Characterization of the activity of the PI3K/mTOR inhibitor XL765 (SAR245409) in tumor models with diverse genetic alterations affecting the PI3K pathway.

Activation of the PI3K (phosphoinositide 3-kinase) pathway is a frequent occurrence in human tumors and is thought to promote growth, survival, and resistance to diverse therapies. Here, we report pharmacologic characterization of the pyridopyrimidinone derivative XL765 (SAR245409), a potent and highly selective pan inhibitor of class I PI3Ks (α, ß, γ, and δ) with activity against mTOR. Broad kinase selectivity profiling of >130 protein kinases revealed that XL765 is highly selective for class I PI3Ks and mTOR over other kinases. In cellular assays, XL765 inhibits the formation of PIP(3) in the membrane, and inhibits phosphorylation of AKT, p70S6K, and S6 phosphorylation in multiple tumor cell lines with different genetic alterations affecting the PI3K pathway. In a panel of tumor cell lines, XL765 inhibits proliferation with a wide range of potencies, with evidence of an impact of genotype on sensitivity. In mouse xenograft models, oral administration of XL765 results in dose-dependent inhibition of phosphorylation of AKT, p70S6K, and S6 with a duration of action of approximately 24 hours. Repeat dose administration of XL765 results in significant tumor growth inhibition in multiple human xenograft models in nude mice that is associated with antiproliferative, antiangiogenic, and proapoptotic effects.

Bridging the gap between preclinical and clinical studies using pharmacokinetic-pharmacodynamic modeling: an analysis of GDC-0973, a MEK inhibitor.

PURPOSE: GDC-0973 is a potent and selective mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor. Pharmacokinetic-pharmacodynamic (PK-PD) modeling was used to relate GDC-0973 plasma and tumor concentrations, tumor pharmacodynamics and antitumor efficacy to establish pharmacokinetic endpoints and predict active doses in the clinic. EXPERIMENTAL DESIGN: A PK-PD model was used to characterize GDC-0973 tumor disposition and in vivo potency in WM-266-4 xenograft mice. Simulations were conducted using the PK-PD model along with human pharmacokinetics to identify a target plasma concentration and predict active doses. In vivo potency and antitumor efficacy were characterized in A375 melanoma xenograft mice, and a population-based integrated PK-PD-efficacy model was used to relate tumor pharmacodynamics (%pERK decrease) to antitumor activity. RESULTS: GDC-0973 showed a sustained tumor pharmacodynamic response due to longer residence in tumor than in plasma. Following single doses of GDC-0973, estimated in vivo IC(50) values of %pERK decrease based on tumor concentrations in xenograft mice were 0.78 (WM-266-4) and 0.52 µmol/L (A375). Following multiple doses of GDC-0973, the estimated in vivo IC(50) value in WM-266-4 increased (3.89 µmol/L). Human simulations predicted a minimum target plasma concentration of 83 nmol/L and an active dose range of 28 to 112 mg. The steep relationship between tumor pharmacodynamics (%pERK decrease) and antitumor efficacy suggests a pathway modulation threshold beyond which antitumor efficacy switches on. CONCLUSIONS: Clinical observations of %pERK decrease and antitumor activity were consistent with model predictions. This article illustrates how PK-PD modeling can improve the translation of preclinical data to humans by providing a means to integrate preclinical and early clinical data.