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

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Abstract
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/cm2). 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.