title: Resistance to photodynamic therapy in radiation induced fibrosarcoma-1 and Chinese hamster ovary-multi-drug resistant. Cells in vitro.
abstract: A degree of resistance to photodynamic therapy (PDT) has been induced in radiation-induced fibrosarcoma-1 (RIF-1) tumor cells by repeated photodynamic treatment with Photofrin (4 or 18 h incubation) in vitro to the 0.1-1% survival level, followed by regrowth from single surviving colonies. The resistance is shown as increased cell survival in the strain designated RIF-8A, compared to the wild-type RIF-1 cells, when exposed to increasing Photofrin concentration for 18 h incubation and fixed light exposure. No difference was found between RIF-1 and RIF-8A in the uptake of Photofrin per unit cell volume at 18 h incubation. Resistance to PDT was also observed in Chinese hamster ovary-multi-drug resistant (CHO-MDR) cells compared to the wild-type CHO cells, possibly associated with decreased cellular concentration of Photofrin in the former. By contrast, the PDT-resistant RIF-8A cells did not show any cross-resistance to Adriamycin, nor was there any significant drug concentration difference between RIF-1 and RIF-8A. These findings suggest that different mechanisms are responsible for PDT-induced resistance and multi-drug resistance.
authors.affiliation: Hamilton Regional Cancer Centre, Ontario, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Singh
authors.forename: B C
authors.initials: BC
authors.lastname: Wilson
authors.forename: S M
authors.initials: SM
authors.lastname: Sharkey
authors.forename: G P
authors.initials: GP
authors.lastname: Browman
authors.forename: P
authors.initials: P
authors.lastname: Deschamps
mesh_terms: D000818:Animals; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D004351:Drug Resistance; D005354:Fibrosarcoma; D017324:Hematoporphyrin Derivative; D006415:Hematoporphyrins / Q000378:metabolism / Q000494:pharmacology*; D008027:Light; D009381:Neoplasms, Radiation-Induced; D010778:Photochemotherapy; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: D006415:Hematoporphyrins; D011838:Radiation-Sensitizing Agents; D017324:Hematoporphyrin Derivative