Hematoporphyrin derivative (HpD), a mixture of compounds chemically prepared from naturally occurring crude hematoporphyrin, is preferentially concentrated in neoplastic cells and produces red fluorescence when irradiated with blue-violet light. In addition, HpD exhibits other photodynamic properties, which, in the presence of oxygen and visible light, result in cytotoxicity. Preliminary reports indicate that early, superficial carcinomas of the upper aerodigestive tract and tracheobronchial tree can be localized and treated successfully with HpD phototherapy (HpD-PT), in which a fiberoptic bundle transmits laser light to the tumors. To assess this modality's potential for treating solid tumors, the cytotoxic effect of HpD-PT was measured in a murine tumor model. We specifically assessed the effect of cooling on the pure photodynamic action of HpD-PT. Adult female mice with typical mammary tumors received interstitial phototherapy 24 hours after HpD was given intraperitoneally. Light from an argon-dye laser was delivered through an optical fiber, along with simultaneous cooling from a cryosurgical probe, for 15 minutes. After being cooled with a cryosurgical probe, tumors were excised 48 hours after treatment and the necrotic area was measured. The results indicate that cooling enhances the tumoricidal action of HpD-PT.
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