Some natural drugs derived from plants, micro-organisms, or marine organisms .
Nature continues to produce a great wealth of natural molecules endowed with cytotoxic activity toward a large panel of tumor cells. Some of these molecules are used in chemotherapy, and others have shown great anti-tumor and anti-metastatic potential in preclinical trials. This review discusses some examples of these molecules that have been studied in our laboratory and others. We report a differential cytotoxic activity of some monoterpenes (carvacrol, tymol, carveol, carvone, and isopulegol) against a panel of tumor cell lines. The carvacrol was the most cytotoxic molecule both in vitro and in vivo as demonstrated by preclinical studies using the DBA2/P815 mice model. On the other hand, polyphenols were also studied with respect to their cytotoxic effects. Interestingly, these compounds showed a prominent cytotoxic activity toward a panel of cancer cells with differential molecular mechanisms. In addition, we report a very strong antitumor efficacy of artemisinin, a sesquiterpen lactone from Artemisia annua, together with an antimetastatic potential as demonstrated by preclinical experiments. Furthermore, some of the molecular mechanisms involved in these effects are described.
- natural products
Natural drugs have formed the basis of traditional medicine systems that have been used for centuries by different cultures . An immense number of these natural sources and their isolated components have demonstrated beneficial therapeutic effects, such as anticancer, antioxidant, immunomodulatory, antimicrobial, and anti-inflammatory properties [2, 3]. Studies reported that plant-derived drugs represent about 25% of the American prescription drug market . Also, natural products play an important role in the health care of 20% of the world’s people who mainly reside in developed countries and 119 chemicals compounds, derived from 90 plant species, can be considered as important drugs in many countries . Based on a recent review, from 79 Food and Drug Administration anticancer and antiviral approved drugs from 1983 to 2002, 9 of them were isolated directly from plants and 21 among them were natural-products-based drug. Furthermore, between 39 conventional anticancer molecules, 13 of them were derived on a pharmacophore obtained from natural drugs [5, 6]. Actually, nature continues to be an attractive source of new molecules discovery due to important chemical diversity of the thousands of plant, animal, marine organisms, and micro-organism species. Today, about 60% of drugs are of natural origin  (Tables 1–3).
|Drug||Utilization||Mechanism of action||Source|
|Aspirine||Analgesic, anti-inflammatory, anti-pyrtic||Inhibition of cyclo-oxygenase||Plant|
|Atropine||Pupil dilatator||Anti-cholinergic on muscarinic receptors||Plant|
|Cafeine||Stimulating||Antagonist of adenosine receptors||Plant|
|Codeine||Analgesic, anti-tussive||Antagonist of opoide receptors||Plant|
|Digoxine||Cardiotonic||Inhibition of membrane pump N+/K+ ATPase||Plant|
|Eugenol||Touth pain||Reduction of sensorial nerve excitability||Plant|
|Morphine||Analgesic||Antagonist of opoide receptors||Plant|
|Pilocarpine||Glaucoma||Antagonist of muscarinic receptors||Plant|
|Quinine||Prophylaxis of malaria||Inhibition of protein synthesis||Plant|
|Penicilline||Antibiotic||Inhibition of cell membrane||Micro-organism|
|Tatracycline||Antibiotic||Inhibition of protein synthesis||Micro-organism|
|Cyclosporine A||Immunosuppressor||Inhibition of lymphocytes T proliferation||Micro-organism|
|Aurantosides||Antifungal||Inhibition of tubulin polymerization||Marine organism|
|Spongistatine 1||Antifungal||Inhibition of tubulin polymerization||Marine organism|
|Manoalide||Analgesic, anti-inflammatory||Inhibition of phospholipase A2||Marine organism|
|Actinomycine||Germinale cells tumor, sarcoma|
|Bléomycine||Cervix cancer, Germinale cells tumor, and neck|
|Doxorubicine||Lymphoma, breast, lung and ovarian cancer, sarcoma|
|Idarubicine||Leukemia and breast cancer|
|Mitomycine C||Colorectal, gastric, anal, and lung cancer|
|Streptozocine||Gastric and endocrine tumors|
|Drug||Utilization||Mechanism of action|
|Citarabine||Leukemia, lymphoma||Inhibition of DNA synthesis|
|Bryostatine 1||Experimental phase||Activation of protein kinase C|
|Dolastatine 10||Experimental phase||Inhibition of microtubules and pro-apoptotic effect|
|Ecteinascidine 743||Experimental phase||Alkylation of DNA|
|Aplidine||Experimental phase||Inhibition cell cycle progression|
|Halicondrine B||Experimental phase||Interaction with tubuline|
|Discodermolide||Experimental phase||Stabilization of tubuline|
|Cryptophycine||Experimental phase||Hyperphosphorylation of Bcl-2|
|Vincristine||Leukemia, lymphoma, breast cancer, and lung cancer|
|Vinblastine||Lymphoma, kidney cancer, germinal cells cancer, and breast cancer|
|Paclitaxel||Breast cancer, ovarian, lung, and d’ovaire, de poumon, bladder, and neck cancer|
|Docetaxel||Breast and lung cancer|
|Topotecan||Ovarian and lung cancer|
|Irinotecan||Colorectal and lung cancer|
2. Phytotherapy and cancer
There is a numerous plants involved in the prevention and/or treatment of cancer. As for other diseases, many anticancer drugs are derived from plants (Table 4). Studies reported that more than 200 drugs are of herbal origin. The vinca-alcaloids and the taxans are the main groups, which occupy an important place in anticancer chemotherapy.
2.2. Examples of natural products with important cytotoxic activity
2.2.1. Cytotoxic activity of some natural monoterpenes
The chemical composition of plant-extracts is known for being very rich and diversified. Thus, a single extract may contain more than hundreds of interactive biomolecules . Therefore, finding and discovering those responsible for the biological Activity become essential. Many monoterpenes, such as eugenol, have been described in the literature to have a wide range of important biological activities ; it possesses
In vitrocytotoxic effect of the products against a panel of target cells
The antitumor activity of the products was evaluated against the following five tumor cell lines: P-815, K-562, CEM, MCF-7, and MCF-7 resistant to gemcetabine (MCF-7-gem). The results are summarized in Figure 1, which shows that the cytotoxic effect depends on the nature of the products as well as on the target cell lines. In general, the effect of the products is dose-dependent. Moreover, the cytotoxic activity of carvacrol, thymol, carveol, carvone, eugenol, and isopulegol is more important against P-815 and CEM tumor cell lines compared to the other tested cell lines. The carvacrol is the most cytotoxic compared to other compounds. Against P-815, K-562 and CEM cancer cell lines, eugenol, carveol, and carvone exhibit also a strong cytotoxic activity. The IC50 values are ranging from 0.09 to 0.24 μM (Table 5). Nevertheless, those compounds showed a less effect toward MCF-7 and very lowest one against MCF-7-gem cancer cell lines as demonstrated by the IC50 values ranging from 0.26 to 0.87 μM. Comparing the activity of thymol and isopulegol on the tumor cell lines studied, it shows that P-815 is the most sensitive with an IC50 = 0.15 and 0.09 μM, respectively. Importantly, acquired resistance to gemcetabine by MCF-7 cell line was linked with a development of resistance to thymol, carveol, carvone, and eugenol but not to isopulegol or carvacrol (Table 5).
Our results demonstrate that the combination of natural monoterpene with MTX or Cis showed a synergistic effect at used concentrations (IC20) of each tested molecules (monoterpenes, cisplatine, and methotrexate). The interactions between these molecules exhibit a cell lysis ranging between 53 and 62%. Furthermore, a slight cytotoxicity was shown after the combinations between monoterpene-cisplatin and monoterpene-methotrexate (Table 6).
184.108.40.206. Effect of carvacrol, thymol, carveol, carvone, eugenol, and isopulego on the cell cycle progression
At the molecular level, carveol- and carvacrol treatment-induced cell cycle arrest in S phase. Nevertheless, thymol and isopulegol stopped it in G0/G1 phase. Regarding the eugenol and carvone, they have no effect cell cycle progression (Figure 2).
In vivoantitumor effect of carvacrol
Our experimental model was based on the use of the P-815 tumor-bearing DBA-2 mice to investigate the cell-killing induced by carvacrol. Experiments were carried out by oral administration (gavage) of carvacrol dissolved in vegetal oil to 6- to 8-week-old DbA-2/6 mice (6 mice for each group) (Orleans, France) weighting 18–22 g for 7 days. The tumor volume was measured for up to 30 days. The tumor volume at day
Studies were carried out by gavage of carvacrol dissolved in vegetable oil to mice (6–8 week-old) for 7 days. Group “A” (untreated) treated with 100 μl/day of vegetal oil only. Groups “B” and “C” received 50 and 100 mg/kg/day of carvacrol dissolved in 100 μl of vegetal oil, respectively. Mice were weighted and the tumor volume was calculated by measurement of the width (
Monoterpenes (carvacrol, thymol, carveol, carvone, eugenol, and isopulegol) have been found to exert antitumor effect. In fact, eugenol was described to exhibit cell death by apoptosis in mastocyte  and melanoma cells . Also, it has been demonstrated not to be mutagenic neither carcinogenic . Carveol has chemopreventive activity against mammary cancer when fed during the initiation phase . Carvone prevents chemically induced lung and for stomach carcinoma development . Carvacrol and thymol significantly reduced the level of DNA damage induced in K-562 cells by the strong oxidant H2O2 . Furthermore, carvacrol has an important
2.2.2. Polyphenols: a potent cytotoxic molecules
Natural polyphenols have received increasing interest in the human health due to their benefit effects against several diseases attributed particularly to their antioxidant activity . Beside their well-known and effective antioxidant activity [32, 33], several polyphenols shown a high cytotoxic effect against cancer cell lines through targeting cellular and molecular processes involved in cancer progression and metastasis. The antitumor potential of these active ingredients is due to their effect as modulators of oxidative stress , apoptosis inducers  cell proliferation inhibitor , tumor cell cycle blockers , and angiogenesis/metastasis suppressors . These bioactive compounds have shown promising antitumor properties in both
220.127.116.11. Polyphenols and apoptosis induction
Large number of studies has focused on the ability to introduce apoptosis on cancer therapy under cellular control conditions [47, 48]. The intrinsic and extrinsic molecular pathways involved in the regulation of the apoptotic process have recently been evaluated and give promising results. Several proapototic receptors have been selectively developed activating the intrinsic pathway, particularly including the antiapoptotic proteins, the Bcl-2 family proteins, and the p53 signaling pathways [49, 50, 51]. In this purpose, polyphenols could inhibit tumor cell proliferation via the programmed cell death (apoptosis) using both intrinsic and extrinsic cell pathways. As reported, polyphenols such as EGCG: (−)-epigallocatechin-3-gallate, resveratrol, naringenin, quercetin, hydroxytyrosol, and curcumin, through different intrinsic signaling pathways from mitochondrial intermembrane space, may inhibit NF-κB-dependent signal related to proliferation and survival , cause cell cycle arrest through upregulation of p53 , stabilize and activate the tumor suppressor gene p53 , and downregulate the expression of Bcl-2, and Bcl-XL anti-death proteins, favoring apoptosis induction via the activation of multiple caspases activity and cytochrome-c (cyt-c) [55, 56]. These polyphenols have been shown to promote apoptosis in different cancers particularly breast, lung, prostate, leukemia, colon, cervical, or melanoma [57, 58]. In breast cancer cells, naringenin demonstrated anti-estrogenic activity in estrogen-rich status and estrogenic activity in estrogen-deficient status . Additionally, few early studies suggested that gavage of polyphenols in green tea (EGCG), even at low doses, prevented colon carcinogenesis by inhibiting metastasis and angiogenesis through apoptosis induction . Few years ago, our research group has published an article  on natural polyphenols extracted from olive mill waste (OMW) and their implication in anticancer activity, where the
|IC50 (μg/ml)||6.95 ± 0.15||5.3 ± 0.1||4.75 ± 0.05||7.75 ± 0.15||5.3 ± 0.2|
Taken together, these data showed the differential and selective cytotoxic effect of natural polyphenols. In this sense, Miccadei et al.  have shown that polyphenolic extracts from the edible part of artichoke (
18.104.22.168. Role of polyphenols in therapy-induced senescence
Cellular senescence is a physiological process of irreversible cell-cycle arrest that contributes to various physiological and pathological processes of aging. It is an alternative and a novel therapeutic strategy to the cytotoxic treatment which leading to cytostasis approach target for aging and aging-related diseases . Although senescence cells have irreversibly lost their capacity for cell division, they are still viable and remain metabolically active . Prosenescence is usually associated with telomere erosion after repeated cell divisions and occurs in response to abnormal oncogenic signaling, oxidative stress, and DNA damage . To this purpose, natural compounds targeting the epigenetic control of senescence are under investigations to develop additional prosenescence cancer therapeutic strategies . Several anticancer polyphenolic compounds from fruit and vegetables have been shown to be potential chemopreventive and anticancer bioactive compounds  to induce cellular growth arrest through the induction of a ROS-dependent premature senescence. Among them, 20(S)-ginsenoside Rg3, a compound extracted from ginseng, and bisdemethoxycurcumin, a natural derivative of curcumin, caused senescence-like growth arrest and increased ROS production, respectively, in human glioma cells  (and human breast cancer cell . Therefore, high doses of polyphenolic extracts from artichoke may induce apoptosis and decrease cell proliferation of the human breast cancer cell line, MDA-MB231 via the induction of premature senescence through epigenetic and ROS-mediated mechanisms . Importantly, the authors have shown that Artichoke extracts have a pro-oxidant activity in breast cancer cells  and an antioxidant effect on normal hepatocytes . Therefore, it has been hypothesized that Polyphenolic artichoke extracts could selectively inhibit the tumor cells growth with no cytotoxicity on healthy cells related on their differential cellular redox status. Furthermore, treatment with a low dose of resveratrol exhibits its chemopreventive and anticancer activities by induction of premature senescence in lung cancer cells. This event is associated with an increase in ROS generation and DNA double strands break through the up-regulation of NAPDH oxidase-5 expression . The inhibitory effect of resveratrol was verified
2.2.3. Artemisinin: a cytotoxic molecule with medical interests
Artemisinin, the active component of Qinghao (Chinese name of
In vitrocytotoxic properties of artemisinin
A significant cytotoxicity of artemisinin against tumors has been recently documented. It suggests that artemisinin, commonly used against malaria, can be used to prevent and treat cancer [80, 81, 82, 83]. It is a relatively safe drug, with known pharmacokinetics and pharmacodynamics studies. In fact,
Several studies have tried to explain, at molecular level, the mechanism of its anti-cancer action. A study on HL-60 cancer cell line demonstrated that rapid production of reactive oxygen species is associated with cell death by apoptosis after artemisinin treated cells . Other factors such as endoplasmic reticulum stress and calcium metabolism can also be associated with the anticancer activity of artemisinins [93, 94]. Endoplasmic reticulum seems to be a possible site for artemisinin action, in HepG2 cancer cell line a derivative fluorescence accumulates preferentially in the endoplasmic reticulum as described by Crespo et al. .
Artemisinin has been described to induce apoptosis effect [86, 96, 97], as well as cell cycle arrest, especially at G0/G1 cell cycle transition phase [89, 98]. Multiple lines of evidence suggest that the apoptotic pathway could be due to intra and/or extra-mitochondrial mode of action, and the involvements of iron/heme as well [81, 99]. Two mechanistic pathways have been frequently described to explain the apoptotic effect of artemisinin, vascular endothelial growth factor decrease [100, 101, 102], and nuclear factor-kappa B inhibition [103, 104]. Recently, other processes have also been illustrated in different cancer cell types, by the involvement of NOXA , mitogen-activated protein kinase (MAPK) , Wnt/β-catenin , surviving , COX , c-MYC oncoprotein [93, 110], and epidermal growth factor . Furthermore, it was also reported that the sensitivity to artemisinin action was related to the expression level of proapoptotic (Bax) and antiapoptotic (Bcl2) genes . Also, artemisinin role in the inhibition of cancer is postulated to be associated with direct DNA damage  or indirectly in tumor cells involving a cascade of signaling pathways in many hallmarks of cancer . Taken together, these results could explain the apoptotic pathway induction by artemisinin on tested cancer cells [101, 102, 115, 116]. However, we have also reported the possibility of the involvement of another cell death process of artemisinin; probably necrosis . Artemsinin-induced necrosis remains not well documented and may be linked with the increasing level of ATP, defective apoptotic pathways, reactive oxygen species-independent mechanism of programmed cell death and cancer cell line type . Furthermore, we have described that artemisinin interacted synergistically and additively with vincristin to reduce cancer cell proliferation , suggesting a possible use of artemisinin as an adjuvant to treat cancer.
In vivoanti-tumor and antimetastatic effects
Artemisinin treatment in oral route at 80 mg/kg considerably reduced the tumor volume growth of P815/DBA2 mice as described by our team . In HepG2 and Hep3B human hepatoma mouse xenograft, artemisinin administered at 50 or 100 mg/kg/day delayed tumor onset, respectively, by 30 and 39.4% . Also, in another study, artemisinin reduced tumor growth at 50% on day 20, when injected intraperitoneally at a concentration of 2.8 mg/kg/day on mammary gland ductal carcinoma in mice . Inhibition of tumor growth and anti-angiogenic effect in MCF-7 mouse xenograft after subcutaneous treatment with artemisinin at dose 100 mg/kg/day for 2 weeks was reported . Interestingly, artemisinin exhibited an anti-metastatic effect . In fact, these authors showed that after orally artemisinin treatment with 50 mg/kg, a reduction of 63.5% of lung metastasis and lymph node metastases decrease in cervical and mediastinal lymph nodes, as well as an inhibition of lymphangiogenesis by 63% of mice. Artemisinin also exhibited inhibitory effects in lung tumor metastasis by 51.8 and 79.6% for 50 and 100 mg/kg/day, respectively. Furthermore, it was described that artesunate given in the drinking water at 167 mg/kg/day suppressed growth of Kaposi’s sarcoma-IMM xenograft tumors in nude mice . The antimetastatic effect of artemisinin seems to be associated with the expression of metalloproteinase genes and their effect on αvβ3 integrins . Moreover, the decrease of MMP2 with an increase of TIMP-2 in HepG2 and SMMC772 cancer cell lines after artemsinin treatment were reported . Interestingly, the antimetastatic effect of artemisinin could be triggered by enhancing Cdc42 and E-cadherin activation . However, in highly metastatic cancer such as nasopharyngeal cancer (CNE-1,CNE-2 cancer cell lines), artemisinin seems to have a low response due to the overexpression of BMI-1 gene that makes these cancer cells more sensitive to artemisinin drug . In highly metastatic MDA-MB-231 breast tumor cells, artesunate induced resistance as described by Beatrice Bachmeier et al. (2011). This resistance was induced by the activation of transcription factors NF-κB and AP-1 . Another study showed suppression of invasive and metastatic non-small cell lung cancer after artesunate treatment by the inhibition of urokinase-type plasminogen activator (u-PA), and matrix metalloproteinases (especially MMP-2 and MMP-7) transcription .
Nature continues to produce a great wealth of natural molecules endowed with cytotoxic activity towards a large panel of tumor cells. More than 60% of these molecules such as vinblastine, vincristine, etoposide, teniposide, taxol, navelbine, and camptothecin are used in chemotherapy and others have shown great anti-tumor and anti-metastatic potential in preclinical trials [124, 125]. Other natural product (i.e., Romidepsin 14,
This work was supported by the Lalla Salma Foundation: Prevention and treatment of cancer-Rabat-Morocco (Research Project N° 09/AP 2013).