore, the unbound Gal recovered its targeting ability toward the asialoglycoprotein receptor. When the pH decreased from 7.4 to 6.8, enzyme-linked immunosorbent assays exhibited that the percentage of exposed Gal on the micellar surface increased 1.9-fold, and flow cytometry showed that HepG2 cellular uptake increased 4.3-fold. More importantly, this process was reversible, confirming the reversible shielding and deshielding of dual ligands. With the encapsulation of a photosensitizer, zinc phthalocyanine (ZnPc), the reversible-shielding micelles showed a 48% improvement in the half-life ( t_1/2) in blood circulation, a 54% decrease in liver capture, a 40% increase in tumor accumulation, and a 10.3% improvement in the tumor inhibition rate compared to the Gal-coated irreversible micelles. This dual-ligand mutual-shielding strategy provides a new perspective on reversible tumor targeting.

Assembly of upconversion nanophotosensitizer in vivo to achieve scatheless real-time imaging and selective photodynamic therapy

A perfect "off" to "on" switch of the therapeutic function is very important to minimize the phototoxicity of nanoplatforms assisted imaging-guided photodynamic therapy (PDT) of cancer. Current approaches rely on preloaded photosensitizers, where the off/on state of PDT is regulated by the sensitizing light of photosensitizers. However, the photoactivities inevitably occur when imaging/diagnosis or exposure to sunlight, etc. These preloading approaches will cause the damage to normal cells and the photosensitivity to the skin. Taking upconversion photodynamic therapy as an example we report here a biorthogonal chemistry solution to circumvent this problem. The luminescence upconversion nanoparticles (UCNPs) are anchored with one handle of click reaction and targeting entity, these nanoplatforms enable the imaging/labelling/tracking, especially for imaging-guided surgery. Once they are targeted, the photosensitizers armed with the other match handle will be injected in situ and click reaction will occur between the two handles to link the photosensitizers closely with the targeted nanoplatforms in a very short time, enabling the PDT function of the nanoplatforms. Proof of principle has been demonstrated in vitro and in vivo. This approach can be readily extended to chemotherapy, radiotherapy, etc. to overcome the side effect of these therapies of cancers.

A Self-Assembled ATP Probe for Melanoma Cell Imaging

In this investigation, a new terpyridine metal complex was developed as a probe for selective detection of ATP and imaging of melanoma cells. The probe takes advantage of the ability of the metal complex to be transformed to its imaging competent turn-on state through assembly with ATP.

Transformative Supramolecular Vesicles Based on Acid-Degradable Acyclic Cucurbit[n]uril and a Prodrug for Promoted Tumoral-Cell Uptake

Smart supramolecular vesicles constructed by host-guest interactions between "acid-degradable" acyclic cucurbit[n]uril (CB[n]) and a doxorubicin prodrug are reported. "Acid-degradable" acyclic CB[n] is a high-affinity host for several common antitumor drugs, and its degradation leads to a more dramatic decrease in binding affinity than that observed for "acid-sensitive" hosts. Supramolecular complexation between acid-degradable acyclic CB[n] and a doxorubicin prodrug resulted in the formation of negatively charged supramolecular vesicles. The prodrug strategy allowed doxorubicin to be conjugated to vesicles in a stable manner with a high drug-loading ratio of 20 %. The resulting supramolecular vesicles were responsive to tumor acidity (pH 6.5). Induced by mildly acidic conditions (pH 6.5-5.5), acid-degradable acyclic CB[n] could be degraded, and this led to a vesicle-to-micelle transition to form positively charged micelles. This transition resulted in a pH-dependent change in size and surface charge, which improved tumoral-cell uptake for doxorubicin.

Strong binding and fluorescence sensing of bisphosphonates by guanidinium-modified calix[5]arene

Based on the indicator displacement assay (IDA) approach, we herein report the fluorescence "switch-on" sensing and quantitative detection of bisphosphonates (BPs), a class of drugs extensively used in the treatment of patients with various skeletal diseases. Guanidinium-modified calix[5]arene (GC5A) affords strong binding on the micromolar to nanomolar level towards BPs dominantly via multiple salt bridge interactions, which was evaluated by fluorescence competitive titrations. Fluorescent IDA enables the highly sensitive and label-free detection of BPs in buffer solution, and more importantly, in artificial urine. Calibration lines were therefore set up in untreated artificial urine, allowing for quantifying the concentrations of BPs in the biologically relevant low range.

Multifunctional supramolecular vesicles for combined photothermal/photodynamic/hypoxia-activated chemotherapy

Multifunctional supramolecular vesicles were constructed by self-assembly of water-soluble pillar[5]arene and NIR-absorbing guest G. They exhibited remarkable antitumor efficacy through simultaneous combination of photothermal, photodynamic and photodynamic-triggered hypoxia-activated chemotherapy.

Differential calixarene receptors create patterns that discriminate glycosaminoglycans

A well-designed fluorescence displacement sensing array based on calixarene receptors realizes the discrimination of glycosaminoglycans.

Pro-guest and acyclic cucurbit[n]uril conjugated polymers for the controlled release of anti-tumor drugs

We report “pro-guest” and acyclic cucurbit[n]uril conjugated polymers as supramolecular drug delivery systems (DDSs).