The Ca2+ channel blocker flunarizine induces caspase-10-dependent apoptosis in Jurkat T-leukemia cells

Abstract

Flunarizine is a Ca2+ channel blocker that can be either cytoprotective or cytotoxic, depending on the cell type that is being examined. We show
here that flunarizine was cytotoxic for Jurkat T-leukemia cells, as well as for other hematological maligancies, but not for
breast or colon carcinoma cells. Treatment of Jurkat cells with flunarizine resulted in caspase-3 activation, poly (ADP-ribose)
polymerase cleavage, and laddering of DNA fragments, all of which are hallmarks of apoptosis. Flunarizine-induced DNA fragmentation
was inhibited by the caspase-3 inhibitor z-DEVD-fmk, the caspase-8/caspase-10 inhibitor z-IETD-fmk, and the caspase-10 inhibitor
z-AEVD-fmk, but was not reduced in caspase-8-deficient Jurkat cells, indicating the involvement of caspase-10 upstream of
caspase-3 activation. Interestingly, FADD recruitment to a death receptor was not involved since flunarizine caused DNA fragmentation
in FADD-deficient Jurkat cells. Flunarizine treatment of Jurkat cells also resulted in reactive oxygen species production,
dissipation of mitochondrial transmembrane potential, release of cytochrome c from mitochondria, and caspase-9 activation, although none of these events were necessary for apoptosis induction. Collectively,
these findings indicate that flunarizine triggers apoptosis in Jurkat cells via FADD-independent activation of caspase-10.
Flunarizine warrants further investigation as a potential anti-cancer agent for the treatment of hematological malignancies.

KeywordsApoptosis-Ca2+ channel-Caspase-10-Flunarizine-T-leukemia cell