Neem Leaf Extract Induces Radiosensitization in Human Neuroblastoma Xenograft Through Modulation of Apoptotic Pathway

Induction of apoptosis is directly correlated with the biological effectiveness of ionizing radiation (IR). Accordingly, we investigated the efficacy of neem leaf extract (NLE) on IR-associated apoptotic transcriptional modulation and cell death in neuroblastoma (NB). NB xenografts exposed to single dose (SDR, 10 Gy) or fractionated (FIR, 2 Gy/d×5d) with or without NLE were examined for transcriptional activation of 84 apoptotic pathway genes using quantitative polymerase chain reaction. Apoptosis was measured using TdT nick-end labeling. FIR induced 55 and suppressed 10 genes, while SDR induced 49 and suppressed 5 genes. Of these, 46 and 4 genes were commonly up/down-regulated after FIR and SDR. NLE inhibited IR-induced NAIP, BIRC6, BIRC8, NOL3 and enhanced BAK1, BAX, BCL10, CASP1, CASP10 CARD8 and CRADD. Furthermore, NLE conferred FIR- and SDR-induced cell death. These data imply that NLE may exert radiosensitization by activating pro-apoptotic signaling and negating survival signaling and may thus potentiate radiotherapy in NB.