ANTIPROLIFERATION EFFECTS OF SELECTED TANZANIA PLANTS

. Abstract Background : Plants still remain a prime source of drugs for the treatment of cancer and can provide leads for the development of novel anticancer agents. Our screening of indigenous medicinal plants from Tanzania has led to the identification of the number of anticancer activity. Material and methods : The current study investigates the cytotoxic activity of methanol extracts of one hundred and thirty seven Tanzania plants used locally for the traditional medicine herb using the MTS assay on the HepG2 cell lines. Result 16% of the tested plant extracts showed moderate to strong inhibitory activity with IC 50 values ranging from 17.1 ± 1.1 μg/ml to 79.2 ± 0.7 μg/ml ; meanwhile, ten extracts (7.3%) could demonstrate cytotoxic activity with IC 50 values less than 27.6 ± 2.0 μg/ml; twelve extracts (8.8%) could demonstrate cytotoxic activity with IC 50 values ranging from 30.4 ± 1.6 μg/ml to 79.2 ± 0.7μg/ml. Conclusion : Especially, a methanol extract from the bark extract of Erythrophleum zimmermannii (Fabaceae) was found to be the most cytotoxicity against HepG2 cell lines (IC 50 = 17.1 ± 1.1 μg/ml).


Introduction
Cancer is one of the most prominent human diseases which has stimulated scientific and commercial interest in the discovery of new anticancer agents from natural sources.Plants have formed the basis for the treatment of diseases in traditional medicine systems for many years, and continue to play a major role in the primary health care of about 80% of the world's inhabitants (Koduru et al, 2007).Research interest has focused on various plants that possess anticancer properties and this has led to the discovery and development of efficacious anticancer agents such as vinblastine and vincristine from Catharanthus roseus, and taxol from Taxus brevifolia (Noble, 1990).Although the use of ethnomedicines is widespread in Africa, many of these plants are yet to be investigated for their anticancer activity.This paper reports the cytotoxic activity of the methanol extracts of one hundred and thirty seven Tanzanian plants against HepG2 cells lines.

Plant material
All the tested methanol extracts of plants parcel out international biological material research centre, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, South Korea.Voucher specimens were deposited at the herbarium of the Research Institute of Bioscience and Biotechnology (KRIBB).

Cell culture and Cytotoxicity assay
Human hepatocarcinoma HepG2 cell lines were maintained in DMEM (Invitrogen, Carlsbad, CA) containing 10% heat-inactivated fetal bovine serum (FBS), 100 units/ml penicillin, 10 μg/ml streptomycin at 37℃ and 5% CO 2 .Cell-Counting Kit (CCK)-8 (Dojindo, Kumamoto, Japan) was used to analyze the effect of compounds on cell cytotoxicity.Cells were cultured overnight in 96-well plate (1 × 10 4 cells/well).Cell cytotoxicity was assessed after the addition of extracts in dose-dependent manner.After 24 h of treatment, 10μl of the CCK-8 solution was added to triplicate wells, and incubated for 1 h.Absorbance was measured at 450 nm to determine viable cell numbers in wells.

Statistical Analysis
All experiments were performed in triplicate.Statistical comparisons of results were made using analysis of variance (ANOVA).Significant differences between the means of control and sample treated cells were analyzed by Student's t-test.

Results
In our search for new classes of anti-cancer constituent from natural resources, we evaluated the anti-proliferative effects of one hundred and thirty seven Tanzania plants used locally for the traditional medicine herb extracts on HepG2 cell line in vitro.Out of the one hundred thirty seven plants tested, twenty-two plants exhibited cytotoxic activity with IC 50 values below 80μg/ml (Table 2), the plants are listed in alphabetical order of their family name, followed by the scientific name, morphological part used, as well as ethnomedicinal used of extract (Table 1).Twenty two plant species which belonging to eleven families were selected.Total of twenty two extracts of Tanzania plants were investigated for their cytotoxic activity against human cancer cell lines such as HepG2.In the US NCI plant screening program, a crude extract is  (7), Erythrophleum zimmermannii (8), Ficus altissima (9), Hypericum roepericanum (10), Khaya anthotheca (11), Landolphia owariensis (12), Monanthotaxis fornicate (14), Newtonia paucijuga (15), Spondias lutea (17), Uvaria leptocladon (19), Uvaria tanzaniae (20), Voacanga thouarsii (21) and Warbugia ugandensis (22) on which few or no phytochemical reports exist in the literatures, seem to be worthwhile.

Discussion and conclusions
Recently, there has been a global trend toward the use of natural phytochemical anticancer present in natural resources, such as herbs, vegetables, fruits and oilseeds (Mann, 2002).Herbs have begun as raw materials for finding new drugs (Lee et al., 2006).Herbal medicines derived from plants are increasingly being utilized to treat a wide variety of clinical diseases, even though relatively little is known about their modes of action.Until now, numerous plants and their constituents have already demonstrated cytotoxic activity (de Mesquita et al., 2009), illustrating that there is still potential for novel innovative cytotoxic activities to be identified from natural plant resources.Vincristine, irinotecan, etoposide, and paclitaxel are examples of plant-derived compounds that are being used in cancer treatment.The taxanes and the camptothecins are presently approved for human use in various countries (da Rocha et al., 2001).This study provides high potent cytotoxic activities of Alchornea hirtella (1), Cedrela odorata (3), Commiphora africana (4), Englerodendron usambarense (6), Entada rheedei (7), Erythrophleum zimmermannii (8), Khaya anthotheca (11), Spondias lutea (17), Toona ciliata (18) and Warbugia ugandensis (22) indicating their ultimate potential for pharmaceutical use among the test samples.Of those, three plants (4, 7 and 18) exhibited considerable anticancer activity (Ma et al., 2005;Nzowa et al., 2010;Zhang et al., 2012).
In conclusion, plants still remain a prime source of drugs for the treatment of cancer and can provide leads for the development of novel anticancer agents.Our screening of indigenous medicinal plants from Tanzania has led to the identification of the number of anticancer activity.

Table 1 :
List of plants used in the cytotoxicity test.

Table 2 :
In vitro cytotoxic activity of the methanol extracts on the HepG2 cell lines measured by the MTS assay a IC 50 : the concentration that caused 50% cell growth inhibition; b Data are presented as mean±SEM of at least three distinct experiments * Significantly different from control (p<0.05).