Synthesis and structure-activity relationship of 3,4'-bispyridinylethylenes: discovery of a potent 3-isoquinolinylpyridine inhibitor of protein kinase B (PKB/Akt) for the treatment of cancer

The Atypical Protein Kinase C Small Molecule Inhibitor ζ-Stat, and Its Effects on Invasion Through Decreases in PKC-ζ Protein Expression

Ovarian cancer is estimated to reach 22,530 diagnoses and cause 13,980 cancer deaths per year. The most common histology diagnosed of ovarian cancer is epithelial ovarian carcinomas (EOC). An aggressive epithelial subtype is clear cell ovarian carcinoma (CCOC) and is characterized as a non-serous ovarian cancer. Protein kinase C (PKC) is an enzymatic family of proteins that have been found to be a component in cancer progression, tissue invasion, and metastasis. The atypical PKC (aPKC) isoforms, PKC-ι and PKC-ζ, have been suggested to participate in the increased proliferation of ovarian cancers. Previous studies have indicated that novel aPKC inhibitors ICA-1S and ζ-Stat decreased the migratory behaviors of colorectal cancer cells and were selective for PKC-ι/λ and PKC-ζ, respectively. The aims of this investigation were to further determine the binding mechanisms of ζ-Stat, expand on the tissue range of these compounds, investigate the therapeutic potential of ζ-Stat in CCOC, and to illustrate the disruption of invasion via the PKC-ζ signaling cascade. The methods utilized were molecular docking and virtual target screening, Western blot analysis, end-point PCR, GST pull down, cell viability and invasion and migration assays. We discovered that the small molecule inhibitor, ζ-Stat, is a prospective drug candidate to investigate as a novel potential treatment for CCOC. We also found that the PKC-ζ/Ect2/Rac1 activation pathway was decreased by ζ-Stat, which in turn decreased invasive behavior of CCOC.

Nanomedicines Eradicating Cancer Stem-like Cells in Vivo by pH-Triggered Intracellular Cooperative Action of Loaded Drugs

Nanomedicines capable of control over drug functions have potential for developing resilient therapies, even against tumors harboring recalcitrant cancer stem cells (CSCs). By coordinating drug interactions within the confined inner compartment of core-shell nanomedicines, we conceived multicomponent nanomedicines directed to achieve synchronized and synergistic drug cooperation within tumor cells as a strategy for enhancing efficacy, overcoming drug resistance, and eradicating CSCs. The approach was validated by using polymeric micellar nanomedicines co-incorporating the pan-kinase inhibitor staurosporine (STS), which was identified as the most potent CSC inhibitor from a panel of signaling-pathway inhibitors, and the cytotoxic agent epirubicin (Epi), through rationally contriving the affinity between the drugs. The micelles released both drugs simultaneously, triggered by acidic endosomal pH, attaining concurrent intracellular delivery, with STS working as a companion for Epi, down-regulating efflux transporters and resistance mechanisms induced by Epi. These features prompted the nanomedicines to eradicate orthotopic xenografts of Epi-resistant mesothelioma bearing a CSC subpopulation.

Lessons from Hot Spot Analysis for Fragment-Based Drug Discovery

Analysis of binding energy hot spots at protein surfaces can provide crucial insights into the prospects for successful application of fragment-based drug discovery (FBDD), and whether a fragment hit can be advanced into a high-affinity, drug-like ligand. The key factor is the strength of the top ranking hot spot, and how well a given fragment complements it. We show that published data are sufficient to provide a sophisticated and quantitative understanding of how hot spots derive from a protein 3D structure, and how their strength, number, and spatial arrangement govern the potential for a surface site to bind to fragment-sized and larger ligands. This improved understanding provides important guidance for the effective application of FBDD in drug discovery.

Pharmacophore modeling, virtual screening, and molecular docking studies for discovery of novel Akt2 inhibitors

Akt2 is considered as a potential target for cancer therapy. In order to find novel Akt2 inhibitors which have different scaffolds, structure-based pharmacophore model and 3D-QSAR pharmacophore model were built and validated by different methods. Then, they were used for chemical databases virtual screening. The selected compounds were further analyzed and refined using drug-like filters and ADMET analysis. Finally, seven hits with different scaffolds were picked out for docking studies. These seven hits were predicted to have high inhibitory activity and good ADMET properties, they may act as novel leads for Akt2 inhibitors designing.

Inhibition of Akt with small molecules and biologics: historical perspective and current status of the patent landscape

INTRODUCTION

Akt plays a pivotal role in cell survival and proliferation through a number of downstream effectors; unregulated activation of the PI3K/PTEN/Akt pathway is a prominent feature of many human cancers. Akt is considered an attractive target for cancer therapy by the inhibition of Akt alone or in combination with standard cancer chemotherapeutics. Both preclinical animal studies and clinical trials in humans have validated Akt as an important target of cancer drug discovery.

AREA COVERED

A historical perspective of Akt inhibitors, including PI analogs, ATP-competitive and allosteric Akt inhibitors, along with other inhibitory mechanisms are reviewed in this paper with a focus on issued patents, patent applications and a summary of clinical trial updates since the last review in 2007.

EXPERT OPINION

A vast diversity of inhibitors of Akt, both small molecule and biologic, have been developed in the past 5 years, with over a dozen in various phases of clinical development, and several displaying efficacy in humans. While it is not yet clear which mechanism of Akt inhibition will be optimal in humans, or which Akt isoforms to inhibit, or whether a small molecule or biologic agent will be best, data to all of these points will be available in the near future.

Targeting PKC-β II and PKB Connection: Design of Dual Inhibitors

Protein kinase C (PKC) has been the center of many cell signaling pathways. PKC isoforms, specifically PKC-β II is linked to both diabetic complications as well as in promotion of angiogenesis and regulation of cancers. PKC-β II activates the PKB/Akt pathway. Enzastaurin, a selective PKC-β II inhibitor has been found to inhibit PKB/Akt by suppressing the regulation of various cancerous pathways. In the present work, we carried out an in depth study on the binding mode of inhibitors of PKC-β II, enzastaurin and ruboxistaurin with the active site residues of PKB and PKC-β II. A ligand based approach has been further used to determine the pharmacophoric features and spatial arrangement of molecules, having common properties necessary for appropriate binding to the active site of both targets. Virtual screening of the respective pharmacophores of both proteins led to identification of hits which may be useful for treatment of diabetic complications and cancer. The study has highlighted important features that may be considered in the future for designing novel inhibitors.

Discovery of 4-amino-1-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperidine-4-carboxamides as selective, orally active inhibitors of protein kinase B (Akt)

Protein kinase B (PKB or Akt) is an important component of intracellular signaling pathways regulating growth and survival. Signaling through PKB is frequently deregulated in cancer, and inhibitors of PKB therefore have potential as antitumor agents. The optimization of lipophilic substitution within a series of 4-benzyl-1-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperidin-4-amines provided ATP-competitive, nanomolar inhibitors with up to 150-fold selectivity for inhibition of PKB over the closely related kinase PKA. Although active in cellular assays, compounds containing 4-amino-4-benzylpiperidines underwent metabolism in vivo, leading to rapid clearance and low oral bioavailability. Variation of the linker group between the piperidine and the lipophilic substituent identified 4-amino-1-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperidine-4-carboxamides as potent and orally bioavailable inhibitors of PKB. Representative compounds modulated biomarkers of signaling through PKB in vivo and strongly inhibited the growth of human tumor xenografts in nude mice at well-tolerated doses.

A comprehensive structure-activity analysis of protein kinase B-alpha (Akt1) inhibitors

Protein kinase B (PKB, also known as Akt) belongs to the AGC subfamily of the protein kinase superfamily. Akt1 has been reported as a central player in regulation of metabolism, cell survival, motility, transcription and cell-cycle progression, among the signalling proteins that respond to a large variety of signals. In this study an attempt was made to understand structural requirements for Akt1 inhibition using conventional QSAR, k-nearest neighbour QSAR and novel GQSAR methods. With this intention, a wide variety of structurally diverse Akt1 inhibitors were collected from various literature reports. The conventional QSAR analyses revealed the key role of Baumann's alignment independent topological descriptors along with other descriptors such as the number of hydrogen bond acceptors, hydrogen bond donors, rotatable bonds and aromatic oxygen (SaaOcount) along with molecular branching (chi3Cluster), alkene carbon atom type (SdsCHE-index) in governing activity variation. Further, the GQSAR analyses show that chemical variations like presence of hetero-aromatic ring, flexibility, polar surface area and fragment length present in the hinge binding fragment (in the present case fragment D) are highly influential for achieving highly potent Akt1 inhibitors. In addition, this study resulted in a k-nearest neighbour classification model with three descriptors suggesting the key role of oxygen (SssOE-index) and aromatic carbon (SaaCHE-index and SaasCE-index) atoms electro-topological environment that differentiate molecules binding to Akt1 kinase or PH domain. The developed models are interpretable, with good statistical and predictive significance, and can be used for guiding ligand modification for the development of potential new Akt1 inhibitors.

The PIK3CA gene as a mutated target for cancer therapy

The development of targeted therapies with true specificity for cancer relies upon exploiting differences between cancerous and normal cells. Genetic and genomic alterations including somatic mutations, translocations, and amplifications have served as recent examples of how such differences can be exploited as effective drug targets. Small molecule inhibitors and monoclonal antibodies directed against the protein products of these genetic anomalies have led to cancer therapies with high specificity and relatively low toxicity. Recently, our group and others have demonstrated that somatic mutations in the PIK3CA gene occur at high frequency in breast and other cancers. Moreover, the majority of mutations occur at three hotspots, making these ideal targets for therapeutic development. Here we review the literature on PIK3CA mutations in cancer, as well as existing data on PIK3CA inhibitors and inhibitors of downstream effectors for potential use as targeted cancer therapeutics.

Targeting Akt in cancer therapy

In an effort to improve therapeutic options in cancer, many investigational drugs are being developed to inhibit signaling pathways that promote the survival of cancer cells. The prototypic pathway that promotes cellular survival is the phosphoinositide 3'-kinase/Akt/mammalian target of rapamycin pathway, which is constitutively activated in many types of cancers. Mechanisms for activation of the serine/threonine kinase, Akt, include loss of tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) function, amplification or mutation of phosphoinositide 3'-kinase, amplification of Akt, activation of growth factor receptors and exposure to carcinogens. Activation of Akt promotes cellular survival as well as resistance to treatment with chemotherapy and/or radiation therapy. Immunohistochemical analyses have shown that Akt is activated in many types of cancers and preneoplastic lesions, and Akt activation is a poor prognostic factor in various cancers. Taken together, these data demonstrate that Akt is a valid target for inhibition. This review will focus on published data using different approaches to inhibit Akt. We will also consider how the complex regulation of the phosphoinositide 3'-kinase/Akt/mammalian target of rapamycin pathway poses practical issues concerning the design of clinical trials, potential toxicities and the likelihood of finding a therapeutic index when targeting such a critical cellular pathway.

Indolinone based phosphoinositide-dependent kinase-1 (PDK1) inhibitors. Part 1: Design, synthesis and biological activity

HTS screening identified 1 with micromolar inhibitory activity against PDK1. Optimization of 1 afforded 4i (BX-517) which has single-digit nanomolar activity against PDK1 and excellent selectivity against PKA.

Design and synthesis of pyridine–pyrazolopyridine-based inhibitors of protein kinase B/Akt

Thr-211 is one of three different amino acid residues in the kinase domain of protein kinase B/Akt as compared to protein kinase A (PKA), a closely related analog in the same AGC family. In an attempt to improve the potency and selectivity of our indazole-pyridine series of Akt inhibitors over PKA, efforts have focused on the incorporation of a chemical functionality to interact with the hydroxy group of Thr-211. Several substituents including an oxygen anion, amino, and nitro groups have been introduced at the C-6 position of the indazole scaffold, leading to a significant drop in Akt potency. Incorporation of a nitrogen atom into the phenyl ring at the same position (i.e., 9f) maintained the Akt activity and, in some cases, improved the selectivity over PKA. The structure-activity relationships of the new pyridine-pyrazolopyridine series of Akt inhibitors and their structural features when bound to PKA are also discussed.

A structural comparison of inhibitor binding to PKB, PKA and PKA-PKB chimera

Although the crystal structure of the anti-cancer target protein kinase B (PKBbeta/Akt-2) has been useful in guiding inhibitor design, the closely related kinase PKA has generally been used as a structural mimic due to its facile crystallization with a range of ligands. The use of PKB-inhibitor crystallography would bring important benefits, including a more rigorous understanding of factors dictating PKA/PKB selectivity, and the opportunity to validate the utility of PKA-based surrogates. We present a "back-soaking" method for obtaining PKBbeta-ligand crystal structures, and provide a structural comparison of inhibitor binding to PKB, PKA, and PKA-PKB chimera. One inhibitor presented here exhibits no PKB/PKA selectivity, and the compound adopts a similar binding mode in all three systems. By contrast, the PKB-selective inhibitor A-443654 adopts a conformation in PKB and PKA-PKB that differs from that with PKA. We provide a structural explanation for this difference, and highlight the ability of PKA-PKB to mimic the true PKB binding mode in this case.

Synthesis and SAR of indazole-pyridine based protein kinase B/Akt inhibitors

A series of heteroaryl-pyridine containing inhibitors of Akt are reported. The synthesis and structure-activity relationships are discussed, leading to the discovery of a indazole-pyridine analogue (K(i)=0.16 nM). These compounds bind in the ATP binding site, are potent, ATP competitive, and reversible inhibitors of Akt activity. No selectivity amongst the Akt isoforms is observed for this analogue, but there is good selectivity against an panel of other kinases. It is least selective for other members of the AGC family of kinases but is nonetheless 40-fold selective for Akt over PKA. The compound shows cellular activity and significantly slows tumor growth in vivo.

Discovery of 2-pyrimidyl-5-amidothiophenes as potent inhibitors for AKT: Synthesis and SAR studies

A series of 2-pyrimidyl-5-amidothiophenes has been synthesized and evaluated for AKT inhibition. SAR studies resulted in potent inhibitors of AKT with IC(50) values as low as single digit nanomolar as represented by compound 2aa. Compound 2aa showed cellular activity including antiproliferation and downstream target modulation. Selectivity profile is described. A co-crystal of 2aa with PKA is determined and discussed.

Identification of a novel 3,5-disubstituted pyridine as a potent, selective, and orally active inhibitor of Akt1 kinase

Based on lead compounds 2 and 3 a series of 3,5-disubstituted pyridines have been designed and evaluated for inhibition of AKT/PKB. Modifications at the 3 position of the pyridine ring led to a number of potent compounds with improved physical properties, resulting in the identification of 11g as a promising, orally active Akt inhibitor. The synthesis, structure-activity relationship studies, and pharmacokinetic data are presented in this paper.

Discovery and SAR of oxindole-pyridine-based protein kinase B/Akt inhibitors for treating cancers

We describe a series of potent and selective oxindole-pyridine-based protein kinase B/Akt inhibitors. The most potent compound 11n in this series demonstrated an IC(50) of 0.17nM against Akt1 and more than 100-fold selectivity over other Akt isozymes. The selectivity against other protein kinases was highly dependent on the C-3 substitutions at the oxindole scaffold, with unsubstituted 9e or 3-furan-2-ylmethylene (11n) more selective and 3-(1H-pyrrol-2-yl)methylene (11f) or 3-(1H-imidazol-2-yl)methylene (11k) less selective. In a mouse xenograft model, 9d, 11f, and 11n inhibited tumor growth but with accompanying toxicity.

Isoquinoline-pyridine-based protein kinase B/Akt antagonists: SAR and in vivo antitumor activity

The structure-activity relationships of a series of isoquinoline-pyridine-based protein kinase B/Akt antagonists have been investigated in an effort to improve the major short-comings of the lead compound 3, including poor pharmacokinetic profiles in several species (e.g., mouse i.v. t(1/2) = 0.3 h, p.o. F = 0%). Chlorination at C-1 position of the isoquinoline improved its pharmacokinetic property in mice (i.v. t(1/2) = 5.0 h, p.o. F = 51%) but resulted in >500-fold drop in potency. In a mouse MiaPaCa-2 xenograft model, an amino analog 10y significantly slowed the tumor growth, however was accompanied by toxicity.