Study design

This trial was a phase 1 randomized, double-blind, placebo-controlled study conducted at a single center in the UK. Prior to study initiation, the protocol and all other appropriate documents were reviewed and approved by an Independent Ethics Committee and local regulatory authorities. The study was conducted in accordance with the ethical principles stated in the Declaration of Helsinki, the International Conference on Harmonisation for Good Clinical Practice guidance, and all local and regional applicable laws and regulations. Prior to the performance of any study-related assessments and procedures, all participants signed a written informed consent form with details of the trial treatment, procedures, and potential risks.

Study participants

The study consisted of eight parts, of which only five are presented in this report (A, D, E, F, and H) and summarized in eTable 1. Eligible participants were healthy individuals aged 18 to 55 years (inclusive at screening, except for Part H) with a body weight ≥ 50 kg for females and ≥ 60 kg for males and a body mass index (BMI) ranging from 18 to 30 kg/m2 at the time of screening and day 1. Part A included White males, whereas Part D included White females who were not pregnant or lactating. Part F included Black males, and Part H included White males aged ≥ 65 years. Participants who had previously received dersimelagon, who had used afamelanotide or melanotan within 6 months prior to the study, or with a history of melanoma and/or dysplastic naevus were not included in the study. Randomization was performed according to a computer-generated randomization list using SAS® version 9.3 (Cary, North Carolina, US) prior to the first administration of study drug.

Study treatments

Dersimelagon was supplied as a 50-mg tablet or as a powder (1 to 600 mg, for oral suspension) of active substance, and placebo was supplied as either a tablet or powder to match dersimelagon dosage strength.

Single doses

Part A of the study was a single ascending dose (SAD) study conducted in seven dosed cohorts. Each cohort was composed of eight participants, and in each cohort, participants were randomized to receive dersimelagon suspension (n = 6) or placebo suspension (n = 2). In total, 56 participants were included and received dersimelagon at doses of 1 mg, 3 mg, 10 mg, 30 mg, 100 mg, 300 mg, and 600 mg. In parts D, F, and H of the study, participants received a single oral dose of either 100 mg of dersimelagon (n = 6) or placebo (n = 2) as a tablet formulation. To evaluate the effect of sex difference Part D included eight female participants, and Part F evaluated the effect of race, and included eight Black participants. Part H evaluated the effect of age in eight participants aged ≥ 65 years.

Multiple ascending doses

The multiple ascending dose (MAD) study (Part E) was conducted in four cohorts in which participants received multiple dose administration of dersimelagon as a tablet or suspension formulation for 14 days in one treatment period. Each cohort was composed of 12 participants who were randomized to dersimelagon (n = 9) or placebo (n = 3). The dose levels of dersimelagon used were 30 mg (Cohort 1, suspension), 150 mg (Cohort 2, tablet), 300 mg (Cohort 3, tablet), and 450 mg (Cohort 4, tablet). A Fitzpatrick scale test was performed at screening to categorize patient skin types into type I (always burns, never tans), type II (usually burns, tans with difficulty), type III (sometimes mild burn, gradually tans), type IV (rarely burns, tans with ease), type V (very rarely burns, tans very easily), or type VI (never burns, always tans) [7]. Participants with Fitzpatrick skin types II to IV were included in the 30-, 150-, and 300-mg cohorts. The protocol was amended following emerging pigmentation data, and only participants with Fitzpatrick skin type V were included in the 450-mg cohort.

Safety assessments

Safety and tolerability were assessed by evaluating vital signs (supine blood pressure, pulse rate, respiratory rate, and body temperature), 12-lead electrocardiogram (ECG) parameters, clinical laboratory assessments, and adverse events (AEs). AEs were considered treatment emergent if they occurred after the first administration of dersimelagon or if a predose event increased in severity following dosing. The frequency and incidence of treatment-emergent AEs (TEAEs) were summarized by system organ class and preferred term for each treatment group. AEs were coded using the Medical Dictionary for Regulatory Activities (MedDRA) version 19.0. Safety laboratory test results, vital signs, and ECG parameters were summarized by treatment group and planned sampling point. All participants in the study (N = 144) were included in the safety analysis population.

Pharmacokinetic assessments

Blood samples for single-dose PK evaluations (Parts A, D, F, and H) were collected at predose and at 0.25, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, 12, 24, and 48 h postdose and at day 5 follow-up (96 h). Blood samples for MAD evaluations (Part E) were collected on day 1 (predose and at 0.25, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, and 12 h postdose), day 2 to day 13 (predose), day 14 (predose and at 0.25, 0.5, 1, 2, 3, 4, 5, 6, 8, 10, and 12 h postdose), day 15 (24 h post last dose), day 16 (48 h post last dose), and day 17 (72 h post last dose). To determine the concentrations of dersimelagon and dersimelagon glucuronide (a primary in vitro human metabolite), plasma samples were analyzed using a validated liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) method with solid phase extraction with a lower limit of quantification (LLOQ) of 0.1 ng/mL. The plasma PK parameters, including maximum observed plasma concentration (Cmax), time to maximum plasma concentration (Tmax), plasma terminal elimination half-life (t½), area under the plasma concentration–time curve from time zero to the last measurable concentration (AUC0-last), to infinity (AUC0-∞), and over the 24-h dosing interval, at steady state (AUC0-τ) were calculated with reference to day 1 dosing and/or the last day of dosing where applicable for dersimelagon and its metabolite dersimelagon glucuronide. The PK parameters were derived by noncompartmental analysis using Phoenix WinNonlin® software version 6.3 (Certara, LP, Princeton, New Jersey, US). For the calculation of PK parameters, data below the LLOQ were imputed a value of zero. Participants who received at least one dose of dersimelagon and who had at least one postdose value of plasma concentration (N = 110) were included in the PK analysis population.

Pharmacodynamic assessments

The effect of dersimelagon treatment on pigmentation was assessed in all participants in Part A by measuring melanin density on three skin segments (lower back, forehead, and cheek) by spectrophotometry (Konica Minolta Spectrophotometry) prior to dersimelagon administration and at days 3, 5, and 15 following a single oral dose of dersimelagon. In Part E, melanin density was measured prior to dersimelagon administration and at days 3, 5, 7, 10, 15, 22, 29, and 57 by spectrophotometry on the lower back, forehead, cheek, neck, inner upper arm, and outer forearm. The melanin density was calculated according to the following formula:

$$\begin\mathrm)} = &\;100\, [0.035307\\& + 0.009974\, \mathrm- R_)}]\end$$

where R400 is the reflection at 400 nm and R420 is the reflection at 420 nm [8, 9]. Participants who received at least one dose of dersimelagon or placebo and who had at least one postdose value of melanin density (Part A: N = 56; Part E: N = 48) were included in the PD analysis population.

Statistical methods

The statistical analysis was performed using SAS® version 9.4 (SAS Institute Inc.; Cary, North Carolina, US). All variables were summarized by dose level for the SAD and MAD parts and by sex, age, and race category as appropriate. Unless otherwise stated, continuous data were summarized descriptively including N (number of participants), n (number of observations), mean, standard deviation, minimum, median, and maximum. Categorical data were summarized using frequency tables (frequency and percent). A linear model was used to analyze log-transformed AUC (AUC0-∞) and Cmax, with race (White vs Black), sex (male vs female), or age (≤ 55 years vs ≥ 65 years) as fixed effects. The difference in least squares (LS) means and corresponding 90% CIs were back-transformed to obtain the estimates and CIs of the geometric mean ratios comparing Black with White, female with male, and participants aged ≥ 65 years with those who were aged ≤ 55 years. In Part A (SAD) and Part E (MAD), PK parameters of interest were used to evaluate dose proportionality. A linear model was used to fit the power model after log transformation of the parameter of interest. The model included the log-transformed dose as a fixed effect. The point estimate and its 95% CI were derived for slope β to evaluate dose proportionality. The results were considered dose proportional if the CI included 1.

Nonclinical animal studies

All animal studies were performed according to the rules for the proper conduct of animal experiments and approved by the Institutional Animal Care and Use Committee of the test facility. Additional details regarding the nonclinical study protocols can be found in the Supplementary methods.

PK study in rats

A study was conducted to characterize the PK of dersimelagon in male Sprague–Dawley rats (n = 4) after a single oral administration (0.3, 1, and 3 mg/kg) and intravenous administration (2 mg/kg).

PK study in monkeys

A study was conducted to evaluate the PK of dersimelagon up to 48 h when administered orally (3 mg/kg) and intravenously (1 mg/kg) to male cynomolgus monkeys (n = 4).

In vitro plasma protein binding of dersimelagon

In vitro binding of radiolabeled [14C] dersimelagon free base to plasma proteins of rats, cynomolgus monkeys, and humans was examined by the equilibrium dialysis method. The [14C] dersimelagon free base (0.1, 1, and 9 µg/mL)-spiked plasma was incubated in a rapid equilibrium dialysis device for 8 h at 37 °C in a CO2 incubator.

Allometric scaling

The prediction of human clearance (CLh) from animal PKs was performed with several allometric approaches, including simple allometry, allometry with bile flow correction factor [10], allometry with the rule of exponent [11], allometry with unbound clearance approach [12], and fu-corrected intercept method [13]. The human distribution volume was predicted by simple allometry. The human bioavailability (F) was calculated employing the following equation:

$$\mathrm \times F_ \times F_}$$

(1)

where Fa, Fg, and Fh are fractions of orally administered drugs absorbed from the intestine, intestinal availability, and hepatic availability, respectively. Human Fa was assumed to be equivalent to rat Fa (0.64, which was calculated from a mass balance study in rats). Human Fg was assumed to be 1.0, because dersimelagon was very stable in human intestinal microsomes. Human Fh was calculated from the following equation:

$$\mathrm = 1 - CL_ \,/\, R_ \,/ \,Q_}$$

(2)

where Rb (blood/plasma concentration ratio) was 0.6 (obtained by in vitro studies), and Qh (hepatic blood flow rate) was 1200 mL/h/kg. Based on these parameters, the plasma concentration–time profile at an oral dose of 100 mg in humans was simulated using 2-compartment model with 70 kg as the body weight and 1.0 h−1 as absorption rate constant, and the resultant Cmax and AUC values were obtained.