Journal of Pharmacological and Toxicological Methods
Original articleUtility of quantitative whole-body autoradiography (QWBA) and imaging mass spectrometry (IMS) by matrix-assisted laser desorption/ionization (MALDI) in the assessment of ocular distribution of drugs
Introduction
In the discovery and development process of novel chemical entities, potential compound liabilities are investigated and findings are used to iteratively improve the drug properties of the candidates and to better predict safety and efficacy in humans. In addition to the routine and standardized in silico, in vitro, and in vivo ADME (absorption, distribution, metabolism and elimination) assays, a selective approach might be chosen to assess specific toxicological effects. For example, if a compound absorbs light in the wavelength range of 290–700 nm (UV-A, UV-B, and visible light) and generates a positive response in a standard in vitro neutral red uptake phototoxicity assay in Balb/c 3T3 mouse fibroblasts, an in vivo study may be conducted to assess the potential for drug-induced phototoxicity in the eyes and skin of pigmented Long–Evans rats. Often, the in vivo phototoxicity assay is only conducted with systemically administered drugs that are known to distribute to the eyes and/or skin (FDA Guidances (Drugs) — Pharm/Tox — Guidance for Industry & Photosafety, 2003). For compounds that induce a positive ocular response in the in vivo phototoxicity assay, data on distribution patterns to substructures of the eye (such as the uveal tract, lens, and/or cornea) can inform decisions regarding the nature of the ocular findings and possibly influence compound advancement.
Quantitative whole-body autoradiography (QWBA) can detect the location and thus generate a tissue distribution image of the radio-labeled dosed analyte as well as provide quantitative information on tissue levels of the analyte; however, it cannot distinguish between the parent compound and possible metabolites or degradants (Solona and Kraus, 2002, Solona and Lee, 2002, Ullberg and Larsson, 1981, Trim et al., 2008, Solon et al., 2010). A complementary label-free technique to resolve compound identity is the imaging mass spectrometry (IMS) by matrix-assisted laser desorption/ionization (MALDI) (Trim et al., 2008, Solon et al., 2010, Drexler et al., 2007, Grey et al., 2009, Heeren et al., 2009, Hsieh et al., 2007, msimaging, 2010). The mass selective detection of analyte specific product ion spectra generated by multiple stage mass spectrometry (MS) can afford the identification (qualitative MS) and an ion density map (relative quantitative MS) of the analytes in the tissue section.
An in vivo phototoxicity study with a proprietary compound resulted in equivocal, corneal-specific lesions. Investigative studies were designed to assess tissue distribution (specifically looking at substructures of the eye) of systemically administered drug and its potential metabolites using complementary application of QWBA (radio-labeled drug) and IMS by MALDI ion trap MS (un-labeled drug). Data from QWBA analysis provided a quantitative distribution of a drug-related radio-labeled material in the tissue; however, the nature of the detected analyte(s), whether intact parent drug or potential metabolites or degradants could not be determined. Multistage MS experiments performed directly on eye tissue sections demonstrated semi-quantitative localization in the uveal tract and no accumulation in the cornea. The analyte was unequivocally identified as the dosed parent drug and no metabolites were detected.
Section snippets
Animals
These studies were conducted in accordance with the NIH Guide for the Care and Use of Laboratory Animals (NIH publication No. 85–23, revised 1996) and were approved by the Bristol-Myers Squibb Company Site Institutional Animal Care and Use Committee. Female pigmented Long–Evans rats (approximately 14 weeks old at study initiation) were purchased from Charles River Laboratories, Wilmington, MA. All animals were housed individually in stainless-steel wire-bottom cages in environmentally controlled
Quantitative whole-body autoradiography (QWBA)
The autoradiograms of whole-body or eye sections (Fig. 1) indicated that the radio-labeled analyte(s) preferentially distributed to the back of the eye (retina and/or uveal tract), with very little present in the cornea and lens. Since QWBA actually detects only the radio-label itself, no information is obtainable on the molecular species of the analyte(s).
Imaging mass spectrometry (IMS) by matrix-assisted laser desorption/ionization (MALDI)
The IMS by MALDI analysis was performed by alternating a universal full scan MS method to survey the sample and targeted full scan MS/MS/MS
Discussion
The ocular distribution of a drug and its potential metabolites was assessed by employing the complementary technologies of quantitative whole-body autoradiography (QWBA) and imaging mass spectrometry (IMS) by matrix-assisted laser desorption/ionization (MALDI) in support of equivocal corneal-specific in vivo phototoxicity findings. While QWBA provided the quantitative localization of the drug-related radio-labeled species in the tissue samples, the use of IMS by MALDI confirmed the
References (11)
- et al.
Utility of imaging mass spectrometry (IMS) by matrix-assisted laser desorption ionization (MALDI) on an ion trap mass spectrometer in the analysis of drugs and metabolites in biological tissues
Journal of Pharmacological and Toxicological Methods
(2007) - et al.
Imaging mass spectrometry: hype or hope?
Journal of the American Society for Mass Spectrometry
(2009) - et al.
Mapping pharmaceuticals in tissues using MALDI imaging mass spectrometry
Journal of Pharmacological and Toxicological Methods
(2007) - et al.
Whole-body autoradiography
Methods in Enzymology
(1981) - FDA Guidances (Drugs) — Pharm/Tox — Guidance for Industry, Photosafety Testing (2003). U.S. Department of Health and...
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