From the Design of Innovative Ti-Pt Heterometallic Complexes to the Development of Highly Anti-Proliferative Water-Soluble Cationic Titanocenes.

Two innovative early/late Ti-Pt-heterobimetallic complexes were synthesized, characterized, and screened in cell-based assays using several human (SW480 and MDA-MB-231) and murine cancer cell lines (CT26 and EMT6) as well as a non-cancerous cell line (HMEC). The combination of the two metals - titanium(IV) and platinum (IV) - in a single molecule led to a synergistic biological activity (higher anti-proliferative properties than a mixture of each of the corresponding monometallic complexes). This study also investigated the benefits of associating a metal-free terpyridine moiety (with intrinsic biological activity) with a water-soluble titanocene fragment. The present work reveals that these combinations results in water-soluble titanocene compounds displaying an anti-proliferative activity down to the submicromolar level. One of these complexes induced an antitumor effect in vivo in CT26 tumor bearing BALB/C mice. The terpyridine moiety was also used to track the complex in vitro by multiphoton microscopy imaging.

Al(III) and Ga(III) Bisphenolate Azadipyrromethene-Based "N2O2" Complexes as Efficient NIR-Fluorophores.

Aza-boron-dipyrromethenes (Aza-BODIPYs) are an increasingly studied class of fluorophores. They can be seen as an azadipyrromethene ("aza-DIPY") ligand rigidified by a metalloid, a boron atom. Based on this idea, a series of complexes of group 13 metals (aluminum and gallium) have been synthesized and characterized. The impact of the metal and of the nature of the substituents of aza-DIPY core were investigated. The photophysical and electrochemical properties were determined, and an X-ray structure of an azaGaDIPY was obtained. These data reveal that azaGaDIPY and azaAlDIPY exhibit significant red-shifted fluorescence compared to their analogue aza-BODIPY. Their emission can go up to 800 nm for the maximum emission length and up to NIR-II for the emission tail. This, associated with their electrochemical stability (no metal release whether oxidized or reduced) makes them a promising class of fluorophores for optical medical imaging. Moreover, X-ray structure and molecular modeling studies have shown that this redshift seems to be more due to the geometry around the boron/metal than to the nature of the metal.

Water-Soluble Aza-BODIPYs: Biocompatible Organic Dyes for High Contrast In Vivo NIR-II Imaging.

A simple NIR-II emitting water-soluble system has been developed and applied in vitro and in vivo. In vitro, the fluorophore quickly accumulated in 2D and 3D cell cultures and rapidly reached the tumor in rodents, showing high NIR-II contrast for up to 1 week. This very efficient probe possesses all the qualities necessary for translation to the clinic as well as for the development of NIR-II emitting materials.

One-Pot, Highly Stereoselective Synthesis of Dithioacetal-α,α-Diglycosides.

A one-step access to dithioacetal-α,α-diglycosides is reported. The synthetic strategy is based on the thioacetalization of aldehydes or ketones via highly stereoselective ring-opening of 1,6 anhydrosugars with bis(trimethylsilyl)sulfide.

WazaGaY: An Innovative Aza-BODIPY-Derived Near-Infrared Fluorescent Probe for Enhanced Tumor Imaging.

Aza-BODIPYs represent a class of fluorophores in which the π-conjugated system is rigidified and stabilized by a boron atom. A promising strategy to enhance their fluorescence properties involves replacing the boron atom with a metal ion. Here, we describe the synthesis and characterization of a water-soluble derivative where the metal is a gallium(III) ion, termed WazaGaY (water-soluble aza-GaDIPY). Water solubility is ensured by two ammonium substituents, inducing a bathochromic shift and a significant increase in quantum yield compared to that of the dimethylamino analog. The cellular behavior of WazaGaY-1 was observed across different tumor cells. In vivo, the distribution and safety profiles were determined, and tumor uptake was assessed in various tumor types. Following intravenous injection, WazaGaY-1 enabled clear discrimination of tumors engrafted subcutaneously in mice with high tumor-to-muscle ratios (ranging from 7 to 20), even in the absence of specific conjugation. Its potential as a contrast agent for fluorescence-guided surgery was confirmed.

Comparison of the In Vitro and In Vivo Behavior of a Series of NIR-II-Emitting Aza-BODIPYs Containing Different Water-Solubilizing Groups and Their Trastuzumab Antibody Conjugates.

The development of new fluorescent organic probes effective in the NIR-II region is currently a fast-growing field and represents a challenge in the domain of medical imaging. In this study, we have designed and synthesized an innovative series of aza-boron dipyrromethenes emitting in the NIR-II region. We have investigated the effect of different water-solubilizing groups not only on the photophysical properties of the compounds but also on their in vitro and in vivo performance after bioconjugation to the antibody trastuzumab. Remarkably, we discovered that the most lipophilic compound unexpectedly displayed the most favorable in vivo properties after bioconjugation. This underlines the profound influence that the fluorophore functionalization approach can have on the efficiency of the resulting imaging agent.

NIR-II Aza-BODIPY Dyes Bioconjugated to Monoclonal Antibody Trastuzumab for Selective Imaging of HER2-Positive Ovarian Cancer.

Using fluorescence-guided surgery (FGS) to cytoreductive surgery helps achieving complete resection of microscopic ovarian tumors. The use of visible and NIR-I fluorophores has led to beneficial results in clinical trials; however, involving NIR-II dyes seems to outperform those benefits due to the deeper tissue imaging and higher signal/noise ratio attained within the NIR-II optical window. In this context, we developed NIR-II emitting dyes targeting human epidermal growth factor receptor 2 (HER2)-positive ovarian tumors by coupling water-soluble NIR-II aza-BODIPY dyes to the FDA-approved anti-HER2 antibody, namely, trastuzumab. These bioconjugated NIR-II-emitting dyes displayed a prolonged stability in serum and a maintained affinity toward HER2 in vitro. We obtained selective targeting of HER2 positive tumors (SKOV-3) in vivo, with a favorable tumor accumulation. We demonstrated the fluorescence properties and the specific HER2 binding of the bioconjugated dyes in vivo and thus their potential for NIR-II FGS in the cancer setting.

Tailored hyaluronic acid-based nanogels as theranostic boron delivery systems for boron neutron cancer therapy.

Boron-rich nanocarriers possess great potential for advanced boron neutron capture therapy (BNCT) as an effective radiation treatment for invasive malignant tumors. If additionally, they can be imaged in a non-invasive and real-time manner allowing the assessment of local boron concentration, they could serve for dose calculation and image-guided BNCT to enhance tumor treatment efficacy. To meet this challenge, this study describes the design of a theranostic nanogel, enriched in 10B and fluorescent dye, to achieve selective imaging, and sufficient accumulation of boron at the tumor site. The boron-rich and fluorescent nanogels can be easily obtained via temperature triggered-assembly of hyaluronic acid (HA) modified with a thermoresponsive terpolymer. The latter was specifically designed to enable the efficient encapsulation of the fluorescent dye - an aza­boron-dipyrromethene (aza-BODIPY) - linked to 10B-enriched sodium borocaptate (BSH), in addition to induce nanogel formation below room temperature, and to enable their core-crosslinking by hydrazone bond formation. The HA nanogel considerably concentrates aza-BODIPY-BSH into the hydrophobic nanodomains made of the terpolymer chains. Here, we present the detailed synthesis of the HA-terpolymer conjugate, nanogel formation, and characterization in terms of size, morphology, and stability upon storage, as well as the biological behavior of the boron nanocarrier using real-time fluorescence imaging in cells and in vivo. This work suggested the potential of the theranostic HA nanogel as a boron delivery system for the implementation of BNCT in brain cancer and sarcoma.

Lipoprotein interactions with water-soluble NIR-II emitting aza-BODIPYs boost the fluorescence signal and favor selective tumor targeting.

Following intravenous administration, the interaction of fluorescent exogenous molecules with circulating endogenous transporters can influence their photophysical properties as well as their fate and distribution, and possibly their recognition by different cell types. This type of interaction can be used to optimize the drug delivery but also the imaging properties of a compound of interest. In this study, we investigated the behavior of SWIR-WAZABY-01 fluorophore, a water-soluble aza-BODIPY dye emitting in the NIR-II region, both in vitro and in vivo. While the fluorescence emission of SWIR-WAZABY-01 was weak in aqueous solutions, it was intensely magnified in plasma (∼ ×30). Further analyses using lipoprotein gel electrophoresis and ultracentrifugation revealed interactions between SWIR-WAZABY-01 and plasma lipoproteins in vitro and ex vivo, in particular with LDL. The tumor uptake mechanism of SWIR-WAZABY-01 was investigated based on the presence of low-density lipoprotein (LDL) receptors and passive tumor uptake. Overall, we found that SWIR-WAZABY-01 interacts with lipoproteins enhancing their NIR-II fluorescence emission, and driving the tumor accumulation with regards to the expression of lipoprotein receptors (LDLR, SR-BI). Moreover, SWIR-WAZABY-01, by exploiting endogenous lipoproteins, arises as a new, potent and relevant tool to efficiently label LDL involved in pathologies.

Aza-BODIPY: A New Vector for Enhanced Theranostic Boron Neutron Capture Therapy Applications.

Boron neutron capture therapy (BNCT) is a radiotherapeutic modality based on the nuclear capture of slow neutrons by stable 10B atoms followed by charged particle emission that inducing extensive damage on a very localized level (<10 µm). To be efficient, a sufficient amount of 10B should accumulate in the tumor area while being almost cleared from the normal surroundings. A water-soluble aza-boron-dipyrromethene dyes (BODIPY) fluorophore was reported to strongly accumulate in the tumor area with high and BNCT compatible Tumor/Healthy Tissue ratios. The clinically used 10B-BSH (sodium borocaptate) was coupled to the water-soluble aza-BODIPY platform for enhanced 10B-BSH tumor vectorization. We demonstrated a strong uptake of the compound in tumor cells and determined its biodistribution in mice-bearing tumors. A model of chorioallantoic membrane-bearing glioblastoma xenograft was developed to evidence the BNCT potential of such compound, by subjecting it to slow neutrons. We demonstrated the tumor accumulation of the compound in real-time using optical imaging and ex vivo using elemental imaging based on laser-induced breakdown spectroscopy. The tumor growth was significantly reduced as compared to BNCT with 10B-BSH. Altogether, the fluorescent aza-BODIPY/10B-BSH compound is able to vectorize and image the 10B-BSH in the tumor area, increasing its theranostic potential for efficient approach of BNCT.

Formation of methyl radicals derived from cumene hydroperoxide in reconstructed human epidermis: an EPR spin trapping confirmation by using 13C-substitution.

Dermal exposure to cumene hydroperoxide (CumOOH) during manufacturing processes is a toxicological issue for the industry. Its genotoxicity, mutagenic action, ability to promote skin tumour, capacity to induce epidermal hyperplasia, and aptitude to induce allergic and irritant skin contact dermatitis are well known. These toxic effects appear to be mediated through the activation to free radical species such as hydroxyl, alkoxyl, and alkyl radicals characterised basically by electron paramagnetic resonance (EPR) and spin-trapping (ST) techniques. To be a skin sensitiser CumOOH needs to covalently bind to skin proteins in the epidermis to form the antigenic entity triggering the immunotoxic reaction. Cleavage of the O-O bond allows formation of unstable CumO•/CumOO• radicals rearranging to longer half-life specific carbon-centred radicals R• proposed to be at the origin of the antigen formation. Nevertheless, it is not still clear which R• is precisely formed in the epidermis and thus involved in the sensitisation process. The aim of this work was to elucidate in conditions closer to real-life sensitisation which specific R• are formed in a 3D reconstructed human epidermis (RHE) model by using 13C-substituted CumOOH at carbon positions precursors of potentially reactive radicals and EPR-ST. We demonstrated that most probably methyl radicals derived from ß-scission of CumO• radicals occur in RHE through a one-electron reductive pathway suggesting that these could be involved in the antigen formation inducing skin sensitisation. We also describe a coupling between nitroxide radicals and ß position 13C atoms that could be of an added value to the very few examples existing for the coupling of radicals with 13C atoms.