Time dependent modulation of tumor radiosensitivity by a pan HDAC inhibitor: abexinostat

// Sofia Rivera 1, 2, 3 , Céline Leteur 1, 2 , Frédérique Mégnin 4 , Frédéric Law 1, 2 , Isabelle Martins 1, 2 , Ioana Kloos 5 , Stéphane Depil 5 , Nazanine Modjtahedi 1, 2 , Jean Luc Perfettini 1, 2 , Christophe Hennequin 6 and Eric Deutsch 1, 2, 3 1 Department of Radiotherapy, Gustave-Roussy Cancer Campus, Villejuif, France 2 INSERM 1030 Molecular Radiotherapy, Villejuif, France 3 Faculté de Médecine, Université Paris-Sud, Université Paris-Saclay, Le Kremlin-Bicêtre, France 4 INSERM U1196/UMR9187 CMIB, Institut Curie-Recherche, Université Paris Saclay, Le Kremlin-Bicêtre, France 5 IRIS: Institut de Recherches Internationales Servier, Suresnes, France 6 Department of Radiation Oncology, Hôpital Saint Louis, APHP, Paris, France Correspondence to: Eric Deutsch, email: eric.deutsch@gustaveroussy.fr Keywords: epigenetics, radiosensitivity modulation, HDAC inhibitors, non-small cell lung cancer, radiotherapy Received: July 22, 2016      Accepted: November 30, 2016      Published: January 25, 2017 ABSTRACT Despite prominent role of radiotherapy in lung cancer management, there is an urgent need for strategies increasing therapeutic efficacy. Reversible epigenetic changes are promising targets for combination strategies using HDAC inhibitors (HDACi). Here we evaluated on two NSCLC cell lines, the antitumor effect of abexinostat, a novel pan HDACi combined with irradiation in vitro in normoxia and hypoxia, by clonogenic assays, demonstrating that abexinostat enhances radiosensitivity in a time dependent way with mean SER10 between 1.6 and 2.5 for A549 and H460. We found, by immunofluorescence staining, flow cytometry assays and western blotting, in abexinostat treated cells, increasing radio-induced caspase dependent apoptosis and persistent DNA double-strand breaks associated with decreased DNA damage signalling and repair. Interestingly, we demonstrated on nude mice xenografts that abexinostat potentiates tumor growth delay in combined modality treatments associating not only abexinostat and irradiation but also when adding cisplatin. Altogether, our data demonstrate in vitro and in vivo anti-tumor effect potentiation by abexinostat combined with irradiation in NSCLC. Moreover, our work suggests for the first time to our knowledge promising triple combination opportunities with HDACi, irradiation and cisplatin which deserves further investigations and could be of major interest in the treatment of NSCLC.