Antiproliferative cardenolides from Periploca graeca

Area of Science:

• Natural Products Chemistry
• Pharmacology
• Medicinal Chemistry

Background:

• Periploca graeca L. (Asclepiadaceae) stems are a source of cardiotonic steroids.
• Cardiotonic steroids, including cardenolides, possess diverse biological activities.
• Understanding structure-activity relationships is crucial for drug development.

Purpose of the Study:

• To isolate and identify cardiotonic steroids from Periploca graeca.
• To evaluate the in vitro antiproliferative effects of these compounds on prostate cancer cells.
• To investigate the impact of stereochemistry (17alpha vs. 17beta) and glycosylation on antiproliferative activity.

Main Methods:

• Phytochemical investigation involving chloroform and chloroform-methanol stem extracts of Periploca graeca.
• Isolation and structural elucidation of nine cardiotonic steroids (six 17beta-cardenolides and three 17alpha-cardenolides).
• In vitro antiproliferative assays using the hormone-independent prostate cancer cell line PC-3 to determine IC50 values.

Main Results:

• Nine cardiotonic steroids were identified, including a new 17alpha-cardenolide (compound 5).
• Five 17beta-cardenolides with a 14beta-OH group and at least one sugar moiety demonstrated potent antiproliferative activity (IC50: 18-50 nM) against PC-3 cells.
• 17alpha-cardenolides exhibited significantly lower activity (IC50: 5.4-7.3 microM) compared to their 17beta-isomers, with glycosylation having minimal impact in the 17alpha series.

Conclusions:

• The study identified novel and known cardiotonic steroids from Periploca graeca.
• 17beta-cardenolides with specific structural features (14beta-OH, glycosylation) are potent inhibitors of prostate cancer cell proliferation.
• A significant difference in cytotoxicity exists between 17alpha- and 17beta-cardenolide isomers, representing a novel finding in cardenolide research.