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Phase II study of single-agent bortezomib for the treatment of patients with fludarabine-refractory B-cell chronic lymphocytic leukemia
Article first published online: 10 JUL 2006
Copyright © 2006 American Cancer Society
Volume 107, Issue 5, pages 916–924, 1 September 2006
How to Cite
Faderl, S., Rai, K., Gribben, J., Byrd, J. C., Flinn, I. W., O'Brien, S., Sheng, S., Esseltine, D.-L. and Keating, M. J. (2006), Phase II study of single-agent bortezomib for the treatment of patients with fludarabine-refractory B-cell chronic lymphocytic leukemia. Cancer, 107: 916–924. doi: 10.1002/cncr.22097
- Issue published online: 21 AUG 2006
- Article first published online: 10 JUL 2006
- Manuscript Accepted: 9 MAY 2006
- Manuscript Revised: 3 MAR 2006
- Manuscript Received: 6 JAN 2006
- Leukemia and Lymphoma Society of America (JCB)
- Chronic Lymphocytic Leukemia (CLL) Research Consortium (CRC)
- The study was sponsored by Millennium Pharmaceuticals, Inc
- chronic lymphocytic leukemia;
- salvage therapy;
- treatment failure
Therapeutic options are limited and the prognosis is poor for patients with fludarabine-refractory B-cell chronic lymphocytic leukemia (CLL). Bortezomib induces apoptosis in vitro in CLL cells, both alone and in combination, including in cells resistant to fludarabine or other agents. The aim of the current randomized, open-label, Phase II study was to investigate the clinical activity of bortezomib in patients with fludarabine-refractory B-cell CLL. Twenty-two patients with histologically confirmed B-cell CLL were treated with bortezomib at doses of 1.0 mg/m2, 1.3 mg/m2, or 1.5 mg/m2 on Days 1, 4, 8, and 11 of a 21-day treatment cycle for a maximum of 9 cycles. None of 19 patients evaluable for response achieved complete remission or partial response; however, signs of biologic activity based on disease site responses (e.g., reduction in lymphocytosis, splenomegaly, and lymphadenopathy) were observed. In the 1.5 mg/m2 dose group, a higher proportion of patients had stable disease, and a lower proportion had progressive disease compared with the 2 lower-dose groups. Eleven patients, all in the 2 higher dose groups, experienced Grade 3/4 adverse events (AEs) (according to National Cancer Institute Common Toxicity Criteria [version 2.0]); 2 patients experienced Grade 4 neutropenia. Grade 3 hematologic AEs included anemia, neutropenia, thrombocytopenia, and hemolytic anemia; Grade 3 nervous system AEs included aphasia; peripheral neuropathy, not otherwise specified; and peripheral sensory neuropathy. Although no objective responses were achieved in patients with fludarabine-refractory B-cell CLL, single-agent bortezomib demonstrated biologic activity. In view of the evidence for its activity, further exploration of bortezomib in combination with other agents is warranted. Cancer 2006. © 2006 American Cancer Society.
Chronic lymphocytic leukemia (CLL) is the most common adult hematologic malignancy in the Western world,1, 2 accounting for 30% of all leukemias in patients age >65 years. CLL is a heterogeneous disease process that translates into variable prognoses, in which overall survival times may range from months to decades.1, 3 Notable changes in establishing the accuracy of prognostic tools, treatment options, and supportive care measures for patients with CLL have occurred over the past 2 decades.1, 4 Although the goals of treatment have traditionally focused on alleviating disease-related symptoms and improving quality of life,4 new insights into the biology of the CLL cell, development of targeted therapies, and the emergence of new treatment concepts are starting to shift the treatment paradigm from palliation toward a curative approach.1, 4, 5
Standard front-line therapy typically consists of chemotherapy, such as alkylating agents (e.g., chlorambucil) or a purine nucleoside analog (e.g., fludarabine), alone or in combination with other agents, such as cyclophosphamide.1, 4, 6–9 Although these therapies yield overall response rates of 80% or higher, complete remission is less frequent and treatment is almost always followed by recurrence and progression.4, 5, 10, 11 More recent experience with fludarabine-based chemotherapy in combination with the monoclonal antibody rituximab indicates that higher clinical and molecular response rates can be achieved using chemoimmunotherapy, although the impact of these regimens on prognosis and overall survival requires further study.11–14 Therapy for relapsed CLL patients continues to be challenging and the prognosis is poor when standard combination chemotherapy is used.5, 15, 16
With response rates hardly exceeding 20% and median survival times of approximately 10 months, prognosis is particularly poor for those patients who have become refractory to treatment with fludarabine-based regimens.1, 17 Alemtuzumab, a humanized monoclonal antibody against the CD52 antigen, has shown encouraging activity as a single agent and in a range of combination regimens in patients with relapsed and refractory CLL, and is the only agent currently approved for the treatment of fludarabine-refractory B-cell CLL.17–23 Other novel agents and combinations have been investigated as salvage therapy, including fludarabine/cyclophosphamide plus oblimersen sodium (Bcl-2 antisense),24 flavopiridol,25–27 and the purine nucleoside analog 2-chlorodeoxyadenosine,28 as has transplantation.22, 29
Bortezomib (Velcade, Millennium Pharmaceuticals, Cambridge, MA, and Johnson & Johnson Pharmaceutical Research & Development, Warren, NJ) is a first-in-class, potent, and reversible inhibitor of the 26S proteasome.30 This proteasome is the final degradative enzyme involved in an important catabolic pathway for many intracellular regulatory proteins, including IκB, the inhibitor protein of the transcription factor NF-κB, the tumor suppressor p53, and the cyclin-dependent kinase inhibitors p21 and p27.31–33 The antineoplastic effect of bortezomib therefore appears to involve several distinct mechanisms, including inhibition of cell growth signaling pathways, induction of apoptosis, and inhibition of cellular adhesion molecule expression.33, 34 Notably, bortezomib induces apoptosis in cells that overexpress Bcl-2 protein,35 a gene that confers unregulated growth and resistance to conventional chemotherapeutics and is particularly relevant to the biology of CLL. In preclinical studies, bortezomib and other proteasome inhibitors, including lactacystin and MG-132, alone or in combination with other agents, have been shown to cause significant apoptosis in CLL cells,36–44 and to sensitize resistant CLL cells to the effects of chemotherapy.36 Bortezomib has also been shown to be active and well tolerated in Phase I, II, and III trials in hematologic malignancies.45–50 The aim of this randomized, open-label, Phase II study was to determine the activity of bortezomib in patients with fludarabine-refractory B-cell CLL.
MATERIALS AND METHODS
Patients age ≥18 years with histologically confirmed B-cell CLL as defined by 1996 National Cancer Institute (NCI)-sponsored Working Group criteria,51 who had received at least 1 course of treatment with a purine analog, and who either experienced recurrence during or within 6 months of, or were intolerant to, this therapy, were enrolled in the study. The main inclusion criteria were: 1) a Karnofsky performance status (KPS) of ≥60%; 2) a life expectancy of ≥3 months; 3) adequate hematologic function (absolute neutrophil count [ANC] ≥1000 cells/μL, platelet count ≥30,000 cells/μL); and 4) adequate renal and hepatic function (total bilirubin ≤2 mg/dL, alanine transaminase [ALT] and aspartate transaminase [AST] ≤2.5 times the upper limit of normal, creatinine clearance ≥30 mL/minute). Patients were excluded if they had: 1) histologically confirmed T-cell CLL or prolymphocytic leukemia; 2) received chemotherapy or major surgery within 4 weeks, or antibody therapy within 8 weeks before study entry; 3) not recovered from all toxic effects of previous chemotherapy or antibody therapy; 4) electrocardiographic evidence of acute ischemia or new conduction system abnormalities; 5) myocardial infarction within 6 months of study entry; 6) known brain metastases or central nervous system disease; or 7) human immunodeficiency virus infection, known active hepatitis B or C, or any uncontrolled intercurrent illness or serious medical or psychiatric condition that could have interfered with treatment.
This randomized, multicenter, open-label, Phase II study was conducted at 5 CLL Research Consortium clinical sites. Patients were assigned randomly in a 1:1 ratio to receive bortezomib at 1 of 2 dose levels. The doses of bortezomib used in the initial 2 treatment groups were 1.0 mg/m2 and 1.3 mg/m2, respectively; the protocol was amended to 1.3 mg/m2 and 1.5 mg/m2, respectively, after 5 patients had received the 1.0 mg/m2 dose. Randomization was stratified on the basis of baseline Rai Stage (0-II versus III-IV)52 and β2-microglobulin (≤2.5 mg/L versus >2.5 mg/L). At all dose levels, a treatment cycle was 21 days in length and comprised 4 bortezomib doses administered via intravenous bolus on Days 1, 4, 8, and 11. As prophylaxis against bacterial and viral infections, patients received concomitant treatment with trimethoprim sulfamethoxazole (1 tablet given twice daily, 3 times weekly) and famciclovir (250 mg twice daily), or accepted substitute(s), from Day 1, Cycle 1, through to the end-of-study visit.
Patients achieving a documented complete response (CR) were to be treated for an additional 3 cycles after confirmed CR, up to a maximum of 9 treatment cycles, and patients achieving a partial response (PR) or stable disease (SD) were to continue in the study for a maximum of 9 treatment cycles. Those who experienced progressive disease (PD) were to discontinue the study drug and be followed biannually for survival until consent withdrawal or death.
Efficacy, Safety, and Other Measurements
The primary objectives of this study were to assess the safety and tolerability of bortezomib and to determine the rate and duration of response (CR and PR), assessed according to the NCI-sponsored Working Group response criteria,51 in patients with CLL. Secondary objectives of the study were to investigate the kinetics of proteasome inhibition in CLL, and to assess whether bortezomib induced apoptosis in vivo and in vitro in CLL cells.
Patients were evaluated at 5 scheduled stages during the study: at screening, while on therapy (Days 1, 4, 8, and 11 of each 21-day treatment cycle), at the end of therapy (10 days after the last dose of bortezomib), at the end of the study (4 weeks after end-of-therapy visit), and long-term follow-up visits. At the screening visit, held within 14 days before administration of the first dose of bortezomib, assessments included: complete physical examination; clinical staging of CLL; disease-related symptoms; body weight and height; KPS; vital signs; complete medical history; blood sample collection for hematology, clinical chemistry, and β2-microglobulin; and bone marrow aspirate and biopsy for cytogenetics, morphology, and immunoglobulin gene rearrangements.
Safety and efficacy evaluations performed during study visits included: assessment of disease-related symptoms; completion of a neurotoxicity questionnaire; symptom-directed physical examination; assessment for enlarged liver, spleen, or lymph nodes; and blood sample collection for hematologic parameters. Adverse events (AEs) and infections, as well as concomitant medication use, were documented. AE intensity was graded according to the NCI Common Toxicity Criteria (NCI CTC; version 2.0). Disease status and response were assessed after each treatment cycle. Patients who were considered to have a CR were to have a bone marrow aspirate and biopsy performed for cytogenetics, morphology, and immunoglobulin gene rearrangements, which was to be repeated after 8 weeks to confirm the CR.
Blood samples for pharmacodynamic evaluation of 20S proteasome activity by a proteasome inhibition assay53 were obtained before and 1 hour after bortezomib dosing on Days 1 and 11 of each treatment cycle.
Approximately 64 patients were to be enrolled in this study and assigned to 1 of the 2 treatment groups. This sample size estimate was based on the calculation of a one-sided 95% confidence interval on the true rate of response to either dose of bortezomib that had a lower bound of at least 10%, given that the observed rate of response was 22.5% or more. The doses in the 2 treatment groups were originally 1.0 mg/m2 and 1.3 mg/m2, but based on preliminary data from the first 9 patients enrolled in the study, 5 of whom received bortezomib at a dose of 1.0 mg/m2, the 1.0 mg/m2 dose group was replaced by the 1.5 mg/m2 dose group.
All descriptive statistical analyses were performed using SAS statistical software (version 8.2; SAS Institute, Inc., Cary, NC). The efficacy and safety conclusions were based on the 1.0 mg/m2, 1.3 mg/m2, and 1.5 mg/m2 dose groups. The primary efficacy variable was response rate (CR and PR). This study was not powered to compare efficacy between treatment groups but rather focused on the estimation of response rates within treatment groups. Safety was evaluated based on the incidence, intensity, and type of treatment-related AEs. Efficacy and safety analyses were performed on all patients who received at least 1 dose of study drug.
Patient Demographics and Disposition
Twenty-five patients were enrolled in the study and 22 were randomly assigned to treatment from June 2001 to January 2003. Patients were initially assigned randomly to the 1.0 mg/m2 and 1.3 mg/m2 dose groups until a protocol amendment (prompted by review of preliminary response and pharmacodynamic data) changed this to randomization between 1.5 mg/m2 and 1.3 mg/m2 dose groups. In total, 9 and 8 patients received the 1.3 mg/m2 and 1.5 mg/m2 doses, respectively. Demographic and baseline characteristics are presented in Table 1. With regard to the randomization strata criteria, the majority of patients had unfavorable prognostic features in terms of β2-microglobulin level and Rai stage, with all but 1 patient (in the 1.5 mg/m2 dose group) having a β2-microglobulin level >2.5 mg/L, and 15 of 22 patients having Rai Stage III-IV disease. Overall, patients received a median of 4.0 (range, 2–11) prior lines of therapy. All patients had received prior chemotherapy including a nucleoside analog, and 13 patients (59%) developed PD during, or disease recurrence within 6 months of, treatment with a course of fludarabine; only 1 patient in the 1.5 mg/m2 dose group had received prior radiation therapy.
|Characteristic||Bortezomib dose group|
|1.0 mg/m2||1.3 mg/m2||1.5 mg/m2||Total|
|(n = 5)||(n = 9)||(n = 8)||(n = 22)|
|Male, n (%)||4 (80)||5 (56)||5 (63)||14 (64)|
|White, n (%)||4 (80)||9 (100)||7 (88)||20 (91)|
|Median age, y (range)||59.0 (55–64)||62.0 (46–74)||67.5 (46–83)||61.5 (46–83)|
|Median KPS, %||90.0||90.0||90.0||90.0|
|Median time from diagnosis of CLL to first dose, y||8.9||5.5||4.8||5.5|
|β2-microglobulin level, n (%)|
|>2.5 mg/L||5 (100)||9 (100)||7 (88)||21 (95)|
|>3.5 mg/L||5 (100)||9 (100)||5 (63)||19 (86)|
|>5.5 mg/L||2 (40)||6 (67)||2 (25)||10 (45)|
|Rai stage, n (%)|
|0-II||1 (20)||3 (33)||3 (38)||7 (32)|
|III-IV||4 (80)||6 (67)||5 (63)||15 (68)|
|Median no. of lines of prior chemotherapy and biotherapy, n (range)||9.0 (3–11)||4.0 (2–9)||3.5 (3–9)||4.0 (2–11)|
|Prior corticosteroids, n (%)||4 (80)||4 (44)||3 (38)||11 (50)|
|Prior alkylating agents, n (%)||5 (100)||8 (89)||6 (75)||19 (86)|
|Prior single-agent nucleoside analog, n (%)||2 (40)||8 (89)||7 (88)||17 (77)|
|Prior antibody therapy, n (%)||5 (100)||7 (78)||5 (63)||17 (77)|
|Prior alkylating agent plus nucleoside analog, or CP, or CVP, n (%)||4 (80)||3 (33)||4 (50)||11 (50)|
|Prior other combination, n (%)||5 (100)||3 (33)||3 (38)||11 (50)|
All patients completed at least 1 bortezomib treatment cycle, with a range of 1 to 6 cycles, and 19 patients completed at least 2 cycles. No patients completed the maximum of 9 cycles. The primary reason for early withdrawal from the study was lack of efficacy/disease progression (14 patients), with unacceptable AEs (4 patients), patient requests (3 patients), and investigator's judgment (1 patient) accounting for the other withdrawals. The mean total dose of bortezomib administered was 23.5 mg, 26.6 mg, and 30.4 mg in the 1.0 mg/m2, 1.3 mg/m2, and 1.5 mg/m2 dose groups, respectively, (overall range, 12.3–59.2 mg). The mean total number of doses was comparable between groups (approximately 11 doses), but the mean total dose administered was not strictly proportional to dose in the 3 dose groups owing to a higher incidence of dose reductions and holds in the higher dose groups. The mean duration of treatment was comparable between groups, at 56.6 days, 52.0 days, and 56.3 days, respectively (overall range, 25–116 days).
Nineteen of the 22 randomized patients were evaluable for response. Two patients, 1 each in the 1.0 mg/m2 and 1.3 mg/m2 groups, had response data (SD) recorded only on the first day of the second cycle, and not at the end of therapy or follow-up visits. One patient in the 1.3 mg/m2 group had no response data recorded. None of the 19 patients had a CR or PR by standard response criteria (Table 2); 25.0%, 28.6%, and 62.5% of patients in the 1.0 mg/m2, 1.3 mg/m2, and 1.5 mg/m2 groups, respectively, achieved SD. However, signs of biologic activity were observed, with ≥50% decreases in absolute lymphocyte count, nodal sites, spleen size, and liver size observed in 23%, 27%, 18%, and 9% of patients, respectively (Table 3). The number of patients was too small, particularly after the third cycle, to evaluate changes from baseline in the levels of β2-microglobulin, C-reactive protein, IL-6, ANC, and immunoglobulins. KPS generally remained stable throughout the treatment period.
|Response||Bortezomib dose group|
|1.0 mg/m2||1.3 mg/m2||1.5 mg/m2|
|(n = 5)||(n = 9)||(n = 8)|
|No. of patients with a response recorded*||4||7||8|
|Stable disease, n (%)||1 (25.0)||2 (28.6)||5 (62.5)|
|Progressive disease, n (%)||3 (75.0)||5 (71.4)||3 (37.5)|
|Disease site||Bortezomib dose group|
|1.0 mg/m2 (n = 5) n (%)||1.3 mg/m2 (n = 9) n (%)||1.5 mg/m2 (n = 8) n (%)||Total (n = 22) n (%)|
|≥50% decrease in ALC||1 (20)||1 (11)||3 (38)||5 (23)|
|≥50% decrease in lymph node sites*||3 (60)||2 (22)||1 (13)||6 (27)|
|≥50% decrease in spleen size||0||2 (22)||2 (25)||4 (18)|
|≥50% decrease in liver size||1 (20)||1 (11)||0||2 (9)|
|Any response at ≥1 disease site||3 (60)||3 (33)||3 (38)||9 (41)|
A total of 17 patients, including 4 patients, 8 patients, and 5 patients in the 1.0 mg/m2, 1.3 mg/m2, and 1.5 mg/m2 groups, respectively, had blood samples taken for determination of 20S proteasome activity. The mean percentage inhibition of 20S proteasome activity relative to baseline by dose group is shown in Figure 1. In general, there was a pattern of dose-related inhibition of 20S proteasome activity at 1 hour after administration of each bortezomib dose, with a return toward baseline activity immediately before administration of the next scheduled dose at which proteasome activity was assessed, as previously noted.45, 54–57
A review of preliminary response and pharmacodynamic data resulted in a protocol amendment to close the 1.0 mg/m2 dose group and add the 1.5 mg/m2 dose group.
All patients except 1 in the 1.5 mg/m2 dose group experienced at least 1 treatment-emergent AE. The most commonly reported AEs, which were generally predictable and manageable, were nausea (41% of patients), headache (27%), and diarrhea, vomiting, dyspnea, and decreased appetite (23% each). Peripheral neuropathy (NOS) was reported in 3 (14%) patients, 1 in each dose group. Eighteen patients experienced an AE that was judged by the investigator to be possibly or probably related to bortezomib, and 5 patients discontinued therapy as a consequence of an AE. There was no obvious pattern indicating an increasing incidence of AEs overall with increasing dose of bortezomib.
Grade 3/4 AEs were experienced by 11 patients, all of whom were in the 1.3 mg/m2 (8/9 patients) and 1.5 mg/m2 (3/8 patients) dose groups. Table 4 shows the incidence of AEs experienced at Grade 3/4 intensity by at least 1 patient. Grade 3 hematologic AEs were reported for 3 patients in the 1.3 mg/m2 dose group, none of whom discontinued bortezomib. Of the Grade 3 nonhematologic AEs, 1 patient in the 1.5 mg/m2 group required hospitalization for abdominal pain and subsequently experienced further pain and vomiting 9 days after discontinuing treatment (patient request). The 3 patients who experienced Grade 3 peripheral neuropathy NOS, peripheral sensory neuropathy, and confusion, respectively, discontinued bortezomib, as did 2 patients who experienced Grade 2 ascites and Grade 1 lymphadenopathy, respectively.
|Adverse Event||Patients, n (%)|
|All Grades||Grade 3||Grade 4|
|Anemia||3 (14)||1 (5)||0|
|Neutropenia||3 (14)||1 (5)||2 (9)|
|Thrombocytopenia||2 (9)||1 (5)||0|
|Hemolytic anemia||1 (5)||1 (5)||0|
|Dyspnea||5 (23)||1 (5)||0|
|Vomiting||5 (23)||2 (9)||0|
|Abdominal pain||3 (14)||2 (9)||0|
|Peripheral neuropathy||3 (14)||1 (5)||0|
|Abdominal pain upper||1 (5)||0||1 (5)|
|Aphasia||1 (5)||1 (5)||0|
|Confusion||1 (5)||1 (5)||0|
|Disease progression||1 (5)||1 (5)||0|
|Hyponatremia||1 (5)||1 (5)||0|
|Inappropriate secretion antidiuretic hormone||1 (5)||1 (5)||0|
|Muscle weakness NOS||1 (5)||1 (5)||0|
|Peripheral sensory neuropathy||1 (5)||1 (5)||0|
|Pitting edema||1 (5)||1 (5)||0|
Three patients experienced Grade 4 AEs, but none discontinued bortezomib as a consequence. Of the 2 patients who experienced Grade 4 neutropenia, toxicity resolved in 1 patient after withholding the bortezomib dose (1.3 mg/m2). In the other patient, toxicity resolved after administration of granulocyte-colony-stimulating factor and bortezomib dose reduction (from 1.5 mg/m2 to 1.3 mg/m2).
Six patients experienced at least 1 serious adverse event (SAE). These included pyrexia, abdominal pain, upper abdominal pain, disease progression, hyponatremia, peripheral sensory neuropathy, confusion, dyspnea, vomiting, and nausea. The SAEs of hyponatremia, peripheral sensory neuropathy, and confusion were assessed by the investigator as possibly or probably related to bortezomib. No patient deaths occurred during the study period (through 38 days after the last dose of bortezomib). Four patient deaths occurred >38 days posttreatment, none of which was related to bortezomib treatment.
The results of this open-label, Phase II study indicate that single-agent bortezomib at doses of 1.0 mg/m2, 1.3 mg/m2, or 1.5 mg/m2 does not demonstrate significant activity in patients with fludarabine-refractory B-cell CLL. This study was terminated prematurely because of the lack of objective response to treatment. No patients achieved a CR or PR by standard response criteria; however, a higher proportion of patients treated with bortezomib at a dose of 1.5 mg/m2 had stable disease (62.5%) and a lower proportion of patients developed disease progression (37.5%) compared with patients who received lower doses. In addition, some patients showed evidence of antitumor activity in lymphocytes, organ-based, and nodal sites, suggesting some degree of biologic activity. The general pattern of 20S proteasome inhibition and the degree of inhibition with dose observed in this study was similar to that observed in other clinical studies.45, 54–57 Bortezomib therapy was generally well tolerated, with the majority of patients discontinuing owing to lack of efficacy rather than toxicity.
The patients in this study had received numerous prior lines of therapy and had limited treatment options available to them. Most had baseline characteristics associated with poor prognosis, including Rai Stage III-IV and β2-microglobulin level >2.5 mg/L. Other Phase II studies have shown a similarly limited degree of activity of single-agent bortezomib in patients with relapsed/refractory CLL. In 2 Phase II studies that evaluated the response to bortezomib in patients with non-Hodgkin lymphoma, 9 patients with refractory or relapsed small lymphocytic lymphoma (SLL) or CLL were treated.47, 48 Two of these patients exhibited a response (1 CR and 1 PR).47, 48
The reasons for the lack of significant activity are not entirely clear, particularly considering the strength of the preclinical data on bortezomib in CLL. The therapeutic agents used most commonly in CLL, including alkylators and nucleoside analogs, have all been shown to trigger apoptosis in vitro, suggesting that induction of apoptosis may also be responsible for in vivo effects. Bortezomib has been shown to induce a significantly higher level of apoptosis than either methylprednisolone or fludarabine in isolated CLL cells, and the combination of fludarabine plus bortezomib increased apoptosis compared with bortezomib alone, even in fludarabine-resistant cells.43 Bortezomib also marginally increased the levels of apoptosis in CLL cells in vivo.43 Similarly, Kelley et al.41 showed that bortezomib induced apoptosis in vitro in cells from CLL patients in a dose- and time-dependent manner, with 10 nM bortezomib causing a greater than 4-fold increase in the percentage of apoptotic cells compared with controls. In addition, Duechler et al.42 recently reported that bortezomib in combination with fludarabine or cladribine offers additive effects in terms of induction of apoptosis in vitro in lymphocytes derived from patients with B-cell CLL, and that these effects are notably higher in CLL cells than in normal, CD3-positive lymphocytes. Meanwhile, Chandra et al.44 demonstrated the effect of several specific proteasome inhibitors on CLL cells. Proteasome inhibition resulted in high levels of DNA fragmentation in all patient samples, including those resistant to glucocorticoid-induced apoptosis. These results suggest that drugs targeting the proteasome may be able to induce apoptosis in CLL cells, even if resistant to conventional chemotherapeutic agents.
These preclinical results warrant further investigation of bortezomib in CLL. On the basis of the observed higher SD rate in the 1.5 mg/m2 group in this study compared with the lower dose groups, further exploration of this or higher doses of bortezomib may be an option. Disappointing results from the pivotal trial investigating rituximab led to skepticism regarding its utility in CLL, yet subsequent studies examining higher rituximab doses demonstrated improved efficacy.58, 59 However, the results of the 20S assay do not support the exploration of higher dose intensity of bortezomib; an altered schedule would likely be required to mitigate toxicity.
As disappointing results have been reported consistently with single-agent therapy, including bortezomib monotherapy, in this high-risk group of patients, and given the strong preclinical data and signs of biologic activity in this study, another approach meriting further investigation is the evaluation of bortezomib in combination with other agents having nonoverlapping toxicity, or evaluation in a less heavily pretreated population. Studies evaluating combinations of therapies with different molecular targets (e.g., purine nucleosides plus monoclonal antibodies) in patients with previously untreated or treated CLL have demonstrated higher response rates compared with historical controls with single-agent therapies.1, 4, 13, 60 For example, adding fludarabine, or fludarabine plus cyclophosphamide, to rituximab in CLL has produced notable increases in response rates compared with rituximab monotherapy.1, 11–14, 58, 60 Similarly, bortezomib in combination with dexamethasone, melphalan, and pegylated liposomal doxorubicin has shown enhanced activity.46, 49, 61, 62 Additional studies to determine potential synergism or potentiation of activity between bortezomib and other targeted therapies appear to be warranted, especially in light of preclinical data, which indicates that apoptosis is augmented when bortezomib is given in combination with other chemotherapeutic agents, such as fludarabine.42, 43
In conclusion, single-agent bortezomib demonstrated biologic activity that did not meet the threshold for objective response in patients with fludarabine-refractory B-cell CLL. However, further evaluation of bortezomib in combination with other agents is warranted on the basis of preclinical and preliminary clinical findings.
We thank Mary L. Browning for following patients at the M. D. Anderson Cancer Center (Houston, TX) and Richard Boyajian for following patients at the Dana-Farber Cancer Institute (Boston, MA).
- 13Addition of rituximab to fludarabine may prolong progression-free survival and overall survival in patients with previously untreated chronic lymphocytic leukemia: an updated retrospective comparative analysis of CALGB 9712 and CALGB 9011. Blood. 2005; 105: 49–53., , , et al.
- 17Subcutaneous Campath-1H (alemtuzumab) in fludarabine-refractory CLL: interim analysis of the CLL2h study of the German CLL Study Group (GCLLSG)]. Blood. 2004; 104:140a., , , et al.
- 19Combined cyclophosphamide, fludarabine, alemtuzumab, and rituximab (CFAR) is active for relapsed and refractory patients with CLL. Blood. 2004; 104:101a., , , et al.
- 24Phase 3 randomized trial of fludarabine/cyclophosphamide chemotherapy with or without oblimersen sodium (Bcl-2 antisense; Genasense; G3139) for patients with relapsed or refractory chronic lymphocytic leukemia (CLL). Blood. 2004; 104:150a., , , et al.
- 26Flavopiridol administered as a pharmacologically-derived schedule demonstrates marked clinical activity in refractory, genetically high risk, chronic lymphocytic leukemia (CLL). Blood. 2004; 104:101a., , , et al.
- 39Proteasome inhibitor-induced apoptosis of B-chronic lymphocytic leukaemia cells involves cytochrome c release and caspase activation, accompanied by formation of an approximately 700 kDa Apaf-1 containing apoptosome complex. Leukemia. 2001; 15: 1388–1397., , , , , .
- 48A multicenter experience with single agent bortezomib in non-Hodgkin's lymphoma reveals marked differences in sub-type sensitivity to proteasome inhibition. 1126: Blood. 2004; 104:175a., , , et al.
- 60Randomized phase 2 study of fludarabine with concurrent versus sequential treatment with rituximab in symptomatic, untreated patients with B-cell chronic lymphocytic leukemia: results from Cancer and Leukemia Group B 9712 (CALGB 9712). Blood. 2003; 101: 6–14., , , et al.
- 61Bortezomib in combination with melphalan in the treatment of relapsed or refractory multiple myeloma: a phase I/II study. Blood. 2004; 104:64a., , , et al.