Determination of an Optimal Dosing Regimen For Fexinidazole, A Novel Oral Drug For the Treatment of Human African Trypanosomiasis: First-In-Human Studies
Antoine Tarral, Séverine Blesson, Olaf Valverde Mordt, Els Torreele, Daniela Sassella, Michael A. Bray, Lionel Hovsepian, Eric Evène, Virginie Gualano, Mathieu Felices, Nathalie Strub Wourgaft
Participants:
All subjects had to be able to communicate well with the Investigator and research staff and to comply with the requirements of the specific study they were enrolled into, to have provided written informed consent to participate as shown by a signature on the volunteer consent form and to be registered with the French Social Security in agreement with French laws on biomedical experimentation [8]. Subjects could be light smokers (less than 5 cigarettes per day) or non-smokers. No smoking (or use of smoking substitute e.g. nicotine patch) was permitted from screening throughout the studies. Finally subjects were required to have a normal arterial blood pressure (BP) and pulse rate measured after resting for 5min (normal BP was considered to be 100–150mmhg systolic and 45–90mmhg diastolic and normal pulse rate to be between 40-100 bpm) or, if abnormal, considered not clinically significant by the principal Investigator.
The following volunteers were excluded from the study:
Those whom, on direct questioning and physical examination, had evidence of any clinically significant acute or chronic disease, including known or suspected HIV, HBV or HCV infection, who had previously received fexinidazole, who had any clinically significant abnormality following review of pre-study laboratory tests (AST, ALT and ALP had to be within normal ranges), vital signs, full physical examination and ECG, who were within the exclusion period defined in the National Register for Healthy Volunteers of the French Ministry of Health, who forfeited their freedom by administrative or legal award, who were under guardianship or who were unwilling to give their informed consent. Any subject who had a positive laboratory test for Hepatitis B surface antigen (HbsAg), or anti-HIV 1/2 or anti- HCV antibodies, who had a history of allergy, intolerance, photosensitivity, asthma, allergic skin rash or sensitivity to any drug, who were known or suspected alcohol or drug abusers (more than 14 units of alcohol per week, one unit=8g or about 10mL of pure alcohol), who drank more than 8 cups daily of beverage containing caffeine or who had a positive laboratory test for urine drug screening (opiates, cocaine, amphetamine, cannabis, benzodiazepines). Subjects were also excluded if they had undergone surgery or had donated blood within 12 weeks prior to the start of Study 1A, had taken any prescribed or over the counter drug (including antacid drug), with the exception of paracetamol (up to 3g per day) within 2 weeks prior to the first dose administration, who had any clinical condition or prior therapy which, in the opinion of the Investigator, made the subject unsuitable for Study 1A or who participated in any clinical trial with an investigational drug in the past 3 months preceding Study 1A entry.
A full history and medical examination of each subject was performed prior to the administration of the study drug.
Design of studies
Study 1A
Nine dose level cohorts were included, each comprising eight subjects randomly assigned to receive either active drug (six subjects per cohort) or placebo (two subjects per cohort). Subjects were hospitalized in the clinical unit on the evening of the day preceding study drug administration (Day -1) and up to 168h post-dose (Day 8 morning). An End of Study (EOS) visit was performed in the morning of Day 8 before final discharge. For each cohort, dosing was staggered across at least two successive days.
Study 1B
The selected dose (1200 mg of either PIB formulation or tablets, corresponding to one third of the highest administered dose) was shown to have been well tolerated in Study 1A, whilst allowing for adequate systemic drug exposure to facilitate PK analyses. In each treatment period, subjects were hospitalized in the clinical unit in the evening of the day preceding study drug administration (Day -1) and up to 168 h post-dose (Day 8 morning). At each period of treatment, safety and tolerability follow-up were carried out up to 48 h post-dose and an EOS visit was performed on the morning of Day8 of the last period of treatment, before final discharge. A wash-out period of at least 14 days between doses was chosen based on the available PK data from Study 1A in order to prevent any carryover effects.
Study 1C
Three cohorts of eight subjects, randomly assigned to active drug or placebo in the same ratio as in Study 1A, were to be enrolled and, as three subjects were replaced during the course of the study, a total of twenty seven subjects were eventually enrolled. Subjects were hospitalized in the clinical unit for two days before the first study drug administration (Day -2 evening) and up to 168 h post-last dose (Day 21 morning) when an EOS visit was performed, before final discharge at the discretion of the investigator.
Study Protocol 2
In each treatment period, subjects resided at the clinical unit from the evening of Day 1 to the morning of Day 3 (48h post-dose). Subjects were asked to come back to the clinical unit on three subsequent occasions (Days 4, 6 and 8 post-dose in the mornings) for further blood sampling for PK analyses.
Study Protocol 3
In vitro parasite killing data, animal data with respect to potential CNS penetration, measurements of protein binding and the available human PK data from the completed FIH single ascending dose study (Study 1A) allowed for a set of simulations to be performed to model potential effective dosage regimens in Stage 2 (and thus by implication also Stage 1) HAT patients. The upper effective in vitro killing concentration for all three active compounds is 2 µg/ml following 72h incubation whilst the brain – blood ratio of fexinidazole related radioactive material in the brain of rats is 0.4 – 0.6 [9] and the free drug fraction in human plasma in vitro for the M1 and M2 metabolites is 74 and 58% respectively [10]. Taking a conservative set of data from these results of 2 µg/ml / 0.4 brain – blood fraction / 50% free fraction then plasma free drug levels of, in particular, the M2 metabolite would need to be at least 10 µg/ml for at least 72 h to provide complete elimination of the parasite. These, albeit theoretical, calculations are in line with the available animal PD data in mice treated with fexinidazole for 5 days indicating that a plasma M2 Cmax of 14,000 and 13,600 ng/mL (AUC0-24 45,000 and 96,000 ng∙h/mL) will cure Stage 2 disease in this model [9]. In addition to the basic target plasma drug concentrations described above, scenarios were constructed assuming a human metabolic pattern for the M1 and M2 metabolites as initially described by Winkleman and Raether [31], a two-compartment model where the clearance of fexinidazole was partitioned between the formation of M1 and all other routes of elimination of fexinidazole and, in addition, clearance of M1 was partitioned between the formation of M2 and all other routes of elimination of M1. The models were built with the available plasma PK data from the previously completed human single ascending dose FIH study (Study 1A).
Simulations were performed using NonMem VI. Data were analysed using SAS version 9.2. AUC (linear trapezoidal method) and Cmax were estimated based on concentrations simulated for the following design:
· Scenario 10= 1,200 mg once daily for 10 days with food
· Scenario 11= 1,800 mg once daily for 10 days with food
· Scenario 14= 1,800 mg for 4 days followed by 1,200 mg for 6 days once daily with food
· Scenario 15= 2,400 mg for 4 days followed by 1,200 mg for 6 days once daily with food
The target of the simulation was to reach the active brain concentrations of at least 10,000 ng/mL, for at least 72h, in line with the theoretical PK/PD data for M2 from in vitro and animal studies, using available data from Study 1A. Scenarios 14 and 15 both seemed to match the desired targets in terms of reaching the required brain concentrations quite early after the start of the treatment and maintaining plasma drug levels of M2 in the range of 20,000 to 25,000 ng/mL for at least 48h, to obtain a significant percentage of subjects with concentration above the required levels for M2.
Study protocol 3 was designed to test both of these dosing regimens (Cohort 1: Scenario 14 and Cohort 2: Scenario 15) on a limited number of healthy subjects in order to check the relevance of the simulation data. Moreover, special attention was paid to biochemistry safety assessments, through follow-up of hepatic enzymes and creatinine, and cardiac safety, through repeated recording of ECG parameters (mainly QT interval) in order to carefully monitor the safety and tolerability of each tested dosing regimen.
Both dosing regimens chosen consisted of once daily oral administration in fed conditions for ten days, with a loading period for four days followed by a maintenance dose for six days. Each dosing regimen was evaluated in a cohort of eighteen subjects randomly assigned to active drug or placebo in a 2/1 ratio (12 subjects receiving active drug and 6 receiving placebo). The subjects resided at the clinical unit from the evening of Day -2 to the afternoon of Day17 (168 h post last dose).
Safety Investigations
Blood and Urine analyses
Haematology: Haemoglobin, red blood cell (RBC), haematocrit, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean cell haemoglobin concentration (MCHC), white blood cell (WBC) including differential, platelet counts, prothrombin time (PT), activated partial thromboplastin time (aPTT) and international normalized ratio (INR).
Clinical biochemistry: Alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma–glutamyltranspeptidase (GGT), creatine phosphokinase (CPK), total bilirubin, total protein, creatinine, fasting glucose, urea, sodium potassium, chlorides.
Urine examination: Glucose, ketones, density, occult blood, pH, proteins, leukocytes.
In Studies 1A, 1B and 2 blood and urine samples were taken for measurement of haematology, clinical biochemistry, and urinalysis at screening, on Day 1 at pre-dose and 24h post-dose of each period of treatment, and at the end of study (EOS) visit.
In Study 1C assessments as for the studies above were done at screening, on the evening of Day-1, on Days4,7 and10 prior to dosing, and on Day14 at 24 h and 168h post-dosing, and at the EOS visit.
In Study protocol 3, the assessments were done at screening, Day-1, and at the EOS visit. Additional limited liver function tests (AST, ALT, ALP, GGT, total and direct bilirubin and creatinine) were done on Days1, 4, 5 and7 prior to dosing, on Day10 prior to dosing and 24h post-dosing and in the mornings of Days13, 15 and17.
ECG
ECG recordings were undertaken both as single recording safety ECGs and triplicate ECGs for further analysis of QT/QTc readings.
Safety ECGs:
a) Single dose studies: In Study 1A, Study 1B, and Study protocol 2, 12-lead ECGs were recorded in single using a MAC 5500 after 5 minutes' supine rest at the following time points:
Study 1A and Study 1B: screening visit, Day-1 evening, on Day1 at pre-dose, 1, 2, 3, 4, 6, 8, 12 and 24h post-dose, and end of study visit.
Study protocol 2: screening visit, at pre-dose and 48h post-dose for each period of treatment, and end of study visit.
b) Multiple dose studies: In Study 1C 12-lead ECGs were recorded in single using a MAC 5500 after 5 minutes' supine rest at the following time points:
Day1: 1, 2, 3, 4, 6, 8, 12 and 24 h post-dose. Day7: pre-dose, 2 and 24h post-dose. Day14: pre-dose, 1, 2, 3, 4, 6, 8, 12 and 24 h post-dose.
When applicable, 24 h post-dose recording was done just before the next study drug administration.
Analytical ECGs:
Other 12-lead ECGs were recorded in triplicate: Day1 pre-dose (3 successive occasions separated by 15 min intervals) taken as mean baseline and after Day14 dosing at 48, 60, 72, 84, 96, 120, 144, and 168h post-dose.
In Study protocol 3 12-lead ECGs were recorded in triplicate using a MAC 5500 after 5 minutes' supine rest at the following time points: Day1 pre-dose (on 3 occasions) and after Day10 dosing at 48, 72, 96, 124, 144, and 168h post-dose.
Moreover, 24 hours 12-lead ECG Holter were recorded in Study 1C (Day-1 and Day14) and in Study protocol 3 (Day-1, Day4, Day7, and Day10). The Core ECG Laboratory (CardiaBase, 78 avenue du XXe Corps, 54000, Nancy, France) extracted triplicate ECG (5 replicate ECG in study protocol 3) a few minutes before the pharmacokinetic blood sampling times, therefore avoiding any interference of blood collection on ECG evaluations. QT intervals were manually calculated.
Pharmacokinetic Assessment
Blood Samples
In Studies 1A, 1B, and study protocol 2 blood samples for pharmacokinetic analysis were taken at pre-dose and 0.5, 1, 2, 3, 4, 6, 9, 12, 16, 24, 48, 72, 96, 120, 144 and 168h post-dose for each period of treatment. In Study protocol 2 blood sampling for determination of free fractions of fexinidazole, M1 and M2 were included at the 1, 4, 12, 24 and 72h post-dose time-points.
In Study 1C, blood samples were taken on Day1 and on Day 7 at pre-dose and 0.5, 1, 2, 3, 4, 6, 9, 12, 16 and 24h post-dose, one pre-dose sample was taken on the morning of Day4 to Day6, Day9, Day11, and Day13, and on Day14 at pre-dose, 0.5, 1, 2, 3, 4, 6, 9, 12, 16, 24, 48, 60, 72, 84, 96, 120, 144 and 168h post-dose.