Scripps unveils innovative screening strategy

This innovative swift screening strategy uncovers new drug candidates more rapidly, opening the door to new biology and giving hope to those suffering from obesity-linked diabetes, a complex metabolic disorder that affects 347 million people worldwide.

The key to TSRI’s findings in obesity-linked diabetes is the identification of the fat-cell enzyme that the compound inhibits—an enzyme that has not yet been a focus of diabetes drug development.

“This integrated strategy we’ve developed has the potential to accelerate the discovery of important biological pathways, and may lead to faster development of new drugs for multiple diseases,” said Enrique Saez, a TSRI associate professor, in a news release.

“Our approach allows the identification of the molecular target of the bioactive compound within one to two weeks,” Saez tells DDNews. “Traditional approaches, such as affinity chromatography, typically require extensive chemical modification and subsequent validation of candidate targets identified by proteomics. This is an arduous process that is seldom successful, and that in a best-case scenario usually takes three to four months. Often it is significantly longer than that.”

Based on the results in mouse models, Saez says, the compound they have identified at TSRI and additional ones that may be discovered around its molecular target can be expected to help obese people, including children, lose weight—though he adds they cannot predict whether this treatment will increase levels of physical activity.

“All our work was performed in animal models using a tool compound not optimized to be used as a clinical drug, though we showed some data indicating that our treatment may also be useful in obese-diabetic humans,” Saez says. “The next step would be for industry to develop a more drug-like compound to assess its efficacy in human models, and then proceed with further preclinical development prior to consideration of human trials.”

Saez and colleague Benjamin F. Cravatt, chair of TSRI’s Department of Chemical Physiology, are the senior authors of “Integrated phenotypic and activity-based profiling links Ces3 to obesity and diabetes,” published Dec. 22, 2013, in an advance online issue of Nature Chemical Biology. The published study described the fruits of the new discovery process.

“Our study validated a new, quick approach to identify molecular targets that may provide novel therapeutic avenues for metabolic diseases,” Saez says. “We described one such molecular target.”

The new strategy “has great potential to streamline drug discovery, a process whose importance to human health can hardly be overemphasized,” the authors wrote.

“Typically, pharmaceutical scientists start the discovery process by ‘screening’ large libraries of chemical compounds in search of one or a few that might treat disease,” the authors stated in their paper. However, the “dominant strategy of recent decades has been to screen compounds for a specific activity against a known target, such as inhibiting the function of a certain enzyme thought to be critical for the disease in question.”

A key advantage of this “target-based” screening is that it uses biochemical tests that can be done relatively simply in a test-tube—or rather, in a large array of tiny test tubes via automated, rapid screening systems that sort through hundreds of thousands of different compounds, according to the Nature article.

On the other hand, target-based screening “has enabled scientists to discover many useful new drugs, but some wonder whether this basic discovery strategy has already taken all the ‘low-hanging fruit’,” the authors state.

In recent years, compounds selected with target-based in-vitro tests have seemed to be failing increasingly often when tested in the more realistic biological environments of cells and animals.

“An older strategy, ‘phenotypic’ screening, avoids much of this problem by testing compounds for their ability to produce a desired effect directly on living cells,” noted TSRI. “Unfortunately, such cell-based tests often leave open the question of how a useful compound works.”

According to Saez, “If you don’t know what its relevant molecular target is, then developing that compound into a drug—optimizing its potency, its selectivity, its half-life in the bloodstream and so on—is going to be difficult.”

Identifying the molecular targets of compounds selected by phenotypic screens is typically burdensome and time-consuming.

However, the Nature article reported that Saez, Cravatt and their colleagues were able to speed up the process dramatically. Indeed, their combined phenotypic screening and target-identification approach enabled them to quickly discover, characterize and carry out preclinical tests of not only a potential new drug for obesity-linked diabetes, but insights into the disease.

Specifically, the researchers used a set of compounds, recently synthesized by Cravatt’s laboratory, that tend to inhibit serine hydrolases—a vast enzyme family whose members participate in most biological processes in mammals.

Starting with a phenotypic screen, the scientists tested their library of compounds for the ability

to make young fat cells mature faster and store more fat. Better fat storage means that less fat leaks from fat cells into the liver, muscles and pancreas—a process that frequently occurs with obesity, often interfering with insulin signaling enough to bring on diabetes.

The screen quickly yielded several compounds that had a strong effect in promoting fat-cell fat storage, according to TSRI study. The researchers then used a method called “activity-based profiling” to identify the fat-cell serine hydrolases that the compounds inhibited most strongly. One of the most potent compounds, WWL113, turned out to work principally by inhibiting Ces3, a serine hydrolase enzyme that scientists have not studied in the context of obesity or diabetes.

The researchers quickly demonstrated WWL113’s effectiveness in two different mouse models of obesity-linked diabetes—one in which the mice are genetically programmed to become obese and diabetic, and another in which normal mice are made obese and diabetic with a high-fat diet.

“The treated animals showed resistance to weight gain—they were not putting on as much weight as the controls,” says Saez. “Their blood biochemistry also was getting normalized; their glucose, triglyceride and cholesterol levels were coming down towards normal levels.”

In these mouse tests, WWL113—without any optimization for use as a drug—performed about as well as the FDA-approved diabetes treatment rosiglitazone (Avandia), according to the study. Notably, the new compound lacked one of the side effects that drugs in rosiglitazone’s class have in mice: the toxic accumulation of lipids in the liver.

“Our compound clears lipids from the diabetic mouse liver, whereas rosiglitazone has the opposite effect,” notes Saez.

To explore the relevance of these results to humans, the TSRI team worked with collaborating researchers in Australia to test fat samples from obese humans and diabetics. The tests confirmed that the human version of Ces3 also is unusually active in such patients, suggesting an inhibitor may also work as a diabetes treatment in people.

“As basic researchers, we will continue to employ and elaborate on our approach to identify additional molecular players that can be translated into treatments for obesity and/or diabetes,” Saez said. “At same the time, we will be happy to work with industry partners to develop our findings further and test their potential in humans.”

Saez and his colleagues will next focus on using the new screening strategy to uncover more biological pathways that could yield new mechanisms to develop potential therapies.

“Scripps has a high-profile paper coming out in Nature shortly (publication date to be determined), which demonstrates a method for modifying organic molecules that significantly expands the possibilities for developing new pharmaceuticals and improving old ones,” Saez says. “Stay tuned.”