The heat shock protein 90 inhibitor, AT13387, displays a long duration of action in vitro and in vivo in non-small cell lung cancer.

A ubiquitously expressed chaperone, heat shock protein 90 (HSP90) is of considerable interest as an oncology target because tumor cells and oncogenic proteins are acutely dependent on its activity. AT13387 (2,4-dihydroxy-5-isopropyl-phenyl)-[5-(4-methyl-piperazin-1-ylmethyl)-1,3-dihydro-isoindol-2-yl] methanone, l-lactic acid salt) a novel, high-affinity HSP90 inhibitor, which is currently being clinically tested, has shown activity against a wide array of tumor cell lines, including lung cancer cell lines. This inhibitor has induced the degradation of specific HSP90 client proteins for up to 7 days in tumor cell lines in vitro. The primary driver of cell growth (mutant epidermal growth factor receptors) was particularly sensitive to HSP90 inhibition. The long duration of client protein knockdown and suppression of phospho-signaling seen in vitro after treatment with AT13387 was also apparent in vivo, with client proteins and phospho-signaling suppressed for up to 72 h in xenograft tumors after treatment with a single dose of AT13387. Pharmacokinetic analyses indicated that while AT13387 was rapidly cleared from blood, its retention in tumor xenografts was markedly extended, and it was efficacious in a range of xenograft models. AT13387's long duration of action enabled, in particular, its efficacious once weekly administration in human lung carcinoma xenografts. The use of longer-acting HSP90 inhibitors, such as AT13387, on less frequent dosing regimens has the potential to maintain antitumor efficacy as well as minimize systemic exposure and unwanted effects on normal tissues.

Biological characterization of AT7519, a small-molecule inhibitor of cyclin-dependent kinases, in human tumor cell lines.

Cyclin-dependent kinases (CDK), and their regulatory cyclin partners, play a central role in eukaryotic cell growth, division, and death. This key role in cell cycle progression, as well as their deregulation in several human cancers, makes them attractive therapeutic targets in oncology. A series of CDK inhibitors was developed using Astex's fragment-based medicinal chemistry approach, linked to high-throughput X-ray crystallography. A compound from this series, designated AT7519, is currently in early-phase clinical development. We describe here the biological characterization of AT7519, a potent inhibitor of several CDK family members. AT7519 showed potent antiproliferative activity (40-940 nmol/L) in a panel of human tumor cell lines, and the mechanism of action was shown here to be consistent with the inhibition of CDK1 and CDK2 in solid tumor cell lines. AT7519 caused cell cycle arrest followed by apoptosis in human tumor cells and inhibited tumor growth in human tumor xenograft models. Tumor regression was observed following twice daily dosing of AT7519 in the HCT116 and HT29 colon cancer xenograft models. We show that these biological effects are linked to inhibition of CDKs in vivo and that AT7519 induces tumor cell apoptosis in these xenograft models. AT7519 has an attractive biological profile for development as a clinical candidate, and the tolerability and efficacy in animal models compare favorably with other CDK inhibitors in clinical development. Studies described here formed the biological rationale for investigating the potential therapeutic benefit of AT7519 in cancer patients.

Multiple metabolic alterations exist in mutant PI3K cancers, but only glucose is essential as a nutrient source.

Targeting tumour metabolism is becoming a major new area of pharmaceutical endeavour. Consequently, a systematic search to define whether there are specific energy source dependencies in tumours, and how these might be dictated by upstream driving genetic mutations, is required. The PI3K-AKT-mTOR signalling pathway has a seminal role in regulating diverse cellular processes including cell proliferation and survival, but has also been associated with metabolic dysregulation. In this study, we sought to define how mutations within PI3KCA may affect the metabolic dependency of a cancer cell, using precisely engineered isogenic cell lines. Studies revealed gene expression signatures in PIK3CA mutant cells indicative of a consistent up-regulation of glycolysis. Interestingly, the genes up- and down-regulated varied between isogenic models suggesting that the primary node of regulation is not the same between models. Additional gene expression changes were also observed, suggesting that metabolic pathways other than glycolysis, such as glutaminolysis, were also affected. Nutrient dependency studies revealed that growth of PIK3CA mutant cells is highly dependent on glucose, whereas glutamine dependency is independent of PIK3CA status. In addition, the glucose dependency exhibited by PIK3CA mutant cells could not be overridden by supplementation with other nutrients. This specific dependence on glucose for growth was further illustrated by studies evaluating the effects of targeted disruption of the glycolytic pathway using siRNA and was also found to be present across a wider panel of cancer cell lines harbouring endogenous PIK3CA mutations. In conclusion, we have found that PIK3CA mutations lead to a shift towards a highly glycolytic phenotype, and that despite suggestions that cancer cells are adept at utilising alternative nutrient sources, PIK3CA mutant cells are not able to compensate for glucose withdrawal. Understanding the metabolic dependencies of PIK3CA mutant cancers will provide critical information for the design of effective therapies and tumour visualisation strategies.

Fragment-Based Discovery of 7-Azabenzimidazoles as Potent, Highly Selective, and Orally Active CDK4/6 Inhibitors.

Herein, we describe the discovery of potent and highly selective inhibitors of both CDK4 and CDK6 via structure-guided optimization of a fragment-based screening hit. CDK6 X-ray crystallography and pharmacokinetic data steered efforts in identifying compound 6, which showed >1000-fold selectivity for CDK4 over CDKs 1 and 2 in an enzymatic assay. Furthermore, 6 demonstrated in vivo inhibition of pRb-phosphorylation and oral efficacy in a Jeko-1 mouse xenograft model.

AT13148 is a novel, oral multi-AGC kinase inhibitor with potent pharmacodynamic and antitumor activity.

PURPOSE: Deregulated phosphatidylinositol 3-kinase pathway signaling through AGC kinases including AKT, p70S6 kinase, PKA, SGK and Rho kinase is a key driver of multiple cancers. The simultaneous inhibition of multiple AGC kinases may increase antitumor activity and minimize clinical resistance compared with a single pathway component. EXPERIMENTAL DESIGN: We investigated the detailed pharmacology and antitumor activity of the novel clinical drug candidate AT13148, an oral ATP-competitive multi-AGC kinase inhibitor. Gene expression microarray studies were undertaken to characterize the molecular mechanisms of action of AT13148. RESULTS: AT13148 caused substantial blockade of AKT, p70S6K, PKA, ROCK, and SGK substrate phosphorylation and induced apoptosis in a concentration and time-dependent manner in cancer cells with clinically relevant genetic defects in vitro and in vivo. Antitumor efficacy in HER2-positive, PIK3CA-mutant BT474 breast, PTEN-deficient PC3 human prostate cancer, and PTEN-deficient MES-SA uterine tumor xenografts was shown. We show for the first time that induction of AKT phosphorylation at serine 473 by AT13148, as reported for other ATP-competitive inhibitors of AKT, is not a therapeutically relevant reactivation step. Gene expression studies showed that AT13148 has a predominant effect on apoptosis genes, whereas the selective AKT inhibitor CCT128930 modulates cell-cycle genes. Induction of upstream regulators including IRS2 and PIK3IP1 as a result of compensatory feedback loops was observed. CONCLUSIONS: The clinical candidate AT13148 is a novel oral multi-AGC kinase inhibitor with potent pharmacodynamic and antitumor activity, which shows a distinct mechanism of action from other AKT inhibitors. AT13148 will now be assessed in a first-in-human phase I trial.

Potent, selective inhibitors of fibroblast growth factor receptor define fibroblast growth factor dependence in preclinical cancer models.

We describe here the identification and characterization of 2 novel inhibitors of the fibroblast growth factor receptor (FGFR) family of receptor tyrosine kinases. The compounds exhibit selective inhibition of FGFR over the closely related VEGFR2 receptor in cell lines and in vivo. The pharmacologic profile of these inhibitors was defined using a panel of human tumor cell lines characterized for specific mutations, amplifications, or translocations known to activate one of the four FGFR receptor isoforms. This pharmacology defines a profile for inhibitors that are likely to be of use in clinical settings in disease types where FGFR is shown to play an important role.

Discovery of (2,4-dihydroxy-5-isopropylphenyl)-[5-(4-methylpiperazin-1-ylmethyl)-1,3-dihydroisoindol-2-yl]methanone (AT13387), a novel inhibitor of the molecular chaperone Hsp90 by fragment based drug design.

Inhibitors of the molecular chaperone heat shock protein 90 (Hsp90) are currently generating significant interest in clinical development as potential treatments for cancer. In a preceding publication (DOI: 10.1021/jm100059d ) we describe Astex's approach to screening fragments against Hsp90 and the subsequent optimization of two hits into leads with inhibitory activities in the low nanomolar range. This paper describes the structure guided optimization of the 2,4-dihydroxybenzamide lead molecule 1 and details some of the drug discovery strategies employed in the identification of AT13387 (35), which has progressed through preclinical development and is currently being tested in man.

Identification of N-(4-piperidinyl)-4-(2,6-dichlorobenzoylamino)-1H-pyrazole-3-carboxamide (AT7519), a novel cyclin dependent kinase inhibitor using fragment-based X-ray crystallography and structure based drug design.

The application of fragment-based screening techniques to cyclin dependent kinase 2 (CDK2) identified multiple (>30) efficient, synthetically tractable small molecule hits for further optimization. Structure-based design approaches led to the identification of multiple lead series, which retained the key interactions of the initial binding fragments and additionally explored other areas of the ATP binding site. The majority of this paper details the structure-guided optimization of indazole (6) using information gained from multiple ligand-CDK2 cocrystal structures. Identification of key binding features for this class of compounds resulted in a series of molecules with low nM affinity for CDK2. Optimisation of cellular activity and characterization of pharmacokinetic properties led to the identification of 33 (AT7519), which is currently being evaluated in clinical trials for the treatment of human cancers.