Blister beetles produce cantharidin, a 10-carbon isoprenoid molecule that is highly bitter and is toxic to most animals. Because cantharidin is so bitter, it discourages predators, and its production may have been selected for in blister beetles because of this bitterness. The molecule is found in only two insect groups: blister beetles, which are members of the family Meloidea, and oedemerid beetles, which are members of the family Oedemeridae.
Cantharidin is thought to be produced via a common and important pathway in living organisms—the isoprenoid pathway. Isoprenoids are molecules made up of five-carbon building blocks, and they include many important compounds in organisms, including heme molecules, which are part of hemoglobin molecules, and cholesterol molecules, which are a precursor to steroid hormones. HMG-CoA reductase (HMGR) is a key enzyme in the isoprenoid pathway, which is why cholesterol-lowering medications called statins target HMGR.
Previous work by Yalin Zhang and colleagues at Northwest Agriculture and Forestry University in China confirmed that HMGR is an important component of the cantharidin-synthesis pathway in blister beetles. But not much is known about where or when cantharidin is synthesized in blister beetles, or how cantharidin production is related to HMGR transcripts. In a study published in April in the open-access Journal of Insect Science, Zhang and colleagues worked on adding to our knowledge of the synthesis and distribution of cantharidin in blister beetles by measuring amounts of HMGR and cantharidin in various tissues in male and female Epicauta chinensis blister beetles. “Our project sought to study how blister beetles produce cantharidin in their bodies,” Zhang commented, “and study how we can follow the pathway to produce cantharidin outside of the beetles.” Cantharidin has been used in traditional Chinese medicine for over 2,000 years for treating cancer. Cantharidin has been observed to inhibit human leukemic cells and breast cancer cells in vitro, and derivatives of cantharidin have been found to inhibit several types of cancer in cancer cell lines, including cervical, colon, and prostate cancers.