Pak. J. Pharm. Sci., Vol.28 No.6, November 2015, pp.2191-2198 2191 REPORT Cytotoxic flavonoids from the young twigs and leaves of Caesalpinia bonduc (Linn) Roxb Olubanke Olujoke Ogunlana 1 , Wen Jun He 2 , Jun Ting Fan 2 , Guang Zhi Zeng 2 , Chang Jiu Ji 2 , Yu Quing Zheng 2 , Joseph Abayomi Olagunju 3 , Afolabi Akintunde Akindahunsi 4 and Ning Hua Tan 2* 1 Department of Biological Sciences, College of Science and Technology, Covenant University, PMB 1023, Ota, Ogun State, Nigeria 2 State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan, China 3 Department of Medical Biochemistry, Faculty of Basic Medical Sciences, College of Medicine, Lagos State University, Ikeja, Lagos State, Nigeria 4 Department of Biochemistry, Federal University of Technology, Akure, Nigeria Abstract: The extraction, fractionation and recognition of flavonoids from the ethanolic extract of young twigs and leaves of C. bonduc were carried out. In addition, cytotoxic study of the flavonoids on two cancer cell lines, BGC-823 and HeLa was carried our using sulphorhodamine B assay. Seven flavonoids, six of which are being reported for the first time in this plant, were isolated. Their structures were identified by MS and NMR spectroscopic methods. Petroleum ether, ethyl acetate and water fractions exhibited moderate cytotoxic activity against HeLa cells. Five compounds showed cytotoxic activity against HeLa cell in comparison with Paclitaxel, while only one compound showed a good degree of cytotoxic activity against BGC-823 cell in comparison to Paclitaxel. The results obtained showed a structure - activity relationship. Keywords: Caesalpinia bonduc; flavonoids; cytotoxic activity. INTRODUCTION The second leading cause of death in the United States of America is cancer; this is exceeded only by cardiovascular disease (Jemal et al., 2005). Since 1990, cancer incidence has resulted in a 22% increase in death rate in the four most frequent cancers namely, stomach, colorectal, lung and breast (Parkin et al., 2001). In the year 2000, more than nine million new cases of cancer were reported, resulting in, over six million death (Parkin et al., 2001). Caesalpinia bonduc, (family: Caesalpiniaceae, genus Fabaceae), commonly known as Gray Nicker nut (English) and Ayo (Yoruba, Nigeria), is a prickly shrub with a hard, grey, globular shaped and smooth shining surface seeds (Nadkarni, 1954). It is a medicinal plant predominantly dispersed in the tropical and subtropical parts of Africa, Asia and the Caribbean (Gupta et al., 2003). It has a lot of applications in folk medicine. The pharmacological screening of the plant extracts reveals their anticancer, antioxidant, antimalarial, antihyperglycemic, anti-inflammatory, antirheumatic, antipyretic and anticonvulsant activities (Adesina, 1982; Gupta et al., 2004; Sonibare et al., 2009). Jäger and Saaby (2011), recently reported the anti-depressant, anti-anxiety, memory inducer and relaxing enhancer of C. bonduc. Previous investigations on the phytochemical constituents from C. bonduc has led to the isolation of various compounds including Bonducellin (Purushothaman et al., 1982), Caesalpinia-F (Pascoe et al., 1986), Bonducellipins-A to -D (Peter et al., 1997), Caesalpin-G and -H (Peter et al., 1998), Caesalpinolide-A to -E (Yadav et al., 2007; Yadav et al., 2009) and others. As a result of the reported anticancer activity of C. bonduc against Ehrlich ascites carcinoma (Gupta et al., 2004) and the dearth of information on its bioactive constituents from Nigeria, this research work was proposed and implemented. This article describes the in vitro cytotoxic activity of extracts and flavonoids isolated from young twigs and leaves of C. bonduc obtained from Nigeria against BGC-823 (Human gastric carcinoma) and HeLa (Human cervical adenocarcinoma) cell lines. MATERIALS AND METHODS Plant material Young twigs and leaves of C. bonduc (Linn) Roxb. were collected from Forestry Research Institute of Nigeria (FRIN), Ibadan, Oyo state, Nigeria. Plant identification was done by Dr. Conrad Omonhinmi, Department of Biological Sciences, College of Science and Technology, *Corresponding author: e-mail: nhtan@mail.kib.ac.cn