Distribution of the phosphatidylinositol 3-kinase inhibitors Pictilisib (GDC-0941) and GNE-317 in U87 and GS2 intracranial glioblastoma models-assessment by matrix-assisted laser desorption ionization imaging.

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults, and the limited available treatment options have not meaningfully impacted patient survival in the past decades. Such poor outcomes can be at least partly attributed to the inability of most drugs tested to cross the blood-brain barrier and reach all areas of the glioma. The objectives of these studies were to visualize and compare by matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry the brain and tumor distribution of the phosphatidylinositol 3-kinase (PI3K) inhibitors pictilisib (GDC-0941, 2-(1H-indazol-4-yl)-6-(4-methanesulfonyl-piperazin-1-ylmethyl)-4-morpholin-4-yl-thieno[3,2-d]pyrimidine) and GNE-317 [5-(6-(3-methoxyoxetan-3-yl)-7-methyl-4-morpholinothieno[3,2-d]pyrimidin-2-yl)pyrimidin-2-amine] in U87 and GS2 orthotopic models of GBM, models that exhibit differing blood-brain barrier characteristics. Following administration to tumor-bearing mice, pictilisib was readily detected within tumors of the contrast-enhancing U87 model whereas it was not located in tumors of the nonenhancing GS2 model. In both GBM models, pictilisib was not detected in the healthy brain. In contrast, GNE-317 was uniformly distributed throughout the brain in the U87 and GS2 models. MALDI imaging revealed also that the pictilisib signal varied regionally by up to 6-fold within the U87 tumors whereas GNE-317 intratumor levels were more homogeneous. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analyses of the nontumored half of the brain showed pictilisib had brain-to-plasma ratios lower than 0.03 whereas they were greater than 1 for GNE-317, in agreement with their brain penetration properties. These results in orthotopic models representing either the contrast-enhancing or invasive areas of GBM clearly demonstrate the need for whole-brain distribution to potentially achieve long-term efficacy in GBM.

Preclinical assessment of the absorption and disposition of the phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor GDC-0980 and prediction of its pharmacokinetics and efficacy in human.

(S)-1-{4-[2-(2-Amino-pyrimidin-5-yl)-7-methyl-4-morpholin-4-yl-thieno[3,2-d]pyrimidin-6-ylmethyl]-piperazin-1-yl}-2-hydroxy-propan-1-one (GDC-0980) is a potent and selective inhibitor of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin, two key components of the PI3K pathway, the deregulation of which is associated with the development of many cancers. The objectives of these studies were to characterize the absorption and disposition of GDC-0980 and assess its efficacy in an MCF7-neo/HER2 human breast cancer xenograft model in immunocompromised mice. Studies in parental Madin-Darby canine kidney cells indicated that GDC-0980 had high permeability (P(app) = 18 × 10⁻6 cm/s), suggesting good absorption potential. However, it was found to be a P-glycoprotein and breast cancer resistance protein substrate in transfected cells and in knockout mice studies. Plasma protein binding was low, with the fraction unbound ranging from 29 to 52% across species. GDC-0980 hepatic clearance (CL) was predicted to be low in all of the species tested from hepatocyte incubations. The plasma CL of GDC-0980 was low in mouse (6.30 ml · min⁻¹ · kg⁻¹), rat (15.4 ml · min⁻¹ · kg⁻¹), and dog (6.37 ml · min⁻¹ · kg⁻¹) and moderate in cynomolgus monkey (18.9 ml · min⁻¹ · kg⁻¹). Oral bioavailability ranged from 14.4% in monkey to 125% in dog. Predicted human plasma CL and volume of distribution using allometry were 5.1 ml · min⁻¹ · kg⁻¹ and 1.8 l/kg, respectively. Parameters estimated from the pharmacokinetic/pharmacodynamic modeling of the MCF7-neo/HER2 xenograft data indicated that the GDC-0980 plasma concentration required for tumor stasis was approximately 0.5 µM. These parameters, combined with the predicted human pharmacokinetic profile, suggested that 55 mg once daily may be a clinically efficacious dose. GDC-0980 preclinical characterization and the predictions of its human properties supported its clinical development; it is currently in Phase II clinical trials.