Homologous adaptation to oxidative stress induced by the photosensitized Pd-bacteriochlorophyll derivative (WST11) in cultured endothelial cells.

Various forms of cellular stress induce adaptive responses through poorly understood mechanisms. In maintaining homeostasis, endothelial cells respond and adapt to changes in oxidative stress that prevail in the circulation. Endothelial cells are also the target of many oxidative stress-based vascular therapies. The objectives of this study were to determine whether endothelial cells adapt to oxidative stress induced upon the photosensitization of WST11 (a water-soluble Pd-bacteriochlorophyll derivative being developed as a photodynamic agent) and to study possible cellular mechanisms involved. The hallmark of WST11-based photodynamic therapy is the in situ generation of cytotoxic reactive oxygen species causing vascular shutdown, hypoxia, and tumor eradication. Here we demonstrated that photodynamic therapy also induces adaptive responses and tolerance following a sublethal preconditioning of endothelial cells with the same (homologous) or different (heterologous) stressor. A link among p38 MAPK activity, expression of hsp70 and hsp27, and homologous adaptation to reactive oxygen species induced by photosensitized WST11 was established. In addition to characterization of some key proteins involved, our observations provide a beneficial new working tool for the studies of mechanisms involved in oxidative stress and adaptation using light-controlled photosensitization.

Control of redox transitions and oxygen species binding in Mn centers by biologically significant ligands; model studies with [Mn]-bacteriochlorophyll a.

Mn-superoxide dismutase (Mn-SOD), which protects the cell from the toxic potential of superoxide radicals (O(2)(-*)), is the only type of SOD which resides in eukaryotic mitochondria. Up-to-date, the exact catalytic mechanism of the enzyme and the relationship between substrate moieties and the ligands within the active site microenvironment are still not resolved. Here, we set out to explore the possible involvement of hydroperoxyl radicals ((*)OOH) in the catalytic dismutaion by following the interplay of Mn(III)/Mn(II) redox transitions, ligands binding, and evolution or consumption of superoxide radical, using a new model system. The model system encompassed an Mn atom chelated by a bacteriochlorophyll allomer macrocycle (BChl) in aerated aprotic media that contain residual water. The redox states of the Mn ion were monitored by the Q(y) electronic transitions at 774 and 825 nm for [Mn(II)]- and [Mn(III)]-BChl, respectively (Geskes, C.; Hartwich, G.; Scheer, H.; Mantele, W.; Heinze, J. J. Am. Chem. Soc. 1995, 117, 7776) and confirmed by electron spin resonance spectroscopy. Evolution of (*)OOH radicals was monitored by the ESR spin-trap technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The experimental data suggest that the [Mn]-BChl forms a (HO(-))[Mn(III)]-BChl(OOH) complex upon solvation. Spectrophotometeric titrations with tetrabutylamonnium acetate (TBAA) and 1-methylimidazole (1-MeIm) together with ESI-MS measurements indicated the formation of a 1:1 complex with [Mn]-BChl for both ligands. The coordination of ligands at low concentrations to [Mn(III)]-BChl induced a release of a (*)OOH radical and a [Mn(III)]-BChl --> [Mn(II)]-BChl transition at higher concentrations. The estimated equilibrium constants for the total redox reaction ( )()are 1.9 x 10(4) +/- 1 x 10(3) M(-)(1) and 12.3 +/- 0.6 M(-)(1) for TBAA and 1-MeIm, respectively. The profound difference between the equilibrium constants agrees with the suggested key role of the ligand's basicity in the process. A direct interaction of superoxide radicals with [Mn(III)]-BChl in a KO(2) acetonitrile (AN) solution also resulted in [Mn(III)]-BChl --> [Mn(II)]-BChl transition. Cumulatively, our data show that the Mn(III) center encourages the protonation of the O(2)(-)(*) radical in an aprotic environment containing residual water molecules, while promoting its oxidation in the presence of basic ligands. Similar coordination and stabilization of the (*)OOH radical by the Mn center may be key steps in the enzymatic dismutation of superoxide radicals by Mn-SOD.

Local photodynamic therapy (PDT) of rat C6 glioma xenografts with Pd-bacteriopheophorbide leads to decreased metastases and increase of animal cure compared with surgery.

Photodynamic therapy (PDT), locally applied to solid C6 rat glioma tumors in the foot of CD1 nude mice, eradicated the primary tumor and also decreased the rate of groin and lung metastases. Pd-Bacteriopheophorbide (Pd-Bpheid), a novel photosensitizer synthesized in our laboratory, was used in our study. The primary lesion in the hind leg was treated by an i.v. injection of 5 mg/kg of Pd-Bpheid and immediate illumination (650-800 nm, 360 J/cm(2)). This protocol and the surgical amputation of the leg were compared for local and metastasis responses. Following PDT, hemorrhage, inflammation with tumor necrosis and flattening were observed and histologically verified in the photodynamically treated tumor. Whereas local tumor control rates were up to 64% following PDT, in surgically treated animals, local tumor control was absolute. The rates of metastases in the groin and the lungs were at least 12-fold lower in the photodynamically treated animals compared with untreated or surgery-treated groups. The overall cure rates after PDT or surgery were 36% and 6%, respectively, at 8 weeks. These findings suggest that local PDT with Pd-Bpheid, which acts primarily on the tumor vasculature, efficiently eradicates the solid C6 tumors. In addition, the local PDT of the primary lesion has beneficial therapeutic effects on remote C6 metastasis, which is not obtained with surgery. It is therefore suggested, that although surgery is highly efficient for the immediate removal of the primary tumor, it lacks such systemic, therapeutic effects on distant metastases. Pd-Bpheid-PDT may thus offer a potentially superior curative therapy for C6 glioma tumors in the limb by eradicating the target tumor and by reducing the rate of metastasis in the groin and lung, possibly due to innate immunity.