**2. Phytotherapy and cancer**

#### **2.1. Generalities**

Studies reported that plant-derived drugs represent about 25% of the American prescription drug market [4]. 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 [5]. 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 [7] (**Tables 1**–**3**).

Several molecules used as conventional chemotherapy are of natural origin. Some of these

receptors

K+ ATPase

Penicilline Antibiotic Inhibition of cell membrane Micro-organism Tatracycline Antibiotic Inhibition of protein synthesis Micro-organism

Manoalide Analgesic, anti-inflammatory Inhibition of phospholipase A2 Marine organism

proliferation

polymerization

polymerization

excitability

Inhibition of cyclo-oxygenase Plant

Plant

Plant

Plant

Micro-organism

Marine organism

Marine organism

/

**Drug Utilization Mechanism of action Source**

Cafeine Stimulating Antagonist of adenosine receptors Plant Codeine Analgesic, anti-tussive Antagonist of opoide receptors Plant

Morphine Analgesic Antagonist of opoide receptors Plant Pilocarpine Glaucoma Antagonist of muscarinic receptors Plant Quinine Prophylaxis of malaria Inhibition of protein synthesis Plant Taxol Anticancer Antimitotic Plant

Atropine Pupil dilatator Anti-cholinergic on muscarinic

Digoxine Cardiotonic Inhibition of membrane pump N<sup>+</sup>

Eugenol Touth pain Reduction of sensorial nerve

Cyclosporine A Immunosuppressor Inhibition of lymphocytes T

**Table 1.** Some natural drugs derived from plants, micro-organisms, or marine organisms [8].

Aurantosides Antifungal Inhibition of tubulin

Spongistatine 1 Antifungal Inhibition of tubulin

molecules and their use are described in **Tables 2** and **3**.

Aspirine Analgesic, anti-inflammatory, anti-pyrtic

66 Cytotoxicity

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 [9]. 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 [10]; it possesses *in vitro* and *in vivo* antiviral activity against human herpesvirus [11]. Carvone promoted protection of 75–87.5% against convulsions at 300–400 mg/kg [12]. Isopulegol and carvone showed significant bactericidal and fungicidal activities [13]. Also, the combination of these molecules between them or with conventional molecules could have a synergistic effect [14, 15]. Furthermore, carvacrol, extract of thyme essential oil, is one of natural products with important biological activities. It has been reported to have an important antitumor effect [9, 16]. Here, we present a summary of our findings [17] on the cytotoxic activity as well as their molecular mechanisms of six natural monoterpenes compounds (carvacrol, thymol, carveol, carvone, eugenol, and isopulegol).

#### *2.2.1.1. In vitro cytotoxic 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 IC<sup>50</sup> = 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**).

**Figure 1.** Cytotoxic effect of carvacrol (A), thymol (B), carveol (C), carvone (D), eugenol (E) and isopulegol (F) against

Natural Products as Cytotoxic Agents in Chemotherapy against Cancer

http://dx.doi.org/10.5772/intechopen.72744

69

**Product P815 CEM K-562 MCF-7 MCF-7/gem** Carvacrol 0.067 0.042 0.067 0.125 0.067 Thymol 0.15 0.31 0.44 0.48 — Carveol 0.11 0.11 0.13 0.26 0.45 Carvone 0.16 0.11 0.17 0.63 0.91 Eugenol 0.10 0.09 0.24 0.41 0.87 Isopulegol 0.09 0.11 0.13 — 0.25

different tumor cell lines: P815 (♦), CEM (◾), K562 (**\_**), MCF-7 (▴) and MCF-7 gem (\*).

**Table 5.** IC50 (μM) of the tested monoterpenes against different target cell lines.

#### *2.2.1.2. Synergy*

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**).

a wide range of important biological activities [10]; it possesses *in vitro* and *in vivo* antiviral activity against human herpesvirus [11]. Carvone promoted protection of 75–87.5% against convulsions at 300–400 mg/kg [12]. Isopulegol and carvone showed significant bactericidal and fungicidal activities [13]. Also, the combination of these molecules between them or with conventional molecules could have a synergistic effect [14, 15]. Furthermore, carvacrol, extract of thyme essential oil, is one of natural products with important biological activities. It has been reported to have an important antitumor effect [9, 16]. Here, we present a summary of our findings [17] on the cytotoxic activity as well as their molecular mechanisms of six natural monoter-

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 IC<sup>50</sup> = 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,

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**).

penes compounds (carvacrol, thymol, carveol, carvone, eugenol, and isopulegol).

*2.2.1.1. In vitro cytotoxic effect of the products against a panel of target cells*

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

**Drugs Utilization**

68 Cytotoxicity

Docetaxel Breast and lung cancer Topotecan Ovarian and lung cancer Irinotecan Colorectal and lung cancer

**Table 4.** Anticancer drugs derived from plants [8].

carveol, carvone, and eugenol but not to isopulegol or carvacrol (**Table 5**).

*2.2.1.2. Synergy*

**Figure 1.** Cytotoxic effect of carvacrol (A), thymol (B), carveol (C), carvone (D), eugenol (E) and isopulegol (F) against different tumor cell lines: P815 (♦), CEM (◾), K562 (**\_**), MCF-7 (▴) and MCF-7 gem (\*).


**Table 5.** IC50 (μM) of the tested monoterpenes against different target cell lines.


**Table 6.** Affected fraction (Fa) and combination index (CI) of molecule combinations.
