Phase 1 dose-escalation study to evaluate the safety, tolerability, pharmacokinetics, and anti-tumor activity of FCN-159 in adults with neurofibromatosis type 1-related unresectable plexiform neurofibromas

This is a multicenter, open-label, single-arm, non-randomized, phase I dose-escalation trial to evaluate the safety, tolerability, pharmacokinetic (PK), and anti-tumor activity of orally administered FCN-159 in adult patients with NF1 (NCT04954001). Phase I commenced with dose escalation in adult patients following a standard 3 + 3 design (Supplementary Table S1) to determine the maximum tolerated dose (MTD) of FCN-159 administered daily under fasting conditions (defined as no food or drink 1 h before and 2 h after each dose) in 28-day cycles. Study drug was dispensed at the study site and patient adherence was monitored by the records of drug dispensation and return. Patients were on treatment until PD, death, patient's voluntary withdrawal from study treatment, or study termination. The study was followed for 2 years after the last patient in. The starting dose was 4 mg, escalating in cohorts of at least three evaluable patients at 6 mg, 8 mg, and 12 mg until the MTD was determined. The starting dose in this study was determined based on available data from a phase 1a, first-in-human study of FCN-159 in patients with advanced NRAS ^mut+ melanoma at the time of study design [26]. In that study, the dose of FCN-159 was escalated from 0.2 mg to 15 mg one daily, and no DLTs or SAEs were observed at 6 mg or lower as of October 20, 2020; systemic exposure to FCN-159 increased as the dose escalated [26]. Therefore, 4 mg was determined to be a safe starting dose for adults with NF1 in the present study. Dose expansion at a likely RP2D level enrolled approximately six patients. The highest dose level with a dose-limiting toxicity (DLT) incidence rate ≤ 33% (0/3 or 1/6 patients) was to be considered the MTD. If patients experienced grade ≥ 3 and/or unacceptable toxic events that were considered as at least possibly related to the study treatment, the study treatment was discontinued and supportive treatment was given in accordance with local treatment routines. If the toxicity returned to grade ≤ 2 within 28 days after the occurrence, and there was no progression on patients’ conditions or the investigator believed that patients could benefit from the study treatment, the original dose could be maintained or reduced after discussion with medical monitor. After completion of the dose escalation part of the study, PK, efficacy, safety, and tolerability data were analyzed to select the RP2D.

Adult patients were eligible to enrol if they were aged between 18 and 70 years with confirmed NF1-related PN with a requirement of systematic therapy per Investigator’s judgment. The diagnosis of NF1 was made if at least one of the two diagnosis criteria was met: (1) positivity for NF1 germline mutation per Clinical Laboratory Improvement Amendments-certified laboratory (or equivalent) testing; (2) the presence of at least 2 of 7 manifestations or features according to the National Institutes of Health consensus criteria [1]. Patients must have been judged by the Investigator to have either PN unsuitable for surgery or have previously received surgical treatment with incomplete PN resection or relapse, and a measurable PN lesion of at least 3 cm in at least one dimension that was amenable to MRI analysis. Full inclusion and exclusion criteria are shown in Supplementary Table S2.

The study was conducted in accordance with the principles of the Declaration of Helsinki and Good Clinical Practice guidelines and with the approval of the local Institutional Review Board/Independent Ethics Committee at the leading study site (Shanghai Ninth People's Hospital, approval number SH9H-2020-C25-6). All patients provided written informed consent to participate.

Primary endpoints of the study were the DLT incidence rate, MTD, and RP2D. Secondary endpoints included other safety assessments, imaging tumor response (complete response [CR], PR, stable disease [SD], or progressive disease [PD]), and PK parameters of FCN-159. Adverse events were graded per CTCAE v5.0.

All patients underwent a complete medical history, physical examination, Eastern Cooperative Oncology Group (ECOG) assessment, and laboratory analysis of test results. Drug-related TEAEs, serious adverse events (SAEs), TEAEs of grade ≥ 3 toxicity, and TEAEs leading to drug discontinuation were reviewed on an ongoing basis. Efficacy was assessed by radiologic scans and clinical assessment. Tumor assessments per Response Evaluation in Neurofibromatosis Schwannomatosis criteria [27] were performed by investigators using MRI volumetric analysis every 4 cycles within the first 2 years (± 7 days) and every 6 cycles after 2 years (± 14 days) until PD, death, patient's voluntary withdrawal from study treatment, or study termination. MRI sequences of tau inversion recovery (STIR), T1- and T2-weighted sequences were chosen and the software of Extended Brilliance Workspace, SIGNA Premier and uExceed were used for MRI volumetric analysis. The same software was used for all tumor assessments at baseline and subsequent assessed timepoints of the same patient. Pain was assessed by an 11-point numerical rating scale (NRS-11).

In order to study the PK characteristics of FCN-159 in plasma, blood samples were collected pre-dose and 0.5, 1, 2, 3, 4, 6, and 10 h post dose on days 1 and 28 of cycle 1, and pre-dose only on days 2, 8, and 15 of cycle 1 and day 1 of cycle 2. Plasma PK parameters of FCN-159 in each dose group were analyzed with standard non-compartmental PK methods using Phoenix WinNonlin, v8.2. PK parameters included area under the curve (AUC)_(0-last), AUC_(0-∞), maximum plasma concentration (C_max), time to maximum plasma concentration (T_max), half-life (T_1/2), oral clearance (CL/F), and volume of distribution (Vd/F) for the single-dose regimen and AUC_(0-tau), C_max, T_max, minimum steady-state plasma concentration (C_ss,min), mean steady-state plasma concentration (C_{ss, avg}), accumulation ratio for AUC (ARAUC), and apparent oral clearance at steady state (CLss/F) for the multiple dose regimen.

The sample size for the dose-escalation study was estimated to be 24 based on the 3 + 3 method. Safety was analyzed in patients who received at least one dose of FCN-159 and had at least one safety assessment. DLT was assessed in the DLT analysis set, defined as patients who were enrolled in the dose-escalation study and met the DLT evaluation criteria. FCN-159 plasma concentration was analyzed in patients who received at least one dose of FCN-159, had at least one PK blood sample collection as scheduled, and had plasma concentration data for FCN-159. PK parameter analysis set comprised patients who received FCN-159 per protocol and had at least one PK parameter during the trial. Data were summarized using descriptive statistics.

Between 26th March 2021 and 4th November 2021, 23 patients were screened for the dose escalation study, and 19 were enrolled across four FCN‑159 dose groups: 4 (n = 3), 6 (n = 4), 8 (n = 8), and 12 mg (n = 4) (Fig. 1). The reasons for screening failure included withdrawal of informed consent (n = 2/4, 50%) and failure to meet study eligibility criteria (n = 1/4, 25%), and one patient withdrew in order to participate in phase II of this study (n = 1/4, 25%). The date of data cutoff was 1st December 2021.

The median age of the entire cohort (n = 19) was 26.0 years (range, 20–57 years; Table 1). Eleven (57.9%) were male and eight (42.1%) female. All patients had NF1 with associated PNs, and all had an ECOG performance status of 0. The most common type of neurofibroma-related complications at baseline were disfigurement (n = 10, 52.6%) and pain (n = 4, 21.1%). Eight (42.1%) patients had a positive NF1 germline mutation, one (5.3%) was confirmed negative. Of the eight (42.1%) patients with a known NF1 zygotic type, all were heterozygotes. The most common locations for patients to present with PN were the face (n = 3, 15.8%), thoracic area (n = 4, 21.1%), and upper leg (n = 3, 15.8%). All PN localizations are shown in Table 1. The mean volume of target lesions at baseline was 47.8 cm³ (range, 2–4,670 cm³), and 15 (78.9%) patients also presented with measurable non-target lesions.

Study-drug-related TEAEs were observed in all patients (n = 19, 100%), the majority of which were grade 1 or 2 in severity. The most common drug-related TEAEs were folliculitis (n = 9/19, 47.4%), stomatitis (n = 7/19, 36.8%), paronychia (n = 6/19, 31.6%), and increased blood alkaline phosphatase (n = 6/19, 31.6%). Twelve patients (63.2%) experienced gastrointestinal disorders that were reported to be drug related, of which stomatitis (n = 7/19, 36.8%) and mouth ulceration (n = 4/19, 21.1%) were the most common. Two (10.5%) patients experienced eye disorders: blurred vision (n = 1/19, 5.3%) and reduced visual acuity (n = 1/19, 5.3%). All drug-related TEAEs are shown in Supplementary Table S3.

Nine (47.4%) patients reported grade 3 drug-related TEAEs, including four patients experiencing paronychia and five experiencing folliculitis, which were the main cause of dose reduction (42.1%) and drug interruption (21.2%). Only one grade 3 drug-related TEAE was observed in patients receiving doses below the MTD (paronychia; 6 mg dose). One patient experienced an SAE during treatment that led to drug withdrawal. The SAE, rhegmatogenous retinal detachment, which was present at baseline, worsened (blurred vision developed) during the study and required elective surgical treatment, but the retinal condition did not get worse after FCN-159 administration; the event was subsequently considered unrelated to the study drug. No patients died during the study.

The median relative dose intensity of drug exposure was 94.4% (range: 46.7–100.4). Of the 16 patients with at least one post-baseline tumor assessment, all (100%) had reduced tumor volume (Fig. 2). Six (37.5%) patients achieved PRs. All other patients had SD, and none experienced PD (Table 2). The largest reduction in tumor volume was 84.2% (Fig. 3). There was no correlation between tumor volume at baseline and the extent of tumor reduction. MRI images for two typical cases are shown in Supplementary Figure S1.

The results of pain score were limited at the data cutoff date. As it was important for patients with PN, we have provided results of pain as of 9 August 2022. Among patients with definite tumor pain (NRS-11 score ≥ 2 points) at baseline, 72.7% (16/22) of them had a reduction in pain intensity of at least 2 points at the assessment of cycles 4 and 5, which was considered clinically meaningful pain improvement; of them, 13 patients achieved complete pain relief at least once (the score reduced to 0). Pain scores decreased by an average of 2.4 points across all patients. At the dose group of 8 mg, 75% (15/20) of patients achieved meaningful improvement, with a mean pain score reduction of 2.5 points.

The mean plasma concentration–time profiles of FCN-159 in single- and multiple-dose levels from 4 to 12 mg are shown in Fig. 4. PK parameters of FCN-159 are shown in Supplementary Tables S4 and S5. As four participants in the 12 mg dose group had dose reduction during multiple dosing due to folliculitis, no PK profile is available for 12 mg at steady state. FCN-159 was absorbed rapidly, with a median T_max of 1.21–2.18 h across all dosing regimens and a mean terminal T_1/2 from 11.4 to 16.2 h for single dose. The geometric mean C_max and AUC_tau of multiple doses over 4 mg to 8 mg ranged from 45.0 to 82.5 ng/mL and 392 to 723 h*ng/mL, respectively. C_max and AUC_tau at steady state were roughly dose proportional over the dose range 4–8 mg. The mean accumulation ratio of AUC from each cohort was 1.5–2.0 (Supplementary Table S6).