| Summary: | TNF-Related Apoptosis-Inducing Ligand (TRAIL) belongs to the TNF cytokine family and can signal to apoptosis by binding to either of two membrane-bound death receptors, TRAIL-R1 or TRAIL-R2. Using ligands specific for TRAIL-R1 (R1L) or TRAIL-R2 (R2L), our laboratory has previously shown that combining a histone deacetylase inhibitor with R1L, but not R2L, induces apoptosis in primary chronic lymphocytic leukaemia cells. The aim of this project was to extend the profiling of TRAIL-Receptor signalling to breast cancer, using breast cancer cell lines and importantly primary breast tumours as model systems. A 3-dimensional explant culturing technique was employed to maintain the primary tumour architecture and mimic the breast tumour microenvironment. In addition, tumour-initiating cells from advanced metastatic breast cancer patients were also tested for their sensitivity to TRAIL. The results obtained from breast cancer cell lines, primary mucinous carcinomas and advanced metastatic breast cancer cells suggest that in breast cancer, TRAIL-R1 is the predominant functional TRAIL death receptor independent of oestrogen receptor status. In contrast, invasive ductal/lobular carcinomas (IDC/ILC) were resistant to TRAIL-induced apoptosis and required the breast cancer chemotherapeutic, doxorubicin as a sensitising agent. Studies using the TRAIL-resistant cell line, T47D, demonstrated that doxorubicin sensitised tumour cells to TRAIL-induced apoptosis via enhanced TRAIL DISC formation. Importantly, in primary tumour explants, the combination of doxorubicin and TRAIL signalled to apoptosis exclusively in the tumour cells, but not in normal cells. Significantly, in four IDC/ILC tumours, doxorubicin sensitised breast tumour cells to R1L more efficiently than R2L. Therefore, using R1L in combination with sub-lethal doses of chemotherapeutic agents could improve the benefit of conventional therapy whilst reducing drug-associated side-effects and potential TRAIL-mediated cell proliferation/survival in apoptosis-resistant tumour cells. My data suggest that using a TRAIL-R1-selective agonist with an appropriate sensitising agent (example, doxorubicin), offers a promising therapeutic approach for treatment of breast cancer.
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