Shripad S. Bhagwat

AC220 is a uniquely potent and selective inhibitor of FLT3 for the treatment of acute myeloid leukemia (AML)

Activating mutations in the receptor tyrosine kinase FLT3 are present in up to approximately 30% of acute myeloid leukemia (AML) patients, implicating FLT3 as a driver of the disease and therefore as a target for therapy. We report the characterization of AC220, a second-generation FLT3 inhibitor, and a comparison of AC220 with the first-generation FLT3 inhibitors CEP-701, MLN-518, PKC-412, sorafenib, and sunitinib. AC220 exhibits low nanomolar potency in biochemical and cellular assays and exceptional kinase selectivity, and in animal models is efficacious at doses as low as 1 mg/kg given orally once daily. The data reveal that the combination of excellent potency, selectivity, and pharmacokinetic properties is unique to AC220, which therefore is the first drug candidate with a profile that matches the characteristics desirable for a clinical FLT3 inhibitor.

Kinase inhibitors for the treatment of inflammatory and autoimmune disorders

Drugs targeting inhibition of kinases for the treatment of inflammation and autoimmune disorders have become a major focus in the pharmaceutical and biotech industry. Multiple kinases from different pathways have been the targets of interest in this endeavor. This review describes some of the recent developments in the search for inhibitors of IKK2, Syk, Lck, and JAK3 kinases. It is anticipated that some of these compounds or newer inhibitors of these kinases will be approved for the treatment of rheumatoid arthritis, psoriasis, organ transplantation, and other autoimmune diseases.

Arylcarboxyamino-substituted diaryl ureas as potent and selective FLT3 inhibitors

A series of diaryl ureas with an amide substitution at the 4-position was prepared and found to be potent and selective FLT3 inhibitors with good oral bioavailability and efficacy in a tumor xenograft model.

Novel series of pyrrolotriazine analogs as highly potent pan-Aurora kinase inhibitors

The synthesis and SAR for a novel series of pyrrolotriazines as pan-Aurora kinase inhibitors are described. Optimization of the cyclopropane carboxamide terminus of lead compound 1 resulted in analogs with high cellular activity and improved rat PK profiles. Notably, compound 17l demonstrated tumor growth inhibition in a mouse xenograft model.

4-Quinazolinyloxy-diaryl ureas as novel BRAFV600E inhibitors.

Aryl phenyl ureas with a 4-quinazolinoxy substituent at the meta-position of the phenyl ring are potent inhibitors of mutant and wild type BRAF kinase. Compound 7 (1-(5-tert-butylisoxazol-3-yl)-3-(3-(6,7-dimethoxyquinazolin-4-yloxy)phenyl)urea hydrochloride) exhibits good pharmacokinetic properties in rat and mouse and is efficacious in a mouse tumor xenograft model following oral dosing.

Chapter 17 MAP Kinase Inhibitors in Inflammation and Autoimmune Disorders

Publisher Summary Mitogen-activated protein kinases (MAPKs) are a family of serine, threonine phosphorelay enzymes activated by cytokines, growth factors, stress, immune receptors and G-protein coupled receptors (GPCRs). The three major MAPK families, whose regulation and function have been conserved during evolution in eukaryotic cells, are extracellular signal-regulated protein kinase (ERK), c-Jun NH2-terminal kinase (JNK) and p38. In inflammatory cells such as macrophages, stimulation of selected Toll family receptors like TLR4 by microbial pathogens or other immunogenic factors leads to the activation of the ERK pathway. Stimulation of TLR4 activates Tpl-2, a MKKK, which phosphorylates and activates MEK1/2 (MKK1/2) leading to the activation of ERK1/2. Activated ERK1/2 regulates expression of tumor necrosis factor-α(TNFα) and other cytokines, which are the key mediators of inflammation and immune responses. The ERK pathway can also be activated in other cell types, by binding of a growth factor such as epidermal growth factor (EGF) to its receptor resulting in the activation of Ras which then activates Raf serine/threonine kinase. The stimulus- and location-selective activation of the p38 MAPK pathway is also controlled by the scaffolding proteins—TAB1 and OSM.

CHAPTER 3. P2 PURINOCEPTORS : A FAMILY OF NOVEL THERAPEUTIC TARGETS

Publisher Summary This chapter discusses the identification of specific ligands, agonists, antagonists, and allosteric modulators to define the physiological/pharmacological function of P 2 purinoceptors. Purinoceptors have been originally divided into P 1 (ADO) and P 2 (adenosine triphosphate; ATP) subclasses. Pharmacological evaluation led to the classification of P 2X and P 2Y classes with the addition of P 2T and P 2Z receptors. Adenosine triphosphate (ATP) is an unusual candidate for a neurotransmitter, this role being conceptually viewed as an unorthodox use of cellular energy stores. As well as interacting with the members of the P 2 receptor family, ATP can be broken down via synaptic ectonucleotidase action to form adenosine (ADO), a neuromodulator in its own right. ATP can also modulate ADO interactions at the A 1 receptor. P 2 receptor nomenclature is currently in a state of considerable flux, evolving from a pharmacological basis to the state that relates receptor cloning to function. From a drug discovery perspective, it is a major step from the cloning and expression of the members of a new receptor family to defining their function. All known agonist ligands for the P 2 receptor family are variations on the purine nucleotide pharmacophore. The identification of novel pharmacophores selective for P 2 receptors that can be used to unambiguously characterize the various members of the receptor superfamily is critical to advancing the field. The P 2 receptor legands are potential of different therapeutic use. ATP is an effective and long-lasting inhibitor of human tumor cell growth. Again, ATP can be used as an adjunct to inhalation anesthetics. ATP and uridine triphosphate (UTP) have been evaluated as treatments for cystic fibrosis. P 2 receptor mechanisms may also be involved in cell adhesion. Thus, P 2 purinoceptors remains a key element in the discovery of new therapeutic agents.

Preface: special issue on medicinal chemistry of purines.

The concept of preparing a special issue of Purinergic Signalling to highlight progress in the medicinal chemistry of purines arose during the 8th International Symposium on Adenosine and Adenine Nucleotides, which was held in Ferrara, Italy, from 24 May to 28 May 2006. This meeting emphasized the accelerated pace of introduction of new compounds, including preclinical and clinical candidates, that act through purine-related mechanisms. The suggestion to broaden the scope to include the intracellular actions of purines, notably through protein kinases, was made by Dr. Michael Williams, as an Associate Editor of this journal. Consequently, this volume reveals new ligands for modulation of the function of proteins that are involved in purine action, encompassing both receptors and enzymes. This purview could be described under the umbrella of the “purinome,” which represents numerous critical interactions in cellular function. Given the limited space available, we are unable to effectively showcase all major aspects of the purinome, but rather have provided representative segments. The issue is written from the perspective of the medicinal chemist but in a manner comprehensible to those in the biological sciences. Both review chapters and original chemical research reports are included in this volume. We commend Prof. Geoff Burnstock, Editor in Chief of the journal, for enthusiastically supporting the inclusion of a dedicated issue on medicinal chemistry of purines and for recognizing a central role played by medicinal chemistry in the recent exponential growth of this field. The protein targets of compounds in this volume include twelve G protein-coupled receptors that respond to nucleosides and nucleotides, i.e., both adenosine (four subtypes) and P2Y receptors (eight subtypes), and seven nucleotide-gated ion channels, i.e., P2X receptors. A chapter by Carroll et al. reviews the P2X7 receptor. In addition, agonists (Baraldi et al., Gao et al., Kim et al.), antagonists (Kalla and Zablocki), and allosteric modulators (Goblyos and IJzerman) of the P1 family of adenosine receptors are described including compounds currently under active development. It is to be noted that at least four subtypes of the P2Y receptors are activated by pyrimidine nucleotides (Jacobson et al.). Thus, this issue is not exclusively limited to purines. These purine and pyrimidine receptors are widespread in the body and govern critical physiological processes, notably in the immune, cardiovascular, skeletal-muscular, and nervous systems. The volume also covers inhibition of the superfamily of >500 kinases, which are involved in intracellular signaling and are relevant to cancer (Garcia-Echeverria) and chronic inflammatory diseases (Bhagwat). The search for novel kinase inhibitors, which has become the focus of recent drug discovery efforts, has yielded eight small molecule drugs and a handful of protein therapeutics approved for human use to date. The number of kinase inhibitor drugs for the treatment of human disease is likely to increase in the near future. Also, the volume describes novel inhibitors of nucleotidase enzymes that interconvert extracellular nucleotides (Baki et al.), leading to a spectrum of biological effects. In conclusion, these fields deriving from the purinome have become a major focus in the pharmaceutical industry, and the promise of new drugs emerging from them is enormous. We hope that this special issue will be a good source of information and reference for basic and applied researchers in this field. 14 May 2008

Abstract 3619: Inhibition of FLT3 autophosphorylation and downstream signaling both in vitro and in vivo by AC220, a second generation potent and selective FLT3 inhibitor

Fms-like tyrosine kinase 3 (FLT3) is thought to be a major driver in the pathogenesis of acute myeloid leukemia (AML). FLT3-activating mutations are found in ∼ 30% of AML patients and are associated with poor outcome in this patient population. AC220 is a small molecule kinase inhibitor with potent and selective FLT3 inhibitory activity. Here we characterize the effect of AC220 on FLT3 autophosphorylation, activation of downstream signaling pathways (STAT5, ERK and AKT), cell cycle distribution, and apoptosis endpoints in multiple leukemia cell lines expressing either wild type FLT3 (FLT3-WT, SEM-K2 cells (FLT3-WT overexpression) and RS4;11 cells (FLT3-WT)) and/or ITD-mutated FLT3 (FLT3-ITD, MV4-11 (FLT3-ITD), MOLM-14 (FLT3-ITD/FLT3-WT)). Across each of these parameters we also compare the effects of AC220 to those of other known FLT3 inhibitors including, sorafenib, sunitinib, lestaurtinib, and midostaurin. AC220 inhibited FLT3 autophosphorylation in both FLT3-WT and FLT3-ITD cells with roughly equal potency, while other FLT3 inhibitors showed differential pFLT3 inhibition across several cell lines. Although AC220-mediated inhibition of FLT3 autophosphorylation was observed in all cell lines, subsequent cell death was only detected in the cell lines with activated FLT3. This contrasts with other FLT3 inhibitors, where potent inhibition of cell proliferation in the non-FLT3 activated RS4;11 cells was observed, highlighting the lack of FLT3 selectivity of these compounds. Consistent with FLT3 inhibition, AC220 also inhibited constitutively activated STAT5, ERK and AKT in these cell lines, suggesting that one or more of these pathways play a role in FLT3-mediated cell growth and survival. Furthermore, the inhibition of these downstream markers correlated with the inhibition of FLT3 across each of the FLT3 inhibitors tested. Lastly, in an MV4-11 murine xenograft model, AC220 administration resulted in the reduction of phosphorylated FLT3 and downstream signaling molecules concomitant with tumor reduction. Together, these data suggest that selective FLT3 inhibition is sufficient to inhibit the growth and induce cell death of FLT3-driven leukemia cells. AC220 is currently being evaluated in a phase II clinical trials in relapsed or refractory AML patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3619.

Patent Update Cardiovascular & Renal: Recent progress in modulators of purinergic activity

As knowledge of the molecular biology of purinergic receptors continues to evolve, the identification of novel compounds that mimic or block the actions of the purine nucleoside and its nucleotide, ATP, at P1 and P2 receptor subtypes, respectively, has continued to be an area of active interest in the pharmaceutical industry. Adenosine A1 receptor selective agonists with reduced cardiovascular liabilities have been recently described, as have novel A3 receptor selective agonists; both classes of agents showing potential as anti-ischaemic agents in animal models. A number of potent and receptor subtype selective agonists for P2 receptors have also been developed that are being used to characterise the functional role of this receptor class in various mammalian tissues. On the antagonist front, selective A1 receptor antagonists are being targeted as cognition enhancers while selective A2a receptor antagonists have been developed with potential use in Parkinsons disease therapy. Despite the clinical failure...