Multicenter Phase II trial of high-dose imatinib mesylate in metastatic melanoma

Significant toxicity with no clinical efficacy

Authors

  • Ken Wyman M.D.,

    1. Division of Hematology/Oncology, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, Tennessee
    Search for more papers by this author
  • Michael B. Atkins M.D.,

    1. Beth Israel Deaconess Medical Center, Harvard Medical School, Division of Hematology/Oncology, Harvard Cancer Center, Cambridge, Massachusetts
    Search for more papers by this author
  • Victor Prieto M.D.,

    1. Department of Pathology, University of Texas M. D. Anderson Cancer Center, Houston, Texas
    Search for more papers by this author
  • Omar Eton M.D.,

    1. Melanoma Department, University of Texas M. D. Anderson Cancer Center, Houston, Texas
    Search for more papers by this author
  • David F. McDermott M.D.,

    1. Beth Israel Deaconess Medical Center, Harvard Medical School, Division of Hematology/Oncology, Harvard Cancer Center, Cambridge, Massachusetts
    Search for more papers by this author
  • Francie Hubbard R.N.,

    1. Division of Hematology/Oncology, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, Tennessee
    Search for more papers by this author
  • Christine Byrnes R.N.,

    1. Beth Israel Deaconess Medical Center, Harvard Medical School, Division of Hematology/Oncology, Harvard Cancer Center, Cambridge, Massachusetts
    Search for more papers by this author
  • Kathleen Sanders M.B.A.,

    1. Division of Hematology/Oncology, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, Tennessee
    Search for more papers by this author
  • Jeffrey A. Sosman M.D.

    Corresponding author
    1. Division of Hematology/Oncology, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, Tennessee
    • Division of Hematology/Oncology, Vanderbilt-Ingram Cancer Center, 777 Preston Research Building, Nashville, TN 37232
    Search for more papers by this author
    • Fax: (615) 343-7602


  • Presented in part as a poster (abstract 2865) at the Annual Meeting of the American Society of Clinical Oncology; Chicago, Illinois, May 31–June 3, 2003.

Abstract

BACKGROUND

Systemic treatment of metastatic melanoma is largely ineffective and alternative approaches are needed. Imatinib mesylate is an oral tyrosine kinase inhibitor that targets bcr-Abl, c-kit, platelet-derived growth factor receptor (PDGFR)-α, and PDGFR-β, leading to remarkable clinical responses in several cancers. Signal transduction via c-kit, PDGFR-α, and PDGFR-β has been demonstrated in malignant melanoma.

METHODS

The primary objective of this Phase II study was to determine the response rate, response duration, and the frequency of 6-month progression-free survival in patients who could receive up to 2 prior therapeutic regimens. Initially, patients received imatinib at at dose of 400 mg twice orally each day. Based on Simon's optimal design, the study allowed entry of 21 patients; if there were ≥ 2 objective responses, accrual would then continue to a total of 41 patients.

RESULTS

Twenty-six patients were enrolled. Patients experienced 29 episodes of Grade 3 and 2 episodes of Grade 4 toxicity (according to National Cancer Institute common toxicity criteria). No objective clinical responses were noted among the 25 evaluable patients. The median time to progression was 54 days and the median overall survival was 200 days. No patient was free of disease progression at 6 months. Paraffin-embedded tumor specimens from 15 patients were tested for expression of imatinib responsive kinases by immunohistochemistry. Three tumors had moderate and 5 tumors had weak staining for c-kit. Five tumor samples had weak staining for PDGFR-α and -β.

CONCLUSIONS

Imatinib is an inactive single agent in metastatic melanoma in a population of predominately pretreated patients. The levels of c-kit and/or PDGFR-α, -β expression in the current study were lower than previously reported. Alternative treatment strategies remain a priority for patients with advanced melanoma. Cancer 2006. © 2006 American Cancer Society.

Metastatic melanoma has a dismal prognosis, with a median survival of 6-10 months.1 Despite objective responses with conventional single-agent chemotherapy, combination chemotherapy, immunotherapy, or combination biochemotherapy, no improvement in overall survival (OS) has been shown compared with single-agent dacarbazine.2 Single-agent dacarbazine remains a very poor standard. Given the ineffectiveness of conventional therapies, a critical need exists for novel therapeutic strategies in patients with advanced melanoma. The successful targeting of signaling pathways has led to advances in the treatment of several cancers. Targeting cell signaling pathways important to malignant transformation and progression is an attractive avenue to explore for patients with melanoma.

Activated intracellular signaling pathways have been identified and characterized for a number of malignancies. When activated, these pathways can lead to uncontrolled proliferation or can inhibit apoptotic cell death. To our knowledge, imatinib is the first example of a tyrosine kinase inhibitor that blocks relevant oncogenic pathways, resulting in dramatic and durable clinical responses. Its activity against the bcr-abl, c-kit, platelet–derived growth factor receptor (PDGFR)-α, and -β tyrosine kinases all have been critical to the clinical responses observed in chronic myelogenous leukemia, gastrointestinal stromal tumors (GISTs), or several other more rare tumors.3–5 C-kit is a receptor for the ligand stem cell factor (c-kit ligand) and can be found on the surface of a number of malignancies, including melanoma.6 The presence and functional activity of both the receptor and ligand in melanoma are evidence to support this trial, even if relatively weak.7 C-kit and stem cell factor (SCF) play an important role in the development of melanocytes.8–10 Injections of recombinant human SCF subcutaneously, as reported in a Phase I study, revealed a striking cutaneous hyperpigmentation at the site of the injection.11 In addition, MITF (micropthalmia-associated transcription factor) expression is induced by stimulation of the c-kit receptor and subsequently linked downstream to expression of the antiapoptotic protein BCL2.12 Fisher and colleagues13 have shown that MITF, the melanocyte master regulator, may play an important role in melanoma pathogenesis, likely by acting as a lineage-specific oncogene. MITF is amplified in some cases of melanoma and associated with a worse prognosis.13 Some studies have associated the loss of c-kit expression with progression of melanoma, but to our knowledge, this finding has been inconsistent.14

Melanocytes and melanoma cells express a number of protein tyrosine kinases, including c-kit, PDGFR-α, PDGFR-β, c-abl, and possibly abelson-related gene (ARG)—all of which are targets of imatinib.15 Melanoma expression of PDGF and its receptor has been confirmed in studies of tumor tissue specimens and melanoma-derived cell lines. With cell surface expression of c-kit, PDGFR-α, or PDGFR-β noted in melanoma, the inhibition of c-kit or PDGFR signaling may be a clinically effective strategy for therapy. We conducted a Phase II study to determine the clinical efficacy and toxicity of high-dose imatinib mesylate and to examine the levels of expression of c-kit, PDGFR-α, -β, c-abl, and ARG on melanoma tissues previously obtained from patients enrolled in the trial. High-dose imatinib (800 mg/day) was chosen on the basis of suggested improved efficacy in other malignancies at higher doses.16, 17

MATERIALS AND METHODS

Eligibility Criteria

Patients aged 16 years and older with histologically confirmed measurable, metastatic melanoma were eligible to participate in this study. All eligible patients provided written informed consent approved by the Institutional Review Board at each participating facility (Vanderbilt Medical Center and Beth Israel Deaconess Medical Center). Patients were not required to have tumor that expressed either c-kit, PDGFR-α or PDGFR-β, c-abl, or ARG18 to be eligible for trial entry. Examination of available fixed or frozen tumor tissue samples was undertaken whenever possible to better define the on-study expression of c-kit and other protein tyrosine kinases in metastatic melanoma and the relation to clinical outcome. Patients may have been treated with interferon as adjuvant therapy and up to 2 prior systemic therapies for advanced disease. The extent of allowed prior therapy was due to availability of other trials as a priority in melanoma patients at the institution while this study was open. Other eligibility criteria included an Eastern Cooperative Oncology Group (ECOG) performance status (PS) ≤1 and adequate end-organ function. Patients were ineligible to participate in the study if they had other significant uncontrolled medical problems or active central nervous system metastases. Patients with prior resected brain metastases were eligible.

Treatment Plan and Evaluation

Before study entry, patients underwent complete medical history and physical examination and radiologic assessment to determine extent of disease. Complete blood count (CBC), comprehensive metabolic profile (CMP), lactate dehydrogenase (LDH), urinalysis, urine pregnancy test for women of childbearing age, electrocardiogram, and chest radiographs were obtained within 14 days of study entry. Computed tomography scans of the chest, abdomen, and pelvis was obtained within 28 days and magnetic resonance imaging of the brain was obtained within 42 days of study entry. All patients determined to have a tumor biopsy within the 12 months prior to enrollment had paraffin-embedded, unstained slides of tumor tissue submitted for immunohistochemical assessment of c-kit, bcr-abl, PDGFR-α and PDGFR-β, and ARG expression.

Patients received imatinib at a dose of 400 mg twice daily by mouth. Patients were instructed to take imatinib with meals and to consume a large (250 mL) glass of water to minimize gastrointestinal irritation. Patients were required to keep a diary of pill usage. Physician visits were required at 2-week intervals through Week 24 with physical examination, ECOG PS, CBC, CMP, and LDH examined at each visit. Formal toxicity assessments occurred initially at 4-week intervals; side effects were graded according to the National Cancer Institute Common Toxicity Criteria (version 2.0). More frequent toxicity assessments were performed as the high rate of side effects became apparent.

Imatinib was held for any Grade 3/4 toxicity until the toxicity resolved to ≤Grade 1. The subsequent daily dose was reduced by 200 mg. Imatinib was discontinued and the patient was removed from the study if Grade 3/4 toxicities occurred after 2 previous dose reductions. Criteria for patient removal from the study included progression of disease or unacceptable toxicity. Patients were assessed for tumor response at 8-week intervals. The standard Response Evaluation Criteria in Solid Tumours (RECIST) criteria for responses were utilized.19

Antibodies and Immunohistochemical Analysis

Routine immunohistochemical staining protocols were used to detect expression of c-kit, c-abl, ARG, PDGFR-α, and PDGFR-β.15 The antibody against c-kit was purchased from Dako Corporation (Carpinteria, CA); the antibodies against PDGFR-α, PDGFR-β, c-abl, and ARG were obtained from Santa Cruz Biotechnology (Santa Cruz, CA). All antibodies had previously been validated. Antigen retrieval was as follows: treatment with pepsin at 37°C for 10 minutes for PDGFR-α and PDGFR-β; microwave treatment for 5 minutes for c-kit; and no antigen retrieval for c-abl or ARG. Diaminobenzidine was used as a chromogen with light hematoxylin as the counterstain. The percentage of positive cells and the intensity of staining were recorded in a semiquantitative scale; results were categorized as negative (<25% cell labeling) or positive (>25% cell labeling). The staining intensity was categorized into negative (−), weak (+), moderate (++), or strong (+++). In all specimens, normal structures were labeled with each antibody (mast cells with anti-c-kit, endothelial cells with anti-abl, anti-ARG, and anti-PDGFR-α and anti-PDGFR-β). These acted as internal positive controls.

Statistical Analysis

The primary objective of this multicenter, Phase II study of imatinib given at a dose of 800 mg/day in patients with advanced melanoma was to determine the overall response rate, response duration, and the number of patients who were free of disease progression at 6 months. Secondary endpoints included overall clinical safety and tolerability of high-dose imatinib. A 2-stage accrual design as described by Simon20 was utilized to ensure that the number of patients exposed to an ineffective experimental drug was minimized. The study was designed to allow further testing of imatinib if there was evidence of a >20% overall response rate (complete response [CR] or partial response [PR]). The design of the study allowed entry of 21 eligible and evaluable patients with termination of the study if there was ≤1 response noted among the first 21 patients. However, if there were ≥2 responses or ≥3 patients who had a 6-month progression-free interval, then accrual would continue to a total of 41 patients. The study design provided 90% statistical power to distinguish between a true objective response rate of <5% versus >20% with a significance level of .05 (type I error) for the objective response rate. The Southwest Oncology Group database of advanced melanoma trials has reported a 6-month progression-free survival (PFS) on Phase II trials of approximately 10% to 15% (unpublished data). The sample size provided at least 90% statistical power to detect a 20% improvement (30% vs. 10%) in the 6-month PFS rate, with a significance level of .05 based on Simon's optimal design.20

RESULTS

Patient Characteristics

A total of 26 patients from the 2 participating institutions were entered onto the trial between April 2002, and November 2002. Accrual was extended beyond 21 patients due to the high rate of early discontinuation and a potential for a number of inevaluable patients without an adequate duration of therapy. Demographic and baseline patient characteristics are listed in Table 1. The median age was 59 years (range, 37-82 yrs). The majority of patients had cutaneous primary tumors (23 of 26 patients; 88%), whereas 3 patients (12%) had ocular (2 patients) or mucosal (1 patient) primary tumors. Fourteen patients (54%) had M1c disease, 4 of whom (15%) had an elevated serum LDH level. A total of 8 patients (31%) had received prior adjuvant interferon-alpha. Although 16 patients (62%) had received ≥1 prior treatments for distant metastatic disease, nearly 70% of patients still received < 2 prior systemic treatments. Prior treatment for metastatic disease included chemotherapy, biotherapy, radiotherapy, and biochemotherapy.

Table 1. Patient Characteristics
 No. of Patients Percentage
  • ECOG: Eastern Cooperative Oncology Group; PS: performance status; LDH: lactate dehydrogenase; IFN: interferon.

  • *

    Therapy for AJCC Stage IV disease including both chemotherapy, biologic therapy, or a combination.

Patients26 100
Male15 58
Female11 42
Median age, y (range) 59 (37–82) 
ECOG PS   
011 42
113 50
Not defined2 8
M classification   
M1a3 11
M1b9 35
M1c14 54
Elevated serum LDH4 15
Prior adjuvant IFN8 31
Prior therapy*
010 38
18 31
26 23
32 8

Responses

A total of 18 patients completed the initial 8 weeks of therapy and were evaluable for response at this intended time point. Other patients had their therapy discontinued due to unacceptable toxicity or rapid disease progression. No objective responses (CR or PR) were observed. Stable disease (at 8 weeks) was documented in only 2 patients, with durations of 96 days (3 mos) and 111 days (3.5 mos), respectively. No patient was found to be free of disease progression 6 months after the initiation of treatment. Overall, the median PFS was 2 months and the median OS was 6.5 months (Fig. 1).

Figure 1.

Overall survival of patients receiving imatinib. Overall survival is presented (−) as a Kaplan-Meier curve in months of survival for all 25 patients.

Toxicity

All 26 patients were evaluable for toxicity. A total of 29 episodes of Grade 3 toxicity and 2 episodes of Grade 4 toxicity were documented (Table 2). Gastrointestinal toxicities were the most common, with a total of 5 Grade 3 toxicities, with nausea and emesis being the most common event. Fatigue was present as a Grade 3 toxicity in 4 patients, Grade 3 anemia was noted in 4 patients, and Grade 3 hemorrhage was reported in 2 patients. These toxicities resulted in 13 dose reductions and led to 7 patients being removed from therapy. One patient was lost to follow-up but toxicity data were available during the first week of therapy and the patient was included in the analysis.

Table 2. Frequency of Significant Toxicities
Adverse eventGrade 3*Grade 4*
  • *

    Toxicity was graded according the National Cancer Institute Common Toxicity Criteria (version 2.0).

Fatigue4 
Fluid retention2 
Gastrointestinal5 
Neurologic4 
Pulmonary3 
Thrombosis 1
Hemorrhage2 
Pain2 
Hypotension1 
Anemia4 
Hyperkalemia1 
Hyponatremia 1
Rash1 
Total292

Melanoma Tissue Samples and Immunohistochemical Staining

Seventeen patients had tumor biopsies of metastatic lesions within 12 months prior to enrollment onto trial, allowing for immunohistochemical staining. Two of these tissue specimens were not evaluable due to the absence of tumor or extensive necrosis of tumor cells in the specimen. In all specimens, normal structures were labeled with each antibody (mast cells with anti-c-kit, endothelial cells with anti-abl, anti-ARG, and anti-PDGFR-α and anti-PDGFR-β). These acted as internal positive controls. Of the remaining 15 melanoma samples, none was found to be strongly positive (+++) for any of the panel of imatinib target kinases. Three patients had moderate (++) staining for c-kit and an additional 5 patients had weak (+) staining (Table 3). Weak (+) staining of PDGFR-α and PDGFR-β was observed in 5 patient and 2 patient samples, respectively. All the samples that expressed either PDGFR-α or PDGFR-β expressed some level of c-kit. None of the samples expressed c-abl or ARG. Of the 3 patients who expressed moderate (++) levels of c-kit, 2 were removed from trial before 8 weeks (1 for toxicity and 1 for disease progression).

Table 3. Expression of Imatinib Target Proteins
Tissue specimen*PDGFR-αPDGFR-βc-kit
  • PDGFR: platelet-derived growth factor receptor.

  • *

    The percentage of positive cells and the intensity of staining were recorded in a semiquantitative scale; results of percentage of cells were categorized as negative (<25% cell labeling) or positive (25% cell labeling). The staining intensity was categorized into negative(-), weak (+), moderate(++), or strong (+++). None of the samples expressed c-abl or abelson-related gene (ARG).

1+0+
2000
3+0++
4+0+
5000
6000
7000
800++
9++++
10+++
11000
1200+
1300+
14000
15000

DISCUSSION

In this Phase II study, there was no apparent evidence of the clinical efficacy of high-dose imatinib in patients with metastatic melanoma. Moreover, the use of high-dose imatinib (800 mg/d) was associated with an unexpectedly high number of significant toxicities in this patient population. The choice of dose for this trial was based on a prior study establishing the tolerability and evidence for greater efficacy of imatinib at higher doses.16, 17 The reasons for the frequency of severe toxicities we observed is not clear. Possible explanations include our selection of patients with poor prognostic factors and heavy pretreatment. Lung or other visceral involvement was present in 23 patients (88%), an elevated serum LDH level in 4 patients (15%), and 16 patients (62%) had received ≥1 therapies for metastatic disease before enrollment.

None of the 25 evaluable patients demonstrated either a clinical response to imatinib and no patient remained free of disease progression for 6 months. Although the poor prognosis of the enrolled population could have contributed to this low response rate, the lack of efficacy was most likely due to the lack of activation of the target pathways that were inhibited by this drug in the study population.15 Although imatinib target receptors were reported by Shen et al.15 to be frequently up-regulated in melanoma tissue specimens (32%+ for c-kit, 61%+ for PDGFR-α, and 68%+ for PDGF-β in 31 specimens), none of the samples assayed in this trial demonstrated strong expression of c-kit, PDGFR-α, or PDGFR-β. A critical requirement for effective tyrosine kinase inhibitor therapy is that the target protein must be activated constitutively. Whether this comes from a “gain of function” mutation, a translocation, or an amplification, the gene product must be activated so that the inhibitor can not only bind to it, but also effectively block the ongoing kinase activity.7, 21 It has been known that GIST tumors have high levels of c-kit expression and a strong association exists between specific activating mutations of c-kit with clinical response to imatinib therapy. We now know that many, if not all, of the imatinib-responsive GIST tumors with wild-type c-kit have an activating mutation in one of the PDGFR genes.7 The other clinical situations in which imatinib has shown some clinical efficacy are characterized by a “gain of function” in one of the critical kinases targeted by imatinib. More recently, the clinical responses due to the epidermal growth factor (EGF) tyrosine kinase inhibitor, gefitinib, in nonsmall cell lung cancer has been strongly linked to activating EGF receptor (EGFR) mutations. The simple expression levels of EGFR on lung cancer cells are of little importance to a gefitinib response.22, 23 To our knowlege, there is little evidence to date that c-kit or PDGFRs are mutated proteins that are constitutively activated in melanoma as a general rule. This is likely a critical reason for the lack of clinical efficacy we observed.

C-kit appears to play a different role in the tumorigenesis of melanoma. A loss of expression has been demonstrated by some investigators during the progression of melanoma.14 Whether the loss of c-kit expression is a function of tumorigenesis or merely an epiphenomenon remains to be elucidated. Using a melanoma xenograft model, Bar-Eli and colleagues.24 have demonstrated that, although imatinib can inhibit the PDGFR-α phosphorylation, it does not affect melanoma tumorigenicity in vivo.

Eton et al.25 recently reported the preliminary results of a trial conducted at the M. D. Anderson Cancer Center with imatinib in patients with metastatic melanoma. In this trial, patients were required to express one of the imatinib target proteins by immunohistochemistry. They reported expression of 1 of the target proteins in all 31 patients screened. Of the 21 patients treated with imatinib, 16 had disease progression by 6 weeks and another 4 within 12 weeks. However, 1 patient with strong c-kit expression in greater than 75% of cells had a near–complete response for more than a year. The patient had the c-kit RNA of his melanoma sequenced, which revealed a deletion in codon 715. This deletion in a kinase domain of c-kit had only been reported in colon cancer and not normal tissue of the same patient. However, updated data indicate that this deletion is not present in other tumors from patients who did not respond to imatinib. Therefore, this one case was unique only for its very high c-kit expression.

As disappointing as the results of the current study are, they still can be viewed as an attempt to evaluate “targeted therapy” for melanoma. Whereas both the current study and the one performed at M. D. Anderson Cancer Center demonstrate minimal, if any, antimelanoma clinical activity, it is possible that a benefit may be observed in a selected group of patients who have a mutation of c-kit.25 However, this must be a rare occurrence, because only 1 of the 47 melanoma patients at the 3 institutions demonstrated an objective clinical benefit. A very recent report from Germany also demonstrated a total lack of efficacy with significant toxicity in a Phase II trial of imatinib in patients with melanoma.26 Other molecules within the MAP kinase pathway or other pathways (i.e., Akt/PI-3 kinase) may be constitutively activated in melanoma and provide better therapeutic targets.27, 28 The improved understanding of melanoma biology hopefully will provide additional insights that lead to better and more rational treatment strategies

Ancillary