Tolerability, pharmacokinetics, and pharmacodynamics of mirogabalin in healthy subjects: Results from phase 1 studies

Abstract Three phase 1 pharmacokinetic (PK)/pharmacodynamics (PD) studies were conducted in healthy men and women to further characterize the safety, tolerability, and PK/PD of mirogabalin administration with or without food and to guide the dose selection and regimen for phase 2 and 3 clinical development. The 3 studies included 2 randomized, double‐blind, placebo‐controlled, single‐ and multiple‐ascending‐dose studies, and 1 open‐label, crossover study to evaluate the PK of mirogabalin administered under fasting and fed (high‐fat meal) conditions. Forty‐eight and 47 healthy volunteers completed the single‐ and multiple‐dose studies, respectively. Thirty subjects were enrolled and completed the food effect study. Mirogabalin was well tolerated in the fed and fasted states. The most frequent treatment‐emergent adverse events (TEAEs)—dizziness and somnolence—were expected based on mirogabalin's mechanism of action. Subjects receiving the highest mirogabalin doses (50 and 75 mg single dose) showed greater dizziness and sedation and higher rates of TEAEs than subjects receiving 3‐30 mg. After oral administration, mirogabalin was rapidly absorbed (time to maximum concentration, ∼1 hour) and eliminated through urine unchanged (61%‐72% urinary excretion). Exposure increased in a dose‐proportional manner after single or multiple mirogabalin doses. No significant accumulation occurred with multiple doses over 14 days. After single doses of mirogabalin (15 mg), the bioavailability was considered equivalent in the fed and fasted states, indicating that mirogabalin can be taken without food restrictions. Based on these data, mirogabalin 15 mg twice daily was selected as the highest target dose for further clinical development.


| INTRODUCTION
The α 2 δ-1 subunit of Cav1-and Cav2-type voltage-gated calcium channels plays a role in neuropathic pain. [1][2][3] Ligands of the α 2 δ-1 subunit reduce Ca 2+ influx into central nervous system (CNS) neurons and exert analgesic effects. [2][3][4] As such, this subunit is the primary therapeutic target for 2 marketed neuropathic pain treatments; pregabalin and gabapentin. 5,6 Mirogabalin monobenzenesulfonate (Daiichi Sankyo Co., Ltd., Tokyo, Japan, herein referred to as mirogabalin) is a preferentially selective ligand of the α 2 δ-1 subunit in development for treatment of neuropathic pain. [1][2][3] In preclinical studies, mirogabalin demonstrated sustained analgesic effects in animal models of pain. 1 Mirogabalin also demonstrated improved analgesia with a wider safety margin than pregabalin. 1 In a phase 2 U.S. study of patients with diabetic peripheral neuropathic pain (DPNP; n = 452), average daily pain scores (ADPSs) were significantly reduced by mirogabalin 15, 20, and 30 mg/day compared with placebo after 5 weeks' treatment. Mirogabalin administered at 30 mg/day (15 mg twice daily [BID]) met the criteria of minimally meaningful effect (defined as a ≥1.0-point decrease in ADPS compared with placebo). 7 Phase 1 randomized studies in healthy adults were conducted to characterize initial safety, tolerability, pharmacokinetic (PK), and pharmacodynamic (PD) profiles of mirogabalin and further characterize the effect of food on mirogabalin PK. These studies included double-blind, placebo-controlled, single-and multiple-ascending-dose studies and an open-label, crossover study to evaluate the effects of mirogabalin administration with or without food. Various pharmacodynamic assessments were used to measure cognitive or nervous system-related effects. Results of these studies guided the dosing regimen selected for phase 2 and 3 clinical development.

| Single-ascending-dose study
The single-ascending-dose study was a randomized, double-blind, placebo-controlled, 6-cohort, sequential, escalating-dose study to determine safety, tolerability, and PK parameters of mirogabalin in healthy subjects, conducted October 2010 to December 2010. This study enrolled healthy adults aged 18-45 years with a body mass index (BMI) 19.0-30.0 kg/m 2 . Detailed inclusion and exclusion criteria for all studies are reported in Data S1.
All subjects provided written informed consent before performing study-specific evaluations. Six cohorts of subjects were dosed sequentially. Within each cohort, subjects were randomly assigned (6:2) to receive single oral doses of mirogabalin (3, 5, 10, 30, 50, or 75 mg) or placebo. Mirogabalin was provided as reconstituted powder (for the 3-mg dose) and 5-, 10-, and 25-mg tablets. Placebo was provided as matching reconstituted powder or tablets. A 7-day minimum safety review period occurred between successive cohorts.

| Multiple-ascending-dose study
The multiple-ascending-dose study was a randomized, double-blind, double-dummy, placebo-controlled, 5-cohort, sequential, escalatingdose study with pregabalin as an active control conducted to determine safety, tolerability, and PK parameters of mirogabalin in healthy elderly subjects, conducted January 2011 to April 2011. This study enrolled healthy adults aged 55-75 years with a BMI 19.0-32.0 kg/m 2 . Five cohorts of subjects were dosed sequentially. Within each cohort, subjects were randomly assigned (6:2:2) to receive an oral dose of mirogabalin 5, 10, 15, 20, or 25 mg; pregabalin 150 mg; or placebo.
All doses were given twice daily for 14 days except for mirogabalin 25 mg, which was given once daily for 5 days, twice daily for 8 days, and then 1 dose of 25 mg on the last day; and pregabalin, which was given 75 mg for 5 days, then 150 mg twice daily for 9 days. Mirogabalin was provided as 5-and 10-mg tablets; pregabalin was provided as over-encapsulated formulations at 75-and 150-mg doses; placebo for mirogabalin and pregabalin was provided as matching tablets or capsules, respectively. A cohort could begin dosing as soon as the previous cohort completed day 14, if the safety profile of the previous cohort was acceptable. The effects of mirogabalin on PD parameters including sedation, attention, dizziness, and ataxia were also assessed.

| Food effect study
The food effect study was an open-label, randomized, 2-treatment, 2-period, 2-sequence crossover study conducted in healthy subjects to evaluate the PK of mirogabalin under fed vs fasted conditions, conducted December 2013. This study enrolled healthy adults aged 18-60 years with a BMI 18.0-30.0 kg/m 2 . A single oral dose of mirogabalin 15 mg was administered in 2 regimens, (A) fasted (overnight fast for ≥10 hours, followed by mirogabalin dosing and an additional 4-hour fast) and (B) fed (overnight fast for ≥10 hours, followed by consumption of a high-fat breakfast within 30 minutes and subsequent dosing of mirogabalin). Subjects were randomly assigned to treatments in the sequence AB or BA, with a ≥3-day washout period between each treatment. Pharmacodynamic parameters, which included sedation, attention, dizziness, and ataxia, were also assessed.

| Safety
For each of the 3 studies, the safety and tolerability was assessed for all subjects who received at least 1 dose of study medication. In the multiple-ascending-dose and food effect studies, the Columbia suicide severity rating scale (C-SSRS) 8 was used to monitor suicidality. The C-SSRS captures the occurrence, severity, and frequency of suicide-related thoughts and behaviors, and was conducted by appropriately trained site personnel. Referral to a psychiatrist was to be made if the C-SSRS showed significant findings.
The PK analysis set included all subjects who received a dose of mirogabalin and had sufficient plasma concentration data for mirogabalin to characterize the PK parameters. The PK parameters were Mirogabalin plasma concentrations were summarized descriptively; plasma and urine concentration-time data were analyzed by noncompartmental methods, with concentrations below the limit of quantitation set to 0. In the single-and multiple-ascending-dose studies, the relationship between dose and PK parameters was examined using a graphical approach and linear regression of dosenormalized parameters. Apparent dose proportionality of PK parameters (single dose, AUC inf , AUC last , and C max ; multiple dose, day 14 AUC 0-τ and steady state C max ) were assessed graphically and using a linear regression analysis of dose-normalized parameters.
In the food effect study, peak and total mirogabalin exposures were compared between fasted (A) and fed (B) conditions using a mixedeffects model for the log-transformed PK values with treatment sequence, period and treatment as fixed effects, and subject nested with sequence fitted as a random effect. Geometric mean ratios of Treatment BA were calculated by exponentiation of the differences in least-squares mean (LSM), along with corresponding 90% confidence intervals (CIs). An absence of food effect was determined if 90% CIs were entirely contained within the 80% to 125% equivalence interval.

| Pharmacodynamic assessments
In the single-and multiple-ascending-dose studies, the PD analysis set included all subjects who received a dose of study medication BROWN ET AL. and for whom at least 1 postdose PD assessment was available. PD variables were evaluated at each measurement point using descriptive statistics and graphics.
The PD variables in the single-and multiple-ascending-dose studies were selected to elucidate the CNS-related tolerability profile of mirogabalin and evaluated sedation, attention, dizziness, and ataxia.
More detail about each assessment is provided in Supplementary Data. No PD assessments were performed in the food effect study.
Sedation was analyzed in the single-and multiple-ascending-dose studies using the Line Analog Rating Scale (LARS). 9,10 Attention was measured by the Digit Symbol Substitution Test (DSST) 11 . Dizziness was measured by the Vertigo Symptom Scale Short Form (VSS-SF); 12 and ataxia was measured by the Brief Ataxia Rating Scale (BARS). 13 Full details of each scale are reported in Data S2.
In the single-ascending-dose study, all scales were assessed before dosing and at 2, 7, and 24 hours after dosing (in order: LARS, DSST, VSS-SF, BARS); the BARS was additionally assessed at 12 hours after dosing. In the multiple-ascending-dose study, LARS, DSST, VSS-SF, and BARS were assessed on study days −1, 1, 3, 6, 8, and 13, at 2 hours (except BARS) and 7 hours postdose (or the time matched hour on study day −1), or at early withdrawal.

| Subject disposition and demographics
In the single-and multiple-ascending-dose studies, 48 healthy subjects were enrolled in each study. All 48 subjects in the single-ascendingdose study completed the study; 1 subject out of 48 from the multipleascending-dose study discontinued (on day 8 after 15 doses of study treatment) because of elevated hepatic transaminase levels.
Thirty subjects were enrolled in the food effect study and randomly assigned 1:1 to treatment sequence AB (n = 15) or BA (n = 15). All 30 subjects completed the study. Baseline demographics are reported in Table S1. More men than women enrolled in all 3 studies (45:3 in the single-ascending-dose study, 31:17 in the multiple-ascending-dose study, and 19:11 in the food effect study), and most subjects were White (56.3%, 91.7%, and 60.0%, respectively). Mean age was 31.4 years in the single-ascending-dose study and 35.9 years in the food effect study. In the multiple-ascending-dose study, which enrolled subjects aged 55-75 years, mean age was 61.4 years.

| Safety
In the single-dose study, most TEAEs were reported in the 50-and 75mg dose cohorts (Table 1); lower doses (≤30 mg) were well tolerated.
The most common TEAEs after mirogabalin dosing were somnolence (20.8%) and dizziness (18.8%). At doses higher than 30 mg, unsteady gait, nausea/vomiting, and blurred vision were observed and were dose limiting. In the multiple-ascending-dose study, doses of mirogabalin 5, 10, and 15 mg BID were well tolerated; however, the 15-mg BID dose was associated with a higher incidence of TEAEs, most notably dizziness/somnolence ( Table 1). Doses of mirogabalin 20 and 25 mg twice daily were not well tolerated. Moderate somnolence was reported in 1,

| Single-ascending-dose study
Mean mirogabalin plasma concentrations increased in a dose-proportional manner ( Figure 1A), as did exposure (Table 2) Urinary PK data are shown in Table 2. Mirogabalin was rapidly eliminated via urinary excretion (61%-72%), the majority during the first 0-to-4-hour collection interval for all doses. The mean amount of mirogabalin excreted increased as the dose administered increased. The mean fraction of the dose excreted as unchanged mirogabalin was similar across dose levels.

| Multiple-ascending-dose study
Mean mirogabalin plasma concentrations increased with increasing doses ( Figure 1B), although exposure seemed to increase in a slightly less than proportional manner. Plasma PK parameters for mirogabalin and pregabalin on day 14 are shown in Table 3. Urinary PK data are shown in Table 3

| Food effect study
Although the mean total exposure was similar under fed and fasting conditions, the C max for mirogabalin was reduced by approxi-

| Sedation
Compared with those in other dose cohorts, subjects receiving higher doses of mirogabalin (30, 50, and 75 mg) in the single-dose study had greater levels of sedation at each postdose assessment, according to LARS ( Figure S1A). For the 30-and 50-mg cohorts, LARS scores returned to baseline by 24 hours postdose. Consistent with these findings, safety assessments indicated that somnolence was reported as a TEAE by more subjects in the 50-mg cohort (66.7%) and the 75-mg cohort (50%) relative to the lower dose cohorts (Table 1). By contrast, mirogabalin did not increase sedation in the multiple-dose study ( Figure S1B). Additionally, the profile of mood however, the frequency of somnolence reported as a TEAE seemed to increase as the mirogabalin dose increased (Table 1).

| Attention
Subjects in the highest dose cohorts (50 and 75 mg) had reduced attention compared with those in other dose cohorts, according to DSST ( Figure S1C) in the single-ascending-dose study. However, T A B L E 2 Plasma and urinary pharmacokinetic parameters in the single-ascending-dose study    Data are expressed as arithmetic mean (SD) unless otherwise specified. Ae, the amount of parent drug or its metabolites excreted in urine during each collection interval; Ae 0-τ , cumulative amount of drug or metabolite excreted into the urine over the entire collection interval; AUC 0-τ , area under the plasma concentration-time curve for a dosing interval; BID, twice daily; C max ss , maximum observed concentration in plasma (at steady state); CL r ss , renal clearance (at steady state); CL ss /F, apparent total body clearance after oral administration (at steady state); Fe 0-T, ss , cumulative fraction of the dose excreted as unchanged parent in urine over the entire collection interval (at steady state); QD, once daily; R obs , observed accumulation ratio, calculated as AUC 0-τ (day 14)/AUC 0-12 (day 1); SD, standard deviation; t 1/2 , terminal half-life; T max , time of maximum observed concentration (at steady state); V z /F ss , apparent volume of distribution (at steady state), based on the terminal elimination phase. a One subject discontinued from the study early owing to a treatment-emergent adverse event.
BROWN ET AL. | 7 of 9 disturbance in attention was reported as a TEAE by only 1 subject in the study (75-mg cohort), suggesting that the detected deficits in attention were subtle and not clinically relevant. In the multiple-dose study, attention was not decreased by any mirogabalin dose evaluated; rather, almost all DSST scores increased over time ( Figure S1D).
Disturbance in attention was reported as a TEAE by 2 subjects in the study (both in the mirogabalin 15-mg BID cohort); however, this TEAE showed no correlation with mirogabalin dose (Table 1).

| Dizziness
In the 50-and 75-mg cohorts of the single-dose study, self-reported dizziness, as measured by the VSS-SF questionnaire, was apparent; values returned to predose levels by 24 hours postdose in the 50mg but not the 75-mg cohort ( Figure S1E). Similarly, dizziness was reported as an AE by more subjects in the 50-mg (n = 3, 50.0%) and 75-mg cohorts (n = 4, 66.7%) than in lower-dose cohorts (n ≤ 1 per cohort) (

| Ataxia
Subjects in the highest dose cohorts (50 and 75 mg) in the singleascending-dose study had greater levels of ataxia as detected than those in other dose cohorts ( Figure S1G). In these dose groups, TEAEs related to balance and gait were also reported.
In the multiple-ascending-dose study, ataxia increased in subjects receiving 15, 20, or 25 mg BID. This ataxia peaked between days 3 and 6 and returned to baseline thereafter; the highest increases in BARS scores were in the 20-mg BID cohort ( Figure S1H). A correlation between impaired balance or gait disturbance and BARS scores is suggested; however, mean BARS scores did not seem to detect symptoms with greater sensitivity than TEAE occurrence. TEAEs of dizziness and somnolence were expected based on the mirogabalin mechanism of action. Therefore, it was not unexpected that, in both the single-and multiple-ascending-dose studies, dizziness and somnolence were among the most commonly reported TEAEs.

| DISCUSSION
However, with pregabalin treatment, subjects developed tolerance to these TEAEs. 15 In the multiple-ascending-dose study, somnolence or dizziness resolved or improved within 4-5 days, suggesting that tolerance developed to these CNS TEAEs. Asymptomatic elevation of hepatic transaminase levels was reported in 1 subject receiving mirogabalin 10 mg BID in the multiple-ascending-dose study. Although mild, these elevations were considered related to study treatment, and the subject was discontinued from the study.
Results of the single-and multiple-ascending-dose studies confirmed that mirogabalin is rapidly absorbed and rapidly eliminated with a dose-proportional increase in exposure, but with no signifi-