Isolation and Initial Characterization of Resistant Cells to Photodynamic Therapy

Abstract

After photodynamic therapy (PDT), the apparition of resistant tumor cells can occur. Laboratory models are being developed in order to understand the potential mechanisms implicated in such resistance. In this sense, we describe the methods published for the isolation and characterization of tumor cells resistant to PDT. We also propose other unpublished procedures that could be of interest for the study of cells resistant to PDT. Factors such as the parental cell line, the photo-sensitizer (PS) (or prodrug), the photodynamic treatment conditions, the treatment interval, and the clonal or total population selection have to be taken into consideration. Treatment doses are generally high and repeated over time. The development of resistant cells to PDT could take several months. The characterization of resistant cell populations vs parental cells can be performed by using different cellular and molecular techniques, including: cell morphology analysis, intracellular PS content measurement, PS localization, migration and invasion capacity, expression and distribution of adhesion proteins, death proteins and evaluation of specific genes implicated in cell proliferation and survival. Transplantation mouse models also contribute to determine the biological activity of the PDT-resistant cells in vivo, allowing the evaluation of their tumorigenicity and aggressiveness. Laboratory cell models will help us to understand how resistance to anticancer PDT affects the biological and functional aspects of tumorigenicity in vitro and in vivo, which are necessary to improve the clinical results.