Frédérique Brégier

Starting from purpurin-18, a stable purpurin-18 imide derivative with intensive absorption in the near infrared has been synthesized. The opening of the exocycle anhydride by a primary alkylamine bearing an adamantyl group, allows after cyclization the formation of an imide function. This reaction led to the purpurinimide adamantane derivative (PIA) which enables the inclusion of a photosensitizer in the cavity of cationic cyclodextrin coupled to cellulose nanocrystals (CNCs/β-CD ⁺ ). Preliminary in vitro results showed that CNCs/β-CD ⁺ complexes improved internalization of photosensitizers into HCT116 and HT-29 colorectal cancer cell lines. Moreover, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay of CNCs/β-CD ⁺ /PIA complexes showed significant dose-dependent phototoxicity after illumination with red light, with IC ₅₀ values of 2.5 and 8.7 nM, for HT 116 and HT-29, respectively, and very low dark toxicity. The current results suggest that these nanoparticle/photosensitizer complexes are promising and useful tools for photodynamic therapy (PDT).

Photodynamic therapy (PDT) is a clinically approved, non-invasive therapy currently used for several solid tumors, triggering cell death through the generation of reactive oxygen species (ROS). However, the hydrophobic nature of most of the photosensitizers used, such as chlorins, limits the overall effectiveness of PDT. To address this limitation, the use of nanocarriers seems to be a powerful approach. From this perspective, we have recently developed water-soluble and biocompatible, fluorescent, organic nanoparticles (FONPs) functionalized with purpurin-18 and its derivative, chlorin p6 (Cp6), as new PDT agents. In this study, we aimed to investigate the induced cell death mechanism mediated by these functionalized nanoparticles after PDT photoactivation. Our results show strong phototoxic effects of the FONPs[Cp6], mediated by intracellular ROS generation, and subcellular localization in HCT116 and HT-29 human colorectal cancer (CRC) cells. Additionally, we proved that, post-PDT, the FONPs[Cp6] induce apoptosis via the intrinsic mitochondrial pathway, as shown by the significant upregulation of the Bax/Bcl-2 ratio, the activation of caspases 9, 3, and 7, leading poly-ADP-ribose polymerase (PARP-1) cleavage, and DNA fragmentation. Our work demonstrates the photodynamic activity of these nanoparticles, making them promising candidates for the PDT treatment of CRC.

Most photosensitizers of interest for photodynamic therapy—especially porphyrinoids and chlorins—are hydrophobic. To circumvent this difficulty, the use of nanocarriers is an attractive strategy. In this perspective, we have developed highly water-soluble and biocompatible fluorescent organic nanoparticles (FONPs) made from citric acid and diethyltriamine which are then activated by ethlynene diamine as nanoplatforms for efficient photosensitizers (PSs). Purpurin 18 (Pp18) was selected as a biosourced chlorin photosensitizer combining the efficient single oxygen generation ability and suitable absorption in the biological spectral window. The simple reaction of activated FONPs with Pp18, which contains a reactive anhydride ring, yielded nanoparticles containing both Pp18 and Cp6 derivatives. These functionalized nanoparticles combine solubility in water, high singlet oxygen generation quantum yield in aqueous media (0.72) and absorption both in the near UV region (FONPS) and in the visible region (Soret band approximately 420 nm as well as Q bands at 500 nm, 560 nm, 660 nm and 710 nm). The functionalized nanoparticles retain the blue fluorescence of FONPs when excited in the near UV region but also show deep-red or NIR fluorescence when excited in the visible absorption bands of the PSs (typically at 520 nm, 660 nm or 710 nm). Moreover, these nanoparticles behave as efficient photosensitizers inducing colorectal cancer cell (HCT116 and HT-29 cell lines) death upon illumination at 650 nm. Half maximal inhibitory concentration (IC50) values down to, respectively, 0.04 and 0.13 nmol/mL were observed showing the potential of FONPs[Cp6] for the PDT treatment of cancer. In conclusion, we have shown that these novel biocompatible nanoparticles, which can be elaborated from biosourced components, both show deep-red emission upon excitation in the red region and are able to produce singlet oxygen with high efficiency in aqueous environments. Moreover, they show high PDT efficiency on colorectal cancer cells upon excitation in the deep red region. As such, these functional organic nanoparticles hold promise both for PDT treatment and theranostics.

We have prepared the first example of a porphyrin linked to an heptazine photoactive antenna. The two entities, linked with an alkyl spacer, demonstrate the activity of both active moieties. While they behave electrochemically independantly, on the other hand the spectroscopy shows the existence of energy transfer between both partners.

Flavonoids are polyphenols with broad known pharmacological properties. A series of 2,3-dihydroflavanone derivatives were thus synthesized and investigated for their anti-inflammatory activities. The target flavanones were prepared through cyclization of 2′-hydroxychalcone derivatives, the later obtained by Claisen–Schmidt condensation. Since nitric oxide (NO) represents an important inflammatory mediator, the effects of various flavanones on the NO production in the LPS-induced RAW 264.7 macrophage were assessed in vitro using the Griess test. The most active compounds were flavanone (4G), 2′-carboxy-5,7-dimethoxy-flavanone (4F), 4′-bromo-5,7-dimethoxy-flavanone (4D), and 2′-carboxyflavanone (4J), with IC50 values of 0.603, 0.906, 1.030, and 1.830 µg/mL, respectively. In comparison, pinocembrin achieved an IC₅₀ value of 203.60 µg/mL. Thus, the derivatives synthesized in this work had a higher NO inhibition capacity compared to pinocembrin, demonstrating the importance of pharmacomodulation to improve the biological potential of natural molecules. SARs suggested that the use of a carboxyl-group in the meta-position of the B-ring increases biological activity, whereas compounds carrying halogen substituents in the para-position were less active. The addition of methoxy-groups in the meta-position of the A-ring somewhat decreased the activity. This study successfully identified new bioactive flavanones as promising candidates for the development of new anti-inflammatory agents.

Most photosensitizers (PS) suffer from a lack of water solubility and from a low selectivity toward tumor cells. Delivery systems using nanoparticles make it possible to improve PS water solubility, and also tumor targeting via the enhanced permeability and retention (EPR) effect. Among the organelles, mitochondria are attractive target sites for drug-delivery strategies since they perform a variety of key cellular processes. Our study was aimed at synthesizing nanoparticles consisting of xylan-carrying porphyrins attached to a triphenylphosphonium moiety, in order to enhance the PDT effect through mitochondrial targeting. Hybrid nanoparticles were designed that consisted of a silica core coated with xylan substituted with porphyrin derivatives carrying a triphenylphosphonium moiety. These hybrid nanoparticles have been constructed, along with their counterparts devoid of silica core, taking into consideration the controversy surrounding the use of silica nanoparticles. Phototoxicity experiments, conducted against the HCT-116 and HT-29 colorectal cancer cell lines, showed that nanoparticles with porphyrins bearing a triphenylphosphonium moiety exhibited an enhanced photocytotoxic effect in comparison with free porphyrin or nanoparticles with porphyrins without the triphenylphosphonium moiety.

The increasing number of hospital-acquired infections demand the development of innovative antimicrobial treatments. Antimicrobial photodynamic therapy (aPDT) is a versatile technique which relies on the production of reactive oxygen species (ROS) generated by light-irradiated photosensitizers (PS) in the presence of oxygen (O₂). 1H-Phenalen-1-one is a very efficient photosensitizer known for its high singlet oxygen quantum yield and its antimicrobial potential in aPDT when covalently bound to quaternary ammonium groups. Triazolium salts are stable aromatic quaternary ammonium salts that recently appeared as interesting moieties endowed with antimicrobial activities. The coupling between phenalenone and triazolium groups bearing various substituents was realized by copper-catalyzed azide-alkyne cycloaddition followed by alkylation with methyl iodide or 2-(bromomethyl)-1H-phenalen-1-one. As expected, most of the compounds retained the initial singlet oxygen quantum yield, close to unity. Minimum inhibitory concentrations (MIC) of 14 new phenalenone-triazolium salt derivatives and 2 phenalenone-triazole derivatives were determined against 6 bacterial strains (Gram-negatives and Gram-positives species). Most of these PS showed significant photoinactivation activities, the strongest effects being observed against Gram-positive strains with as low as submicromolar MIC values.

The poor solubility of most photosensitizers (PS) hampers their practical use as clinical agents. Conjugation of PS with water‐soluble nanoparticles has been often used to bypass this hurdle. We describe in this study the extraction of glucuronoacetylxylan from chestnut sawdust, the hemisynthesis of pheophorbide‐a (Pha) and its covalent attachment to xylan. The resulting conjugates (xyl‐Pha) spontaneously form water‐soluble spherical nanoparticles (xyl‐Pha NPs) ranging between 100 and 250 nm in diameter. Assayed against the HT‐29 colorectal cancer cell line, xyl‐Pha NPs exhibited a dose‐dependent phototoxicity only when irradiated with red light.