**3. Animal venoms**

Venoms are molecular cocktails constituted by mixtures of different families of proteins, peptides, amines, salts, polypeptides and enzymes, [24, 25] designed by natural selection to act on the vital systems of the prey or victim. Components of venoms can act on receptors, channels, or through their enzymatic activity, causing the dysfunction of the central nervous system (CNS) and peripheral nervous system (PNS), the cardiovascular system, blood coagulation and homeostasis of the prey. Venoms are a rich source of pharmacological bioactive compounds, but research on them is scarce, considering that there are 700 species of cone snails, 725 snakes, 1500 scorpions, and 37,000 spiders identified [26, 27].

#### **3.1 Snake venoms**

Since the discovery in 1980 of captopril, a drug derived from the venom of the *Bothrops jararaca* snake, it has been demonstrated that components of venoms are beneficial in the medical area to treat different diseases including cancer [25]. Among the snake venom components, phospholipases A2 (PLA2s) of *Bothrops jararacussu* showed antitumor activity on cell lines of breast cancer, acute T-cell leukemia and Ehrlich ascitic tumor [28]. A metalloproteinase of the *Bothrops jararaca* venom induced apoptosis and decreased the proliferation and metastasis in melanoma [29]. The L-amino acid oxidase (LAAO) isolated from *Daboia russelii russelii* induced apoptosis on breast cancer [30].
