Cancer cell behaviour in response to chemotherapeutics - a study of docetaxel induced inflammatory cytokine production and the effect of lipopolysaccharides

Abstract

The study of cancer is an ever‐evolving discipline and since the 1950's it has been driven by fundamental scientific research using cultured human tumour cell lines isolated from human cancer patients. Over the years it has become evident that patients with cancer of the breast, ovaries, and several other tissues, often respond well to initial chemotherapy treatment, only to be left with tumours that have become resistant to the cytotoxic effects of chemotherapy. This has prompted decades of cellular and mouse‐based studies to characterize the many biomolecular processes by which tumour cells in their microenvironments survive and reproduce in the presence of chemotherapy drugs. This dissertation discusses the role of cytokine production in chemotherapy drug efficacy both in the laboratory and the clinic. Cytokines are naturally released by healthy epithelial, endothelial, and immune cells to convey important messages to other cells and tissues of the body, driving immune responses upon recognition of pathogens or cellular damage. Cytokines have become increasingly considered for their roles in stalling or accelerating cancer progression as well as improving or limiting drug efficacy. In this thesis, we present primary research results that provide novel insight into the mechanism by which chemotherapy drugs induce inflammatory cytokine production and release from human tumour cells. We show that the semi‐synthetic taxane derivative docetaxel, as well as other structurally distinct chemotherapy drugs, induce the release of the inflammatory cytokine TNF‐α from breast and ovarian tumour cell lines. Constitutively increased production and release of TNF‐α and CXCL1 from breast and ovarian tumour cells was also observed upon their selection for survival in increasing concentrations of docetaxel. Docetaxel‐resistant cells were less responsive to acute treatment with docetaxel than their drug‐naive parental cell lines. These cells exhibited increased expression of the plasma membrane‐bound drug‐export protein, P‐glycoprotein, which promotes the efflux of docetaxel and other drugs from tumour cells. Interestingly, restoration of drug into the docetaxel‐ resistant cells not only restored the drugs' cytotoxic effect but also the ability of the cells to respond to drug with increased TNF‐α release. Current paradigms suggest that this response occurs through activation of the pathogen recognition receptor Toll‐like receptor 4 (TLR4), involving direct interaction with docetaxel at the cell surface. This model appears inconsistent with our results showing that cellular drug accumulation is necessary for the response of increased TNF‐α release to occur. We also show that the TLR4 agonist, lipopolysaccharides (LPS), causes increased production of TNF‐ in the presence of docetaxel and increased docetaxel cytotoxicity for both wildtype and docetaxel‐resistant MCF‐7 tumour cells, representing a potential novel strategy to restore chemoresponsiveness in chemoresistant tumours.