Abstract
Bexicaserin (LP352) is a selective 5‐hydroxytryptamine 2C (5‐HT2C) superagonist in development for the treatment of seizures in developmental and epileptic encephalopathies (DEEs). This double‐blind, placebo‐controlled, single ascending dose (SAD) Phase 1 study aimed to assess the safety, tolerability, and pharmacokinetic (PK) and pharmacodynamic (PD) profiles of single oral doses of bexicaserin and determine any relevant food effects. Forty healthy adult females were randomized to six treatment groups (1, 3, 6, 12, and 24 mg fasted; 6 mg fed) or placebo. Bexicaserin was generally safe and well tolerated: treatment‐related adverse events were mild to moderate. Bexicaserin was rapidly absorbed into circulation (median T max 1.02–1.54 h), with a mean terminal elimination half‐life ranging from 4.67–6.66 h. Mean C max and AUClast of bexicaserin increased by at least >55‐fold for a 24‐fold dose increase. Three pharmacologically inactive circulatory metabolites (M9, M12, and M20) were further characterized. M20 was the major metabolite, with levels ranging from 3.47 to 10.8 times higher than bexicaserin. In comparison, M12 ranged from 0.35 to 0.98 times, and M9 from 0.037 to 0.53 times, relative to bexicaserin. Metabolism was the major route of clearance, as <5% of parent bexicaserin was eliminated in the urine. A high‐fat meal did not alter the exposure of bexicaserin, supporting administration without regard to food. Increases in prolactin concentrations, a potential PD marker, were dose‐dependent, suggesting central 5‐HT2C receptor engagement. In summary, this Phase 1 SAD study demonstrated safety, tolerability, and adequate characterization of PK/PD of bexicaserin, which is currently in Phase 3 clinical development.
Keywords: single dose, 5‐HT2c, prolactin, epilepsy, bexicaserin, pharmacokinetics, pharmacodynamics
Developmental and epileptic encephalopathies (DEEs) are the most severe group of epilepsies in which drug‐resistant seizures and developmental slowing or regression are observed. Because DEEs are phenotypically complex and etiologically diverse, the need for effective treatment of the associated seizures remains unmet. 1 , 2 , 3 , 4
Modulation of the serotonergic system via one or more of the 14 receptor subtypes 5 has relevance to a variety of psychiatric and neurological disorders including depression, anxiety, 6 migraines, 7 and seizure disorders. 5 , 8 Bexicaserin (LP352) is a selective serotonin (5‐hydroxytryptamine; 5‐HT) 2C (5‐HT2C) receptor subtype superagonist 9 , 10 in development for the treatment of seizures associated with DEEs. Epileptic seizures can result from an imbalance of excitatory and inhibitory neurons. Bexicaserin is thought to increase the activity of inhibitory neurons in epileptogenic regions of the brain, thereby augmenting their activity. Bexicaserin was shown in preclinical studies to reduce motor seizures and epileptiform activity in DEEs originating from diverse etiologies. Bexicaserin is highly selective to the 5‐HT2C receptor subtype with no appreciable binding activity at other molecular targets at clinically relevant doses. 9 This selectivity reduces the potential for adverse effects associated with (off‐target) engagement of either 5‐HT2A (e.g., hallucinogenic activity) 11 or 5‐HT2B (e.g., cardiovascular disease). 12 , 13 Bexicaserin is currently in Phase 3 clinical development with Breakthrough Therapy designation from the US Food and Drug Administration for the treatment of seizures associated with DEEs and Orphan Drug and Rare Pediatric Disease designations for the treatment of individuals with the DEE Dravet syndrome.
This is the first in human study of bexicaserin and was designed to assess the safety, tolerability, and pharmacokinetic (PK) and pharmacodynamic (PD) profile of single doses of bexicaserin in healthy adult female participants, as well as to assess the effect of a high‐fat/high‐calorie meal on the PK and relative bioavailability of bexicaserin.
Methods
This study was performed in accordance with the principles of the Declaration of Helsinki and in compliance with the International Council on Harmonisation Guidelines for Good Clinical Practice. The clinical study protocol, protocol amendments, and informed consent forms were reviewed and approved by an Institutional Review Board. All participants provided written informed consent before participation. The first participant was enrolled on September 24 2019, and the last participant was discharged from the clinic on January 26, 2020.
Participants
Eligible participants were healthy females aged 18–55 years with a body mass index of 18.5–30 kg/m2, weight of at least 50 kg, and no medical history relevant to the study as defined by the following key exclusion criteria: history of any uncontrolled illness, a positive urine drug screen or history of drug or alcohol abuse, were pregnant, had current or recent (in the past 6 months) gastrointestinal disease that would have been expected to influence the absorption of drugs, a positive result for hepatitis B surface antigen or hepatitis C virus antibody, known history of human immunodeficiency virus infection, or used nicotine containing products. Female subjects were either of non‐childbearing potential (e.g., postmenopausal or surgically sterile) or, if of childbearing potential, agreed to use dual contraception (including one highly effective method) and avoid pregnancy during the study and for 30 days afterward.
Single Ascending Dose Study
A phase 1, randomized, double‐blind, placebo‐controlled, single‐dose escalation study (single ascending dose; SAD) was performed on five cohorts comprising eight participants each (Supplemental Figure S1). Six of the eight participants in each cohort were randomly assigned to a single dose of bexicaserin and two participants to placebo (powder in capsule (PIC) containing bexicaserin or placebo) after fasting overnight. The doses studied ranged from 1 to 24 mg of bexicaserin.
A sentinel dosing (n = 2) approach was used, in which initially one participant received bexicaserin and one received placebo in each cohort. After the 48‐h post‐dose safety and tolerability data for these two participants were reviewed and considered acceptable, the remaining six participants (5 bexicaserin and one placebo) in each cohort were administered study drug. A‐priori, the dose escalation strategy was put in place to ensure safe up‐titration with consideration of at least a 2‐fold increase in dose. However, the actual dose escalation decisions occurred after full review of the blinded safety, tolerability and PK data from the preceding cohort.
Bexicaserin or placebo was administered on the morning of day 1 after a fast of approximately 10 h. Participants in all cohorts then continued to fast for an additional 4 h after dosing. Participants could consume water ad libitum, except during the period 1 h before and 1 h after dosing.
Food‐Effect Study
Participants from the 6 mg SAD cohort were given a second treatment of 6 mg bexicaserin (n = 6) or placebo (n = 2) following at least 10 days of washout period (Supplemental Figure S1). In the second period, participants received 6 mg of bexicaserin or placebo following a high‐fat breakfast within 30 min prior to dosing. All participants were instructed to complete the meal in the allocated time of 30 min. A 3 mL blood sample was collected in fasted and fed state pre‐dose on day 1 (approximately 30 min before dosing) and at 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 16, 24, 36, 48, 72, and 96 h post‐dose for pharmacokinetic analysis.
Sample Collection
A 3 mL blood sample was collected pre‐dose on day 1 (in the 45 min before dosing) and at 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 16, 24, 36, 48, 72, and 96 h post‐dose for pharmacokinetic analysis. Additional 4.5 mL blood samples (for quantitation of prolactin levels) were collected at pre‐dose (between 7–9 am to account for circadian rhythm effects on prolactin, before dosing) and 2 h post‐dose on day 1.
Urine samples were collected pre‐ and post‐dose on day 1 for pharmacokinetic analysis. The first collection was within 12 h pre‐dose, and then collections were on the following schedule post‐dose: 0 to 4, 4 to 8, 8 to 12, 12 to 24, 24 to 48, and 48 to 72 h. Urine volume was measured and recorded within 2 h of the end of the collection period.
Safety Evaluation
Safety was evaluated throughout SAD and food effect studies by monitoring for adverse events (AEs) and by performing clinical laboratory tests, vital sign measurements, 12‐lead electrocardiograms (ECGs) and physical examinations.
For safety analyses, baseline samples for clinical laboratory tests were collected after participants had fasted for at least 10 h overnight and in accordance with acceptable laboratory procedures.
Vital signs including oral temperature, respiration rate, heart rate and blood pressure were assessed on day‐1 (pre‐dose), on day 1 at pre‐dose, 0.5, 1, 2, 4, 8, and 12 h post‐dose, on days 2, 3, 4, and 10.
Bioanalytical Methods
Concentrations of bexicaserin and its metabolites (M9, M12, and M20) were measured in plasma and bexicaserin concentrations were measured in urine using a validated high‐performance liquid chromatography with tandem mass spectrometry methods. 14 , 15 The bexicaserin and respective stable isotope labeled internal standard were extracted from human plasma and urine matrices by a solid‐phase extraction procedure; metabolites and their respective stable isotope labeled internal standards were extracted by protein precipitation followed by phospholipid removal and sample dilution methods. The mass spectrometer was operated in positive polarity using multiple reaction monitoring mode (MRM). The plasma standard curve ranges for bexicaserin and M9 metabolite were linear over the curve range of 0.1 to 100 ng/mL, M12 and M20 metabolite ranges were 0.5 to 500 and 1 to 1000 ng/mL, respectively. The urine assay range for bexicaserin was 1 to 1000 ng/mL. These assays were validated as per the bioanalytical regulatory guidelines in place and all validation parameters met the established method acceptance criteria.
Prolactin was assessed as part of the hormone laboratory panel that was collected on day 1. Samples were collected pre‐dose (between 7am–9am), and then 2 h post‐dose.
Pharmacokinetic and Pharmacodynamic Analyses
The PK parameters were estimated from plasma concentration–time data using standard non‐compartmental analysis (NCA) methods with Phoenix WinNonlin version 8.2 or higher (Certara, Princeton, NJ, USA). Plasma PK parameters included area under the plasma concentration–time curve from zero to the time of the last quantifiable concentration (AUClast), area under plasma concentration–time curve from zero to infinity (AUC∞), maximum plasma concentration (C max), apparent plasma clearance of drug after extravascular administration (CL/F; for bexicaserin only), terminal elimination half‐life (t 1/2), time to C max (T max), apparent volume of distribution during the terminal phase after extravascular administration (Vz/F; for bexicaserin only) and metabolic‐to‐parent ratio (MPR; calculated as [AUC∞ (M9, M12 or M20) × [bexicaserin molecular weight] / [AUC∞ (bexicaserin) × [M9, M12, or M20 molecular weight]−1). Results from the Fed cohort were compared to those from the corresponding fasted cohort. Food effect was assessed using geometric mean ratios of Fed/Fasted treatments and percent change in C max, AUClast and AUC∞ with food. Concentration time data and PK parameters were summarized using descriptive statistics.
Urine PK parameters included cumulative amount of drug excreted unchanged in urine from zero to 72 h (Ae72), fraction of dose excreted unchanged into urine (f e; for bexicaserin only) and renal clearance of drug (CLR). PD parameters included change from baseline in prolactin concentration with Dose on day 1 at 2 h. The time course profile of prolactin following single oral doses of bexicaserin or placebo was also evaluated.
Statistical Analyses
All data analyses were performed using SAS software version 9.3 (SAS Institute Inc., Cary, NC, USA). Data for PK parameters for bexicaserin and its metabolites are presented using descriptive statistics throughout. Dose proportionality for C max and AUClast was assessed using visual inspection using boxplots.
The effect of food on bexicaserin bioavailability was evaluated via point estimates of the log transformed geometric mean ratios of fed/fasting conditions and their 90% CIs for C max, AUClast and AUC∞ for bexicaserin and metabolites.
AEs were summarized as the number and percentage of participants who experienced at least one AE.
Results
In total, 40 healthy adult female participants (n = 30 bexicaserin; n = 10 placebo) were enrolled in the SAD study across a total of five cohorts (1, 3, 6, 12, and 24 mg). Prior to the follow‐up visit, participants from the third fasting cohort (6 mg dose) underwent a second treatment period, during which they received 6 mg bexicaserin or placebo following a high‐fat breakfast within 30 min prior to dosing. All participants completed the studies. Participant demographics are presented in Supplemental Table S1.
Safety and Tolerability
Participants had no adverse events leading to study drug or study visit discontinuation. There were no deaths or other serious AEs reported. Single doses of bexicaserin ranging from 1 to 24 mg were well tolerated, with mild to moderate treatment emergent adverse events (TEAEs) reported (Supplemental Table S2). Five (50.0%) of the 10 participants who received placebo and 23 (76.7%) of the 30 who received bexicaserin reported a total of 10 and 94 TEAEs, respectively. No severe TEAEs were reported.
The most commonly (≥20%) reported TEAEs were headache (53.3% of active participants, n = 16; versus 40% of placebo participants, n = 4) dizziness postural (26.7% of active participants, n = 8; versus 0% of placebo) and nausea (20.0% of active participants, n = 6; versus 0% of placebo).
In the food effect study, 5 subjects (83.3%) receiving bexicaserin 6 mg in both the fasted and fed groups reported TEAEs. In the placebo group, 1 subject (50.0%) in the fasted cohort and 2 subjects (100%) in the fed cohort reported TEAEs. The most common TEAEs (≥20%) were headache (50.0%) and paresthesia (33.3%) in the fasted group, and headache (50.0%) and postural dizziness (33.3%) in the fed group (Supplemental Table S3). Moderate TEAEs occurred in 4 fasted (66.7%) and 2 fed (33.3%) bexicaserin‐treated subjects, and included headache, presyncope, nausea, dysmenorrhoea, and lower abdominal pain. No participant experienced a severe TEAE.
No clinically significant abnormalities in clinical laboratory tests (including hormone levels), or changes from baseline in vital signs, physical examinations, comprehensive eye examinations or ECG measurements were observed during the study at any dose.
Pharmacokinetics
The single dose pharmacokinetics of bexicaserin were evaluated across a dose range of 1 to 24 mg in healthy participants (Table 1). Mean plasma bexicaserin C max ranged from 1.08 ng/mL for the 1 mg dose to 59.3 ng/mL for the 24 mg dose (Table 1). Regardless of the dose level, bexicaserin was absorbed rapidly, and peak concentration (C max) was reached within a median T max value between 1.02–1.54 h (Figure 1). Mean exposure of bexicaserin increased by >54‐fold, for a 24‐fold dose increase (Table 1).
Table 1.
Summary of bexicaserin plasma and urine PK parameters.
| Dose | |||||
|---|---|---|---|---|---|
| Bexicaserin PK parameters | 1 mg N = 6 | 3 mg N = 6 | 6 mg N = 6 | 12 mg N = 6 | 24 mg N = 6 |
| C max (ng/mL) | 1.08 (45.9) | 6.36 (33.4) | 9.52 (53.5) | 17.0 (30.6) | 59.3 (43.1) |
| T max (h) | 1.54 (0.68–2.00) | 1.02 (1.00–1.70) | 1.50 (1.00–3.02) | 1.25 (0.98–3.00) | 1.07 (0.50–1.50) |
|
AUClast (h*ng/mL) |
4.90 (72.9) | 35.7 (52.2) | 57.0 (59.1) | 99.5 (46.0) | 285 (43.9) |
| AUC∞ (h*ng/mL) | NC | 40.9 (47.2) | 58.7 (57.9) | 101 (45.6) | 288 (43.5) |
| t 1/2 (h) | NC | 4.94 (25.9) | 6.66 (43.2) | 4.67 (32.1) | 5.09 (13.8) |
| CL/F (L/h) | NC | 92.4 (58.6) | 134 (52.3) | 150 (58.6) | 93.7 (32.6) |
| Vz/F (L) | NC | 608 (38.8) | 1230 (67.6) | 929 (46.3) | 697 (37.8) |
| Ae (µg) | 17.5 (68.7) | 138 (55.7) | 215 (79.0) | 405 (36.2) | 1080 (46.2) |
| CLR (L/h) | 3.00 (19.1) | 3.62 (24.5) | 3.42 (24.3) | 4.25 (17.7) | 3.75 (22.5) |
Arithmetic mean (CV%) reported except for T max, for which median (min, max) values are reported. All data are presented as arithmetic mean (%CV) unless otherwise indicated. %CV indicates percentage coefficient of variance; AUC∞, area under the plasma concentration‐vs‐time curve extrapolated to infinity; AUClast, area under the plasma concentration‐vs‐time curve from time 0 to the last quantifiable concentration; C max, maximum observed plasma concentration of drug; t ½, terminal elimination half‐life; T max, time of the observed C max.
Figure 1.
Mean plasma concentration–time profiles of bexicaserin and its metabolites after administration of a single oral dose. Concentrations (ng/mL) of bexicaserin (A) and metabolites M9 (B), M12 (C), and M20 (D) by hour following administration of bexicaserin (1, 3, 6, 12, or 24 mg).
At the starting dose of 1 mg, bexicaserin was not measurable beyond 12 h after dosing and therefore, complete PK characterization was not possible at this dose. However, at subsequent doses full characterization of the bexicaserin PK profiles was achieved.
Mean AUC∞ (% coefficient of variation [%CV]) ranged from 40.9 [47.2] ng*h/mL for the 3 mg dose to 288 [43.5] ng*h/mL for the 24 mg dose (Table 1). Mean C max ranged from 1.08 [45.9] ng/mL for the 1 mg dose and 59.3 [43.1] ng/mL for the 24 mg dose (Table 1). In other words, bexicaserin increased by at least >54.9‐fold for a 24‐fold dose increase. Both exposure parameters showed very high variability (C max had a coefficient of variation [CV] of 31–54% and AUC∞ had a CV of 44–58%) and were reasonably similar across dose levels. The apparent oral clearance (CL/F) was within 2‐fold and ranged between 92.4 to 150 L/h for the various doses. The apparent volume of distribution (Vz/F) was also nearly within 2‐fold across the doses and ranged between 608 to 1230 L. However, there was a tendency for both CL/F and Vz/F to decrease with increasing doses (Table 1). The terminal t 1/2 values ranged between 4.67 to 6.66 h and were dose independent. Urinary excretion data indicate that only a small percent (<5%) of dose was eliminated as unchanged bexicaserin by the renal route after single dose administration and was found to be dose independent. The CLr ranged from 3.00 to 4.25 L/h.
Bexicaserin dose normalized exposure parameters (C max and AUClast) evaluated using box plots suggested that there was a slightly greater than dose proportional increase in the exposure parameters of bexicaserin at higher doses relative to the starting dose of 1 mg (Figure 2). As shown in Table 1, the mean arithmetic exposures increase as the dose increases. Specifically, as the dose increases in a 1:3:6:12:24 ratio, the corresponding increases in C max are approximately 1:5.9:8.8:15.8:54.9, and for AUClast, 1:7.3:11.6:20.3:58.2. However, the exposure parameters at doses ranging from 3 to 24 mg generally appeared to be somewhat less deviant from showing dose proportionality. Overall, given the high variability in the PK parameters, the box plots appeared to suggest that single doses of bexicaserin exhibited a slightly greater than proportional increase in exposure at higher doses.
Figure 2.
PK parameters following single doses of bexicaserin. Boxplots of dose‐ normalized bexicaserin plasma C max (A) and AUClast (B) by dose cohort.
Pharmacokinetics of Metabolites
M9 Pharmacokinetics. The C max of M9 occurred with median T max ranges of 3.02 to 6.00 h post oral dosing of bexicaserin indicating that there was a slight delay in the formation and appearance of M9 in systemic circulation. The C max of M9 ranged from 0.140 ng/mL for the 1 mg dose to 2.15 ng/mL for the 24 mg dose and AUC∞ ranged from 9.48 ng*h/mL for the 3 mg dose to 41.2 ng*h/mL for the 24 mg dose (Figure 1 and Table 2). The M9 C max had a coefficient of variation [CV] of 49.9–81.5% and M9 AUC∞ had a CV of 20.5–76.5%. The t 1/2 for M9 was slightly longer than bexicaserin ranging between 7.45 to 10.3 h. Based on the M9/bexicaserin ratio, the MPR AUC∞ values were variable across cohorts, ranging from 0.15 to 0.53. The MPR C max values ranged from 0.04 to 0.13. Based on the M9/parent exposure ratio, M9 levels in the circulatory system were approximately 0.1‐fold of bexicaserin.
Table 2.
Summary of metabolite M9, M12, and M20 plasma PK parameters following administration of a single oral dose of bexicaserin.
| Dose | |||||
|---|---|---|---|---|---|
| PK parameter | 1 mg N = 6 | 3 mg N = 6 | 6 mg N = 6 | 12 mg N = 6 | 24 mg N = 6 |
| Metabolite M9 | |||||
| C max (ng/mL) | 0.140 | 0.431 (49.9) | 0.752 (81.5) | 0.581 (80.4) | 2.15 (67.5) |
| T max (h) | 3.02 (3.02–3.02) | 5.10 (3.00–6.03) | 6.00 (3.00–6.00) | 4.03 (3.00–12.0) |
5.98 (3.00–6.00) |
| AUClast (h*ng/mL) | 0.324 | 5.55 (56.1) | 10.7 (92.5) | 8.50 (96.1) | 33.0 (72.3) |
| AUC∞ (h*ng/mL) | NC | 9.48 (20.5) | 24.5 (50.0) | 16.7 (76.5) | 41.2 (57.1) |
| t 1/2 (h) | NC | 9.17 (25.2) | 10.3 (27.6) | 7.45 (9.6) | 7.55 (18.5) |
| MPR C max | 0.131 | 0.0746 (61.4) | 0.103 (94.4) | 0.0367 (103.1) | 0.0390 (72.4) |
| MPR AUC∞ | NC | 0.383 (NC) | 0.531 (14.7) | 0.223 (79.6) | 0.151 (63.1) |
| Metabolite M12 | |||||
| C max (ng/mL) | 0.982 (16.1) | 3.20 (27.0) | 4.29 (21.6) | 8.43 (16.6) | 17.9 (9.2) |
| T max (h) |
1.75 (1.00–2.03) |
2.01 (1.00–4.22) |
2.50 (2.00–3.02) |
2.02 (1.52–12.0) |
3.02 (1.50–4.02) |
| AUClast (h*ng/mL) | 3.53 (57.0) | 28.1 (43.2) | 40.6 (32.2) | 85.3 (31.9) | 200 (27.4) |
| AUC∞ (h*ng/mL) | NC | 50.1 (24.9) | 48.0 (38.7) | 92.5 (32.8) | 215 (23.9) |
| t 1/2 (h) | 5.09 (19.1) | 7.32 (38.2) | 7.60 (34.8) | 5.90 (23.5) | 6.77 (17.4) |
| MPR C max | 0.980 (31.9) | 0.524 (40.1) | 0.546 (63.4) | 0.520 (42.3) | 0.352 (57.5) |
| MPR AUC∞ | NC | 0.865 (1.1) | 0.804 (32.3) | 0.948 (24.9) | 0.754 (18.3) |
| Metabolite M20 | |||||
| C max (ng/mL) | 17.3 (52.5) | 67.9 (49.0) | 146 (48.1) | 296 (21.6) | 475 (46.1) |
| T max (h) |
1.01 (0.53–1.12) |
1.26 (0.50–1.70) |
1.50 (1.00–3.02) |
1.25 (0.52–2.02) |
1.07 (0.50–1.50) |
| AUClast (h*ng/mL) | 47.3 (54.5) | 246 (30.9) | 642 (35.1) | 1270 (17.4) | 2200 (30.9) |
| AUC∞ (h*ng/mL) | 49.0 (59.1) | 286 (15.2) | 662 (33.2) | 1280 (17.5) | 2230 (30.7) |
| t 1/2 (h) | 3.72 (93.2) | 5.24 (26.6) | 6.20 (37.2) | 5.21 (18.5) | 5.04 (15.4) |
| MPR C max | 10.4 (71.9) | 7.37 (81.7) | 10.2 (54.8) | 10.8 (37.3) | 4.83 (44.3) |
| MPR AUC∞ | 3.47 (NC) | 5.36 (76.2) | 6.65 (51.7) | 8.76 (50.7) | 4.71 (33.5) |
Arithmetic mean (CV%) reported except for T max, for which median (min, max) values are reported. %CV indicates percentage coefficient of variance; AUC∞, area under the plasma concentration‐vs‐time curve extrapolated to infinity; AUC0– t , area under the plasma concentration‐vs‐time curve from time 0 to the last quantifiable concentration; C max, maximum observed plasma concentration of drug; t ½, terminal elimination half‐life; T max, time of the observed C max.
M12 Pharmacokinetics. The C max of M12 occurred with a median T max range of 1.75 to 3.02 h indicating a rapid formation of M12 with a slight delay as compared to the C max of bexicaserin. The C max of M12 ranged from 0.98 ng/mL for the 1 mg dose to 17.9 ng/mL for the 24 mg dose and AUC∞ ranged from 48.0 ng*h/mL for the 6 mg dose to 215 ng*h/mL for the 24 mg dose (Figure 1 and Table 2). The M12 C max had a coefficient of variation [CV] of 9.2–27.0% and M12 AUC∞ had a CV of 23.9–38.7%. The t 1/2 was consistent with that reported for bexicaserin ranging between 5.09 and 7.60 h. Based on the M12/bexicaserin ratio, the MPR AUC∞ values ranged from 0.75 to 0.95. The MPR C max values were also variable across cohorts, ranging from 0.35 to 0.98.
M20 Pharmacokinetics. The T max of M20 coincided with the T max of bexicaserin (i.e., 1.01–1.50 h versus 1.02–1.54 h). The C max of M20 ranged from 17.3 ng/mL for the 1 mg dose to 475 ng/mL for the 24 mg dose and AUC∞ ranged from 49.0 ng*h/mL for the 1 mg dose to 2230 ng*h/mL for the 24 mg dose (Figure 1 and Table 2). The M20 C max had a coefficient of variation [CV] of 21.6–52.5% and M20 AUC∞ had a CV of 15.2–59.1%. The t 1/2 was similar to that observed for bexicaserin ranging between 3.72 to 6.20 h. Based on the M20/bexicaserin ratio, the MPR AUC∞ values were variable across cohorts, ranging from 3.47 to 8.76. The MPR C max values were also variable across cohorts, ranging from 4.83 to 10.8.
Evaluation of Food‐Effect on Bexicaserin
Single dose food effect was evaluated for 6 mg bexicaserin and the mean PK parameters are provided in Tables 3, 4. The ingestion of high‐fat food delayed the appearance of C max of bexicaserin by approximately 1.5 h. However, the rate of absorption as measured by C max showed similarity in the values between fasted (9.52 ng/mL) versus fed (9.94 ng/mL). Conversely, the extent of absorption, measured by AUC∞, showed a higher (∼25%) bioavailability in the fed condition (72.6 ng*h/mL) relative to fasted condition (58.7 ng*h/mL). The t 1/2 values were similar between fasted (6.66 h) and fed treatments (5.48 h).
Table 3.
Food‐effect: bexicaserin plasma and urine PK parameters following administration of single dose in fasted and fed conditions.
| Parameter | Fasted (N = 6) | Fed (N = 6) |
|---|---|---|
| Plasma | ||
| C max (ng/mL) | 9.52 (53.5) | 9.94 (49.7) |
|
T max (h) Median (min, max) |
1.50 (1.00, 3.02) |
3.02 (1.48, 4.00) |
| AUC∞ (ng*h/mL) | 58.7 (57.9) | 72.6 (53.6) |
| t 1/2 (h) | 6.66 (43.2) | 5.48 (31.1) |
| CL/F (L/h) | 134 (52.3) | 108 (56.5) |
| Urine | ||
| Ae (µg) | 215 (79.0) | 245 (67.4) |
| %UR | 3.59 (79.0) | 4.08 (67.4) |
| CLR (L/h) | 3.42 (24.3) | 3.27 (19.6) |
Arithmetic mean (CV%) reported except for T max, for which median (min, max) values are reported
Abbreviations: %UR, percent of drug excreted in urine; Ae, cumulative amount excreted in urine; AUC∞, area under the concentration–time curve extrapolated to infinity; CL/F, apparent oral clearance; CLr, renal clearance; C max, maximum concentration; F, bioavailability; N, number of participants in PK Analysis Set; SD, standard deviation; t 1/2, half‐life; T max, time to C max.
Table 4.
Food‐effect: bexicaserin plasma PK parameters following administration of single dose in fasted and fed conditions.
| Parameter (Unit) | n | Fed geometric mean ratio | n | Fasted geometric mean ratio | Point estimate (90% CI) | Intra CV% |
|---|---|---|---|---|---|---|
| C max (ng/mL) | 6 | 8.844 | 6 | 8.474 | 104.37 [84.17, 129.42] | 18.7 |
| AUClast (h*ng/mL) | 6 | 61.89 | 6 | 49.22 | 125.74 [116.05, 136.25] | 6.9 |
| AUC∞ (h*ng/mL) | 6 | 63.62 | 6 | 50.97 | 124.83 [115.80, 134.58] | 6.5 |
Abbreviations: AUC, area under the plasma concentration–time curve; AUC0–last, AUC from time 0 to last measurable concentration; AUC∞, AUC extrapolated to infinity; CI, confidence interval; C max, maximum observed plasma concentration; CV, coefficient of variation; n, number of observations.
Urine bexicaserin concentration data showed no apparent differences between fasted and fed treatment, including excreted amount (fasted: 215 µg, fed: 245 µg) and excreted percent (fasted: 3.59%, fed: 4.08%) (Figure 3). The renal clearance of bexicaserin was similar between fasted (3.42 L/h) and fed (3.27 L/h) and represented a small fraction of the total clearance (∼2.6–3.0%).
Figure 3.
Mean plasma concentration–time profiles of bexicaserin following administration of a single oral dose under fasted and fed conditions. Plasma concentration (ng/mL) of bexicaserin over time following a single oral dose of bexicaserin (6 mg, fasted or fed condition).
Evaluation of Food‐Effect on Metabolites
M9 Food Effect. The fed condition resulted in a 25% higher AUClast of M9, with a 23% higher C max at a similar T max compared to fasted, but these differences were within the range of PK variability. The M9 half‐life of 8.24 h was slightly shorter in the fed than in fasted, with a half‐life of 10.3 h (Supplemental Figure S2 and Supplemental Table S4).
M12 Food Effect. The fed condition resulted in a 19% higher AUClast of M12, with a 5% higher C max at a later T max (4.00 h) compared to fasted (T max 2.50 h). The difference in C max between the fasted and fed periods was not statistically significant. The M12 half‐life of 7.78 h is similar in the fed period compared to the fasted period, with a half‐life of 7.60 h (Supplemental Figure S2 and Supplemental Table S4).
M20 Food Effect. The fed condition resulted in a 13% lower AUClast of M20, with a 43% lower C max at a later T max (3.02 h) compared to fasted (T max 1.50 h). There was no appreciable food effect on peak systemic exposures. The M20 half‐life of 5.54 h was similar in fed and fasted, with a half‐life of 6.20 h (Supplemental Figure S2 and Supplemental Table S4).
Pharmacodynamic Effects
5‐HT has been shown to positively regulate prolactin (PRL) secretion in experimental animals and in healthy human volunteers, and serum PRL levels have been utilized to evaluate effective engagement of central 5‐HT receptors. 16 , 17 , 18 To explore pharmacodynamic effects of bexicaserin during this first‐in‐human study, PRL levels were assessed. At 2 h following administration of single bexicaserin doses (1–24 mg, fasted, day 1), PRL levels consistently demonstrated acute, dose dependent increases (Figure 4). Additional PRL plot(s) with or without food following bexicaserin administration is provided in (Supplemental Figure S3).
Figure 4.
Prolactin levels following bexicaserin administration. Fold change in mean serum prolactin (PRL) concentration (± standard error of mean) 2 h after single dose placebo or bexicaserin administration (1, 3, 6, 12, or 24 mg).
Discussion
The present study describes the safety, tolerability, pharmacokinetics and pharmacodynamics of single 1, 3, 6, 12, and 24 mg oral doses of bexicaserin administered to healthy participants. Bexicaserin was safe and well tolerated across all tested single doses. The most commonly (≥20%) reported TEAEs pooled across doses were headache (53.3%), postural dizziness (26.7%), and nausea (20.0%) (Supplemental Table S2). Participants had no adverse events leading to study drug or study visit discontinuation. There were no SAEs, deaths, or dose‐limiting toxicities observed.
The starting dose of 1 mg was selected based on the minimal anticipated biological effect level (MABEL) of bexicaserin, using the projected efficacious preclinical exposure. Based on the preclinical data a starting dose of 1 mg of bexicaserin in humans was expected to result in a C max of approximately 2.0 ng/mL, equivalent to 6.2 nm (0.14‐fold the Ki of 44 nm bexicaserin), providing an expected receptor occupancy of approximately 10% (unpublished data). Females were selected for this study because LP352 was initially being developed for the treatment of stress urinary incontinence (SUI) and stress‐predominant mixed urinary incontinence (MUI) in women.
All tested single doses of bexicaserin were absorbed rapidly with C max occurring at a median T max range of 1.02 to 1.54 h after oral administration (Figure 1). The systemic appearance of the glucuronide metabolite M20 (median T max: 1.01–1.50 h) coincided with that of bexicaserin, suggesting that its formation was presystemic in nature. The systemic appearance of oxidative metabolites M12 (T max 1.75–3.05 h) and M9 (T max 3.02–6.00 h) respectively, suggested a lag time in the formation of these metabolites. Based on exposure parameters, M9 showed the highest variability among the metabolites (CV: 103.1%) compared to either M12 (CV: 63.4%) and M20 (CV: 81.7%). The FIH study confirmed that bexicaserin undergoes metabolism to form several circulatory metabolites.
The metabolite to parent ratio (MPR) based on C max indicated that M9 levels in the circulatory system ranged from approximately 0.0367‐ to 0.131‐fold relative to bexicaserin, while M12 levels ranged from 0.352‐ to 0.980‐fold. In contrast, M20 levels were substantially higher, ranging from 4.83‐ to 10.8‐fold greater than bexicaserin, indicating that M20 is the major metabolite (Table 2). Similarly, MPR values based on AUC∞ were highest for M20 (3.47–8.76), followed by M12 (0.754–0.948) and M9 (0.151–0.531). Bexicaserin was eliminated from plasma with a mean t 1/2 of approximately 4.67–6.66 h. None of the measured metabolites including M20 appeared to remain in systemic circulation, with elimination half‐lives slightly less (i.e., M20; 3.72–6.20 h) or slightly more (i.e., M9: 7.45–9.17 h) than that of bexicaserin itself.
The CL/F (92.4 to 150 L/h) of bexicaserin was approximately 1.5 to 2‐fold greater than the expected hepatic blood flow in healthy participants (87 L/h) 19 suggesting a significant contribution of the first‐pass gut/hepatic metabolism of bexicaserin. The Vz/F (608 to 1230 L) of bexicaserin was 15 to 30‐fold greater than the total body water of healthy participants (42 L), 19 suggesting extensive tissue distribution of bexicaserin.
Across single oral doses of 1 to 24 mg, bexicaserin exposure (i.e., C max and AUClast) appeared to be slightly greater than expected for a dose proportional increase, particularly at higher doses, despite the small sample size and high intra‐subject pharmacokinetic variability (Figure 2). The observed apparent CL/F values of bexicaserin were within a 2‐fold range. In addition, Vz/F generally showed a decreasing trend as dose increased. Overall, such single dose bexicaserin pharmacokinetic data appear to show that bioavailability, rather than drug disposition (i.e., metabolism and excretion), might be affected by the ascending single oral doses of bexicaserin, suggesting the occurrence of presystemic metabolism in the gut. 20
Urinary excretion data indicate that only a small percent (<5%) of dose was eliminated as unchanged bexicaserin by the renal route after single dose administration. This was supported by the relatively low renal clearance value (3 to 4.25 L/h) compared to apparent total clearance (92.4 to 150 L/h) of bexicaserin. Furthermore, the observed renal clearance of bexicaserin was fully accounted for by the passive glomerular filtration rate (7.5 L/h). 19 Such a low urinary recovery of bexicaserin suggests that the major route of elimination of bexicaserin is through hepatic metabolism. Previously published work has suggested that glucuronidation is the major metabolic pathway for bexicaserin by which human hepatocytes form M20. 21 Oxidative metabolism results in M9 and M12 formation, observed in circulation. All metabolites are pharmacologically inactive. 10 Our Phase 1 data further confirmed that M20 was the major circulating moiety in the plasma compared to either bexicaserin, M9, or M12.
Although not a formal food‐effect assessment, the limited data collected in this study suggested there was no significant food effect on the pharmacokinetics of bexicaserin. There was a less than 5% increase in mean C max and an approximately 25% increase in mean AUC∞ in the fed state compared to the fasted state. However, the median T max doubled to about 3 h following food ingestion compared to the fasted state (1.5 h). As bexicaserin is a water‐soluble compound, it was not expected to have a significant food effect, and this is supported by the clinical data gathered in this study. Given that the food effect is minor and not clinically significant, bexicaserin can be administered without regard to food.
Evaluation of PRL increase as an indicator of pharmacodynamics revealed an acute dose‐dependent effect measured approximately 2 h following bexicaserin administration. The observed acute response in PRL was suggestive of a rapid central target engagement upon oral bexicaserin dosing. Furthermore, because PRL is known to display a diurnal rhythm with an observed peak effect during the night, 22 , 23 the morning measurement of PRL in this study was an ideal time to capture any drug‐related effect.
Conclusions
Bexicaserin was quickly absorbed into circulation following a single oral dose of bexicaserin. Mean terminal elimination half‐life ranged from 4.67–6.66 h across the doses studied. There was no clinically meaningful effect of food on AUC∞ or C max. Metabolism appears to be the major route of clearance for bexicaserin, with M20 being the major circulating metabolite in the plasma compared to either bexicaserin or metabolites M9, or M12. Bexicaserin was safe and well tolerated after a single oral administration up to 24 mg in healthy adult female participants with greater than dose‐proportional increase in systemic exposure observed over the dose range evaluated. Prolactin concentrations increased in a dose‐dependent manner following bexicaserin administration, likely reflecting successful engagement of central 5‐HT2C receptors and downstream PD effects. There were no SAEs, and all TEAEs were mild to moderate. Bexicaserin was overall well tolerated with no adverse events leading to study drug discontinuation.
Conflicts of Interest
The authors are current or former employees and shareholders of Longboard Pharmaceuticals or Lundbeck LLC.
Funding
This study was funded by Longboard Pharmaceuticals, now a part of Lundbeck LLC.
Supporting information
Supporting Information
Acknowledgments
The authors wish to thank Outpost, Clinical Operations Team and Parexel for their contribution to the progression of the bexicaserin project and Hilary North, PhD, for manuscript preparation. All studies were funded by the sponsor, Longboard Pharmaceuticals Company, Ltd. Some of the data in this manuscript were previously presented as a poster at the American Academy of Neurology (AAN) annual meeting in 2022: Parasrampuria D et al., Single Ascending Dose Pharmacokinetics (PK), Pharmacodynamics (PD), and Tolerability of LP352 in Healthy Subjects (P14‐8.001). Neurology. 2022;98:18 supplement.
Data Availability Statement
The authors declare that all the data supporting the findings of this study are available within the paper and its Supplemental Data.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Supporting Information
Data Availability Statement
The authors declare that all the data supporting the findings of this study are available within the paper and its Supplemental Data.