Novel photosensitizers trigger rapid death of malignant human cells and rodent tumor transplants via lipid photodamage and membrane permeabilization.
BACKGROUND
Apoptotic cascades may frequently be impaired in tumor cells; therefore, the approaches to circumvent these obstacles emerge as important therapeutic modalities.


RESULTS
Our novel derivatives of chlorin e(6), that is, its amide (compound 2) and boronated amide (compound 5) evoked no dark toxicity and demonstrated a significantly higher photosensitizing efficacy than chlorin e(6) 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 e(6) 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
The multimembrane photodestruction and cell necrosis induced by photoactivation of 2 and 5 are directly associated with membrane permeabilization caused by lipid photodamage.
Moisenovich
Mikhail M
MM
Biological Department, Moscow State University, Moscow, Russia.
Ol'shevskaya
Valentina A
VA
Rokitskaya
Tatyana I
TI
Ramonova
Alla A
AA
Nikitina
Roza G
RG
Savchenko
Arina N
AN
Tatarskiy
Victor V
VV
Kaplan
Mikhail A
MA
Kalinin
Valery N
VN
Kotova
Elena A
EA
Uvarov
Oleg V
OV
Agapov
Igor I
II
Antonenko
Yuri N
YN
Shtil
Alexander A
AA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000378:metabolism* / Q000627:therapeutic use; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism
D017319:Photosensitizing Agents; D017382:Reactive Oxygen Species