"Using Old Solutions to New Problems - Natural Drug Discovery in the 21st Century", book edited by Marianna Kulka, ISBN 978-953-51-1158-0, Published: June 19, 2013 under CC BY 3.0 license

Chapter 6

Anticancer Properties of Phytochemicals Present in Medicinal Plants of North America

By Wasundara Fernando and H. P. Vasantha Rupasinghe
DOI: 10.5772/55859

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Anticancer Properties of Phytochemicals Present in Medicinal Plants of North America

Wasundara Fernando1 and H. P. Vasantha Rupasinghe1

1. Introduction

Cancer is one of the most severe health problems in both developing and developed countries, worldwide. Among the most common (lung, stomach, colorectal, liver, breast) types of cancers, lung cancer has continued to be the most common cancer diagnosed in men and breast cancer is the most common cancer diagnosed in women. An estimated 12.7 million people were diagnosed with cancer across the world in 2008, and 7.6 million people died from the cancer during the same year [1]. Lung cancer, breast cancer, colorectal cancer and stomach cancer accounted for two-fifths of the total cases of cancers diagnosed worldwide [1]. More than 70% of all cancer deaths occurred in low- and middle-income countries. Deaths due to cancer are projected to continuously increase and it has been estimated that there will be 11.5 million deaths in the year 2030 [1] and 27 million new cancer cases and 17.5 million cancer deaths are projected to occur in the world by 2050 [2]. According to Canadian cancer statistics, issued by the Canadian Cancer Society, it is estimated that 186,400 new cases of cancer (excluding 81,300 non-melanoma skin cancers) and 75,700 deaths from cancer will occur in Canada in 2012 [1]. The lowest number of incidences and mortality rate is recorded in British Columbia. Both incidence and mortality rates are higher in Atlantic Canada and Quebec [3].

More than 30% of cancers are caused by modifiable behavioral and environmental risk factors, including tobacco and alcohol use, dietary factors, insufficient regular consumption of fruit and vegetable, overweight and obesity, physical inactivity, chronic infections from Helicobacter pylori, hepatitis B virus (HBV), hepatitis C virus (HCV) and some types of human papilloma virus (HPV), environmental and occupational risks including exposure to ionizing and non-ionizing radiation [4].

Conventional treatment of cancer includes interventions such as psychosocial support, surgery, radiotherapy and chemotherapy [4]. Currently, the most commonly use cancer chemotherapy includes mainly alkylating agents, antimetabolites, antitumor antibiotics, platinum analogs and natural anticancer agents. However, due to the increasing rate of mortality associated with cancer and adverse or toxic side effects of cancer chemotherapy and radiation therapy, discovery of new anticancer agents derived from nature, especially plants, is currently under investigation. Screening of medicinal plants as a source of anticancer agents was started in the 1950s, with the discovery and development of vinca alkaloids, vinblastine and vincristine and the isolation of the cytotoxic podophyllotoxins [5] (Figure 01). The cool temperate climate of North America supports the growth of an enormous number of plant species which are important sources of unique phytochemicals having anticancer properties (Table 01). In this chapter, selected medicinal plants grown in the cool climate of North America (mainly Canada and USA) are discussed. The major bioactive phytochemicals and their mechanisms of action are also reviewed.

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(a) Vinblastine – [dimethyl (2β,3β,4β,5α,12β,19α)- 15-[(5S,9S)- 5-ethyl- 5-hydroxy- 9-(methoxycarbonyl)- 1,4,5,6,7,8,9,10-octahydro- 2H- 3,7-methanoazacycloundecino[5,4-b]indol- 9-yl] - 3-hydroxy- 16-methoxy- 1-methyl- 6,7-didehydroaspidospermidine- 3,4-dicarboxylate] (b) Vincristin – [(3aR,3a1R,4R,5S,5aR,10bR)-methyl 4-acetoxy-3a-ethyl-9-((5S,7S,9S)-5-ethyl-5-hydroxy-9-(methoxycarbonyl)-2,4,5,6,7,8,9,10-octahydro-1H-3,7-methano[1]azacycloundecino[5,4-b]indol-9-yl)-6-formyl-5-hydroxy-8-methoxy-3a,3a1,4,5,5a,6,11,12-octahydro-1H-indolizino[8,1-cd]carbazole-5-carboxylate] (c) Podophyllotoxin – [(10R,11R,15R,16R)-16-hydroxy-10-(3,4,5-trimethoxyphenyl)-4,6,13-trioxatetracyclohexadeca-1,3(7),8-trien-12-one]

Figure 1.

Some selected currently used phytochemical-based anticancer agents

PlantFamilyParts usedMajor bioactive compoundsGrowing regionsRef
Achyranthes aspera
(Devil’s Horsewhip)
AmaranthaceaeLeaf Triterpenoid saponinsUSA14
Annona glabra
(Pond apple)
AnnonaceaeLeaf and fruitAcetogeninsUSA15
Aralia nudicaulis
(Wild sarsaparilla)
AraliaceaWhole plantSteroids, sarsasapogenin, smilagenin, sitosterol, stigmasterol, pollinastrenol, glycosides, saponins, sarsasaponin parillin, smilasaponin, smilacin, sarsaparilloside, and sitosterol glucosideMainly Canada16
Aster brachyactis
(Rayless aster)
AsteraceaeAerial partsNot knownNorth America 17
Carduus nutans
(Nodding plumeless thistle)
AsteraceaeAerial partsLinalool derivatives, aliphatic acids, diacids, aromatic acids, and phenolsNorth America18, 19
Erythronium americanum
(Adder’s tongue)
LiliaceaeWhole plantAlpha-methylenebutyrolactoneNorth America20, 21
Eupatorium cannabinum
(Bonesets)
AsteraceaeWhole plant Sesquiterpene lactone, pyrrolizidine alkaloid, and flavonoid North America20, 21,19, 22
Foeniculum vulgare
(Wild pepper fennel)
ApiaceaeSeedα-pinene, anisic aldehyde, cineole, fecchone, limonene, and myrceneNorth America23
Hydrastis canadensis
(Orange root)
RanunculaceaeWhole plantIsoquinoline alkaloids (hydrastine, berberine, berberastine, candaline), resin and lactoneCanada, USA20, 21
Hypericum perforatum
(St. John’s wort)
ClusiaceaeFlower Hypericin and hyperforinUSA, Canada (British Columbia)24
Lactuca sativa
(Garden lettuce)
AsteraceaeLeaf Sesquiterpene lactoneUSA, Canada25
Lantana camara
(Wild sage)
VerbenaceaeWhole plantAlkaloids (camerine, isocamerine, micranine, lantanine, lantadene), phenols, flavonoids, tannins, saponins, and phytosterolsUSA26, 27, 28
Larrea tridentate
(Creosote bush)
ZygophyllaceaeWhole plantResins and lignansSouthwestern USA18, 29, 30
Linum usitatissimum
(Common Flax)
LinaceaeSeed Enterodiol, enterolactone, lignans, and omega-3 fatty acidsCanada, USA31, 32
Olea europrae
(Olive)
OleaceaeLeaf and oilOleuropein, hydroxytyrosol, hydroxytyrosol acetate, luteolin-7-O-glucoside, luteolin-4’-O-glucoside and luteolin, oleic acid and polyphenol USA33, 34, 35, 36, 37
Panax quinquefolius
(North American Ginseng)
AraliaceaeRoot, LeafGinsenosides and saponinsEastern North America20, 21
Plantago lanceolata
(Ribwort plantain)
PlantaginaceaeAerial partsPhenolics and flavonoidsCanada, USA38
Podophyllum peltatum
(Mayapple)
BerberidaceaeRhizome PodophyllotoxinsEastern North America39
Polygonatum multiflorum
(Tuber fleece flower)
PolygonaceaeWhole plantSaponin and flavonoid and vitamin AUSA20, 21, 40
Pyrus malus
(Apple)
RosaceaeBark and fruitQuercetin, catechin, flavonoid, coumaric and gallic acids, phloridzin and procyanidinNorth America21
Rhodiola rosea
(Golden root)
CrassulaceaeRhizome Monoterpene alcohols and their glycosides, cyanogenic glycosides, aryl glycosides, phenylethanoids, phenylpropanoids and their glycosides, flavonoids, flavonlignans, proanthocyanidins and gallic acid derivativesEastern Canada41, 42
Saponaria vaccaria
(Cowherb)
CaryophyllaceaeSeedFlavonoids, cyclopeptides, and bisdesmosidic saponinsWestern Canada43
Silybum marianum
(Milk thistle)
AsteraceaeDried fruit, seedSilymarin-polyphenoic flavolignans (silybin, isosilybin, silychristin, silydianin and taxifoline)Canada, USA44, 45
Sonchus arvensis
(Perennial sow-thistle)
AsteraceaeWhole plantAlkanes, n-alkenes, n-aldehydes and n-alcohols, shikimate metabolites, carotenoid-derived compounds, terpenoids, steroids, and phenolsCanada 46, 47
Tanacetum vulgare
(Tansy)
AsteraceaeAerial partsMonoterpenes, sesqueterpenes, and oxygenated sesqueterpenesCanada, USA 48
Taraxacum officinale
(Dandelions)
AsteraceaeRoot and leafSesquiterpene lactones, triterpenoids, sterols, tannins, alkaloids, inulin, caffeic acid, and flavonoidsNorth America 49
Taxus brevifolia
(Pacific yew tree)
TaxaceaeBarkTaxol (diterpene)Pacific Northwest50
Thuja occidentalis
(White cedar)
CupressaceaeWhole plant Flavonoid, tannin, and volatile oil Northeastern USA,
Eastern Canada
13, 51
Xanthium strumarium
(Cocklebur)
AsteraceaeFruit Sesquiterpene lactones (Xanthatin and Xanthinosin)Canada17

Table 1.

Medicinal plants with potential anticancer properties grown in North America

2. Pathophysiology of cancer

Cancer is a population of abnormal cells which divide without control, with the ability to invade other tissues. Cancer and some of the other chronic diseases share common pathogenesis mechanisms, such as DNA damage, oxidative stress, and chronic inflammation [10]. It is understood that both environmental factors and chemical carcinogens play a key role in the initiation and progression of cancer. Among the major environmental factors are asbestos, polluted air near industrial emission sources, exposure to secondary tobacco smoke, indoor air pollution such as radon, drinking water containing arsenic, chlorination by-products, and other pollutants [11]. Chemicals with carcinogenic activity can be classified as DNA reactive (e.g.: nitrogen mustards, chlorambucil, epoxides, aliphatic halides, aromatic amines), epigenetic (e.g.: chlordane, pentachlorophenol, hormones, cyclosporin, purine analogs), dichlorodiphenyltrichloroethane, phenobarbital, minerals (e.g.: asbestos), metals (e.g.: arsenic, beryllium, cadmium) and unclassified carcinogens (e.g.: acrylamide, acrylonitrile, dioxane) [12]. DNA-reactive carcinogens act in the target cells of tissue(s) of their carcinogenicity to form DNA adducts that are the basis for neoplastic transformation [12]. Epigenetic carcinogens lack chemical reactivity and hence, do not form DNA adducts. These carcinogens are produced in the target cells of tissue(s) of their carcinogenicity. Effects of epigenetic carcinogens indirectly lead to neoplastic transformation or enhance the development of tumors from cryptogenically transformed cells [12].

Carcinogenesis is a multi-step process consisting of tumor initiation, promotion and progression [13]. Cancer initiation can be blocked by activating protective mechanisms, either in the extracellular environment or intracellular environment by modifying trans-membrane transport, modulating metabolism, blocking reactive oxygen and nitrogen species, maintaining DNA structure, modulating DNA metabolism and repair, and controlling gene expression [10]. Tumor promotion is the second stage of carcinogenesis and is followed by tumor progression. Both stages can be suppressed by inhibiting genotoxic effects, favoring antioxidant and anti-inflammatory activity, inhibiting proteases and cell proliferation, inducing cell differentiation, modulating apoptosis and signal transduction pathways and protecting intercellular communications [10]. In addition, tumor progression can also be inhibited by affecting the hormonal status and the immune system in various ways and by inhibiting tumor angiogenesis [10].

3. In vitro anticancer activity of phytochemicals and extracts of medicinal plants

Cultured cancer-derived cell lines with comparison to normal healthy cell lines are commonly used to assess the anticancer properties of isolated phytochemicals and extracts of medicinal plants (Table 2). The anticancer properties of ethanolic extract of leaves, pulp and seeds of, Annona glabra (L.), commonly known as pond apple, were shown, using human drug-sensitive leukemia (CEM) and its multidrug-resistant-derived (CEM/VLB) cell lines [52]. The most potent anticancer activity was shown in the seed extract of A. glabra [52]. Both dried rhizome hexane extract and dried fruit hexane extract, partitioned from total methanol extract, of Aralia nudicaulis (L.) caused death of cancer cell lines such as human colon cancer cell (WiDr), human leukemia cell (Molt) and human cervix cancer cell (HeLa) at a lower concentration, than that of required for the death of normal cells [53]. Eupatoriopicrin, a sesquiterpene lactone isolated from Eupatorium cannabinum (L.) (Bonesets), indicated anticancer properties on FIO 26 (fibrosarcoma) cells with an IC50=1.5 µg/ml [22]. Methanolic extracts of Hypericum perforatum (L.) (St. Johns wort) possessed strong antiproliferative activity in the human prostate cell line (PC-3) and the major constituents, hyperforin and hypericin, synergistically contributed to the reduction of the PC-3 cells proliferation [24]. Maslinic acid, (Figure 2(a)) a triterpene from Olea europaea (L.) (Olive), has shown to be significantly inhibitory in cell proliferation of the human colorectal adenocarcinoma cell line (HT29) in a dose dependent manner [33]. The major components in the extract were identified to be oleuropein, hydroxytyrosol, hydroxytyrosol acetate, luteolin-7-O-glucoside, luteolin-4’-O-glucoside and luteolin [34] (Figure 2). All these phytochemicals inhibited the proliferation of cancer and endothelial cells with IC50, at the low micromolar range [37]. Methanolic leaf extract of Plantago lanceolata (L.) (Ribwort plantain) inhibited the growth of three different cell lines; human renal adenocarcinoma (TK-10), the human breast adenocarcinoma (MCF-7) and the human melanoma (UACC-62) cell lines and the MCF-7 was totally inhibited [54]. Further, the ethanolic extract of P. lanceolata (L.), produced by maceration with ethanol : water, showed significant antiproliferative activity on cervix epithelioid carcinoma (HeLa), breast adenocarcinoma (MCF-7), colon adenocarcinoma (HT-29) and human fetal lung carcinoma (MRC-5) [38]. Several chemical constituents (Figure 3) from Silybum marianum (Milkthistle) have been isolated and their cytotoxic and anticancer potential has been investigated, in vitro, using both cancer and normal healthy cell lines. Silymarin, isolated from seeds of S. marianum, is a mixture of series of flavolignans, major constituents being: silybin A and B, (also known as silibinin), isosilybin A and B, silychristin, and silydianin [55, 56].

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IC50: Concentration which inhibited 50% of cell proliferation; MOA: Mode of Action; BBCE: Bovine Brain Capillary Endothelial cells; T24: Human Urinary Bladder Carcinoma cells; MCF-7: Human Breast Adenocarcinoma cells; HL60: Human Promyelocytic Leukaemia cells; HT29: Colon Adenocarcinoma cells

(a) Maslinic acid - [(2a, 3b)-2,3-dihydroxyolean-12-en-28-oic acid]: (b) Oleuropein – [(4S,5E,6S)-4-[2-[2-(3,4-dihydroxyphenyl)ethoxy]-2-oxoethyl]- 5-ethylidene-6-[[(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)- 2-tetrahydropyranyl]oxy]-4H-pyran-3-carboxylic acid, methyl ester] : (c) Hydroxytyrosol – [4-(2-Hydroxyethyl)-1,2-benzenediol]: (d) Hydroxytyrosol acetate – [2-(3,4-dihydroxy)Phenyl ethyl acetate;4-[2-(Acetyloxy)ethyl]-1,2-benzenediol]: (e) Luteolin- 7-O-glucoside - [2-(3,4-dihydroxyphenyl)-5-hydroxy-4-oxo-4H-chromen-7-yl beta-D-glucopyranoside; 4H-1-benzopyran-4-one, 2-(3,4-dihydroxyphenyl)-7-(beta-D-glucopyranosyloxy)-5-hydroxy-; 2-(3,4-Dihydroxy-phenyl)-5-hydroxy-7-((2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-hydroxymethyl-tetrahydro-pyran-2-yloxy)-chromen-4-one] (f) Luteolin-4’-O-glucoside – [3',5,7-Trihydroxy-4'-(β-D-glucopyranosyloxy)flavone;2-(4-β-D-Glucopyranosyloxy-3-hydroxyphenyl)-5,7-dihydroxy-4H-1-benzopyran-4-one;2-[3-Hydroxy-4-(β-D-glucopyranosyloxy)phenyl]-5,7-dihydroxy-4H-1-benzopyran-4-one] (g) Luteolin - [2-(3,4-Dihydroxyphenyl)- 5,7-dihydroxy-4-chromenone]

Figure 2.

Major bio-active compounds present in Olea europaea (a,b,c,d,e,f and g) and Plantago lanceolata (f and g)

Silybin possessed a dose-dependent growth inhibitory effect on parental ovarian cancer cells (OVCA 433), drug-resistant ovarian cancer cells (A2780 WT) and doxorubicin (DOX)-resistant breast cancer cells (MCF-7) [55]. Both L and D diastereoisomers of silybin inhibited A2780 WT cell growth at low IC50 reported with L-diastereoisomer [55]. Furthermore, silybin potentiated the effect of Cisplatin (CDDP, a platinum analog; cis-diamminedichloroplatinum [II]) in inhibiting A2780 WT and CDDP-resistant cell growth. Cisplatin is an inorganic metal complex which acts as an alkylating agent [57]. Similar results recorded with doxorubicin (DOX) on MCF-7 DOX-resistant cells when silybin associated with doxorubicin. Doxorubicin ((7S,9S)-7-[(2R,4S,5S,6S)-4-amino-5-hydroxy-6-methyloxan-2-yl]oxy-6,9,11-trihydroxy-9-(2-hydroxyace tyl)-4-methoxy-8,10-dihydro-7H-tetracene-5,12-dione) is an anthracycline antibiotic isolated from Streptomyces peucetius var caesius [57]. The effect of silybin-CDDP and silybin-DOX combinations resulted in a synergistic action, as assessed by the Berembaum isobole method [55]. Silymarin demonstrated to have marked inhibition of cell proliferation with almost 50% inhibition in a time dependent manner on the human breast cancer cell line (MDA-MB 468), at 25 μg/mI concentration, after five days of treatment. Its potential anticancer activity was dose dependent and showed a complete inhibition of cancer cells at 50 and 75 μg/mI concentrations at the beginning of Day 2 of exposure [56]. Induction of apoptotic cell death of human prostate cancer (DU145) treated with silibinin is shown to be due to activation of caspase 9 and caspase 3 enzymes [58].

4. Evidence from animal studies for anticancer activity of North American medicinal plants

Anticancer and antiproliferative potential of some North American medicinal plants has also been studied in animal studies (Table 3). In vivo antitumor activities of Achyranthes aspera (L.) (Devil’s Horsewhip) on athymic mice, with are subcutaneous xenograft, harboring human pancreatic tumor were demonstrated, using the leaf extract. The leaf extract significantly reduced both tumor weight and volume in mice treated with leaf extract intraperitonealy [14]. Intravenous administration of 40 mg/kg body weight eupatoriopicrin, a sesquiterpene lactone present in E. cannabinum, significantly delayed the growth of tumor in Lewis lung tumour-bearing syngeneic C57B1 female mice [22]. A 70% inhibition of tumor growth in PC-3 cells, orthopedically implanted into the dorsal prostatic lobe in athymic nude mice, was observed, upon their receiving 15 mg/kg intraperitoneal H. perforatum methanolic extract [24]. Lantadene A is a pentacyclic triterpenoid, isolated from the weed, Lantana camara (L) [59]. Feeding of female Swiss albino mice (LACCA) with a dose of 50 mg/kg body weight of Lantadene A twice a week for 20 weeks, showed potential chemopreventive activity. This chemopreventive activity could be linked to the expression of transcriptional factors and a significant decrease in the mRNA expression of AP-1 and c-fos), NF-kB (p-65) and p53 was observed in Lantadene A treated mice skin tumors [59]. Silibinin decreased tumor multiplicity by 71% (P < 0.01) in wild type mice, but did not show any such considerable effect in iNOS-/- mice upon oral feeding of 742 mg/kg body weight silibinin for 5 days per week for 18 weeks [60]. Lesser effects of silibinin in iNOS-/- mice suggested that most of its chemopreventive and angiopreventive effects were through its inhibition of iNOS expression in lung tumors [60]. Treatment of a purified diet, containing 0.5% to 1.0% silibinin on a transgenic adenocarcinoma of are mouse prostate (TRAMP) model, decreased the weight of the tumor in both the prostate and seminal vesicle, when compared with control mice [61].

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IC50: Concentration which inhibited 50% of cell proliferation; MOA: Mode of Action; MCF-7: Doxorubicin-resistant breast cancer cells; OVCA 433: Parental ovarian cancer cells; A2780: Drug-resistant ovarian cancer cells; 22Rv1, LAPC4, LNCaP, DU 145: Human prostate cancer cells

(a) Silybin A – [(2R,3R)-3,5,7-trihydroxy-2-[(2R,3R)-3-(4-hydroxy-3-methoxyphenyl)-2-(hydroxymethyl)-2,3-dihydrobenzo[b] [1,4]dioxin-6-yl]chroman-4-one]: (b) Silybin B – [(2R,3R)-3,5,7-trihydroxy-2-[(2S,3S)-3-(4-hydroxy-3-methoxyphenyl)-2-(hydroxymethyl)-2,3-dihydrobenzo[b] [1,4]dioxin-6-yl]chroman-4-one]: (c) Isosilybin A –[(2R,3R)-3,5,7-Trihydroxy-2-[(2R,3R)-2-(4-hydroxy-3-methoxyphenyl)-3-(hydroxymethyl)-2,3-dihydrobenzo[1,4]dioxin-6-yl]-4-chromanone]: (d) (c) Isosilybin B –[(2R,3R)-3,5,7-Trihydroxy-2-[(2R,3R)-2-(4-hydroxy-3-methoxyphenyl)-3-(hydroxymethyl)-2,3-dihydrobenzo[1,4]dioxin-6-yl]-4-chromanone]: (e) Silychristin – [(2R,3R)-3,5,7-trihydroxy-2-[(2R,3S)-7-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-3-(hydroxymethyl)-2,3-dihydro-1-benzofuran-5-yl]-2,3-dihydrochromen-4-one]:

Figure 3.

Major bio-active flavonolignans present in Silybum marianum

Treatment of silibinin significantly decreased tumor angiogenesis and proliferation and also there was increased apoptosis in prostate tumor tissue samples in the TRAMP model [61]. The protective effect of silibinin was also demonstrated in mouse skin with tumors caused by acute and chronic UVB-exposure-caused mitogenic and survival signaling and associated biological responses [62]. Mice were treated with silibinin, either topically (9 mg in 200 ml acetone/mouse) or orally (1% of diet), and both administrations strongly inhibited UVB-induced skin tumorigenesis in a long-term study [62]. Thymine dimers are formed in DNA, immediately after UVB irradiation, and are considered as an early and important biomarker for UVB induced DNA damage [62]. A noticeable, 71% reduction (P < 0.001) of thymine positive cells was obtained in the mice treated with 1% (w/w) silibinin before the UVB exposure, compared with the UVB alone group [62]. Oral feeding of 200 mg/kg of silibinin for 5 days per week, for 33 days, significantly inhibited human non–small-cell lung cancer cells (NSCLC A549) tumor xenograft growth in nude mice, in a time-dependent manner [63]. This accounted for 58% (P = 0.003) reduction in tumor weight per mouse and intraperitoneal administration of 4 mg/kg doxorubicin, once a week for four weeks, showed 61% (P = 0.005) reduction in tumor weight. However, interestingly, in silibinin-doxorubicin combination, 76% (P = 0.002, versus control) decrease in tumor weight per mouse was observed, that which was significantly different from either treatment alone, showing enhanced efficacy [63].

5. Mode of action of selected phytochemicals of North American medicinal plants

Apoptosis (programmed cell death) is the principal mechanism through which unwanted or damaged cells are safely eliminated from the body. This programmed cell death is mediated via either an extrinsic apoptotic pathway or an intrinsic apoptotic pathway [65]. These two apoptosis signaling pathways differ in the origin of their apoptosis signal, but converge upon a common pathway [66].

The extrinsic pathway is initiated by the stimulation of the cell surface ‘death receptor’ due to the binding of death ligand and the intrinsic pathway is also known as the mitochondrial pathway in which an intracellular apoptotic signal initiates the process [68]. Various natural extracts, obtained from medicinal plants grown in North America, have been found to induce apoptosis pathways at different levels (Figure 4 and Table 04). Leaf extract of Achyranthes aspera activated caspase-3 and induced caspase-3 mRNA in tumor cells. It also decreased Akt-1 transcription, as well its phosphorylation. Suppression of pAkt-1 and a corresponding activation of caspase 3 by the leaf extract, induced apoptosis of tumor cells [14]. It was also found that maslinic acid, isolated from O. europaea, inhibited considerably the expression of Bcl-2 (B-cell lymphoma 2), whilst increasing that of Bax. Maslinic acid stimulated the release of mitochondrial cytochrome-c and activated caspase-9 and caspase-3 [33]. These results showed the activation of the mitochondrial apoptotic pathway, in response to the treatment of HT29 colon-cancer cells with maslinic acid. The major flavonoid present in P. lanceolata, luteolin-7-O-β-glucoside, as well as aglycon luteolin, acted as potent poisons for DNA topoisomerase I on cancer cell lines [54]. Silibinin (major bioactive component from S. marianum) markedly activated the DNA-PK-p53 pathway for apoptosis, in response to UVB-induced DNA damage [69]. DNA-PK pull-down assay showed that silibinin pre-treatment strongly increased binding of DNA protein kinase with p53 [69].

PlantExtraction solvent and concentrationType of cancer cell lineIC50 or growth reductionKey findingsRef.
Annona glabra
(Pond apple)
Ethanolic extract of lyophilized plant material in powder form Human drug-sensitive leukemia (CEM) and its multidrug-resistant-derived (CEM/VLB) cell linesLeaf-1.00 (CEM/VLB) Pulp-0.65 (CEM/VLB), Seed-0.10 (CEM/VLB) and Leaf-0.30 (CEM), Pulp-0.35 (CEM), Seed-0.07 (CEM) µg/mlIC50 values were significantly lower than Adriamycin (Doxorubicin) (CEM=0.13 μg/ml and CEM/VLB=13.4 μg/ml) indicates its potential for cancer drug discovery programs52
Aralia nudicaulis
(Wild sarsaparilla)
Methanol extracts of rhizome, stem, leaf and fruit were further partitioned with hexane, ethyl acetate, butanol and water WiDr (colon), Molt (leukemia), HeLa (cervix) Hexane rhizome extract 30.1 (WiDr), 7.0 (Molt), 33.33 (HeLa) µg/mlThe concentrations of Rhizome hexane and Fruit hexane required for normal cell death was significantly higher than those required for the cancer cells 53
Eupatorium cannabinum
(Bonesets)
Eupatoriopicrin concentrations of 0.1 - 50 µg/ml in 96% ethanol FIO 26 (Fibrosarcoma)1.5 µg/mlPossess significant anticancer activity22
Foeniculum vulgare
(Wild pepper fennel)
Not specifiedBreast (MCF-7), liver (HepG2)-Remarkable anticancer potential23
Hypericum perforatum
(St. John’s wort)
Methanolic extractProstate (PC-3)0.42 mg/mlExtract components synergistically contribute to the reduction of the PC-3 cells proliferation24
Linum
Usitatissimum
(Common flax)
Ethanol extractBreast (MCF-7, MDA-MB-231)Growth reduction of 15.8% in MCF-7 and 11.4% in MDA-MB-231 Significantly reduced cell growth and induced apoptotic cell death 31
Olea europrae
(Olive)
maslinic acid 0–100 µg/mLColon (HT29)28.8 µg/mlCell proliferation inhibition in a dose-dependent manner and causes apoptotic death 33
Aqueous extract and methanol artificial mixtureBreast (MCF-7), Human urinary bladder (T-24), Bovine brain (BBCE)72 (MCF-7), 100 (T-24), and 62 (BBCE) for aq. 565 (MCF-7), 135 (T-24), and 42 (BBCE) for methanol µg/mlAntiproliferative activity of the extracts should mainly be attributed to its identified phytochemicals 34
Plantago lanceolata
(Ribwort plantain)
Methanolic extractRenal (TK-10), breast (MCF-7), melanoma (UACC-62)"/>250 (TK-10), 47.2 (MCF-7), 50.6 (UACC-62) μg/mIGrowth of MCF-7 was totally inhibited54
Extracted by maceration with ethanol/water during 72 hr at room temperaturecervix epitheloid (HeLa),breast (MCF-7), colon (HT-29), fetal lung (MRC-5)172.3 (HeLa), 142.8 (MCF-7), 405.5 (HT-29), 551.7 (MRC-5) µg/mlShowed significant antiproliferative activity38
Rhodiola rosea
(Golden root)
Not specifiedUrinary bladder (RT4, UMUC-3, T24, 5637, J82)264 (RT4),100 (UMUC-3), 71 (T24), 151 (5637), 165 (J82) μg/mlSelectively inhibit the growth of cancer cell lines with minimal effect on nonmalignant cells41
Saponaria vaccaria
(Cowherb)
70% Methanol extractcolon (WiDr), breast (MDA-MB-231), lung (NCI-417), prostate (PC-3), nontumorigenic fibroblast BJ (CRL-2522) 3.8-9.4 (WiDr), 11.4-19.6 (MDA-MB-231), 12.6-18.4 (NCI-417) mg/mIDose-dependent growth inhibitory and selective apoptosis-inducing activity. Strong in a breast and a prostate cancer cell lines43
Silybum marianum
(Milkthistle)
silybin, a flavonoidDoxorubucin resistant breast (MCF-7), Parental ovarian (OVCA 433), Drug-resistant ovarian (A2780)4.8-24 μM (MCF-7), 14 & 20 μM - L & D diastereoisomers respectively (A2780)
25 μg/mI
Dose-dependent growth inhibitory effect on all three cell lines55
Silymarin at a dosages of 10- 75 μg/mI in ethanolBreast (MDA-MB 468)-
-
Inhibits the cell proliferation in a dose- and time dependent manner56
Silibinin in DMSOProstate (DU145)-Strongly inhibited activation of Stat3 and causes caspase activation and apoptotic death 58
Isosilybin A and BProstate (LNCaP, 22Rv1)
Prostate (DU 145)
Iso A:32 μM (DU 145)
Iso B:20 μM (DU 145)
Anti-prostate cancer activity mediated via cell cycle arrest and apoptosis induction69
Taraxacum officinale
(Dandelions)
Water (lyophilized or reconstituted)Acute T-cell leukemia (Jurkat clone E6-1), dominant-negative FADD Jurkat cells (clone I 2.1)-Effectively and selectively induced apoptosis in human leukemia cell lines in a dose and time dependent manner 49

Table 2.

Anti-cancer properties of phytochemicals and extracts of medicinal plants revealed from in vitro studies using cancer cell lines

PlantPreparationAnimal model usedDosageKey findingsRef.
Achyranthes aspera
(Devil’s Horsewhip)
5% suspension in hexane followed by extraction in acetone overnight and residue was dissolved in methanolAthymic nude mice50, 100 and 200 mg/kg extract in 1 ml PBS administered IPThe tumor weight and volume was significantly reduced in the mice treated for 36 days with 50 mg/kg. In one treated mouse tumor completely disappeared14
Eupatorium cannabinum
(Bonesets)
Eupatoriopicrin, a sesquiterpene lactoneSyngeneic C57B1 female micei.v. injection of 20 or 40 mg/kgSignificantly stronger growth delay of both lung tumours and fibrosarcoma22
Hypericum perforatum
(Orange root)
Methanolic extractHuman prostatic carcinoma cell line orthotopically implanted athymic male nude mice ip with a dose of 15 mg/kg dissolved in 1% DMSOInhibited tumor growth by 70% with no observed side effects24
Lantana camara
(Wild sage)
Lantadene A, pentacyclic triterpenoidFemale Swiss albino mice (LACCA)50 mg/kg body weight twice a week for 20 weeksActivity could be linked to the expression of transcriptional factors 59
Silybum marianum
(Milkthistle)
SilibininLung - Male B6/129-Nos2tm1Lau (iNOS-/-) and B6/129PF2 WT mice742 mg/kg body weight for 5 d/wk for 18 weeksSignificantly decreases urethane-induced tumor number and size in WT mice. Decreased tumor multiplicity in WT mice, but not in iNOS-/- mice 60
SilibininProstate - A transgenic adenocarcinoma of mouse prostate (TRAMP) modelPurified diet containing 0% and 1%
(w/w) silibinin until
Decreased the weight of tumor + prostate + seminal vesicle. Significantly decreased tumor angiogenesis and proliferation and increased apoptosis also.61
Topically applied silibinin in acetone or oral feeding of silibininSkin – mouse9 mg in 200 ml acetone/mouse or 1% in dietsilibinin (both topical and oral) strongly inhibited UVB-induced skin tumorigenesis in long-term study62
Silibinin
Skin - SKH-1 hairless mouse1% (w/w) silibinin in diet for 2 weeksStrong suppression of UVB-induced damage by dietary feeding of silibinin63
SilibininAthymic (BALB/c,nu/nu) male nude mice200 mg/kg body weight, 5 d/wk for 33 days
Significantly inhibits human NSCLC A549 tumor xenograft growth in a time dependent manner64

Table 3.

Anti-cancer properties of medicinal plants revealed from in vivo studies using experimental animals

media/image2.png

Figure 4.

Schematic representation of current knowledge of mode of action of some selected anticancer phytochemicals in North America (in a hypothetical cancer cell).

Akt (Protein kinase B); Bcl-2 (Protein kinase B); Bax (Bcl-2–associated X protein); Topo-1 (Topoisomerase 1); p53 (tumor protein 53); Ser15 (Serine 15); NF-kB (nuclear factor kappa-light-chain-enhancer of activated B cells); AR (Androgen Receptor)

  1. Methanolic leaf extract of Achyranthes aspera (MLAa) induces caspase -3 mRNA and suppress expression of the kinase Akt-1. Apoptosis is induced by activation of caspase-3 and inhibiting Akt-phosphorylation.

  2. The mechanism of Maslinic acid (MSA) (isolated from Olea europaea) is regulated via Bcl-2 inhibition and Bax induction, producing mitochondrial disruption, cytochrome-c release, leading finally to the activation of caspases 9 and caspase 3.

  3. Luteolin-7-O-β-glucoside and its aglycon, luteolin (major bio-active constituents of Plantago lanceolata) showed DNA topoisomerase I poison activities and Topoisomerase mediated DNA damage might be the possible mechanism which induce apoptosis.

  4. Silibinin (SBN) (extracted from Silybum marianum) pretreatment enhance DNA-PK (DNA Protein kinase) associated kinase activity as well as the physical interaction of p53 with DNA-PK and it preferentially activates the DNA-PK-p53 pathway for apoptosis.

  5. SBN inhibits active Stat3 phosphorylation, and causes caspase activation and apoptosis.

  6. Isosilybin A (ISBN) (extracted from Silybum marianum) activates apoptotic machinery in human prostate cancer cells via targeting Akt–NF-kB–AR axis.

  7. ISBN increases p53 protein levels.

PlantMode of actionReferences
Achyranthes aspera
(Devil’s Horsewhip)
Significantly induced caspase-3 mRNA and suppressed expression of the pro survival kinase Akt-1. Apoptosis was induced by activation of caspase-3 and inhibiting Akt phosphorylation.14
Olea europaea
(Olive)
Activation of the mitochondrial apoptotic pathway
Significant block of G1 to S phase transition manifested by the increase of cell number in G0/G1 phase
33
37
Plantago lanceolata
(Ribwort plantain)
The topoisomerase-mediated DNA damage seems to be a candidate mechanism, by which some flavonoids may exert their cytotoxic potential54
Silybum marianum
(Milkthistle)
Induces G1 arrest in cell cycle progression
Up-regulates DNA-protein kinase-dependent p53 activation to enhance UVB-induced apoptosis
Activates apoptotic machinery in human prostate cancer cells via targeting Akt–NF-kB–AR axis
Inhibits active Stat3 phosphorylation, and causes caspase activation
Increases total p53 levels
56
67
68
58
69
Podophyllum peltatum
(Mayapple)
Inhibition of microtubule assembly70

Table 4.

Mode of action of anticancer activity of phytochemicals present in selected North American medicinal plants

6. Conclusion

Currently, natural products, especially plant secondary metabolites such as isoprenoids, phenolics and alkaloids, have been demonstrated to be the leading providers of novel anticancer agents. Thiese important groups of phytochemicals represent a vast majority of chemical groups, including alkaloids, flavonoids, flavonols, flavanols, terpenes and terpenoids, phenols, flavonolignans and steroids. Potential anticancer properties of these phytochemicals have been shown by both cell culture (in vitro methods) and animal (in vivo methods) studies. However, in vitro and in vivo findings should be strengthened by valid human clinical trial data before introducing to the medicine cabinet as natural therapeutics or drugs.

Abbreviations

CEM, Human drug-sensitive leukemia cells; CEM/VLB, Human multidrug-resistant-derived leukemia cells; Jurkat clone E6-1, Acute T-cell leukemia cells; WiDr and HT29, Human colon cancer cells; Molt, Human leukemia cancer cell; FIO 26, Human fibrosarcoma cells; MCF-7 and MDA-MB-231, Human breast cancer cells; HepG2, Human hepatocarcinoma cells; LNCaP, 22Rv1, PC-3 and DU145, Human prostate cancer cells; RT4, UMUC-3, T24, 5637 and J82, Human urinary bladder cancer cells; BBCE, Bovine brain capillary endothelial cells, TK-10, Human renal cancer cells; UACC-62, Human melanoma cells; HeLa, Human cervical epithelioid cells; MRC-5, Fetal lung cancer cells; NCI-417, Human lung cancer cells; CRL-2522, Human nontumorigenic fibroblast cells; OVCA 433, Parental ovarian cancer cells; A2780, Drug-resistant ovarian cancer cells.

References

1 - Cancer Research UK and International Agency for Research on Cancer, Cancerstats Cancer Worldwide; 2011.
2 - American cancer society. Global Cancer Facts and Figures 2007. American Cancer Society, Atlanta; 2007.
3 - Canadian Cancer Society’s Steering Committee on Cancer Statistics. Canadian Cancer Statistics 2012. Toronto, ON: Canadian Cancer Society; 2012.
4 - Cancers, NMH Facts sheet. World Health Organization; 2010.
5 - Cragg, G. M. and Newman, D. J., Plants as a source of anti-cancer agents, Journal of Ethnopharmacology, 2005; 100: 72-79.
6 - Nobler, L., The discovery of the vinca alkaloids-chemotherapeutic agents against cancer. Biochem. Cell Biol. 1990; 68: 1344-1351.
7 - Jordan, M. A., Thrower, D. and Wilson L., Mechanism of Inhibition of Cell Proliferation by Vinca Alkaloids, Cancer Recearch, 1991; 51: 2212-2222.
8 - Krishan, A., Paika, K. and Frei E., Cytofluorometric Studies on the action of Podophyllotoxin and Epipodophyllotoxins (Vm-26, Vp-16-213) on the Cell Cycle Traverse of Human Lymphoblasts, Journal of Cell Biology, 1975; 66: 521-530.
9 - Nerendra Nagar1*, Rakesh K. Jat1, Rajkumar Saharan1, Sanjay Verma1, Daljeet Sharma1, Kuldeep bansal, Podophyllotoxin and their Glycosidic Derivatives, Pharmacophore, 2011; 2(2): 124-134.
10 - De Flora, S. and Ferguson, L. R., Overview of mechanisms of cancer chemopreventive agents, Mutation Research, 2005; 591: 8–15.
11 - Boffetta, P. and Nyberg, F., Contribution of environmental factors to cancer risk, British Medical Bulletin, 2003; 68: 71–94.
12 - Williams, G. M., Mechanisms of chemical carcinogenesis and application to human cancer risk assessment, Toxicology, 2001; 166: 3–10.
13 - Sebastian, M., Ninan, N., and Elias, E., Nanomedicine and Cancer therapies, Volume 2, Apple Academic Press., 2013.
14 - Subbarayan, P. R., Sarkar, M., Rao, S. N., Philip, S., Kumar, P., Altman, N., Reis, I., Ahmed, M., Ardalan, B. and Lokeshwar. B. L., Achyranthes aspera (Apamarg) leaf extract inhibits human pancreatic tumor growth in athymic mice by apoptosis, Journal of Ethnopharmacology, 2012; 142: 523–530.
15 - Cochrane, C. B., Nair, P. K. R., Melnick, S. J., Resek, A. P. and Ramachandran, C., Anticancer Effects of Annona glabra Plant Extracts in Human Leukemia Cell Lines, Anticancer Research, 2008; 28: 965-972.
16 - Wang, J., Li, Q., Ivanochko, G. and Huang. Y., Anticancer Effect of Extracts from a North American Medicinal Plant – Wild Sarsaparilla, Anticancer Research, 2006; 26: 2157-2164.
17 - Ramirez-Erosa, I., Huang, Y., Hickie, R. A., Sutherland, R. G. and Barl, B., Xanthatin and xanthinosin from the burs of Xanthium strumarium L. as potential anticancer agents, Can. J. Physiol. Pharmacol. 2007; 85: 1160-1172.
18 - Wilkins, A. L., Lu, Y. and Tan, S., Extractives from New Zealand Honeys. 4. Linalool Derivatives and Other Components from Nodding Thistle (Carduus nutans) Honey. J. A. Food Chem. 1993; 41: 873-878.
19 - Woerdenbag, H.J., Lemstra, W., Malingre, T.M. and Konings, A.W.T., Enhanced cytostatic activity of the sesquiterpene lactone eupatoriopicrin by glutathione depletion. Br. J. Cancer. 1989; 59: 68-75.
20 - Jitendra Jena, Rakesh Ranjan, Poonam Ranjan and Manoj Kumar Sarangi. A Study on Natural Anticancer Plants. International Journal of Pharmaceutical and Chemical Sciences 2012; 1 (1): 365 – 368.
21 - S. Madhuri and Govind Pandey. Some anticancer medicinal plants of foreign origin. Current Science 2009; 96(6): 779-78.
22 - Woerdenbag, H.J., Eupatorium cannabinum L. A review emphasizing the sesquiterpene lactones and their biological activity. Pharm Weekbland [Sci], I986; 8: 245-51.
23 - Timsina, B., Shukla, M. and Nadumane, V. K., A review of few essential oils and their anticancer property. Journal of Natural Pharmaceuticals, 2012; 3(1): 1-8.
24 - Martarelli, D., Martarelli, B., Pediconi, D., Nabissi, M. I., Perfumi, M. and Pompei. P., Hypericum perforatum methanolic extract inhibits growth of human prostatic carcinoma cell line orthotopicall yimplanted in nude mice. Cancer Letters, 2004; 210: 27–33.
25 - Han, Y. F., Cao, G. X., Gao X. J., and Xia. M., Isolation and characterisation of the sesquiterpene lactones from Lactuca sativa L var. anagustata. Food Chemistry, 2010; 120: 1083–1088.
26 - Kalita, S., Kumar, G., Karthik, L., Venkata, K. and Rao, B., Phytochemical Composition and In Vitro Hemolytic Activity of Lantana Camara L. (Verbenaceae) Leaves, Pharmacologyonline, 2011; 1: 59-67.
27 - Ghangale, G. D., Tambe, R.Y., Gaykar, A.J. and Dama G.Y., Antimitotic activity of Lantana Camara Flowers, International Journal of Institutional Pharmacy and Life Sciences, 2011; 1(1): 1-6.
28 - Patel, S., A weed with multiple utility: Lantana camara, Rev Environ Sci Biotechnol, 2011; 10: 341–351.
29 - Lambert, J. D., Sang, S., Dougherty, A., Caldwell, C. G., Meyers, R. O., Dorr, R. T. and Timmermann, B. N., Cytotoxic lignans from Larrea tridentate. Phytochemistry, 2005; 66: 811–815.
30 - Arteaga, S., Andrade-Cetto, A. and C´ardenas, R., Larrea tridentata (Creosote bush), an abundant plant of Mexican and US-American deserts and its metabolite nordihydroguaiaretic acid. Journal of Ethnopharmacology, 2005; 98: 231–239.
31 - Lee, J. and Cho, K., Flaxseed sprouts induce apoptosis and inhibit growth in MCF-7 and MDA-MB-231 human breast cancer cells. In Vitro Cell. Dev. Biol.—Animal, 2012; 48: 244–250.
32 - Reuben, S. C., Gopalan, A., Petit, D. M. and Bishayee, A., Modulation of angiogenesis by dietary phytoconstituents in the prevention and intervention of breast cancer. Mol. Nutr. Food Res. 2012; 56: 14–29.
33 - J., Fernando, Eva, R. Z., Rufino-Palomares, E., Lupiáñez, J. A. and Cascante, M., Maslinic acid, a natural triterpene from Olea europaea L., induces apoptosis in HT29 human colon-cancer cells via the mitochondrial apoptotic pathway. Cancer Letters, 2009; 273: 44–54.
34 - Goulas, V., Exarchou, V., Troganis, A. N., Psomiadou, E., Fotsis, T., Briasoulis E. and Gerothanassis. I. P., Phytochemicals in olive-leaf extracts and their antiproliferative activity against cancer and endothelial cells, Mol. Nutr. Food Res. 2009; 53: 600 – 608.
35 - Han, J., Talorete, T. P. N., Yamada P. and Isoda H., Anti-proliferative and apoptotic effects of oleuropein and hydroxytyrosol on human breast cancer MCF-7 cells. Cytotechnology, 2009; 59: 45–53.
36 - Çinar, A., Cansev A. and Şahan. Y., Phenolic Compounds of Olive by-products and Their Function in the Development of Cancer Cells. Biologi Bilimleri Araştırma Dergisi. 2011; 4(2): 55-58.
37 - Goulas, V., Exarchou, V., Troganis, A. N., Psomiadou, E., Fotsis, T., Briasoulis, E. and Gerothanassis, I. P., Phytochemicals in olive-leaf extracts and their antiproliferative activity against cancer and endothelial cells. Mol. Nutr. Food Res. 2009; 53: 600 – 608.
38 - Beara, I. N., Lesjak, M. M., Orcic, D. Z., Simin, N. Ð., Cetojevic-Simin, D. D., Bozin, B. N. and Mimica-Duki, N. M., Comparative analysis of phenolic profile, antioxidant, anti-inflammatory and cytotoxic activity of two closely-related Plantain species: Plantago altissima L. and Plantago lanceolata L. LWT - Food Science and Technology, 2012; 47: 64-70.
39 - Giri A. and Narasu M. L., Production of podophyllotoxin from Podophyllum hexandrum: a potential natural product for clinically useful anticancer drugs. Cytotechnology, 2000; 34: 17–26.
40 - Khan, H., Saeed, M. and Muhammad N., Pharmacological and phytochemical updates of genus Polygonatum. Phytopharmacology. 2012; 3(2): 286-308.
41 - Liu, Z., Li, X., Simoneau, A. R., Jafari, M. and Zi. X., Rhodiola rosea Extracts and Salidroside Decrease the Growth of Bladder Cancer Cell Lines via Inhibition of the mTOR Pathway and Induction of Autophagy. Molecular Carcinogenesis. 2012; 51: 257–267.
42 - Panossian, A., Wikman G. and Sarris. J., Rosenroot (Rhodiola rosea): Traditional use, chemical composition, pharmacology and clinical efficacy. Phytomedicine, 2010; 17: 481–493.
43 - Balsevich, J. J., Ramirez-Erosa, I., Hickie, R. A., Dunlop, D. M., Bishop, G. G. and Deibert, L. K., Antiproliferative activity of Saponaria vaccaria constituents and related compounds. Fitoterapia 2012; 83: 170–181.
44 - Agarwal, R., Agarwal, C., Ichikawa, H., Singh, R. P., and B. B., Aggarwal, Anticancer Potential of Silymarin: From Bench to Bed Side. Anticancer Research, 2006; 26: 4457-4498.
45 - Rnonel, A., Erlini, U. and Narot, A., Constituents of Silybum marianum. Structure of Isosilybin and Stereochemistry of Silybin. J.C.S. Chem. Comm., 1979; 696-697.
46 - Zheng-Xiang, X. and Jing-Yu, L., Steroids and Phenols from Sonchus arvensis. Chin J Nat Med. 2010; 8(4): 267-269.
47 - Radulović, N., Blagojević, P. and Palić, R., Fatty acid derived compounds--the dominant volatile class of the essential oil poor Sonchus arvensis subsp. uliginosus (Bieb.) Nyman. Nat Prod Commun. 2009; 4(3): 405-410.
48 - Mockute, D. and Judzentiene, A., Composition of the Essential Oils of Tanacetum vulgare L. Growing Wild in Vilnius District (Lithuania). Journal of Essential Oil Research, 2004; 16: 550-553.
49 - Ovadje, P., Chatterjee, S., Griffin, C., Tran, C., Hamm C. and Pandey, S., Selective induction of apoptosis through activation of caspase-8 in human leukemia cells (Jurkat) by dandelion root extract. Journal of Ethnopharmacology. 2011; 133: 86–91.
50 - Altmann, K. H. and Gertsch, J., Anticancer drugs from nature—natural products as a unique source of new microtubule-stabilizing agents. Nat. Prod. Rep., 2007; 24: 327–357.
51 - Biswas, R., Mandal, S. K., Dutta, S., Bhattacharyya, S. S., Boujedaini, N. and Khuda-Bukhsh, A. R., Thujone-Rich Fraction of Thuja occidentalis Demonstrates Major Anti-Cancer Potentials: Evidences from In Vitro Studies on A375 Cells. Evidence-Based Complementary and Alternative Medicine, 2011; 1-16.
52 - Wang, J., Li, Q., Ivanochko, G. and Huang, Y., Anticancer Effect of Extracts from a North American Medicinal Plant – Wild Sarsaparilla. Anticancer Research. 2006; 26: 2157-2164.
53 - Babich, H. and Visioli, F., In vitro cytotoxicity to human cells in culture of some phenolics from olive oil, Farmaco, 2003; 58: 403-407.
54 - Gálvez, M., Mart´ın-Cordero, C., López-Lázaro, M., Cortés, F. and Ayuso. M. J., Cytotoxic effect of Plantago spp. on cancer cell lines. Journal of Ethnopharmacology, 2003; 88: 125–130.
55 - Scambia, G., De Vincenzo, R., Ranelletti, F. O., Panici, P.B., Ferrandina, G., D'Agostino, G., Fattorossi, A., Bombardelli, E. and Mancuso, S., Antiproliferative effect of silybin on gynaecological malignancies: synergism with cisplatin and doxorubicin. Eur J Cancer. 1996; 32(5): 877-882.
56 - Zi, X., Feyes, D. K. and R., Agarwal, Human breast cancer cells MDA-MB 468: induction of G1 arrest through an increase in Cip1/p21 concomitant with a decrease in kinase activity of cyclin-dependent kinases and associated cyclins. Clin Cancer Res, 1998; 4: 1055-1064.
57 - Katzung, B.G., Basic and Clinical Pharmacology, 10th Edition, McGraw Hill, 2006.
58 - Agarwal, C., Tyagi, A., Kaur, M. and Agarwal, R., Silibinin inhibits constitutive activation of Stat3, and causes caspase activation and apoptotic death of human prostate carcinoma DU145 cells. Carcinogenesis, 2007; 28(7) 1463–1470.
59 - Kaur, J., Sharma, M., Sharma, P. D. and Bansal, M. P., Antitumor Activity of Lantadenes in DMBA/TPA Induced Skin Tumors in Mice: Expression of Transcription Factors. Am. J. Biomed. Sci. 2010; 2(1): 79-90.
60 - Ramasamy, K., Dwyer-Nield, L. D., Serkova, N. J., Hasebroock, K. M., Tyagi, A., Raina, K., Singh, R. P., Malkinson, A. M. and Agarwal, R., Silibinin Prevents Lung Tumorigenesis in Wild-Type but not in iNOS-/- Mice: Potential of Real-Time Micro-CT in Lung Cancer Chemoprevention Studies. Clin Cancer Res, 2011; 17: 753-761.
61 - Deep, G. and Agarwal, R., Chemopreventive Efficacy of Silymarin in Skin and Prostate Cancer. Integrative Cancer Therapies, 2007; 6(2): 130-145.
62 - Gu, M., Dhanalakshmi, S., Mohan, S., Singh, R. P. and Agarwal, R., Silibinin inhibits ultraviolet B radiation-induced mitogenic and survival signaling, and associated biological responses in SKH-1 mouse skin. Carcinogenesis, 2005; 26(8): 1404—1413.
63 - Gu, M., Dhanalakshmi, S., Singh, R. P. and Agarwal, R., Dietary Feeding of Silibinin Prevents Early Biomarkers of UVB Radiation–Induced Carcinogenesis in SKH-1 Hairless Mouse Epidermis. Cancer Epidemiol Biomarkers Prev, 2005; 14: 1344-1349.
64 - Singh, R. P., Mallikarjuna G. U., and Sharma, G., Oral Silibinin Inhibits Lung Tumor Growth in Athymic Nude Mice and Forms a Novel Chemocombination with Doxorubicin Targeting Nuclear Factor kB- Mediated Inducible Chemoresistance. Clin Cancer Res, 2004; 10: 8641-8647.
65 - Elmore, S., Apoptosis: A Review of Programmed Cell Death. Toxicologic Pathology, 2007; 35:495–516.
66 - Elmorea, S. W., Oostb T. K. and Park, C. M., Inhibitors of Anti-apoptotic Proteins for Cancer Therapy. Annual Reports In Medicinal Chemistry, 2005; 40: 255-270.
67 - Dhanalakshmi, S., Agarwal, C., Singh, R. P. and Agarwal, R., Silibinin Up-regulates DNA-Protein Kinase-dependent p53 Activation to Enhance UVB-induced Apoptosis in Mouse Epithelial JB6 Cells. The Journal of Biological Chemistry, 2005; 280(21) 20375–20383.
68 - Deep, G., Gangar, S. C., Oberlies, N. H., Kroll, D. J. and Agarwal, R., Isosilybin A Induces Apoptosis in Human Prostate Cancer Cells via Targeting Akt, NF-kB, and Androgen Receptor Signaling. Molecular Carcinogenesis, 2010; 49: 902–912.
69 - Deep, G., Oberlies, N. H., Kroll D. J. and Agarwal, R., Isosilybin B and isosilybin A inhibit growth, induce G1 arrest and cause apoptosis in human prostate cancer LNCaP and 22Rv1 cells, Carcinogenesis, 2007; 28: 1533–1542.
70 - Giri, A. and Narasu, M. L., Production of podophyllotoxin from Podophyllum hexandrum: a potential natural product for clinically useful anticancer drugs. Cytotechnology, 2000 34: 17–26.