First-in-Human Phase I Study of the Novel Injectable Calcimimetic Agent Upacicalcet in Healthy Adult Japanese Participants

This study was a phase I, single-center, double-blinded, randomized, placebo-controlled, dose-escalation study. The primary objective was to assess the safety and tolerability of upacicalcet. In the first dose cohort, eight eligible participants were enrolled and randomly assigned to receive upacicalcet (n = 6) or placebo (n = 2). At the end of the cohort study, the investigator determined whether it was safe to start the next cohort study, after which the second dose cohort was initiated. Each subsequent cohort underwent the same procedure. Participants who participated in one cohort were not allowed to participate in another cohort.

To ensure safety before starting the next dose cohort, the blinded data were opened and assessed to determine whether any of the following had occurred: (1) moderate or severe adverse events (AEs) in which a causal relationship to the study drug in three or more participants could not be ruled out; (2) serious AEs in which a causal relationship to the study drug in any subject could not be ruled out; (3) corrected serum calcium level < 8.0 mg/dL in two or more participants; (4) corrected serum calcium level < 7.0 mg/dL and presence of symptoms associated with low serum calcium (tetany, arrhythmia, psychiatric symptoms) in any subject; and (5) Fridericia-corrected QT interval (QTcF) > 500 ms or QTcF increase > 60 ms compared with baseline (before treatment) in any subject. The enrollment and assignment of participants in this study are shown in Fig. 1.

Participants who met all the inclusion criteria and did not meet any exclusion criteria at the screening test were enrolled in the study. The inclusion criteria were as follows: healthy male Japanese adults; aged 20–40 years; body weight 50–80 kg; body mass index 18.5–25.0 kg/m²; and able to provide written informed consent. The main exclusion criteria were as follows: serum albumin-corrected calcium (cCa) < 8.5 mg/dL; estimated glomerular filtration rate < 90 mL/min/1.73 m²; QTcF > 450 ms; serum iPTH < 10 pg/mL; dependence on alcohol or drugs; allergy or hypersensitivity to drugs or food; smoking habit of more than ten cigarettes/day; alcohol consumption of > 20 g/day; intake of any medication or supplements within 2 weeks prior to study drug administration; unable to consent to contraceptive use during the study duration; positive for HIV antigen/antibody, anti-hepatitis B antibody, hepatitis C virus antigen, or syphilis; or judged to be clinically inappropriate by the investigators or subinvestigators. The participants were randomly assigned according to an assignment form prepared by the external organization for case registration (EPS Corporation, Tokyo, Japan).

For any dose cohort, participants who were eligible for the screening test were hospitalized 1 day before study drug administration; this day was termed as day −1. Upacicalcet or placebo was administered intravenously once on day 1. The starting dosage of upacicalcet for this first-in-human clinical trial was determined using the following procedure. The no-observed-adverse-effect level (NOAEL) of upacicalcet in preclinical 4-week repeated-dose studies was 10 mg/kg in rats and 3 mg/kg in dogs. The human equivalent dose (HED), calculated by converting the NOAEL to body surface area, was calculated as 1.61 mg/kg in rats and 1.67 mg/kg in dogs. Based on the HED calculated from the NOAEL in rats, the maximum recommended starting dose (MRSD) was 0.161 mg/kg with a safety factor of 10. Based on these calculations, the starting dosage of upacicalcet was set at 1.0 mg, assuming that a dose one-tenth of the MRSD was administered to a human weighing approximately 60 kg. The planned dosages of upacicalcet or placebo were 1.0, 2.5, 5, 10, 20, 30, and 40 mg for each cohort. Changes in dosing regimens during the study meant that two cohorts—the 0.01 and 0.1 mg cohorts—were added, whereas the cohorts receiving doses of ≥5 mg were discontinued (as described in Sect. 3 and in Fig. 1). The participants underwent medical examinations and tests for up to 48 h after administration and were discharged on day 3 when the investigator or subinvestigator judged that there were no clinical abnormalities. The participants returned to the hospital on day 7 for final observations, during which observation of the participants was completed if no abnormalities were found.

To determine the plasma concentrations of upacicalcet and its predominant metabolites (M1, M2, and M3), blood samples were collected before administration and at 5, 10, 20, 30 min and 1, 2, 4, 6, 8, 12, 24, and 48 h after administration. To evaluate the urinary excretion rate of upacicalcet and its metabolites, pooled urine samples were collected from immediately after administration to 6, 6–12, 12–24, and 24–48 h after administration.

Blood samples were collected in a vacuum blood collection tube containing sodium heparin 3 mL (Terumo Co., Tokyo, Japan) at each time point. The collected blood was immediately centrifuged (4 °C, 3000 rpm, 10 min), and plasma was separated into two 0.5-mL bottles. The urine volume was measured, and two samples of 0.5 mL each were taken from the urine samples at each time point.

Both plasma and urine samples were frozen below − 20 °C for storage and transported to a drug concentration assay laboratory (Shin Nippon Biomedical Laboratories, Ltd., Tokyo, Japan). The concentrations of upacicalcet and its metabolites (M1, M2, and M3) in plasma and urine were measured using liquid chromatography–tandem mass spectrometry. Thereafter, the pharmacokinetic parameters (maximum plasma drug concentration [C_max], time to C_max, area under the plasma concentration–time curve [AUC]_0-t, AUC_inf, elimination half-life [t_½], mean residence time [MRT]_0-t, MRT_0-∞, plasma clearance [CL_p]_, volume of distribution at steady [Vd_ss] state, and urinary excretion rate) of upacicalcet were calculated.

As upacicalcet is a calcimimetic developed for the treatment of SHPT, the pharmacodynamic parameters determined were serum iPTH, cCa, and phosphorus levels. Blood samples for determining plasma levels of iPTH, cCa, and phosphorus were collected before administration and 10 and 30 min and 1, 2, 4, 6, 8, 12, 24, and 48 h after administration. To determine the urinary excretion of calcium and phosphorus, urine samples were collected from immediately after administration to 6, 6–12, 12–24, and 24–48 h. Pharmacodynamic samples were stored below 10 °C or below −20 °C and assayed by an outsourced laboratory (LSI Medience Corporation, Tokyo, Japan).

AEs were recorded from the start of study drug administration to the last observation. AEs judged to be related to the investigational drug were defined as adverse drug reactions (ADRs). AEs and ADRs were classified according to the Japanese Medical Dictionary for Regulatory Activities system organ class and preferred term (version 17.1).

Laboratory tests were performed at the screening tests on days −1, 2, 3, and 7. Twelve-lead electrocardiograms (ECGs) were performed at the screening tests on day −1, day 1 (just before administration and 20 min and 2, 4, 8, and 12 h after administration), day 2, day 3, and day 7. Vital signs, such as systolic and diastolic blood pressure, heart rate, and body temperature, were measured during the screening tests on day −1, day 1 (just before administration and 1 h after administration), day 2, day 3, and day 7.

Data from all randomized participants were included in the analysis. Data from the participants assigned to the placebo groups in each cohort were combined into the placebo dose group.

The pharmacokinetic parameters were calculated using noncompartmental methods with WinNonlin version 6.1 (Pharsight Corp, Mountain View, CA, USA). SAS version 9.3 (SAS Institute, Cary, NC, USA) was used to perform other statistical analyses and summarize the data.

In dose cohort 2, vomiting and nausea were observed with the administration of upacicalcet 2.5 mg. Although these AEs were mild and nonserious, further increases in the dosage of upacicalcet were considered likely to increase the incidence of adverse effects and have poor tolerability. Thus, the study protocol was amended to confirm the safety, pharmacokinetics, and pharmacodynamics of upacicalcet at doses lower than 1.0 mg (shown in Fig. 1).

Data from all randomized participants were included in the safety, pharmacokinetic, and pharmacodynamic analyses. The characteristics of participants in each group were similar (Table 1). All participants were appropriately assigned and completed the study.

Figure 2 shows the mean plasma concentrations of upacicalcet and its metabolites over time. The mean t_½ was 1.05–2.06 h. Further, 78.9–95.0% of upacicalcet was excreted in the urine within 48 h. The only metabolite present in the blood was M2, which was found in the 1.0 mg and 2.5 mg dose groups. M2 in all urine samples was less than the lower limit of quantification. Plasma concentrations of upacicalcet increased with increasing dose from a C_max of 1.08 ng/mL in the 0.01 mg group to a C_max of 280 ng/mL in the 2.5 mg dose group. The C_max and AUC_inf values of upacicalcet increased in a dose-dependent manner (Fig. 2A and Table 2). Table 3 shows the results of the dose-proportionality assessment for C_max and AUC_inf based on the power model.