Additive cytotoxic effect of bortezomib in combination with anti-CD20 or anti-CD52 monoclonal antibodies on chronic lymphocytic leukemia cells

The immunological function of CD52 and its targeting in organ transplantation

INTRODUCTION

CD52 (Campath-1 antigen), a glycoprotein of 12 amino acids anchored to glycosylphosphatidylinositol, is widely expressed on the cell surface of immune cells, such as mature lymphocytes, natural killer cells (NK), eosinophils, neutrophils, monocytes/macrophages, and dendritic cells (DCs). The anti-CD52 mAb, alemtuzumab, was used widely in clinics for the treatment of patients such as organ transplantation. In the present manuscript, we will briefly summarize the immunological function of CD52 and discuss the application of anti-CD52 mAb in transplantation settings.

FINDINGS

We reviewed studies published until July 2016 to explore the role of CD52 in immune cell function and its implication in organ transplantation. We showed that ligation of cell surface CD52 molecules may offer costimulatory signals for T-cell activation and proliferation. However, soluble CD52 molecules will interact with the inhibitory sialic acid-binding immunoglobulin-like lectin 10 (Siglec10) to significantly inhibit T cell proliferation and activation. Although the physiological and pathological significances of CD52 molecules are still poorly understood, the anti-CD52 mAb, alemtuzumab, was used widely for the treatment of patients with chronic lymphocytic leukemia, autoimmune diseases as well as cell and organ transplantation in clinics.

CONCLUSION

Studies clearly showed that CD52 can modulate T-cell activation either by its intracellular signal pathways or by the interaction of soluble CD52 and Siglec-10 expressing on T cells. However, the regulatory functions of CD52 on other immune cell subpopulations in organ transplantation require to be studied in the near future.

A Multicenter Phase II Study of Twice-Weekly Bortezomib plus Rituximab in Patients with Relapsed Follicular Lymphoma: Long-Term Follow-Up

Single-agent bortezomib (B) has shown activity in heavily pretreated patients with relapsed/refractory indolent lymphoma. On the basis of these findings, we performed a phase II study of B combined with rituximab (R) in patients with relapsed follicular lymphoma (FL). Forty-five patients with fairly good prognostic profiles were enrolled from 2007 to 2011 and received a total of 6 cycles of the B+R combination. The endpoints were the overall response rate (ORR), progression-free survival (PFS), duration of remission (DoR), overall survival (OS), and toxicity evaluation. When considering all the enrolled patients the ORR was 64%. At 5 years, the estimated PFS, DoR, and OS were 34, 49, and 70%, respectively. After excluding the 7 R-naïve patients, the ORR was 58%, with a PFS of 19 months. The most common grade >2 toxicities were thrombocytopenia (18%), peripheral neuropathy (13%), and neutropenia (2%). Our study shows the feasibility, long-term efficacy, and excellent tolerability of the B+R combination. We are aware that our study has specific limitations, such as the small sample size consisting of patients with a relatively good prognostic profile. However, because FL patients will be treated with subsequent chemotherapy regimens, a well-tolerated and effective chemotherapy-free therapy could be considered an additional tool for long-term disease control.

Novel agents in indolent lymphomas

Indolent non-Hodgkin's lymphomas (iNHLs) include follicular lymphomas (FL), marginal-zone lymphoma, lymphoplasmacytic lymphoma/Waldenström macroglobulinemia and small lymphocytic lymphoma. First-line standard therapy in advanced, symptomatic iNHL consists of rituximab-based immunochemotherapy. The recent rediscovery of the 'old' chemotherapeutic agent bendamustine, an alkylating agent with a peculiar mechanism of action, has added a new effective and well-tolerated option to the therapeutic armamentarium in iNHL, increasing response rates and duration. However, patients invariably relapse and subsequent active and well-tolerated agents are needed. In recent years a large number of new targeted agents have been tested in preclinical and clinical experimentation in FL and indolent nonfollicular lymphoma (iNFL), including the new monoclonal antibodies binding CD20 or other surface antigens, immunoconjugates and bispecific antibodies. Moreover novel agents directed against intracellular processes such as proteasome inhibitors, mTOR inhibitors and agents that target the tumour microenvironment, notably the immunomodulatory agent lenalidomide, are under active clinical investigation. The development of these new drugs may change in the near future the approach to iNHL patients, leading to better tolerated and effective therapy regimens.

ZGDHu-1 promotes apoptosis of chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is a low-grade lymphoid malignancy incurable with conventional modalities of chemotherapy. We aimed to examine the proapoptotic effects of a novel proteasome inhibitor, N,N'-di-(m-methylphenyi)-3,6- dimethyl-1,4-dihydro-1,2,4,5-tetrazine-1,4-dicarboamide (ZGDHu-1), on CLL cells. B lymphocytes were isolated from CLL patients and normal healthy controls, and treated with various concentrations of ZGDHu-1 for different days. CLL cell viability was detected by MTT assay. The apoptosis, mitochondrial membrane potential (∆ψm) and reactive oxidative species (ROS) were examined by flow cytometry. The expression of caspase-3 and Bcl-2/Bax ratio was detected by western blotting. ZGDHu-1 significantly reduced the viability of CLL cells and induced apoptosis in comparison to the control cells (both P<0.05). Normal peripheral B cells were resistant to the apoptosis-inducing effects of ZGDHu-1. Apoptosis induced by ZGDHu-1 was accompanied with generation of ROS, loss of ∆ψm, downregulation of Bcl-2 and increase of caspase-3 cleavage. Results of this study indicate that ZGDHu-1 is a promising specific treatment for CLL in the clinic.

The HB22.7 Anti-CD22 monoclonal antibody enhances bortezomib-mediated lymphomacidal activity in a sequence dependent manner

Most non-Hodgkin's lymphomas (NHL) initially respond to chemotherapy, but relapse is common and treatment is often limited by chemotherapy-related toxicity. Bortezomib, is a highly selective proteasome inhibitor with anti-NHL activity; it is currently FDA approved for second-line treatment of mantle cell lymphoma (MCL). Bortezomib exerts its activity in part through the generation of reactive oxygen species (ROS) and also by the induction of apoptosis.We previously validated CD22 as a potential target in treating NHL and have shown that the anti-CD22 ligand blocking antibody, HB22.7, has significant independent lymphomacidal properties in NHL xenograft models. We sought to determine whether or not these agents would work synergistically to enhance cytotoxicity. Our results indicate that treatment of NHL cell lines with HB22.7 six hours prior to bortezomib significantly diminished cell viability. These effects were not seen when the agents were administered alone or when bortezomib was administered prior to HB22.7. Additionally, HB22.7 treatment prior to bortezomib increased apoptosis in part through enhanced ROS generation. Finally, in a mouse xenograft model, administration of HB22.7 followed 24 hours later by bortezomib resulted in 23% smaller tumor volumes and 20% enhanced survival compared to treatment with the reverse sequence. Despite the increased efficacy of HB22.7 treatment followed by bortezomib, there was no corresponding decrease in peripheral blood cell counts, indicating no increase in toxicity. Our results suggest that pre-treatment with HB22.7 increases bortezomib cytotoxicity, in part through increased reactive oxygen species and apoptosis, and that this sequential treatment combination has robust efficacy in vivo.

Alemtuzumab induction of intracellular signaling and apoptosis in malignant B lymphocytes

The molecular changes induced by alemtuzumab following binding of CD52 on B tumor cells were investigated. Alemtuzumab alone had no detectable impact on cell signaling but cross-linking of alemtuzumab on the surface of B tumor lines with anti-human Fc antibodies induced a transient Ca(2+) flux followed by phosphorylation of several kinases involved in stress and survival pathways, and expression of associated proteins including TNF-α. Cross-linking of alemtuzumab also induced capping and caspase-dependent apoptosis of the tumor lines. When using primary cells from B-CLL patients, alemtuzumab alone was capable of inducing protein phosphorylation and apoptosis through the cross-linking of alemtuzumab by FcγRIIb receptors on B-CLL cells. Apoptosis was prevented by blocking of FcγRIIb receptors with anti-CD32 antibody. Overall, our results indicate that cross-linking of alemtuzumab on B tumor cells can occur naturally through Fc receptor interaction and leads to the activation of specific cellular pathways and induction of apoptosis.

Bortezomib plus rituximab versus rituximab alone in patients with relapsed, rituximab-naive or rituximab-sensitive, follicular lymphoma: a randomised phase 3 trial

BACKGROUND

Bortezomib and rituximab have shown additive activity in preclinical models of lymphoma, and have been shown to be active and generally well tolerated in a randomised phase 2 study in patients with follicular and marginal zone lymphoma. We compared the efficacy and safety of rituximab alone or combined with bortezomib in patients with relapsed or refractory follicular lymphoma in a phase 3 setting.

METHODS

In this multicentre phase 3 trial, rituximab-naive or rituximab-sensitive patients aged 18 years or older with relapsed grade 1 or 2 follicular lymphoma were randomly assigned (1:1) to receive five 35-day cycles consisting of intravenous infusions of rituximab 375 mg/m(2) on days 1, 8, 15, and 22 of cycle 1, and on day 1 of cycles 2-5, either alone or with bortezomib 1·6 mg/m(2), administered by intravenous injection on days 1, 8, 15, and 22 of all cycles. Randomisation was stratified by FLIPI score, previous use of rituximab, time since last therapy, and region. Treatment assignment was based on a computer-generated randomisation schedule prepared by the sponsor. Patients and treating physicians were not masked to treatment allocation. The primary endpoint was progression-free survival analysed by intention to treat. This trial has been completed and is registered with ClinicalTrials.gov, number NCT00312845.

FINDINGS

Between April 10, 2006, and Aug 12, 2008, 676 patients were randomised to receive rituximab (n=340) or bortezomib plus rituximab (n=336). After a median follow-up of 33·9 months (IQR 26·4-39·7), median progression-free survival was 11·0 months (95% CI 9·1-12·0) in the rituximab group and 12·8 months (11·5-15·0) in the bortezomib plus rituximab group (hazard ratio 0·82, 95% CI 0·68-0·99; p=0·039). The magnitude of clinical benefit was not as large as the anticipated prespecified improvement of 33% in progression-free survival. Patients in both groups received a median of five treatment cycles (range 1-5); 245 of 339 (72%) and 237 of 334 (71%) patients in the rituximab and bortezomib plus rituximab groups, respectively, completed five cycles. Of patients who did not complete five cycles, most discontinued early because of disease progression (77 [23%] patients in the rituximab group, and 56 [17%] patients in the bortezomib plus rituximab group). Rates of adverse events of grade 3 or higher (70 [21%] of 339 rituximab-treated patients vs 152 [46%] of 334 bortezomib plus rituximab treated patients), and serious adverse events (37 [11%] patients vs 59 [18%] patients) were lower in the rituximab group than in the combination group. The most common adverse events of grade 3 or higher were neutropenia (15 [4%] patients in the rituximab group and 37 [11%] patients in the bortezomib plus rituximab group), infection (15 [4%] patients and 36 [11%] patients, respectively), diarrhoea (no patients and 25 [7%] patients, respectively), herpes zoster (one [<1%] patient and 12 [4%] patients, respectively), nausea or vomiting (two [<1%] patients and 10 [3%] patients, respectively) and thrombocytopenia (two [<1%] patients and 10 [3%] patients, respectively). No individual serious adverse event was reported by more than three patients in the rituximab group; in the bortezomib plus rituximab group, only pneumonia (seven patients [2%]) and pyrexia (six patients [2%]) were reported in more than five patients. In the bortezomib plus rituximab group 57 (17%) of 334 patients had peripheral neuropathy (including sensory, motor, and sensorimotor neuropathy), including nine (3%) with grade 3 or higher, compared with three (1%) of 339 patients in the rituximab group (no events of grade ≥3). No patients in the rituximab group but three (1%) patients in the bortezomib plus rituximab group died of adverse events considered at least possibly related to treatment.

INTERPRETATION

Although a regimen of bortezomib plus rituximab is feasible, the improvement in progression-free survival provided by this regimen versus rituximab alone was not as great as expected. The regimen might represent a useful addition to the armamentarium, particularly for some subgroups of patients.

FUNDING

Johnson & Johnson Pharmaceutical Research & Development and Millennium Pharmaceuticals, Inc.

Management of mantle cell lymphoma: key challenges and next steps

Mantle cell lymphoma (MCL) is regarded as an aggressive lymphoid malignancy that exhibits varied clinical behavior and prognoses, reflecting the biologic heterogeneity of the disease. In most cases, patients with MCL achieve a shorter median survival compared with more common B-cell lymphomas, such as follicular lymphoma, and are less likely to achieve a durable response with chemotherapy. Currently, there is no defined standard of care for patients with MCL. Rituximab-containing immunochemotherapy strategies are commonly used, but the addition of rituximab to conventional induction chemotherapy has produced suboptimal responses that are relatively short-lived and have not resulted in a survival advantage. Further intensification of the chemotherapy component, including autologous stem cell transplantation, has increased response and survival rates but has not proven to be curative while being associated with higher toxicity. Clearly, there is a need for developing novel agents and strategies that will improve clinical outcomes for patients with MCL. Targeted therapies and new cytotoxic agents are showing great promise and may have a role in maintenance and/or initial therapy. This summary highlights current challenges in the management of MCL, and outlines expert perspectives, key questions, and future directions. For the third consecutive year, a panel of global experts in MCL assembled to deliberate on topical issues in MCL including advances in pathobiology, strategies for risk-adapted therapy, front-line treatment options, consolidation approaches, and novel therapeutic strategies. The proceedings of this workshop, held December 3, 2009 in New Orleans, LA, are summarized here. It must be emphasized that this synopsis is not meant to serve as an exhaustive review of MCL biology and management, but is a distillation of the expert discussions, highlighting key questions and future directions identified.

Phase I trial of bortezomib in combination with rituximab-HyperCVAD alternating with rituximab, methotrexate and cytarabine for untreated aggressive mantle cell lymphoma

Mantle cell lymphoma (MCL) outcomes have improved over the last two decades; however, late relapses occur. Bortezomib has shown single agent activity of 33% in relapsed MCL and has an additive/synergistic effect in vitro when combined with drugs currently used to treat MCL. We hypothesized that a combination of bortezomib with current intense non-transplant chemoimmunotherapy might prevent late relapses. The toxicity of bortezomib when combined with methotrexate and cytarabine is unknown. Patients aged 18-79 years with untreated aggressive MCL were treated with R-HyperCVAD (rituximab, cyclophosphamide, vincristine, doxorubicin, dexamethasone) alternating with rituximab-methotrexate/cytarabine (R-M/A). Bortezomib was added to the R-Hyper-CVAD combination as a fixed dose of 1·3 mg/m(2) IV on days 2 and 5 and was added to the R-M/A regimen after rituximab, in increasing doses of 0·7, 1, and 1·3 mg/m(2) in cohorts of three patients. Twenty patients were assessed for toxicity of the regimen. The principal toxicity was haematological and did not differ from that observed with a similar regimen without the bortezomib. In particular, there was no pulmonary or neurological dose-limiting toxicity, showing that bortezomib can be safely combined with R-HyperCVAD and R-M/A.

Combination therapy of bortezomib with novel targeted agents: an emerging treatment strategy

Clinical trials evaluating combinations of targeted agents with bortezomib, the first-in-class proteasome inhibitor, have been initiated, with the objective of enhancing its single agent activity in hematologic malignancies (myeloma, mantle cell lymphoma), as well as expanding its efficacy in solid tumors. In most cases, preclinical studies have provided a supportive rationale for designing these doublet combination studies. Novel, small molecule-targeted agents being investigated with bortezomib in clinical trials include protein deacetylase inhibitors, kinase inhibitors, farnesyltransferase inhibitors, heat-shock protein 90 inhibitors, pan-Bcl-2 family inhibitors, and other classes of targeted inhibitors. Preliminary clinical data, available from a number of ongoing trials, suggest that most of these combinations are well tolerated and some have promising clinical efficacy that will require subsequent confirmation. Translational studies, conducted as part of the trials, may provide important insights into the putative mechanism of action delineated by preclinical studies of the combinations. The emergence of novel proteasome inhibitors may also expand the opportunities for optimizing these combination therapies. There is potential for an increasingly broad clinical trials program to investigate this therapeutic approach in a range of tumor types, as well as to consider additional agents in sequence or in combination.

Mantle cell lymphoma: biological insights and treatment advances

Mantle cell lymphoma (MCL) exhibits considerable molecular heterogeneity and complexity, and is regarded as one of the most challenging lymphomas to treat. With increased understanding of the pathobiology of MCL, it is proposed that MCL is the result of 3 major converging factors, namely, deregulated cell cycle pathways, defects in DNA damage responses, and dysregulation of cell survival pathways. In the present era of targeted therapies, these biologic insights have resulted in the identification of several novel rational targets for therapeutic intervention in MCL that are undergoing active clinical testing. To date, there is no standard of care in MCL. Several approaches including conventional anthracycline-based therapies and intensive high-dose strategies with and without stem cell transplantation have failed to produce durable remissions for most patients. Moreover, considering the heterogeneity of MCL, it is increasingly being recognized that risk-adapted therapy might be a relevant therapeutic approach in this disease. At the first and second Global Workshops on Mantle Cell Lymphoma, questions addressing advances in the pathobiology of MCL, optimization of existing therapies, assessment of current data with novel therapeutic strategies, and the identification of molecular or phenotypic risk factors for utilization in risk-adapted therapies were discussed and will be summarized herein.

Multicenter Randomized Phase II Study of Weekly or Twice-Weekly Bortezomib Plus Rituximab in Patients With Relapsed or Refractory Follicular or Marginal-Zone B-Cell Lymphoma

Purpose

To determine overall response rate (ORR), time to progression (TTP), and duration of response (DOR) with twice-weekly/weekly bortezomib plus rituximab, and evaluate safety/tolerability, in patients with relapsed or refractory CD20+ follicular lymphoma (FL) or marginal-zone lymphoma.

Patients and Methods

Patients were randomly assigned (minimization method) to bortezomib 1.3 mg/m2 twice weekly (days 1, 4, 8, and 11; 21-day cycle, five cycles; arm A) or bortezomib 1.6 mg/m2 weekly (days 1, 8, 15, and 22; 35-day cycle, three cycles; arm B) plus rituximab 375 mg/m2 weekly for 4 weeks (both arms). Response/progression was determined by International Workshop Response Criteria using oncologist/radiologist-adjudicated data from independent radiology review and investigator assessment.

Results

Eighty-one patients (arm A, n = 41; arm B, n = 40) were enrolled. Dose-intensity was higher in arm A; mean total bortezomib received was similar between arms (18.5 and 17.1 mg/m2). In arm A, ORR was 49% (14% complete response [CR]/CR unconfirmed [CRu]), median TTP was 7.0 months, and median DOR was not reached. In arm B, ORR was 43% (10% CR/CRu), and median TTP/DOR were 10.0/9.3 months. The weekly combination regimen seemed better tolerated. Grade 3 or worse adverse events seemed more common in arm A (54%) versus arm B (35%), including thrombocytopenia (10% v 0%) and peripheral neuropathy (10% v 5%), but diarrhea seemed less frequent (7% v 15%). No grade 4 toxicities were reported in arm B.

Conclusion

Both bortezomib plus rituximab regimens seem feasible in relapsed or refractory indolent lymphomas. The more convenient weekly combination regimen is being compared with single-agent rituximab in an ongoing phase III study in relapsed FL.

Molecular mechanisms of resistance to Rituximab and pharmacologic strategies for its circumvention

The introduction of Rituximab has greatly improved therapeutic options for patients with B-cell non-Hodgkin lymphoma (B-NHL). However, a substantial fraction of patients with aggressive B-NHL fails first-line therapy, and most patients with relapsing indolent B-NHL eventually acquire Rituximab resistance. Molecular understanding of the underlying mechanisms facilitates the development of pharmacologic strategies to overcome resistance. Rituximab exerts its activity on CD20-expressing B-cells by indirect and direct effector mechanisms. Indirect mechanisms are complement-dependent cytotoxicity (CDC), and antibody-dependent cell-mediated cytotoxicity (ADCC). Direct activities, such as growth inhibition, induction of apoptosis and chemosensitisation, have been reported, but are less defined. Moreover, the relative contribution of CDC, ADCC and direct mechanisms to the activity of Rituximab in vivo is unclear. Down-regulation of CD20 and expression of complement inhibitors have been described as escape mechanisms in B-NHL. Recent reports suggest that deregulated phosphoinositide-3-kinase (PI3K)/Akt, mitogen-activated kinases (MAPK) and nuclear-factor kappaB (NF-kappaB), as well as up-regulation of anti-apoptotic proteins may determine the efficacy of Rituximab to kill B-NHL cells in vitro and in vivo. The latter signalling pathways are attractive targets for pharmacologic modulation of resistance to Rituximab. With the advent of new inhibitors and antibodies, rationally designed clinical trials addressing Rituximab resistance are feasible.

Cytotoxic effect of R-etodolac (SDX-101) in combination with purine analogs or monoclonal antibodies on ex vivo B-cell chronic lymphocytic leukemia cells

R-etodolac (SDX-101) is an isoform of the non-steroidal anti-inflammatory drug, etodolac, and is currently being tested in phase II clinical trials for the treatment of refractory B-cell chronic lymphocytic leukemia (B-CLL). The aim of this study was to evaluate the cytotoxicity of SDX-101 combined with agents proven to be effective as first-line treatment of B-CLL: the purine nucleoside analogs, fludarabine (FA) and cladribine (2-CdA), and the monoclonal antibodies, anti-CD52 (alemtuzumab; ALT) and anti-CD20 (rituximab; RIT). The cytotoxicity and specific pro-apoptotic effects of the study drugs on B-CLL cells were assessed in vitro in samples from overall 37 untreated patients. The combinations of SDX-101 with 2-CdA, FA or RIT exerted additive effects in B-CLL cells, with the following combination indices (CI): 0.89 for SDX-101 + 2-CdA, 0.95 for SDX-101 + RIT, and 1.17 for SDX-101 + FA. The main mechanism of these interactions was caspase-mediated apoptosis. The SDX-101 plus ALT combination resulted in only sub-additive cytotoxicity (CI = 1.25). In conclusion, these data obtained in vitro indicate that addition of 2-CdA, FA or RIT to SDX-101 significantly enhance cytotoxicity in B-CLL cells.

Bortezomib blocks Bax degradation in malignant B cells during treatment with TRAIL

Proapoptotic Bcl-2 family member Bax is a crucial protein in the induction of apoptosis, and its activation is required for this process. Here we report that Bax is a short-lived protein in malignant B cells and Bax protein levels decreased rapidly when protein synthesis was blocked. Malignant B cells were relatively resistant to tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-induced apoptosis, and this correlated with low basal Bax protein levels. Furthermore, during treatment with TRAIL, the resistant cell lines showed prominent Bax degradation activity. This degradation activity was localized to mitochondrial Bax and could be prevented by truncated Bid, a BH3-only protein; in contrast, cytosolic Bax was relatively stable. The proteasome inhibitor bortezomib is a potent drug in inducing apoptosis in vitro in malignant B-cell lines and primary chronic lymphocytic leukemic (CLL) cells. In CLL cells, bortezomib induced Bax accumulation, translocation to mitochondria, conformational change, and oligomerization. Accumulation and stabilization of Bax protein by bortezomib-sensitized malignant B cells to TRAIL-induced apoptosis. This study reveals that Bax instability confers resistance to TRAIL, which can be reversed by Bax stabilization with a proteasome inhibitor.

Increased proteasomal degradation of Bax is a common feature of poor prognosis chronic lymphocytic leukemia

Many biologic markers are associated with poor prognosis in chronic lymphocytic leukemia (CLL), but their mechanistic role remains unclear. Bax is an essential proapoptotic protein and decreased levels in malignant cells lead to resistance to apoptosis. Using a Bax degradation activity (BDA) assay, CLL cells were found to show variable Bax instability. However, BDA did not correlate with Bax protein levels: BDA positive and negative cases had high and low baseline Bax levels. BDA positive cases showed a marked accumulation of poor prognostic markers-unmutated immunoglobulin heavy chain variable genes, ZAP-70/CD38 positivity, 11q22/17p13 deletion, and short lymphocyte doubling time. Patients with BDA positive cells had a shorter median overall survival (OS; 126 months vs not reached, P = .011) and time to first treatment (16 vs 156 months, P = .029) than BDA negative cases. Dual BDA and ZAP-70 positivity had a median OS of 84 months (P = .012). The BDA assay measures the intrinsic ubiquitin/proteasome activity of CLL cells and dynamic changes in Bax protein levels over time. Mechanistically, Bax instability may represent a final common pathway for disparate prognostic markers, as well as being itself an indicator of poor prognosis.

Multicenter Clinical Trial of Bortezomib in Relapsed/Refractory Waldenstrom's Macroglobulinemia: Results of WMCTG Trial 03-248

PURPOSE

Waldenstrom's macroglobulinemia (WM) is a B-cell disorder. Despite advances in the therapy, WM remains incurable. As such, novel therapeutic agents are needed for the treatment of WM.

EXPERIMENTAL DESIGN

In this multicenter study, 27 patients with WM received up to eight cycles of bortezomib at 1.3 mg/m(2) on days 1, 4, 8, and 11. All but one patient had relapsed/or refractory disease.

RESULTS

Following therapy, median serum IgM levels declined from 4,660 to 2,092 mg/dL (P < 0.0001). The overall response rate was 85%, with 10 and 13 patients achieving minor and major responses, respectively. Responses were prompt and occurred at median of 1.4 months. The median time to progression for all responding patients was 7.9 (range, 3-21.4+) months. The most common grade III/IV toxicities occurring in > or =5% of patients were sensory neuropathies (22.2%), leukopenia (18.5%), neutropenia (14.8%), dizziness (11.1%), and thrombocytopenia (7.4%). Sensory neuropathies resolved or improved in nearly all patients following cessation of therapy.

CONCLUSIONS

The results of these studies show that bortezomib is an active agent in relapsed and refractory WM.

Proteasome inhibitors: antitumor effects and beyond

Proteasome inhibitors are emerging as effective drugs for the treatment of multiple myeloma and possibly certain subtypes of non-Hodgkin's lymphoma. Bortezomib (Velcade) is the first proteasome inhibitor proven to be clinically useful and will soon be followed by a second generation of small molecule inhibitors with improved pharmacological properties. Although it is now understood that certain types of malignancies have an exquisite dependence on a functional proteasome for their survival, the underlying reason(s) remain unclear as of now. In this context, addiction to nuclear factor-kappaB (NF-kappaB)-induced survival signals, activation of the unfolded protein response as well as a reduced proteasomal activity in differentiated plasma cells have all been proposed to justify proteasome inhibitors' activity in susceptible tissues. In addition to their anticancer properties, bortezomib and related drugs modulate inflammatory and immune responses by affecting function and survival of immune cells such as lymphocytes and dendritic cells. The present review offers an overview of the biological effects that have been involved in proteasome inhibitors' antitumor activity and suggests prospective future applications for these drugs based on their recently characterized anti-inflammatory and immunomodulatory effects.