Using a bigger “cell” to accelerate drug discovery and development

By Susan Gammon, Ph.D.
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Until now, a significant challenge in the early phases of drug discovery and development has been producing enough of a drug’s metabolites to fully analyze its chemical and biological properties. By combining two emerging technologies, Sanford-Burnham scientists have created a synthetic system that generates the same drug by-products as those produced in the liver, in amounts sufficient for a full analysis and interpretation of their safety. This innovative approach, recently published in the journal ACS Medicinal Chemistry Letters, may shorten the time it takes to get new drugs to market.

Romain Stalder, Ph.D., a postdoctoral fellow, and his advisor, Gregory P. Roth, Ph.D., associate professor at Sanford-Burnham at Lake Nona (Orlando, Fla.), combined a microfluidic system with a high-capacity electrochemical cell to allow scientists to simulate the chemistry that occurs in the liver when drugs are metabolized. Drugs are introduced into the instrument, oxidized by an electrochemical cell, and the output is the production of the metabolite(s) most likely to match those produced by the liver. For the first time, the process is efficiently performed while producing sufficient amounts that can be used for nuclear magnetic resonance (NMR) analysis.

“Ideally, to get the full picture of the chemical properties of a drug’s by-products, NMR is performed. The NMR picture allows medicinal chemists to assess toxicity and to further improve the drug by making molecular modifications to increase activity, improve stability, decrease toxicity, and other desirable drug traits,” Stalder said.

To validate the procedure, the scientists ran six drugs with known metabolic by-products through the system. Each metabolite was produced correctly, in amounts several orders of magnitude greater compared to standard technology, enabling NMR analysis.

Traditionally, scientists have evaluated drug by-products using biological material in in-vitro model systems such as liver tissue slices, isolated microsomes, perfused liver, and liver cells. The output of these tests is a “soup” that contains only trace amounts of by-products that may or may not be toxic. The “soup” is analyzed by mass spectrometry, an analytical technique that identifies individual molecules by their size and charge, allowing scientists to identify known toxins.

“Although in-vitro tests using biological material are close to the physiological environment of the liver, the tests produce a limited amount of metabolites, enabling mass spectrometry but making precise chemical structural analysis by NMR difficult. Our synthetic system produces enough material in a ‘clean’ enough state for NMR, and when combined with existing technology, will enable a comprehensive analysis of the key metabolic products that impact drug efficacy. The more information we have about a drug up front, the faster we can proceed through the development process,” Stalder said.

Romain Stalder and Gregory P. Roth (2013). Preparative Microfluidic Electrosynthesis of Drug Metabolites ACS Med. Chem. Lett. DOI: 10.1021/ml400316p
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Susan Gammon, Ph.D.

Susan is an associate director of Communications at Sanford-Burnham.

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