Safety/tolerability of the anti-semaphorin 4D antibody VX15/2503 in a randomized phase 1 trial

Study drug.

VX15/2503 was produced by Catalent Pharma Solutions (Madison, WI) and vialed by Ajinomoto Althea, Inc. (San Diego, CA)^14,16; generic and proprietary names have not been assigned. A matched placebo was supplied for comparison of safety observations (see appendix e-1 at Neurology.org/nn).

Study design.

This phase 1 study was a single-dose, dose-escalation, randomized, double-blind, placebo-controlled trial enrolling adult patients diagnosed with relapsing or progressive MS for at least 1 year as defined by the McDonald criteria.¹⁷ The primary protocol-specified objective was to determine the safety and tolerability of VX15/2503 in patients with MS; secondary and exploratory objectives were to characterize the single-dose pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of VX15/2503 (see appendix e-1). No interim analysis was planned, and no changes were made to study objectives or trial design after study initiation.

The study was conducted at 11 US clinical centers. Each of the 5 dose cohorts included 10 patients; ascending dose levels of 1, 3, 6, 15, and 20 mg/kg were used based on results of completed toxicology and clinical studies.^14,16 Enrolled participants were randomly assigned (4:1 randomization ratio, drug to placebo) on study day 1 to receive a single IV dose of either VX15/2503 or placebo; each cohort contained 8 antibody-treated patients. The randomization schedule was software generated; patient treatment assignments were communicated using an interactive voice response system. This system also prescribed, for each patient, specific numbered vials of investigational agent.

Vital signs were measured before, during, and after study drug infusion. Intracohort patient dosing was staggered by at least 24 hours after the first 4 patients in the prior cohort had been dosed; study drug administration to the remaining patients in a cohort was staggered by at least 2 hours between patients. No more than 3 patients were infused in any 1-day period; all patients were monitored for 24 hours after dosing. On study day 2, serum chemistry, hematology, PK/PD, and lymphocyte enumeration samples, among others, were obtained from each subject. Participants also received an in-person or telephonic clinical assessment on day 4. Safety follow-up periods of 6 weeks (cohort 1), 8 weeks (cohorts 2 and 3), 12 weeks (cohort 4), or 27 weeks (cohort 5), based on expected durations of cSEMA4D saturation, were specified for collection of comprehensive safety, PK, and PD samples.

Escalation to the next dose cohort proceeded only after the DESC (consisting of three independent neurologists with clinical expertise in MS, the sponsor's representatives, and the study medical monitor) determined by data review that the previous dose level was safe and well tolerated. Cohort data reviews were blinded and included adverse events (AEs), ECGs, vital signs, and clinical laboratory and lymphocyte subset results through day 15, and human anti-humanized antibody (HAHA)¹⁸ and PK/PD data; the committee made no requests for review of unblinded data.

Stopping rules.

The infusion for any patient was to be stopped if the patient experienced a possibly drug-related serious AE (SAE) or a possibly drug-related significant non–serious AE which, in the opinion of the principal investigator, study medical monitor, or sponsor's medical representative, warranted discontinuation of the study for that patient. The occurrence of any of the following drug-related safety events also warranted DESC evaluation and possible subject discontinuation: one or more SAEs; a severe AE or an elevation in a protocol-specified liver enzyme occurring in ≥2 participants at the same dose level; or an increase in corrected QT interval (QTc) of 60 milliseconds over baseline on 2 consecutive days or any QTc >500 milliseconds in ≥2 patients in the same dose cohort (see appendix e-1 for additional details).

Standard protocol approval, registrations, and patient consents.

Institutional review board approvals for the study protocol, amendments, and informed consent documents were obtained before use in the study; written informed consent was obtained from study participants before the initiation of study procedures. This study was conducted in accordance with the Declaration of Helsinki, International Conference on Harmonization (ICH) guidelines, and applicable portions of the United States Code of Federal Regulations. The ClinicalTrials.gov identifier (NCT01764737) was obtained before study initiation.

Study participants.

Men or women 18–60 years of age previously diagnosed with MS for at least 1 year as defined by the McDonald criteria, and who had an Expanded Disability Status Scale (EDSS) score of 0–6.5, inclusive, at screening were eligible for enrollment if they met the following criteria: a body mass index of 18–32 kg/m², inclusive; willingness to undergo and had no contraindications to brain MRI; willingness to use a medically acceptable method of contraception throughout the study period and for 6 months after the dose of study drug, unless patient was surgically sterile or postmenopausal. Before study drug administration, male patients had to agree to defer from donating sperm for 6 months, and women of childbearing potential were required to have a negative serum pregnancy test at screening (confirmed via baseline urinalysis). Finally, participants on stable treatment regimens of interferon β, glatiramer acetate, or dalfampridine were allowed to enroll.

Exclusionary criteria were an MS relapse that did not stabilize within 30 days before the start of screening; any clinically significant cardiac, endocrine, hematologic, hepatic, immunologic, metabolic, urologic/gynecologic, pulmonary, neurologic, psychiatric, or renal conditions; a history of relevant clinically significant allergic or anaphylactic reactions; any other clinically significant major disease that, as assessed by the investigator, could have posed a risk to patient safety or interfered with the study evaluations, procedures, or completion; any clinically significant laboratory value outside the normal range at screening; or abnormal hematologic, renal, or hepatic function based on laboratory tests.

Pregnant or breastfeeding women were excluded. Patients who had received treatment with any MS disease-modifying therapy other than interferon β or glatiramer acetate within 3 months before dosing were also excluded, as were subjects who had received natalizumab, daclizumab, or fingolimod for any indication within 6 months before dosing, or had any prior treatment with alemtuzumab, rituximab, mitoxantrone, total lymphoid irradiation, bone marrow transplantation, or T cell or T-cell receptor vaccination. Patients were also excluded if they had received any experimental agent within 6 months before dosing, or within a period equivalent to 5 half-lives of the agent (whichever was longer); or were currently involved in any other research study, or had undergone any major surgical procedure within 4 weeks before dosing. Participants were also excluded if they had a history of congestive heart failure, symptomatic ischemia, conduction abnormalities uncontrolled by conventional intervention, or myocardial infarction within 6 months before dosing, or had a clinically significant ECG finding at screening, as determined by the investigator. Finally, patients with sensitivity to VX15/2503 or its excipients, with a known or suspected HIV or hepatitis B or hepatitis C infection, or with a known or suspected allergy to gadolinium (Gd) or other contraindications to brain MRI were excluded.

Safety assessments.

In addition to determining the safety and tolerability of VX15/2503 in patients with MS, we also characterized the single-dose PK, PD, and immunogenicity of VX15/2503. Safety assessments included AEs and SAEs; immunogenicity (Ig levels; HAHA); enumeration of T/B lymphocytes and natural killer cells; clinical laboratory evaluations (hematology, coagulation parameters, serum chemistry, and urinalysis); vital signs; 12-lead ECGs; physical examination findings; and Columbia–Suicide Severity Rating Scale (C-SSRS); these assessments were used in the determination of an maximum tolerated dose (MTD) by the DESC (see appendix e-1 for additional information).

AE severity was rated according to the Common Terminology Criteria for Adverse Events (CTCAE) version 4.03; AEs that were possibly or probably related to the study drug and were ongoing at the time a patient completed the study or discontinued early were followed until resolution or until stabilized. All treatment-emergent AEs were reported to the Food and Drug Administration.

PK/PD assays.

Blood samples were collected at screening, pre-dose, after the end of infusion (EOI), and on days 1, 2, and 4 and then periodically thereafter; PK/PD samples were analyzed as described.¹⁶ No CSF samples were collected for analysis. PK parameters were estimated for the PK population using noncompartmental analyses. Standard PK parameters (C_max; C_L; T_max; and effective half-life, etc.) were determined by cohort and time point. Analyses of area under the time-concentration curve (AUC) and C_max to assess dose proportionality were performed as described.¹⁹ PD evaluations for peripheral blood T-cell cSEMA4D expression and saturation levels as well as for serum sSEMA4D levels were performed as described,^16,20 using samples collected at PK time points (see supplemental materials). As VX15/2503 half-life increased with dose level, final cSEMA4D saturation samples were collected on day 43 (cohort 1), day 57 (cohorts 2 and 3), and day 85 (cohorts 4 and 5), respectively; cohort 5 subjects showing persistent cSEMA4D saturation had additional samples collected on days 155 and 190 for analysis, as necessary.

Statistical analysis.

Because the primary objective of this study was assessment of the safety and tolerability of VX15/2503, statistical analyses of typical efficacy variables were not performed. Results from the PK population were used for summary statistics and determination of mean serum VX15/2503 concentrations. Descriptive statistics (number of patients, mean, SD, percent coefficient of variation, median, minimum, maximum, and the 25th and 75th percentiles) were used to summarize the serum concentrations at each scheduled time point by treatment. Geometric mean values were presented for C_max, C_L, and AUC values.

Disease activity assessments.

Biological activity was assessed in an exploratory manner using brain MRI and EDSS data.²¹ EDSS measurements were performed at baseline, on day 29 and at time points specified for PK assessments. Brain scans were performed at baseline and study day 29 with and without Gd; all MRIs were centrally analyzed and evaluated for the number of Gd-enhancing lesions, the number of new and existing unenhancing T1 lesions, the number of new and enlarging T2 lesions, and total volume of T1 and T2 lesions (see appendix e-1).