Phytochemical research of the anticancer potential of Aloe turkanensis

Abstract. Adem FA, Yenessew A, Yusuf AO, Wanjohi JM. 2022. Phytochemical research of the anticancer potential of Aloe turkanensis. Asian J Nat Prod Biochem 20: 75-88. The number of people diagnosed with cancer is rising worldwide, particularly in Sub-Saharan Africa. The search for new cancer treatments continues to benefit greatly from nature as a rich supply of promising chemicals. The anticancer effects of quinones have made them a popular medicinal class among natural chemicals (e.g., daunomycin and doxorubicin). Aloe turkanensis Christian, like other members of the genus Aloe, is a good place to get quinones. Dried and powdered A. turkanensis rhizomes and leaves were cold percolated in a mixture of dichloromethane and methanol (1:1). The crude extracts significantly decreased the viability of the human extrahepatic bile duct cancer cell line (TFK-1). Twelve chemicals were isolated from the crude extracts through chromatographic separations on silica gel, Sephadex LH-20, and preparative TLC. Spectroscopic techniques such as UV, 1H, and 13C NMR, COSY, NOESY, HMBC, and HSQC were used to determine the structures of the isolated compounds. Two naphthoquinones [3,5,8-trihydroxy-2-methylnaphthalene-1,4-dione (1) and 5,8-dihydroxy-3-methoxy-2-methylnaphthalene-1,4-dione (2)], seven anthraquinones [chrysophanol (3), aloesaponarin I (4), aloesaponarin II (5), laccaic acid D methyl ester (6) helminthosporin (8) aloe-emodin (10) and ?-L-11-O-rhamnopyranosylaloe-emodin (11)], a pre-anthraquinone [aloesaponol I (7)] a pyrone derivative [feralolide (9)] and a benzoic acid derivative [3,4-dihydroxybenzoic acid (12)] were the chemicals that made up these substances. This study reported again that the Aloe genus produced the naphthoquinones [3,5,8-trihydroxy-2-methylnaphthalene-1,4-dione (1) and 5,8-dihydroxy-2-methoxy-2-methylnaphthalene-1,4-dione (2)]. In addition, this study made the first report of 3,5,8-trihydroxy-2-methylnaphthalene-1,4-dione (1) from the Asphodelaceae family. Human extrahepatic bile duct carcinoma (TFK-1) and liver cancer (HuH7) cell lines were used to test the extracted compounds for in-vitro anticancer activity. The anthraquinone aloe-emodin (10) and the naphthoquinone 5,8-dihydroxy-3-methoxy-2-methylnaphthalene-1,4-dione (2) showed significant inhibition against TFK-1 cell lines using the 3- [4,5-dimethylthiazol-2-yl]-2-,5-diphenyltetrazolium bromide (MTT) assay, with IC50 values of 6.0 and Aloesaponol I (7), a pre-anthraquinone, inhibited the development of TFK-1 cells with IC50 values of 10.0 µg/mL and HuH7 cells with 88.0 µg/mL. Both ?-L-11-O- rhamnopyranosyl aloe-emodin (11) and aloesaponarin II (4), an anthraquinone, decreased TKF-1 cell line viability with IC50 values of 23.0 and 34.0 µg/mL, and HuH7 cell line viability with IC50 values of 47.0 and 55.0 µg/mL, respectively. IC50 values of 46.0 µg/mL for helminthosporin (8) showed considerable inhibition of TFK-1 cell growth, although it did not affect HuH7 cells at those concentrations. Extrahepatic bile duct (TFK-1) and liver (HuH7) cancer cell lines are sensitive to these chemicals identified here for the first time. Before these chemicals can be established as potentially effective anticancer medicines, more research on normal cell lines and their mechanism of action is required.