Inherently Antimicrobial P(MMA-ran-DMAEMA) Copolymers Sensitive to Photodynamic Therapy: A Double Bactericidal Effect for Active Wound Dressing

In this work, two compounds belonging to the BODIPY family, and previously investigated for their photosensitizing properties, have been bound to the amino-pendant groups of three random copolymers, with different amounts of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in the backbone. The P(MMA-ran-DMAEMA) copolymers have inherently bactericidal activity, due to the amino groups of DMAEMA and to the quaternized nitrogens bounded to BODIPY. Systems consisting of filter paper discs coated with copolymers conjugated to BODIPY were tested on two model microorganisms, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). On solid medium, irradiation with green light induced an antimicrobial effect, visible as a clear inhibition area around the coated disks. The system based on the copolymer with 43% DMAEMA and circa 0.70 wt/wt% of BODIPY was the most efficient in both bacterial species, and a selectivity for the Gram-positive model was observed, independently of the conjugated BODIPY. A residual antimicrobial activity was also observed after dark incubation, attributed to the inherently bactericidal properties of copolymers.

Preliminary Toxicity Evaluation of a Porphyrin Photosensitizer in an Alternative Preclinical Model

In photodynamic therapy (PDT), a photosensitizer (PS) excited with a specific wavelength, and in the presence of oxygen, gives rise to photochemical reactions that lead to cell damage. Over the past few years, larval stages of the G. mellonella moth have proven to be an excellent alternative animal model for in vivo toxicity testing of novel compounds and virulence testing. In this article, we report a series of preliminary studies on G. mellonella larvae to evaluate the photoinduced stress response by a porphyrin (PS) (TPPOH). The tests performed evaluated PS toxicity on larvae and cytotoxicity on hemocytes, both in dark conditions and following PDT. Cellular uptake was also evaluated by fluorescence and flow cytometry. The results obtained demonstrate how the administration of PS and subsequent irradiation of larvae affects not only larvae survival rate, but also immune system cells. It was also possible to verify PS's uptake and uptake kinetics in hemocytes, observing a maximum peak at 8 h. Given the results obtained in these preliminary tests, G. mellonella appears to be a promising model for preclinical PS tests.

Free and Poly-Methyl-Methacrylate-Bounded BODIPYs: Photodynamic and Antimigratory Effects in 2D and 3D Cancer Models

Several limitations, including dark toxicity, reduced tumor tissue selectivity, low photostability and poor biocompatibility hamper the clinical use of Photodynamic therapy (PDT) in cancer treatment. To overcome these limitations, new PSs have been synthetized, and often combined with drug delivery systems, to improve selectivity and reduce toxicity. In this context, BODIPYs (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) have recently emerged as promising and easy-to-handle scaffolds for the preparation of effective PDT antitumor agents. In this study, the anticancer photodynamic effect of newly prepared negatively charged polymethyl methacrylate (nPMMA)-bounded BODIPYs (3@nPMMA and 6@nPMMA) was evaluated on a panel of 2D- and 3D-cultured cancer cell lines and compared with free BODIPYs. In particular, the effect on cell viability was evaluated, along with their ability to accumulate into the cells, induce apoptotic and/or necrotic cell death, and inhibit cellular migration. Our results indicated that 3@nPMMA and 6@nPMMA reduce cancer cell viability in 3D models of HC116 and MCF7 cells more effectively than the corresponding free compounds. Importantly, we demonstrated that MDA-MB231 and SKOV3 cell migration ability was significantly impaired by the PDT treatment mediated by 3@nPMMA and 6@nPMMA nanoparticles, likely indicating the capability of this approach to reduce metastatic tumor potential.

BODIPYs in PDT: A Journey through the Most Interesting Molecules Produced in the Last 10 Years

Over the past 30 years, photodynamic therapy (PDT) has shown great development. In the clinical setting the few approved molecules belong almost exclusively to the porphyrin family; but in the scientific field, in recent years many researchers have been interested in other families of photosensitizers, among which BODIPY has shown particular interest. BODIPY is the acronym for 4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene, and is a family of molecules well-known for their properties in the field of imaging. In order for these molecules to be used in PDT, a structural modification is necessary which involves the introduction of heavy atoms, such as bromine and iodine, in the beta positions of the pyrrole ring; this change favors the intersystem crossing, and increases the ¹O₂ yield. This mini review focused on a series of structural changes made to BODIPYs to further increase ¹O₂ production and bioavailability by improving cell targeting or photoactivity efficiency.

In vitro photodynamic treatment of cancer cells induced by aza-BODIPYs

Two aza-BODIPY photosensitizes (PSs, compounds 7 and 8), featuring an iodine atom on each pyrrolic unit of their structure, were synthesized in fairly good yields starting from commercial products and tested in vitro on two human cancer cell lines (HCT116 and SKOV3) to assess their photodynamic efficacy. After treating the cell cultures with variable concentrations of 7 or 8 and incubating for the desired incubation time, the cells were irradiated for two hours with a red-light emitting diode (LED) device; afterwards the extent of cell death was determined by MTT assay. Besides the killing effect, the new PSs were also studied to determine further parameters related to photodynamic efficacy, such as the resistance towards photobleaching, the rate of singlet oxygen production, the fluorescence quantum yields, the cellular uptake and the localization inside the cells and, finally, flow cytometric analysis for apoptosis. Considering the results as a whole, these aza-BODIPYs can be considered to be promising photosensitizers because of their IC₅₀ values being below micromolar concentrations and for more rather interesting features. Actually, these molecules have proved to be: (a) quite stable towards photobleaching; (b) good producers of singlet oxygen and (c) highly penetrating the cells with a wide distribution in the cytosol. Furthermore, in accordance with the good rate of singlet oxygen production, the apoptotic cells reach 30% and this allows us to assume a low inflammatory effect of the in vivo PDT treatment; thus a possible in vivo application of these aza-BODIPYs might be plausible.

Cationic diarylporphyrins: In vitro versatile anticancer and antibacterial photosensitizers

The visible light combined with photosensitizers (PSs) is exploited in both antitumoral and antimicrobial fields inducing a photo-oxidative stress within the target cells. Among the different PSs, porphyrins belong to the family of the most promising compounds to be used in clinical photodynamic applications. Although in the last years many porphyrins have been synthesised and tested, only a few reports concern the in vitro effects of the 5,15-diarylporphyrins. In this work, the activity of four 5,15-diarylporphyrins (compounds 7-10), bearing alkoxy-linked pyridinium appendixes, have been tested on cancer cell lines and against bacterial cultures. Among the synthetized PSs, compounds 7 and 9 are not symmetrically substituted porphyrins showing one cationic charge tethered at the end of one 4C or 8C carbon chains, respectively. On the other hand, compounds 8 and 10 are symmetrically substituted and show two chains of C4 and C8 carbons featuring a cationic charge at the end of both chains. The dicationic 8 and 10 were more hydrophilic than monocationic 7 and 9, outlining that the presence of two pyridinium salts have a higher impact on the solubility in the aqueous phase than the lipophilic effect exerted by the length of the alkyl chains. Furthermore, these four PSs showed a similar rate of photobleaching, irrespective of the length and number of chains and the number of positive charges. Among the eukaryotic cell lines, the SKOV3 cells were particularly sensitive to the photodynamic activity of all the tested diarylporphyrins, while the HCT116 cells were found more sensitive to PSs bearing C4 chain (7 and 8), regardless the number of cationic charges. The photo-induced killing effect of these porphyrins was also tested against two different bacterial cultures. As expected, the Gram positive Bacillus subtilis was more sensitive than the Gram negative Escherichia coli, and the dicationic porphyrin 8, bearing two C4 chains, was the most efficient on both microorganisms. In conclusion, the new compound 8 seems to be an optimal candidate to deepen as versatile anticancer and antibacterial photosensitizer.

Tailored-BODIPY/Amphiphilic Cyclodextrin Nanoassemblies with PDT Effectiveness

Amphiphilic cyclodextrins (aCDs) are an intriguing class of carrier systems which, recently, have been proposed to deliver porphyrinoids and anticancer drugs or combined dose of both for dual therapeutic applications. The design of nanoassemblies based on aCD and photosensitizers (PSs) aims to preserve the photodynamic therapy (PDT) efficacy of PS, reducing the tendency of PS to self-aggregate, without affecting the quantum yield of singlet oxygen (¹O₂) production, and, not less importantly, minimizing dark toxicity and reducing photosensitization effects. With this idea in mind, in this paper, we focus on nanoassemblies between a non-ionic aCD (SC6OH) and halo-alkyl tailored iodinated boron-dipyrromethenes (BODIPY) dye, a class of molecules which recently have been successfully proposed as a stimulating alternative to porphyrinoids for their high photodynamic efficacy. Nanoassemblies of BODIPY/aCD (BL01I@SC6OH) were prepared in different aqueous media by evaporation of mixed organic film of aCD and BODIPY, hydration, and sonication. The nanostructures were characterized, measuring their hydrodynamic diameter and ξ-potential and also evaluating their time-stability in biological relevant media. Taking advantage of emissive properties of the not-iodinated BODIPY analogue (BL01), nanoassemblies based on aCD and BL01 were investigated as model system to get insight on entanglement of BODIPY in the amphiphile in aqueous dispersion, pointing out that BODIPY is well-entrapped in monomeric form (τ ≅ 6.5 ns) within the colloidal carriers. Also morphology and fluorescence emission properties were elucidated after casting the solution on glass. BL01@SC6OH is easily detectable in cytoplasm of HCT116 cell lines, evidencing the remarkable intracellular penetration of this nanoassembly similar to free BODIPY. On the same cell lines, the photodynamically active assembly BL01I/aCD shows toxicity upon irradiation. Despite the fact that free BL01I is more PDT active than its assembly, aCD can modulate the cell uptake of BODIPY, pointing out the potential of this system for in vivo PDT application.