**1. Introduction**

Natural drugs have formed the basis of traditional medicine systems that have been used for centuries by different cultures [1]. 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].

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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


**2. Phytotherapy and cancer**

**Drug Utilization**

Daunomycine Leukemia

Epirubicine Breast cancer

Actinomycine Germinale cells tumor, sarcoma

Idarubicine Leukemia and breast cancer

Streptozocine Gastric and endocrine tumors

**Table 2.** Some anticancer drugs derived from micro-organisms [8].

Bléomycine Cervix cancer, Germinale cells tumor, and neck

Doxorubicine Lymphoma, breast, lung and ovarian cancer, sarcoma

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

Dolastatine 10 Experimental phase Inhibition of microtubules and pro-apoptotic effect

Natural Products as Cytotoxic Agents in Chemotherapy against Cancer

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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

groups, which occupy an important place in anticancer chemotherapy.

**Drug Utilization Mechanism of action** Citarabine Leukemia, lymphoma Inhibition of DNA synthesis Bryostatine 1 Experimental phase Activation of protein kinase C

Mitomycine C Colorectal, gastric, anal, and lung cancer

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

**2.2. Examples of natural products with important cytotoxic activity**

*2.2.1. Cytotoxic activity of some natural monoterpenes*

**Table 3.** Some anticancer drugs derived from marine organisms [8].

**2.1. Generalities**

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


**Table 2.** Some anticancer drugs derived from micro-organisms [8].


**Table 3.** Some anticancer drugs derived from marine organisms [8].
