The phosphatidylinositol 3-kinase (PI3K)/Akt signal transduction pathway plays critical roles in cell growth and proliferation making it an attractive target for anticancer agents.{12235} Ins(1,3,4,5,6)P5 is one of the many inositol phosphate isomers that act as small, soluble second messengers in the transmission of cellular signals.{8344,8672,13727} It can be interconverted with Ins(3,4,5,6)P4 by a 1-kinase/1-phosphatase cycle, as well as with Ins(1,4,5,6)P4 in a 3-kinase/3-phosphatase cycle.{13727} Ins(1,3,4,5,6)P5 inhibits the phosphorylation and kinase activity of Akt/PKB, inducing apoptosis in ovarian, lung, and breast cancer cells.{13723} It exhibits antiangiogenic activity in vitro, blocking capillary tube formation of HUVEC, as well as antitumor effects against cancer xenografts in nude mice.{13728} Ins(1,3,4,5,6)P5 binds to the PH domain of Grp1 with a Kd value of 590 nM.{13724}