Dillapiole effects on apoptosis in human nasal epithelial carcinoma, RPMI 2650 cells involves BCL-2 and caspase -8 signalling pathway / Nur Batrisyia Ruslan

The incidence of developing cancers of nasal cavity or paranasal sinuses is higher among the Southeast Asian compared to European countries. In Malaysia, they occurred as early as in the third and fourth decade of life with no sex predominance. However, the current treatments such as surgery, chemo-, radio- and adjuvant therapies are toxic with various undesirable side-effects . Dillapiole, 4, 5-dimethoxy-6-prop-2-enyl-1,3-benzodioxole is a phenylpropanoid extract of Peperomia pellucida was highly cytotoxic to cancer cells such as estrogen receptor-positive and -negative breast cancers cells but not to normal cells. However, its effect on cancers in the head and neck region remains ambiguous. In the present study the cytotoxic effect of dillapiole on human nasal epithelial carcinoma, RPMI 2650 cells and the underlying mechanism was investigated. Normal human gingival fibroblast, HGnF cells was used as a comparison. The cell cytotoxicity effect of dillapiole was determined using WST-1 assay; and validated by MTT and trypan blue exclusion assays. Flow cytometric analysis of cells stained with annexin-V-FITC/PI was used to determine the cell death mechanism induced by dillapiole. The expression of CASP8 and BCL2 proteins were assessed by enzyme-linked immunosorbent assay (ELISA). Cisplatin and untreated cells were used as positive and negative controls, respectively. Dillapiole was more cytotoxic and selective to RPMI 2650 cells compared to HGnF cells. Its action was dose dependent. Respective IC50 and IC75 of 46 μM and 125 μM were obtained for RPMI 2650 cells but none for HGnF cells up to 150 μM. On the contrary, respective IC50 of 8 μM and 70 μM were obtained in cisplatin treatment on both RPMI 2650 and HGnF cells. The results from MTT and trypan blue exclusion assays were in accordance with WST-1. At the respective IC50 and IC75 concentrations, dillapiole induced apoptosis in RPMI 2650 cells by 27.83 ± 2.35 % (p<0.05, n=3) and 58.86 ± 8.45 % (p<0.05, n=3), while cisplatin induced 92.8 ± 2.5% (p<0.05, n=3) apoptosis at its IC50 concentration. At the same dose of treatments as above, dillapiole and cisplatin up-regulated the expression of pro-apoptotic CASP8 protein and down-regulated anti-apoptotic BCL2 protein in RPMI 2650 cells. These findings indicated that similar to cisplatin, dillapiole activated apoptosis in RPMI 2650 cells via both the extrinsic and intrinsic pathways through the involvement of CASP8 and BCL2. Findings from this study may provide crucial roles for enhancement into in vivo studies and good baseline reference for future downstream experimental of gene and protein study.