Radiolabeled anti-CD20 monoclonal antibodies for the treatment of B-cell lymphoma

Ongoing trials with yttrium 90-labeled ibritumomab tiuxetan in patients with non-Hodgkin's lymphoma

Targeted radiation therapy or radioimmunotherapy has been an important recent advance in the treatment of patients with B-cell non-Hodgkin's lymphoma (NHL). Yttrium 90-labeled ibritumomab tiuxetan (Zevalin) comprises the murine monoclonal antibody ibritumomab, the linker chelator tiuxetan, and the radiolabeled isotope yttrium 90. Yttrium 90 ibritumomab tiuxetan has been shown to be efficacious in the treatment of B-cell NHL. Initial phase I/II trials established the therapeutic dose of ibritumomab tiuxetan for low-grade NHL to be 0.4 mCi/kg, or 0.3 mCi/kg for patients with mild thrombocytopenia. Currently, there are many ongoing trials of ibritumomab tiuxetan with different dose schedules and dose intensities in combination with chemotherapy and autologous or allogeneic stem cell transplantation in an attempt to improve response rate and duration and to study its effectiveness in other B-cell lymphomas including mantle cell lymphoma, and chronic lymphocytic leukemia. This article reviews the ongoing trials with 90Y ibritumomab tiuxetan. Radioimmunotherapy has great promise, and the safe incorporation of 90Y ibritumomab tiuxetan into treatment will hopefully result in improved survival for patients with NHL.

The Na+/I- symporter mediates iodide uptake in breast cancer metastases and can be selectively down-regulated in the thyroid

PURPOSE

The Na(+)/I(-) symporter (NIS) is a key plasma membrane protein that mediates active iodide (I(-)) transport in the thyroid, lactating breast, and other tissues. Functional NIS expression in thyroid cancer accounts for the longstanding success of radioactive iodide ((131)I) ablation of metastases after thyroidectomy. Breast cancer is the only other cancer demonstrating endogenous functional NIS expression. Until now, NIS activity in breast cancer metastases (BCM) was unproven.

EXPERIMENTAL DESIGN

Twenty-seven women were scanned with (99m)TcO(4)(-) or (123)I(-) to assess NIS activity in their metastases. An (131)I dosimetry study was offered to patients with I(-)-accumulating tumors. Selective down-regulation of thyroid NIS was tested in 13 patients with T(3) and in one case with T(3) + methimazole (MMI; blocks I(-) organification). NIS expression was evaluated in index and/or metastatic tumor samples by immunohistochemistry.

RESULTS

I(-) uptake was noted in 25% of NIS-expressing tumors (two of eight). The remaining cases did not show NIS expression or activity. Thyroid I(-) uptakes were decreased to </=2.8% at 24 h in T(3)-treated patients and 1/100 normal with T(3)/MMI. Uptake (2.9%) was calculated in a peribronchial metastasis on (131)I dosimetry scans at 4 h with disappearance of the signal by 24 h. We estimated a therapeutic dose of 3000 cGy could be achieved in this metastasis with 100 mCi of (131)I if the tumor exhibited the same dynamics as the T(3)/MMI-suppressed thyroid.

CONCLUSIONS

This is the first article of in vivo, scintigraphically detected, NIS-mediated I(-) accumulation in human BCM. T(3)/MMI down-regulation of thyroid NIS makes (131)I-radioablation of BCM possible with negligible thyroid uptake and radiation damage.

The Role of Radioimmunotherapy with Yttrium-90 Ibritumomab Tiuxetan in the Treatment of Non-Hodgkin Lymphoma

Radioimmunotherapy (RIT) is among the newest modalities for treating the diverse neoplasms known as non-Hodgkin lymphomas (NHLs). The first RIT agent approved by the US FDA was yttrium-90 (90Y) ibritumomab tiuxetan in February 2002. This radioimmunoconjugate consists of the monoclonal IgG1 antibody ibritumomab (the murine parent of rituximab) bound to the chelator tiuxetan and linked by a stable thiourea covalent bond to the beta-emitting radionuclide 90Y. RIT with 90Y ibritumomab tiuxetan is completed in 7-9 days on an outpatient basis, with only minimal (universal) precautions required. The dosing of 90Y ibritumomab tiuxetan is based on patient weight and platelet count, after normal biodistribution with indium-111 ibritumomab tiuxetan has been confirmed. Treatment with 90Y ibritumomab tiuxetan has produced high response rates and long-term benefits in patients with relapsed or refractory follicular and low-grade NHL, including those in whom rituximab therapy has failed. Its toxicity is primarily hematologic, with the hematologic nadirs generally occurring at 7-9 weeks after treatment. Severe infections are uncommon, with infrequent need for supportive measures such as administration of growth factors and transfusions of blood components. There is little nonhematologic toxicity with RIT and it is generally related to infusion-associated reactions. Clinical trials are investigating ways of increasing the efficacy of RIT. In particular, using RIT earlier in the course of treatment of NHL appears to be a promising approach and has been shown to produce better results than when it is used later. Ongoing research is needed to maximize the efficacy of RIT and minimize adverse events, with the goal of developing a multimodality approach that combines RIT with other biologic agents and possibly chemotherapy as frontline treatment to improve the outcomes in patients with NHL.

Refractory humoral cardiac allograft rejection successfully treated with a single dose of rituximab

Despite improvements in immunosuppression over the last two decades, the risk of allograft rejection is still high in the early postoperative period. Cellular rejection accounts for the majority of these episodes. However, humoral rejection is a distinct phenomenon that carries a high rate of graft loss and mortality. The currently available treatments for this serious clinical problem include anti-lymphocyte antibodies, immune globulin infusions, as well as plasmapheresis, all of which have limitations. We describe a case of refractory humoral cardiac rejection successfully treated with a single dose of rituximab (375 mg/m2). No further episodes occurred with 2 years of follow-up.

Radiobiology of radioimmunotherapy: targeting CD20 B-cell antigen in non-Hodgkin's lymphoma

The radiobiology of radioimmunotherapy is an important determinant of both the toxicity and the efficacy associated with the treatment of B-cell non-Hodgkin's lymphoma with radiolabeled anti-CD20 monoclonal antibodies. The properties of the target, CD20, and the mechanisms of action of both the monoclonal antibodies and the associated exponentially decreasing low-dose-rate radiotherapy are described. The radiation dose and dose-rate effects are discussed and related to both the tumor responses and normal organ toxicity. Finally, the use of either unlabeled or radiolabeled anti-CD20 monoclonal antibodies as a component of combined modality therapy (including the sequential or concurrent use of sensitizers) and future directions of the field are discussed.

Yttrium-90 ibritumomab tiuxetan radioimmunotherapy in Richter syndrome

BACKGROUND

(90)Y ibritumomab tiuxetan is a radioimmunotherapeutic construct that is reported to be an effective treatment for patients with lymphoma. The aim of the current analysis was to evaluate retrospectively the efficacy and safety of (90)Y ibritumomab tiuxetan in patients with Richter syndrome (RS).

METHODS

Patients with histologically proven CD20-positive RS and < 25% lymphoma and/or chronic lymphocytic leukemia in the bone marrow were treated. Patients received an imaging dose of (111)In-labeled ibritumomab tiuxetan of 1.6 mg (5.0 mCi of (111)In) intravenously. One week later, they received 0.3 or 0.4 mCi/kg of (90)Y ibritumomab tiuxetan. Rituximab, at a dose of 250 mg/m(2) intravenously, was given immediately before ibritumomab tiuxetan on Days 1 and 8.

RESULTS

Seven patients were treated. Their median age was 56 years (range, 44-70 years). The median time to transformation was 7.9 years (range, 0.7-28.4 years). The median number of previous therapies received was five (range, one to seven previous therapies). The median number of previous therapies received for RS was one (range, none to three previous therapies). Six patients were treated previously with hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone alternating with methotrexate and cytosine arabinoside. No patient responded to (90)Y ibritumomab tiuxetan therapy. All patients developed disease progression. The median time to disease progression was 41 days (range, 39-89 days). Side effects included hematologic toxicity. Grade 3-4 (according to the second version of the National Cancer Institute Common Toxicity Criteria) thrombocytopenia and neutropenia occurred in 5 patients (71%) and 2 patients (29%), respectively. There was one episode of septic shock in a patient with Grade 4 neutropenia.

CONCLUSIONS

(90)Y ibritumomab tiuxetan had no significant antitumor activity and hematologic toxicity was severe in these heavily pretreated patients with RS.

Monoclonal antibodies as therapeutic agents for cancer

Targeted therapies are the focus of much research in oncology. After the development of imatinib for the treatment of chronic myeloid leukaemia, biological therapies that target tumour-associated antigens give hope for improvement of survival in many cancers. At the American Society of Clinical Oncology (ASCO) conference in 2003, data for the antibodies bevacizumab and cetuximab highlighted promising results in clinical trials, including an improvement in survival for metastatic colorectal cancer. Positive results for other antibodies in various stages of clinical development provide hope that anticancer antibodies will have an effect on clinical oncology practice in the next 10 years.

Emerging antibody-targeted therapy in leukemia and lymphoma: current concepts and clinical implications

The success of immune-mediated therapies has encouraged studies on passive and active immunotherapy in leukemia and lymphoma. This review outlines the impact of increasing insights from basic immunology studies on the potentiation of effective immune responses and the identification of new antigens as targets for antibody (Ab)-targeted therapies. The principles of treatment in leukemia and lymphoma based on current knowledge on the classification of hematologic malignancies are reviewed, and discussed in the context of a rationale to implement new Ab-targeted immunotherapeutic approaches. An update is provided on the use of Ab-targeted therapies in clinical trials with emphasis on new emerging strategies to further expand the successful field of immunotherapy in leukemia and lymphoma.

Imaging and therapy of tumors induced to express somatostatin receptor by gene transfer using radiolabeled peptides and single chain antibody constructs

The fields of radioimmunodetection and radioimmunotherapy began with an initial paradigm that a targeting molecule (eg, antibody) carrying a radioisotope had the potential of selectively imaging and delivering a therapeutic dose of radiation to tumor sites. A second paradigm was developed in which injection of the targeting molecule was separated from injection of a short-lived radioisotope-labeled ligand (so-called "pretargeting strategy"). This strategy has improved radioisotope delivery to tumors in animal models, enhanced radioimmune imaging in man, and therapeutic trials are in an early phase. We proposed a third paradigm to achieve radioisotopic localization at tumor sites by inducing tumor cells to synthesize a membrane expressed receptor with a high affinity for infused radiolabeled ligands. The use of gene transfer technology to induce expression of high affinity membrane receptors can enhance the specificity of radioligand localization, while the use of radioisotopes with the ability to deliver radiation damage across several cell diameters will compensate for less than perfect transduction efficiency. This approach was termed "Genetic Radioisotope Targeting Strategy." Using this strategy, induction of high levels of gastrin releasing peptide receptor or human somatostatin receptor subtype 2 expression and selective tumor uptake of radiolabeled peptides was achieved. The advantages of the genetic transduction approach are (1) constitutive expression of a tumor-associated antigen/receptor is not required; (2) tumor cells are altered to express a new target receptor or increased quantities of an existing receptor at levels that may significantly improve tumor targeting of radiolabeled ligands compared with normal tissues; (3) gene transfer can be achieved by intratumoral or regional injection of gene vectors; (4) it is feasible to target adenovirus vectors to receptors overexpressed on tumor cells by modifying adenoviral tropism (binding) so that the virus will be targeted specifically to the desired tumor; and (5) it is possible to coexpress the receptor gene and a therapeutic gene, such as cytosine deaminase, for molecular prodrug therapy to produce an enhanced therapeutic effect.

Safety and efficacy of radioimmunotherapy with Yttrium 90 ibritumomab tiuxetan (Zevalin)

Patients with low-grade, follicular non-Hodgkin's lymphoma usually present with advanced disease, which is not considered curable with conventional therapies. New approaches are needed to improve the outcomes in patients with this disease. Yttrium 90 ibritumomab tiuxetan (Zevalin; Biogen Idec Inc, Cambridge, MA), is highly effective, with overall response rates of 73% to 83% and complete response rates of 15% to 51%, with a median duration of response in complete responders of 23 months. The response rates tend to be higher in patients who have been treated with fewer prior therapies, and (90)Y ibritumomab tiuxetan may be suitable for use early in the course of therapy. Delayed myelosuppression is the most common adverse effect, and it is predictable, reversible, and manageable. Yttrium 90 ibritumomab tiuxetan has less nonhematologic toxicity than chemotherapy, with only minimal alopecia, mucositis, nausea, or vomiting, and a lower incidence of infections. The ibritumomab tiuxetan regimen is routinely and safely given in an outpatient setting and is completed in 7 to 9 days, and is thus more convenient for patients than chemotherapy.

New strategies in radioimmunotherapy for lymphoma

Treatment options for patients with indolent non-Hodgkin's lymphoma historically involved radiation or chemotherapy. Although initial response rates are excellent, treatment is increasingly less effective with each successive relapse. The advent of immunotherapy heralds a new era for the treatment of these patients. Radioimmunotherapy adds the benefits of cytotoxic radiation to immunotherapy and represents a significant addition to the treatment armamentarium. Various antigens for lymphoma have been targeted, of which anti-CD20 antibodies are the furthest in development. Ibritumomab tiuxetan (Zevalin; IDEC Pharmaceuticals, San Diego, CA), a (90)yttrium-labeled agent, and (131)iodine-labeled tositumomab (Bexxar; Corixa, Seattle, WA) are approved by the US Food and Drug Administration. Both agents have shown utility in therapy for relapsed and refractory low-grade and transformed lymphomas. This review highlights features of radioimmunotherapy that are relevant to non-Hodgkin's lymphoma, focusing on the two anti-CD20 antibodies.

Monoclonal antibody therapy for lymphoma

Monoclonal antibodies are an exciting advance in the treatment of lymphoma. They are safe and well-tolerated, and exhibit little cross-resistance with conventional chemotherapeutic agents. In indolent lymphomas, antibody therapy has shown useful response rates, both as first-line therapy and in relapsed disease. Follicular lymphomas appear to be particularly sensitive to rituximab, and chronic lymphocytic leukaemia to alemtuzumab. In aggressive lymphomas, the addition of rituximab to CHOP chemotherapy significantly lengthens disease-free and overall survival compared to CHOP alone as first-line therapy. Newer agents, including radiolabelled antibodies, immunotoxin-linked antibodies and antibodies against novel target antigens are showing promise in phase I and II trials in a variety of clinical settings.

Treatment of low-grade B-cell lymphoma with the monoclonal antibody rituximab

The anti-CD20 chimeric monoclonal antibody has been a tremendous addition to the therapeutic armamentarium against low-grade lymphoma. In indolent lymphoma, rituximab as a single agent is associated with 50% to 60% objective response rates in the relapsed setting and 60% to 75% as front-line therapy. Chemotherapy plus rituximab combinations have been associated with response rates of 85% to 95% and randomized trials have confirmed a higher response rate for various chemotherapy plus rituximab combinations compared to the same chemotherapy alone. Concurrent chemotherapy with rituximab does not increase toxicity and appears superior to sequences of chemotherapy followed by rituximab. Repeated intermittent therapy is associated with higher response rates and longer duration of remission. When used alone, the activity of rituximab is probably due to a combination of complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and regulatory effects that enhance apoptosis. Dosing could probably be optimized by monitoring serum levels of rituximab in individual patients, because of the tremendous variability in lymphoma tumor burden, rates of tumor proliferation, rates of CD20 antigen production and expression, and clearance of rituximab. Combinations of rituximab with other monoclonal antibodies are currently being tested.

Therapy of non-Hodgkin's lymphoma

Non-Hodgkin's lymphomas are a heterogeneous group of malignancies of the lymphoid system. The exact etiology for most lymphomas has not been determined, but both viral and bacterial infections have been shown to be important etiologic factors. The WHO classification of hematopoietic and lymphoid tumours classifies lymphomas into B-cell and T-cell neoplasms. B-cell lymphomas account for more than 85% of all lymphomas. The Ann Arbor staging classification has been adopted by the AJCC and UICC as a standard for classifying extent of anatomic disease. The two most common histologic disease entities are follicular lymphomas and diffuse large B-cell lymphomas. The management of follicular lymphomas is used as a paradigm for the management of all indolent lymphomas. Radiation therapy is used for stage I and II disease, while alkylating agent chemotherapy, immunotherapy and radioimmunotherapy are most frequently used in stage III and IV disease that requires treatment. Most patients with follicular lymphoma enjoy prolonged survival, but at present there is no evidence that those with stage III and IV follicular lymphoma can be cured. Diffuse large B-cell lymphomas serve as a paradigm for treating aggressive lymphomas. Stage I and II diffuse large cell lymphomas are generally treated with combined modality therapy with doxorubicin-based chemotherapy followed by involved field radiation therapy, while those with stage III and IV disease are treated with chemotherapy alone. Patients who fail initial management are treated with further chemotherapy. High-dose chemotherapy with stem cell rescue has been shown to be particularly effective as salvage treatment for diffuse large cell lymphomas. The management of a heterogeneous group of primary extranodal lymphomas in general follows the above treatment principles, with additional treatment being required for those with a high risk of CNS failures, or involvement of contralateral paired organs. The management of MALT lymphomas, especially gastric MALT lymphoma, deserves special attention because of the high response rate to Helicobacter pylori eradication therapy.

Renaissance of cancer therapeutic antibodies

In the past five years therapeutic monoclonal antibodies have established themselves as perhaps the most important and rapidly expanding class of therapeutic drugs. More than 25% of pharmacological agents that are currently under development are based on antibodies and the total income generated from them in 2002 exceeded $3 billion, and is predicted to rise to $10-20 billion by 2010. Many experts feel that antibodies directed at cancer targets are likely to dominate the market for the foreseeable future. In this review, we will discuss some of the factors that, after more than 25 years of development, have led to this transformation in the antibody field.

Advancing role of radiolabeled antibodies in the therapy of cancer

This review focuses on the use of radiolabeled antibodies in the therapy of cancer, termed radioimmunotherapy (RAIT). Basic problems concerned with the choice of antibody, radionuclide, and physiology of the tumor and host are discussed, followed by a review of the pertinent clinical publications of various radioantibody constructs in the treatment of hematopoietic and solid tumors of diverse histopathology, grade, and stage, and in different clinical settings. Factors such as dose rate delivered, tumor size, and radiosensitivity play a major role in determining therapeutic response, while target-to-nontarget ratios and, particularly, circulating radioactivity to the bone marrow determine the principal dose-limiting toxicities. RAIT appears to be gaining a place in the therapy of hematopoietic neoplasms, such as non-Hodgkin's lymphoma: several agents are advancing in clinical trials toward registration, and one has recently been approved by the FDA. Although RAIT of solid tumors has shown less progress, use of pretargeting strategies, such as an affinity-enhancement system consisting of bispecific antibodies separating targeting from delivery of the radiotherapeutic, appears to enhance tumor-to-nontumor ratios, and may increase radiation doses to tumors more selectively than directly labeled antibodies.

Monoclonal antibody therapy of chronic lymphocytic leukemia

Chemotherapeutic approaches during the last decade have failed to result in major advances in the outcome of patients with chronic lymphocytic leukemia (CLL). The recent availability of an increasing number of active monoclonal antibodies, immunotoxins, and radioimmunoconjugates (RICs) has stimulated considerable interest in clinical research in CLL. Alemtuzumab was the first antibody approved for CLL on the basis of responses in one third of patients with advanced disease. However, infusion reactions and immunosuppression with opportunistic infections present a challenge that may be overcome with altered schedules and routes of administration. Rituximab has limited activity as a single agent in patients relapsed or refractory after prior chemotherapy; however, response rates seem to be higher in previously untreated patients. More importantly, combinations with chemotherapy drugs such as fludarabine are showing promise in early trials. Newer antibodies in development as single agents and in combinations include apolizumab (Hu1D10), a humanized antibody against an epitope of HLA-DR, and IDEC-152, a primatized anti-CD23 antibody. BL22, an immunotoxin with impressive activity in hairy cell leukemia, is in phase II trials in CLL as well. The safe use of RICs is complicated by the elevated peripheral blood B-cell count, and the extent of bone marrow involvement in CLL; studies will explore the use of agents to eliminate malignant cells from the bone marrow before RIC therapy. It is hoped that the rational development of combinations of the various promising antibodies with chemotherapy and each other will lead to more effective approaches for patients with CLL.