The protocol and informed consent documentation for the two phase I clinical studies were reviewed and approved by the independent ethics committee or institutional review board specific for the study center and are listed in Additional file 1. The studies were conducted in accordance with the International Conference on Harmonisation and Good Clinical Practice regulations and guidelines. Written informed consent was obtained from all study participants before any screening or study-related procedures were performed.
Single-ascending dose study in healthy volunteers
This was a randomized, double-blind, placebo-controlled, sequential, single-ascending dose study conducted from 18 January 2005 through 12 January 2006 at a single study site. Inclusion criteria for enrollment followed the standard practice for first-in-human studies. Briefly, eligible healthy male and female volunteers were studied, who were of non-child bearing potential between 18 and 55 years of age (inclusive), with a body mass index (BMI) of 18 to 29 kg/m2. Clinical laboratory measurements and 12-lead electrocardiogram intervals were assessed for general health during the 21-day screening period. The day before dosing, subjects were randomized to a single dose of AMG 403 or placebo in a 3:1 ratio for each dose regimen. The double-blind treatment/follow-up period was either 49 (1 and 3 mg AMG 403) or 91 (10 and 30 mg AMG 403) days in duration. Single doses of AMG 403 were administered by either one-hour intravenous (IV) infusion (1, 3, 10, and 30 mg) or subcutaneous (SC) injection (10 and 30 mg).
Multiple-ascending dose study in patients with knee OA
This was a randomized, double-blind, placebo-controlled, sequential, multiple-dose study conducted at three sites from 13 December 2006 through 17 January 2008. Eligible male and female subjects 18 to 65 years of age (inclusive), body weight <125 kg, and diagnosed with knee OA (as defined by the following American College of Rheumatology criteria: knee pain and radiographic evidence of osteophytes, and morning stiffness for ≤30 minutes and/or crepitus on motion) were enrolled. At screening, subjects were to have visual analog scale (VAS) pain scores ≥30 mm for the index knee and clinically acceptable laboratory tests and electrocardiogram results. If patients were taking any non-prescribed supplements or prescription medications including pain medication, the doses were to have been stable for at least 1 month.
Key exclusion criteria included active or prior history of peripheral neuropathy, paresthesia, or dysesthesia or any other previously diagnosed neurologic condition causing the above noted symptoms; uncontrolled diabetes, cardiovascular disease or hypertension; diagnosis of a condition other than knee OA that could cause or affect pain or pain assessment in the index knee (e.g., radiculopathy or neuropathy, vasculopathy, fibromyalgia or active depression); neuromodulatory agents used as analgesic therapy for neuropathic pain; planned surgical treatment for OA during the study period; inflammatory arthropathy including secondary OA; smoking more than 20 cigarettes per day within the 12 months prior to first dose administration; women of child-bearing potential; current or recent use of opiates or Diacerein (≤1 week prior to first AMG 403 dose administration).
The study design consisted of a 21-day screening, 112-day double-blind efficacy, and 126-day post-treatment follow-up period. In each dose cohort (3, 10, or 20 mg AMG 403), subjects were randomized 3:1 to receive AMG 403 or placebo, once every 4 weeks (Q4W) by SC injection for a total of four dose administrations. Administration of the second, third, and fourth doses occurred only after the previous dose was found to be safe and well-tolerated based on protocol-specified stopping rules. Dose escalation to the next dose cohort proceeded only when the previous dose cohort was found to be safe and well-tolerated following a review of all available safety data to day 22.
Safety assessments included vital signs, laboratory tests, 12-lead electrocardiogram, and neurological and injection site evaluations for the determination of adverse events (AE) and serious adverse events (SAE) from study enrollment to end of study.
Serum samples were collected from healthy volunteers (single-dose study) on study days 1 (pre-dose), 29, 50 (only 1, 3, and 10 mg IV), or day 92 (only 10 and 30 mg IV, and 10 and 30 mg SC), and from patients with knee OA (multiple-dose study) on study days 1 (pre-dose), 29 (pre-dose), 57 (pre-dose), 85 (pre-dose), 197 (only 3 and 10 mg SC Q4W), or 211 (20 mg SC Q4W). All samples were first tested for anti-drug antibodies (ADA) using a validated electrochemiluminescent (ECL) immunoassay to screen and confirm antibodies capable of binding AMG 403. Samples testing positive in the ECL immunoassay were subsequently tested in a validated cell-based bioassay to detect AMG 403 neutralizing or inhibitory effects in vitro. Samples that tested negative in the ECL immunoassay were not tested in the bioassay. Subjects were designated with a positive immune response if antibodies to AMG 403 were detected at any time point subsequent to the first dose administration.
Serum samples were collected from subjects while on study at protocol-specific time points. Serum AMG 403 levels were measured using validated enzyme-linked immunosorbent assays with a lower limit of quantification (LLOQ) of 0.0016 or 0.0051 μg/mL for the single- and multiple-dose studies, respectively. PK parameters were derived from non-compartmental analysis using Phoenix WinNonlin 6.3 (Pharsight, Mountain View, CA, USA).
Population PK modeling with covariate analysis
From model development a two-compartment model was identified as the appropriate choice for a combined analysis of the individual PK data from healthy volunteers and patients with knee OA, using NONMEM 7.2 (ICON Development Solutions, Ellicott City, MD, USA). The following population PK (pop PK) parameters were estimated: first-order SC absorption rate (ka), clearance (CL), central volume of distribution (Vc), peripheral volume of distribution (Vp), intercompartmental CL (Q), and bioavailability (F) of a SC dose. Baseline body weight was evaluated as a continuous covariate on CL and Vc. Knee OA diagnosis and ADA development to AMG 403 were independently tested as dichotomous covariates on CL.
Efficacy in patients with knee OA
A 100-mm VAS was used for patients’ self-assessment of knee OA as “very good” to “very poor” . Physician disease assessment rated the condition of the study subject’s knee on a scale of 0 to 4 (0 = very good and 4 = very poor). Study subjects independently reported answers to the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) 3.1 questionnaire to measure the three components of OA symptoms: pain, stiffness, and physical function. Baseline determinations for all three efficacy endpoints were assessed prior to the first dose administration and at various time points during treatment.
All subjects who received at least one dose of AMG 403 were included in the safety and efficacy analyses. Adverse events, PK, and efficacy endpoints were descriptively compared across the various treatment groups, as the study was not powered to perform formal statistical testing.