The Surprising Landscape of CDK Inhibitor Selectivity in Live Cells

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

nanobret technology for kinase target engagement

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.

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Illuminating the Function of a Dark Kinase (DCLK1) with a Selective Chemical Probe

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

NanoBRET target engagement

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).

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RiboMAX and the Effort to Find Antiviral Drugs to Fight Coronaviruses and Enteroviruses

Prior to 2020, there were two major outbreaks of coronaviruses. In 2003, an outbreak of SARS-CoV sickened 8098 people and killed 774. In 2012, an outbreak of MERS-CoV began which so far has sickened 2553 and killed 876. Although the overall number of MERS cases is low, the disease has a high fatality rate, and new cases are still being reported. Even though fatality rates are high for these two outbreaks, containment was quickly achieved. This makes development of a treatment not commercially viable so no one had undertaken a large effort to develop an approved treatment for either coronavirus infection.

Fast forward to late 2019/2020… well, you know what has happened. There is currently no reliable antiviral treatment for SARS-CoV-2, the coronavirus that causes COVID-19 infections.

Zhang, et al. thought of a way to make an antiviral treatment commercially viable. If the treatment is actually a broad-spectrum antiviral, it could be used to treat more than one infection, meaning, it can be used to treat more people and thus be seen as more valuable and worth the financial risk to pharmaceutical companies. So, they decided to look at the similarities between coronaviruses and enteroviruses.

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Public-Private Initiative to Increase COVID-19 Testing Capacity by Using Promega Maxwell Instrument in India

This blog is written by guest blogger, Dr Rajnish Bharti, General Manager of Promega Biotech India Pvt Ltd.

As COVID-19 cases accelerate, the country of India has decided to scale up testing capacity to 100,000 tests per day in the coming days.

In a major step to counter the coronavirus crisis, Promega India is supporting government agencies through our automated instruments. The Maxwell® RSC instrument is a compact, automated RNA extraction platform that processes up to 48 samples simultaneously in less than 35 minutes. The automated Promega solution allows laboratories to process up to 400 samples in a typical 8-hour shift.

Scientists in India train on the Maxwell RSC 48
Forensic Science Laboratory-Jaipur and SMS Hospital Jaipur join hands together to use Promega Maxwell® RSC 48 to Increase COVID-19 Testing capacity.
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A Valuable AP Biology Throwback

Today’s blog is written by guest blogger, Isobel Utschig, a science teacher at Dominican High School in Whitefish Bay, WI. We bring this to you in celebration of #TeacherAppreciationWeek 2020

About 10 years ago, I attended a field trip at the Biopharmaceutical Technology Center Institute with my AP Biology classmates. I felt apprehensive upon seeing the micropipettes and other “foreign” lab supplies on the benchtops. We learned that we would be using enzymes to cut DNA and visualize those different fragments on a gel. I marveled at the glowing streaks and found it incredible that I was looking (albeit indirectly) at real pieces of DNA. As we moved into the genetic transformation activity I was even more intrigued. We opened the tubes of bacteria and added some luciferase DNA, which would allow the bacteria to create a light-producing protein.  We then “heat shocked” the bacteria to coax them to take up these plasmids from their environment looking at the bacteria later, their glow revealed our success. The day flew by and at the end I marveled at all that we had done!

Students from Dominican High School AP Biology busy at work 
during a BTC Institute field trip
Students from Dominican High School AP Biology busy at work
during a BTC Institute field trip

Three years later I joined a research lab at Marquette University. Upon seeing the lab benches full of unfamiliar equipment, the same wave of apprehension came over me. My PI introduced me to the first task: digest a plasmid with restriction enzymes and verify the cut with gel electrophoresis. Memories of the high school field trip flooded my mind as I gripped a micropipette and attempted to nimbly load the wells. While I greatly improved in my skills over the course of the summer, the familiarity I had from my trip to the BTC Institute put me at ease from the beginning.  

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Getting a PhD in Sweatpants: Guest Blog by Dr. Susanna Harris

Today’s blog is guest-written by Susanna Harris, who recently defended her PhD thesis at the University of North Carolina in Chapel Hill.


I just defended my PhD. Nearly six years of blood, sweat, and tears, most of which were cleaned up with Kimwipes while sitting at my desk in a laboratory facing out towards the UNC Chapel Hill football field. Nearly six years of work, all summed up in a handful of slides. Nearly six years of work, explained to my friends, family, and colleagues – a moment I had dreamed of since the fall of 2014.

What I hadn’t dreamed of? That I would be sitting at my small desk in the corner of my room, with no present audience aside from my snoring dogs. That there would be no dinner celebration that carried into a night of fun along Franklin Street. That, unseen by the viewers of my defense, I would be wearing sweatpants as my name changed from Ms. to Dr. Harris.

Pictured: The audience for Susanna’s thesis defense.

Why did I wear sweatpants when I could have worn literally anything in my closet? Because I think it’s hilarious. I believe this situation will end and we will walk away with memories and lessons learned from an extremely difficult time in the history of the world. I want to walk away with one more ridiculous story to add to a long list of “What even was that?” tales from grad school.

Working towards a PhD is hard at any time; let’s not pretend this pandemic isn’t making things even worse. I was fortunate in many ways that my advisor had already moved our laboratory to a new state in 2019, allowing me to adjust to meeting through webcams and working from home before the pandemic changed the lives of all North Carolinians. This has given me a unique perspective to tease out which problems come from distance working and which are the result of Safer-At-Home orders. Based on my experiences, here are a few tips, tricks, and words of warning.

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Just Keep Swimming: How the Wisdom of a Blue Cartoon Fish Can Inspire Us Amid COVID-19

Today’s blog is written by guest blogger Karen Stakun, Global Brand Manager at Promega.

Wise words from a forgetful blue fish are uniting Promega employees during these trying days. Initiated by our VP of Operations as a rallying call to employees and reinforced through a kind gesture from the Hollywood writer and director who dreamed up the fish, I invite you to join Promega as we “Just Keep Swimming.”

Those words were uttered by Dory, a blue tang with short-term memory loss, in the 2003 animated movie Finding Nemo. Now a classic, it tells the story of Marlin, an overprotective clownfish, who searches the ocean for his missing son Nemo. Dory is his sometimes-unwelcome companion. Desperate to find his son, Marlin grows exhausted and begins to feel defeated, but Dory will not let him give up. Her motivation is simple yet potent. “Just Keep Swimming.”

Setting the Scene

As COVID-19 was emerging in China, Promega began scaling up manufacturing in January to meet the growing global need for testing products. As epidemic became pandemic, and demand quickly became unprecedented, we moved swiftly to increase capacity and add more shifts at our Madison manufacturing facilities, all while ensuring the safety of our employees.

All of this takes dedicated people, especially those on our operations team, working long hours in an atmosphere of global uncertainty. Dedication is in abundance at Promega, as every employee feels a deep commitment to humanity’s struggle against this disease. However, Chuck York, our VP of Operations, says he began seeing the team struggle with the never-ending increases in demand. Despite record product totals, it could be demoralizing for a group that prides itself on always being able to deliver what customers need.

That’s when Chuck recalled one of his family’s favorite movies. “I love the never-give-up aspect of Finding Nemo and in particular the net scene.” Toward the end of the movie, Dory and several other fish find themselves caught in a fishing net. With Nemo’s help, the fish realize they can turn Dory’s mantra into action. They keep swimming together in the same direction and break free of the net.   

“I wanted the team to focus on what we could control, doing all we can each day to keep product flowing. And we were and are doing an outstanding job of that. I also hoped to lighten the mood and bring a smile to peoples’ faces. Our ‘net’ is the ever surging COVID-19 demand, but eventually we will overcome if we just keep swimming.”

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Fighting the COVID-19 Pandemic With Antibody Testing: The Importance of Serological Assays

Today’s blog is written by Ashley G. Anderson, MD, Chief Medical Officer at Promega.

The need for reliable virus detection methods is central to the global response to COVID-19. These test results not only inform health decisions for individual patients, but they also help us build projections of how the virus will spread, which can in turn influence policy decisions.

Following the emergence of COVID-19, PCR-based tests were developed and deployed to detect the virus in patients in hospitals. PCR, or Polymerase Chain Reaction, is a common technique used in labs to amplify large quantities of DNA. The detection tests use swabs placed deep into the back of the nose to detect genetic material carried by SARS-CoV-2, the virus causing COVID-19.

Those tests have been crucial to monitoring infection rates and informing patient treatment, but at this point they have fallen short of providing an overall picture of the pandemic. We know that thousands more cases have likely gone untested due to mild or unnoticed symptoms or lack of access to tests. Since PCR-based methods can only tell us if the virus is active in the patient at the time of sample and offer no information about whether a patient has been infected in the past, we currently have no way to determine how many of these unconfirmed cases exist or which patients have recovered. Serological assays are the one of the most promising tools to address that question.

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Wisconsin’s Public-Private Partnership to Increase COVID-19 Testing Capacity

This blog is written by Sara Mann, General Manger, Promega North America Branch

Promega is part of a new public-private partnership among Wisconsin industry leaders to increase the state’s laboratory testing capacity for COVID-19. I am pleased to represent Promega in this effort. The valuable insight we at Promega are gaining every day through our participation in this innovative partnership not only benefits Wisconsin labs, it also provides unique understandings about how we can best meet the testing needs of our customers around the world.

Promega Maxwell Instrument shown in a laboratory.

The new partnership includes laboratory support from Exact Sciences, Marshfield Clinic Health System, UW Health, as well as Promega. These organizations, along with the Wisconsin Clinical Lab Network, are sharing knowledge, resources, and technology to bolster Wisconsin’s testing capacity. Our goal is to help labs find the quickest approach to the most tests with their validated methods.

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