There is an unmet need to develop new agents or strategies against therapy resistant pancreatic cancer (PanCA). Recent studies from our laboratory showed that STAT3 negatively regulates NF-κB and that inhibition of this crosstalk using Nexrutine® (Nx) reduces transcriptional activity of COX-2. Inhibition of these molecular interactions impedes pancreatic cancer cell growth as well as reduces fibrosis in a preclinical animal model. Nx is an extract derived from the bark of Phellodendron amurense and has been utilized in traditional Chinese medicine as antidiarrheal, astringent, and anti-inflammatory agent for centuries. We hypothesized that “Nx-mediated inhibition of survival molecules like STAT3 and NF-κB in pancreatic cancer cells will improve the efficacy of the conventional chemotherapeutic agent, gemcitabine (GEM)”. Therefore, we explored the utility of Nx, one of its active constituents berberine and its derivatives, to enhance the effects of GEM. Using multiple human pancreatic cancer cells we found that combination treatment with Nx and GEM resulted in significant alterations of proteins in the STAT3/NF-κB signaling axis culminating in growth inhibition in a synergistic manner. Furthermore, GEM resistant cells were more sensitive to Nx treatment than their parental GEM-sensitive cells. Interestingly, although berberine, the Nx active component used, and its derivatives were biologically active in GEM sensitive cells they did not potentiate GEM activity when used in combination. Taken together, these results suggest that the natural extract, Nx, but not its active component, berberine, has the potential to improve GEM sensitivity, perhaps by down regulating STAT3/NF-κB signaling.

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Lysine deacetylases (KDACs) are enzymes that reverse the post-translational modification of lysine acetylation. Recently, a series of N-acetylthioureas were synthesized and reported to enhance the activity of KDAC8 with a fluorogenic substrate. To determine if the activation was general, we synthesized three of the most potent N-acetylthioureas and measured their effect with peptide substrates and the fluorogenic substrate under multiple reaction conditions and utilizing two enzyme purification approaches. No activation was observed for any of the three N-acetylthioureas under any assayed conditions. Further characterization of KDAC8 kinetics with the fluorogenic substrate yielded a kcat/KM of 164 ± 17 in the absence of any N-acetylthioureas. This catalytic efficiency is comparable to or higher than that previously reported when KDAC8 was activated by the N-acetylthioureas, suggesting that the previously reported activation effect may be due to use of an enzyme preparation that contains a large fraction of inactive enzyme. Further characterization with a less active preparation and additional substrates leads us to conclude that N-acetylthioureas are not true activators of KDAC8 and only increase activity if the enzyme preparation is below the maximal basal activity.

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