Towards Personalised Medicine: use of volatile metabolites

Wider research context: Patient-specific toxic side effects and lack of efficacy often hamper the therapeutic benefit of drugs. Our inability to predict individual drug responses represents a major obstacle to providing personalized medicine. The use of biomarkers as predictors to drug response would significantly advance this field, the benefits of which would be enormous. A test could assess a patient’s ability to metabolize a drug, leading to improved patient care through the prescription of suitable drugs that are administered at the correct dosage.

Objectives: Extensive polymorphisms in a major group of drug-metabolizing enzymes, the cytochrome P450 family (CYPs), cause differences in metabolism. We will test different substrates with a key CYP, CYP3A4, for the production and use of unique volatile biomarkers to provide a measure of its activity. Volatiles that are not normally present in exhaled breath will permit the development of a strategy that would lead to considerable reductions in the dose of a substrate needed for the clinical implementation of a breath test, toxic side-effects and medical costs.

Approach: We will employ an interdisciplinary research programme to involve molecular modeling for substrate selection and engineering, and the use of cell-cultures for in vitro testing and metabolic analyses. Two cell-based systems will test the selectivity and specificity of substrates: HepG2 cells expressing ecombinant CYP3A4 and primary cell-like upcyte hepatocytes. Microsome ractions of HepG2 CYP3A4 cells will be prepared to enrich CYP activity for the selectivity tests. These will confirm the suitability of substrates, and guide what modifications are required to optimize kinetic parameters, rate of metabolism and volatility. The analytical techniques of gas-chromatography mass spectrometry and proton transfer reaction time of flight mass spectrometry will be employed to facilitate the identification, quantification and monitoring of volatile metabolites. Based on the headspace measurements, promising substrates will be further investigated using ultra-high pressure liquid chromatography mass spectrometry to identify and quantify non-volatile metabolites and intermediates in the cell culture for possible use in serum tests to complement breath tests.

Innovation: The identification of unique biomarkers resulting from CYP3A4 metabolism provides the underpinning knowledge to develop non-invasive breath tests that can assess an individual’s response to a drug. These tests can be used to assess the best therapeutic outcome at reduced costs. Importantly, the approach we are proposing can be adopted to other CYPs relevant in drug metabolism, e.g. 2D6, 2C9, and 2C19.

Primary researchers involved: University of Innsbruck: Dr. Veronika Ruzsanyi and Prof. Klaus Liedl; Medical University of Innsbruck: Prof. Jakob Troppmair; University of Vienna: Prof. Thierry Langer; Brandenburg University of Technology Cottbus: Dr. Sarah Kammerer.