Phosphatidylinositol-3-kinase (PI3K) is an important target in cancer due to the deregulation of the PI3K/ Akt signaling pathway in a wide variety of tumors. A series of thieno[3,2-d]pyrimidine derivatives were prepared and evaluated as inhibitors of PI3 kinase p110alpha. The synthesis, biological activity, and further profiling of these compounds are described. This work resulted in the discovery of 17, GDC-0941, which is a potent, selective, orally bioavailable inhibitor of PI3K and is currently being evaluated in human clinical trials for the treatment of cancer.

The phosphatidylinositide 3-kinase pathway is frequently deregulated in human cancers and inhibitors offer considerable therapeutic potential. We previously described the promising tricyclic pyridofuropyrimidine lead and chemical tool compound PI-103. We now report the properties of the pharmaceutically optimized bicyclic thienopyrimidine derivatives PI-540 and PI-620 and the resulting clinical development candidate GDC-0941. All four compounds inhibited phosphatidylinositide 3-kinase p110α with IC 50 ≤ 10 nmol/L. Despite some differences in isoform selectivity, these agents exhibited similar in vitro antiproliferative properties to PI-103 in a panel of human cancer cell lines, with submicromolar potency in PTEN-negative U87MG human glioblastoma cells and comparable phosphatidylinositide 3-kinase pathway modulation. PI-540 and PI-620 exhibited improvements in solubility and metabolism with high tissue distribution in mice. Both compounds gave improved antitumor efficacy over PI-103, following i.p. dosing in U87MG glioblastoma tumor xenografts in athymic mice, with treated/control values of 34% (66% inhibition) and 27% (73% inhibition) for PI-540 (50 mg/ kg b.i.d.) and PI-620 (25 mg/kg b.i.d.), respectively. GDC-0941 showed comparable in vitro antitumor activity to PI-103, PI-540, and PI-620 and exhibited 78% oral bioavailability in mice, with tumor exposure above 50% antiproliferative concentrations for >8 hours following 150 mg/kg p.o. and sustained phosphatidylinositide 3-kinase pathway inhibition. These properties led to excellent dose-dependent oral antitumor activity, with daily p.o. dosing at 150 mg/kg achieving 98% and 80% growth inhibition of U87MG glioblastoma and IGROV-1 ovarian cancer xenografts, respectively. Together, these data support the development of GDC-0941 as a potent, orally bioavailable inhibitor of phosphatidylinositide 3-kinase. GDC-0941 has recently entered phase I clinical trials.

The discovery of 2 (GDC-0980), a class I PI3K and mTOR kinase inhibitor for oncology indications, is described. mTOR inhibition was added to the class I PI3K inhibitor 1 (GDC-0941) scaffold primarily through the substitution of the indazole in 1 for a 2-aminopyrimidine. This substitution also increased the microsomal stability and the free fraction of compounds as evidenced through a pairwise comparison of molecules that were otherwise identical. Highlighted in detail are analogues of an advanced compound 4 that were designed to improve solubility, resulting in 2. This compound, is potent across PI3K class I isoforms with IC(50)s of 5, 27, 7, and 14 nM for PI3Kα, β, δ, and γ, respectively, inhibits mTOR with a K(i) of 17 nM yet is highly selective versus a large panel of kinases including others in the PIKK family. On the basis of the cell potency, low clearance in mouse, and high free fraction, 2 demonstrated significant efficacy in mouse xenografts when dosed as low as 1 mg/kg orally and is currently in phase I clinical trials for cancer.

The PI3K/AKT/mTOR pathway has been shown to play an important role in cancer. Starting with compounds 1 and 2 (GDC-0941) as templates, (thienopyrimidin-2-yl)aminopyrimidines were discovered as potent inhibitors of PI3K or both PI3K and mTOR. Structural information derived from PI3K gamma-ligand cocrystal structures of 1 and 2 were used to design inhibitors that maintained potency for PI3K yet improved metabolic stability and oral bioavailability relative to 1. The addition of a single methyl group to the optimized 5 resulted in 21, which had significantly reduced potency for mTOR. The lead compounds 5 (GNE-493) and 21 (GNE-490) have good pharmacokinetic (PK) parameters, are highly selective, demonstrate knock down of pathway markers in vivo, and are efficacious in xenograft models where the PI3K pathway is deregulated. Both compounds were compared in a PI3K alpha mutated MCF7.1 xenograft model and were found to have equivalent efficacy when normalized for exposure.

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Of the four class I phosphoinositide 3-kinase (PI3K) isoforms, PI3Kα has justly received the most attention for its potential in cancer therapy. Herein we report our successful approaches to achieve PI3Kα vs PI3Kβ selectivity for two chemical series. In the thienopyrimidine series of inhibitors, we propose that select ligands achieve selectivity derived from a hydrogen bonding interaction with Arg770 of PI3Kα that is not attained with the corresponding Lys777 of PI3Kβ. In the benzoxepin series of inhibitors, the selectivity observed can be rationalized by the difference in electrostatic potential between the two isoforms in a given region rather than any specific interaction.

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In our continued effort to identify selective MRP1 modulators, we have developed two novel templates, 3 and 4, through rational drug design by identifying the key pharmacophore interaction at the 7-position of the pyrrolopyrimidine template 1. Further synthesis and SAR work on these novel templates gave a number of potent MRP1 modulators with great selectivity against Pgp. Additional studies to reduce the CYP3A4 inhibition are also reported. Several compounds of these classes were subjected to in vivo xenograft studies and in vivo efficacies were demonstrated.