This excerpt taken from the SNY 6-K filed Jun 4, 2009.
About PI3K inhibitors
The phosphoinositide-3-kinase (PI3K) pathway is triggered in normal cells upon exposure to growth factors. It regulates a cascade of proliferation and survival signals. The PI3K pathway is one of the primary deregulated signaling pathways in human cancer. Activation of the PI3K pathway is a frequent event in human tumors, promoting cell proliferation, survival, and resistance to chemotherapy and radiotherapy. Novel therapeutics impacting the PI3K pathway, alone or in combination, are therefore considered to have a high therapeutic potential.