The Molecular Mechanism of Ambrosin Induced Toxicity of Breast Cancer and Bladder Cancer Cells
Sesquiterpene lactones (STL) are lipophilic compounds synthesized as secondary metabolites in species across the plant kingdom, most notably in the family Asteraceae. One STL, found in North African Ambrosia maritima (A. maritima), and Caribbean Ambrosia hispida (A. hispida), is the compound ambrosin. Ambrosin exhibits several desirable pharmacologic characteristics, including compliance with the Rule of Five (RO5) pharmacokinetic profile. We have extracted ambrosin from A. maritima and A. hispida and demonstrated its cytotoxicity in bladder cancer and breast cancer cell lines in low micromolar ranges. Ambrosin also inhibited cancer stem cells and secondary spheroid formation of multiple bladder cancer and breast cancer cell lines. RNA Bru-Seq of ambrosin treated bladder cancer and breast cancer cells revealed a mitochondrial apoptotic gene signature as well as activation of glutathione metabolism, indicating the generation of reactive oxygen species (ROS). RNA Bru-Sequencing and drug target mapping also revealed potential antagonistic activity of ambrosin against the EGFR tyrosine kinase and Rho/Rac GTPases. Further studies showed that ambrosin inhibited EGFR auto-phosphorylation at tyrosine 1068 (Y1068) as well as the inhibition of Cdc42 GTPase and RhoC GTPase activity. These findings indicate novel mechanisms of action and justify further considerations for ambrosin pharmaco-development as a potential chemotherapeutic agent for advanced bladder cancer and triple negative breast cancer. Overall design: Two bladder cancer cell lines (UMUC5 and UMUC9) and two breast cancer cell lines (BT20 and MDA231) were treated with vehicle (Veh) or ambrosin (Amb) for 4h prior to harvest. Bromouridine labeling was performed 30 min prior to harvest for nascent RNA sequencing (Bru-seq).  Three replicates per condition were produced for a total of 24 samples.