Phytochemical Investigation And Biological Activities Of Selected Species From Genus Cucumis In Ethiopia: A Combined Experimental And Computational Study

Abstract

The Genus Cucumis has been used in Ethiopia in a traditional medicine for the treatment of many diseases including cancer, cholera, diabetes, infectious diseases, malaria and respiratory tract disorders. In view of its traditional use, the leaves, stems, fruits and roots of C. ficifolius, fruits of C. dipsaceus and leaves of C. prophetarum were successively extracted with n-hexane/petroleum ether, EtOAc and methanol furnish 25 compounds.The compounds were identified using spectroscopic methods as cucurbitacin B (24), cucurbitacin D (26), α-spinasterol (58), isocucurbitacin D (100), 23,24- dihydroisocucurbitacin D (102), lignoceric acid (104), eicosane (105), stearic acid (106), 12-hydroxyoctacosa-9,13-dienoic acid (107), 13-hydroxyoctadeca-9,11-dienoic acid (108), kuguaglycoside E-3-acetate (109), octacosane (110), docosane (111), 17-(-5-ethyl-2,6- dihydroxy-6-methylhept-3-en-2-yl)-9-(hydroxymethyl)-13-methyl-1H cyclopenta[α]phenanthren-3-ol (112), erythrodiol (113), (9,12)-propyl icosa-9,12-dienoate (114), 2-heptylcyclohexanol (115), decanoic acid (116) and 1,3-dihydroxypropan-2-yl dodecanoate (117). Most of the compounds were new to the genus except compound 24, 26, 58, 100, 102 and 116. Compounds 157 (57.08%), 149 (54.90%), 166 (99.76%) and 105 (37.8%) were identified as a major constituent from the essential oils of the leaves, stems, fruits and roots of C. ficifolius, respectively. The essential oils of the leaves, stems and fruits of C. dipsaceus furnished hydrocarbons including compound 170 (33.40%), 173 (98.93%) and 166 (96.65%) as a major constituent, respectively whereas compound 166 (99.75%), 160 (96.31%) and 105 (51.79%) were identified from the essential oils of the leaves, stems and roots of C. prophetarum. The essential oils and isolated compounds were evaluated for their in vitro antibacterial activity using disc diffusion method. The essential oil of the leaves of C. dipsaceus exhibited better inhibition zone diameter (IZD) of 11.93±0.42 mm against E. coli while the other displayed modest activities compared with the positive control (ciprofloxacin). The n-hexane extract of the stem of C. ficifolius exhibited IZD of about 14.00±0.20 mm, 13.50 ±0.50 mm and 13.00 ± 0.50 mm against P. aeruginosa, S. pyogenes and E. coli at 400 µgmL-1 while root extract also displayed activity against P. aeruginosa and S. aureus with IZD of 14.00±0.10 mm and 13.67±0.53 mm respectively. Compound 58 showed IZD of 13.67±0.57, 15.00 ±0.10 and 13.33±0.57 mm against E. coli, P. aeruginosa and S. pyogenes respectively. The results of MTT assay against MCF-7 breast cancer cell lines revealed that EtOAc extract of the stem of C. dipsaceus showed better cytotoxicity relative to the other samples at low xvimicromolar concentrations (IC50 = 10.41 µg/mL) and comparable to standard drug (IC50 = 7.96 µg/mL). Compounds 109, 113, 24, 112, (26 & 100) and 102 exhibited better DPPH radical scavenging activities with IC50 values of 4.83, 7.09, 7.24, 7.99, 8.84 and 8.95 μgmL-1, respectively. The result was close to with ascorbic acid (IC50 = 2.31 µg/mL). The in silico molecular docking analysis of isolated compounds were done using AutoDock vina against DNA gyrase, protein kinase and human topoisomerase IIβ. Compounds 24 and 26 displayed binding affinity of −9.1 and −9.8 kcal/mol against DNA gyrase, respectively. Compounds 58 (-8.0 kcal/mol) and 112 (-7.6 kcal/mol) displayed better binding affinity against DNA gyrase compared to ciprofloxacin (-7.3 kcal/mol). The binding affinities of compounds 58, 26 and 109 were found to be -9.6, - 9.4 and -9.4 kcal/mol against human topoisomerase IIβ, respectively. Most of the isolated compounds obeyed Lipinski’s rule of five. Swiss ADME prediction has shown that compounds 104˗108, 111 and 115 inhibited CYP1A2 cytochromes, compounds 106, 107 and 108 inhibited CYP2C9 cytochromes, compounds 107 and 108 inhibited CYP2D6 cytochromes, while compounds 24, 26, 100 and 102 were found to inhibite CYP3A4 and substrate of permeability glycoprotein (P-gp). The toxicological prediction gave results of endpoints such as hepatotoxicity, carcinogenicity, immunotoxicity, mutagenicity, and cytotoxicity. The studied compounds were predicted to be non-hepatotoxic, non-mutageni, non-cytotoxicity and non-irritant. Therefore, the antibacterial, cytotoxic and radical scavenging activities displayed by the constituents of C. ficifolius C. dipsaceus and C. prophetarum corroborate the traditional use of this plant against bacteria and cancer.