Phytomedicine 18 (2011) 199–204 Contents lists available at ScienceDirect Phytomedicine journal homepage: www.elsevier.de/phymed Stemona alkaloids, from traditional Thai medicine, increase chemosensitivity via P-glycoprotein-mediated multidrug resistance Wisinee Chanmahasathien a , Chadarat Ampasavate b , Harald Greger c , Pornngarm Limtrakul a,∗ a Department of Biochemistry, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand b Department of Pharmaceutical Science, Faculty of Pharmacy, Chiang Mai University, 50200, Thailand c Comparative and Ecological Phytochemistry Department, Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria article info Keywords: Stemona aphylla Stemona burkillii Stemocurtisine Oxystemokerrine Stemofoline P-glycoprotein abstract P-glycoprotein-mediated drug efflux can cause a multidrug resistance (MDR) phenotype that is associated with a poor response to cancer chemotherapy. Through bioassay-guided fractionation, active Stemona alkaloids were isolated from the roots of Stemona aphylla and S. burkillii. The chemical structures of iso- lated alkaloids were confirmed by HPLC, LC–MS and NMR as stemocurtisine and oxystemokerrine from S. aphylla, and stemofoline from S. burkillii. The isolated alkaloids were evaluated for synergistic growth inhibitory effect with cancer chemotherapeutic agents including vinblastine, paclitaxel and doxorubicin of KB-V1 cells (MDR human cervical carcinoma with P-gp expression), but not in KB-3-1 cells (drug sensi- tive human cervical carcinoma, which lack P-gp expression). Verapamil was employed as a comparative agent. The results showed that among these three isolated alkaloids; stemofoline exhibited the most potent effect in vitro in the reversal of P-gp-mediated MDR. Treatment with stemofoline at the vari- ous concentrations up to 72 h was able to significantly increase sensitivity of anticancer drugs including vinblastine, paclitaxel and doxorubicin in dose- and time-dependent manner in KB-V1 cells. The result obtained from this study indicated that Stemona alkaloids may play an important role as a P-gp mod- ulator as used in vitro and may be effective in the treatment of multidrug-resistant cancers. This is the first report of new pharmacological activity of Stemona alkaloids, which could be a new potential MDR chemosensitizer. © 2010 Elsevier GmbH. All rights reserved. Introduction Chemotherapy is the treatment of choice in many malignant tumors. Cancer cells may develop a multidrug resistant (MDR) phenotype in prolonged treatment. Multidrug resistance is a sig- nificant reason for failure in the treatment of cancer patients. It is often related to the overexpression of a 170 kDa plasma membrane glycoprotein (P-gp) encoded by the mdr1 gene. P-gp belongs to the superfamily of transporter protein containing an ATP-binding cassette. It is thought to function as a broad substrate ATP-dependent pump to reduce intracellular drug concentration below a cell-killing threshold (Gottesman et al. 1996; Litman et al. 2001; Ambudkar et al. 2003; Nobili et al. 2006). Overexpression of P-gp causes cancer cells to be resistant to a variety of structurally and functionally dissimilar anticancer drugs, such as vinblastine, doxorubicin and paclitaxel. The calcium channel blocker, verapamil, was the first compound able to enhance intracellular accumulation of many anticancer ∗ Corresponding author. Tel.: +66 53 945323; fax: +66 53 894031. E-mail addresses: plimtrak@mail.med.cmu.ac.th, porngarm@chiangmai.ac.th (P. Limtrakul). drugs such as vincristine, vinblastine, doxorubicin and daunoru- bicin (Tsuruo et al. 1981; Nobili et al. 2006). Since this original observation, many compounds have been shown to antagonize MDR in a variety of cell lines and in vivo tumor models when co-administered with chemotherapeutic agents to which the cells are resistant. In general, agents used to antagonize MDR, termed “chemosensitizers” or “resistance modifiers,” affect the drug accu- mulation defect present in MDR cells, and cause no potentiation of drug cytotoxicity in sensitive cells. The magnitude of chemosensi- tizers’ effects have been determined by comparing the IC 50 values for a cytotoxic drug in the absence and presence of a relatively non-toxic, fixed concentration of chemosensitizer (Ford and Hait 1990). However, the use of verapamil, quinidine, cyclosporine A, and other compounds of first-generation as MDR reverser was an intrinsic toxicity due to their pharmacological activity. The search for non-toxic second-generation modulators, such as dexverapamil, emopamil, PSC833, resulted in newer analogs of the first-generation agents, which more potent and considerably less toxic. Furthermore, a reduction in drug excretion to prolong terminal half-life, the third-generation P-gp inhibitors without pharmacokinetic interactions are in developments. These agents are currently being studied in clinical trials (Krishna and Mayer 2000; Leonard et al. 2003; Nobili et al. 2006). 0944-7113/$ – see front matter © 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.phymed.2010.07.014