siRNA mediated knockdown of Bcl-2 and low-dose taxol treatment in human glioblastoma U251MG cells induces apoptosis, inhibits cell invasion, angiogenesis, and tumor growth in nude mice

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RNA interference using siRNA is a powerful tool to knockdown the mRNA and thus protein level of a target gene. Taxol is an anti-cancer drug that binds to β-tubulin to prevent tumor cell division; however, higher doses of taxol may be toxic to normal cells. The anti-apoptotic molecule Bcl-2 is upregulated in cancer cells for protection from apoptosis. The aim of our present study was to downregulate Bcl-2 expression using cognate siRNA in a highly invasive glioblastoma cell line (U251MG) during a low-dose taxol treatment and to examine apoptosis, inhibition of cell invasion, angiogenesis, and tumor growth. Human glioblastoma U251MG cells were treated with 100 nM taxol or 100 nM Bcl-2 siRNA or both for 72 h. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting demonstrated around 80% knockdown of Bcl-2 mRNA and protein levels. Fluorescent activated cell sorting (FACS) analysis and the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay demonstrated apoptosis in almost 60% of cells after combination treatment with taxol and Bcl-2 siRNA. Matrigel invasion studies demonstrated a significant decrease in cell invasion after treatment with taxol and Bcl-2 siRNA. In vivo angiogenesis assays in immunocompromised mice showed complete inhibition of neo-vasculature after treatment with both agents. The combination treatment with taxol and Bcl-2 siRNA further demonstrated a remarkable decrease in growth of both subcutaneous and intracerebral tumors in nude mice. Taken together, the results of our study indicated that the combination treatment with taxol and Bcl-2 siRNA effectively induced apoptosis and inhibited cell invasion, angiogenesis, and tumor growth. Therefore, this combination therapeutic strategy offers a potential tool for the controlling the growth of human glioblastoma. This work was supported by the R01 CA-91460 grant from the NCI.