Guillard and colleagues profiled gene expression following treatment A-674563 of human glioma cells with the class I PI3K/mTOR inhibitor PI 103 and detected altered expression of genes encoding regulators of the cell cycle and cholesterol metabolism, together with genes modulated by insulin or IGF1 signalling, rapamycin treatment or nutrient starvation. Expression profiling of ex vivo treated peripheral blood mononuclear cells has also detected a gene signature associated with inhibition of PI3K inhibition, this . Further validation of selected cell surface proteins identified from the gene signature determined that the altered expression was specifically induced by PI3K inhibition and not induced by selected cytotoxic agents, MEK inhibitors or the mTORC1 inhibitor rapamycin in vitro or in vivo.
Some of the biomarkers described herein have been reported as having been examined in early clinical studies of PI3K inhibitors. AZ 960 While it is preferable to look at the effects of PI3K inhibitors on pathway activation in tumours, and this has been done, it is sometimes difficult to access the tumour, or to obtain repeat biopsies. Therefore assessment of PI3K signalling in alternative surrogate normal tissues has also been considered. One option is the hair follicle, which is convenient for repeat sampling and importantly has high PI3K pathway basal activity. For example, in mouse studies the PI3K inhibitor PX 866 decreased phosphorylation AKTSER473 in both hair follicles and skin, also NVP BEZ235 has been reported to decrease RPS6SER240/244 and AKTSER473 phosphorylation in mouse skin.
Significantly, early clinical studies of XL765 have reported activity against phosphorylation of PRAS40THR246, 4EBP1THR37/46, RPS6SER240/244 and AKTSER473 in patient hair follicles, while another study has reported decreased RPS6SER240/244 in skin samples from patients treated with BMK120. PBMCs and platelet rich plasma have also been considered as alternate tissues to determine PI3K pathway inhibition. Measurement of AKTSER473 phosphorylation in PBMC lysates has proved too variable to be useful, however, analysis of AKTSER473 levels in platelet rich plasma has proved to be a successful alternative, and decreased AKTSER473 has been reported following treatment of patients with GDC 0941 and GDC 0980.
Importantly, the extent of decreased AKTSER473 phosphorylation in platelet rich plasma correlated with the dose of GDC 0941 and was concomitant with decreased RPS6SER240/244 phosphorylation in tumour biopsies. Demonstration of inhibition of PI3K signalling, generally using AKTSER473 or RPS6SER240/244 phosphorylation, has also been made in biopsies from solid tumours treated with XL147, GDC 0941, PX 866 and XL765 while a study with the p110???specific inhibitor CAL 101 reported decreased AKTTHR308 in isolated lymphocytes from CLL patients. In summarizing this section, various pharmacodynamic and proof of mechanism biomarkers have been developed which can be utilised to measure inhibition of the PI3K pathway in tumour biopsies and surrogate normal tissues. Use of these in early clinical trials is providing confidence that the pathway is inhibited by a given drug, and allows optimization of the dose and administration schedule.