Identification of 2-oxatriazines as highly potent pan-PI3K/mTOR dual inhibitors.

We recently described several highly potent, triazine (1) and triazolopyrimidine (2) scaffold-based, dual PI3K/mTOR-inhibitors (e.g., 1, PKI-587) that were efficacious in both in vitro and in vivo models. In order to further optimize these compounds we devised a novel series, the 2-oxatriazines, which also exhibited excellent potency and good metabolic stability. Some 2-oxatriazines showed promising in vivo biomarker suppression and induced apoptosis in the MDA-MB-361 breast cancer xenograft model.

Antitumor efficacy of PKI-587, a highly potent dual PI3K/mTOR kinase inhibitor.

PURPOSE: The aim of this study was to show preclinical efficacy and clinical development potential of PKI-587, a dual phosphoinositide 3-kinase (PI3K)/mTOR inhibitor. EXPERIMENTAL DESIGN: In vitro class 1 PI3K enzyme and human tumor cell growth inhibition assays and in vivo five tumor xenograft models were used to show efficacy. RESULTS: In vitro, PKI-587 potently inhibited class I PI3Ks (IC(50) vs. PI3K-α = 0.4 nmol/L), PI3K-α mutants, and mTOR. PKI-587 inhibited growth of 50 diverse human tumor cell lines at IC(50) values of less than 100 nmol/L. PKI-587 suppressed phosphorylation of PI3K/mTOR effectors (e.g., Akt), and induced apoptosis in human tumor cell lines with elevated PI3K/mTOR signaling. MDA-MB-361 [breast; HER2(+), PIK3CA mutant (E545K)] was particularly sensitive to this effect, with cleaved PARP, an apoptosis marker, induced by 30 nmol/L PKI-587 at 4 hours. In vivo, PKI-587 inhibited tumor growth in breast (MDA-MB-361, BT474), colon (HCT116), lung (H1975), and glioma (U87MG) xenograft models. In MDA-MB-361 tumors, PKI-587 (25 mg/kg, single dose i.v.) suppressed Akt phosphorylation [at threonine(T)308 and serine(S)473] for up to 36 hours, with cleaved PARP (cPARP) evident up to 18 hours. PKI-587 at 25 mg/kg (once weekly) shrank large (∼1,000 mm(3)) MDA-MB-361 tumors and suppressed tumor regrowth. Tumor regression correlated with suppression of phosphorylated Akt in the MDA-MB-361 model. PKI-587 also caused regression in other tumor models, and efficacy was enhanced when given in combination with PD0325901 (MEK 1/2 inhibitor), irinotecan (topoisomerase I inhibitor), or HKI-272 (neratinib, HER2 inhibitor). CONCLUSION: Significant antitumor efficacy and a favorable pharmacokinetic/safety profile justified phase 1 clinical evaluation of PKI-587.

Synthesis of phosphatidylinositol 3-kinase (PI3K) inhibitory analogues of the sponge meroterpenoid liphagal.

Analogues of the sponge meroterpenoid liphagal have been synthesized and evaluated for inhibition of PI3Kα and PI3Kγ as part of a program aimed at developing new isoform-selective PI3K inhibitors. One of the analogues, compound 24, with IC50 values of 66 nM against PI3Kα and 1840 nM against PI3Kγ, representing a 27-fold preference for PI3Kα, exhibited enhanced chemical stability and modestly enhanced potency and selectivity compared with the natural product liphagal.

PKI-179: an orally efficacious dual phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibitor.

A series of mono-morpholino 1,3,5-triazine derivatives (8a-8q) bearing a 3-oxa-8-azabicyclo[3.2.1]octane were prepared and evaluated for PI3-kinase/mTOR activity. Replacement of one of the bis-morpholines in lead compound 1 (PKI-587) with 3-oxa-8-azabicyclo[3.2.1]octane and reduction of the molecular weight yielded 8m (PKI-179), an orally efficacious dual PI3-kinase/mTOR inhibitor. The in vitro activity, in vivo efficacy, and PK properties of 8m are discussed.

Antitumor efficacy profile of PKI-402, a dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor.

PKI-402 is a selective, reversible, ATP-competitive, equipotent inhibitor of class I phosphatidylinositol 3-kinases (PI3K), including PI3K-alpha mutants, and mammalian target of rapamycin (mTOR; IC(50) versus PI3K-alpha = 2 nmol/L). PKI-402 inhibited growth of human tumor cell lines derived from breast, brain (glioma), pancreas, and non-small cell lung cancer tissue and suppressed phosphorylation of PI3K and mTOR effector proteins (e.g., Akt at T308) at concentrations that matched those that inhibited cell growth. In MDA-MB-361 [breast: Her2(+) and PIK3CA mutant (E545K)], 30 nmol/L PKI-402 induced cleaved poly(ADP-ribose) polymerase (PARP), a marker for apoptosis. In vivo, PKI-402 inhibited tumor growth in MDA-MB-361, glioma (U87MG), and lung (A549) xenograft models. In MDA-MB-361, PKI-402 at 100 mg/kg (daily for 5 days, one round) reduced initial tumor volume of 260 mm(3) to 129 mm(3) and prevented tumor regrowth for 70 days. In MDA-MB-361 tumors, PKI-402 (100 mg/kg, single dose) suppressed Akt phosphorylation (at T308) and induced cleaved PARP. Suppression of phosphorylated Akt (p-Akt) was complete at 8 hours and still evident at 24 hours. Cleaved PARP was evident at 8 and 24 hours. In normal tissue (heart and lung), PKI-402 (100 mg/kg) had minimal effect on p-Akt, with no detectable cleaved PARP. Preferential accumulation of PKI-402 in tumor tissue was observed. Complete, sustained suppression of Akt phosphorylation may cause tumor regression in MDA-MB-361 and other xenograft models. We are testing whether dual PI3K/mTOR inhibitors can durably suppress p-Akt, induce cleaved PARP, and cause tumor regression in a diverse set of human tumor xenograft models. Mol Cancer Ther; 9(4); 976-84. (c)2010 AACR.

B-Raf kinase inhibitors: hit enrichment through scaffold hopping.

In continuation of our efforts toward hit identification and optimization for a B-Raf kinase project, we have employed a scaffold hopping strategy. The original HTS hit scaffold pyrazolo[1,5-a]pyrimidine was replaced with different thienopyrimidine and thienopyridine scaffolds to append the optimal pharmacophore moieties in order to generate novel B-raf kinase inhibitors with desirable potency and properties. This strategy led to the identification of additional lead compound 11b which had good enzyme and cell potency, while maintaining selectivity over a number of kinases.

Synthesis and SAR of novel 4-morpholinopyrrolopyrimidine derivatives as potent phosphatidylinositol 3-kinase inhibitors.

Significant evidence suggests that deregulation of the PI3K/Akt pathway is important in tumor progression. Mechanisms include loss of function of the tumor suppressor PTEN and high frequency of mutation of the PI3K p110alpha isoform in human malignancies. This connection between PI3K and tumor genesis makes PI3K a promising target for cancer treatment. A series of 4-morpholinopyrrolopyrimidine derivatives were synthesized and evaluated as inhibitors of PI3Kalpha and mTOR, leading to the discovery of PI3Kalpha selective inhibitors (e.g., 9) and dual PI3Kalpha/mTOR kinase inhibitors (e.g., 46 and 48). PI3Kalpha/mTOR dual inhibitors demonstrated inhibition of tumor cell growth in vitro and in vivo and caused suppression of the pathway specific biomarkers [e.g., the phosphorylation of Akt at Thr308 (T308) and Ser473 (S473)] in the human breast cancer cell line MDA361. In addition, compound 46 demonstrated good in vivo efficacy in the MDA361 human breast tumor xenograft model.

Bis(morpholino-1,3,5-triazine) derivatives: potent adenosine 5'-triphosphate competitive phosphatidylinositol-3-kinase/mammalian target of rapamycin inhibitors: discovery of compound 26 (PKI-587), a highly efficacious dual inhibitor.

The PI3K/Akt signaling pathway is a key pathway in cell proliferation, growth, survival, protein synthesis, and glucose metabolism. It has been recognized recently that inhibiting this pathway might provide a viable therapy for cancer. A series of bis(morpholino-1,3,5-triazine) derivatives were prepared and optimized to provide the highly efficacious PI3K/mTOR inhibitor 1-(4-{[4-(dimethylamino)piperidin-1-yl]carbonyl}phenyl)-3-[4-(4,6-dimorpholin-4-yl-1,3,5-triazin-2-yl)phenyl]urea 26 (PKI-587). Compound 26 has shown excellent activity in vitro and in vivo, with antitumor efficacy in both subcutaneous and orthotopic xenograft tumor models when administered intravenously. The structure-activity relationships and the in vitro and in vivo activity of analogues in this series are described.

Novel imidazolopyrimidines as dual PI3-Kinase/mTOR inhibitors.

This article describes the syntheses and SAR of a series of imidazolopyrimidine derivatives, which are evaluated as inhibitors of PI3-Kinase (PI3K) and mTOR. These compounds were found to be ATP competitive with good tumor cell growth inhibition, and suppression of pathway specific biomakers such as phosphorylation of Akt at T308.

Lead optimization of N-3-substituted 7-morpholinotriazolopyrimidines as dual phosphoinositide 3-kinase/mammalian target of rapamycin inhibitors: discovery of PKI-402.

Herein we describe the identification and lead optimization of triazolopyrimidines as a novel class of potent dual PI3K/mTOR inhibitors, resulting in the discovery of 3 (PKI-402). Compound 3 exhibits good physical properties and PK parameters, low nanomolar potency against PI3Kalpha and mTOR, and excellent inhibition of cell proliferation in several human cancer cell lines. Furthermore, in vitro and in vivo biomarker studies demonstrated the ability of 3 to shut down the PI3K/Akt pathway and induce apoptosis in cancer cells. In addition, 3 showed excellent in vivo efficacy in various human cancer xenografts, validating suppression of PI3K/mTOR signaling as a potential anticancer therapy.

Novel purine and pyrazolo[3,4-d]pyrimidine inhibitors of PI3 kinase-alpha: Hit to lead studies.

Series of purine and pyrazolo[3,4-d]pyrimidine inhibitors of phosphatidylinositol-3-kinases (PI3K) have been prepared. The optimized purine inhibitors show good potency in a PI3K p110alpha (PI3K-alpha) fluorescence polarization assay with good selectivity versus PI3K p110gamma (PI3K-gamma) and the mammalian target of rapamycin (mTOR). The related pyrazolo[3,4-d]pyrimidines show potent PI3K-alpha and mTOR inhibition with good selectivity versus PI3K-gamma. Representative compounds showed activity in a cellular proliferation assay against Caco-2 colorectal, LoVo colorectal and PC3MM2 prostate adenocarcinoma cancer cells. Signaling through the PI3K pathway was confirmed via inhibition of phospho-AKT in MDA-361 cells.

Hit to lead optimization of pyrazolo[1,5-a]pyrimidines as B-Raf kinase inhibitors.

Our continued effort towards optimization of the pyrazolo[1,5-a]pyrimidine scaffold as B-Raf kinase inhibitors is described. Structure guided design was utilized to introduce kinase hinge region interacting groups in the 2-position of the scaffold. This strategy led to the identification of lead compound 9 with enhanced enzyme and cellular potency, while maintaining good selectivity over a number of kinases.

Non-hinge-binding pyrazolo[1,5-a]pyrimidines as potent B-Raf kinase inhibitors.

As part of our research effort to discover B-Raf kinase inhibitors, we prepared a series of C-3 substituted N-(3-(pyrazolo[1,5-a]pyrimidin-7-yl)phenyl)-3-(trifluoromethyl)benzamides. X-ray crystallography studies revealed that one of the more potent inhibitors (10n) bound to B-Raf kinase without forming a hinge-binding hydrogen bond. With basic amine residues appended to C-3 aryl residues, cellular activity and solubility were enhanced over previously described compounds of this class.

Scalarane-based sesterterpenoid RCE-protease inhibitors isolated from the Indonesian marine sponge Carteriospongia foliascens.

Two new 20,24-bishomo-25-norscalaranes, compounds 1 and 2, and two new and two known 20,24-bishomoscalaranes, compounds 3-6, have been isolated from the Indonesian marine sponge Carteriospongia foliascens. The structures of 1-6 were determined by spectroscopic analysis. Compounds 1 and 3-6 inhibit RCE-protease activity.

Identification of pyrazolo[1,5-a]pyrimidine-3-carboxylates as B-Raf kinase inhibitors.

B-Raf kinase plays a critical role in the Raf-MEK-ERK signaling pathway and inhibitors of B-Raf could be used in the treatment of melanomas, colorectal cancer, and other Ras related human cancers. We have identified novel small molecule pyrazolo[1,5-a]pyrimidine derivatives as B-Raf kinase inhibitors. Structure-activity relationship was generated for various regions of the scaffold to improve the biochemical profile.

4-Anilino-7-alkenylquinoline-3-carbonitriles as potent MEK1 kinase inhibitors.

A series of substituted 7-alkenyl 4[3-chloro-4-(1-methyl-1H-imidazol-2-ylsulfanyl)]anilino-3-quinolinecarbonitrile analogs were synthesized and evaluated as MEK1 kinase inhibitors. The synthetic details, structure-activity relationships, biological activity, and selected oral exposure studies of these analogs are described. From these studies, compound 5m was chosen as a strong candidate for further evaluation. The selectivity of 5m was ascertained against a panel of 17 kinases, where activity was observed against EGFR, Src, Lyn, and IR kinases. Western blot studies in WM-266 cells demonstrated that 5m inhibited phosphorylation of ERK, while additional kinase pathways tested showed no inhibition at up to 10 microM of 5 m. PK studies, as well as a xenograft and in vivo biomarker studies are described for 5m.

A directly labeled TR-FRET assay for monitoring phosphoinositide-3-kinase activity.

Phosphoinositide 3-kinases (PI3Ks) comprise a family of kinases that transfer the terminal phosphate of adenosine triphosphate to phosphoinositides at the 3-hydroxyl of the inositol ring to form phosphoinositide (3,4,5) triphosphate (PIP3). The PI3Ks have been shown to play key roles in cell growth, motility, morphology, and survival and thus are of interest as targets in anti-inflammatory and anti-oncogenic drug development. To facilitate identification of novel and selective inhibitors of PI3Ks, we have developed a TR-FRET assay that uses directly labeled reagents. The assay makes use of the high affinity binding of phosphoinositides to a Pleckstrin homology (PH) domain in the general receptor for phosphoinositides 1 (Grp1) protein. It monitors PIP3 produced from the enzymatic reaction by measuring its competition with Bodipy-FL-labeled PIP3 for binding to Terbium chelate-labeled Grp1. By using directly labeled reagents, this assay configuration offers higher sensitivity and faster binding/dissociation kinetics than existing non-radioactive assays, which are critical for competitive assay formats. The assay is homogenous, robust (Z' = 0.88), and simple and, thus, compatible with high throughput screening (HTS) processes.

Liphagal, a Selective inhibitor of PI3 kinase alpha isolated from the sponge akacoralliphaga: structure elucidation and biomimetic synthesis.

[structure: see text] Liphagal (1), a selective inhibitor of PI3K alpha, has been isolated from the marine sponge Aka coralliphaga collected in Dominica. The "liphagane" meroterpenoid carbon skeleton of liphagal (1) is new. A biomimetic total synthesis has been used to confirm the constitution of liphagal (1) and support a proposed biogenesis.

Identification of 4-anilino-3-quinolinecarbonitrile inhibitors of mitogen-activated protein/extracellular signal-regulated kinase 1 kinase.

A high-throughput screen for Ras-mitogen-activated protein kinase (MAPK) signaling inhibitors identified two series (class 1 and 2) of substituted 4-anilino-3-quinolinecarbonitriles as potent (IC(50)s <10 nmol/L) mitogen-activated protein/extracellular signal-regulated kinase 1 (MEK1) kinase inhibitors. These compounds had cyanoquinoline cores, but differed in their respective aniline groups [1a, 1b: 4-phenoxyphenylaniline; 2a, 2b: 3-chloro-4-(1-methylimidazol-2-sulfanyl)aniline]. These compounds were competitive inhibitors of ATP binding by MEK1 kinase, and they had minimal or no effect on Raf, epidermal growth factor receptor (EGFR), Akt, cyclin-dependent kinase 4 (CDK4), or MK2 kinases at concentrations >100-fold higher than those that inhibited MEK1 kinase. Both class 1 and 2 compounds inhibited in vitro growth of human tumor cell lines. A class 2 compound (2b) was the most potent inhibitor of human tumor cell growth in vitro, and this effect was linked to distinct suppression of MAPK phosphorylation in cells. Compound 2b did not affect phosphorylation status of other kinases, such as EGFR, Akt, and stress-activated protein (SAP)/c-jun-NH kinase (Jnk); nor did it affect overall tyrosine phosphorylation level in cells. However, compound 2b did inhibit MEK1 phosphorylation in cells. Inhibition of MEK1 phosphorylation by 2b was not due to a major effect on Raf kinase activity, because enzyme assays showed minimal Raf kinase inhibition. We believe compound 2b inhibits kinase activity upstream of Raf, and thereby affects MEK1 phosphorylation in cells. Even with the dual effect of 2b on MEK and MAPK phosphorylation, this compound was well tolerated and significantly inhibited growth of the human colon tumor cell line LoVo (at 50 and 100 mg/kg BID, i.p.) in a nude mouse xenograft model.

Synthesis and evaluation of 4-anilino-6,7-dialkoxy-3-quinolinecarbonitriles as inhibitors of kinases of the Ras-MAPK signaling cascade.

4-[3-Chloro-4-(1-methyl-1H-imidazol-2-ylsulfanyl)]anilino-6,7-diethoxy-3-quinolinecarbonitrile (3) was identified as a MEK1 kinase inhibitor with exceptional activity against LoVo cells. The structure-activity relationships of the C-4 aniline substituents were explored, and water-solubilizing groups were added at the C-7 position to improve physical properties. Secondary cellular assays revealed that a compound possessing the appropriate aniline substituents inhibited MEK1 as well as MAPK phosphorylation, thereby acting as a dual inhibitor of the Ras-MAPK signaling cascade.