Introduction
The PD-1 pathway represents a major immune control switch that may be engaged by tumor cells to overcome active T-cell immune surveillance [
1]. The ligands for PD-1 (PD-L1 and PD-L2) are constitutively expressed or can be induced in various tumors, including melanoma [
2‐
5]. The high expression of PD-L1 (and to a lesser extent, PD-L2) on tumor cells is correlated with poor prognosis and poor survival in various cancer types, including renal cell carcinoma, pancreatic carcinoma, hepatocellular carcinoma, ovarian carcinoma, and non-small-cell lung cancer (NSCLC) [
6‐
10]. Furthermore, it has been suggested that PD-1 regulates tumor-specific T-cell expansion in patients with melanoma [
11]. Preclinical in vitro and in vivo experiments have shown that PD-1 and/or PD-L1 blockade using monoclonal antibodies enhances tumor cell-specific T-cell activation, cytokine production, anti-tumor effector mechanisms, and the clearance of tumor cells by the immune system [
12‐
16]. PD-1 and PD-L1 inhibitors have validated PD-1 as an attractive target for clinical therapeutic intervention. PD-1 inhibition was tested in a clinical study of patients with a range of solid tumor types, and promising clinical activity was noted in multiple tumor types, including melanoma and NSCLC [
17].
Pembrolizumab (formerly known as MK-3475) is a potent, highly selective, IgG4-k humanized monoclonal antibody that prevents PD-1 from binding with PD-L1 and PD-L2. This agent was generated by grafting the variable region sequences of a mouse antihuman PD-1 antibody onto a human IgG4-k isotype framework containing a stabilizing S228P mutation of the Fc region. Pembrolizumab exhibited high affinity for the PD-1 receptor, strong inhibition of PD-L1 and PD-L2, and robust activity in a functional ex vivo T-cell modulation assay using human donor blood cells (data on file; Merck & Co., Inc.).
A first-in-human phase 1 study was conducted to evaluate the safety, pharmacokinetics, and pharmacodynamics of pembrolizumab in non-Japanese patients with advanced solid tumors. No dose-limiting toxicities (DLTs) were observed, and the maximum administered dose (MAD) was 10 mg/kg every 2 weeks (Q2W). Pharmacokinetic and pharmacodynamic analyses showed that the lowest dose with the full potential for antitumor activity was 2 mg/kg every 3 weeks (Q3W) [
18].
In the present study, the safety and tolerability, pharmacokinetics (PK), and immunogenicity of pembrolizumab were investigated in Japanese patients with advanced solid tumors. The tumor response to pembrolizumab was also evaluated as an exploratory objective.
Materials and methods
Patient eligibility
This study was conducted based on the Declaration of Helsinki and the Guidelines for the Clinical Evaluation Methods of Anti-Cancer Drugs in Japan (Japanese Ministry of Health, Labour, and Welfare notification, November 1, 2005). The study was approved by the institutional review board of each study site.
The main eligibility criteria were as follows: a histologically or cytologically confirmed diagnosis of locally advanced or metastatic solid tumors in a patient who had experienced disease progression while on standard therapy or in a patient intolerant of, or not eligible for standard therapy; a patient age of 20 years or older; an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1; and adequate hematologic, hepatic, and renal functions. The exclusion criteria included the administration of chemotherapy, radiotherapy, or biological therapy in the 4 weeks (2 weeks for palliative radiotherapy and kinase inhibitors) prior to enrollment; previous treatment with a PD-1, PD-L1, or cytotoxic T-lymphocyte-associated protein 4 inhibitor; untreated and/or unstable central nervous system metastasis; or the presence of autoimmune disease.
All patients provided informed consent, and the study was conducted in accordance with current Good Clinical Practice standards. This study was registered at ClinicalTrials.gov as NCT01840579.
Study design and evaluation
This study was an open-label, non-randomized, phase 1 study of pembrolizumab in Japanese patients with advanced solid tumors that was conducted at two sites in Japan. This study was designed to investigate the safety and tolerability, PK, immunogenicity, and anti-tumor activity of pembrolizumab monotherapy. Pembrolizumab was administered as a 30-min intravenous (i.v.) infusion at a dose of 2 or 10 mg/kg. Dose escalation was conducted using the conventional “3 + 3 design,” with cohorts of three patients sequentially enrolled at pembrolizumab doses of 2 and 10 mg/kg administered on days 1 and 28 and Q2W thereafter until disease progression or intolerable toxicity occurred. The initial 28 days after the first administration (cycle 1) were regarded as the DLT evaluation period. Three or six patients were enrolled at each dose based on the toxicity probability intervals [
19]. In the DLT assessments, if none of the three patients or none/one of the six patients had a DLT at a certain dose, that dose was considered to be tolerable.
Adverse events (AEs) were graded using the National Cancer Institute Common Terminology Criteria for AEs, version 4.0. A DLT was defined as any of the following events occurring during cycle 1 (the initial 28 days): grade 4 neutropenia lasting for ≥7 days; grade 3 or 4 neutropenia with a fever >38.5 °C and/or infection requiring antibiotic or anti-fungal treatment; grade 4 thrombocytopenia; grade 4 non-hematologic toxicity; or a grade 3 non-hematologic toxicity (laboratory value) persisting for >1 week or requiring medical intervention.
Anti-tumor activity was evaluated at baseline and every 6 weeks according to the Response Evaluation Criteria In Solid Tumors, version 1.1 (RECIST v1.1) and the immune-related response criteria (irRC) [
20].
Pharmacokinetics and immunogenicity (presence of anti-drug antibody)
Blood samples for the PK analyses were collected predose, postdose (<30 min after infusion), and 6, 24, and 48 h after the start of the first infusion; on days 8, 15, 22, and 29 of cycle 1; predose and postdose in cycle 2 and every other cycle thereafter for the first 12 months; and 30 days after the last pembrolizumab dose. The pembrolizumab serum concentrations were quantified using a validated electrochemiluminescent assay (lower limit of quantification, 10 ng/mL). The PK data are described using a noncompartmental approach. Blood samples for anti-drug antibody (ADA) analyses were collected predose and 24 h after the start of the first infusion, predose in cycle 2 and every other cycle thereafter for the first 12 months, and 30 days after the last pembrolizumab dose.
The presence of ADA was determined using bridging electrochemiluminescence and was evaluated using the standard three-step method consisting of a screening test, a confirmation test, and an antibody titer test. ADA was determined to be positive if the result for at least one predose or postdose sample was positive on the confirmation test.
PD-L1 expression
PD-L1 expression was measured using immunohistochemistry performed on formalin-fixed, paraffin-embedded tissue sections at QualTek Clinical Laboratories. PD-L1 positivity was defined as staining in ≥1 % of the tumor cells (modified proportion score) or stroma using immunohistochemistry with the PD-L1 22C3 antibody.
Discussion
The primary objective of the present study was to investigate the safety and tolerability of single-agent pembrolizumab administered in Japanese patients with advanced solid tumors. The dosing schedules in the present study were selected based on the results of a phase 1 study of pembrolizumab in non-Japanese patients with advanced solid tumors. The previous study showed that the MAD was 10 mg/kg Q2W, and the lowest dose with the full potential for antitumor activity was 2 mg/kg Q3W [
18]. No DLTs were observed at either dose in the present study. The most common drug-related AEs were nausea, malaise, pyrexia, and AST/ALT elevations (
n = 2 each). One case each of grade 3 ALT elevation, grade 3 AST elevation, grade 1 pneumonitis, and grade 1 TSH elevation were reported as immune-related AEs. The AEs observed in the present study have also been reported for clinical studies of pembrolizumab in non-Japanese patients. Although the number of Japanese patients was limited, the safety profile of pembrolizumab in Japanese patients with advanced solid tumors in the present study was generally consistent with that observed previously in non-Japanese patients. Drug-induced autoimmune-like toxicities have been observed in patients treated with immune checkpoint inhibitors (such as those used in anti-PD-1 therapy) through the infiltration of immune cells into normal noncancerous tissues. Immune-related AEs can affect multiple organs such as the skin, bowel, kidney, peripheral and central nervous system, liver, lymph nodes, eyes, pancreas, and endocrine tissues. Steroid therapy is recommended for the management of immune-related AEs [
21,
22]. In the present study, most AEs were of grade 1 or 2 and were manageable by interrupting pembrolizumab treatment and/or medical intervention without steroid therapy.
Pembrolizumab exposure at a dose of 10 mg/kg was generally similar for Japanese and non-Japanese patients with advanced solid tumors (AUC
0-∞: 3410 vs. 3270 μg day/mL, C
max: 250 vs. 256 μg/mL, respectively). The mean CL, t
1/2, and Vz values were generally similar between the two populations for doses in the range 1–10 mg/kg. In addition, the individual values for AUC
0-∞, C
max, t
1/2, Vz, and CL for doses in the range 1–10 mg/kg overlapped (Fig.
2) [
18]. These results indicated that the PK of pembrolizumab in Japanese patients with advanced solid tumors was generally similar to that in non-Japanese patients with advanced solid tumors.
As an exploratory analysis, the tumor responses were also evaluated. Partial responses were observed in two of the nine patients (22.2 %) treated with 10 mg/kg Q2W by an investigator review according to both RECIST v1.1 and irRC criteria. One of the five patients with advanced NSCLC and one of the three patients with advanced melanoma achieved partial responses. A durable response (response duration of more than 225 days according to irRC) was observed in one patient with metastatic acral lentiginous melanoma, which is the most common subtype of melanoma in Asian countries (superficial spreading melanoma is more common in Caucasians). This result is encouraging for the further development of pembrolizumab treatment for melanoma in Japan.
Because of the limited number of patients and tumor samples, a relationship between tumor response and PD-L1 expression was not observed in the present study. Recent data have shown that PD-L1 expression, microsatellite instability high, increased mutation burden, and the immune gene expression signature are correlated with the improved efficacy of pembrolizumab [
23‐
26], indicating the importance of biomarker development to identify patients suitable for anti-PD-1 and anti-PD-L1 therapy. Based on the safety data from this phase 1 study, Japanese patients are currently being enrolled in late-phase global studies of pembrolizumab for the treatment of various types of tumors, such as NSCLC, gastric cancer, head and neck cancer, bladder cancer, and colorectal cancer. Further biomarker analyses in these clinical studies are on-going.
Recent randomized studies of pembrolizumab demonstrated that no clinically meaningful differences in the safety and efficacy of pembrolizumab were evident between 2 mg/kg Q3W and 10 mg/kg Q3W or between 10 mg/kg Q3W and 10 mg/kg Q2W [
27‐
31]. The administration of pembrolizumab at 2 mg/kg Q3W is currently approved in the United States and other countries for the treatment of patients with unresectable or metastatic melanoma or metastatic NSCLC expressing PD-L1.
In conclusion, pembrolizumab at dosages of 2 and 10 mg/kg Q2W was well tolerated in Japanese patients with advanced solid tumors and showed encouraging anti-tumor activity against melanoma and NSCLC.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.