Lipid-restricted culture media reveals unexpected cancer cell sensitivities

Cancer cell culture models frequently rely on fetal bovine serum as a source of protein and lipid factors that support cell survival and proliferation; however, serum-containing media imperfectly mimics the in vivo cancer environment. Recent studies suggest that typical serum-containing cell culture conditions can mask cancer dependencies, for example on cholesterol biosynthesis enzymes, that exist in vivo and emerge when cells are cultured in media that provides more realistic levels of lipids. Here we describe a high-throughput screen that identified fenretinide and ivermectin as small molecules whose cytotoxicity is greatly enhanced in lipid-restricted media formulations. Mechanism of action studies indicate that the ivermectin-induced cell death involves oxidative stress, while fenretinide likely targets DEGS1, a lipid desaturase necessary for ceramide synthesis, to induce cell death. Notably, both fenretinide and ivermectin have previously demonstrated in vivo anticancer efficacy despite their low cytotoxicity under typical cell culture conditions. These studies reveal ceramide synthesis as a targetable vulnerability of cancer cells cultured under lipid-restricted conditions and suggest a general screening strategy for identifying additional cancer dependencies masked by culture conditions unrepresentative of the in vivo environment. DLD1 cells were cultured in 10% FBS or lipoprotein deficient serum and treated with Fenretinide or Ivermectin