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De Toni, Enrico N.; Ziesch, Andreas; Rizzani, Antonia; Török, Helga-Paula; Hocke, Sandra; Lü, Shuai; Wang, Shao-Chun; Hucl, Tomas; Göke, Burkhard; Bruns, Christiane; Gallmeier, Eike (2016): Inactivation of BRCA2 in human cancer cells identifies a subset of tumors with enhanced sensitivity towards death receptor-mediated apoptosis. In: Oncotarget, Vol. 7, No. 8: pp. 9478-9491
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Abstract

Purpose: DNA repair defects due to detrimental BRCA2-mutations confer increased susceptibility towards DNA interstrand-crosslinking (ICL) agents and define patient subpopulations for individualized genotype-based cancer therapy. However, due to the side effects of these drugs, there is a need to identify additional agents, which could be used alone or in combination with ICL-agents. Therefore, we investigated whether BRCA2-mutations might also increase the sensitivity towards TRAIL-receptors (TRAIL-R)-targeting compounds. Experimental design: Two independent model systems were applied: a BRCA2 gene knockout and a BRCA2 gene complementation model. The effects of TRAIL-R-targeting compounds and ICL-agents on cell viability, apoptosis and cell cycle distribution were compared in BRCA2-proficient versus -deficient cancer cells in vitro. In addition, the effects of the TRAIL-R2-targeting antibody LBY135 were assessed in vivo using a murine tumor xenograft model. Results: BRCA2-deficient cancer cells displayed an increased sensitivity towards TRAIL-R-targeting agents. These effects exceeded and were mechanistically distinguishable from the well-established effects of ICL-agents. In vitro, ICL-agents expectedly induced an early cell cycle arrest followed by delayed apoptosis, whereas TRAIL-R-targeting compounds caused early apoptosis without prior cell cycle arrest. In vivo, treatment with LBY135 significantly reduced the tumor growth of BRCA2-deficient cancer cells in a xenograft model. Conclusions: BRCA2 mutations strongly increase the in vitro-and in vivo-sensitivity of cancer cells towards TRAIL-R-mediated apoptosis. This effect is mechanistically distinguishable from the well-established ICL-hypersensitivity of BRCA2-deficient cells. Our study thus defines a new genetic subpopulation of cancers susceptible towards TRAIL-R-targeting compounds, which could facilitate novel therapeutic approaches for patients with BRCA2-deficient tumors.