Improved knowledge of drug dosage via precise measurements of drug levels will help reducing these problems. The majority of antiretroviral drugs exert their action in target cells for HIV infection, i.e. CD4 positive T cells and monocytes. Enzymatic activity of RT and protease is inhibited directly by non-nucleoside RT inhibitors (NNRTI) and protease inhibitors (PI) respectively. Nucleoside RT inhibitors exert their antiviral activity only after phosphorylation in the cell. Currently, extracellular concentrations of antiretroviral drugs can be measured accurately, but these correlate poorly to the intracellular concentrations due to bioprocesses such as active drug transport and metabolism. The understanding of the intracellular pharmacology of antiretroviral drugs is largely hampered by the lack of proper analytical tools. In particular more sensitive tools to monitor the intracellular drug metabolism and pharmacokinetics (DMPK) of treatment regimens as a whole are investigated and will be exploited.

Pharmaceutical industry will also benefit from these newly developed tools for the selection of lead compounds that have good intracellular DMPK properties in early phase drug discovery. In addition, the DMPK of new treatment regimens can be investigated in a preclinical phase, and intracellular drug-drug interactions could be exploited to boost the levels of other antiretroviral drugs. In a clinical setting, such tools will be used to improve the current treatment of HIV-1 infected children and adults.
This project concerns the development of a platform to assess all aspects of the intracellular pharmacology of antiretroviral drugs. 

This platform will consist of:

• An assay for very high throughput quantitative analysis of protease inhibitors, NNRTIs, and their metabolites.
• An assay for quantitative analysis of NRTIs, endogenous (deoxy)-nucleosides, and all of their phosphorylated forms.
• An assay for rapid isolation of different target cells for HIV infection.

We will use this platform:

• To define in vitro the intracellular inhibitory concentrations for currently approved antiretroviral drugs and lead compounds using clinically relevant HIV strains.
• To assess in vitro intracellular drug-drug interactions and to assess how these interactions can be exploited to simplify therapy in patients.
• To assess the intracellular DMPK of a set of lead compounds generated by GSK.
• To assess the intracellular DMPK of complete treatment regimens in HIV-1 infected children and adults, and correlate these findings to therapy outcome parameters.

The techniques developed by this platform will aid to define new and more effective combinations of antivirals. We expect that this platform can be used to decrease the failure rate in drug development by early selection of lead compounds that have good DMPK properties. The platform can be used to improve the pharmacotherapy of HIV-1 infected children and adults. In addition, techniques can be extended to other priority viral infections, such as Hepatitis B, Hepatitis C and Herpes infections.

MALDI en nano-liquid chromatography mass spectrometry

A new trick with an existing mass spectrometerFor the project T4-212 'A multidisciplinary approach to monitor and select effective therapy in HIV infection' , a MALDI/nano-liquid chromatography (LC) triple quadrupole mass spectrometer (MS) has been purchased. It enables the monitoring of anti-HIV drugs in serum and in lymphocytes. Besides the classical electrospray and nano-LC source it can use a newly developed matrix-assisted laser desorption and ionization (MALDI) source, that allow for ultra-sensitive and fast (seconds per sample) measurement of drugs that are absorbed to matrix crystals. The mass spectrometer can select pre-defined masses from complex samples and quantify the compounds with these masses at the femtomolar level (10-15 mol). The advantage is that large numbers of samples from patient studies can be analysed discriminating different combinations of drugs that are given to patients. Owing to the excellent reproducibility of the measurements, less than 10% variation, small differences in concentration can be detected. Through these measurements, the administration of drug medication in patients can be monitored.

This MALDI/nano-LC mass spectrometer is the first commercially obtained mass spectrometer with this multi-source combination in Europe. Besides the quantification of drugs in medical samples, the device can also quantify selected peptides in body fluids or tissues. This allows the mass spectrometer to be used for the validation of candidate biomarkers for various diseases:including cancers of the prostate; breast; brain and for multiple sclerosis. The sensitivity of the measurements is expected to further improve through automated sample preparation, new types of matrix crystals and miniaturization.

Legenda  figure: (Above) The FlashQuant mass spectrometer has been installed in April 2008. Dr. Jeroen van Kampen (photo) and Dr. Lennard Dekker perform the first experiments on the new mass spectrometer. (Middle) Overview of the mass spectrometer: (a) three quadrupole segments are placed in series. In the first segment a molecule of interest can be selected, in the second quadrupole the selected molecules are fragmented through collision with an inert gas and in the third quadrupole quantification takes place on basis of a specific fragment from the selected molecule (b) the newly developed MALDI source and (c) the nano-liquid chromatography system. (Below) Most remarkable innovation of this mass spectrometer is the option to measure MALDI target plates. On these target plates hundreds of samples can be placed and measured, directly or after storage, with great speed (seconds per sample) at a high sensitivity. 

Jeroen van Kampen¹, Lennard Dekker¹, Rob Gruters², Albert Osterhaus², Theo Luider¹ ¹Department of Neurology, Erasmus MC, ²Department of Virology, Erasmus MC

Publications:

van Kampen J.J.A., Verschuren E.J., Burgers P.C., Luider T.M., de Groot R., Osterhaus A.D.M.E., and Gruters R.A. (2007) Validation of an HIV-1 inactivation protocol that is compatible with intracellular drug analysis by mass spectrometry.J Chromatogr B Analyt Technol Biomed Life Sci 847, 38-44

van Kampen J.J.A., Burgers P.C., de Groot R, Osterhaus A.D.M.E., Reedijk M.L., Verschuren E.J., Gruters R.A. and Luider T.M. (2008) Quantitative analysis of HIV-1 protease inhibitors in cell lysates using MALDI-FTICR mass spectrometry. Anal Chem 80, 3751-3756

van Kampen J.J.A., Burgers P.C., Gruters R.A., Osterhaus A.D.M.E, de Groot R., Luider T.M., Volmer D.A. (2008) Rapid quantitative analysis of antiretroviral drugs in lysates of peripheral blood mononuclear cells using MALDI-triple quadrupole mass spectrometry. Anal Chem. In press 

Coulier L, van Kampen J.J.A., de Groot R., Gerritsen H.W.,. Bas R.C, van Dongen W.D., Brüll L.P., Luider T.M. Simultaneous determination of endogenous deoxynucleotides and phosphorylated nucleoside reverse transcriptase inhibitors in peripheral blood mononuclear cells using ion-pair liquid chromatography coupled to mass spectrometry. PRCA in press