In vitro photosensitization II. An electron microscopy study of cellular destruction with mono‐L‐aspartyl chlorin e₆ and photofrin II

Abstract

Primary sites of subcellular destruction with photofrin II (PfII) and mono-L-aspartyl chlorin e6 (MACE) were determined by transmission electron microscopy (TEM). Potorous tridactylus (PTK2) cells were grown in Rose chambers and incubated for 24 hr with a sensitizer concentration sufficient to provide 100% mortality. Cells were irradiated with laser light and fixed and processed for electron microscopy at various times post-irradiation. The results indicate that PfII initially destroys mitochondria, whereas MACE destroys lysosomes. Both conclusions are consistent with fluorescence subcellular localization studies.

Release of cytochrome c and activation of pro-caspase-9 following lysosomal photodamage involves bid cleavage

“…An electron microscopy study has also shown that lysosomes are specifically destroyed in NPe6 sensitized, irradiated cells. 10 Although Stoka et al 19 have shown that a lysosomal extract can activate Bid in vitro, the current investigation is the first we know of to: (1) demonstrate that targeted lysosome disruption in vivo is associated with Bid cleavage, and (2) provide a mechanistic basis for how lysosomal sensitizers in PDT protocols cause cytochrome c release and procaspases-9/-3 activation. Given the susceptibility of lysosomes to oxidant-induced injury, it is conceivable that lysosomal disruption may be a relatively common initiator of the mitochondrial/intrinsic apoptotic pathway.…”

“…1,3 ± 6 In contrast, irradiation of cells preloaded with the photsensitizers CPO, HPPH and Pc 4 has no effect on lysosomes. Instead, one sees a rapid loss of DC m and release of cytochrome c. 1,3,7 ± 9 These effects most likely reflect: (a) the sites of sensitizer accumulation 6,10,11 because the reactive oxygen species formed upon irradiation have a limited ability to migrate from the site(s) of formation; 12 and (b) the unique ability of some photosensitizers to photo oxidize and cleave Bcl-2 upon excitation. 13,14 Irradiation of cells preloaded with lysosomal photosensitizers eventually causes the release of cytochrome c and the activation of pro-caspase-3.…”

ATG7 deficiency suppresses apoptosis and cell death induced by lysosomal photodamage

“…[18][19][20] Although Mazor et al postulated an endocytic mechanism for WST11 accumulation, 16 very little is known about the subcellular localization of WST11. We could detect intracellular WST11 fluorescence only with an electron-multiplying CCD camera.…”

“…1). 16,17 Although the lysosomal accumulation of NPe6 is well characterized, [18][19][20] we were initially uncertain about the pattern of WST11 cellular localization. Once we established that WST11 localized to lysosomes, it was included in this study.…”

Pilot Study of Topical Delivery of Mono-L-aspartyl Chlorin e6 (NPe6): Implication of Topical NPe6-Photodynamic Therapy

“…FAX: +886- E-mail: twwong@mail.ncku.edu.tw localizes in the lysosomal compartment and has in vivo tissue distribution properties similar to those of Photofrin (6,7). Lysosomal damage is primarily responsible NPe6-PDT mediated cell death (8), while plasma membrane and mitochondria were the major targets for Photofrin (9). In vivo, NPe6 also targets vessels as Photofrin does even though the subcellular sites were differ for the two photosensitizers (10).…”