A13 : A Potential Anti-Proliferative and Resistance Reversal Agent in Pancreatic Cancer

Abstract

Curcumin is a natural compound that has previously been investigated as a ‘dual-role’ cytotoxic/resistance reversal agent in pancreatic cancer. It has shown promising activity in preclinical studies but had limited efficacy in patients due to its poor pharmacokinetic profile. An analogue of curcumin, A13, has been synthesised which lacks the structural moiety responsible for curcumin’s instability. Preliminary studies with A13 have indicated that it has more potent anticancer effects and an improved disposition compared to curcumin. The aim of this study was to characterise the potential of A13 as a cytotoxic and resistance reversal agent in pancreatic cancer. A13 demonstrated more potent anti-proliferative effects than curcumin in pancreatic cancer cells and the ability to inhibit NF-κB activation, a contributor to pancreatic cancer resistance. Up-regulation of MRP5 is considered another resistance mechanism. A13 significantly increased the accumulation of a fluorescent MRP5 substrate, BCECF using flow cytometry in MRP5-overexpressing cells, indicating that it is a more potent MRP5 inhibitor than curcumin. However, A13 was unable to decrease the MRP5-mediated resistance in these transfected cells to the MRP5 substrates, raltitrexed and methotrexate using cytotoxicity studies. Potential synergism between A13 and gemcitabine was also evaluated. Curve-shift analysis of combinations of the two compounds demonstrated mainly additive effects but high concentrations of A13 produced antagonistic effects on gemcitabine potency. This finding was consistent in subsequent cell proliferation studies using gemcitabine and a fixed, non-toxic concentration of A13/curcumin. As A13 did not reverse gemcitabine resistance in these pancreatic cancer cells, the effect of a known MRP inhibitor, NPPB, in combination with gemcitabine was assessed but no improvement to gemcitabine potency was observed, indicating that resistance to gemcitabine may not be due to MRP5-mediated efflux. This was supported by MRP5-overexpressing HEK cells, which showed no increased resistance to gemcitabine compared to their parental controls. Overall, these results suggest that a combination of gemcitabine and A13/curcumin will not produce synergistic therapeutic benefits in pancreatic cancer treatment. The combination may indeed be detrimental to the patient, producing antagonistic effects, possibly by inhibition of gemcitabine uptake into cancer cells. Further investigation will be necessary to resolve this intriguing question.