Recent Development of Rhenium-Based Materials in the Application of Diagnosis and Tumor Therapy

Rhenium (Re) is widely used in the diagnosis and treatment of cancer due to its unique physical and chemical properties. Re has more valence electrons in its outer shell, allowing it to exist in a variety of oxidation states and to form different geometric configurations with many different ligands. The luminescence properties, lipophilicity, and cytotoxicity of complexes can be adjusted by changing the ligand of Re. This article mainly reviews the development of radionuclide 188Re in radiotherapy and some innovative applications of Re as well as the different therapeutic approaches and imaging techniques used in cancer therapy. In addition, the current application and future challenges and opportunities of Re are also discussed.

A novel ruthenium polypyridyl complex for the selective imaging and photodynamic targeting of the Golgi apparatus

A well-designed heteroleptic ruthenium(ii) polypyridyl complex demonstrated stable target-specific in vitro Golgi apparatus imaging abilities in HeLa cell lines. After utilizing photodynamic therapy via UV excitation, the Ru-SL complex could be triggered to generate singlet oxygen (1O2) and red fluorescence signals. 1O2 was highly cytotoxic and could induce DNA damage and the disappearance of the Golgi apparatus. The red fluorescence signals disappeared gradually, suggesting that the live or dead state of the cells can be estimated from the fluorescence signal intensity.

Strategies to promote permeation and vectorization, and reduce cytotoxicity of metal complex luminophores for bioimaging and intracellular sensing

Transition metal luminophores are emerging as important tools for intracellular imaging and sensing. Their putative suitability for such applications has long been recognised but poor membrane permeability and cytotoxicity were significant barriers that impeded early progress. In recent years, numerous effective routes to overcoming these issues have been reported, inspired in part, by advances and insights from the pharmaceutical and drug delivery domains. In particular, the conjugation of biomolecules but also other less natural synthetic species, from a repertoire of functional motifs have granted membrane permeability and cellular targeting. Such motifs can also reduce cytotoxicity of transition metal complexes and offer a valuable avenue to circumvent such problems leading to promising metal complex candidates for application in bioimaging, sensing and diagnostics. The advances in metal complex probes permeability/targeting are timely, as, in parallel, over the past two decades significant technological advances in luminescence imaging have occurred. In particular, super-resolution imaging is enormously powerful but makes substantial demands of its imaging contrast agents and metal complex luminophores frequently possess the photophysical characteristics to meet these demands. Here, we review some of the key vectors that have been conjugated to transition metal complex luminophores to promote their use in intra-cellular imaging applications. We evaluate some of the most effective strategies in terms of membrane permeability, intracellular targeting and what impact these approaches have on toxicity and phototoxicity which are important considerations in a luminescent contrast or sensing agent.

Synthesis and high antiproliferative activity of dehydroabietylamine pyridine derivatives in vitro and in vivo

Several bioactive dehydroabietylamine Schiff-bases (L1-L4), amides (L5-L11) and complex CuL3(NO3)2, Cu(L5)3, Co(L6)2Cl2 had been synthesized successfully for developing more efficient but lower toxic antiproliferative compounds. Their antiproliferative activities to Hela (cervix), HepG2 (liver), MCF-7 (breast), A549 (lung) and HUVEC (umbilical vein, normal cell) were investigated in vitro. The toxicity of all compounds was less than dehydroabietylamine (L0). For HepG2 cells, L1, L2 and L3 had higher anti-HepG2 activity, especially L1 (0.52 µM) had highest anti-HepG2 activity but low toxicity. For MCF-7 cells, L1, L2, L3 and L4 had higher anti-MCF-7 activity, especially L3(0.49 µM) had highest anti-MCF-7 activity but low toxicity. For A549 cells, L2 and L3 had higher anti-A549 activity. Furthermore, L1 and L3 may be the great promise antiproliferative drugs with nontoxic side effects, due to the high anti-HepG2 and anti-MCF-7 inhibition rate in vivo, 65% and 61%, respectively. L1, L2 and L3 could induce apoptosis through intercalating into DNA.

The Role of NIR Fluorescence in MDR Cancer Treatment: From Targeted Imaging to Phototherapy

BACKGROUND

Multidrug Resistance (MDR) is defined as a cross-resistance of cancer cells to various chemotherapeutics and has been demonstrated to correlate with drug efflux pumps. Visualization of drug efflux pumps is useful to pre-select patients who may be insensitive to chemotherapy, thus preventing patients from unnecessary treatment. Near-Infrared (NIR) imaging is an attractive approach to monitoring MDR due to its low tissue autofluorescence and deep tissue penetration. Molecular NIR imaging of MDR cancers requires stable probes targeting biomarkers with high specificity and affinity.

OBJECTIVE

This article aims to provide a concise review of novel NIR probes and their applications in MDR cancer treatment.

RESULTS

Recently, extensive research has been performed to develop novel NIR probes and several strategies display great promise. These strategies include chemical conjugation between NIR dyes and ligands targeting MDR-associated biomarkers, native NIR dyes with inherent targeting ability, activatable NIR probes as well as NIR dyes loaded nanoparticles. Moreover, NIR probes have been widely employed for photothermal and photodynamic therapy in cancer treatment, which combine with other modalities to overcome MDR. With the rapid advancing of nanotechnology, various nanoparticles are incorporated with NIR dyes to provide multifunctional platforms for controlled drug delivery and combined therapy to combat MDR. The construction of these probes for MDR cancers targeted NIR imaging and phototherapy will be discussed. Multimodal nanoscale platform which integrates MDR monitoring and combined therapy will also be encompassed.

CONCLUSION

We believe these NIR probes project a promising approach for diagnosis and therapy of MDR cancers, thus holding great potential to reach clinical settings in cancer treatment.

Luminescent Rhenium(I)-Polypyridine Complexes Appended with a Perylene Diimide or Benzoperylene Monoimide Moiety: Photophysics, Intracellular Sensing, and Photocytotoxic Activity

This communication reports novel luminescent rhenium(I)-polypyridine complexes appended with a perylene diimide (PDI) or benzoperylene monoimide (BPMI) moiety through a non-conjugated linker. The photophysical and photochemical properties originating from the interactions of the metal polypyridine and perylene units were exploited to afford new cellular reagents with thiol-sensing capability and excellent photocytotoxic activity.

Mitochondria-Accumulating Rhenium(I) Tricarbonyl Complexes Induce Cell Death via Irreversible Oxidative Stress and Glutathione Metabolism Disturbance

Mitochondria play a critical role in tumorigenesis. Targeting mitochondria and disturbing related events have been emerging as a promising way for chemotherapy. In this work, two binuclear rhenium(I) tricarbonyl complexes of the general formula [Re₂(CO)₆(dip)₂L](PF₆)₂ (dip = 4,7-diphenyl-1,10-phenanthroline; L = 4,4'-azopyridine (ReN) or 4,4'-dithiodipyridine (ReS)) were synthesized and characterized. ReN and ReS can react with glutathione (GSH). They exhibit good in vitro anticancer activity against cancer cell lines screened. Besides, they can target mitochondria, cause oxidative stress, and disturb GSH metabolism. Both ReN and ReS can induce necroptosis and caspase-dependent apoptosis simultaneously. We also demonstrate that ReN and ReS can inhibit tumor growth in nude mice bearing carcinoma xenografts. Our study shows the potential of Re(I) complexes as chemotherapeutic agents to kill cancer cells via a mitochondria-to-cellular redox strategy.

Linker chemistry dictates the delivery of a phototoxic organometallic rhenium(i) complex to human cervical cancer cells from core crosslinked star polymer nanoparticles

We have investigated core-crosslinked star polymer nanoparticles designed with tunable release chemistries as potential nanocarriers for a photoactive Re(i) organometallic complex. The nanoparticles consisted of a brush poly(oligo-ethylene glycol)methyl ether acrylate (POEGA) corona and a cross-linked core of non-biodegradable N,N'-methylenebis(acrylamide) (MBAA) and either pentafluorophenyl acrylate (PFPA), 3-vinyl benzaldehyde (VBA) or diacetone acrylamide (DAAM). Each star was modified with an amine functionalized photodynamic agent (i.e. a rhenium(i) organometallic complex) resulting in the formation of either a stable amide bond (POEGA-star-PFPA), or hydrolytically labile aldimine (POEGA-star-VBA) or ketimine bonds (POEGA-star-DAAM). These materials revealed linker dependent photo- and cytotoxicity when tested in vitro against non-cancerous lung fibroblast MRC-5 cells and HeLa human cervical cancer cells: the toxicity results correlated with final intracellular Re concentrations.

NIR/blue light emission optimization of NaY1−(x+y)YbxF4:Tmy upconversion nanoparticles via Yb3+/Tm3+ dopant balancing

A data driven approach provides better understanding of the role of dopant balancing in the upconversion process and presents an effective strategy to enhance the optical properties of upconversion nanoparticles.

Synthesis of Core-shell Lanthanide-doped Upconversion Nanocrystals for Cellular Applications

Lanthanide-doped upconversion nanocrystals (UCNs) have attracted much attention in recent years based on their promising and controllable optical properties, which allow for the absorption of near-infrared (NIR) light and can subsequently convert it into multiplexed emissions that span over a broad range of regions from the UV to the visible to the NIR. This article presents detailed experimental procedures for high-temperature co-precipitation synthesis of core-shell UCNs that incorporate different lanthanide ions into nanocrystals for efficiently converting deep-tissue penetrable NIR excitation (808 nm) into a strong blue emission at 480 nm. By controlling the surface modification with biocompatible polymer (polyacrylic acid, PAA), the as-prepared UCNs acquires great solubility in buffer solutions. The hydrophilic nanocrystals are further functionalized with specific ligands (dibenzyl cyclooctyne, DBCO) for localization on the cell membrane. Upon NIR light (808 nm) irradiation, the upconverted blue emission can effectively activate the light-gated channel protein on the cell membrane and specifically regulate the cation (e.g., Ca²⁺) influx in the cytoplasm. This protocol provides a feasible methodology for the synthesis of core-shell lanthanide-doped UCNs and subsequent biocompatible surface modification for further cellular applications.

Non-invasive tracking of hydrogel degradation using upconversion nanoparticles

Tracking the distribution and degradation of hydrogels in vivo is important for various applications including tissue engineering and drug delivery. Among various imaging modalities, fluorescence imaging has attracted intensive attention due to their high sensitivity, low cost and easy operation. Particularly, upconversion nanoparticles (UCNPs) that emit visible lights upon near-infrared (NIR) light excitation as tracking probes are promising in deciphering the fate of hydrogels after transplantation. Herein, we reported a facile and non-invasive in vivo hydrogel tracking method using UCNPs, where the degradation of hydrogels was determined using the decrease in fluorescence intensity from the UCNPs encapsulated in the hydrogels. We found that the change in the fluorescence intensity from the UCNPs was well consistent with that of the fluorescein isothiocyanate (FITC) covalently conjugated to hydrogels and also with the weight change of the hydrogels, suggesting the accuracy of the UCNPs in tracking the degradation of hydrogels. Furthermore, the in vivo fluorescence signals were only observed from the UCNPs instead of FITC after implantation for 7days due to the deep tissue penetration of UCNPs, demonstrating the capability of UCNPs in longitudinal, consecutive and non-invasive monitoring the in vivo degradation of hydrogels without causing any damage to the major organs (heart, lung, liver and kidney) of model rats. This study thus paves the way for monitoring the in vivo behaviors of biomimetic materials via deep tissue imaging with great clinical translation potentials.

STATEMENT OF SIGNIFICANCE

Long-term noninvasive in vivo tracking of the distribution and degradation of biodegradable hydrogels using fluorescent probes is important in tissue regeneration and drug delivery. Unlike the widely used fluorescent dyes and quantum dots (QDs) that suffer from photobleaching and undesired toxicity, upconversion nanoparticles (UCNPs) with high stability, deep tissue penetration as tracking probes are promising in deciphering the fate of hydrogels after transplantation. Herein, we reported a noninvasive in vivo hydrogel tracking method using UCNPs and found that the fluorescence intensity change from the UCNPs was well consistent with the weight change of the hydrogels, suggesting the accuracy of UCNPs in tracking hydrogel degradation. This study provides inspirations on developing advanced NIR light regulated probes with great clinical translation potentials.

Development of Semiconducting Polymer Nanoparticles for Photoacoustic Imaging

Semiconducting polymer nanoparticles (SPNs) have evolved into a new class of photonic materials with great potential for biomedical applications. Depending on the polymer structures, SPNs can be developed into optical agents for fluorescence and chemiluminescence imaging, photosensitizers for photodynamic therapy, and heat converters for photothermal therapy. In this feature article, recent work is summarized on the development of SPNs for in vivo photoacoustic (PA) imaging, a state-of-the-art imaging modality that converts light energy into mechanical acoustic waves to provide deep tissue penetration. The structure-property relationship and doping approaches are discussed to reveal the importance of promoting nonradiative decay in amplifying the PA brightness of SPNs. Moreover, their imaging applications, including lymph node mapping, tumor imaging, and monitoring of pathological indexes, are highlighted. These studies demonstrate that SPNs can serve as versatile PA agents for advanced molecular imaging applications.

Recent development of luminescent rhenium(i) tricarbonyl polypyridine complexes as cellular imaging reagents, anticancer drugs, and antibacterial agents

This Perspective summarizes recent advances in the biological applications of luminescent rhenium(i) tricarbonyl polypyridine complexes.