Neuroblastoma is the childhood
malignancy that mainly occurs in adrenal glands and is found also in the neck, chest, abdomen, and pelvis. New therapeutic strategies are urgently needed for successful treatment of this pediatric
cancer. In this investigation, we examined efficacy of the
retinoid N-(4-hydroxyphenyl)
retinamide (4-HPR) and the isoflavonoid
genistein (GST) alone and also in combination for controlling the growth of human malignant
neuroblastoma SK-N-BE2 and SH-SY5Y xenografts in nude mice. Combination of
4-HPR and GST significantly reduced
tumor volume in vivo due to overwhelming apoptosis in both
neuroblastoma xenografts. Time-dependently, combination of
4-HPR and GST caused reduction in
body weight,
tumor weight, and
tumor volume. Combination of
4-HPR and GST increased Bax:Bcl-2 ratio, mitochondrial release of Smac, downregulation of baculovirus inhibitor-of-apoptosis repeat containing (BIRC)
proteins including BIRC-2 and BIRC-3, and activation of
caspase-3 and
apoptosis inducing factor (AIF). Further, downregulation of
nuclear factor-kappa B (
NF-kappaB),
vascular endothelial growth factor (
VEGF), and
fibroblast growth factor 2 (
FGF2) was also detected. In situ immunofluorescent labelings of
tumor sections showed overexpression of
calpain,
caspase-12, and
caspase-3, and also AIF in the course of apoptosis. Combination
therapy increased apoptosis in the xenografts but did not induce kidney and liver toxicities in the animals. Results demonstrated that combination of
4-HPR and GST induced multiple molecular mechanisms for apoptosis and thus could be highly effective for inhibiting growth of malignant
neuroblastoma in preclinical animal models.