LC-MS-based phytochemical characterization of an antiproliferative Daphne altaica stem bark extract

Abstract

Daphne altaica Pall. (Thymelaeaceae) is a deciduous shrub native to central Asia. The plant has long been used in traditional Kazakh Medicine to treat different types of cancer and ailments like rheumatism, common cold and sore throat. In a previous study, D. altaica stem bark extracts have been shown to possess antiproliferative activity in human esophageal squamous cell carcinoma, gastric carcinoma, hepatoma and cervical carcinoma cells [1]. In the current investigation, D. altaica stem bark was submitted to sequential extraction with n-hexane, dichloromethane (CH2Cl2) and methanol, and the extracts were tested for antiproliferative activity in human CCRF-CEM leukemia and MDA-MB-231 breast cancer cells. The most active CH2Cl2 extract was analyzed by LC-DAD-MSn and by LC-DAD-HRESIMS in positive mode. This allowed the unambiguous identification of the four diterpene orthoesters daphnetoxin,1,2-dihydrodaphnetoxin, gnidicin and excoecariatoxin, of the bis-coumarin daphnoretin (Fig. 1), and the tentative identification of 9 further diterpene orthoesters. All compounds were identified in D. altaica for the first time. Daphnane-type diterpene orthoesters are characteristic of the Thymelaceae family. For daphnetoxin, gnidicin, excoecariatoxin and some of the tentatively identified diterpene orthoesters, anticancer activity has been described [2, 3]. We found that 1,2-dihydrodaphnetoxin was moderately active in CCRF-CEM and MDA-MB-231 cells. Also, daphnoretin is known to possess anticancer effects in vitro [4, 5]. Therefore, it can be assumed that the identified constituents are of high relevance for the antiproliferative activity of the D. altaica CH2Cl2 extract.