DOI: 10.5061/dryad.w3r2280t2
title: Migraine monoclonal antibodies against CGRP change brain activity depending on ligand or receptor target – an fMRI study

description: Background: Monoclonal antibodies (mAbs) against calcitonin gene-related
 peptides (CGRP) are novel treatments for migraine prevention. Based on a
 previous functional imaging study which investigated the CGRP receptor mAb
 (erenumab), we hypothesized that (i) the CGRP ligand mAb galcanezumab
 would alter central trigeminal pain processing; (ii) responders to
 galcanezumab treatment would show specific hypothalamic modulation in
 contrast to non-responders; and (iii) the ligand and the receptor antibody
 differ in brain responses. Methods: Using an established trigeminal
 nociceptive functional magnetic imaging paradigm, 26 migraine patients
 were subsequently scanned twice: before and 2–3 weeks after administration
 of galcanezumab. Results: We found that galcanezumab decreases
 hypothalamic activation in all patients and that the reduction was
 stronger in responders than in non-responders. Contrasting erenumab and
 galcanezumab showed that both antibodies activate a distinct network. We
 also found that pre-treatment activity of the spinal trigeminal nucleus
 (STN) and coupling between the STN and the hypothalamus covariates with
 the response to galcanezumab. Conclusions: These data suggest that despite
 relative impermeability of the blood-brain barrier for CGRP mAb, mAb
 treatment induces certain and highly specific brain effects which may be
 part of the mechanism of their efficacy in migraine treatment. Funding:
 This work was supported by the German Ministry of Education and Research
 (BMBF) of ERA-Net Neuron under the project code BIOMIGA (01EW2002 to AM)
 and by the German Research Foundation (SFB936-178316478-A5 to AM). The
 funding sources did not influence study conduction in any way. 
 Clinical trial number: The basic science study was preregistered in the
 Open Science Framework (https://osf.io/m2rc6).
description: <strong>Experimental
 paradigm</strong> Patients
 were asked to attend two functional magnetic resonance imaging (fMRI)
 scanning sessions before and after the first administration of
 galcanezumab. Both visits took place approximately three weeks apart
 (pharmacokinetic drug peak blood level) and followed the same protocol.
 Following the first scan, the loading dose of galcanezumab 240 mg was
 administered subcutaneously by the patient under the prior instruction of
 a headache specialist. During
 the experiment, which has been described in detail previously,
 participants received 15 repetitive painful trigeminal stimulations by
 administering gaseous ammonia (mixed in a stream of air) into the left
 nostril and 15 puffs of air, 15 trials of rose scent and 15 repetitive
 visual stimuli as control conditions. All stimuli were presented in a
 pseudo-randomized order, with painful trigeminal stimuli not presented in
 immediate succession. After each trial, participants were asked to rate
 the intensity as well as the unpleasantness on a numeric rating scale from
 0 to 100, each of which was tested with a paired t-test if the criteria of
 the Gaussian distribution were fulfilled or otherwise with a Wilcoxon
 sign-rank test. Standardized headache calendars were collected at visit 1,
 visit 2 and in a follow-up interview by telephone and email after a total
 of 3 months of therapy. 
 <strong>MRI
 acquisition</strong> All
 images were recorded at a Siemens PRISMA 3T MR system (Siemens, Erlangen,
 Germany) using a 64-channel head coil. During the experimental protocol
 1095 functional images were acquired for each subject and for each session
 using an echoplanar imaging sequence (EPI) optimized for blood-oxygenation
 level dependent (BOLD) brainstem imaging: voxel size 1,3 x 1,3 x 2,5
 mm<sup>3</sup>, 38 axial slices (no gap), repetition time 2.64
 s, echo time 28 ms, flip angle 80°, GRAPPA acceleration mode, field of
 view readout 216 mm, phase partial Fourier 7/8, two saturation pulses were
 added anterior and posterior to the target volume, which covered the whole
 volume from the corpus callosum to the foramen magnum (MNI z-range 25 to
 -72). Simultaneously, we recorded pulse and breathing (Expression,
 Philipps, Best, Netherlands) to correct for cardiovascular
 artifacts. Functional imaging was followed by field mapping
 MRI sequence (repetition time 0,8 s, echo time 1: 5.51 ms, echo time 2:
 7.97 ms, flip angle 40°, field of view readout 215 mm) and a
 high-resolution magnetization-prepared rapid gradient echo sequence
 (MPRAGE) image (voxel size 1 mm<sup>3</sup>, repetition time
 2.3 s, echo time 2.98 ms, flip angle 9°, field of view 256 mm2, 240 axial
 slices gap 50%). <strong>Preprocessing</strong> In general, the preprocessing followed the established basis for functional imaging preprocessing steps consisting of: denoising functional images (spatially adaptive non-local mean filter), realignment and unwarping by the aforementioned field-maps, slice-time correction, co-registration to the anatomical images and transformation into Montreal Neurological Institute (MNI) space as implemented in SPM12 (Wellcome Trust Center for Neuroimaging, London, UK). Functional images were then smoothed using a 4 mm<sup>3</sup> full-width at half maximum Gaussian kernel. <strong>Statistical analysis</strong> A General Linear Model (GLM) analysis was used within each participant providing β-estimates which were used for group statistical analysis. These β values were calculated for each voxel and signify the condition-specific neuronal activity. Therefore, we were using a hemodynamic response function (HRF) to model all four stimulus conditions (ammonia, rose, air puff, visual) and three confound conditions (key press/assessment, attention task, anticipation phase) by convolving their onsets and durations and applying them as regressors in the GLM. For further correction of movements that were not intercepted by the realignment processing, we included the 6 movement regressors provided in the realign and unwarp step mentioned earlier. For physiological noise correction, we included an additional 18 to 20 regressors extracted from each participants' breath and pulse signals using the approach described by Deckers and colleagues. For the main effect the results were corrected for multiple comparisons (family-wise error corrected, p &lt; 0.05), for the sub-analysis with a strong a-priori hypothesis (see preregistration) we calculated paired and independent one-sided t-test as implemented in the SPM toolbox and used an uncorrected statistical threshold of p &lt; 0.001. <strong>Arterial Spin Labelling</strong> As galcanezumab is potentially a vasoactive drug, arterial spin labelling (ASL) was also recorded to exclude that any BOLD changes were due to general changes in cerebral blood flow (CBF). To cover the blood flow of the entire brain, we performed separate measurements of the brainstem and the cerebrum. The ASL sequence used pulsed ASL (PASL) recorded with 91 repetitions in 17 slices with a TR of 2.6 s (TE 12 ms, 90° flip angle, bolus duration 1800 ms, inversion time 700 ms, PICORE Q2T perfusion mode, voxel size 2 mm x 2mm x 5 mm). The relative CBF maps calculated by the scanner software were co-registered to the anatomical image, warped into MNI space using the transformation calculated on the anatomical image, and smoothed using a 12 mm isotropic Gaussian kernel again using SPM12 (Wellcome Trust Center for Neuroimaging, London, UK). Results were corrected for multiple comparisons [family-wise error corrected, p &lt; 0.05, T &gt; 6.1, df = 25]). <strong>Effect of trigeminal stimulation</strong> First, both visits were pooled to observe the effect of the trigeminal nociceptive ammonia stimulation (main effect). A statistical threshold of p &lt; 0.05 (FWE corrected for multiple comparisons) was used for a one-sided, independent t-test. <strong>Effect of galcanezumab on trigeminal stimulation</strong> To estimate significant differences before versus after administration of galcanezumab, a one sided, paired t-tests in each voxel was performed using SPM12 [14] for the contrast of pain &gt; control at visit 1 vs. pain &gt; control at visit 2 (further classified as [ammonia-air puffs]<sub>visit 1</sub> &gt; [ammonia-air puffs]<sub>visit 2</sub>) and [ammonia-air puffs]<sub>visit 1</sub> &lt; [ammonia-air puffs]<sub>visit 2</sub>). A statistical threshold of p &lt; 0.001 (uncorrected) was used, since we had a strong a priori hypothesis, see preregistration and. <strong>Differences between galcanezumab (CGRP-L-mAb) and erenumab (CGRP-R-mAb)</strong> As this study followed a previously conducted study on the CGRP receptor mAb Erenumab, we also compared the two effects caused by these medications. To ensure direct comparability, we also included a subgroup consisting of patients with the same migraine phase in the analyses and compared the respective contrasts ([ammonia-air puffs]<sub>visit 1</sub> vs [ammonia-air puffs]<sub>visit 2</sub>) in a one-sided, two-sample t-test. For this analysis, the existing erenumab data sets were reassessed and included in above mentioned analysis routine. A statistical threshold of p &lt; 0.001 (uncorrected) was used, since we had a strong a priori hypothesis, see preregistration. <strong>Therapy prediction analysis</strong> Following the protocol of the previous study we defined and pre-registered “being a responder” by showing a 30% reduction in headache frequency after 3 treatment months. Since a maximal response was not to be expected at three weeks we used the accepted time span of 3 months to calculate responders. However, we asked all patients at the time of the second scan whether they felt the medication to be effective and the number of patients who answered this subjective question positively, corresponded with the 30% response at 3 months (two-tailed Pearson correlation, r= 0.778, p&lt;0.001). To detect possible predictors of treatment outcome in the processing of trigemino-nociceptive stimuli, we used the visit 1contrast [ammonia-air puffs]<sub>visit 1</sub> and co-varied the model with the individual response after 3 months (in % reduction of monthly headache days (MHD)) in all patients (n=26) in an one-sided, independent t-test as implemented into the SPM toolbox. An additional nuisance covariate of migraine-phase was used to eliminate possible variance caused by the presence of headache. A statistical threshold of p &lt; 0.001 (uncorrected) was used for hypothesis generation. <strong>Alterations in functional connectivity</strong> Galcanezumab-induced functional connectivity changes were estimated for the whole group (n=26) by psychophysiological interaction analysis, using the region of interest (i.e., STN) resulting from the previous analysis as a starting point and contrasting ammonia (nociceptive input) and air puffs (control condition) between the 2 visits as before. A statistical threshold of p &lt; 0.001 (uncorrected) was used in the one-sided, independent t-test, since we had a strong a priori hypothesis, see preregistration.