The cytotoxic effect of 2-acylated-1,4-naphthohydroquinones on leukemia/lymphoma cells

Abstract

Here, we tested seven 2-acylated-1,4-hydronaphthoquinones for their cytotoxic effects on a panel of cancer lymphoma/leukemia cells and compared to a non-cancer origin cell line. Several naphthohydroquinones exhibited selective cytotoxic effects on lymphoma/leukemia cells with lowest activity on non-cancer cells. The mode of cell death induced by an acylated naphthohydroquinone, which has a long alkyl chain, was found to be via apoptosis. Furthermore, the naphthohydroquinone provoked mitochondria depolarization and activation of its downstream effector, caspase-3, thus implicating the intrinsic apoptotic pathway as its mechanism to exert cell death.

Keywords: Acylated hydroquinones; Anti-lymphoma; Apoptosis; Cytotoxicity; Photochemistry.

Figure 1

Seven naphthohydroquinones assayed for activity.

Figure 2

Compound 3, but no compound 7, induce PS translocation on human T-leukemic CEM cells.

Figure 3

Compound 3-mediated cytotoxicity appeared to be initiated via mitochondrial Δψm disruption on T-lymphocyte CEM cells. CEM cells were treated for 6 and 8 h with compound 3 and changes in the mitochondrial Δψm were determined by staining with the aggregate-forming lipophilic cationic fluorophore JC-1 and monitored via flow cytometry. In panel A, cells emitting green fluorescence signal (y-axis) versus treatment type (x-axis) are depicted. Panels B–E, representative flow cytometric dot plots used to determine the results depicted in A.

Figure 4

Compound 3 exerts its toxic activity via caspase-3 activation. To examine whether caspase-3 activation is involved in the cytotoxicity provoked by compound 3, a cell permeable fluorogenic substrate was used for detection. This caspase-3 substrate allows the detection of caspase-3 activity in living cells via flow cytometry. In panel A, the total numbers of cells with active caspase-3 are graphed along the y-axis, whereas different treatments are plotted along the x-axis. Panels B–E are representative flow cytometric dot plots used to determine the distribution of cells with active caspase-3, where the FL1 and FL2 detectors were set on the x- and y-axis, respectively.