Ridaifen-G Induces Caspase-independent Atypical Cell Death

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 RIDG- treated U937 cells showed less DNA ladder formation than when treated with etoposide. In addition， Z-VADfmk 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 RIDG induces caspase-independent atypical cell death， which is accompanied by mitochondrial dysfunction.

CSTR: 32200.14.cjcb.2011.06.0005