Characterization of Photodegradation of Meta‐tetra (Hydroxyphenyl)chlorin (mTHPC) in Solution: Biological Consequences in Human Tumor Cells

Abstract

The photobleaching of meta-tetra(hydroxyphenyl)chlorin (mTHPC) (irradiation wavelength 413 nm) in protein-containing solution was evaluated by decay in absorbance in Soret band and in fluorescence (lambda exc = 423 nm, lambda em = 655 nm). Light exposure resulted in a decrease in absorption throughout the spectrum and simultaneous appearance of new absorption bands in the spectral region 325-450 nm. The rate of mTHPC photodegradation, followed by decay in absorbance, was 15-fold lower than that observed in fluorescence. This fact reflects the photobleaching of presumably monomeric, fluorescing species of mTHPC. In order to determine the consequences of photobleaching of fluorescing mTHPC material on cellular uptake and photocytotoxicity, human HT29 colon adenocarcinoma cells were incubated with photobleached mTHPC during 5 h with or without following irradiation with the fixed fluence. Surprisingly, but up to the time when the fluorescence decreased by 50%, only a slight decrease in photocytotoxicity was detected. Either aggregated forms that have been taken up undergo intracellular monomerization (but we did not observe increase in fluorescence in living cells) or the photodynamic activity is mostly due to aggregates. The discrepancy of mTHPC-photodynamic therapy (PDT) effect and fluorescence measurements may suggest that aggregated mTHPC plays an important role in mTHPC-PDT.

Unusual Photoinduced Response of mTHPC Liposomal Formulation (Foslip)

“…Numerous studies have addressed the mechanism of mTHPC photobleaching in cells and cell-free systems (13)(14)(15)(16)(17)(18)(19). This process is oxygen dependent and is inhibited by singlet oxygen quenchers in serum-enriched solutions (13).…”

“…This process is oxygen dependent and is inhibited by singlet oxygen quenchers in serum-enriched solutions (13). The monomer forms of mTHPC are supposed to be particularly receptive to irradiation in solution, demonstrating a much higher photobleaching rate than aggregates (14). Kasselouri et al (15) detected mono-, di-and tri-hydroxy-mTHPC as major photoproducts of mTHPC in ethanol-water medium.…”

Matrix-assisted laser desorption/Ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry: a method to characterize temoporpfin photoproducts

“…This process, usually called 'photobleaching', involves a decrease in absorbance for certain spectral bands, variations of the fluorescence intensity or the formation of new absorption and emission bands. 7 The m-THPC photodegradation has been observed in aqueous 8 and organic solutions, 9 in vitro, 10 in vivo in tumor-bearing mice 11 and in clinical practice. 12 Studyies of the photobleaching reaction are particularly important for two reasons: (1) Identification of photobleaching products, which can be photodynamically active, thus opening the possibility for 'extended' photodynamic therapy; (2) Measurement of the photochemical reactions that reflect the potential therapeutic effect and thus help to match the light dose.…”

Photobleaching of Sn(IV) chlorine e6 dichloride trisodium salt in different environments

“…Porphyrin's derivatives, which are hydrophobic in nature, showed a strong decrease in the absorption at all bands in buffer (Belitchenko et al, 1998;Maestrin et al, 2004). The reduction in absorption at all absorption bands can be due to the aggregation of the photosensitizer in the polar environment.…”