Abstract #2829: NF-kb inhibition by quinacrine induces apoptosis in human colon carcinoma cell lines (cc) and sensitizes them to agents that target the TRAIL receptors.

Colon cancer continues to be a major cause in cancer-related deaths in USA. Although advancement in chemotherapy with 5-Fluorouracil in combination with Leucovorin (FUra/LV) and other agents has increased the survival rate to 22 months, curative therapy is still unknown. We previously demonstrated Fas-dependent component in thymidylate synthase (TS)-dependent cell death in cc. Fas is frequently downregulated in human colorectal cancer and is upregulated following treatment with IFN-gamma, which synergistically sensitizes cells to Fas-induced and to FUra/LV-induced cytotoxicity. We have shown that FUra/LV combined with IFN-gamma is synergistically active in a xenograft model and is in Phase II trial. Further, enhancement of therapeutic activity has been demonstrated by employing agents that target the TRAIL death receptors. NF-kB is frequently constitutively activated in human cancers, and can attenuate the cytotoxic activity of both FUra/LV as well as Fas- and TRAIL-induced apoptosis. We evaluated the agent quinacrine as an inhibitor of constitutive NF-kB activation or as an inhibitor of induced NF-kB activation following treatment with rhTRAIL or lexatumumab (a cytolytic agonist TRAIL-R2 (DR5) specific antibody), with the goal of further enhancing therapeutic response. HT29 and RKO colon carcinoma cell lines express constitutively active NF-kB and are sensitive to quinacrine whereas HCT8 cells have significantly lower amounts of constitutive NF-kB expression and are comparatively resistant to quinacrine-induced cell death. Importantly, HT29 cells transfected with the super repressor IkB-mutant also demonstrated resistance to quinacrine-induced cell death. At IC50 concentrations, quinacrine inhibited constitutively activated NF-kB as well as TNF-inducible NF-kB activation in HT29 and RKO cell lines. Since NF-kB can upregulate the expression of additional survival factors including members of the Bcl-2 and IAP families as well as FLICE inhibitory protein (FLIP). RKO and HT29 cells were treated with 1-10uM quinacrine for 24 hr and were examined for changes in levels of expression of these proteins. While there was no significant change observed in the levels of c-IAP1, c-IAP2 or XIAP, there was a dose dependent decrease in the other survival factors at 24 hr. Importantly, quinacrine also downregulated expression of phospho-Akt as well as Akt kinase activity in these cells. Pretreatment with quinacrine for 2hr followed by 24 hr exposure to lexatumumab or to TRAIL increased the cytotoxic activity of these agents. Our data also demonstrate that the effect of quinacrine is independent of p53 and that activated NF-kB may be a novel therapeutic target, which can be downregulated by quinacrine and further sensitizes the cellular response of colorectal cancers to agents that target the TRAIL receptors. Supported by NCI awards CA 32613 and CA 108929. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 2829.