The C-19 quassinoid eurycomalactone
(1) has recently
been shown to be a potent (IC50 = 0.5 μM) NF-κB
inhibitor in a luciferase reporter model. In this study, we show that 1 with similar potency inhibited the expression of the NF-κB-dependent
target genes ICAM-1, VCAM-1, and E-selectin in TNFα-activated
human endothelial cells (HUVECtert) by flow cytometry experiments.
Surprisingly, 1 (2 μM) did not inhibit TNFα-induced
IKKα/β or IκBα phosphorylation significantly.
Also, the TNFα-induced degradation of IκBα remained
unchanged in response to 1 (2 μM). In addition,
pretreatment of HUVECtert with 1 (2 μM) had no
statistically significant effect on TNFα-mediated nuclear translocation
of the NF-κB subunit p65 (RelA). Quantitative RT-PCR revealed
that 1 (0.5–5 μM) exhibited diverse effects
on the TNFα-induced transcription of ICAM-1, VCAM-1, and SELE genes since
the mRNA level either remained unchanged (ICAM-1, E-selectin, and
VCAM-1 at 0.5 μM 1), was reduced (VCAM-1 at 5 μM 1), or even increased (E-selectin at 5 μM 1). Finally, the time-dependent depletion of a short-lived protein
(cyclin D1) as well as the measurement of de novo protein synthesis in the presence of 1 (2–5
μM) suggested that 1 might act as a protein synthesis
inhibitor rather than an inhibitor of early NF-κB signaling.