ABSTRACT: We have investigated antitumor activities of Ridaifens (RIDs), which are a series of synthesized Tamoxifen (TAM) derivatives. In this study, we focused on one of RIDs, Ridaifen-G (RID-G), and investigated the cell death-inducing activity of it in four neoplastic hematopoietic cell lines, U937, Raji, THP-1, and IM-9 cells in
the presence or absence of a pan-caspase inhibitor, Z-VAD-fmk. The aim of this study is to characterize the mode of RID-G-induced cell death, as compared with a typical apoptosis of etoposide-treated U937 cells, which die mainly through mitochondria-mediated apoptotic pathway in a caspase-dependent manner. To obtain reliable results, we analyzed RID-G-induced cell death by four methods, i.e., MTT assay, MitoTracker staining, AnnexinV-FITC/Propidium Iodide double staining, and DNA ladder formation. These analyses revealed that RID-G-induced cell death is accompanied by mitochondrial dysfunction and executed in a caspase-independent manner except DNA ladder formation. Z-VAD-fmk did not suppress the death, but suppressed etoposide-induced apoptosis in U937 cells. In DNA ladder formation analysis, RID-G induced a smear of DNA fragmentation in Raji and THP-1 cells, and RID-G-treated U937 cells showed less DNA ladder formation than when treated with etoposide. In addition, Z-VAD-fmk showed different effects on these DNA fragmentations: it largely suppressed, partialy suppressed, and on the contrary, enhanced DNA fragmentaion in U937, THP-1, and Raji cells, respectively. These results suggest that RID-G induces caspase-independent atypical cell death, which is accompanied by mitochondrial dysfunction.
Chinese Journal of Cell Biology. 01/2011; 33:635–44.