title: Evidence for different mechanisms of EMT-6 tumor necrosis by photodynamic therapy with disulfonated aluminum phthalocyanine or photofrin: tumor cell survival and blood flow.
abstract: A comparison was made of photodynamic therapy (PDT) mediated by two photosensitizers, the disulfonated aluminum phthalocyanine (AlPcS2) and Photofrin* (PII) with regard to their mechanism of action on murine tumors. Balb/c mice bearing intradermally growing EMT-6 tumors were injected intravenously with either 1 mumol kg-1 body weight of AlPcS2 or 5 mg/kg of PII 24 h prior to red light irradiation from a Xenon lamp (650-700 nm, 200 mW cm-2, for AlPcS2 and 600-650 nm, 400 J cm-2 for PII. Tumor cell survival following in vivo PDT was determined by an in vitro clonogenicity assay on the dissociated tumors. Immediately after the completion of light irradiation, a reduction of approximately 72% in the number of clonogenic cells was seen with AlPcS2-treated tumor versus approximately 24% of that for PII-treated tumor. Further loss of clonogenic cell survival progressed as a function of time following PDT, and was considered to be the consequence of indirect PDT action, however, the decline in cell viability was steeper in the first 6 h with PII-PDT than with AlPcS2-PDT. 24 h after PDT, the clonogenic capacity of both AlPcS2-and PII-PDT treated tumor fell to approximately 3% of the control tumor. The PDT effect on tumor blood flow as a measure of the tumor vascular damage was monitored by the retention of 99mTc-MIBI in the tumor. Little effect on tumor blood flow was seen with AlPcS2-PDT at 0 h after the completion of light treatment. Thereafter the blood flow declined slowly and remained at approximately 50% the level of the control by 24 h post-PDT. In contrast, PII provoked a approximately 40% reduction of tumor blood flow immediately after the completion of photo irradiation, which then fell to approximately 20% within 2 h and approximately 7% by 24 h post-PDT. These results indicate the involvement of both direct and indirect mechanisms in the PDT induced tumor necrosis. However, AlPcS2-PDT exerted a larger direct tumor cell phototoxic effect, whereas PII-PDT induced tumor cell death to a greater extent via an indirect effect that parallels the extensive damage to the tumor vasculature.
authors.affiliation: Department of Nuclear Medicine and Radiobiology, Faculty of Medicine, Université de Sherbrooke, Quebec, Canada.
authors.forename: W S
authors.initials: WS
authors.lastname: Chan
authors.forename: N
authors.initials: N
authors.lastname: Brasseur
authors.forename: C
authors.initials: C
authors.lastname: La Madeleine
authors.forename: J E
authors.initials: JE
authors.lastname: van Lier
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use* / Q000633:toxicity; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D017323:Dihematoporphyrin Ether / Q000627:therapeutic use* / Q000633:toxicity; D005260:Female; D007211:Indoles / Q000627:therapeutic use* / Q000633:toxicity; D008027:Light; D008325:Mammary Neoplasms, Experimental / Q000098:blood supply / Q000188:drug therapy* / Q000473:pathology*; D051379:Mice; D009336:Necrosis; D009942:Organometallic Compounds / Q000627:therapeutic use* / Q000633:toxicity; D010778:Photochemotherapy; D011838:Radiation-Sensitizing Agents / Q000627:therapeutic use* / Q000633:toxicity; D012039:Regional Blood Flow / Q000187:drug effects; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay
chemical_list: D000970:Antineoplastic Agents; D007211:Indoles; D009942:Organometallic Compounds; D011838:Radiation-Sensitizing Agents; C064331:aluminum phthalocyanine disulfonate; D017323:Dihematoporphyrin Ether