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 surgerytreated 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. © 2002 Wiley-Liss, Inc. Key words: photodynamic therapy; surgery; Pd-bacteriopheophorbide; C6 glioma tumor; metastasisPhotodynamic therapy (PDT) is based on the destruction of tumors by cytotoxic reactive oxygen species (ROS) produced upon local tumor illumination in patients administered with a photosensitizer. 1-3 Following health agency approval for photofrin-based PDT in many countries, this anti-cancer treatment modality entered clinical use for the local treatment of an increasing number of indications including skin, esophageal, lung, gastric, cervical and bladder cancers. 4 PDT is usually considered a local anti-tumor treatment modality. However, reports from several laboratories suggest that PDT also induces beneficial systemic effects. Following in vitro hematoporphyrin-based PDT, adhesiveness and metastatic potential decline in DHD-K12-cultured colon carcinoma cells. Moreover, intravenous or s.c. injection of these PDT-treated cells to rats resulted in a reduced number of lung metastases compared with untreated cell injection. 5,6 Although this observation may be due to local photodynamic damage, the potential beneficial effect may be viewed as systemic. Other in vivo studies showed that local PDT with various photosensitizers mediates ...

Chlorophyll (Chl) and bacteriochlorophyll (Bchl) have been made water soluble by transesterfication with serine (Ser) at the propionyl residue and tested as potential reagents for photodynamic therapy (PDT). Photocytotoxicity of the conjugates Chl-Ser and Bchl-Ser in M2R mouse melanoma was tested in cell cultures. Tissue uptake and clearance of the photosensitizers in CDI nude and C57Bl mice implanted with M2R tumors are described, Photocytotoxicity in cell cultures was determined microscopically and by [3Hlthymidine incorporation. The LD.u values in vitro were 0.05-0

WST11 is a novel negatively charged water-soluble palladium-bacteriochlorophyll derivative that was developed for vascular-targeted photodynamic therapy (VTP) in our laboratory. The in vitro results suggest that WST11 cellular uptake, clearance and phototoxicity are mediated by serum albumin trafficking. In vivo, WST11 was found to clear rapidly from the circulation (t1/2=1.65 min) after intravenous bolus injection in the mouse, whereas a longer clearance time (t1/2=7.5 min) was noted in rats after 20 min of infusion. The biodistribution of WST11 in mouse tissues indicates hepatic clearance (t1/2=20 min), with minor (kidney, lung and spleen) or no intermediary accumulation in other tissues. As soon as 1 h after injection, WST11 had nearly cleared from the body of the mouse, except for a temporal accumulation in the lungs from which it cleared within 40 min. On the basis of these results, we set the VTP protocol for a short illumination period (5 min), delivered immediately after WST11 injection. On subjecting M2R melanoma xenografts to WST11-VTP, we achieved 100% tumor flattening at all doses and a 70% cure with 9 mg/kg and a light exposure dose of 100 mW/cm2. These results provide direct evidence that WST11 is an effective agent for VTP and provide guidelines for further development of new candidates.

New negatively charged water-soluble bacteriochlorophyll (Bchl) derivatives were developed in our laboratory for vascular-targeted photodynamic therapy (VTP). Here we focused on the synthesis, characterization and interaction of the new candidates with serum proteins and particularly on the effect of serum albumin on the photocytotoxicity of WST11, a representative compound of the new derivatives. Using several approaches, we found that aminolysis of the isocyclic ring with negatively charged residues markedly increases the hydrophilicity of the Bchl sensitizers, decreases their self-association constant and selectively increases their affinity to serum albumin, compared with other serum proteins. The photocytotoxicity of the new candidates in endothelial cell culture largely depends on the concentration of the serum albumin. Importantly, after incubation with physiological concentrations of serum albumin (500-600 microM), WST11 was found to be poorly photocytotoxic (>80% endothelial cell survival in cell cultures). However, in a recent publication (Mazor, O. et al. [2005] Photochem. Photobiol. 81, 342-351) we showed that VTP of M2R melanoma xenografts with a similar WST11 concentration resulted in approximately 100% tumor flattening and >70% cure rate. We therefore propose that the two studies collectively suggest that the antitumor activity of WST11 and probably of other similar candidates does not depend on direct photointoxication of individual endothelial cells but on the vascular tissue response to the VTP insult.

Successful application of anticancer therapy, and especially photodynamic therapy (PDT) mediated by type I1 (PDTII) processes, depends on the oxygen content within the tumor before, during and after treatment. The high consumption of oxygen during type I1 PDT imposes constraints on therapy strategies. Although rates of oxygen consumption and repletion during PDTII were suggested by theoretical studies, direct measurements have not been reported. Application of a novel oxygen sensor allowed continuous and direct in sifu measurements (up to a depth of 8-9 mm from the tumor surface and for several hours) of temporal variations in the oxygen partial pressure (pOz) during PDT. Highly pigmented M2R mouse melanoma tumors implanted in CD1 nude mice were treated with bacteriochlorophyll+erine (Bchl-Ser; a new photodynamic reagent) and were subjected to fractionated illumination (700 < A < 900 nm) at a fluence rate of 12 mW cm+. This illumination led to total oxygen depletion with an average consumption rate of 7.2 pM(Oz) s-l. Spontaneous reoxygenation (at an average rate of 2.5 pM(O,)/s) was observed during the following dark period. These rates are in good agreement with theoretical considerations (Foster et al., Radiat. Res. 126, 296,1991 and Henning et al., Radiut. Res. 142,221,1995). The observed patterns of oxygen consumption and recovery during prolonged periods of Iightldark cycles were interpreted in terms of vasculature damage and sensitizer clearance. The presented data support the previously suggested advantages of fractionated illumination for type I1 photodynamic processes.