Although the
indazole compound, YC-1, is reported to exert anticancer activities in several
cancer cell types, its target and mechanism of action have not been well explored. The objectives of this study were to ascertain whether YC-1 directly induces apoptosis in
prostate cancer cells and to explore the mechanism(s) whereby YC-1 causes cell death.
Hormone-refractory metastatic human
prostate cancer PC-3 cells were selected for this study. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium
bromide assay indicated that YC-1 suppresses growth of PC-3 cells in a concentration-dependent and time-dependent manner. Apoptosis was determined using
4',6-diamidino-2-phenylindole staining, and cell cycle progression was examined by FACScan flow cytometry. YC-1 treatment showed
chromatin condensation and increased the percentage of PC-3 cells in the hypodiploid sub-G0-G1 phase, indicative of apoptosis. Additionally, exposure to YC-1 was found to induce activation of
caspase-3 and cleavage of
poly(ADP-ribose) polymerase. Translocation and activation of
nuclear factor-kappaB (
NF-kappaB) were determined by immunofluorescent staining and ELISA, respectively. The results showed that YC-1 abolished constitutive nuclear translocation and activation of
NF-kappaB/p65. Furthermore, inhibition of inhibitor of kappaBalpha (
IkappaBalpha) phosphorylation and accumulation of
IkappaBalpha were observed. The antitumor effects of YC-1 were evaluated by measuring the growth of
tumor xenografts in YC-1-treated severe combined immunodeficient mice. The volumes of PC-3
tumors produced in severe combined immunodeficient mice were observed to decline significantly
after treatment with YC-1 compared with vehicle controls. We concluded that the antitumor effects of YC-1 in PC-3 cells include the induction of apoptosis and the suppression of
NF-kappaB activation. Given these unique actions, further investigations of the effects of YC-1 against
hormone-refractory
prostate cancer are warranted.