(541.6) Jadomycin B Acts Synergistically with NSAIDs to Produce Cytotoxic Effects in Human Breast Cancer Cells in vitro

Poster Board Number: B144

Brendan McKeown (Dalhousie University, Beatrice Hunter Cancer Research Institute), Kerry Goralski (Dalhousie University, Dalhousie University, Dalhousie University and IWK, Beatrice Hunter Cancer Research Institute)

Background
Breast cancer is the most prevalent cancer in North American women. Jadomycin B is a novel compound that is effective in killing triple negative human breast cancer cells that have become resistant to anthracycline and taxane chemotherapies. The mechanism through which jadomycin B exerts its cytotoxic effect remains to be fully characterized. A quantitative PCR (qPCR) array of cancer drug targets identified cyclooxygenase-2 (COX-2) as a gene of interest in jadomycin B resistant breast cancer cells.

Objective
To explore the effects of COX-2 signalling on jadomycin B cytotoxicity in MDA-MB-231 cells as a model of invasive triple-negative, human breast cancer requiring more effective treatments.

Methods and Results
Control MDA-MB-231 (231-CON) cells exposed to increasing concentrations of jadomycin B (0-2.2 µM) over 7 months developed a 3-fold resistance to jadomycin B as determined using methyl-tetrazolium (MTT) cell viability assays. By qPCR, there was a significant increase in COX-2 (40 fold, p lt; 0.05) but not cyclooxygenase-1 (COX-1) (0.17 fold, p lt; 0.05), mRNA expression in jadomycin resistant (231-JB) versus 231-CON cells. A similar increase in COX-2 was not observed in mitoxantrone resistant MDA-MB-231 cells (231-MITX). We therefore hypothesized that inhibition of COX-2 signalling would increase the susceptibility of breast cancer cells to jadomycin B. The 231-CON and 231-JB cells were treated with jadomycin B with or without the COX-2 selective inhibitor celecoxib (CXB), or COX-1/2 inhibitors ibuprofen (IBU) or Naproxen (NAP). The SynergyFinder 2.0 web application was used to analyze the cytotoxicity (MTT assays) of these combinations and calculate synergy scores using the Bliss model. IBU and NAP were found to act synergistically with jadomycin B in both control and jadomycin resistant cells, while CXB acted additively (Table 1).

Conclusions
Jadomycin B acts additively or synergistically with inhibitors of COX-2 in vitro, resulting in increased cytotoxic effect. These results justify further investigation into the COX-2 signaling pathway as a means to elucidate the mechanism of action of jadomycin B. Additionally, our research has the potential to contribute to an improved understanding of breast cancer relevant COX-2 signalling, facilitating the use of COX-2 inhibitors as chemosensitizers.

This work was supported by a research grant from the Dalhousie Pharmacy Endowment. B.T.M. is a trainee in the Cancer Research Training Program of the Beatrice Hunter Cancer Research Institute, with funds provided by the Saunders Matthey Foundation for Cancer Prevention. B.T.M. is supported by funds provided from the Natural Sciences and Engineering Research Council of Canada (Create grant number 510963).



Table 1. Bliss synergy scores for combined use of jadomycin B (JB) and celecoxib (CXB), ibuprofen (IBU), or naproxen (NAP). Data represents mean synergy score (95% CI) of four experiments performed in triplicate, calculated using the Bliss method. Scores of -10 to 10 show an additive effect, while >10 represents synergy. Experiments were conducted in vitro  (MTT assay) to determine viability and calculate synergistic effect in control (231-CON), or jadomycin resistant (231-JB) MDA-MB-231 cells.