Cell adhesion mechanisms involved in resistance to Photodynamic Therapy of Ras-expressing tumors

RODRÍGUEZ, LORENA; DI VENOSA, GABRIELA; RIVAS, M.; MAMONE, LEANDRO; GANDARA, LAUTARO; JUARRANZ, ANGELES; SANZ- RODRIGUEZ, F; BATLLE, ALCIRA; CASAS, ADRIANA

Cardiff

Congreso; International Porphyrins and Porphyrias Meeting; 2011

British Association of Dermatologists

Photodynamic therapy (PDT) is an anticancer tretament that involves administration of a tumour-localising photosensitizer and its subsequent activation by visible light to result primarily in singlet oxygen?induced photodamage to the tumour. The photosensitizer absorbs light and in the presence of oxygen transfers energy, producing short-lived cytotoxic oxygen species such as singlet oxygen or other oxygen radicals.    The aim of this work was to explain the mechanisms that induce resistance to PDT observed in previous work in a normal/tumor cell line pair. We employed the tumor cell line HB4a-ras transfected with the oncogene H-Ras and its parental normal mammary epithelium cell line HB4a counterpart.    We analyzed by means of confocal fluorescence microscopy, the subcellular localization of a panel of photosensitizers: Verteporfirin, Acridine Orange, Foscan, Photofrin II, Chlorin e6 and Merocyanine 540.  We did not find significant differences on subcellular distribution between both cellular lines.   We have also analyzed the expression of adhesion molecules as well as molecules related to the processes of multiple resistance to drugs such as survivin and.  We did not find differences between both cell lines neither in distribution nor in expression of both molecules employing inmunofluorescence assays and Western Blots techniques.    On the other hand, we found in both cell lines equal expression of vinculin, (involved in adhesion to the substratum), actin (cytoskeleton protein), and E-cadherin (involved in cell-cell adhesion) its subcellular distribution was different.    We have also performed tests of cell adhesion to extracellular matrix (ECM) proteins such as Fibronectin, Collagen I and IV, Vitronectin and Laminin. We observed that HB4a-Ras cells showed major adhesion than HB4a to all the ECM proteins except for Vitronectin, which showed equal adhesion to both cell lines.    In PDT studies employing cell suspensions of HB4a and its Ras transfected counterpart, we showed an increased resistance to the phtotodynamic treatment, showing that cell adhesion is highly involved in the mechanism of photoresistance.