One of the more recent innovations in drug discovery,high-throughput screening (HTS), is made feasible through advances in roboticsand high-speed computer technology.
For scientists working in HTS laboratories, there are myriadchallenges, including pressure to find increasing numbers of drug leads whilecontaining costs. As a result, many are seeking larger compound sets, moreautomated systems to screen them faster, and an integrated set of equipment andconsumables.
High-throughput screening requires the miniaturization andautomation of in-vitro bioassays so thatmillions of variables can be tested. HTS is often an important step in thediscovery of new medicines.
In this first installment of a multi-part series in ddn, we focus on some of the key developments in recentyears with regard to screening technology and look ahead to see what the futureholds.
Today's trends
J. Fraser Glickman, director and research assistantprofessor of the High-Throughput Screening Resource Center at RockefellerUniversity, points out that there have been several key developments in HTS inrecent years.
"Among them, I would place the improved throughput andanalysis of high-content technologies based on image analysis of cell samples,and so-called 'fragment-based' approaches for measuring binding of compoundfragments," he says. "Also, we have seen a vast improvement in the automationof microtiter plate processing and the associated scheduling software.Cheminformatic software has also become phenomenally more effective."
Houston, Texas-based Selleck Chemicals is a worldwidesupplier of high-performance kinase inhibitors and antibodies for cellsignaling and oncology research. Sales director Sunny Xu notes that functionalgenomics with their RNAi and cDNA technologies are well-known recentapplications of HTS.
"They are called siRNA high-throughput screening and cDNAlibrary high-throughput screening," Xu says. "Particularly, the former willhelp scientists to understand the molecular basis of tumorigenesis,identification of therapeutic targets and so on. Capillary electrophoresis (CE)or HPLC-based HTS systems could be applicable to complex and even unpurifiedchemical mixtures, speeding up the identification of active components."
Dr. Rathnam Chaguturu is the director of HTS laboratoriesand courtesy research professor of molecular biosciences and medicinalchemistry at the University of Kansas.
He sees an increased awareness of label-free, HCS/HCA andmultiplexed assays for screening and profiling.
Label-free: The way to be?
Chaguturu points out that there is a growing tendency now toadopt label-free platforms.
"Currently, most assays for the detection of biologicallyrelevant binding events use either radioactive or fluorescent dyes to tag oneor more molecules, over expression of the biological target of interest, orreporter proteins," he says.
Simply put, Chaguturu explains that this is quite anunnatural set-up. Furthermore, researchers are restricted to a simplisticbiology assessment with just point-of-contact measures and one signalingpathway per ligand-receptor complex.
"We know that the therapeutic targets do not function inisolation, but operate in a systems biology context involving a complex set ofintegrated biochemical pathways, and we need to find a way to quantitate theseprocesses," he says. "This is where label-free technologies come in to play as99.5 percent of human genome has not yet been fully exploited for drugdiscovery."
The main reason, according to Chaguturu, is because thepharmaceutical industry has operated mainly in low-risk territory withpotential for greater return on investment.
"Academia is the one that feeds new therapeutic targets forthe pharmaceutical industry to pursue," he says. "Academia, by the nature ofits mission, works in this unchartered territory of high risk and low reward,but for it to make headway, it is limited by the availability of easilyadaptable technology formats to deorphanize the highly refractory targets. Thelabel-free assay technology is widely applicable for many classes of targetsand cellular processes."
Chaguturu explains this is especially useful in a systemsbiology context in charting metabolic pathways.
"Label-free technology is the way to go in deorphanizingthese refractory targets, and that can be done without long and costly assaydevelopment process," he says. "Next, this technology allows us to generatebiologically relevant data in a systems biology context. It is especiallyuseful as an alternate readout technology for use in the hit-to-leadoptimization process, and you can work with primary cell lines and without theneed for engineered cell lines."
Growing pains
Glickman points out that over the last 15 years, the fieldof HTS has gone from infancy into a mature and robust approach, as evidenced bythe growing number of labs throughout the world and in various sectors, whichno longer view it as an experimental new technology, but rather as arequirement in order to have a healthy and competitive research program.
"We always keep a certain capacity for scanning the horizonfor new screening technologies, and for being creative in the way we improveour efficiency," he notes. "Many of the pitfalls associated with HTS have nowbecome transparent, and the community have actively presented resolutions tothese issues."
As with any developing technology, change can be rapid, andin recent years, acoustic technology has been playing a large role in HTS. Withso much technology changing so rapidly, there remain plenty of challengesfacing scientists in HTS laboratories.
Xu notes that examples of key changes are robotics,miniaturization, sophisticated assay chemistry to sophisticated software anddatabase.
According to Glickman, the main challenge "is keeping costsdown and efficiency up. This does not only apply to HTS but to drug discoveryin general, which is facing and will continue to face sustainability issuesrelated to the cost burden on society."
According to Chaguturu, assay development is the mostcritical component leading up to a screening campaign.
"For assay development work, robotics is not a decidingfactor, but for screening campaigns, liquid handling robotics is a must withoutwhich no amount of FTE could measure up to the throughput needed, and do thetasks in a timely manner," he says. "So the biggest challenge is thedevelopment of appropriate assays in a timely fashion."
Adapting to changes can be analogous to trying to turn abattleship, and Chaguturu contends that pharma greatly underestimates thesignificance of toxicobiology, and doesn't understand it well enough to pickthe right drug targets.
"Pharma is not set up to do this sort of research," he said,noting it "warrants collaboration between industry and academia."
The trend he views is pharma developing partnerships withacademia in an open-platform paradigm to advance drug discovery endeavors. Hepoints out several examples, including Novartis and Institutes for BiomedicalResearch; GlaxoSmithKline (GSK) and Centers for Excellence for Drug Discovery;Pfizer and the Biotherapeutics and Bioinnovation Center; Lilly and PhenotypicDrug Discovery (PD2) Initiative; and Merck and Sage Bionetworks.
Moreover, a dozen competing drug companies have agreed toshare data on thousands of Alzheimer's patients in hopes that the extrainformation will spark new ideas for treatments. Called the Coalition AgainstMajor Diseases, the collaboration pairs patient-advocacy groups with suchpharmaceutical giants as GSK, Pfizer and AstraZeneca. It is led by the CriticalPath Institute, a nonprofit partnership associated with the U.S. Food and DrugAdministration (FDA) that aims to speed discovery of new drugs.
A new decade, a new mantra
Even with the ever-changing technologies, Chaguturu notesthat the drug discovery landscape is at a crossroads with profound changeslooming in the horizon, and open innovation becoming the new mantra for reinvigoratingthe pharmaceutical R&D's lackluster drug candidate pipeline.
"To fill this void, academia has now ventured from itstraditional role of exploring the fundamental aspects of disease biology intothe high -throughput screening arena in a big way, thanks to the NIH RoadmapInitiative and the EuOpen Screen program for facilitating this transition," hesays. "The oft-quoted myth that high-throughput screening has not been thepanacea for drug discovery, as one was led to believe at first, has now beensquashed as the origins of many of the drug candidates in pharma's pipeline cannow be traced back to in-house HTS campaigns. HTS has found its niche inacademia with research priorities in drug discovery endeavors."
Researchers, Glickman points out, are continually lookingways to improve their processes and striking the right "economy of scale."
"Scientifically, the main question for us is how we canimprove the predictive value of the in-vitro tests we perform to translate well into in-vivo results," he says. "As academics, we also try toplace ourselves in target areas where there is little published information.Another challenge is finding talented, classically trained medicinal chemiststo improve the properties of hits, which can be a long, unpredictable andarduous task."
Chaguturu points out that with the flow of toppharmaceutical drug discovery scientific talent in to academia and theindustrialization of small molecule library synthesis, academia is poised totake drug discovery to new heights.
"There is also a much-needed collaborative spirit betweenpharma and academia in closing the risk-reward gap as exemplified by a numberof industry-academia collaborative agreements that are being put in place," hesays. "The technology transfer offices are now generally charged in guiding theresearcher in IP disclosures, patenting decisions and commercialization ofresearch results. This has transformed the faculty in to entrepreneurs inmanaging their inventions. So, the long-term future is quite bright."
Xu concludes that HTS technologies will be more widelyaccepted by pharmaceutical and biotechnology companies as an integral part oftheir drug discovery processes and the HTS market will continue to grow.
"Technological advancements will revolutionize the market,"Xu says. "Technological advancements such as the use of robotics and cell-basedassays have had a significant impact on the HTS market. HTS reagents and assaysare experiencing increasing demand, leading to intense competition among reagentmanufacturers, much more than among instrument manufacturers."
Glickman is very positive about the future of HTS, in thesense that as an approach to identify chemical lead compounds, it has become a"proven performer."
"I also feel that many of the technological innovations that have beendesigned for HTS drug discovery purposes, are starting to bleed over into otherfields, such as RNAi screening, and in addressing basic scientific issues usingthe analytical techniques performed in microtiter plates," he says.
