**11. Targeted therapy**

Selected somatic changes such as BRAF mutations have been described, and then applied to the targeted treatments. BRAF gene is located in chromosomal region 7q34; it consists of 18 exons and transcribed mRNA length was 2478 bp. Targeted therapy is based on the knowledge of the molecular biology of the gene encoding the BRAF kinase, belonging to the RAF kinase family. It is a serine/threonine kinase that takes part in the Mitogen Activated

**Figure 2.** Mechanism of action of kinase inhibitors. This figure shows a schema of signaling pathways triggered by binding of growth factors to tyrosine kinase receptor that triggers RAS, RAF, MEK and ERK pathways leading to cell growth and proliferation. Mutations in BRAF (V600E) can lead to accelerated cell growth and cancer formation of melanoma cells. Inhibition of mutant BRAF by dabrafenib, vemurafenib in the melanoma cells shuts down the signaling pathway causing tumor regression following cell apoptosis, tumor antigen expression and decreased release of cytokines and VEGF. MEK is a member of the MAPK signaling cascade that is activated in melanoma. Inhibition of MEK by selumetinib, trametinib blocks cell proliferation and induces apoptosis (controlled cell death). MAPK, mitogen activated protein kinase; ERK, extracellular signal-regulated kinase; VEGF, vascular endothelial growth factor.

Protein Kinase (MAPK) cascade, which modulates cell growth and proliferation. This pathway is activated by binding of the extracellular physiological growth factor to its receptor. Conformational change of the receptor leads to the activation of RAS protein (GTP-binding), which activates RAF protein, which activates other kinases MEK and ERK. This pathway may be activated by mutation of specific proteins, including BRAF [52]. It is reported that 40–60% of melanomas have a mutation of the gene leading to the pathological-activated signaling pathways and to uncontrolled growth of malignant transformed cells [53]. The most common gene mutations are V600E or V600K known as an amino acid substitution at position 600 in BRAF, from a valine (V) to a glutamic acid (E) or to a lysine (K), respectively. In the structure of protein kinases there is a DFG motif, which is a highly specific site for interaction with kinase inhibitors. It contains Asp (D), Phe (F) and Gly (G) and exists in a conformational active or inactive state. Just the knowledge in this field has led to the development and screening of new selective inhibitors of BRAF and MEK (**Figure 2**) [54]. Targeted therapy is associated with improved clinical benefit; however, the mechanism of resistance often varies and includes activation of alternative signaling pathways [55].
