Safety, tolerability, pharmacokinetics, and pharmacodynamics of PF-06650833, a selective interleukin-1 receptor-associated kinase 4 (IRAK4) inhibitor, in single and multiple ascending dose randomized phase 1 studies in healthy subjects

Study 1 (B7921001; NCT02224651) was a 96-day, phase 1, within-cohort, randomized, double-blind, sponsor-open, placebo-substitution, five-period crossover, SAD study in healthy adult subjects (Fig. 1a). Subjects were sequentially enrolled into four cohorts of ten subjects each. Within each cohort, the subjects were randomized into a maximum of five periods. Within each period, eight subjects and two subjects were randomized to receive PF-06650833 and placebo, respectively. In this placebo-substitution design, all subjects within a cohort received one or more doses of PF-06650833 and/or placebo. Single oral doses of PF-06650833 IR formulations from 1 to 6000 mg, and MR formulations from 30 to 300 mg, were administered in fasted (overnight fast of ≥ 10 h) and/or fed (high-fat breakfast meal) states. Doses were escalated sequentially by period within each cohort (see Fig. 1a for final dosing scheme), based upon the evaluation of ≥ 48 h of safety and tolerability for all subjects and ≥ 8 h of PK data for at least six subjects receiving PF-06650833 and one subject receiving placebo. Dose escalation was to cease when either the limits of safety and/or tolerability were reached, the projected exposure at the subsequent dose exceeded the toxicokinetic limit (TK) established based on the no observable adverse effect level (NOAEL) in relevant animal studies, or a plateau in exposure was reached.

The effects of food on the plasma PK profile of the IR and MR formulations were explored in cohorts 1 and 3, respectively, by administering 30 mg doses of PF-06650833 in a fasted state and after a high-fat meal. A 1000-mg dose of the IR formulation was also tested in cohort 3 in an attempt to identify a maximum tolerated dose (MTD). Since TK limits were not reached with the IR formulation at doses up to 1000 mg, the IR doses were escalated to 2000 and 6000 mg with a high-fat meal in cohort 4 (Fig. 1a).

Study 2 (B7921002; NCT02485769) was a 14-day, phase 1, randomized, double-blind, sponsor-open, placebo-controlled, sequential group, MAD study in healthy adult subjects (Fig. 1b).

Subjects were enrolled sequentially into seven cohorts. Within each cohort, eight subjects and two subjects were randomized to receive PF-06650833 and placebo, respectively. Doses for all cohorts were administered after a standard (not high-fat) meal. Multiple dosing regimens (once daily [QD] 24 h apart, twice daily [BID] 12 h apart, three times per day [TID] 8 h apart, and four times per day [QID] 6 h apart) were used to provide required total daily doses. In the final dosing scheme, multiple oral doses of PF-06650833 IR suspension formulations at 25, 100, 250, and 750 mg BID and 1000 mg QID were administered in cohorts 1–5. PF-06650833 IR 330 mg TID (cohort 6) and an MR tablet at a dose of 300 mg QD (cohort 7) were also evaluated (see Fig. 1b for final dosing scheme).

Dose escalation (cohorts 1–5) or dose selection (cohorts 6–8) was based upon the evaluation of ≥ 7 days of safety and tolerability for all subjects and ≥ 12 h of PK data for at least six subjects receiving PF-06650833. To establish an MTD, dose escalation was to cease when the limit of tolerability was achieved.

In study 1, one subject was discontinued and withdrawn per investigator request on the first day of administration due to pre-existing benign ethnic neutropenia after receiving a single dose of PF-06650833 IR 10 mg, since this would have complicated the interpretation of safety data.

In study 2, four subjects were discontinued: one each in the placebo, PF-06650833 IR 750 mg BID, IR 1000 mg QID, and MR 300 mg QD dose groups. The subjects in the placebo and MR 300 mg QD dose groups were no longer willing to participate in the study, and two subjects were discontinued due to treatment-related TEAEs as described below.

One subject in the IR 750 mg BID dose group of study 2 was discontinued on day 8 due to decreased appetite, after a prolonged period (beginning after the first dose of study drug on day 1) of pronounced gastrointestinal complaints and symptoms. The subject experienced mild nausea soon after dosing on day 1 that was exacerbated by food intake, and the subject had frequent episodes of vomiting after meals. The nausea became moderate after several days of dosing and was accompanied by moderate lack of appetite until the subject was discontinued. The TEAE was considered treatment-related, but other etiologies, such as viral gastroenteritis, could not be excluded. No other subject in the same or next higher (1000 mg PF-06650833) dose group demonstrated similar nausea symptoms.

One subject in the IR 1000 mg QID dose group of study 2 was discontinued on day 7 due to neutropenia. The subject’s absolute neutrophil count (ANC) declined from 2000/mm³ at screening and 1600/mm³ at the time of randomization to 900/mm³ on day 4, 1400/mm³ on day 5, and 1300/mm³ on day 7, which met the individual subject discontinuation criterion of ANC < 1500/mm³ on two consecutive scheduled measurements. The TEAE was considered treatment-related due to a temporal relationship with initial PF-06650833 dosing; however, further review revealed a history prior to study entry of low ANC in the subject. Although a causal relationship to PF-06650833 cannot be excluded, it is possible that the observed fluctuation in ANC was due to the previously undiagnosed cyclic (benign ethnic) neutropenia.

All nine remaining subjects in cohort 5 (IR 1000 mg QID dose group) were electively discontinued after the second dose on day 9 due to the observation of higher abundance (> 15/hpf) atypical crystals in the urine of four of these subjects on day 7. All subjects were asymptomatic and demonstrated no clinical or laboratory evidence of renal injury. These subjects were followed for safety, underwent early termination visit assessments on day 10, and were discharged from the study after follow-up on day 22.

In study 1, more all-causality TEAEs were reported with higher dose levels of IR PF-06650833, but no clear dose relationship was observed at doses ≥ 1000 mg (Table 1). The highest number of TEAEs occurred in subjects who received the IR 100 mg formulation (11 TEAEs in 3 subjects) and in subjects who received placebo (6 TEAEs in 4 subjects). Four TEAEs in 2 subjects were reported with the 300 mg MR formulation, while no TEAEs were reported with the 300 mg IR formulation. A total of 10 treatment-related TEAEs were reported in 4 subjects receiving IR PF-06650833, including 1 reporting acne (IR 30 mg; fed state), 2 reporting headache (IR 2000 mg and 6000 mg; both fed state), and 1 whose reported TEAEs, numbering 7 overall, included multiple gastrointestinal disorders (IR 100 mg; fasted). No treatment-related TEAEs were reported in subjects receiving PF-06650833 MR formulations or placebo.

In study 2, a total of 62 all-causality TEAEs were reported in 35 subjects, with PF-06650833 IR 750 mg BID having the highest number of TEAEs (n = 17), followed by IR 1000 mg QID (n = 11) and placebo (n = 9) (Table 2). No clear dose or regimen relationship was observed with respect to the number of TEAEs. A total of 36 treatment-related TEAEs were reported in 20 subjects, with headache, nausea, upper abdominal pain, and acne being the most common.

In both studies, all TEAEs were mild or moderate in severity, and most resolved without intervention. There were no dose reductions and/or temporary discontinuations due to TEAEs, serious AEs, or deaths reported in either study. There were no clinically significant changes in vital signs, ECGs, laboratory data, or dose-limiting TEAEs for either study.

In study 2, the presence of asymptomatic, non-adverse, atypical crystals in the urine was identified in 25 subjects (including 3 subjects receiving placebo). The presence of urine crystals at higher abundance (≥ 15/hpf) was restricted to PF-06650833 doses ≥ IR 750 mg BID and was not persistent. None of the subjects presenting with urine crystals had TEAEs, other abnormal clinical signs or symptoms, or clinical laboratory data (serum creatinine or estimated glomerular filtration rate) suggestive of adverse effects on renal function.

Median plasma concentration-time profiles of SAD of the PF-06650833 IR and MR oral formulations are presented in Fig. 2. Plasma PK parameters for both formulations are summarized in Table 3.

When administered in the fasted state, plasma concentrations of PF-06650833 increased in a dose-dependent manner with SAD of ≤ 100 mg for both IR and MR formulations and in a less than proportional manner with higher doses; lower C_max values were observed for all comparable doses of MR versus IR formulations as expected. Dose-normalized C_max and AUC from time zero extrapolated to infinity (AUC_inf) values for PF-06650833 IR and MR formulations are shown in Additional file 1: Figure S1. Absorption was rapid for the PF-06650833 IR formulation (median time of C_max [T_max] 0.5–2.0 h across the 1–1000 mg dose range) compared with the more gradual absorption of the MR formulation (median T_max 4.0–8.0 h over the 30–300 mg dose range). Half-life was similar for PF-06650833 IR versus MR formulations at comparable nominal doses of 30–100 mg (mean terminal half-life [t_½] 10.2–15.0 and 9.4–11.7 h, respectively) but was longer for MR 300 mg (mean t_½ 38.8 h) versus IR 300 mg (mean t_½ 19.9 h), for which a longer terminal phase was measured.

Following single oral doses of PF-06650833 IR and MR 30 mg formulations, absorption was delayed in the fed (high-fat meal) versus fasted (≥ 10 h) state for the IR 30 mg dose (median T_max 4.0 versus 0.5 h), but was not affected by food for the MR 30 mg dose (median T_max 6.0 h for both). Half-life was reduced in the fed state for both IR (t_½ 10.2 to 4.4 h) and MR (t_½ 11.7 to 6.33 h) formulations.

Co-administration of IR 30 mg with a high-fat meal increased total exposure by 33% (AUC_inf [ng•h/mL] 211.3 versus 316.1 for fasted and fed conditions, respectively; fasted/fed ratio 66.8% [95% CI 57.49, 77.71]), but did not have an effect on C_max (57.62 versus 54.21 ng/mL for fasted and fed conditions, respectively; fasted/fed ratio 106.30% [95% CI 83.69, 135.03]). Conversely, C_max increased by 62% in the fed state for MR 30 mg (C_max 14.97 versus 39.34 ng/mL for fasted and fed conditions, respectively; fasted/fed ratio 38.05% [95% CI 29.45, 49.16]), while total exposure remained unaffected (AUC_inf 260.9 versus 287.1 ng h/mL for fasted and fed conditions, respectively; fasted/fed ratio 90.86% [95% CI 78.40, 105.29]).

When 2000 and 6000 mg IR doses were administered in the fed state, median T_max was 4.0 and 6.0 h, respectively. Following the attainment of C_max, PF-06650833 concentrations demonstrated a multiphasic decline. Mean t_½ was 72.1 h for PF-06650833 IR 6000 mg (and was not able to be determined for IR 2000 mg). In general, the increase in exposure was less than proportional to the increase in dose for the 2000 and 6000 mg IR formulations compared with the lower dose groups.

Median plasma concentration-time profiles at steady state on day 14 administration of oral MAD of PF-06650833 IR and MR formulations are presented in Fig. 3. Plasma and urine PK parameters for both formulations on day 1 and day 14 are summarized in Table 4.

The PF-06650833 absorption rate was slightly faster on day 1 following initial oral doses of IR 25 to 1000 mg under fed (standard meal) conditions (median T_max 2–4 h), compared with the more gradual absorption of the MR formulation (median T_max 4 h). On day 14, absorption rates were comparable with day 1 values for PF-06650833 IR (median T_max 2 h) and MR (median T_max 4 h) formulations.

Steady state was reached by day 4 for all PF-06650833 dose groups. Across all dosages, mean oral clearance values ranged from 122.4 to 308.0 L/h, and mean volume of distribution values ranged from 8064 L to 13,160 L. Mean half-life values calculated for IR 750 mg BID, IR 330 mg TID, and MR 300 mg QD dosages ranged from 25.4 to 31.4 h. On day 14, AUC from time 0 to time tau (AUC_tau; where tau is the dosing interval [6, 8, 12, and 24 h for QID, TID, BID, and QD dosing, respectively]) and C_max increased proportionally for IR 25 to 100 mg BID doses, with less than proportional increases observed at doses ≥ 250 mg.

Accumulation ranged from 0.9-fold to 1.4-fold for AUC_tau and 0.9-fold to 1.3-fold for C_max. Less than 1% of the dose was recovered unchanged in the urine for all dose groups, with renal clearance ranging from 14 to 19 mL/min for IR 25 mg BID, IR 330 mg TID, and MR 300 mg QD, and 23 mL/min for IR 750 mg BID. Dose-normalized C_max and AUC_tau following MAD of PF-06650833 IR and MR formulations on day 14 are shown in Additional file 1: Figure S2.

Ratios of 4β-hydroxycholesterol to cholesterol were comparable (< 20% mean change) between day 14 (4 h post-dose) and day 1 (pre-dose) across the dose groups for doses up to 750 mg BID, indicating no apparent trend for CYP3A induction or inhibition [21].

Geometric mean serum hsCRP levels ranged from 0.067 to 0.101 mg/dL across the dose groups at baseline. There was a sustained decrease from baseline in serum hsCRP, which, in general, reached maximal reduction by day 7, following administration of PF-06650833 IR formulations ≥ 250 mg BID and in the MR 300 mg QD dose group (Fig. 4). On day 14, reductions from baseline in hsCRP of approximately 60–70% (geometric mean percentage) were seen in the highest dose groups.