Effect of the TAT-RasGAP317–326 peptide on apoptosis of human malignant mesothelioma cells and fibroblasts exposed to meso-tetra-hydroxyphenyl-chlorin and light

Background5,10,15,20-Tetrakis(m-hydroxyphenyl)chlorin (mTHPC)-mediated photodynamic therapy (PDT) has shown insufficient tumor selectivity for the treatment of pleural mesothelioma. Tumor selectivity of mTHPC-PDT may be enhanced in the presence of the TAT-RasGAP317–326 peptide which has the potential to specifically sensitize tumor cells to cytostatic agents.Materials and methodsH-meso-1 and human fibroblast cell cultures, respectively, were exposed to two different mTHPC doses followed by light delivery with and without TAT-RasGAP317–326 administration. mTHPC was added to the cultures at a concentration of 0.04 μg/ml and 0.10 μg/ml, respectively, 24 h before laser light illumination at 652 nm (3 J/cm2, 40 mW/cm2). TAT-RasGAP317–326 was added to the cultures immediately after light delivery at a concentration of 20 μM. The apoptosis rate was determined by scoring the cells displaying pycnotic nuclei. Cell viability was measured by using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay.ResultsLight delivery associated with 0.04 μg/ml mTHPC resulted in a significantly higher apoptosis rate in the presence of TAT-RasGAP317–326 than without in H-meso-1 cells (p < 0.05) but not in fibroblasts. In contrast, 1.0 μg/ml mTHPC and light resulted in a significantly higher apoptosis rate in both H-meso-1 cells and fibroblasts as compared to controls (p < 0.05) but the addition of TAT-RasGAP317–326 did not lead to a further significant increase of the apoptosis rate of both H-meso-1 cells and fibroblasts as compared to mTHPC and light delivery alone.ConclusionTAT-RasGAP317–326 selectively enhanced the effect of mTHPC and light delivery on H-meso-1 cells but not on fibroblasts. However, this effect was mTHPC dose-dependent and occurred only at a low sensitizer dose.