The sesquiterpene lactone thapsigargin is found in the plant Thapsia garganica L., and is one of the major constituents of the roots and fruits of this Mediterranean species. In 1978, the first pharmacological effects of thapsigargin were established and the full structure was elucidated in 1985. Thapsigargin is a potent inhibitor of Sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) and is widely used to study Ca2+-signaling. Thapsigargin is a non-cell-type specific toxin with documented ability to kill a broad spectrum of cancer cell lines as well as normal endothelial cells, fibroblasts and osteoblasts. It induces a rapid and pronounced increase in the concentration of cytosolic calcium, due to blockade of the Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase (SERCA) pump to which it binds with high affinity. The increase in cytosolic calcium leads to induction of apoptosis and ensuing cell death. A prodrug, G-202 (mipsagargin) has been designed to target the blood vessels of cancer cells; the death of these blood vessels then leads to tumor necrosis. G-202 consists of a cytotoxic analog of thapsigargin coupled to a masking peptide which inhibits its biologic activity until proteolytic cleavage at the tumor site. The first clinical trials of this drug were initiated in 2008 for the treatment Advanced Solid Tumors.