Benzyl isothiocyanate chemosensitizes BxPC-3 human pancreatic cancer cells to gemcitabine induced growth inhibition and apoptotic death Free

4776

The increase in systemic toxicity and drug resistance is the major drawback of chemotherapeutic agents in the treatment of pancreatic cancer. Although combination therapy may have increased the therapeutic index of some chemotherapeutic agents, it has been associated with toxicities, which acts as a barrier to chemotherapy. Therefore, the new strategy is to find non-toxic agents with known mechanisms of action that can increase the efficacy of chemotherapeutic agents at low concentrations and reduce overall systemic toxicity. We have shown previously that benzyl isothiocyanate (BITC), a constituent of cruciferous vegetables, inhibits the growth of human pancreatic cancer cells and induces apoptosis. In the present study, we determined whether BITC could sensitize BxPC-3 human pancreatic cancer cells to increase the therapeutic potential of gemcitabine, which is currently being used to treat advanced pancreatic cancer. Our results demonstrate that pretreatment of BxPC-3 cells with BITC for 24h followed by gemcitabine for 72h resulted in 56% to 80% growth inhibition compared with 26% to 55% when gemcitabine was used alone. In BxPC-3 cells, combination index (CI) indicated synergistic effects (CI<1) following treatment with BITC and gemcitabine. This combination caused 3.8-fold apoptotic cell death compared with about 1.9 fold by gemcitabine alone. The underlying mechanism of apoptosis inducing effect of the combination treatment revealed a significantly higher expression of cytochrome c in the cytosolic fraction of the cells as compared to either treatment alone. Similarly, we observed cleavage of caspase-3 and PARP in combination treatment. Our results also reveal that BITC but not gemcitabine treatment causes significant decrease in mitochondrial membrane potential of cells. These results suggest that the plausible mechanism by which BITC chemosensitizes BxPC-3 cells to gemicitabine is by depolarizing the mitochondria resulting in the release of cytochrome c and activating caspase-3 cascade, leading to apoptosis. Taken together, our results demonstrate that combination of chemopreventive BITC with low concentrations of gemcitabine dramatically inhibited the growth of humanpancreatic cancer cells, providing the experimentalbasis for the potential clinical use of this combination. [Supported in part by RO1 grant CA 106953 (to S.K.S.) awarded by the National Cancer Institute].