Novel Photosensitizers Trigger Rapid Death of Malignant Human Cells and Rodent Tumor Transplants via Lipid Photodamage and Membrane Permeabilization

Abstract

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.

Boronated derivatives of chlorin e 6 and fluoride-containing porphyrins as penetrating anions: a study using bilayer lipid membranes

“…Dodecaborate [27,28] and monocarborane [29] have the greatest prospects in terms of new drug development, for they are di and monoanions and provide water solubility. Boronated por phyrin [30], chlorin [31], and hemin [32] were found to be more effective photosensitizers both in vitro and in vivo than their predecessors. Compound 1 was previously shown to accumulate in intracellular organelles such as the Golgi apparatus, endoplasmic reticulum, and other membrane compartments [31].…”

“…Boronated por phyrin [30], chlorin [31], and hemin [32] were found to be more effective photosensitizers both in vitro and in vivo than their predecessors. Compound 1 was previously shown to accumulate in intracellular organelles such as the Golgi apparatus, endoplasmic reticulum, and other membrane compartments [31]. In addition, this com pound has a higher light induced cytotoxic activity com pared to non boronated chlorin e 6 .…”

Photodynamic inactivation of gramicidin channels in bilayer lipid membranes: Protective efficacy of singlet oxygen quenchers depends on photosensitizer location

“…6, in this system chlorin e 6 exhibits intermediate activity between the smallest for AlPcS 3 and the highest for amide of chlorin e 6 dimethyl ester, which is in agreement with data on fluorescence quenching by iodide. It should be taken into account that the studied photosensitizers are characterized by different quantum yields of singlet oxygen generation, which, according to [24,30], are 61% for amide of chlorin e 6 dimethyl ester, 76% for chlorin e 6 , and 38% for AlPcS 3 ; however, these differences are significantly less than the observed difference in the ability of these compounds to sensitize photodynamic liposome permeabilization.…”

“…(1) N (2 aminoethyl) amide 15(2),17(3) dimethyl ester of chlorin e 6 , synthesized as described ear lier [24], was provided by V. A. Olshevskaya (A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences). Chlorin e 6 and tri sul fonated aluminum phthalocyanine (AlPcS 3 ) were obtained from Porphyrin Products (USA).…”

Synthesis and antitumor activity of novel tetrakis[4-(closo-carboranylthio)tetrafluorophenyl]porphyrins

“…Dark cyto toxicity was tested by MTT assay, 23 photoinduced cell death was assessed as earlier described. 24 …”