Novel anticancer agents, kayeassamins CI from the flower of Kayea assamica of Myanmar Nwet Nwet Win a , Suresh Awale a , Hiroyasu Esumi b , Yasuhiro Tezuka a , Shigetoshi Kadota a, * a Institute of Natural Medicine, University of Toyama, 2630-Sugitani, Toyama 930-0194, Japan b National Cancer Center Research Institute East, 6-5-1 Kashiwa, Chiba 277-8577, Japan article info Article history: Received 2 July 2008 Revised 30 July 2008 Accepted 31 July 2008 Available online 6 August 2008 Keywords: Anti-austerity strategy Human pancreatic PANC-1 cells Anti-cancer agent Kayeassamin abstract A CHCl 3 -soluble fraction of 70% EtOH extract of the flower of Kayea assamica from Myanmar exhibited 100% preferential cytotoxicity (PC 100 ) against human pancreatic cancer PANC-1 cells under nutrient-deprived conditions at 1 lg/mL. Bioassay-guided fractionation and isolation afforded nine new coumarins, kayeassa- mins A (8), B (9), and CI(17), together with nine known coumarins (1018). The structures of these com- pounds were identified by extensive spectroscopic techniques as well as by comparison with published data. Absolute configuration at C-1 0 of 1 was established as S-configuration by the modified Mosher method. All the isolates were evaluated for their in vitro preferential cytotoxicity using novel anti-austerity strategy. Among them, the novel coumarins, kayeassamins A (8), B (9), D (2), E (3), and G (5) exhibited the most potent preferential cytotoxicity (PC 100 1 lM) in a concentration- and time- dependent manner and induced apop- tosis-like morphological changes of PANC-1 cells within 24 h of treatment. Based on the observed cytotox- icity, structure-activity relationships have been established. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Pancreatic cancer is the fifth leading cause of cancer death with a median survival of <6 months and a relative 5-year survival rate of 5.5%. In 2005, it was estimated that 22,926 men and women died of pancreatic cancer in Japan. 1,2 It is most intrinsically resistant to the conventional anticancer drugs in clinical use such as 5-fluoro- uracil, taxol, doxorubicin, cisplatin and camptothecin, and is a ma- jor cause of treatment failure in pancreatic cancer. Therefore, the development of effective adjunct strategies is urgently necessary. Gemcitabine currently represents the standard chemotherapeutic drug for metastatic and advanced disease, but it only leads to a modest improvement in quality of life and survival. 3 Pancreatic tu- mors are known to have poor angiogenesis that leads to insuffi- cient nutrition supply to the aggressively proliferating cancer cells. However, pancreatic cancer cells have inherent tolerance to survive under low nutrient conditions. Therefore, the ability of can- cer cells to tolerate nutrient starvation (austerity) is regarded as another critical factor for tumor progression under hypovascular conditions. Hence, an agent that can retard the cancer cells’ toler- ance to nutrient starvation (anti-austerity agent) was considered as a novel target in anticancer drug discovery. 4–7 In our continuing program to discover new anticancer agents based on a novel ‘anti-austerity strategy’, 8–12 we found that the CHCl 3 -soluble fraction of 70% EtOH extract of the flower of Kayea assamica King & Prain (Clusiaceae) collected from Myanmar, showed potent cytotoxicity to PANC-1 cells preferentially in nutri- ent-deprived conditions at 1 lg/mL. K. assamica is a slow growing, tall, evergreen tree and blooms from early in October to May. It is locally known as ‘Tharapi’ and has been used to reduce extreme hotness in the body, dizziness, dry skin, and fever. In India, the fruits of this species are used as a fish poison, and the aqueous ex- tract of the stem bark is used as remedy for treating fevers. The pollen is used for sores, fistulas, fever, and malaria. 13 Previous investigation of this plant reported cytotoxic and antimalarial alkylated coumarins from the bark, root bark, and fruit. 14 In the present study, we carried out bioassay-guided fractionation and isolation to identify preferentially cytotoxic anticancer agents, which afforded nine novel coumarins, kayeassamins A–I, together with nine known ones. Among the new compounds, kayeassamins A(8) and B (9) were reported in our preliminary communication. 15 In this paper, we report the isolation and identification of seven no- vel anticancer agents, kayeassamins C–I (1–7), together with the preferential cytotoxic activity of the isolated compounds. 2. Results and discussions 2.1. Isolation and identification The 70% EtOH extract of the flowers of K. assamica showed 100% preferential cytotoxicity (PC 100 ) against PANC-1 cancer cells under 0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2008.07.091 * Corresponding author. Tel.: +81 76 434 7625; fax: +81 76 434 5059. E-mail address: kadota@inm.u-toyama.ac.jp (S. Kadota). Bioorganic & Medicinal Chemistry 16 (2008) 8653–8660 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry journal homepage: www.elsevier.com/locate/bmc