[Proteasome inhibitors sensitize ovarian cancer cells to cisplatin]

To explore the sensitivity and the molecular mechanism of cisplatin-resistance ovarian cancer cell line C13 to proteasome inhibitors and the combination with cisplatin.

After different treatments, methyl thiazolyl tetrazolium (MTT) assay was applied to examine the cell viability, annexin-V/propidium iodide (PI) apoptosis detection kit was used to determine the apoptosis rate of different groups, western blot assay was introduced to evaluate the expression levels of Fas-associated death domain-like interleukin-1 beta converting enzyme inhibitory protein (cFLIPs), and the activity of caspase-8 was examined.

MTT assay shown that the cell viability ratios of combination group at serial time points from 12, 24, 36, 48, 60, 72 hours were (56.0 ± 8.4) %, (44.7 ± 7.3) %, (33.7 ± 11.2) %, (27.6 ± 8.0) %, (27.6 ± 7.6) % and (28.1 ± 2.4) %, which were much lower than those of cisplatin group (P < 0.05). After treated for 24 hours, apoptosis rates of cisplatin group, bortezomib group and combination group were (16.7 ± 1.7) %, (23.4 ± 2.1) % and (26.9 ± 1.6) %, respectively. The rate of combination group was much higher than that of non-treated group and that of cisplatin group or bortezomib group (P < 0.05). Western blot assay showed the changes of expression levels of cFLIPs, which were down-regulated seriously after cisplatin, bortezomib or combination treatment [(43.2 ± 2.3) % vs (75.7 ± 3.0) % vs (67.9 ± 2.1) %, P < 0.05]. The caspase-8 activity of combination group was (5.6 ± 1.6) folds than that of non-treated group, which was higher than those of other two groups [(2.3 ± 1.0) and (4.2 ± 0.9) folds, P < 0.05].

The tumor cell lethal effect of cisplatin could be increase significantly by the combination application of proteasome inhibitors, bortezomib. And the cFLIPs/caspase-8 signaling pathway may be play an important role in the molecular mechanism of the combination treatment.