The alkaloid, soyauxinium chloride, displays remarkable cytotoxic effects towards a panel of cancer cells, inducing apoptosis, ferroptosis and necroptosis.

The cytotoxic potential of a naturally occurring indoloquinazoline alkaloid, soyauxinium chloride (SCHL), was determined on a broad panel of animal and human cancer cell lines, including various sensitive and drug-resistant phenotypes. The cytotoxicity, SCHL-induced autophagic, ferroptotic, and necroptotic cell death were evaluated by the resazurin reduction assay (RRA). Caspase-Glo assay was used to detect the activity of caspases using spectrophotometric analysis. Flow cytometry was applied for cell cycle analysis (PI staining), apoptosis (annexin V/PI staining), mitochondrial membrane potential (MMP) (JC-1) and reactive oxygen species (ROS) (H2DCFH-DA). SCHL and doxorubicin (reference molecule) exhibited cytotoxic effects towards the 18 cancer cell lines tested. The IC50 values obtained ranged from 3.64 μM (towards CCRF-CEM leukemia cells) to 16.86 μM (against the BRAF-wildtype SKMel-505 melanoma cells for SCHL). Collateral sensitivity of the resistant HCT116 p53-/- colon adenocarcinoma cells to SCHL was observed as well as the normal sensitivity of CEM/ADR5000 leukemia cells, MDA-MB-231-BCRP breast adenocarcinoma cells and U87. MGΔEGFR glioblastoma cells. SCHL induced apoptosis in CCRF-CEM cells via caspases 3/7-, 8- and 9-activation, MMP alteration and increased ROS production, and otherwise ferroptosis and necroptosis. SCHL is a prominent cytotoxic alkaloid that should be further studied to develop a novel drug to combat cancers including refractory phenotypes.