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Purpose: The identification of novel targets for developing synergistic drug-radiation combinations would pave the way to overcome tumor radioresistance. We conducted cell-based screening of a human kinome siRNA library to identify a radiation-specific kinase that has a synergistic toxic effect with radiation upon inhibition and is not essential for cell survival in the absence of radiation., Experimental Design: Unbiased RNAi screening was performed by transfecting A549 cells with a human kinome siRNA library followed by irradiation. Radiosensitizing effects of a target gene and involved mechanisms were examined., Results: We identified the nonreceptor protein tyrosine kinase FES (FEline Sarcoma oncogene) as a radiosensitizing target. The expression of FES was increased in response to irradiation. Cell viability and clonogenic survival after irradiation were significantly decreased by FES knockdown in lung and pancreatic cancer cell lines. In contrast, FES depletion alone did not significantly affect cell proliferation without irradiation. An inducible RNAi mouse xenograft model verified in vivo radiosensitizing effects. FES-depleted cells showed increased apoptosis, DNA damage, G 2 -M phase arrest, and mitotic catastrophe after irradiation. FES depletion promoted radiation-induced reactive oxygen species formation, which resulted in phosphorylation of S6K and MDM2. The radiosensitizing effect of FES knockdown was partially reversed by inhibition of S6K activity. Consistent with the increase in phosphorylated MDM2, an increase in nuclear p53 levels was observed, which appears to contribute increased radiosensitivity of FES-depleted cells., Conclusions: We uncovered that inhibition of FES could be a potential strategy for inducing radiosensitization in cancer. Our results provide the basis for developing novel radiosensitizers., (©2019 American Association for Cancer Research.)

PDGF-C, which is abundant in the malignant breast tumor microenvironment, plays an important role in cell growth and survival. Because tumor-associated macrophages (TAMs) contribute to cancer malignancy, macrophage survival mechanisms are an attractive area of research into controlling tumor progression. In this study, we investigated PDGF-C-mediated signaling pathways involved in anti-apoptotic effects in macrophages. We found that the human malignant breast cancer cell line MDA-MB-231 produced high quantities of PDGF-C, whereas benign MCF-7 cells did not. Recombinant PDGF-C induced PDGF receptor α chain phosphorylation, followed by Akt and Bad phosphorylation in THP-1-derived macrophages. MDA-MB-231 culture supernatants also activated macrophage PDGF-Rα. PDGF-C prevented staurosporine-induced macrophage apoptosis by inhibiting the activation of caspase-3, -7, -8, and -9 and cleavage of poly(ADP-ribose) polymerase. Finally, TAMs isolated from the PDGF-C knockdown murine breast cancer cell line 4T1 and PDGF-C knockdown MDA-MB-231-derived tumor mass showed higher rates of apoptosis than the respective WT controls. Collectively, our results suggest that tumor cell-derived PDGF-C enhances TAM survival, promoting tumor malignancy.

This study evaluated oxidative stress-induced apoptosis as a possible mechanism of arsenite toxicity in zebrafish liver cell line (ZFL cells). The heat shock protein 70 (HSP70), a chaperone protein, appears to provide protection against oxidative stress and apoptosis. Using the MTT assay, we demonstrated that survival of ZFL cells treated with arsenite for 24h decreased in a dose-dependent manner. The possible mechanisms that promote the cytotoxicity of arsenite were addressed. Cell viability assays revealed that arsenite caused a dose-dependent increase in cell death, and pretreatment of the ZFL cells with antioxidants blunted these effects. Antioxidants such as N-acetyl-cysteine (NAC, 5 mM) and dithiothreitol (DTT, 80 microM) significantly prevented ZFL cells from arsenite-induced death. Nuclear staining was performed using 1 microg/ml Hoechst, and cells were analyzed with a fluorescent microscope. Arsenite (30 microM) induced massive apoptosis that was identified by morphology and condensation and fragmentation of the nuclei of the ZFL cells. Pretreatment with NAC or DTT before arsenite insult effectively protected the cells against oxidative stress-induced apoptosis from the arsenite. Using a transfected human hsp 70 promoter-enhanced green fluorescent protein (EGFP) reporter, pHhsp70-EGFP, the induction of HSP70 against oxidative stress-induced apoptosis by arsenite was observed. The induction of HSP70 by arsenite increased in a dose-dependent manner, and pretreatment of transfected ZFL cells with NAC or DTT before arsenite insult reduced EGFP expression. Taken together, our results provide evidence that stimulation of the heat shock response is a sensitive biomarker of arsenic exposure and that arsenite causes oxidative stress-induced apoptosis in ZFL cells.