Towards Novel Photodynamic Anticancer Agents Generating Superoxide Anion Radicals: A Cyclometalated IrIII Complex Conjugated to a Far-Red Emitting Coumarin.

Although cyclometalated IrIII complexes have emerged as promising photosensitizers for photodynamic therapy, some key drawbacks still hamper clinical translation, such as operability in the phototherapeutic window and reactive oxygen species (ROS) production efficiency and selectivity. In this work, a cyclometalated IrIII complex conjugated to a far-red-emitting coumarin, IrIII -COUPY, is reported with highly favourable properties for cancer phototherapy. IrIII -COUPY was efficiently taken up by HeLa cells and showed no dark cytotoxicity and impressive photocytotoxicity indexes after irradiation with green and blue light, even under hypoxia. Importantly, a clear correlation between cell death and intracellular generation of superoxide anion radicals after visible light irradiation was demonstrated. This strategy opens the door to novel fluorescent photodynamic therapy agents with promising applications in theragnosis.

Selective Photokilling of Human Pancreatic Cancer Cells Using Cetuximab-Targeted Mesoporous Silica Nanoparticles for Delivery of Zinc Phthalocyanine.

BACKGROUND: Photodynamic therapy (PDT) is a non-invasive and innovative cancer therapy based on the photodynamic effect. In this study, we sought to determine the singlet oxygen production, intracellular uptake, and in vitro photodynamic therapy potential of Cetixumab-targeted, zinc(II) 2,3,9,10,16,17,23,24-octa(tert-butylphenoxy))phthalocyaninato(2-)-N29,N30,N31,N32 (ZnPcOBP)-loaded mesoporous silica nanoparticles against pancreatic cancer cells. RESULTS: The quantum yield (ΦΔ) value of ZnPcOBP was found to be 0.60 in toluene. In vitro cellular studies were performed to determine the dark- and phototoxicity of samples with various concentrations of ZnPcOBP by using pancreatic cells (AsPC-1, PANC-1 and MIA PaCa-2) and 20, 30, and 40 J/cm² light fluences. No dark toxicity was observed for any sample in any cell line. ZnPcOBP alone showed a modest photodynamic activity. However, when incorporated in silica nanoparticles, it showed a relatively high phototoxic effect, which was further enhanced by Cetuximab, a monoclonal antibody that targets the Epidermal Growth Factor Receptor (EGFR). The cell-line dependent photokilling observed correlates well with EGFR expression levels in these cells. CONCLUSIONS: Imidazole-capped Cetuximab-targeted mesoporous silica nanoparticles are excellent vehicles for the selective delivery of ZnPcOBP to pancreatic cancer cells expressing the EGFR receptor. The novel nanosystem appears to be a suitable agent for photodynamic therapy of pancreatic tumors.

NanoDCFH-DA: A Silica-based Nanostructured Fluorogenic Probe for the Detection of Reactive Oxygen Species.

A biocompatible fluorescent nanoprobe for the detection of reactive oxygen species in biological systems has been designed, synthesized and characterized, circumventing some of the limitations of the molecular probe diacetyl 2',7'-dichlorodihydrofluorescein (DCFH-DA). It has been synthetized the nanoparticulate form of DCFH-DA by covalently attaching the widely used fluorescent probe DCFH-DA to a mesoporous silica nanoparticle through a linker. The reactivity of nanoDCFH-DA has been tested toward several reactive oxygen species. In addition, it has been proved to slow down DCFH-DA reaction with molecular oxygen and it hampers from interactions with proteins. As a final piece of evidence, in vitro studies showed that the nanoprobe is internalized by HeLa cancer cells, thus being capable of detecting intracellularly generated reactive oxygen species. To sum up, it can be stated that nanoDCFH-DA overcomes two major problems of free DCFH-DA, namely oxidation of the probe by air and interaction with proteins in biological systems. This "nano" approach has thus proven useful to extend the utility of an existing and valuable fluorescent probe to complex biological systems.

Redesigning the Coumarin Scaffold into Small Bright Fluorophores with Far-Red to Near-Infrared Emission and Large Stokes Shifts Useful for Cell Imaging.

Among the palette of previously described fluorescent organic molecules, coumarins are ideal candidates for developing cellular and molecular imaging tools due to their high cell permeability and minimal perturbation of living systems. However, blue-to-cyan fluorescence emission is usually difficult in in vivo applications due to the inherent toxicity and poor tissue penetration of short visible light wavelengths. Here, we introduce a new family of coumarin-based fluorophores, nicknamed COUPY, with promising photophysical properties, including emission in the far-red/near-infrared (NIR) region, large Stokes shifts, high photostability, and excellent brightness. COUPY fluorophores were efficiently synthesized in only three linear synthetic steps from commercially available precursors, with the N-alkylation of a pyridine moiety being the key step at the end of the synthetic route, as it allows for the tuning of the photophysical properties of the resulting dye. Owing to their low molecular weights, COUPY dyes show excellent cell permeability and accumulate selectively in nucleoli and/or mitochondria of HeLa cells, as their far-red/NIR fluorescence emission is easily detected at a concentration as low as 0.5 µM after an incubation of only 20 min. We anticipate that these coumarin scaffolds will open a way to the development of novel coumarin-based far-red to NIR emitting fluorophores with potential applications for organelle imaging and biomolecule labeling.

Photodynamic Synergistic Effect of Pheophorbide a and Doxorubicin in Combined Treatment against Tumoral Cells.

A combination of therapies to treat cancer malignancies is at the forefront of research with the aim to reduce drug doses (ultimately side effects) and diminish the possibility of resistance emergence given the multitarget strategy. With this goal in mind, in the present study, we report the combination between the chemotherapeutic drug doxorubicin (DOXO) and the photosensitizing agent pheophorbide a (PhA) to inactivate HeLa cells. Photophysical studies revealed that DOXO can quench the excited states of PhA, detracting from its photosensitizing ability. DOXO can itself photosensitize the production of singlet oxygen; however, this is largely suppressed when bound to DNA. Photodynamic treatments of cells incubated with DOXO and PhA led to different outcomes depending on the concentrations and administration protocols, ranging from antagonistic to synergic for the same concentrations. Taken together, the results indicate that an appropriate combination of DOXO with PhA and red light may produce improved cytotoxicity with a smaller dose of the chemotherapeutic drug, as a result of the different subcellular localization, targets and mode of action of the two agents.

Synthesis, photophysical characterization, and photoinduced antibacterial activity of methylene blue-loaded amino- and mannose-targeted mesoporous silica nanoparticles.

Over the last 20 years, the number of pathogenic multi-resistant microorganisms has grown steadily, which has stimulated the search for new strategies to combat antimicrobial resistance. Antimicrobial photodynamic therapy (aPDT), also called photodynamic inactivation, is emerging as a promising alternative to treatments based on conventional antibiotics. We have explored the effectiveness of methylene blue-loaded targeted mesoporous silica nanoparticles (MSNP) in the photodynamic inactivation of two Gram negative bacteria, namely Escherichia coli and Pseudomonas aeruginosa. For E. coli, nanoparticle association clearly reduced the dark toxicity of MB while preserving its photoinactivation activity. For P. aeruginosa, a remarkable difference was observed between amino- and mannose-decorated nanoparticles. The details of singlet oxygen production in the nanoparticles have been characterized, revealing the presence of two populations of this cytotoxic species. Strong quenching of singlet oxygen within the nanoparticles is observed.