Glucagon-like peptide-1 analogues: a new way to quit smoking? (SKIP)—a structured summary of a study protocol for a randomized controlled study

Background Cigarette smoking is the leading preventable cause of premature death. Despite dedicated programmes, quit rates remain low due to barriers such as nicotine withdrawal syndrome or post-cessation weight gain. Glucagon-like peptide-1 (GLP-1) analogues reduce energy intake and body weight and seem to modulate addictive behaviour. These GLP-1 properties are of major interest in the context of smoking cessation. The aim of this study is to evaluate the GLP-1 analogue dulaglutide as a new therapy for smoking cessation. Methods This is a placebo-controlled, double-blind, parallel group, superiority, single-centre randomized study including 255 patients. The intervention consists of a 12-week dulaglutide treatment phase with 1.5 mg once weekly or placebo subcutaneously, in addition to standard of care (behavioural counselling and pharmacotherapy with varenicline). A 40-week non-treatment phase follows. The primary outcome is the point prevalence abstinence rate at week 12. Smoking status is self-reported and biochemically confirmed by end-expiratory exhaled carbon monoxide measurement. Further endpoints include post-cessational weight gain, nicotine craving analysis, glucose homeostasis and long-term nicotine abstinence. Two separate substudies assess behavioural, functional and structural changes by functional magnetic resonance imaging and measures of energy metabolism (i.e. resting energy expenditure, body composition). Discussion Combining behavioural counselling and medical therapy, e.g. with varenicline, improves abstinence rates and is considered the standard of care. We expect a further increase in quit rates by adding a second component of medical therapy and assume a dual effect of dulaglutide treatment (blunting nicotine withdrawal symptoms and reducing post-cessational weight gain). This project is of high relevance as it explores novel treatment options aimed at preventing the disastrous consequences of nicotine consumption and obesity. Trial registration ClinicalTrials.gov NCT03204396. Registered on June 26, 2017. Supplementary Information The online version contains supplementary material available at 10.1186/s13063-023-07164-9.


Background
Smokers compared to non-smokers exhibit increased functional brain activations in the prefrontal and limbic regions when exposed to craving-related smoking cue videos [1]. In this clinical trial (SKIP-study) the GLP-1 analogue Dulaglutide (Trulicity®) is evaluated as a treatment for smoking cessation. Supposing that GLP-1 and analogues modulates nicotine induced reward system [2,3] we hypothesize that treatment with Dulaglutide (Trulicity®) attenuates craving and therefore functional brain activation. The aim of the present substudy is to evaluate effects of Dulaglutide treatment on functional neuronal changes in smokers who want to quit smoking.

Recruitment and screening
All SKIP-participants meeting the following in-and exclusion criteria are invited to participate in this substudy (until target sample size is reached).

Inclusion criteria
-Age 18-60 years -Written informed consent signed -Daily smokers who are willing to quit and exhibit one of the following criteria:  ≥10 cigarettes per day and  At least moderate nicotine dependence defined by a Fagerstroem Score of ≥5 points  Treatment with Varenicline (Champix®)

Exclusion criteria
-Pregnancy (incl. wish to become pregnant within next 3 months) or breast feeding -Pre-existing treatment with GLP-1 agonists -History of pancreatitis -Severe renal insufficiency (estimated glomerular filtration rate <30 ml/min/1,73 m2) -Instable psychiatric conditions including Anorexia nervosa -Medical conditions that affect brain function (e.g. stroke, epilepsy, space occupying lesions, multiple sclerosis, Parkinson's disease, dementia, transient ischemic attack) -Current use of medications that alter brain function -Current illicit drug abuse including marijuana (alcohol ≤ 1 drink per day allowed) -Claustrophobia -Cardiac pacemaker, electronic device or ferromagnetic metal foreign bodies -Known or suspected allergy to trial product or related products 3. Objective, outcome, assumptions

Objective
To investigate the influence of the GLP-1 analogue Dulaglutide (Trulicity®) versus placebo on functional neuronal changes in the prefrontal cortex and limbic region measured by different methods of fMRI in smokers who want to quit smoking.

Outcome
a) Behavioural outcomes include:  Craving measured by a Visual Analogue Scale (VAS) [1].
 Working memory performance investigated by the N-back task scores. b) Functional neuronal changes are assessed through the surrogate of blood oxygenated level dependent (BOLD) signal, an indirect measure of neural activity. Three echo-planar imaging (EPI) sequences will be performed to investigate neural substrates of nicotine craving, working memory and resting state functional networks. c) Structural outcomes include structural plasticity of grey and white matter in regions parts of the reward pathway (i.e. anterior cingulate cortex, insula, striatum) and in subcortical regions. One T1 sequence and one DTI sequence will be performed to investigate changes in grey and white matter.
Changes in the reward pathway are also assessed in the cerebro-spinal fluid (CBF) from the Arterial Spin Labelling (ASL) sequence.  Positive correlation between brain atrophy and the severity of nicotine dependence, nicotine exposure and and craving.

Assessment and Procedures
In addition to the regular study visits fMRI will be conducted at baseline (after inclusion and before injection of the first trial medication) and after 3 months of treatment (a time frame between visit 8 and 12 will be accepted).
Before fMRI examination, smoking abstinence of at least 2 hours is required. Exposure to nicotine is Week 7 Week 8 Week 9 Week 10 Week 11 Week 12 Week 24 Week

Substudy fMRI
fMRI X X X

fMRI procedure and acquisition
Participants undergo a block-design fMRI study performing two structural sequences: T1-weighting (T1) to investigate changes in grey matter and diffusor tensor imaging (DTI) to investigate changes in white matter.
Additionally, an Arterial Spin Labelling (ASL) sequence will be performed to assess changes in arterial perfusion.
Finally three functional sequences (EPI) will be performed to investigate changes in the BOLD signal: Resting State Sequence, a Nicotine Craving Task [1] to investigate nicotine craving, and an N-Back Task to investigate working memory-related brain activations.

Nicotine craving task
The paradigm consists of an on-off block-design with two active conditions (smoking cue and control videos) and a neutral condition (cross displayed). The active condition uses video cues developed by Brody et al. [1,4].

N-Back Task
A rapid, mixed trial, event-related fMRI design is used with jittered interstimulus intervals incorporating random event presentation to optimize statistical efficiency [5]. During the N-back task [6], all subjects see series of letters with an interstimulus interval of 2 s. Each stimulus is presented for 1 s. During a baseline (0-back) condition, subjects are required to press the button with the right hand when the letter "X" appears.
During 1-back and 2-back conditions, participants are instructed to press the button if the currently presented letter is the same as that presented 1 (1-back condition) or 2 trials beforehand (2-back condition). The three conditions will be presented in ten alternating 30 s blocks (2 × 1-back, 3 × 2-back and 5 × 0-back) matched for the number of target letters per block (i.e., 2 or 3), in a pseudo-random order.

Resting State Sequence
For the resting-state scan (5 minutes), subjects are instructed to lie in dimmed light with their eyes open, to think of nothing in particular, and not to fall asleep.

T1, DTI and ASL sequences
During the structural scans, subjects are instructed to lie in scan without performing any particular tasks.

Sample Size
In total 60 patients who are willing to participate in the main and the substudy and meet the additional eligibility criteria. The decision to include 60 patients is based on feasibility criteria such as costs, availability of staff, infrastructure, and readiness of patients to participate. We suppose that 60 patients are sufficient to generate meaningful results that allow generation of hypotheses. Measurement of functional Smoking cessation by GLP-1 analogues -The SKIP-Study -Substudy "SKIP-fMRI" V1 13.10.2017 Page 6 of 7 brain activity by fMRI poses low risk to the patient. Therefore, the sample size is only limited by feasibility criteria.

Planned Analysis
The fMRI will be pre-processed using FSL (FSL Version 5.0.9; http://fsl.fmrib.ox.ac.uk) to make the data ready for statistical analyses. Details will be provided in a data management plan. There is an option to alter and add variables in an iterative process during statistical analysis.
The analysis set includes all patients that signed the informed consent of this substudy and performed at least one fMRI. Missing data will not be imputed but frequency and reasons for missingness described. No hypotheses will be tested. Explorative analyses are performed for hypothesis generation.
Summary statistics will be performed including reporting of frequencies of nominal and ordinal data and distribution parameters of numerical data.
All outcomes will be analysed by two group comparison at 12 weeks relative to baseline. Groups at 12week visit are intervention or control arm, either quitters or persistent smokers. Analyses will be focussed on predefined assumptions described above. However, each possible combination of head-to-head comparisons will be made. Differences of outcomes between two groups will be analysed and frequentist pvalues provided for each outcome of each comparison.
Further analyses include comparison of outcomes before and after Varenicline (Champix®) exposure in placebo treated participants and correlation of outcomes with the following variables: severity of nicotine dependence (Fagerstroem Score) nicotine exposure (pack years, actual number of cigarettes per day, urinary cotinine, end-expiratory exhaled carbon monoxide in ppm) craving (QSU-G, VAS) age sex All alpha error levels will be reported. Despite alpha error inflation due to multiple testing, no alpha error correction will be performed. Interpretation of p-values will be of explorative nature and always reported as a whole.
Detailed description of variables, statistical models, and presentation of results will be provided in a statistical analysis plan.
Motivated by results, further explorative analyses that are not defined a priori in the statistical analysis plan might be carried out.