Refining antimicrobial photodynamic therapy: effect of charge distribution and central metal ion in fluorinated porphyrins on effective control of planktonic and biofilm bacterial forms

Antibiotic resistance represents a pressing global health challenge, now acknowledged as a critical concern within the framework of One Health. Photodynamic inactivation of microorganisms (PDI) offers an attractive, non-invasive approach known for its flexibility, independence from microbial resistance patterns, broad-spectrum efficacy, and minimal risk of inducing resistance. Various photosensitizers, including porphyrin derivatives have been explored for pathogen eradication. In this context, we present the synthesis, spectroscopic and photophysical characteristics as well as antimicrobial properties of a palladium(II)-porphyrin derivative (PdF2POH), along with its zinc(II)- and free-base counterparts (ZnF2POH and F2POH, respectively). Our findings reveal that the palladium(II)-porphyrin complex can be classified as an excellent generator of reactive oxygen species (ROS), encompassing both singlet oxygen (Φ△ = 0.93) and oxygen-centered radicals. The ability of photosensitizers to generate ROS was assessed using a variety of direct (luminescence measurements) and indirect techniques, including specific fluorescent probes both in solution and in microorganisms during the PDI procedure. We investigated the PDI efficacy of F2POH, ZnF2POH, and PdF2POH against both Gram-negative and Gram-positive bacteria. All tested compounds proved high activity against Gram-positive species, with PdF2POH exhibiting superior efficacy, leading to up to a 6-log reduction in S. aureus viability. Notably, PdF2POH-mediated PDI displayed remarkable effectiveness against S. aureus biofilm, a challenging target due to its complex structure and increased resistance to conventional treatments. Furthermore, our results show that PDI with PdF2POH is more selective for bacterial than for mammalian cells, particularly at lower light doses (up to 5 J/cm2 of blue light illumination). This enhanced efficacy of PdF2POH-mediated PDI as compared to ZnF2POH and F2POH can be attributed to more pronounced ROS generation by palladium derivative via both types of photochemical mechanisms (high yields of singlet oxygen generation as well as oxygen-centered radicals). Additionally, PDI proved effective in eliminating bacteria within S. aureus-infected human keratinocytes, inhibiting infection progression while preserving the viability and integrity of infected HaCaT cells. These findings underscore the potential of metalloporphyrins, particularly the Pd(II)-porphyrin complex, as promising photosensitizers for PDI in various bacterial infections, warranting further investigation in advanced infection models.

Microwave-assisted synthesis of [52Mn]Mn-porphyrins: Applications in cell and liposome radiolabelling

BACKGROUND

Manganese porphyrins have several therapeutic/imaging applications, including their use as radioprotectants (in clinical trials) and as paramagnetic MRI contrast agents. The affinity of porphyrins for lipid bilayers also makes them candidates for cell/liposome labelling. We hypothesised that metalation with the positron emission tomography (PET) radionuclide 52Mn (t1/2 = 5.6 d) would allow long-term in vivo biodistribution studies of Mn-porphyrins, as well as a method to label and track cells/liposomes, but methods for fast and efficient radiolabelling are lacking.

RESULTS

Several porphyrins were produced and radiolabelled by addition to neutralised [52Mn]MnCl2 and heating using a microwave (MW) synthesiser, and compared with non-MW heating. MW radiosynthesis allowed >95 % radiochemical yields (RCY) in just 1 h. Conversely, non-MW heating at 70 °C for 1 h resulted in low RCY (0-25 % RCY) and most porphyrins did not reach radiolabelling completion after 24 h. Formation of the 52Mn-complexes were confirmed with radio-HPLC by comparison with their non-radioactive 55Mn counterparts. Following this, several [52Mn]Mn-porphyrins were used to radiolabel liposomes resulting in 75-86 % labelling efficiency (LE). Two lead [52Mn]Mn-porphyrins were taken forward to label MDA-MB-231 cancer cells in vitro, achieving ca. 11 % LE. After 24 h, 32-45 % of the [52Mn]Mn-porphyrins was retained in cells.

CONCLUSIONS

In contrast to standard methods, MW heating allows the fast synthesis of [52Mn]Mn-porphyrins with >95 % radiochemical yields that avoid purification. [52Mn]Mn-porphyrins also show promising cell/liposome labelling properties. Our reported technique can potentially be exploited for the in vivo imaging of Mn-porphyrin therapeutics, as well as for the accurate in vivo quantification of Mn-porphyrin MRI agents.

Main Strategies for the Synthesis of meso-Arylporphyrins

meso-Arylporphyrins as most accessible tetrapyrrole macroheterocycles have always been the focus of attention from researchers concerned with practically useful properties of these compounds. The first syn­theses of meso-arylporphyrins date back to about 90 years ago. Up to now, the yields of these compounds have been improved from 5 to 80%. The present review analyzes different ways and strategies for the synthesis of meso-aryl-substituted porphyrins. The most efficient methods that can be scaled up to an industrial level have been identified.

Monoterpene-based metallophthalocyanines: Sustainable synthetic approaches and photophysical studies

Tetra-substituted zinc(II) and copper(II) phthalocyanines bearing peripheral alkoxy-monoterpene groups were prepared by conventional vs. non-conventional synthetic approaches (ultrasound and microwave irradiation). The synthesis of (1[Formula: see text]-(–)-myrtenol (a) and (1[Formula: see text],2[Formula: see text],5[Formula: see text]-([Formula: see text]-menthol (b) derived phthalonitrile precursors was performed through ipso-nitro aromatic substitution reactions, with optimal conditions being obtained using ultrasound irradiation, which allowed us to achieve full conversions in 4.5 h, with isolated yields up to 74%. The subsequent cyclotetramerization of monoterpene-based phthalonitriles was carried out using Zn(II) or Cu(II) salts as metal templates, and also using conventional and non-conventional heating methods. Microwave-assisted synthesis was shown to be the most efficient approach, providing complete conversions in 1 h, yielding the target monoterpene-based metallophthalocyanines in up to 70% isolated yields. Furthermore, photophysical and photochemical studies revealed that Zn(II) phthalocyanines possess fluorescence quantum yields in the range of [Formula: see text] 0.27–0.29, while Cu(II) phthalocyanines exhibited room temperature phosphorescence. In addition, the monoterpene-based Zn(II) phthalocyanines led to high singlet oxygen quantum yields ([Formula: see text] 0.55–0.69).