A phosphatidylinositol 3,4,5-trisphosphate analogue with low serum protein-binding affinity

Phosphatidylinositol 3,4,5-trisphosphate (PIP₃) plays an important role in the regulation of diverse physiological functions. Recent evidence indicates that PIP₃ is cell permeant, and can be added exogenously to modulate cellular responses. However, like many other phospholipids, PIP₃ binds serum proteins with high affinity, resulting in rapid deactivation of this lipid second messenger. Our study indicates that bovine serum albumin (BSA) at concentrations as low as 10 μg/mL abrogated the biological activity of dipalmitoyl-PIP₃. This nonspecific interaction with serum proteins hampers the use of PIP₃ in biological studies where serum is needed. We report here an ether-linked PIP₃ analogue, 1-O-(1-O-hexadecyl-2-O-methyl-sn-glycero-3-phosphoryl)-myoinositol 3,4,5-trisphosphate (C₁₆Me-PIP₃), which displays low serum protein-binding affinity while retaining the biological function of PIP₃. The affinity of C₁₆Me-PIP₃ with BSA was two orders of magnitude lower than that of its dipalmitoyl-counterpart. Biochemical data indicate that C₁₆Me-PIP₃ was able to stimulate Ca²⁺ influx in T cells in the presence of moderate levels (up to 1 mg/mL) of BSA. Thus, C₁₆Me-PIP₃ may provide a useful tool to study the physiological function of phosphoinositide (PI) 3-kinase in vivo.