Radiation mitigation of the intestinal acute radiation injury in mice by 1-[(4-nitrophenyl)sulfonyl]-4-phenylpiperazine

The objective of the study was to identify the mechanism of action for a radiation mitigator of the gastrointestinal (GI) acute radiation syndrome (ARS), identified in an unbiased high-throughput screen. We used mice irradiated with a lethal dose of radiation and treated with daily injections of the radiation mitigator 1-[(4-nitrophenyl)sulfonyl]-4-phenylpiperazine to study its effects on key pathways involved in intestinal stem cell (ISC) maintenance. RNASeq, quantitative reverse transcriptase-polymerase chain reaction, and immunohistochemistry were performed to identify pathways engaged after drug treatment. Target validation was performed with competition assays, reporter cells, and in silico docking. 1-[(4-Nitrophenyl)sulfonyl]-4-phenylpiperazine activates Hedgehog signaling by binding to the transmembrane domain of Smoothened, thereby expanding the ISC pool, increasing the number of regenerating crypts and preventing the GI-ARS. We conclude that Smoothened is a target for radiation mitigation in the small intestine that could be explored for use in radiation accidents as well as to mitigate normal tissue toxicity during and after radiotherapy of the abdomen. Significance statement Exposure to lethal doses of ionizing radiation manifests in a symptom complex that is summarized as acute radiation syndrome (ARS) and the extent of radiation damage to the hematopoietic and gastrointestinal (GI) systems codetermine the acute survival of the exposed individual. So far, no person who experienced a full-scale GI-ARS has ever survived. This creates a—so far—mostly unmet need to develop countermeasures that mitigate the effects of lethal radiation doses when given after radiation exposure. This study presents that a piperazine compound prevents GI-ARS in mice when given 24 hours after a lethal dose of radiation and uncovers the underlying mechanism of action, thus providing a basis for a future rational development of effective radiation mitigators.