Pro-apoptotic effect of Δ2-TGZ in "claudin-1-low" triple-negative breast cancer cells: involvement of claudin-1

40% of triple-negative breast cancer (TNBC) do not express claudin-1, a major constituent of tight junction. Patients with these "claudin-1-low" tumors present a higher relapse incidence. A major challenge in oncology is the development of innovative therapies for such poor prognosis tumors. In this context, we study the anticancer effects of a dagger 2-TGZ, a compound derived from troglitazone (TGZ), on cell models of these tumors. In MDA-MB-231 and Hs578T "claudin-1-low" TNBC cells, Delta 2-TGZ treatment induced claudin-1 protein expression and triggered apoptosis as measured by FACS analysis (annexin V/PI co-staining). Interestingly, in the non-tumorigenic human breast epithelial cell line MCF-10A, the basal level of claudin-1 was not modified following Delta 2-TGZ treatment, which did not induce apoptosis. Furthermore, claudin-1-transfected MDA-MB-231 and Hs578T cells displayed a significant increase of cleaved PARP-1 and caspase 7, caspase 3/7 activities, and TUNEL staining. RNA interference was performed in order to inhibit Delta 2-TGZ-induced claudin-1 expression in both the cells. In absence of claudin-1, a decrease of cleaved PARP-1 and caspase 7 and caspase 3/7 activities were observed in MDA-MB-231 but not in Hs578T cells. Claudin-1 overexpression and Delta 2-TGZ treatment are associated to apoptosis in MDA-MB-231 and Hs578T "claudin-1-low" TNBC. Moreover, in MDA-MB-231 cells, claudin-1 is involved in the pro-apoptotic effect of Delta 2-TGZ. Our results suggest that claudin-1 re-expression could be an interesting therapeutic strategy for "claudin-1-low" TNBC.