Abstract 5478: Curcumin mediates reversion to oxaliplatin-acquired resistance in colorectal cancer cell lines through modulation of nuclear factor κB (NFκB) and cyclin-dependent kinase 5 (CDK5)
Authors: Ruiz de Porras Vicenç , Bystrup Sara , Martinez-Cardus Anna , Ginés Alba , Layos Laura , Manzano José Luis , Bugés Cristina , Abad Albert , Martinez-Balibrea Eva 
Published: August 2015

Background: In previous work we have observed hyper-activation of the transcription factor (TF) NF-κB and an up-regulation of the Cyclin-dependent kinase 5 (CDK5) in human colorectal cancer cell lines with acquired resistance to oxaliplatin (OXA). Moreover, OXA treatment induced NF-κB activation. Curcumin (diferuloylmethane, CURC), the major active ingredient of turmeric (Curcuma longa), without discernable toxicity, has been shown to inhibit the growth of colon tumor cells in vitro and in vivo partly by suppressing activation of NF-κB. The aim of this study was to demonstrate whether a combined treatment with CURC and OXA could revert the acquired resistance phenotype to the latter in in vitro models and to elucidate the molecular mechanisms behind this effect.

Material and Methods: HT29- and LoVo-derived OXA-resistant HTOXAR3 and LoVOXAR3 cells (p53 mutant and WT respectively) as well as HCT116 and its isogenic derivative with a targeted inactivation of p53 (HCT116 p53 null) cell lines were used in the present study. The IC50s and combination index for CURC and OXA in the six cell lines was determined by MTT assay and the data was analysed using the median effect lines and the Chou and Talalay method, respectively. Survival and clonogenic expansion of cells after OXA and CURC treatment was assessed by colony assay. Cell death was measured by flow cytometry and propidium iodide staining. Dose-response-associated phosphorylation status of P65 (S536), IκBα(S32/S36) and expression of Survivin and CDK5 was analysed by Western Blotting after oxaliplatin and CURC treatments. Nuclear translocation of p65 was assessed by inmunocytochemistry.

Results: CURC had a similar effect on proliferation in all cell lines (IC50 range 7.5-14.7uM). In terms of synergism, the best combination of CURC and OXA was the 24h concomitant treatment. CURC inhibited OXA-induced activation of NF-κB, downregulated the expression of Survivin, an NF-κB-regulated gene product, and it also inhibited CDK5 expression in a dose-dependent manner. Combination of OXA and CURC resulted in an OXA resistance reversion in HTOXAR3, LoVOXAR3 and HCT116 p53 null cells but it was only synergistic in HTOXAR3 and HCT116 p53 null cells, suggesting a possible role of p53 on OXA/CURC synergism. The concomitant treatment also reduced the number of colonies formed compared with OXA or CURC alone. This was further supported by preliminary experiments showing that the combination also increased cell death.

Conclusions: These results demonstrate that the OXA/CURC combination can revert OXA acquired resistance in our resistant models through the inhibition of the NFκB TF and for the first time, suggest a role of CDK5 in the CURC mechanism of action. Further experiments are ongoing in order to elucidate a possible link between CDK5 and NF-κB, and their role in acquisition of OXA resistance.

Citation Format: Vicenç Ruiz de Porras, Sara Bystrup, Anna Martinez-Cardus, Alba Ginés, Laura Layos, José Luis Manzano, Cristina Bugés, Albert Abad, Eva Martinez-Balibrea. Curcumin mediates reversion to oxaliplatin-acquired resistance in colorectal cancer cell lines through modulation of nuclear factor κB (NFκB) and cyclin-dependent kinase 5 (CDK5). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5478. doi:10.1158/1538-7445.AM2015-5478