SP-1-161

**SP-1-161** is a preclinical pan-HDAC (histone deacetylase) inhibitor developed by Shuttle Pharmaceuticals as a radiation-sensitizing agent for cancer therapy. It activates the mutated ataxia-telangiectasia mutated (ATM) response pathway, selectively increasing sensitivity of cancer cells (e.g., MCF7 breast cancer cells) to ionizing radiation while protecting normal cells (e.g., 184A1 breast epithelial cells). This dual mechanism differentiates it from other HDAC inhibitors, positioning it as a potential direct chemotherapeutic or adjuvant to radiotherapy, particularly in breast cancer and cervical cancer models.[1][5][11][13]