The living cell is constantly bombarded by extracellular signals. In humans, and many other organisms, these signals are communicated from the extracellular environment to the intracellular environment through signaling proteins such as G-protein-coupled receptors (GPCRs). These seven-transmembrane proteins are like the first runner in the relay race that comprises a signal transduction pathway. Upon the binding of a natural ligand (e.g. hormones) to a GPCR, the receptor initiates a signaling cascade that may culminate in a multitude of biological processes, such as cellular growth or differentiation. Due to their constitutive activation, mutated forms of GPCRs have been implicated in cancer. GPCRs are present in almost every human tissue, with large distributions in nervous, muscle, cardiac, and gastrointestinal tissues.

Like many signaling receptors, GPCRs transmit their messages intracellularly via the synthesis or release of second messenger molecules such as cyclic adenosine monophosphate (cAMP), beta arrestin, or calcium, thus passing the baton to the next element in the pathway. Activation of any of these second messenger systems will trigger one of the various protein-based cascades (depending on the pathway involved), culminating in the terminal biological outcome that was intended by the initial signal that activated the GPCR.

Because of their role in human disease, GPCRs have been drug discovery targets for decades. Among the drug classes used to target GPCRs are agonists, antagonists, and allosteric inhibitors, depending whether activation or inhibition of the target GPCR was the objective of the drug. With the astronomical increase in GPCR drug discovery over the last decade, there has been a concomitant increase in the development of a number of platforms to screen GPCR-targeted compound libraries. Many of these screening platforms measure second messenger molecules as an assay of GPCR function.

Pharma/tech marriages
Collaboration has become quite common in the pharmaceutical industry, especially between pharmaceutical companies and technology providers. Such partnerships offer a range of benefits to all parties involved, including expertise, services, and exchange of technology. Collaboration between BioFocus (Essex, UK) and DiscoveRx Corporation (Fremont, Calif.) is one recent example of such collaborative partnerships.

DiscoveRx Corporation is an assay development and tool provider whose primary product portfolio is in the GPCR space. The beta arrestin assay, which is the leading assay developed by DiscoveRx, is premised on the concept of enzyme fragment complementation in which GPCR targets are fused to a tag that facilitates detection of GPCR activity. Because of the use of these technologies in the GPCR drug discovery space, DiscoveRx has developed and commercialized over 400 assays for use in GPCR screening to measure a lot of different downstream signaling events like synthesis of cAMP or activation of beta arrestin over the past two years. “In the past, we have made our products available to pharmaceutical companies so that they can do internal discovery whether it is assay development or high throughput screening or downstream lead optimization,” says Sailaja Kuchibhatla, head of business development, DiscoveRx Corporation. “However, we have seen over the last two years that the market has changed and that there are a lot more partnerships among leading companies.” The main reason that DiscoveRx is working with companies such as BioFocus is to perform integrated drug discovery programs. “BioFocus has expertise and offers such programs to Pharma; hence, it was a good partnership whereby we can offer our technology platforms and products to BioFocus so that they can provide these benefits to our joint customers such as pharmaceutical and biotechnology companies.”

click to enlarge Domain Therapeutics scientist works on technical manipulation using DTect-All, its technology platform. (Image: Domain Therapeutics)

So what are some of the other reasons for this collaboration?

“I think that today’s market is definitely moving towards the use of integrated service providers,” says Richard Gordon, PhD, senior director at BioFocus. “In a competitive market in today’s recession, companies are looking for that something extra to complement their full range of services. Such alliances are becoming more commonplace in the marketplace as two integrated marketing approaches are bound to be more powerful than one.”

BioFocus is a contract research organization that offers a comprehensive suite of discovery products and services providing an integrated approach to the gene-to-drug candidate drug discovery process. “We can maximize each other’s strengths in terms of marketing and scientific know-how and this is something we are trying to build upon. We see this as a trial to see how this kind of relationships could work,” says Gordon. “So this partnership has allowed us to access the technologies, communication channels and presence that DiscoveRx has and vice versa.

“Collaborating with DiscoveRx allows us to expose our clients to unique screening technologies that they may not have been aware of previously,” says David Cronk, senior director of biology at BioFocus. “The integration of the service and the technology provides clients with the ability to outsource their screening to a single contract research organization, saving time and money, and accelerating their drug discovery.”

Adds DiscoveRx’s Kuchibhatla, “Collaborations allow people to bring their specific skill sets to the table. And, as the projects and programs are becoming more complex, it is becoming difficult for any one company to bring all the expertise and skills to the table. So partnerships are almost necessary moving forward.”
 

Saving an Ailing Heart Trevena, Inc. (King of Prussia, Pa.) is using the biased ligand approach to increase specificity and selectivity of novel GPCR-targeted drugs for the treatment of heart failure. “When an inhibitor binds to specific receptor, it actually activates not one, but several different pathways. And Trevena is interested in switching on or off these different pathways,” says Maxine Gowen, PhD, MBA, president and chief executive officer of Trevena Inc. Using the biased ligand approach, Trevena has been able to select their first clinical candidate for a cardiovascular indication known as decompensated heart failure. “To our knowledge, this is the first biased ligand to be taken forward to the clinic, and we hope that we will take it into the clinic in the first half of [2010],” says Gowen. Gowen explains that the natural ligand has both beneficial and detrimental actions in a heart failure patient. “We have discovered that the beneficial effects are mediated through the beta arrestin pathway; standard drugs for this receptor antagonize both pathways,” she adds. “The compound we currently have prepared for clinical trials is a full antagonist of the G-protein signaling pathway but activates the beta arrestin pathway, and in doing this, represents a ligand with additional beneficial effects that are normally lost by antagonizing the second pathway.” Preclinical data from large animal studies of heart failure showed distinct differences between Trevena’s molecule and the full antagonist. “The trial uncovered these unexpected benefits that appear to be well-suited for the treatment of acute heart failure,” says Gowen. With a huge unmet need in acute heart failure and in chronic heart failure, development of new drugs is essential. Although this is not as popular an area in current GPCR drug discovery as oncology, there have been a number of successful GPCR-targeted drugs in areas of unmet need in the past—remember the well-known beta blockers or beta agonists for asthma?

Mutual technology transfer
So what’s so special about the beta arrestin platform? “From a platform technology standpoint, PathHunter beta arrestin and HitHunter cAMP assay platforms from DiscoveRx brings a few advantages that complement existing technologies that BioFocus has in-house,” says Tom Wehrman, PhD, senior research director, DiscoveRx. “We have found that the beta arrestin platform works for about 85% of GPCR as they signal through beta arrestin.”

Wehrman cites that one of the main advantages of the assay system is that, unlike second messenger assays, the assay improves specificity by restricting the generation of signal transduction to activation of the target GPCRs only, thereby reducing false positives.

“For certain classes of receptors such as the single lipid receptors that have several of these endogenous receptors on cells, it is a lot easier to generate these beta arrestin assays versus doing second messenger assays,” says Wehrman. “Since you don’t have to predict which coupling pathway it will be, such as calcium or cyclic AMP, you can use beta arrestin.”

Wehrman adds that the beta arrestin assay could be used as a stand-in for difficult GPCR targets that don’t currently have assays. A number of GPCRs have been rescued using the beta arrestin format. The reason the beta arrestin assay format complements second messenger assays is that the beta arrestin pathway is fundamentally different from the G-protein-dependent pathways, so it is not dependent on G-protein activation for activity.

Other examples
Domain Therapeutics (Strasbourg, France) is a biopharmaceutical company whose sole focus is to develop compounds against difficult GPCRs including orphans. The company has developed the DTect-All technology—a ligand-binding-based assay designed to detect every ligand on the surface of GPCRs. The assay measures the interaction between the GPCR target and Domain Therapeutics’ proprietary collection of fluorescently-labeled compounds, called GPCR frequent hitters. According to Pascal Neuville, PhD, chief executive officer of Domain Therapeutics, the assay (which relies on fluorescence resonance energy transfer or FRET) is sensitive enough to pick up faint signals between ligands and orphan GPCR targets. Through a current collaboration with Domain Therapeutics, Takeda Pharmaceuticals (Osaka, Japan) is using the DTect-All platform to revisit their GPCR-targeted compound library to identify interesting scaffolds that are normally missed by traditional compound screening processes.

An example of a marriage between a chemistry services provider and a pharmaceutical company is the collaboration between Sygnature Chemical Services (Nottingham, UK) and Heptares Therapeutics (Hertfordshire, UK).

The collaboration involves the building of a designed chemical library using Sygnature’s array synthesis capabilities. “Sygnature Chemical Services is very good at making combichem arrays around defined pharmacophores, which we have designed for these structure-based design libraries,” says Malcolm Weir, PhD, chief executive officer of Heptares Therapeutics. “What we have done is to use our knowledge of the [GPCR] targets that we are interested in to come up with ideas for compounds that fit the array synthesis design paradigm. And we are working with them to actually build those libraries. Then they will come back to us for testing.”

The pharmaceutical industry has not, historically, been a big fan of collaboration. But for the last decade, collaborations between pharmaceutical companies and between pharmaceutical companies and technology providers have become quite common. Recently, there have been several successful marriages between drug developers and technology providers. Exchanges of skill sets, technology, and services make these partnerships mutually beneficial. The fact that such partnerships have occurred in the GPCR drug discovery space makes them all the more important.

About the Author
James Netterwald is president and CEO of BioPharmaComm LLC, a provider of writing, editing, and consulting services to the life science, pharma-biotech, and public relations industries.

This article was published in Drug Discovery & Development magazine: Vol. 13, No. 1, January/February, 2010, pp. 12-14.