A phase 2 study of pegylated interferon α-2b (PEG-Intron®) in children with diffuse intrinsic pontine glioma

Authors


Abstract

BACKGROUND:

Interferon-α is a cytokine that has demonstrated activity in patients with supratentorial gliomas, but its ideal dose and schedule of administration is unknown. Studies suggest that low-dose, continuous exposure is more efficacious than intermittent, high doses. The authors performed a phase 2 study of recombinant interferon α-2b with monomethoxy polyethylene glycol (PEG-Intron®) in children with diffuse intrinsic pontine glioma (DIPG), a population with dismal survival despite decades of clinical investigation. The primary objective was to compare 2-year survival with a historic cohort that received radiation therapy alone.

METHODS:

Patients received weekly subcutaneous PEG-Intron® at a dose of 0.3 μg/kg beginning 2 to 10 weeks after the completion of radiation therapy until they developed disease progression. Patients were evaluated clinically and radiographically at regular intervals. Serum and urine were assayed for biomarkers before each cycle. Quality-of-life (QOL) evaluations were administered at baseline and before every other cycle of therapy to the parents of patients ages 6 to 18 years.

RESULTS:

Thirty-two patients (median age, 5.3 years; range, 1.8-14.8 years) were enrolled and received a median of 7 cycles of therapy (range, from 1 cycle to ≥70 cycles). PEG-Intron® was well tolerated, and no decrease in QOL scores was noted in the subset of patients tested. The 2-year survival rate was 14%, which was not significantly improved compared with the historic cohort. However, the median time to progression was 7.8 months, which compared favorably with recent trials reporting a time to progression of 5 months in a similar population.

CONCLUSIONS:

Although low-dose PEG-Intron® therapy did not significantly improve 2-year survival in children with DIPG compared with an historic control population, it did delay the time to progression. Cancer 2012;3607–3613. © 2011 American Cancer Society.

INTRODUCTION

Diffuse intrinsic pontine gliomas (DIPG) account for up to 80% of brainstem tumors in the pediatric population,1 and an estimated 300 children are diagnosed in the United States each year. Because of the tenuous location of these tumors, surgical resection is not possible, and the mainstay of treatment is radiation therapy. The majority of patients (approximately 75%) initially will improve clinically with radiation therapy, but tumor control is short-lived. Adjuvant chemotherapy has not significantly improved outcomes. Recent Pediatric Brain Tumor Consortium (PBTC) trials2, 3 have demonstrated an expected median progression-free survival (PFS) of <5 months in a homogeneously defined population of children with DIPG (personal communication, James Boyett). Two most recent national consortia trials (Children's Oncology Group trial COG ACNS0126 and Children's Cancer Group trial CCG-9941) reported mean (±standard deviation) 1-year overall survival (OS) rates of 40% ± 6.5% and 32% ± 6%, respectively,4 confirming the absence of progress in improving outcome and emphasizing the need for new approaches to therapy.

The interferons (IFNs) are a family of glycoproteins with antiproliferative, antiviral, and immune-modulating effects.5-7 Clinical studies using α, β, and γ IFNs in patients with malignant brain tumors, including brainstem gliomas, have been performed with reported response rates of up to 40%.8-10 Despite the various clinical studies performed using IFNs, the ideal route of administration, schedule, and dose necessary to produce maximum antitumor effects remain unknown. IFN traditionally has been administered intravenously at high doses (≥3,000,000 U/m2, 2-3 times weekly), but significant side effects, including neurotoxicity, have limited its use.8 In a follow-up study of pediatric patients with brainstem glioma who received intravenous recombinant β-IFN during hyperfractionated radiation therapy, 13 of 32 patients (41%) required dose modifications because of hepatic or hematologic toxicity.11

A recent in vitro study compared high-dose administration versus frequent low-dose administration of IFN-α-2a.12 Frequent low-dose administration produced more significant inhibition of angiogenesis-regulating genes, tumor vascularization, and tumor growth compared with the higher intermittent dose schedule.12 These effects were lost at higher doses, suggesting that metronomic administration of IFNs may have a more robust antitumor effect.

A covalent conjugate of recombinant IFN α-2b with monomethoxy polyethylene glycol (PEG-Intron®) has received approval from the US Food and Drug Administration (FDA) for use in patients with hepatitis C at a dose of 1 μg/kg per week. Pegylation increases the biologic half-life of the compound, enabling once weekly administration and reducing the peaks and troughs in IFN α-2b blood levels. Maximum serum concentrations of PEG-Intron® occur between 15 and 44 hours after dosing and are sustained for up to 72 hours.13

We performed a study administering weekly dosing of PEG-Intron® as a means of establishing continuous low-dose levels of IFN in children with DIPG. The dose selected was the human equivalent of the IFN α2a dose with greatest observed antitumor activity used in the study by Slaton et al.12 Our primary objectives were to determine its tolerability and to compare the 2-year survival of children with DIPG who received weekly low-dose PEG-Intron® after standard radiation therapy versus historic controls who received radiation therapy alone. Secondary objectives of this trial included determination of the time to progression, exploration of potential biomarkers, and evaluation of quality of life.

MATERIALS AND METHODS

Patient Eligibility

Patients aged ≤21 years with a DIPG who received radiation only and no prior chemotherapy or radiosensitizers were eligible. For this study, DIPG was defined as a diffuse intrinsic tumor on magnetic resonance imaging (MRI) with the epicenter presumed to be in the pons, a signal abnormality involving ≥50% of the pons on the T2-weighted sequence at diagnosis, involvement of the ventral pons, and no primary exophytic component. Patients with known or suspected neurofibromatosis type 1 were excluded. Eligible patients had an Eastern Cooperative Oncology Group performance status ≤3; adequate hematologic function defined as an absolute neutrophil count >1000/mm3, hemoglobin >8 g/dL, and platelet count >100,000/mm3; adequate renal function defined as a normal, age-adjusted creatinine level or creatinine clearance ≥60 mL/minute/1.73 m2; and adequate hepatic function defined as a total bilirubin level ≤2.0 times the upper limit of normal, direct bilirubin within normal limits, and an alanine aminotransferase level <2.5 times the upper limit of normal. Patients had to be on a stable or decreasing dose of steroids for ≥1 week before study entry. The study was approved by the Institutional Review Board, and continuing approval was maintained throughout the study. All patients or their legal guardians signed a document of informed consent, and verbal assent was obtained from patients when appropriate.

Study Design

Treatment with PEG-Intron® was initiated 2 to 10 weeks after completion of radiation therapy. Each cycle of therapy consisted of 0.3 μg/kg PEG-Intron® administered subcutaneously weekly for 4 weeks. Initially, patients were instructed to receive premedication with acetaminophen or ibuprofen, but this was omitted later because of an absence of PEG-Intron® side effects. Treatment with PEG-Intron® continued until patients developed unacceptable toxicity or disease progression. Disease progression was defined radiographically as the presence of new areas of tumor or an increase ≥25% in tumor size, defined clinically as worsening neurologic symptoms despite an increase in steroids, or worsening neurologic symptoms with any increase in tumor size. Attempts were made using proton spectroscopy, fluorodeoxyglucose-positron emission tomography imaging, and steroid trials to distinguish radiation necrosis from tumor progression in children with worsening neurologic symptoms and debatable findings on MRI.

Dosing of PEG-Intron® was held for any grade 3 or 4 nonhematologic toxicity probably or definitely attributed to PEG-Intron®, with the exception of fever, myalgias, arthralgias, and rigors. If a toxicity did not return to grade ≤1 within 14 days, then PEG-Intron® was discontinued. If the toxicity returned to grade ≤1 within 14 days, then the patient was permitted to restart PEG-Intron® at 50% of the dose (ie, 0.15 μg/kg once weekly) and to remain at that dose. If the toxicity recurred and was attributable to PEG-Intron®, then no further PEG-Intron® was given. Patients who had hematologic toxicity defined as an absolute neutrophil count <500 for ≥5 consecutive days or who required platelet transfusions on >2 days of any 1 cycle for platelet counts <50,000/μL discontinued PEG-Intron® therapy. Patients who discontinued PEG-Intron® therapy remained on study for endpoint analysis only.

Patient Evaluation

Patients received a monthly physical examination, including a detailed neurologic examination. A complete blood count, electrolytes, blood urea nitrogen, creatinine, serum total bilirubin, and alanine aminotransferase levels were obtained at baseline and weekly during the first cycle. If no laboratory toxicity grade >1 was observed during the first cycle, then a complete blood count was performed every 2 weeks on subsequent cycles and as clinically indicated.

Prothrombin time, partial thromboplastin time, calcium, phosphorous, magnesium, uric acid, and urinalysis were evaluated before each cycle and as clinically indicated. Serum and urine were assayed for both basic fibroblast factor (bFGF) and vascular endothelial growth factor (VEGF) levels before the start of each new cycle (ie, every 28 days). Parents of children ages 6 to 18 years with DIPG completed the Impact of Pediatric Illness (IPI) Scale14 to assess quality of life (QOL) at baseline and every other cycle. This scale measures 4 domains: daily activities, medical/physical status, emotional functioning, and cognitive problems. Items are rated on a 5-point Likert scale, and higher scores indicate better QOL.

Radiographic Response Assessment

Standard MRI scans to determine disease status were obtained before cycles 1, 2, 3, 5, and 7, every other month thereafter, and when clinically indicated. Brain MRI scans included proton nuclear magnetic resonance spectroscopy, and diffusion-weighted, dynamic-enhanced, and dynamic susceptibility MR sequences when possible.

Biomarker Analysis

Patient specimens were collected and immediately stored at −80°C until assayed. Samples were thawed on wet ice 3 hours before assay. Serum/urine bFGF-1 and matrix metalloproteinase 9 (MMP-9) enzyme-linked immunosorbent assays (ELISAs) were completed according to manufacturer protocols (R&D Systems, Minneapolis, Minn). Samples were plated onto 96-well plates in duplicate, and conjugated secondary antibody was added. The substrate solution (H202/tetramethylbenzidine) was then administered for 30 minutes, and the reaction subsequently was quenched with sulfuric acid. Plates were read at an absorbance of 450 nm on a Victor 3 plate reader (Perkin Elmer, Boston, Mass). The extrapolated absorbance was analyzed using Masterplex Readerfit ELISA software (Hitachi, Waltham, Mass), and the concentration was determined following a 4 Parameter Logistic curve fit according to the manufacturer's recommendation. VEGF levels in serum and urine specimens were measured using an electrochemiluminescent immunoassay according to the manufacturer protocol (Meso Scale Discovery, Gaithersburg, Md). Samples were assayed in 96-well plates, incubated with antihuman-VEGF antibody, and read with an MSD Sector imager (Meso Scale Discovery). Concentrations were determined using a 4 Parameter Logistic curve fit. Urinary biomarker values were normalized for creatinine levels obtained using the Bayer DCA 2000+ Analyzer (Bayer Healthcare, Elkhart, Ind) according to manufacturer's instructions.

Statistical Analysis

The primary objective of this trial was to compare the survival of patients who received radiation therapy followed by PEG-Intron® versus an historic cohort of patients who received radiation alone. On the basis of a literature review from 1980 to 2000, the median survival for children who received radiation therapy only was approximately 11 months, and the 2-year survival rate was <20%.15-17 A 1-tailed exact binomial test of p = 0.2 at the 0.1 significance level was used for analysis. With a sample size of 32 patients, the power to distinguish a 2-year survival rate of 40% (H1) from the historic control rate of 20% (H0) was 88%. OS was measured from the date of diagnosis to the date of death. Analyses of toxicity and tolerability were descriptive.

Evaluations for the secondary objectives were planned for all patients, although neuropsychological testing was not performed if the patient was ill. Total mean parent IPI Scale scores were compared from baseline to precycle 3 using repeated-measures analyses of variance.

RESULTS

Patients

Patient characteristics are listed in Table 1. Thirty-two patients were enrolled and evaluable for the primary study endpoint. The median patient age at study entry was 5.3 years (range, 1.8-14.8 years), and 3 patients were aged ≤3 years at diagnosis. The majority of patients began radiation within 6 weeks of becoming symptomatic; 1 patient who was diagnosed with DIPG as an incidental finding deferred radiation therapy for 5 months, at which time she was symptomatic. Another patient had an abnormal MRI scan with a “lacy signal abnormality” in the pons 3.5 years before enrolling on study; his symptoms at that time were headaches and vertigo. Because the radiographic and clinical features were atypical for DIPG, he was not treated at the time and was followed by imaging. His tumor progressed 3.5 years later both clinically and radiographically, evolving into a typical radiographic appearance for DIPG. He began radiation therapy within 1 month of progression.

Table 1. Patient Characteristics, n = 32
CharacteristicNo. of Patients
  1. Abbreviations: ECOG PS, Eastern Cooperative Oncology Group performance status; Gy, grays; XRT, external-beam radiation therapy.

Age at diagnosis: Median (range), y5.3 (1.8-14.8)
Males:females13:19
Radiation dose: Median (range), Gy54.7 (50.4-67.2)
Response to XRT, tumor size 
 Stable/decreased26
 Increased6
Steroids at study entry18
ECOG PS at study entry: Median (range)1 (0-3)

Overall, the median time from end of radiation to enrollment on protocol was 38 days (range, 15-64 days). Six patients had an increase in tumor size between diagnosis and their first postradiation scan, before starting PEG-Intron®. Eighteen patients remained on steroids at the time they started PEG-Intron®.

Toxicity

PEG-Intron® therapy was clinically well tolerated. Initially, parents were instructed to administer acetaminophen and ibuprofen before and for 24 hours after the administration of PEG-Intron®. This was amended later to administer as needed, as most families were not administering acetaminophen or ibuprofen because of the lack of PEG-Intron® toxicity. There were no grade 4 toxicities attributed to PEG-Intron®. Twenty episodes of grade 3 toxicities at least possibly attributed to PEG-Intron® therapy were reported, including asymptomatic laboratory abnormalities (neutropenia, n = 11; leukopenia, n = 1; lymphopenia, n = 2; and elevated alanine aminotransferase, n = 1), fever (n = 1), cranial neuropathy (n = 2), and seizure (n = 1). No patient discontinued PEG-Intron® for toxicity.

Response

The overall 2-year survival rate from diagnosis was 14.3%. Characteristics of the patients who survived for at least 2 years from diagnosis are listed in Table 2. Two patients remain on study for endpoint analysis; 1 patient recently progressed after receiving >70 cycles of PEG-Intron®. The median time to progression from diagnosis was 235 days, and the median OS from diagnosis was 351 days. The Kaplan-Meier OS estimate (±standard error) at 1-year was 0.4643 ± 0.0918 (Figure 1). With the 2 outlying patients (ie, those who delayed the start of radiation) excluded, the median time to progression was 231 days, the median OS remained 351 days, and the Kaplan-Meier OS estimate (±standard error) at 1-year was 0.425 ± 0.095.

Figure 1.

The Kaplan-Meier estimate (±standard error) of overall survival (OS) at 1 year was 0.4643 ± 0.0918. PFS indicates progression-free survival.

Table 2. Characteristics of the Patients who Remained Alive >2 Years After Diagnosis
PatientAge at Diagnosis, yStatus
  1. Abbreviations: DIPG, diffuse intrinsic pontine glioma; DOD, dead of disease; MRI, magnetic resonance imaging; PEG-Intron®, pegylated interferon alfa-2b; XRT, external-beam radiation therapy.

13.7DOD at 2.1 y
22.6Alive with new enhancing lesion >5 years after enrollment on study (70+ cycles of PEG-Intron®)
37.0Abnormal MRI with a questionable DIPG diagnosis >3 y before the study; tumor subsequently progressed and appeared as “typical” DIPG radiographically and clinically; patient DOD 17 mo after beginning treatment for DIPG
45.0Alive with disease; XRT was delayed for 5 mo after diagnosis

Biomarkers

Serial serum and urine samples were available for 27 patients. We used a stepwise threshold analysis to evaluate whether biomarkers could be used as markers of treatment futility. Because VEGF and bFGF are 2 presumptive effector molecules for IFN α-2b therapy, we initially used a threshold of 2.2 pg/mg for normalized urinary VEGF and 6.0 pg/mL for serum bFGF. By using these thresholds, 17 patients had VEGF values >2.2 pg/mg and bFGF values >6.0 pg/mL, and each of these patients progressed before 2 years. In the remaining 10 patients, using a threshold for serum MMP-9 of 5 ng/mL after the first cycle of therapy, 4 additional patients failed within 2 years. Of the remaining 6 patients, those 4 patients with a low initial VEGF and bFGF values and a nonrising MMP-9 value survived for >2 years.

Quality-of-Life Analysis

Of the 32 children enrolled, 11 were in the age range for the IPI Scale and received a baseline QOL assessment. Of these patients, 3 were not evaluated before cycle 3 because of scheduling issues, and 1 discontinued PEG-Intron® because of progressive disease; therefore, precycle 3 evaluations were completed on 7 patients. The mean age of these patients at baseline was 9.4 years (range, 7.5-12.3 years). Total mean scores improved significantly from baseline to the precycle 3 assessment (baseline, from 3.59 to 3.89 [precycle 3]; F = 6.51; p = .0434), suggesting an early improvement in QOL over the first 2 months of the study. Four patients had an improvement in their mean total score (scores increased by ≥0.5 standard deviation), 3 had stable scores, and none of the 7 patients' mean total scores declined by ≥0.5 standard deviation.

DISCUSSION

Although IFNs have several effects on the growth and proliferation of cells and have demonstrated variable activity against gliomas in clinical trials, the ideal dose, schedule, and type of IFN for antiglioma activity have not been identified. In the current clinical trial evaluating continuous, low-dose exposure of IFN α-2b in children with DIPG, our results indicate that PEG-Intron® administered as monotherapy after radiation therapy was not effective in significantly improving 2-year survival compared with our defined historic cohort of children who received radiation only. However, compared with more recent trials that had a similarly defined patient populations, our results suggest that the time to progression may be prolonged.

The historic control cohort initially defined in this protocol was based on a literature review that spanned the period when routine use of MRI scans was increasing and when subsets of brainstem gliomas were being defined.17 Although brainstem tumors are now recognized as a heterogeneous group of tumors with some subsets, such as focal or primary exophytic, that have superior outcomes compared with diffuse intrinsic lesions,18 many clinical trials performed within the historic period did not distinguish these tumors. Consequently, the median survival and the OS of the historic cohort may be erroneously high. Our results compare favorably with more recent clinical studies of defined DIPG populations, including the ACNS0126 trial, which reported a 2-year OS rate of 3.6% ± 2.5%,4 and the series of recent PBTC clinical trials, in which the estimated time to progression from diagnosis was <5 months. Two patients had a somewhat atypical course, in that they delayed radiation therapy after initial diagnosis, as indicated in Table 2. However, those patients met criteria for the diagnosis of DIPG and, at the time they began radiation therapy, followed a typical course. One of these patients died of disease 17 months after beginning radiation therapy for DIPG. The other remained alive 34 months after radiation therapy but had progressive disease identified <2 years from diagnosis. This suggests that, although the preradiation course was prolonged, once the patients required standard treatment for their DIPG, they followed a more typical course.

The current study highlights the difficulties and limitations of performing clinical trials in children with DIPG. In addition to a limited historic cohort, several restrictions exist, including the lack of a tissue diagnosis and absence of a standard definition of progression. The small number of patients makes it difficult to complete trials quickly and to detect modest improvements in outcome. Evaluating response to therapy for patients with brain tumors, particularly DIPG, also is challenging, because MRI cannot clearly distinguish tumor progression from the effects of treatment. This is made even more complicated when evaluating noncytotoxic agents, including those with an unclear or multipronged mechanism of action, such as the IFNs.

The antitumor mechanism of action of IFNs is not fully understood. The IFNs are involved in the control of cell function and replication. The type I IFNs, IFN-α and IFN-β, are negative regulators of cell growth and can modify cell differentiation.19 They inhibit mitotic activity, block transition from the G0/G1 phase into the S phase of the cell cycle, and suppress expression of receptors for certain growth factors.20-23 They down-regulate the expression of proangiogenic molecules including, bFGF, interleukin 8, MMP-2 and MMP-912;and chronic systemic administration has produced regression of vascular tumors.24-26 The type I IFNs also play a role in tumor immunosurveillance.27 Impaired IFN-α production has been associated with an increased risk of cancer and an increased rate of tumor growth in mouse glioma models.28

To date, no blood or tissue biomarker has been identified that reliably predicts response to treatment or reflects response to antiangiogenic agents, although several potential candidates are under investigation. Evaluations of blood and urine markers rather than tissue markers are more appropriate for the DIPG population because of the inability to sample tumor tissue. VEGF, bFGF, and MMPs have demonstrated prognostic value in different tumor types.29 It was reported previously that urinary VEGF levels are predictive of outcome in cancer patients who receive radiation therapy,30 and bFGF levels in urine have been correlated with disease status in cancer patients.31 IFN α-2b inhibits angiogenic factor expression by decreasing production.32 An intriguing finding in our current study was the use of early biomarkers to identify long-term survivors. Although the number of patients was small, 4 of 6 patients who had low urine VEGF, low serum bFGF levels, and a nonrising MMP-9 level survived for ≥2 years; whereas no patient with a high urine VEGF level, a high serum bFGF level, or a rising MMP-9 level was a long-term survivor. Thus, a combination of biomarkers may be useful in identifying patients who may respond to IFN α-2b therapy.

The current clinical trial demonstrates the tolerability of PEG-Intron® in this patient population. This was not unexpected, because we used a dose much lower than the FDA-approved dose of PEG-Intron®. Although the QOL results should be interpreted with caution because of the limited number of patients evaluated, and although improved QOL scores may be related at least in part to symptomatic improvement from radiation therapy, a detrimental effect on QOL was not observed in any patient assessed. This is in marked contrast to prior studies of IFNs that demonstrated significant toxicities, resulting in dose reduction or discontinuation.10, 11, 33

In conclusion, this study demonstrates that PEG-Intron® administered to children with DIPG after radiation therapy does not improve 2-year OS compared with an historic control population. However, patients on this study had prolonged time to progression compared with a contemporary, similarly defined population, and no significant adverse effect on QOL was observed in the small number of patients evaluated. Thus, PEG-Intron® may not be adequate as monotherapy, but its use in combination studies may be appropriate.

FUNDING SOURCES

This research was supported by the Intramural Research Program of the National Institutes of Health, National Cancer Institute, Center for Cancer Research.

CONFLICT OF INTEREST DISCLOSURES

The authors made no disclosures.

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