The PI3K pathway as drug target in human cancer

Abstract

The phosphatidylinositol 3-kinase (PI3K) signaling axis impacts on cancer cell growth, survival, motility, and metabolism. This pathway is activated by several different mechanisms in cancers, including somatic mutation and amplification of genes encoding key components. In addition, PI3K signaling may serve integral functions for noncancerous cells in the tumor microenvironment. Consequently, therapeutics targeting the PI3K pathway are being developed at a rapid pace, and preclinical and early clinical studies are beginning to suggest specific strategies to effectively use them. However, the central role of PI3K signaling in a large array of diverse biologic processes raises concerns about its use in therapeutics and increases the need to develop sophisticated strategies for its use. In this review, we will discuss how PI3K signaling affects the growth and survival of tumor cells. From this vantage, we will consider how inhibitors of the PI3K signaling cascade, either alone or in combination with other therapeutics, can most effectively be used for the treatment of cancer.

Fig 1.

The phosphatidylinositol 3-kinase (PI3K) signaling cascade. PI3K signaling impacts on cell growth, survival, and metabolism. Arrows represent activation, while bars reflect inhibition. A negative feedback loop has been described from the downstream target S6 kinase (S6K) to the adaptor protein IRS-1. RTK, receptor tyrosine kinase; GPCR, G-protein coupled receptor; P, phosphate; G, G protein; PTEN, phosphatase and tensin homolog; IRS-1, insulin receptor substrate 1; eIF4E, eukaryotic initiation factor 4E; S6, ribosomal S6 protein; PIP₂, phosphatidylinositol 4,5-bisphosphate; mTORC2, rapamycin (mTOR) –containing protein complex 2. (*) p110 alpha, beta, or delta.