Cationic diarylporphyrins: In vitro versatile anticancer and antibacterial photosensitizers

Photodynamic inactivation of E. coli with cationic imidazolyl-porphyrin photosensitizers and their synergic combination with antimicrobial cinnamaldehyde

Bacterial infections are a global health concern, particularly due to the increasing resistance of bacteria to antibiotics. Multi-drug resistance (MDR) is a considerable challenge, and novel approaches are needed to treat bacterial infections. Photodynamic inactivation (PDI) of microorganisms is increasingly recognized as an effective method to inactivate a broad spectrum of bacteria and overcome resistance mechanisms. This study presents the synthesis of a new cationic 5,15-di-imidazolyl porphyrin derivative and the impact of n-octanol/water partition coefficient (logP) values of this class of photosensitizers on PDI efficacy of Escherichia coli. The derivative with logP = -0.5, IP-H-OH2+, achieved a remarkable 3 log CFU reduction of E. coli at 100 nM with only 1.36 J/cm2 light dose at 415 nm, twice as effective as the second-best porphyrin IP-H-Me2+, of logP = -1.35. We relate the rapid uptake of IP-H-OH2+ by E. coli to improved PDI and the very low uptake of a fluorinated derivative, IP-H-CF32+, logP ≈ 1, to its poor performance. Combination of PDI with cinnamaldehyde, a major component of the cinnamon plant known to alter bacteria cell membranes, offered synergic inactivation of E. coli (7 log CFU reduction), using 50 nM of IP-H-OH2+ and just 1.36 J/cm2 light dose. The success of combining PDI with this natural compound broadens the scope of therapies for MDR infections that do not add drug resistance. In vivo studies on a mouse model of wound infection showed the potential of cationic 5,15-di-imidazolyl porphyrins to treat clinically relevant infected wounds.

Cationic Porphyrins as Antimicrobial and Antiviral Agents in Photodynamic Therapy

Antimicrobial photodynamic therapy (APDT) has received a great deal of attention due to its unique ability to kill all currently known classes of microorganisms. To date, infectious diseases caused by bacteria and viruses are one of the main sources of high mortality, mass epidemics and global pandemics among humans. Every year, the emergence of three to four previously unknown species of viruses dangerous to humans is recorded, totaling more than 2/3 of all newly discovered human pathogens. The emergence of bacteria with multidrug resistance leads to the rapid obsolescence of antibiotics and the need to create new types of antibiotics. From this point of view, photodynamic inactivation of viruses and bacteria is of particular interest. This review summarizes the most relevant mechanisms of antiviral and antibacterial action of APDT, molecular targets and correlation between the structure of cationic porphyrins and their photodynamic activity.

Ruthenium(II)-Arene Curcuminoid Complexes as Photosensitizer Agents for Antineoplastic and Antimicrobial Photodynamic Therapy: In Vitro and In Vivo Insights

Photodynamic therapy (PDT) is an anticancer/antibacterial strategy in which photosensitizers (PSs), light, and molecular oxygen generate reactive oxygen species and induce cell death. PDT presents greater selectivity towards tumor cells than conventional chemotherapy; however, PSs have limitations that have prompted the search for new molecules featuring more favorable chemical-physical characteristics. Curcumin and its derivatives have been used in PDT. However, low water solubility, rapid metabolism, interference with other drugs, and low stability limit curcumin use. Chemical modifications have been proposed to improve curcumin activity, and metal-based PSs, especially ruthenium(II) complexes, have attracted considerable attention. This study aimed to characterize six Ru(II)-arene curcuminoids for anticancer and/or antibacterial PDT. The hydrophilicity, photodegradation rates, and singlet oxygen generation of the compounds were evaluated. The photodynamic effects on human colorectal cancer cell lines were also assessed, along with the ability of the compounds to induce ROS production, apoptotic, necrotic, and/or autophagic cell death. Overall, our encouraging results indicate that the Ru(II)-arene curcuminoid derivatives are worthy of further investigation and could represent an interesting option for cancer PDT. Additionally, the lack of significant in vivo toxicity on the larvae of Galleria mellonella is an important finding. Finally, the photoantimicrobial activity of HCurc I against Gram-positive bacteria is indeed promising.

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.

Photo-Inactivation of Staphylococcus aureus by Diaryl-Porphyrins

Photodynamic Antimicrobial Chemotherapy (PACT) has received great attention in recent years since it is an effective and promising modality for the treatment of human oral and skin infections with the advantage of bypassing pathogens' resistance to antimicrobials. Moreover, PACT applications demonstrated a certain activity in the inhibition and eradication of biofilms, overcoming the well-known tolerance of sessile communities to antimicrobial agents. In this study, 13 diaryl-porphyrins (mono-, di-cationic, and non-ionic) P1-P13 were investigated for their potential as photosensitizer anti-Staphylococcus aureus. The efficacy of the diaryl-porphyrins was evaluated through photo-inactivation tests. Crystal-violet staining combined with viable count techniques were aimed at assaying their anti-biofilm activity. Among the tested compounds, the neutral photosensitizer P4 was better than the cationic ones, irrespective of their corresponding binding rates. In particular, P4 was active in inhibiting the biofilm formation and in impairing the viability of the adherent and planktonic populations of a 24 h old biofilm. The inhibitory activity was also efficient against a methicillin resistant S. aureus strain. In conclusion, the diaryl-porphyrin family represents a reservoir of promising compounds for photodynamic applications against the pathogen S. aureus and in preventing the formation of biofilms that cause many infections to become chronic.

Carbazole appended trans-dicationic pyridinium porphyrin finds supremacy in DNA binding/photocleavage over a non-carbazolyl analogue

A carbazolyl appended trans-pyridyl porphyrin (1) was synthesized and its dicationic form 2 was obtained by methylation of the pyridyl group. Copper and zinc complexes of porphyrin 2 (Cu(II), 3; Zn(II), 4) were isolated and characterized by various modern spectroscopic techniques. The DNA binding properties of 2, 3, and 4 have been explored against calf thymus-DNA (CT-DNA). DNA binding was quantized using the intrinsic binding constant (K_b) that was calculated by UV-visible absorption spectroscopy, and the value K_b = 1.6 × 10⁶ M^-1 for compound 2 reveals a better interaction of 2 towards CT-DNA than those of 3 (3.1 × 10⁵ M^-1) and 4 (3.4 × 10⁵ M^-1), which follows the order 2 > 4 > 3. The fluorescence quenching efficiency and ethidium bromide quenching assay also indicated a good binding affinity of all the compounds towards CT-DNA. Furthermore, the spectroscopic data suggest that the possible mode of interaction is intercalation. The docking studies were in accordance with the experimental results. Notably, DNA cleavage studies reveal that 2 shows better damage than 3 and 4 which is in accordance with the binding affinity order 2 > 4 > 3. The observed quantum yield (2: 0.65, 3: 0.33, and 4: 0.97) and no change in DNA cleavage in the presence of NaN₃ reveal the involvement of singlet oxygen. The singlet excited state lifetimes were in the range of 6.3-1.2 ns. Furthermore, these porphyrins can be investigated as interesting photosensitizers in photodynamic therapy and photochemotherapy.

Photo-damage promoted by tetra-cationic palladium(II) porphyrins in rapidly growing mycobacteria

Antimicrobial photodynamic therapy (aPDT) has gained prominence in microbiology, especially in treating non-invasive infections. Diseases such as mycobacteriosis, which causes localized infections and has a slow treatment, tend to be future targets for this type of technology. Therefore, this study aimed to explore the action of two isomeric Pd(II)-porphyrins on fast-growing mycobacterial strains (RGM). Tetra-cationic porphyrins (4-PdTPyP and 3-PdTPyP) were synthesized and applied against standard strains of Mycobacteroides abscessus subsp. abscessus (ATCC 19977), Mycolicibacterium fortuitum (ATCC 6841), Mycolicibacterium smegmatis (ATCC 700084), and Mycobacteroides abscessus subsp. massiliense (ATCC 48898). Reactive oxygen species (ROS) scavengers were used in an attempt to determine possible ROS produced by the photosensitizers (PS) under study. Moreover, the impact of porphyrin on the mycobacterial surface was further evaluated by atomic force microscopy (AFM), and we observed significant damage on cells walls and altered nanomechanical and electrostatic adhesion properties. The results presented herein show that the positively charged porphyrin at the meta position (3-PdTPyP) was the most efficient PS against the RGM strains, and its bactericidal activity was proven in two irradiation sessions, with singlet oxygen species being the main ROS involved in this process. This study demonstrated the therapeutic potential of porphyrins, especially the 3-PdTPyP derivative.

Nitric Oxide Photo-Donor Hybrids of Ciprofloxacin and Norfloxacin: A Shift in Activity from Antimicrobial to Anticancer Agents

The potential anticancer effect of fluoroquinolone antibiotics has been recently unveiled and related to their ability to interfere with DNA topoisomerase II. We herein envisioned the design and synthesis of novel Ciprofloxacin and Norfloxacin nitric oxide (NO) photo-donor hybrids to explore the potential synergistic antitumor effect exerted by the fluoroquinolone scaffold and NO eventually produced upon light irradiation. Anticancer activity, evaluated on a panel of tumor cell lines, showed encouraging results with IC50 values in the low micromolar range. Some compounds displayed intense antiproliferative activity on triple-negative and doxorubicin-resistant breast cancer cell lines, paving the way for their potential use to treat aggressive, refractory and multidrug-resistant breast cancer. No significant additive effect was observed on PC3 and DU145 cells following NO release. Conversely, antimicrobial photodynamic experiments on both Gram-negative and Gram-positive microorganisms displayed a significant killing rate in Staphylococcus aureus, accounting for their potential effectiveness as selective antimicrobial photosensitizers.

Drug delivery systems for the photodynamic application of two photosensitizers belonging to the porphyrin family

Photodynamic therapy involves the concomitant action of three components, light with an appropriate wavelength, molecular oxygen, and a molecule, able to absorb an electromagnetic radiation, called photosensitizer (PS). A fundamental aspect is the bioavailability of the PS that is directly related to some physicochemical properties of the PS itself as it should feature a certain degree of lipophilicity to easily cross the cell membrane, however, at the same time, should be sufficiently water-soluble to navigate in the bloodstream. Consequently, the use of a system for drug delivery becomes essential when photosensitizers with a high degree of lipophilicity are considered. In this work, we present three different drug delivery systems, microemulsions, emulsions and liposomes all capable of carrying a PS belonging to the porphyrin family: the tetraphenyl porphyrin (TPP) and the 4-hydroxyphenyl porphyrin (THPP), which show a relevant different degree of lipophilicity. A series of microemulsions (ME) and emulsions (E) were prepared, among which two formulations, one for THPP and one for TPP, have been chosen. The stability of these two carriers was monitored over time and under various temperature conditions. With the same criteria, two liposomal formulations have been also identified and analyzed. The four formulations mentioned above (one ME, one E and two liposomes) have been tested on SKOV3 tumor cell line comparing the photodynamic activity of the porphyrin formulations versus the aqueous/organic (DMSO) solution of the same two PSs. The results show that all the formulations have proved to be excellent carriers and that the liposomal formulation enhance the photodynamic efficacy of both porphyrins.

Photoinactivation of Pseudomonas aeruginosa Biofilm by Dicationic Diaryl-Porphyrin

In recent years, antimicrobial photodynamic therapy (aPDT) has received increasing attention as a promising tool aimed at both treating microbial infections and sanitizing environments. Since biofilm formation on biological and inert surfaces makes difficult the eradication of bacterial communities, further studies are needed to investigate such tricky issue. In this work, a panel of 13 diaryl-porphyrins (neutral, mono- and di-cationic) was taken in consideration to photoinactivate Pseudomonas aeruginosa. Among cationic photosensitizers (PSs) able to efficiently bind cells, in this study two dicationic showed to be intrinsically toxic and were ruled out by further investigations. In particular, the dicationic porphyrin (P11) that was not toxic, showed a better photoinactivation rate than monocationic in suspended cells. Furthermore, it was very efficient in inhibiting the biofilms produced by the model microorganism Pseudomonas aeruginosa PAO1 and by clinical strains derived from urinary tract infection and cystic fibrosis patients. Since P. aeruginosa represents a target very difficult to inactivate, this study confirms the potential of dicationic diaryl-porphyrins as photo-activated antimicrobials in different applicative fields, from clinical to environmental ones.

Photophysical and Bactericidal Properties of Pyridinium and Imidazolium Porphyrins for Photodynamic Antimicrobial Chemotherapy

Despite advances achieved over the last decade, infections caused by multi-drug-resistant bacterial strains are increasingly becoming important societal issues that need to be addressed. New approaches have already been developed in order to overcome this problem. Photodynamic antimicrobial chemotherapy (PACT) could provide an alternative to fight infectious bacteria. Many studies have highlighted the value of cationic photosensitizers in order to improve this approach. This study reports the synthesis and the characterization of cationic porphyrins derived from methylimidazolium and phenylimidazolium porphyrins, along with a comparison of their photophysical properties with the well-known N-methylpyridyl (pyridinium) porphyrin family. PACT tests conducted with the tetracationic porphyrins of these three families showed that these new photosensitizers may offer a good alternative to the classical pyridinium porphyrins, especially against S.aureus and E.coli. In addition, they pave the way to new cationic photosensitizers by the means of derivatization through amide bond formation.

BODIPY-Based Photosensitizers as Potential Anticancer and Antibacterial Agents: Role of the Positive Charge and the Heavy Atom Effect

Boron-dipyrromethene derivatives, including cationic and iodinated analogs, were obtained and subjected to physicochemical and in vitro photodynamic activity studies. Iodinated derivatives revealed a substantial heavy atom effect manifested by a bathochromic shift of the absorption band by about 30 nm and fluorescence intensity reduced by about 30-35 times, compared to that obtained for non-iodinated ones. In consequence, singlet oxygen generation significantly increased with Φ_Δ values in the range 0.69-0.97. The in vitro photodynamic activity was evaluated on Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli, and on human androgen-sensitive prostate adenocarcinoma cells (LNCaP). The novel cationic, iodinated BODIPY, demonstrated the highest activity toward all studied cells. An excellent cytotoxic effect was found against LNCaP cells with an IC₅₀ value of 19.3 nM, whereas the viability of S. aureus was reduced by >5.6 log₁₀ at 0.25 μM concentration and by >5.3 log₁₀ in the case of E. coli at 5 μM. Thus, this analog seems to be a very promising candidate for the application in both anticancer and antimicrobial photodynamic therapy.

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.

Photodynamic Therapy by Diaryl-Porphyrins to Control the Growth of Candida albicans

Candida albicans is an opportunistic pathogen that often causes skin infections such as oral thrush, nail fungus, athlete’s foot, and diaper rash. Under particular conditions, C. albicans alters the natural balance of the host microbiota, and as a result, the skin or its accessory structures lose their function and appearance. Conventional antimycotic drugs are highly toxic to host tissues, and long-lasting drug administration induces the arising of resistant strains that make the antimycotic therapy ineffective. Among new antimicrobial approaches to combine with traditional drugs, light-based techniques are very promising. In this study, a panel of dyes was considered for photodynamic therapy (PDT) applications to control the growth of the model strain C. albicans ATCC 14053. The chosen photosensitizers (PSs) belong to the family of synthetic porphyrins, and in particular, they are diaryl-porphyrins. Among these, two monocationic PSs were shown to be particularly efficient in killing C. albicans upon irradiation with light at 410 nm, in a light-dose-dependent manner. The elicited photo-oxidative stress induced the loss of the internal cellular architecture and death. The photodynamic treatment was also successful in inhibiting the biofilm formation of clinical C. albicans strains. In conclusion, this study supports the great potential of diaryl-porphyrins in antimicrobial PDT to control the growth of yeasts on body tissues easily reachable by light sources, such as skin and oral cavity.