Photophysical and Photosensitizing Properties of Benzoporphyrin Derivative Monoacid Ring a (Bpd‐ma)*

Abstract

The photophysical properties of benzoporphyrin derivative monoacid ring A (BPD-MA), a second-generation photosensitizer currently in phase II clinical trials, were investigated in homogeneous solution. Absorption, fluorescence, triplet-state, singlet oxygen (O2 (1 delta g)) sensitization studies and photobleaching experiments are reported. The ground state of this chlorin-type molecule shows a strong absorbance in the red (lambda approximately 688 nm, epsilon approximately 33,000 M-1 cm-1 in organic solvents). For the singlet excited state the following data were determined in methanol: energy level, Es = 42.1 kcal mol-1, lifetime, tau f = 5.2 ns and fluorescence quantum yield, phi f = 0.05 in air-saturated solution. The triplet state of BPD-MA has a lifetime, tau T > or = 25 microseconds, an energy level, ET = 26.9 kcal mol-1 and the molar absorption coefficient is epsilon T = 26,650 M-1 cm-1 at 720 nm. A dramatic effect of oxygen on the fluorescence (phi f) and intersystem crossing (phi T) quantum yields has been observed. The BPD-MA presents rather high triplet (phi T = 0.68 under N2-saturated conditions) and singlet oxygen (phi delta = 0.78) quantum yields. On the other hand, the presence of oxygen does not significantly modify the photobleaching of this photostable compound, the photodegradation quantum yield (phi Pb) of which was found to be on the order of 5 x 10(-5) in organic solvents.

One- and two-photon activated phototoxicity of conjugated porphyrin dimers with high two-photon absorption cross sections

“…These singlet oxygen production efficiencies are comparable to those of clinical photosensitisers. 37 Moreover, the singlet oxygen yields are substantially higher in methanol (" ! = 0.5-0.9), so the in vivo singlet oxygen yields should also be high, since the 95 dimers are likely to be disaggregated in the hydrophobic compartments of cells, where they are bound to proteins or lipids.…”

Photophysical properties and intracellular imaging of water-soluble porphyrin dimers for two-photon excited photodynamic therapy

“…f = 0.05 in D 2 O). 35 The two-photon absorption properties were determined as reported 385 previously, 48 by means of monitoring the fluorescence intensity. Briefly, freshly prepared samples of the dimers in DMF containing 1% pyridine (ca 1 %M in 1 cm cuvette) were excited using linearly polarised light from a tuneable femtosecond optical parametric amplifier (TOPAS, Quantronix).…”

“…An efficient PDT photosensitiser requires a favourable combination of the following factors: (i) light absorption at 35 wavelengths which penetrate effectively into biological tissue (700-950 nm), 4 (ii) a high quantum yield for singlet oxygen generation (! !…”

Endoplasmic reticulum and Golgi apparatus are the preferential sites of Foscan® localisation in cultured tumour cells

“…Despite numerous studies on Foscan s 's mechanisms of action, an enigma still persists regarding the reason(s) for the high photodynamic efficiency of this sensitiser. Its photophysical properties, such as quantum yields of triplet state and singlet oxygen generation (Bonnett et al, 1999), are comparable or even inferior to other clinically relevant photosensitisers (Blum and Grossweiner, 1985;Aveline et al, 1994). Another factor determining the effective outcome of Foscan s photosensitisation could be its intracellular localisation.…”