title: Identification of novel radiosensitizers in a high-throughput, cell-based screen for DSB repair inhibitors.
abstract: Most cancer therapies involve a component of treatment that inflicts DNA damage in tumor cells, such as double-strand breaks (DSBs), which are considered the most serious threat to genomic integrity. Complex systems have evolved to repair these lesions, and successful DSB repair is essential for tumor cell survival after exposure to ionizing radiation (IR) and other DNA-damaging agents. As such, inhibition of DNA repair is a potentially efficacious strategy for chemo- and radiosensitization. Homologous recombination (HR) and nonhomologous end-joining (NHEJ) represent the two major pathways by which DSBs are repaired in mammalian cells. Here, we report the design and execution of a high-throughput, cell-based small molecule screen for novel DSB repair inhibitors. We miniaturized our recently developed dual NHEJ and HR reporter system into a 384-well plate-based format and interrogated a diverse library of 20,000 compounds for molecules that selectively modulate NHEJ and HR repair in tumor cells. We identified a collection of novel hits that potently inhibit DSB repair, and we have validated their functional activity in a comprehensive panel of orthogonal secondary assays. A selection of these inhibitors was found to radiosensitize cancer cell lines in vitro, which suggests that they may be useful as novel chemo- and radio sensitizers. Surprisingly, we identified several FDA-approved drugs, including the calcium channel blocker mibefradil dihydrochloride, that demonstrated activity as DSB repair inhibitors and radiosensitizers. These findings suggest the possibility for repurposing them as tumor cell radiosensitizers in the future. Accordingly, we recently initiated a phase I clinical trial testing mibefradil as a glioma radiosensitizer.
authors.affiliation: Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Goglia
authors.affiliation: Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York.
authors.forename: Robert
authors.initials: R
authors.lastname: Delsite
authors.affiliation: High Throughput and Spectroscopy Resource Center, Rockefeller University, New York, New York.
authors.forename: Antonio N
authors.initials: AN
authors.lastname: Luz
authors.affiliation: Section of Medical Oncology, Yale Cancer Center, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: David
authors.initials: D
authors.lastname: Shahbazian
authors.affiliation: Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Ahmed F
authors.initials: AF
authors.lastname: Salem
authors.affiliation: Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Ranjini K
authors.initials: RK
authors.lastname: Sundaram
authors.affiliation: High Throughput and Spectroscopy Resource Center, Rockefeller University, New York, New York.
authors.forename: Jeanne
authors.initials: J
authors.lastname: Chiaravalli
authors.affiliation: Flow Cytometry Core Facility, Memorial Sloan Kettering Cancer Center, New York, New York.
authors.forename: Petrus J
authors.initials: PJ
authors.lastname: Hendrikx
authors.affiliation: Flow Cytometry Core Facility, Memorial Sloan Kettering Cancer Center, New York, New York.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Wilshire
authors.affiliation: Developmental Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York.
authors.forename: Maria
authors.initials: M
authors.lastname: Jasin
authors.affiliation: Section of Medical Oncology, Yale Cancer Center, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Harriet M
authors.initials: HM
authors.lastname: Kluger
authors.affiliation: High Throughput and Spectroscopy Resource Center, Rockefeller University, New York, New York.
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Glickman
authors.affiliation: Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York. ranjit.bindra@yale.edu powells@mskcc.org.
authors.forename: Simon N
authors.initials: SN
authors.lastname: Powell
authors.affiliation: Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut. ranjit.bindra@yale.edu powells@mskcc.org.
authors.forename: Ranjit S
authors.initials: RS
authors.lastname: Bindra
mesh_terms: D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects*; D004354:Drug Screening Assays, Antitumor; D049452:Green Fluorescent Proteins / Q000378:metabolism; D057166:High-Throughput Screening Assays / Q000379:methods*; D059765:Homologous Recombination / Q000187:drug effects; D006801:Humans; D010865:Pilot Projects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D015203:Reproducibility of Results; D054852:Small Molecule Libraries / Q000494:pharmacology
chemical_list: D011838:Radiation-Sensitizing Agents; D054852:Small Molecule Libraries; D049452:Green Fluorescent Proteins