The transcriptional factor, NF-κB, has been suggested as a mediator in both the tumorigenesis and chemoresistance of pancreatic cancer. The inhibition of NF-κB has been proposed to be a target for developing anticancer drugs for pancreatic cancer. Our laboratory has previously shown that certain analogs of tylophorine have differential activity against HepG2 and KB cell lines and could inhibit the NF-κB-mediated signaling pathway. In the current study, we examined the activity of one of the tylophorine analogs, DCB-3503, against PANC-1. In growth-inhibition and clonogenecity assays, the EC50 was determined to be 50.9 ± 3.4 nM and 98.9 ± 9.5 nM, respectively. We examined the effect of DCB-3503 on cell-cycle distribution by flow cytometry. There was a preferential arrest in the G2/M phase at the lower dose, whereas the cells were arrested in the S phase and even in all phases at the higher dose. By studying the cell-cycle related proteins, the results are that cyclin D1, cyclin B1 and the phosphorylated form of cdc2 decreased with time, whereas there was no significant change in cyclin E, cdc25a, cdc25b, cdc25c and total amount of cdc2. These results indicate that DCB-3503 altered the cell-cycle distribution via affecting those cell-cycle related proteins. The impact of DCB-3503 on NF-κB activity was also assessed in PANC-1 cells using the luciferase reporter vector containing κB response element. DCB-3503 reduced TNFα-induced NF-κB activity in a dose-dependent manner with an ED50 of 72 nM. The mechanism of action is different from PS-341, a known NF-κB inhibitor that acts by the inhibition of IκBα degradation. DCB-3503 did not prevent TNFα-stimulated NF-κB translocation from the cytoplasm to the nucleus and then binding to κB response element. Also the translocation was not induced in spite of IκBα being downregulated by DCB-3503 alone. The total amount of p65 was not changed either in the nucleus or in the cytoplasm, but the phosphorylated form of p65 was decreased in the nucleus and not changed in the cytoplasm. These results indicate that NF-κB can translocate into the nucleus and bind to its specific sequence, but the active form of NF-κB is actually decreased, and thus the NF-κB activity is also decreased. As for the other NF-κB family proteins, we did not observe any significant change in RelB, c-Rel, p50/p105, or p52/p100. Taken together, our results suggest that DCB-3503 has the potential of having anti-pancreatic cancer activity, and one of the mechanisms could be mediated through the inhibition of NF-κB transcription activity, which could have an impact on cell-cycle regulatory proteins such as cyclin D1 and other proteins. The mechanism of the inhibition of NF-κB transcription appears to be related to the phosphorylated status of p65. Further explorations are underway. (This work was supported, in part, by NIH grant no. R01 CA87863.)

[Proc Amer Assoc Cancer Res, Volume 45, 2004]