Abstract B45: A cell-based screening to identify nucleolar disruptors in cancer cells

Abstract

Abstract Cancer cells require highly elevated levels of ribosome biogenesis to meet the demand for increased protein synthesis. Ribosome biogenesis, one of the most energy demanding processes, takes place in nucleoli. Notably, changes in number, size and morphology of nucleoli have been long recognized as a reliable feature of cancer cells. Interestingly, the nucleolus is well known to be a hub in the stress response. Approximately 70% of the ~4500 nucleolus-associated proteins are involved in functions other than ribosome biogenesis, including cell cycle control, apoptosis or DNA repair. This places the nucleolus as an important integrator between ribosome synthesis, cell cycle progression and stress signaling. A large variety of cellular insults trigger alterations in the dynamics of nucleolar proteins and/or ribosomal RNA. Stabilization of the tumor suppressor p53 has been observed as a result of the relocalization of certain ribosomal proteins in the nucleoplasm, notably L5 and L11, where they can bind and inhibit MDM2. The aim of this work is to identify new potential anti-tumoral drugs by means of disrupting the nucleolar integrity. By using a high content cell-based screening in which nucleolar morphology is monitored by GFP-L37, we have identified several compounds that cause nucleolar disruption thereby leading cancer cells to proliferative arrest or apoptosis. Interestingly, one of our best hits is compound 2,4,7,9-tetramethylbenzo[b][1,8]naphthyridin-5-amine (TMBNA). This compound has been previously reported by other investigators to intercalate DNA and to activate p53, although the underlying molecular pathway is unknown. Our data indicates that TMBNA activates p53 through nucleolar disruption and binding of the ribosomal protein L11 to MDM2, ultimately resulting in cell cycle arrest and apoptosis. These results highlight the relevance of the nucleolus as a main target of cancer drugs. Citation Format: Lucia Morgado-Palacin, Susana Llanos, Carmen Blanco-Aparicio, Diego Megias, Joaquin Pastor, Manuel Serrano. A cell-based screening to identify nucleolar disruptors in cancer cells. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr B45.