Unravelling the modes of phototoxicity of NIR absorbing chlorophyll derivative in cancer cells under normoxic and hypoxic conditions

The efficacy of photodynamic treatment (PDT) against deep-seated tumor is hindered by low penetration depth of light as well as hypoxic conditions which prevails in tumor. To overcome this limitation, Near-infrared (NIR) absorbing photosensitizers have been investigated actively. In the present study we evaluated the PDT efficacy of an NIR absorbing chlorophyll derivative 'Cycloimide Purpurin-18 (CIPp-18)' in Human Breast carcinoma (MCF-7) and cervical adenocarcinoma (Hela) cells under normoxic and hypoxic conditions. PDT with CIPp-18 (2.0 µM, 3 h) and NIR light (700 ± 25 nm, 0.36-1.4 J /cm2) induced potent phototoxicity in both the cell lines. Under hypoxic conditions, PDT induced ~ 32% and 42% phototoxicity at LD50 and LD70 light dose, respectively, which corresponds to phototoxic dose under normoxia. CIPp-18 in neat buffer (pH 7.4) showed generation of singlet oxygen (1O2) as well as superoxide (O2·-) radicals. Studies on ROS generation in cells using fluorescence probes and the effect of mechanistic probes of 1O2 (Sodium Azide, Histidine, D2O) and free radicals (DMSO, Mannitol, Cyanocobalamin, SOD-PEG) on phototoxicity show that 1O2 plays major role in phototoxicity under normoxia. Whereas, under hypoxic conditions, PDT led to no significant generation of ROS and phototoxicity remained unaffected by cyanocobalamin, a quencher of O2·-. Moreover, CIPp-18 showed localization in cell membrane and PDT led to more pronounced loss of membrane permeability in cells under hypoxia than for normoxia. These results demonstrate that CIPp-18 is suitable for PDT of cancer cells under hypoxia and also suggest that phototoxicity under hypoxia is mediated via ROS-independent contact-dependent mechanism.

Copper and Copper Complexes in Tumor Therapy

Copper (Cu), a crucial trace element in physiological processes, has garnered significant interest for its involvement in cancer progression and potential therapeutic applications. The regulation of cellular copper levels is essential for maintaining copper homeostasis, as imbalances can lead to toxicity and cell death. The development of drugs that target copper homeostasis has emerged as a promising strategy for anticancer treatment, with a particular focus on copper chelators, copper ionophores, and novel copper complexes. Recent research has also investigated the potential of copper complexes in cancer therapy.

Absolute chlorophyll composition of commercial green food colorants and coloring foodstuff by HPLC-ESI-QTOF-MS/MS: Copper chlorophyllins

Sodium copper chlorophyllins (SCC) are used worldwide to brightly color green foods as authorized food colorants, although their composition is only partially known. This study applied a combination of experimental and in silico techniques to describe the SCC profile in commercial colorant products and coloring foods. Different approaches have allowed identifying five new chlorophyll compounds in the food colorants besides the description of unique product ions able to distinguish among different chlorophyll isomers for the first time. In addition, a detailed isotope cluster analysis has revealed the formation of two new structures of copper chlorophyllins, featuring the copper in peripheral positions instead of the central pocket. Finally, a computational study of thermodynamic parameters and molecular descriptors has determined the factors responsible for the formation of the two main copper chlorophyllins present in the food colorants. This information will sustain alternative processing leading to SCC products with tailored composition.

Effect of the nature of the chelated metal on the photodynamic activity of metalloporphyrins

Coordination of metal ions by the tetrapyrrolic macrocyclic ring of porphyrin-based photosensitizers (PSs) affects their photophysical properties and consequently, their photodynamic activity. Diamagnetic metals increase the singlet oxygen quantum yield while paramagnetic metals have the opposite effect. Since singlet oxygen is considered the main cell-damaging species in photodynamic therapy (PDT), the nature of the chelated cation would directly affect PDT efficacy. This expectation, however, is not always supported by experimental results and numerous exceptions have been reported. Understanding the effect of the chelated metal is hindered because different chelators were used. The aim of this work was to investigate the effect of the nature of chelated cation on the photophysical and photodynamic properties of metalloporphyrins, using the same tetrapyrrole core as a chelator of Ag(II), Cu(II), Fe(III), In(III), Mn(III), or Zn(II). Results demonstrated that with the exception of Ag(II), all paramagnetic metalloporphyrins were inefficient as generators of singlet oxygen and did not act as PSs. In contrast, the coordination of diamagnetic ions produced highly efficient PSs. The unexpected photodynamic activity of the Ag(II)-containing porphyrin was attributed to reduction of the chelated Ag(II) to Ag(I) or to demetallation of the complex, caused by cellular reductants and/or by exposure to light. Our results indicate that in biological systems, where PSs localize to various organelles and are subjected to the action of enzymes, reactive metabolites, and reducing or oxidizing agents, their physicochemical and photosensitizing properties change. Consequently, the photophysical properties alone cannot predict the anticancer efficacy of a PS.

Potential Application of Photosensitizers With High-Z Elements for Synergic Cancer Therapy

The presence of heavy elements in photosensitizers (PS) strongly influences their electronic and photophysical properties, and hence, conjugation of PS with a suitable element is regarded as a potential strategy to improve their photodynamic properties. Moreover, PS conjugated to metal ion or metal complex and heavy atoms such as halogen have attracted considerable attention as promising agents for multimodal or synergistic cancer therapy. These tetrapyrrole compounds depending on the type and nature of the inorganic elements have been explored for photodynamic therapy (PDT), chemotherapy, X-ray photon activation therapy (PAT), and radiotherapy. Particularly, the combination of metal-based PS and X-ray irradiation has been investigated as a promising novel approach for treating deep-seated tumors, which in the case of PDT is a major limitation due to low light penetration in tissue. This review will summarize the present status of evidence on the effect of insertion of metal or halogen on the photophysical properties of PS and the effectiveness of various metal and halogenated PS investigated for PDT, chemotherapy, and PAT as mono and/or combination therapy.

Rational design of type I photosensitizers based on Ru(ii) complexes for effective photodynamic therapy under hypoxia

Photodynamic therapy (PDT) has been widely used in conjunction with molecular oxygen to cause cancer cell death. Hypoxia, the inherent property in solid tumors, is the obstacle during the process of PDT. It is urgent to develop PDT photosensitizers independent of the oxygen concentration. Herein, triphenylamine-modified Ru(ii) complexes have been used as photosensitizers to produce superoxide anions (O2-˙) and hydroxyl radicals (˙OH) through a type I photochemical process. Ru(ii) complexes with triphenylamine can provide a possibility to drive the reactive oxygen species production through low oxidation potential and good light-harvesting abilities. The investigation on light-mediated radical production showed that Ru4 could produce abundant ˙OH and O2-˙ compared to Ru1-Ru3 under hypoxic environments owing to the strong absorption. These radicals exhibit potent toxicity, which can damage the neighbouring biomolecules and cause the apoptosis of cancer cells. The PDT effect was evaluated in vitro under hypoxia, suggesting that Ru4 could maintain excellent performance in inducing a sharp decrease in the activity of cancer cells.

Self-assembly of chlorin-e6 on γ-Fe2O3 nanoparticles: Application for larvicidal activity against Aedes aegypti

Aedes aegypti mosquitos are widespread vectors of several diseases and their control is of primary importance for biological and environmental reasons, and novel safe insecticides are highly desirable. An eco-friendly photosensitizing magnetic nanocarrier with larvicidal effects on Aedes aegypti was proposed. The innovative core-shell hybrid nanomaterial was synthesized by combining peculiar magnetic nanoparticles (called Surface Active Maghemite Nanoparticles - SAMNs, the core) and chlorin-e6 as photosensitizer (constituting the shell) via self-assembly in water. The hybrid nanomaterial (SAMN@chlorin) was extensively characterized and tested for the photocidal activity on larvae of Aedes aegypti. The SAMN@chlorin core-shell nanohybrid did not present any toxic effect in the dark, but, upon light exposure, showed a higher photocidal activity than free chlorin-e6. Moreover, the eco-toxicity of SAMN@chlorin was determined in adults and neonates of Daphnia magna, where delayed toxicity was observed only after prolonged (≥4 h) exposure to intense light, on the green alga Pseudokirchneriella subcapitata and on the duckweed Lemna minor on which no adverse effects were observed. The high colloidal stability, the physico-chemical robustness and the magnetic drivability of the core-shell SAMN@chlorin nanohybrid, accompanied by the high photocidal activity on Aedes aegypti larvae and reduced environmental concerns, can be proposed as a safe alternative to conventional insecticides.

Enhancement of radiosensitivity of oral carcinoma cells by iodinated chlorin p6 copper complex in combination with synchrotron X-ray radiation

The combination of synchrotron X-ray radiation and metal-based radiosensitizer is a novel form of photon activation therapy which offers the advantage of treating malignant tumors with greater efficacy and higher precision than conventional radiation therapy. In this study the anticancer cytotoxic efficacy of a new chlorophyll derivative, iodinated chlorin p₆ copper complex (ICp₆-Cu), combined with synchrotron X-ray radiation (8-10 keV) in two human oral cancer cell lines is explored. Pre-treatment of cells with 20 µM and 30 µM ICp₆-Cu for 3 h was found to enhance the X-ray-induced cytotoxicity with sensitization enhancement ratios of 1.8 and 2.8, respectively. ICp₆-Cu localized in cytoplasm, mainly in lysosomes and endoplasmic reticulum, and did not cause any cytotoxicity alone. The radiosensitization effect of ICp₆-Cu accompanied a significant increase in the level of reactive oxygen species, damage to lysosomes, inhibition of repair of radiation-induced DNA double-strand breaks, increase in cell death and no significant effect on cell cycle progression. These results demonstrate that ICp₆-Cu is a potential agent for synchrotron photon activation therapy of cancer.

Spectroscopic investigations on the binding of an iodinated chlorin p6-copper complex to human serum albumin

An iodinated chlorin p₆ copper complex showed high affinity to bind human serum albumin, the binding site was predicted and it was demonstrated that binding did not affect protein conformation.