title: Determination of the threshold dose distribution in photodynamic action from in vitro experiments.
abstract: The concept of threshold in photodynamic action on cells or microorganisms is well observed in experiments but not fully explored on in vitro experiments. The intercomparison between light and used photosensitizer among many experiments is also poorly evaluated. In this report, we present an analytical model that allows extracting from the survival rate experiments the data of the threshold dose distribution, ie, the distribution of energies and photosensitizer concentration necessary to produce death of cells. Then, we use this model to investigate photodynamic therapy (PDT) data previously published in literature. The concept of threshold dose distribution instead of "single value of threshold" is a rich concept for the comparison of photodynamic action in different situations, allowing analyses of its efficiency as well as determination of optimized conditions for PDT. We observed that, in general, as it becomes more difficult to kill a population, the distribution tends to broaden, which means it presents a large spectrum of threshold values within the same cell type population. From the distribution parameters (center peak and full width), we also observed a clear distinction among cell types regarding their response to PDT that can be quantified. Comparing data obtained from the same cell line and used photosensitizer (PS), where the only distinct condition was the light source's wavelength, we found that the differences on the distribution parameters were comparable to the differences on the PS absorption. At last, we observed evidence that the threshold dose distribution matches the curve of apoptotic activity for some PSs.
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970, São Carlos, SP, Brazil. Electronic address: claramgf@ifsc.usp.br.
authors.forename: Clara Maria Gonçalves
authors.initials: CMG
authors.lastname: de Faria
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970, São Carlos, SP, Brazil.
authors.forename: Natalia Mayumi
authors.initials: NM
authors.lastname: Inada
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970, São Carlos, SP, Brazil.
authors.forename: Cristina
authors.initials: C
authors.lastname: Kurachi
authors.affiliation: São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970, São Carlos, SP, Brazil.
authors.forename: Vanderlei Salvador
authors.initials: VS
authors.lastname: Bagnato
mesh_terms: D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D066298:In Vitro Techniques; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000627:therapeutic use
chemical_list: D014408:Biomarkers, Tumor; D017319:Photosensitizing Agents
keywords: Cells; Photodynamic therapy; Photosensitizers; Threshold dose