Subcellular Localization Patterns and Their Relationship to Photodynamic Activity of Pyropheophorbide‐a Derivatives

Abstract

To determine if subcellular localization is important to photodynamic therapy (PDT) efficacy, an in vitro fluorescence microscopy study was conducted with a congeneric series of pyropheophorbide-a derivatives in human pharyngeal squamous cell carcinoma (FaDu) cells and murine radiation-induced fibrosarcoma (RIF) mutant cells. In the FaDu cells the octyl, decyl and dodecyl ether derivatives localized to the lysosomes at extracellular concentrations less than needed to produce a 50% cell kill (LD50). At extracellular concentrations equal or greater than the LD50 the compounds localized mainly to mitochondria. The propyl, pentyl, hexyl and heptyl ether derivatives localized mainly to the mitochondria at all concentrations studied. This suggested that mitochondria are a sensitive PDT target for these derivatives. Similar experiments were performed with two Photofrin-PDT resistant RIF cell lines, one of which was found to be resistant to hexyl ether derivative (C6) mediated-PDT and the other sensitive to C6-PDT relative to the parent line. At extracellular concentrations of C6 below the LD50 of each cell line, the mutants exhibited lysosomal localization. At concentrations above these values the patterns shifted to a mainly mitochondrial pattern. In these cell lines mitochondrial localization also correlated with PDT sensitivity. Localization to mitochondria or lysosomes appeared to be affected by the aggregation state of the congeners, all of which are highly aggregated in aqueous medium. Monomers apparently were the active fraction of these compounds because equalizing the extracellular monomer concentrations produced equivalent intracellular concentrations, photoxicity and localization patterns. Compounds that were mainly aggregates localized to the lysosomes where they were rendered less active. Mitochondria appear to be a sensitive target for pyropheophorbide-a-mediated photodamage, and the degree of aggregation seems to be a determinant of the localization site.

Physical and chemical properties of pyropheophorbide-a methyl ester in ethanol, phosphate buffer and aqueous dispersion of small unilamellar dimyristoyl-l-α-phosphatidylcholine vesicles

“…Type I mechanisms are predominant in polar media while type II mechanisms are predominant in hydrophobic environments 27,28 . Thus, the mechanisms (type I or type II) of cell destruction depend on the localization of the sensitizer because it was shown that the photosensitizer localization in cancer cells is related to its lipophilic or hydrophobic character 29 . Consequently, we have detailed the aggregation process of PPME and the consequences on its ROS production.…”

ROS: Reactive Oxygen Species

“…Monomers apparently were the active fraction of these compounds because equalizing the extracellular monomer concentration, produced equivalent intracellular concentrations, phototoxicity, and localization patterns. On the other hand, aggregates localized in the lysosomes where they were less active (MacDonald et al 1999). These results suggest the importance of the parameters governing the aggregation state of PS by an indirect eVect on their pharmacokinetics and on their intracellular distribution (Kessel et al 1987;MacDonald et al 1999).…”

“…Cellular uptake and subcellular localization of a series of Ppe ethers bearing C3-C12 acyl chains were studied on human pharyngeal squamous cell carcinoma (FaDu) and radiation-induced Wbrosarcoma (RIF) cells in the work of MacDonald et al (1999). The results revealed a relationship between the lateral chain length, the aggregation state, the subcellular localization and the phototoxicity of these compounds.…”

Selectivity of the photosensitiser Tookad® for photodynamic therapy evaluated in the Syrian golden hamster cheek pouch tumour model

“…The binding of the PS molecules to plasma protein after injection can be different in human and in the hamster. This is of importance as the distribution of the PS in the different physiological, tissular and subcellular compartments (MacDonald et al, 1999) is strongly dependent on the degree of molecular microaggregation and on the injected formulation of the PS.…”