Abstract:
Cancer is the second leading cause of death globally. Several chemotherapeutic agents
used for the treatment of cancer have many side effects. This necessitated a search for
new potent chemotherapeutic agents with high selectivity in order to minimise the
occurrence of debilitating side effects. This led to the ethnobotanical survey of plants
used for treatment of cancer in Akinyele Local Government area of Oyo State. This
study was aimed at evaluating the cytotoxicity of the selected plants, isolate and
characterise their active constituents.
Different morphological parts of six plants selected from the survey were macerated
separately in redistilled methanol at room temperature (26-33 oC) and evaluated for
preliminary in vitro cytotoxicity using Brine Shrimp Lethality (BSL) assay and MTT
(3(4,5-dimethylthiazol-2-yl)-2diphenyltetrazoliumbromide) colorimetric assay against
human carcinoma Rhabdomyosarcoma (RD), breast (AU565), cervix (Hep-2C) and
African green monkey kidney epithelial (normal) cell lines. Cyclophosphamide and
doxorubicin were used as standards. The two most active plants, Aframomum
melegueta seeds (Ams) FHI 112374 and Strophanthus hispidus whole plant (Shw) FHI
112443 were selected based on their significant cytotoxic activities. The Methanolic
extracts of Ams and Shw were successively partitioned into n-hexane,
dichloromethane and ethyl acetate fractions and screened against cancer cell lines. The
active fractions of Ams and Shw were then subjected to various chromatographic
techniques (Vacuum Liquid Chromatography, column chromatography, HPLC) for
isolation of bioactive compounds. Isolated compounds were characterised using
spectroscopic techniques (UV, IR, and 1D and 2D NMR). Data were analysed using
one-way ANOVA and Dunnet Multiple Comparison test at α0.05.
The Methanolic extracts of Ams and Shw showed significant BSL activity at LC50 of
7.22±0.01 and 9.23±0.12 µg/mL, respectively. The Ams hexane fraction had the best
cytotoxic activity with LC50 of 2.27±0.18 µg/mL against brine shrimp. Strophanthus
hispidus whole plant (CC50 of 2.94±0.01; 1.66±0.03 µg/mL) and Ams (CC50 =
5.18±2.10 and 9.74±0.16 µg/mL) had good cytotoxic activity on RD and Hep -2C,
respectively. The Ams hexane (CC50 of 0.98±0.1 µg/mL) showed significant
cytotoxicity on RD cell, with a good selectivity of 98.97 compared to
iii
cyclophosphamide (32.32). The n-hexane and dichloromethane fractions of Shw
showed cytotoxicity of 10.72±0.18 and 1.26±0.06 µg/mL on AU565 with selectivity of
1.31 and 1.92, respectively. The Ams hexane afforded compounds 6-shogaol (1), 6-
paradol (2), 1-dehydrogingerdione (3), while Ams dichloromethane afforded zingerone
(4), 6-gingerol (5), [6]-isodehydrogingerdione (6), (Z)-3-hydroxy-1-(4-hydroxy-3-
methoxyphenyl) dec-3-en-5-one (7). The Shw hexane afforded Daucosterol (8),
stigmasterol (9) and a novel compound; 2-(4-ethoxy-3-methoxyphenyl)-5-hydroxy 3,7,8-trimethoxy-4H-chromen-4-one (10), while Shw dichloromethane afforded
pityriacitrin (11), ursolic acid (12), strophanthidin digitoxoside (13) and urs-12-en-28-
oic acid, 2,3,23,-trihydroxy-(2β,3β,4α) (14). Compound 1 showed significant
cytotoxicity (CC50 = 0.11±0.01 µg/mL) on RD with selectivity of 215.45, while ursolic
acid (CC50 = 8.07 ± 0.02 µM) and strophanthidin-digitoxoside (CC50 = 11.42 ± 0.60
µM) had highest cytotoxicity on AU565 both with selectivity ˃100.
Aframomum melegueta seeds and Strophanthus hispidus whole plant exhibited
significant cytotoxic properties. Ursolic acid, strophanthidin-digitoxoside isolated from
Strophanthus hispidus and 6-shogaol isolated from Aframomum melegueta could serve
as leads in anticancer drug discovery.
