TRPV1 and cancer: Polygodial (2), its epimer 49 and warburganal (24) were found to be agonists of the non-selective ion channel TRPV1 (transient receptor potential vanilloid 1), which is expressed on the cell surface of several cancer cell lines as well as on the mitochondrial membrane of different human cells [81,82,83,84,85,86,87,88,89,90,91].