BackgroundApoptotic cascades may frequently be impaired in tumor cells; therefore, the approaches to circumvent these obstacles emerge as important therapeutic modalities.Methodology/Principal FindingsOur novel derivatives of chlorin e6, that is, its amide (compound 2) and boronated amide (compound 5) evoked no dark toxicity and demonstrated a significantly higher photosensitizing efficacy than chlorin e6 against transplanted aggressive tumors such as B16 melanoma and M-1 sarcoma. Compound 5 showed superior therapeutic potency. Illumination with red light of mammalian tumor cells loaded with 0.1 µM of 5 caused rapid (within the initial minutes) necrosis as determined by propidium iodide staining. The laser confocal microscopy-assisted analysis of cell death revealed the following order of events: prior to illumination, 5 accumulated in Golgi cysternae, endoplasmic reticulum and in some (but not all) lysosomes. In response to light, the reactive oxygen species burst was concomitant with the drop of mitochondrial transmembrane electric potential, the dramatic changes of mitochondrial shape and the loss of integrity of mitochondria and lysosomes. Within 3–4 min post illumination, the plasma membrane became permeable for propidium iodide. Compounds 2 and 5 were one order of magnitude more potent than chlorin e6 in photodamage of artificial liposomes monitored in a dye release assay. The latter effect depended on the content of non-saturated lipids; in liposomes consisting of saturated lipids no photodamage was detectable. The increased therapeutic efficacy of 5 compared with 2 was attributed to a striking difference in the ability of these photosensitizers to permeate through hydrophobic membrane interior as evidenced by measurements of voltage jump-induced relaxation of transmembrane current on planar lipid bilayers.Conclusions/SignificanceThe multimembrane photodestruction and cell necrosis induced by photoactivation of 2 and 5 are directly associated with membrane permeabilization caused by lipid photodamage.

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We studied the effect of photodynamic therapy with photoditasine at different protocols of photoenergy exposure on morphofunctional parameters of M-1 sarcoma. It was found that proliferative activity of tumor cells (evaluated by immunostaining for PCNA) nonlinearly decreases after exposure to 150, 300, and 600 J/cm2. The main form of cell death during the early period after photodynamic therapy was direct photocoagulation necrosis caused by destruction of sensitized cell structures and ischemic necrosis developing as a result of alteration of vascular network in the tumors. Photoenergy density was not essential for the intensity of induced apoptosis.

We report the synthesis and characterization of a new sulfur-containing derivative of bacteriochlorophyll a. The latter was isolated from biomass of the nonsulfur purple bacterium Rhodobacter capsulatus strain B10. The developed photosensitizer is N-aminobacteriopurpurinimide with an exocyclic amino group acylated with a lipoic acid moiety, which is a biogenic substance that acts as a cofactor of the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes in the body. The disulfide moiety of lipoic acid confers the compound aurophilicity, thus allowing its conjugation with gold nanoparticles (NP-Au) via S-Au bonds. The shape and the size of the resulting nanoconjugate with immobilized photosensitizer (PS-Au) were assessed by dynamic light scattering and transmission electron microscopy. The conjugated nanoparticles are spherical with hydrodynamic diameter of 100-110 nm. The PS-Au conjugate absorbs light at 824 nm and emits strong fluorescence at 830 nm, which allowed in vivo study of its dynamic biodistribution in rats bearing sarcoma M-1. Compared to the free photosensitizer, PS loaded on the gold nanoparticles (PS-Au) showed extended circulation time in the blood and enhanced tumor uptake due to nonspecific passive targeting when the drug accumulates in tumor sites through the leaky tumor neovasculature and does not return to the circulation.