G protein-coupled receptors (GPCRs) comprise a large group of cell surface receptors, characterized by the unique structural property of crossing the cell membrane seven times. They respond to a diverse group of signaling molecules, such as peptides, neurotransmitters, cytokines, hormones and other small molecules (1). Upon activation, GPCRs interact with GTP-binding (G) proteins and arrestins to regulate a wide variety of signaling pathways. This broad range of functions makes GPCRs attractive targets for drug discovery. The importance of GPCR research was highlighted in 2012, with the Nobel Prize in chemistry being awarded to Robert Lefkowitz and Brian Kobilka “for studies of G-protein–coupled receptors”.
Based on structure and function, GPCRs are categorized into six classes, A–F. The class A GPCRs, or rhodopsin-like receptors, have been studied extensively due to their association with many types of diseases (2). Within the class A GPCRs is a group that share a highly conserved structural motif (3) and respond to chemokines—small “chemotactic cytokines” that stimulate cell migration, especially that of white blood cells (4). A subfamily of class A GPCRs respond to chemokines that have two cysteine residues near the N-terminus, known as CC chemokines. GPCRs activated by CC chemokines are called CC chemokine receptors or CCRs, and these interactions have been implicated in both pro- and anti-cancer pathways (5).
Cyclin-dependent kinases (CDKs) are promising therapeutic targets in cancer and are currently among the most intensely studied enzymes in drug discovery. The FDA has recently approved three drugs for breast cancer that target members of this kinase subfamily, fueling interest in the entire family. Although broad efforts in drug discovery have produced many CDK inhibitors (CDKIs), few have been characterized in living cells. So just how potent are these compounds in a cellular environment? Are these compounds selective for their intended CDK target, or do they bind many similar kinases in cells? To address these questions, teams at the Structural Genomics Consortium and Promega used the NanoBRET™ Target Engagement technology to uncover surprising patterns of selectivity for touted CDKIs and abandoned clinical leads (1). The results offer exciting opportunities for repurposing some inhibitors as selective chemical probes for lesser-studied CDK family members.
CDKs and CDKIs
Cyclin-dependent kinases (CDKs) regulate a number of key global cellular processes, including cell cycle progression and gene transcription. As the name implies, CDK activity is tightly regulated by interactions with cyclin proteins. In humans, the CDK subfamily consists of 21 members and several are validated drivers of tumorigenesis. For example, CDKs 1, 2, 4 and 6 play a role in cell cycle progression and are validated therapeutic targets in oncology. However, the majority of the remaining CDK family is less studied. For example, some members of the CDK subfamily, such as CDKs 14–18, lack functional annotation and have unclear roles in cell physiology. Others, such as the closely related CDK8/19, are members of multiprotein complexes involved broadly in gene transcription. How these kinases function as members of such large complexes in a cellular context remains unclear, but their activity has been associated with several pathologies, including colorectal cancer. Despite their enormous therapeutic potential, our knowledge of the CDK family members remains incomplete.
The understudied kinome represents a major challenge as well as an exciting opportunity in drug discovery. A team of researchers lead by Nathanael Gray at the Dana Farber Cancer Institute was able to partially elucidate the function of an understudied kinase, Doublecortin-like kinase 1 (DCLK1), in pancreatic ductal adenocarcinoma cells (PDAC). The characterization of DCLK1 in PDAC was realized by developing a highly specific chemical probe (1). Promega NanoBRET™ Target Engagement (TE) technology enabled intracellular characterization of this chemical probe.
The Dark Kinome
Comprised of over 500 proteins, the human kinome is among the broadest class of enzymes in humans and is rife with targets for small molecule therapeutics. Indeed, to date, over 50 small molecule kinase inhibitors have achieved FDA approval for use in treating cancer and inflammatory diseases, with nearly 200 kinase inhibitors in various stages of clinical evaluation (2). Moreover, broad genomic screening efforts have implicated the involvement of a large fraction of kinases in human pathologies (3). Despite such advancements, our knowledge of the kinome is limited to only a fraction of its family members (3,4). For example, currently less than 20% of human kinases are being targeted with drugs in clinical trials. Moreover, only a subset of kinases historically has garnered substantial citations in academic research journals (4). As a result, a large proportion of the human kinome lacks functional annotation; as such, these understudied or “dark” kinases remain elusive to therapeutic intervention (4).
NanoLuc® luciferase has been discussed many times on this blog and our web site because the enzyme is integral to studying genetic responses and protein dynamics. While NanoLuc® luciferase was first introduced as a reporter enzyme to assess promoter activity, its capabilities have expanded far beyond a genetic reporter, creating tools used to study endogeneous protein interactions, target engagement, protein degradation and more. So where did the NanoLuc® luciferase come from and how does a one enzyme power several technologies?
Kinase target engagement is a new way to study kinase inhibitors for target selectivity, potency and residency. The NanoBRET™ TE Intracellular Kinase Assays enable you to quantitate kinase-inhibitor binding in live cells, making these assays an exciting new tool for kinase drug discovery research.
BTK (Bruton Tyrosine Kinase): Importance in Health and Disease
Bruton’s tyrosine kinase (BTK) was initially identified as a mediator of B-cell receptor signaling in the development and functioning of adaptive immunity. More recent and growing evidence supports an additional role for BTK in mononuclear cells of the innate immune system, especially dendritic cells and macrophages. For example, BTK functions in receptor-mediated recognition of infectious agents, cellular maturation and recruitment processes, and Fc receptor signaling. BTK has recently been identified as a direct regulator of a key innate inflammatory machinery, the NLRP3 inflammasome (2). Continue reading “Kinase Drug R & D: Helping Your Inhibitor Make the Cut”
The review “Kinase Inhibitors: the road ahead” was recently published in Nature Reviews Drug Discovery. In it, authors Fleur Ferguson and Nathanael Gray provide an up-to-date look at the “biological processes and disease areas that kinase-targeting small molecules are being developed against”. They note the related challenges and the strategies and technologies being used to efficiently generate highly-optimized kinase inhibitors.
This review describes the state of the art for kinase inhibitor therapeutics. To understand why kinase inhibitors are so important in the development of cancer (and other) therapeutics research, let’s start with the role of kinases in cellular physiology.
Joins Nominees for Best New Drug Discovery & Development Product 2017
We were honored recently to have NanoBRET™ Target Engagement Intracellular Kinase Assays nominated by SelectScience® as one of the Best New Drug Discovery & Development Products of 2017. This is a Scientists’ Choice Award®, an opportunity for scientists like you worldwide to vote for your favorite new drug discovery/development product.
We are super excited about both the nomination and the NanoBRET™ Target Engagement Intracellular Kinase Assay. Here is a little information about the assay.
Research surrounding drug discovery has historically been highly competitive and expensive. Unfortunately, many late-stage drug failures have occurred over recent years, often due to lack of efficacy. These failures have left the industry searching for new means by which to improve early drug discovery efforts aimed at understanding the drug target and its role in disease. One idea that is gaining traction is partnerships to openly share information at the early, precompetitive stages of drug discovery.
I used to think of open access only in terms of publishing data and information—online sites where you could freely access data without a subscription or membership, and without payment.
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