Upregulating DAB2IP Expression via EGR-1 Inhibition, A New Approach for Overcoming Fractionated-irradiation-induced Cross-tolerance to Ionizing Radiation and Mitomycin C in Tumor Cells

<b>Purpose:</b> In this study, we evaluated the effect of fractionated irradiation (FI) on tumor cells sensitivity to ionizing radiation (IR) and antineoplastic drugs, and examined the potential of early growth response-1 (EGR-1) inhibition to sensitize tumor cells to IR. <b>Materials and methods:</b> PC3 and HepG2 cells were subjected to γ-rays at 2 Gy for ten times. Survived cells were named PC3/R and HepG2/R, respectively. Cells sensitivity to irradiation and chemotherapeutic drugs, including cisplatin (PT), doxorubicin (DOX), mitomycin C (MMC) and 5-fluorouracil (5-FU) were identified by colony formation assay and MMT method, respectively. Quantitative real-time polymerase chain reaction (RT-qPCR) analysis was utilized to compare the difference of gene expression between radioresistant cells and parental cells. The small interfering RNA system was implemented to inhibit endogenous EGR-1 expression in radiation resistant cells. Western blot was employed to identify the possible mechanism by which EGR-1 regulates cells radiosensitivity. <b>Results:</b> FI induced cross-resistant to IR and MMC in tumor cells. Along with the reduction of ovarian cancer-2/disabled homolog 2 (DOC-2/DAB2) interactive protein (DAB2IP) expression, EGR-1 gene was upregulated in FI-treated cells. On the other hand, downregulation of EGR-1 gene expression sensitized radioresistant cells to IR accompanied by DAB2IP overexpression and STAT3 inactivation. In addition, NF-κB inhibitor, BAY11-7082 enhanced resistant cells radiosensitivity and chemosensitity. <b>Conclusions:</b> Conventionally FI has a higher risk of forming acquired radioresistance (ARR) in vitro. EGR-1 gene-targeted drug design could be an effective strategy to overcome DAB2IP-dysregulation induced ARR in tumor patients.