Natural products have been used and coveted for centuries for their “curative” properties. However, modern medicine seeks to evaluate deeper anecdotal and traditional remedies for actual healing properties. While the medicinal properties of the of the Indian long pepper (Piper longum) date back thousands of years, scientists were skeptical when relatively recent reports concerning the anticancer effects of the plant began to surface, but they diligently began to search for the potential underlying biological mechanisms.
Now, investigators at UT Southwestern Medical Center have uncovered the biochemical process behind the spicy Indian pepper plant’s cancer-thwarting assets. The secret lies in a chemical called piperlongumine (PL), which has shown activity against many cancers, including prostate, breast, lung, colon, lymphoma, leukemia, primary brain tumors, and gastric cancer. The UT Southwestern researchers were able to utilize x-ray crystallography to create molecular structures that show how the chemical is transformed after being ingested.
“We are hopeful that our structure will enable additional drug development efforts to improve the potency of PL for use in a wide range of cancer therapies,” noted senior study investigator Kenneth Westover, M.D., Ph.D., assistant professor of biochemistry and radiation oncology at UT Southwestern. “This research is a spectacular demonstration of the power of x-ray crystallography.”
The research team found that after ingestion PL is hydrolyzed to an active drug form (hPL), which inhibits glutathione S-transferase pi 1 (GSTP1), an enzyme that is frequently overexpressed in many cancerous tumors.
“This data in tandem with other information led to the conclusion that PL inhibits GSTP1, which forms covalent bonds between GSH [glutathione] and various electrophilic compounds, through covalent adduct formation at PL’s C7-C8 olefin, while PL’s C2-C3 olefin was postulated to react with GSH,” the authors wrote. “However, direct evidence for this mechanism has been lacking. To investigate, we solved the x-ray crystal structure of GSTP1 bound to PL and GSH at 1.1 Ångstrom resolution to rationalize previously reported structure activity relationship studies.”
The findings from this study were published recently in the Journal of Biological Chemistry in an article entitled “Structural and Biochemical Analyses Reveal the Mechanism of Glutathione S-Transferase Pi 1 Inhibition by the Anti-Cancer Compound Piperlongumine.”
The long pepper, a plant native to India, is found in southern India and Southeast Asia. Although rare in European fare, it is commonly found in Indian stores and used as a spice or seasoning in stews and other dishes. It dates back thousands of years in the Indian subcontinent and is tied to Ayurveda, one of the world's oldest medical systems; it was referred to by Hippocrates, the ancient Greek physician known as the father of medicine.
“This study illustrates the importance of examining and re-examining our theories. In this case, we learned something fundamentally new about a 3000-year-old medical claim using modern science,” Dr. Westover concluded.