Identification of Novel Radiosensitizers in a High-Throughput Cell-Based Screen for DSB Repair Inhibitors

摘要

Most cancer therapies involve a component of treatment which 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 radio-sensitization. Homologous recombination (HR) and nonhomologous end-joining (NHEJ) represent the two major pathways by 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 which selectively modulate NHEJ and HR repair in tumor cells. We identified a collection of novel hits which potently inhibit DSB repair, and we have validated their functional activity in comprehensive panel of orthogonal secondary assays. A selection of these inhibitors were found to radiosensitize cancer cell lines in vitro, which suggests they may be useful as novel chemo- and radio-sensitizers. Surprisingly, we identified several FDA-approved drugs, including the calcium channel blocker, mibefradil dihydrochloride, which 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 glioma radiosensitizer.