The RAS/RAF/MEK/ERK and the PI3K/AKT signalling pathways: role in cancer pathogenesis and implications for therapeutic approaches

Introduction: The RAS/RAF/MAP kinase--ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) (MAPK) and the PI3K/AKT/mammalian target of rapamycin (mTOR) (PI3K) pathways are frequently deregulated in human cancer as a result of genetic alterations in their components or upstream activation of cell-surface receptors. These signalling cascades are regulated by complex feedback and cross-talk mechanisms. Areas covered: In this review the key components of the MAPK and AKT pathways and their molecular alterations are described. The complex interactions between these signalling cascades are also analysed. Expert opinion: The observation that the MAPK and the PI3K pathways are often deregulated in human cancer makes the components of these signalling cascades interesting targets for therapeutic intervention. Recently, the presence of compensatory loops that activate one pathway following the blockade of the other signalling cascade has been demonstrated. Therefore, the blockade of both pathways with combinations of signalling inhibitors might result in a more efficient anti-tumor effect as compared with a single agent. In addition, the MAPK and PI3K pathways are activated by mutations that coexist or can be mutually exclusive. In this regard, a large-scale characterization of the cancer genome might offer personalized cancer genomic information, which may improve the anti-tumor efficacy of signalling inhibitors.