- © 2004 by American Society of Clinical Oncology
Phase I Study of the Proteasome Inhibitor Bortezomib in Pediatric Patients With Refractory Solid Tumors: A Children's Oncology Group Study (ADVL0015)
- Susan M. Blaney,
- Mark Bernstein,
- Kathleen Neville,
- Jill Ginsberg,
- Brenda Kitchen,
- Terzah Horton,
- Stacey L. Berg,
- Mark Krailo and
- Peter C. Adamson
- From the Texas Children's Cancer Center/Baylor College of Medicine, Houston, TX; Children's Oncology Group Operations Center, Arcadia, CA; Rainbow Babies and Children's Hospital, Cleveland, OH; Hospital Ste-Justine, Montréal, Canada; and Children's Hospital of Philadelphia, Philadelphia, PA.
- Address reprint requests to Susan M. Blaney, MD, Texas Children's Cancer Center, 6621 Fannin, CC 1410.00, Houston, TX 77030; e-mail: sblaney{at}txccc.org
Abstract
Purpose To determine the maximum-tolerated dose, dose-limiting toxicity (DLT), and pharmacodynamics of the proteasome inhibitor bortezomib (formerly PS-341) in children with recurrent or refractory solid tumors.
Patients and Methods An intravenous bolus of bortezomib was administered twice weekly for 2 consecutive weeks at either 1.2 or 1.6 mg/m2/dose followed by a 1-week rest. The pharmacodynamics of bortezomib were evaluated by measurement of whole blood 20S proteasome activity.
Results Fifteen patients, 11 assessable, were enrolled between November 2001 and February 2003. Dose-limiting thrombocytopenia, which prevented administration of a complete course (four doses in 2 weeks) of therapy, occurred in two of five assessable children enrolled at the 1.6 mg/m2 dose level. There were no other DLTs. Inhibition of 20S proteasome activity seemed to be dose dependent. The average inhibition 1 hour after drug administration on day 1 was 67.2% ± 7.6% at the 1.2 mg/m2/dose and 76.5% ± 3.3% at the 1.6 mg/m2/dose. There were no objective antitumor responses.
Conclusion Bortezomib is well tolerated in children with recurrent or refractory solid tumors. The recommended phase II dose of bortezomib for children with solid tumors is 1.2 mg/m2/dose, administered as an intravenous bolus twice weekly for 2 weeks followed by a 1-week break.
INTRODUCTION
Bortezomib (formerly PS-341, Velcade; Millennium Pharmaceuticals Inc, Cambridge, MA), a dipeptidyl boronic acid, is a novel agent that exerts an antitumor effect through specific and selective inhibition of the 26S proteasome. The 26S proteasome is an adenosine triphosphate–dependent multicatalytic protease that is central to the ubiquitin-proteasome pathway. This pathway plays a pivotal role in the regulated degradation of proteins involved in cell cycle control and tumor growth.1 There are many important regulatory proteins that are affected by inhibition of the ubiquitin proteasome pathway, including nuclear factor kappa β, p53, and the cyclin-dependent kinase inhibitor p21. Aberrant regulation or dysfunction of cell cycle proteins can result in accelerated and uncontrolled cell division, leading to tumorigenesis, cancer growth, and metastasis.
In preclinical studies, bortezomib has been shown to have antitumor activity at nanomolar concentrations in a variety of cell lines. Activity has been observed against a broad range of tumor types, including CNS malignancies, melanoma, non–small-cell lung cancer, and colon, ovarian, renal, and prostate carcinomas.2 Preclinical antitumor activity of proteasome inhibitors has also been observed in leukemias and lymphomas and childhood tumors such as neuroblastoma,3,4 rhabdomyosarcoma,5 and Ewing's sarcoma.6 The pattern of growth inhibition and cytotoxic activity of bortezomib is unique compared with other anticancer agents, suggesting a novel mechanism of cytotoxicity.7
Two bortezomib dosing schedules have been evaluated in adult phase I clinical trials: a twice weekly for 4 weeks schedule followed by a 2-week rest, and a twice weekly for 2 weeks schedule followed by a 2-week rest. The maximum-tolerated dose (MTD) for the twice weekly for 4 weeks schedule was 1.04 mg/m2. Dose-limiting toxicities at higher dose levels (1.20 or 1.38 mg/m2) included thrombocytopenia, hyponatremia, hypokalemia, fatigue, and malaise.8 Other serious adverse events included one episode of postural hypotension and one hypersensitivity reaction.8 Antitumor activity was observed in patients with refractory multiple myeloma and non-Hodgkin's lymphoma.8 The MTD for the twice weekly for 2 weeks schedule was 1.56 mg/m2.9 The dose-limiting toxicities on this schedule were diarrhea and sensory neurotoxicity. There was no dose-limiting hematologic toxicity.9 There was one objective response in a patient with non–small-cell lung carcinoma.9
The antitumor activity of bortezomib was confirmed in two recently completed phase II clinical trials in adults with multiple myeloma.10 The overall objective response rate after bortezomib administration was 33% in a heavily pretreated population. This high level of antitumor activity resulted in recent US Food and Drug Administration approval of bortezomib for third-line treatment in adults with multiple myeloma. A randomized phase III trial of bortezomib versus high-dose dexamethasone in patients with multiple myeloma is in progress.
This report presents the results of a phase I trial and pharmacodynamic study of bortezomib, given twice weekly for 2 consecutive weeks every 21 days, in pediatric patients with refractory solid tumors. The objectives of this study were to identify the optimal bortezomib dose for phase II pediatric trials, to determine the incidence and severity of toxicities associated with bortezomib administration, and to evaluate inhibition of the 20S proteasome after bortezomib administration.
PATIENTS AND METHODS
Patient Eligibility
Patients younger than 22 years of age with a histologically confirmed solid tumor refractory to standard therapy were eligible for this trial. Patients with intrinsic brainstem gliomas or optic pathway tumors were excluded from the requirement for histologic verification. Other eligibility criteria included: a Karnofsky or Lansky performance score of ≥ 50; a life expectancy of greater than 8 weeks; adequate bone marrow function [absolute neutrophil count ≥ 1,500/μL, platelet count ≥ 75,000 μL (transfusion independent), and hemoglobin ≥ 8 gm/dL]; adequate liver function (serum bilirubin < 1.5 mg/dL, ALT < 5 × the upper limit of normal for age, and albumin ≥ 2 g/dL); adequate renal function (serum creatinine below the upper limits or normal for age or a radioisotope glomerular filtration rate ≥ 70/mL/min/1.73 m2); recovery from the toxic effects of prior chemotherapy, radiotherapy, and immunotherapy with a minimum elapsed period of at least 3 months for prior allogeneic stem-cell transplant and of at least 6 months for prior craniospinal or hemipelvic radiation. Study exclusion criteria included pregnancy or lactation in women of childbearing age, uncontrolled infection, receipt of concomitant anticonvulsants, or prior receipt of study drug.
Informed consent was obtained from the patient or his or her parent in accordance with the US National Cancer Institute (NCI), Children's Oncology Group, and individual institutional policies before entry onto this study.
Dosage and Drug Administration
Bortezomib was supplied by the Cancer Therapy Evaluation Program (NCI, Bethesda, MD) as a lyophilized formulation containing 35 mg of mannitol. A 3.5-mg vial of the drug product was reconstituted with 3.5 mL normal saline (USP), such that the reconstituted solution contained 1 mg/mL of bortezomib. The appropriate dose of drug was administered as an intravenous push over 3 to 5 seconds.
Trial Design
The starting dose of bortezomib in this pediatric phase I trial was 1.2 mg/m2/dose, which was based on data from an adult trial using the same schedule. This dose was approximately 80% of the adult MTD. Subsequent planned dose escalations were in increments of 30%. Drug was administered twice weekly for 2 consecutive weeks (days 1, 4, 8, and 11) followed by a 1-week break. Courses were repeated every 21 days if the absolute neutrophil count was ≥ 1,500/μL, the platelet count ≥ 75,000/μL, and any other treatment-related adverse events were ≤ grade 1. If a patient experienced any ongoing drug-related grade 2 toxicities at the time of a scheduled bortezomib dose, then subsequent doses in that cycle were reduced to the previous dose level. Similarly, for drug-related grade 3 or greater toxicities during a course of therapy, the next dose of bortezomib was either withheld or omitted.
A minimum of three patients were entered at each dose level and the dose level was expanded to up to six patients if one patient experienced dose-limiting toxicity during the first course of therapy. When dose-limiting toxicity was observed in two patients of a cohort of three to six patients receiving the same dose of drug, the MTD was exceeded and an additional three to six patients were added at the dose level immediately below the dose level at which the unacceptable level of toxicity was observed. The MTD of bortezomib was defined as the dose level immediately below the level at which at least two patients experience dose-limiting toxicity.
Toxicities were graded according to the NCI Common Toxicity Criteria (version 2.0). Dose-limiting nonhematologic toxicity was defined as any grade 3 or 4 adverse event attributable to the study drug with the specific exclusion of grade 3 nausea or vomiting, grade 3 hepatic transaminase (AST and/or ALT) elevation returning to ≤ grade 1 before the next treatment course, and grade 3 fever or infection. Dose-limiting hematologic toxicity was defined as grade 4 neutropenia or grade 4 thrombocytopenia of more than 7 days duration or requiring transfusion therapy on more than two occasions in 7 days. Hematologic toxicity resulting in a delay of more than 14 days beyond the planned interval between treatment courses was also considered dose-limiting. In addition, any drug-related adverse event that resulted in a dose reduction or dose omission during the first course of therapy was considered dose-limiting.
Patient history, physical examination, and laboratory studies were obtained before treatment and then weekly throughout the first course of therapy and before subsequent courses thereafter. CBCs were obtained at least twice weekly throughout the first course of study and then weekly. Patients with measurable disease had appropriate radiographic or bone marrow evaluations at baseline, after the first and second course of therapy, and then every other course thereafter.
Criteria for Assessment of Response
Patients with measurable disease at the time of enrollment were considered assessable for response. Response was evaluated using the Response Evaluation Criteria in Solid Tumors from the NCI. Disease burden was quantified by calculating the sum of the longest diameter of up to 10 measurable target lesions. A complete response (CR) was defined the disappearance of all target lesions. A partial response (PR) was defined as at least a 30% decrease in the disease measurement. Progressive disease was defined as at least a 20% increase in the disease measurement (taking as reference the smallest disease measurement recorded since the start of treatment), or the appearance of one or more new lesions. Stable disease was defined as failing to fulfill the criteria for a CR, a PR, or progressive disease. Two objective status determinations of CR or PR before progression were required.
Pharmacodynamic Studies
Blood samples for assessment of percentage inhibition of 20S proteasome activity were obtained during the first cycle of therapy before and 1, 4, and 24 hours after the first dose, and before and 1 hour after the second and third doses. Blood samples (2 mL) were collected in heparinized tubes at a site contralateral from the study drug infusion. The tube was gently inverted to prevent a clot and then placed in wet ice until transfer to a cryogenic tube and storage at −70°C.
Inhibition of 20S proteasome activity was measured using a previously described assay developed by investigators at Millennium Pharmaceuticals Inc.11 Briefly, blood cells were lysed with 5 mmol/L EDTA (pH 8.0) for 1 hour and then centrifuged at 600 × g for 10 minutes at 40°C. The resultant whole blood lysate samples were added to substrate buffer (20 mmol/L HEPES, 0.5 mmol/L EDTA, 0.05% sodium dodecyl sulfate, and 60 mmol/L chymostrypsin substrate–Suc-Leu-Leu-Val-Tyr–amido-4-methylcoumarin [AMC]; Bachem, King of Prussia, PA). The reaction was carried out for 37°C for 5 minutes, and the in vitro chymotryptic activity of the 20S proteasome was measured by monitoring the release of the fluorophore AMC from the synthetic peptide substrate LLVY-AMC. The protein content of the samples was determined using a Coomassie protein assay (Pierce Corp, Rockford, IL).
RESULTS
Fifteen patients were enrolled onto this study, of whom 11 were fully assessable for toxicity and response. Two patients were not fully assessable for toxicity because they did not complete the first course of bortezomib secondary to rapid disease progression; two additional patients were not fully assessable because twice-weekly CBCs were not obtained during course 1. These inassessable patients did not experience any unusual or severe bortezomib-related toxicity. Patient characteristics for the assessable patients are listed in Table 1.
Patient Characteristics for Fully Assessable Patients (n = 11)
Nine patients assessable for response—five at dose level 1 (1.2 mg/m2/dose) and four at dose level 2 (1.6 mg/m2/dose)—received one course of therapy. One patient enrolled at the 1.6 mg/m2/dose level received two courses of therapy. One patient enrolled at the 1.2 mg/m2/dose level received six courses of therapy. There were no objective antitumor responses.
Adverse Events
Bortezomib was generally well tolerated. Grade 2 or higher adverse events that were possibly, probably, or definitely related to bortezomib for all patients who received at least one dose of bortezomib are reported in Table 2. Only cycle 1 adverse events are reported because more than 80% of patients received only one cycle of bortezomib. No other categories of grade 2 or higher adverse events were observed in the two patients who received more than one cycle of therapy. Adverse events that were scored as unlikely to be related or unrelated to bortezomib were reviewed and are not included in this report.
Cycle 1 Adverse Events Possibly, Probably, or Definitely Related to Bortezomib for All Patients Who Received at Least One Dose (n = 15)
thrombocytopenia, which prevented administration of the complete first course of therapy, was dose-limiting in two of five assessable patients at the 1.6 mg/m2/dose level. Both of these patients had baseline platelet counts that exceeded 100,000/μL. Grade 1 peripheral neuropathy was reported in one patient; however, there was no dose-limiting peripheral neuropathy. There were no other severe or unusual adverse events.
Pharmacodynamics
The results of the 20S proteasome inhibition determinations at 1 hour after bortezomib are shown in Table 3. Inhibition of 20S proteasome activity seemed to increase with increasing dose. However, this observation should be interpreted cautiously because of the limited number of patients and dose levels in this trial. There was no significant difference in the mean percentage of proteasome inhibition at 1 hour after dosing on days 1, 4, and 8. Proteasome inhibition assays performed on samples drawn immediately before treatment on days 4 and 8 consistently demonstrated that there was complete recovery of activity to baseline.
Percentage 20S Proteasome Inhibition Following Bortezomib Dosing for All Patients From Whom Samples Were Obtained
Children's Oncology Group Investigators Participating in This Study (ADVL0015)
DISCUSSION
In this trial, we evaluated the clinical toxicities of bortezomib administered twice weekly for 2 consecutive weeks followed by a 1-week rest. Bortezomib is a novel anticancer agent that selectively inhibits the Z6S proteasome, an ATP-dependent multisubunit protein that degrades proteins involved in multiple cellular processes including cell cycle regulation, transcription factor activation, apoptosis, and cell trafficking.12 Bortezomib was well tolerated with minimal systemic toxicity. The toxicity profile of bortezomib in children was similar to that in adults. However, in contrast to the experience in adults, peripheral neuropathy was not a predominant toxicity. This may be a reflection of the fact that peripheral neuropathy associated with anticancer agents seems to be less common in children than in adults. However, it may also be a reflection of the limited exposure to bortezomib of the children treated; the median number of cycles administered was only one. Therefore, children who receive multiple cycles of bortezomib in future trials should be observed closely for the occurrence of this toxicity. thrombocytopenia, which prevented administration of a complete course of therapy at the assigned dose level, was the dose-limiting toxicity at the 1.6 mg/m2 dose level. Thus, the recommended dose of bortezomib for additional evaluation in children with solid tumors is the 1.2 mg/m2/dose.
There are numerous preclinical studies demonstrating that bortezomib potentiates the cytotoxic effect of multiple chemotherapeutic agents, including dexamethasone,13 doxorubicin, and melphalan.14 Similarly, bortezomib has been shown to increase mouse mammary tumor sensitivity to cyclophosphamide and cisplatin, pancreatic and colorectal cell line sensitivity to irinotecan,15,16 and pancreatic cell line sensitivity to gemcitabine.17 There is also evidence that bortezomib may be synergistic with other apoptotic agents such as tumor necrosis factor–related apoptosis inducing ligand,18 and with heat-shock binding proteins, such as geldanamycin or 17-allylaminogeldanamycin.19,20 Thus, on the basis of the results of these preclinical studies, the preliminary results of adult clinical trials, and the favorable toxicity profile of this agent in phase I clinical trials, it is reasonable to pursue additional pediatric development of bortezomib despite the fact that there was no objective antitumor activity observed in this phase I trial. It is not uncommon for there to be minimal or no observed antitumor activity in pediatric phase I clinical trials because they involve a limited number of heavily pretreated patients who have diverse tumor types, and are not designed to assess antitumor activity as a study end point.
In summary, bortezomib was well tolerated in children with refractory solid tumors, and the recommended dose for additional study in children (1.2 mg/m2/dose) is similar to doses administered to adults. Because the dose-limiting toxicity of bortezomib in children with solid tumors was hematologic, a separate phase I study in children with recurrent or refractory leukemias will be performed in an attempt to identify the nonhematologic dose-limiting toxicity of this agent. In addition, the results of preclinical studies in pediatric tumor cell lines will be used to guide additional pediatric development of this novel agent in pediatric solid tumors.
Authors' Disclosures of Potential Conflicts of Interest
The authors indicated no potential conflicts of interest.
Footnotes
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Supported by National Cancer Institute grant No. U01 CA97552 and National Center for Research Resources grant No. M01 RR00188-37.
Authors' disclosures of potential conflicts of interest are found at the end of this article.
- Received December 26, 2003.
- Accepted September 22, 2004.
