¹⁸⁸Rhenium-induced cell death and apoptosis in a panel of tumor cell lines

Assessment of "in vitro" tumor growth inhibition and radiobiological effects, such as apoptosis, have been evaluated in human neoplastic cells of different histotypes (H460 lung cancer cells, U87 glioblastoma, LnCaP prostate tumor cells) treated using solutions of ¹⁸⁸Rhenium-perrhenate. The MTT assay, which measures mitochondrial metabolism in the entire cell culture is a recognized test for cytotoxicity and was used in cells exposed 48-72 h to specific activities ranged from 37 to 148 GBq/l. Whereas H460 and LnCaP were particularly sensitive to treatment, U87 glioblastoma cells behaved as radioresistant ones. However, evaluation of ¹⁸⁸Re-induced apoptosis indicated that this kind of cell death contributed only marginally to the reduction in cell viability of H460 and LNCaP lines, suggesting the existence of protective mechanisms against apoptosis. In this respect, the membrane receptor, CD44, whose expression is dysregulated in most malignant cell types has proven to alter the response of cancer cells to apoptotic stimuli, including ionizing radiation. Cell samples decorated with a FITC-labelled CD44 antibody indicated, that in H460 and U87 cells the CD44(+) correlated well with an apoptosis-resistant response. Conversely, LnCap cells proven as CD44(-) did not display however sensitivity to radio-induced apoptosis.