Application Note # MT-103 FAST-SRM: A new Single Reaction Monitoring Method for Fast, Targeted Drug Distribution Testing in Tissue Sections

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1 ruker Daltonics pplication Note # MT-103 FST-SRM: new Single Reaction Monitoring Method for Fast, Targeted Drug Distribution Testing in Tissue Sections Targeted analysis of drug molecules and metabolites in tissue sections by MLDI imaging is a powerful tool for evaluating drug safety and pharmacology in general. To achieve the necessary specificity against the low molecular weight background (matrix, lipids, etc.), drug imaging requires either the selection of a specific drug fragment in an MS/MS experiment (single reaction monitoring, SRM) or very high mass resolution and accuracy. MLDI-TOF/TOF instruments have been used for SRM. However, measuring a single fragment of a single precursor ion does not require TOF/TOF ion optics. Here we report a new method that enables SRM to be performed on a reflector-only MLDI- TOF instrument. This technique is easy to set up and makes fast reflector instruments such as the autoflex speed perfectly suited for small molecule MLDI imaging, as demonstrated here for the analysis of Erlotinib in mouse liver. Introduction MLDI imaging of drug molecules and metabolites presents the challenge of measuring the intensity of the targeted drug signal against a complex background of matrix signals and endogenous metabolites. The required specificity in such analyses is usually achieved by measuring a specific fragment of the targeted drug in MS/MS mode (single reaction monitoring; SRM). If just one compound is to be analyzed in a targeted fashion, a single fragment ion must be monitored just like SRM analysis on a QqQ. variety of instruments have been used for this kind of analysis, including MLDI-ion traps, q-tof, triple quad (QqQ) and TOF/ TOF instruments [1]. However, a TOF/TOF for full MS/MS spectra recording is not an absolute requirement. Selecting the parent ions of interest in the precursor ion selector, fragmenting the drug molecular ions and monitoring a single fragment in a very narrow mass spectrum are sufficient. Here we describe the new FST-SRM assay [4], which is based on MLDI-TOF technology and does not require a TOF/TOF design (Fig. 1). In a TOF instrument, precursor ions are selected using a pulsed ion gate, which only allows ions to pass at a given time. On a TOF/TOF instrument, quadrupole 1(Q1) in the QqQ only allows ions to pass with a given frequency. In both instruments the selected parent ions fragment in a collision cell. In case of the TOF, fragmentation may also occur as Laser Induced unimolecular Decomposition (LID) in the field-free region between ion source and reflector. The ion reflector voltage is reduced so that only a narrow mass range of fragment ions are reflected to the detector, similar to the effect of Q3 in the QqQ. For the selective detection of a single fragment, the reflector voltage is reduced to permit the fragment ion of interest to travel along the same ion trajectory through the reflector as the parent ion at full reflector voltage.

2 Single Reaction Monitoring (SRM) Parent ion selection Fragmentation Fragment ion selection SRM on QqQ Q 1 CID: Q 2 Q 3 detector SRM on TOF pulsed ion gate CID cell / LID ion reflector detector Figure 1: The classical setup for SRM comprises a triple quadrupole for selection and fragmentation of the desired compound and the detection of the characteristic fragment. Similarly the SRM mode on a tof uses a pulsed ion gate for the selection, CID or laser induced decomposition for the fragmentation of the compound, and the reflector at lowered voltage to enable the detection of the desired fragment. The CID cell is placed in this figure between the ion gate and the reflector for easier understanding of this method. Since the field-free drift section in this TOF spreads between ion source and reflector, the fragmentation can in fact take place anywhere in this region with no influence to the result. s the reflector potential URf for SRM measurements is reduced by the ratio of the fragment mass to the parent mass, this is a simple calculation: U R f (SRM) = U R f (parent) m/z SRM m/z parent In this particular configuration, ions with higher m/z ratios travel through the ion reflector and lighter fragment ions are reflected on trajectories that are not focused to the detector. Using such settings means that there is no trade-off in achieving a reasonable MS/MS performance of the instrument over a larger mass range, and memory consumption for SRM datasets is small compared to full MS/MS or high-resolution images. The sensitivity of this approach arises from the low number of background ions that hit the detector. FST-SRM provides exceptionally high specificity and a precise m/z value of the targeted transition is determined, even if there are several fragments present with similar m/z values. This is very different from SRMs on a QqQ. The user interface of fleximaging versions and later includes the SRM mode. CompassFlex 1.3 adds a convenient user interface for simple SRM acquisition control. Users can switch between parent mode (with full reflector voltage) and fragment mode, and run SRM with collision gas either on or off. Here we applied the new FST-SRM mode for the analysis of mouse liver after administration of Erlotinib. Erlotinib is a tyrosine kinase inhibitor that acts on epidermal growth factor (EGFR) and is used to treat pancreatic and non-small cell lung cancers. MLDI imaging of animals dosed with Erlotinib has been previously reported [2, 3]. The structure and main fragmentation schema of Erlotinib in MLDI-TOF is shown in Fig. 2. Fragmentation of desmethyl Erlotinib a metabolite formed by demethylation is shown in Fig. 2.

3 Erlotinib Fragmentation of Erlotinib Erlotinib MLDI imaging of Erlotinib 0 mg/kg 200 mg/kg 50 mg/kg [M+H + ] = Da [M+H + ] = Da des-methyl-erlotinib C C des-methyl-erlotinib D D [M+H + ] = Da Figure 2: [M+H + ] = Da : Structure of Erlotinib with m/z values of the major fragments. : One of two possible structures of desmethyl Erlotinib, with m/z values of the major fragments produced when either side chain is cleaved. In the alternative desmethyl Erlotinib structure, the upper side chain is demethylated. oth structures give rise to fragments of the same mass that cannot be differentiated in an ms 2 experiment. Figure 3: : Optical image of mouse liver sections on a glass slide. From left to right: Control (0 mg/kg), 200 mg/kg and 50 mg/kg. : FST-SRM measurement of Erlotinib, observed transient Da Da C: FST-SRM measurement of desmethyl Erlotinib, observed transient Da Da D: FST-SRM measurement of desmethyl Erlotinib, observed transient Da Da. In figures, C, and D, areas with intensities 50% of the most intense signal result in maximum pixel intensity. Experimental To evaluate the sensitivity of FST-SRM, three mice were dosed with 0 (control), 50 and 200 mg Erlotinib/ kg body weight. Mice were sacrificed two hours post dose and livers were frozen in liquid nitrogen. The animal experiments were conducted in accordance with German federal animal protection laws and approved by the local Institutional nimal Care and Use Committee. 10 μm cryosections of the livers were cut on a cryomicrotome and transferred onto Indium-Tin-Oxide coated glass slides (ruker Part #237001) and dried. α-cyano-4- hydroxycinnamic acid (CHC) matrix was applied to the glass slide with the ImagePrep station (ruker) using the standard preparation method with the maximum wetness setting. For MLDI imaging, 200 laser shots were accumulated per pixel, with a raster width of 300 μm and a pixel diameter of 150 μm (laser spot size ~100 μm). This allowed acquisition of multiple SRM datasets in consecutive runs from the same sample area using a grid offset of 150 μm. The imaging experiments were set up and evaluated using fleximaging 2.1 software. One MS and three SRM datasets , and (based on the fragment ions of Erlotinib and desmethyl Erlotinib) were acquired from each sample. For the statistical plots, the intensity values were exported from fleximaging into a text file and processed with R [5].

4 Metabolization of Erlotinib SRM enables quantitation C 394-> > > r 2 = r 2 = r 2 = Figure 4: Mean and 95% confidence intervals (CI) of the intensity over all pixels of the respective section plotted against dose (FST-SRM mode). : Erlotinib, observed transition Da Da. (CI is too small to be seen on this scale) : Desmethyl Erlotinib, observed transition Da Da C: Desmethyl Erlotinib, observed transition Da Da Results Figure 3 shows optical images of the selected mouse liver sections and the results of the FST- SRM measurements of Erlotinib () and its metabolite desmethyl Erlotinib (C, D). The distribution of Erlotinib was determined from the SRM dataset , and shows an unambiguous linear correlation of signal intensity and administered dose (r² = ) (Fig. 4). The low intensity of the metabolite signals indicates that 2 hours post-dose, very little of the Erlotinib had been metabolized. t a dose of 200 mg/ kg, the relative response of desmethyl Erlotinib compared to Erlotinib indicates that 5% of the drug had been metabolized (Fig. 4). Due to the low concentration of the metabolite, variations across the images are quite large (CVs ~40 %). However, due to the large number of spectra that were analyzed, a good linear correlation of SRM response of drug and metabolite to the dose of Erlotinib was observed and the mean intensities for the different doses could still be quantified. In addition to the three SRM transitions, we also acquired an MS image dataset to monitor drug and metabolite distributions (images not shown). t high concentrations, the MS readout provided similar CVs of approx. 40 % (Tab. 1). However, in the control sample (0 mg/kg), a dramatic increase in CV in the MS image indicated a high level of background noise compared to that seen using the FST-SRM approach. Comparing the analyses of Erlotinib and desmethyl Erlotinib in MS and SRM modes shows a clear advantage of the SRM approach. While the Da signal for Erlotinib in the MS mode shows a linear relationship with the dose, a similar relationship was not observed for the Da desmethyl Erlotinib signal in MS-mode (Fig. 5). major reason for this is interference from a matrix signal (CHCH: 2MH++1). In contrast, all signals measured using the FST-SRM mode showed a linear intensity:dose relationship (Fig. 4). Table 1: Coefficients of variation (CV) for the measured intensities of the Erlotinib signal in MS-mode and FST-SRM mode (calculated over all pixels of the respective liver sections). In the control sample, the CV value is significantly higher in MS mode than in FST-SRM mode. This suggests higher specificity and a lower influence of chemical noise in the FST-SRM measurement. 0 mg/kg 50 mg/kg 200 mg/kg MS (m/z ) 167 % 42 % 39 % FST-SRM (m/z mz ) 44 % 36 % 45 %

5 Erlotinib and des-methyl-erlotinib in MS-mode ms mode 394 ms mode 380 R 2 = R 2 = Figure 5: Mean and 95% confidence intervals (CI) of the intensity over all pixels of the respective section plotted against dose (MS mode). : Da (CI too small to be seen on this scale) : Da Conclusion The new FST-SRM mode described here is suitable for highly specific and robust analysis of drugs and metabolites in tissue with low background interference (see also [4]). We have shown in this proof-of-concept study that the FST-SRM mode provides a significantly lower detection limit than the MS mode, although an absolute number requires more detailed study. Using FST-SRM turns fast reflector MLDI-TOF instruments (such as the utoflex speed with its 1 khz operation) into universal imaging instruments. uthors Isabel Winkelmann 1, xel Walch 1, arbara Maria Grüner 2 und Jens Siveke 2, rne Fütterer 3, Detlev Suckau 3, Michael ecker 3, Sören Deininger 3, Cesar arahona 3, rmin Holle 3 [1] Institute for Pathology, Helmholtz-Centre Munich, Germany [2] 2 nd Department of Internal Medicine, Technical University of Munich, Germany [3] ruker Daltonik GmbH, remen, Germany References [1] Walch, Rauser S, Deininger SO, Höfler H. MLDI imaging mass spectrometry for direct tissue analysis: a new frontier for molecular histology. Histochem Cell iol Sep; 130(3): [2] Signor L, Varesio E, Staack RF, Starke V, Richter WF, Hopfgartner G. (2007) nalysis of erlotinib and its metabolites in rat tissue sections by MLDI quadrupole time-of-flight mass spectrometry. J Mass Spectrom. 42(7):900-9 [3] Laukien S, Creedon E, Kowalski JM, Kowalski P, Kellersberger K, gar N. Small Molecule Drug Imaging of Mouse Tissue by MLDI- TOF/TOF Mass Spectrometry and FTMS ruker Daltonics pplication note MT-93/FTMS38. [4] Marshall PS; Toteu-Djomte V, iggadike K. Percutaneous bsorption of drug compounds into skin measured by a new MLDI-TOF SRM mode SMS 2010, Session ThP16, Poster 397 [5] R Development Core Team (2010) R: Language and Environment for Statistical Computing, R Foundation for Statistical Computing, ISN For research use only. Not for use in diagnostic procedures. Keywords Tissue imaging drug distribution Instrumentation & Software autoflex speed fleximaging ImagePrep

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