Imaging, dosimetry, and radioimmunotherapy with iodine 131-labeled anti-CD37 antibody in B-cell lymphoma

Cutaneous Lymphoma and Antibody-Directed Therapies

The introduction of monoclonal antibodies such as rituximab to the treatment of cancer has greatly advanced the treatment scenario in onco-hematology. However, the response to these agents may be limited by insufficient efficacy or resistance. Antibody–drug conjugates are an attractive strategy to deliver payloads of toxicity or radiation with high selectivity toward malignant targets and limited unwanted effects. Primary cutaneous lymphomas are a heterogeneous group of disorders and a current area of unmet need in dermato-oncology due to the limited options available for advanced cases. This review briefly summarizes our current understanding of T and B cell lymphomagenesis, with a focus on recognized molecular alterations that may provide investigative therapeutic targets. The authors reviewed antibody-directed therapies investigated in the setting of lymphoma: this term includes a broad spectrum of approaches, from antibody–drug conjugates such as brentuximab vedotin, to bi-specific antibodies, antibody combinations, antibody-conjugated nanotherapeutics, radioimmunotherapy and, finally, photoimmunotherapy with specific antibody–photoadsorber conjugates, as an attractive strategy in development for the future management of cutaneous lymphoma.

Radiolabeled Antibodies for Cancer Imaging and Therapy

Simple Summary

Monoclonal antibodies (mAbs) have the ability to specifically target tumor-cell antigens. This unique property has led to their use in the delivery of radioisotopes to tumor sites (scintigraphic imaging and radioimmunotherapy (RIT)). The choice of the radionuclide depends on its unique physical properties and intended use. Using radiolabeled mAbs with imaging techniques provides critical data that are essential for predicting side effects and determining an optimal antibody dose and treatment schedule. While RIT has been successful in the management of hematological malignancies, the treatment of solid tumors remains challenging. Various strategies are being investigated to improve the efficacy of RIT in solid tumors.

Abstract

Radioimmunoconjugates consist of a monoclonal antibody (mAb) linked to a radionuclide. Radioimmunoconjugates as theranostics tools have been in development with success, particularly in hematological malignancies, leading to approval by the US Food and Drug Administration (FDA) for the treatment of non-Hodgkin’s lymphoma. Radioimmunotherapy (RIT) allows for reduced toxicity compared to conventional radiation therapy and enhances the efficacy of mAbs. In addition, using radiolabeled mAbs with imaging methods provides critical information on the pharmacokinetics and pharmacodynamics of therapeutic agents with direct relevance to the optimization of the dose and dosing schedule, real-time antigen quantitation, antigen heterogeneity, and dynamic antigen changes. All of these parameters are critical in predicting treatment responses and identifying patients who are most likely to benefit from treatment. Historically, RITs have been less effective in solid tumors; however, several strategies are being investigated to improve their therapeutic index, including targeting patients with minimal disease burden; using pre-targeting strategies, newer radionuclides, and improved labeling techniques; and using combined modalities and locoregional application. This review provides an overview of the radiolabeled intact antibodies currently in clinical use and those in development.

Myelosuppression in patients treated with 177Lutetium-lilotomab satetraxetan can be predicted with absorbed dose to the red marrow as the only variable

BACKGROUND

The aim of this study was to investigate dosimetry data and clinical variables to predict hematological toxicity in non-Hodgkin lymphoma (NHL) patients treated with [¹⁷⁷Lutetium]Lu-lilotomab satetraxetan.

MATERIAL AND METHODS

A total of 17 patients treated with [¹⁷⁷Lu]Lu-lilotomab satetraxetan in a first-in-human phase 1/2a study were included. Absorbed dose to the red marrow was explored using SPECT/CT-imaging of the lumbar vertebrae L2-L4 over multiple time points. Percentage reduction of thrombocytes and neutrophils at nadir compared to baseline (PBN) and time to nadir (TTN) were chosen as indicators of myelosuppression and included as dependent variables. Two models were applied in the analysis, a multivariate linear model and a sigmoidal description of toxicity as a function of absorbed dose. A total of 10 independent patient variables were investigated in the multivariate analysis.

RESULTS

Absorbed dose to the red marrow ranged from 1 to 4 Gy. Absorbed dose to the red marrow was found to be the only significant variable for PBN for both thrombocytes and neutrophils. The sigmoid function gave similar results in terms of accuracy when compared to the linear model.

CONCLUSION

Myelosuppression in the form of thrombocytopenia and neutropenia in patients treated with [¹⁷⁷Lu]Lu-lilotomab satetraxetan can be predicted from the SPECT/CT-derived absorbed dose estimate to the red marrow.

CD37 high expression as a potential biomarker and association with poor outcome in acute myeloid leukemia

BACKGROUND

CD37, a member of the transmembrane 4 superfamilies (TM4SF), has been proved to be abnormally expressed in a range of malignancies. Herein, we investigate the effects of CD37 expression and analyze its clinical outcome in acute myeloid leukemia (AML) patients.

METHODS

The RNA-seq and clinical data of AML patients were obtained from cBioPortal database. CD37 correlated genes, the expression prolife and survival curve of eight key genes were acquired from Gene Expression Profiling Interactive Analysis (GEPIA) and UALCAN. Pathway enrichment and protein-protein interaction (PPI) network analysis were performed based on metascape databases.

RESULTS

Our results showed that CD37 mRNA expression level was significantly up-regulated in patients with AML compared with healthy persons. Patients with high CD37 expression had shorter overall survival (OS) and disease-free survival (DFS). Pathway analysis data showed that CD37 is involved in DNA replication, RNA transport, Salmonella infection, ribonucleoprotein complex biogenesis, cell cycle phase transition and so on. Furthermore, we found eight genes correlated with CD37 are all highly expressed in AML patients, and high expression is associated with poor prognosis.

CONCLUSION

Our study described systematical expression profiles and the prognostic values of CD37 in AML; our data suggested CD37 might be novel therapeutic target and promising prognostic biomarker in the patients.

Molecular imaging in lymphoma beyond 18F-FDG-PET: understanding the biology and its implications for diagnostics and therapy

Mature lymphoproliferative diseases are a heterogeneous group of neoplasms arising from different stages of B-cell and T-cell development. With improved understanding of the molecular processes in lymphoma and novel treatment options, arises a growing need for the molecular characterisation of tumours. Molecular imaging with single-photon-emission CT and PET using specific radionuclide tracers can provide whole-body information to investigate cancer biology, to evaluate phenotypic heterogeneity, to identify resistance to targeted therapy, and to assess the biodistribution of drugs in patients. In this Review, we evaluate the existing literature on molecular imaging in lymphoma, other than ¹⁸F-fluordeoxyglucose molecular imaging. The aim is to examine the contribution of molecular imaging to the understanding of the biology of lymphoma and to discuss potential implications for the diagnostics and therapy of this disease. Finally, we discuss possible applications for molecular imaging of patients with lymphoma in the clinical context.

Analysis of antiglobulin (HAMA) response in a group of patients with B-lymphocytic malignancies treated with 131I-Lym-1

Host development of human anti-mouse antibodies (HAMA) in response to administered antibodies has been reported as a problem for antibody imaging and therapy. However, radioimmunotherapy has been shown to be effective in patients with B-cell malignancies because their immunodeficient state precludes or delays development of a HAMA response to mouse antibodies. Baseline HAMA activity was assayed in 60 patients with B-lymphocytic non-Hodgkin's lymphoma or chronic lymphocytic leukemia and sequentially in 43 patients who were subsequently treated with radiolabeled Lym-1 antibody. Pre-existing “HAMA” activity was found in 3 (5%) of the 60 patients screened for treatment consideration. The incidence of development of HAMA in the 43 patients treated with multiple doses of radiolabeled Lym-1 antibody was 12 (28%). There was no evidence for an anaphylactoid or related response in the HAMA positive patients. HAMA activity interrupted therapy in 14% of the patients (6 of 43) but did not preclude therapeutic responses to radiolabeled Lym-1 therapy. Median survival for the HAMA positive patients was longer (18 months) than for those who did not develop HAMA activity (9 months).

Safety, tolerability, and preliminary activity of IMGN529, a CD37-targeted antibody-drug conjugate, in patients with relapsed or refractory B-cell non-Hodgkin lymphoma: a dose-escalation, phase I study

Background CD37 is expressed on B-cell lymphoid malignancies, thus making it an attractive candidate for targeted therapy in non-Hodgkin lymphoma (NHL). IMGN529 is an antibody-drug conjugate comprising a CD37-binding antibody linked to the maytansinoid DM1, a potent anti-mitotic agent. Methods This first-in-human, phase 1 trial recruited adult patients with relapsed or refractory B-cell NHL. The primary objective was to determine the maximum tolerated dose (MTD) and recommended phase 2 dose. Secondary objectives were to evaluate safety, pharmacokinetics, and preliminary clinical activity. IMGN529 was administered intravenously once every 3 weeks, and dosed using a conventional 3 + 3 dose-escalation design. Results Forty-nine patients were treated at doses escalating from 0.1 to 1.8 mg/kg. Dose limiting toxicities occurred in eight patients and included peripheral neuropathy, febrile neutropenia, neutropenia, and thrombocytopenia. The most frequent treatment-emergent adverse events were fatigue (39%), neutropenia, pyrexia, and thrombocytopenia (each 37%). Adverse events led to treatment discontinuation in 10 patients (20%). Eight patients (16%) had treatment-related serious adverse events, the most common being grade 3 febrile neutropenia. The MTD (with growth factor support) was 1.4 mg/kg every 3 weeks. IMGN529 plasma exposure increased monotonically with dose and was consistent with target-mediated drug disposition. Five (13%) of 39 response-evaluable patients achieved an objective response (one complete response and four partial responses), four of which occurred in the subgroup of patients with diffuse large B-cell lymphoma. Conclusions The manageable safety profile of IMGN529 and preliminary evidence of activity, particularly in DLBCL patients, support the continued development of this novel CD37-targeting agent.

Investigational therapies targeting CD37 for the treatment of B-cell lymphoid malignancies

INTRODUCTION

While chemotherapy still remains a cornerstone of oncologic therapy, immunotherapy with monoclonal antibodies has steadily improved the treatment strategy for several hematologic malignancies. New treatment options need to be developed for relapsed and refractory non-Hodgkin lymphoma (NHL) patients. Currently, novel agents targeting specific molecules on the surface of lymphoma cells, such as anti-CD37 antibodies, are under considerable investigation. Here we report on anti-CD37 targeting for the treatment of patients with B-cell NHL.

AREAS COVERED

CD37 seems to be the perfect therapeutic target in patients with NHL. The CD37 antigen is abundantly expressed in B-cells, but is absent on normal stem cells and plasma cells. It is hoped that anti-CD37 monoclonal antibodies will increase the efficacy and reduce toxicity in patients with both newly diagnosed and relapsed and refractory disease. Recent clinical trials have shown promising outcomes for these agents, administered both as monotherapy and in combination with standard chemotherapeutics.

EXPERT OPINION

The development of new therapeutic options might help to avoid cytotoxic chemotherapy entirely in some clinical settings. This article presents the latest state of the art on the new treatment strategies in NHL patients. It also discusses recently approved agents and available clinical trial data.

Lymphoma: current status of clinical and preclinical imaging with radiolabeled antibodies

Lymphoma is a complex disease that arises from cells of the immune system with an intricate pathology. While lymphoma may be classified as Hodgkin or non-Hodgkin, each type of tumor is genetically and phenotypically different and highly invasive tissue biopsies are the only method to investigate these differences. Noninvasive imaging strategies, such as immunoPET, can provide a vital insight into disease staging, monitoring treatment response in patients, and dose planning in radioimmunotherapy. ImmunoPET imaging with radiolabeled antibody-based tracers may also assist physicians in optimizing treatment strategies and enhancing patient stratification. Currently, there are two common biomarkers for molecular imaging of lymphoma, CD20 and CD30, both of which have been considered for investigation in preclinical imaging studies. In this review, we examine the current status of both preclinical and clinical imaging of lymphoma using radiolabeled antibodies. Additionally, we briefly investigate the role of radiolabeled antibodies in lymphoma therapy. As radiolabeled antibodies play critical roles in both imaging and therapy of lymphoma, the development of novel antibodies and the discovery of new biomarkers may greatly affect lymphoma imaging and therapy in the future.

90 Y-ibritumomab tiuxetan: a nearly forgotten opportunityr

Y-ibritumomab tiuxetan (90Y-IT) combines the benefits of a monoclonal antibody with the efficacy of radiation in the treatment of B-cell non-Hodgkin lymphoma (NHL), a remarkably radiosensitive hematologic malignancy. 90Y-IT activity has been well established in the indolent setting, being approved in front-line treatment of follicular lymphoma (FL) patients as well as salvage therapy. However, no advantage in OS was observed with respect to standard treatment. Promising data are available also for aggressive B-cell lymphoma. In particular, the addition of RIT to short-course first line chemotherapy enables reduction of chemotherapy while maintaining cure rates in elderly, untreated diffuse large B-cell lymphoma (DLBCL) patients. Furthermore, 90Y-IT improves response rate and outcomes of relapsed/refractory DLBCL patients, eligible and ineligible for autologous stem cell transplantation (ASCT). Clinical results have shown a role of 90Y-IT even in mantle cell lymphoma (MCL). RIT might improve responses and treat minimal residual disease when used as consolidation after first-line chemotherapy in MCL. Moreover, 90Y-IT has demonstrated its efficacy in combination with high-dose chemotherapies as conditioning regimen for ASCT, with evidence suggesting the ability to overcome chemotherapy resistance. Herein, we review the available evidence for this approved drug and examine the recently published and ongoing trials for potential novel indication in aggressive B-cell NHL.

Targeted Cancer Therapy with a Novel Anti-CD37 Beta-Particle Emitting Radioimmunoconjugate for Treatment of Non-Hodgkin Lymphoma

177Lu-DOTA-HH1 (177Lu-HH1) is a novel anti-CD37 radioimmunoconjugate developed to treat non-Hodgkin lymphoma. Mice with subcutaneous Ramos xenografts were treated with different activities of 177Lu-HH1, 177Lu-DOTA-rituximab (177Lu-rituximab) and non-specific 177Lu-DOTA-IgG1 (177Lu-IgG1) and therapeutic effect and toxicity of the treatment were monitored. Significant tumor growth delay and increased survival of mice were observed in mice treated with 530 MBq/kg 177Lu-HH1 as compared with mice treated with similar activities of 177Lu-rituximab or non-specific 177Lu-IgG1, 0.9% NaCl or unlabeled HH1. All mice injected with 530 MBq/kg of 177Lu-HH1 tolerated the treatment well. In contrast, 6 out of 10 mice treated with 530 MBq/kg 177Lu-rituximab experienced severe radiation toxicity. The retention of 177Lu-rituximab in organs of the mononuclear phagocyte system was longer than for 177Lu-HH1, which explains the higher toxicity observed in mice treated with 177Lu-rituximab. In vitro internalization studies showed that 177Lu-HH1 internalizes faster and to a higher extent than 177Lu-rituximab which might be the reason for the better therapeutic effect of 177Lu-HH1.

AGS67E, an Anti-CD37 Monomethyl Auristatin E Antibody-Drug Conjugate as a Potential Therapeutic for B/T-Cell Malignancies and AML: A New Role for CD37 in AML

CD37 is a tetraspanin expressed on malignant B cells. Recently, CD37 has gained interest as a therapeutic target. We developed AGS67E, an antibody-drug conjugate that targets CD37 for the potential treatment of B/T-cell malignancies. It is a fully human monoclonal IgG2 antibody (AGS67C) conjugated, via a protease-cleavable linker, to the microtubule-disrupting agent monomethyl auristatin E (MMAE). AGS67E induces potent cytotoxicity, apoptosis, and cell-cycle alterations in many non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL) cell lines and patient-derived samples in vitro. It also shows potent antitumor activity in NHL and CLL xenografts, including Rituxan-refractory models. During profiling studies to confirm the reported expression of CD37 in normal tissues and B-cell malignancies, we made the novel discovery that the CD37 protein was expressed in T-cell lymphomas and in AML. AGS67E bound to >80% of NHL and T-cell lymphomas, 100% of CLL and 100% of AML patient-derived samples, including CD34(+)CD38(-) leukemic stem cells. It also induced cytotoxicity, apoptosis, and cell-cycle alterations in AML cell lines and antitumor efficacy in orthotopic AML xenografts. Taken together, this study shows not only that AGS67E may serve as a potential therapeutic for B/T-cell malignancies, but it also demonstrates, for the first time, that CD37 is well expressed and a potential drug target in AML.

Otlertuzumab (TRU-016), an anti-CD37 monospecific ADAPTIR(™) therapeutic protein, for relapsed or refractory NHL patients

CD37 is cell surface tetraspanin present on normal and malignant B cells. Otlertuzumab (TRU-016) is a novel humanized anti-CD37 protein therapeutic. Patients with relapsed or refractory follicular non-Hodgkin lymphoma (FL), mantle cell lymphoma (MCL), or Waldenström's macroglobulinaemia (WM) received otlertuzumab at 20 mg/kg administered intravenously once a week for up to 8 weeks followed by 4 monthly doses. Sixteen patients were treated; median age was 62·5 years (range, 41-81), and median number of prior regimens was 4 (range, 1-7). Twelve patients were refractory to prior treatment, 5 were refractory to rituximab. The mean terminal half-life was 9·5 days. Lymph node reduction of ≥50% by computerized tomography scan measurements was seen in 3 of 12 patients, including one FL patient who had a partial response. One WM patient had a minor response. The most frequent adverse events were neutropenia, fatigue, nausea, thrombocytopenia, diarrhoea, and peripheral oedema; most were grade 1/2. Otlertuzumab treatment appears to have been well tolerated by the patients in this study. Clinical activity was observed in this small heterogeneous cohort of highly refractory, heavily pretreated B-cell non-Hodgkin lymphoma patients. These data suggest that further clinical investigation in non-Hodgkin lymphoma is warranted.

177Lu-DOTA-HH1, a novel anti-CD37 radio-immunoconjugate: a study of toxicity in nude mice

BACKGROUND

CD37 is an internalizing B-cell antigen expressed on Non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia cells (CLL). The anti-CD37 monoclonal antibody HH1 was conjugated to the bifunctional chelator p-SCN-Bn-DOTA and labelled with the beta-particle emitting radionuclide 177Lu creating the radio-immunoconjugate (RIC) 177Lu-DOTA-HH1 (177Lu-HH1, trade name Betalutin). The present toxicity study was performed prior to initiation of clinical studies with 177Lu-HH1.

METHODOLOGY/PRINCIPAL FINDINGS

Nude mice with or without tumor xenografts were treated with 50 to 1000 MBq/kg 177Lu- HH1 and followed for clinical signs of toxicity up to ten months. Acute, life threatening bone marrow toxicity was observed in animals receiving 800 and 1000 MBq/kg 177Lu-HH1. Significant changes in serum concentrations of liver enzymes were evident for treatment with 1000 MBq/kg 177Lu-HH1. Lymphoid depletion, liver necrosis and atrophy, and interstitial cell hyperplasia of the ovaries were also observed for mice in this dose group.

CONCLUSIONS/SIGNIFICANCE

177Lu-DOTA-HH1 was well tolerated at dosages about 10 times above those considered relevant for radioimmunotherapy in patients with B-cell derived malignancies.The toxicity profile was as expected for RICs. Our experimental results have paved the way for clinical evaluation of 177Lu-HH1 in NHL patients.

A phase 1 study evaluating the safety and tolerability of otlertuzumab, an anti-CD37 mono-specific ADAPTIR therapeutic protein in chronic lymphocytic leukemia

Otlertuzumab is a novel humanized anti-CD37 protein therapeutic. This study evaluated the safety of otlertuzumab administered intravenously to patients with chronic lymphocytic leukemia (CLL). Otlertuzumab was administered weekly for up to 8 weeks followed by 1 dose per month for 4 months ranging from 0.03 to 20 mg/kg in the dose-escalation phase and 10 to 30 mg/kg in the dose-expansion phase. Responses were determined by using the 1996 National Cancer Institute (NCI-96) and 2008 International Workshop on Chronic Lymphocytic Leukaemia (IWCLL) criteria. Fifty-seven patients were treated in the dose-escalation phase and 26 in the dose-expansion phase. A maximum-tolerated dose was not identified. Response occurred in 19 (23%) of 83 treated patients by NCI-96 criteria. All responses were partial and occurred more commonly in patients with symptomatic untreated CLL (6/7) or 1 to 2 prior therapies (12/28) vs 3 or more therapies (1/48). Twenty percent (12/61) with serial computed tomography scan assessment had a response per IWCLL criteria. The most frequent adverse events were infusion reactions, fatigue, nausea, and diarrhea and were not dose related. Otlertuzumab was well tolerated, and modest clinical activity was observed. Otlertuzumab warrants further evaluation in combination with other agents for the treatment of CLL. This trial was registered at www.clinicaltrials.gov as #NCT00614042.

Biodistribution and dosimetry of (177)Lu-tetulomab, a new radioimmunoconjugate for treatment of non-Hodgkin lymphoma

The biodistribution of the anti-CD37 radioimmunoconjugate ¹⁷⁷Lu-tetraxetan-tetulomab (¹⁷⁷Lu-DOTA-HH1) was evaluated. Biodistribution of ¹⁷⁷Lu-tetraxetan-tetulomab was compared with ¹⁷⁷Lu-tetraxetan-rituximab and free ¹⁷⁷Lu in nude mice implanted with Daudi lymphoma xenografts. The data showed that ¹⁷⁷Lu-tetulomab had a relevant stability and tumor targeting properties in the human lymphoma model. The half-life of ¹⁷⁷Lu allowed significant tumor to normal tissue ratios to be obtained indicating that ¹⁷⁷Lu-tetraxetan-tetulomab could be suitable for clinical testing. The biological and effective half-life in blood was higher for ¹⁷⁷Lu-tetraxetan-tetulomab than for ¹⁷⁷Lu-tetraxetan-rituximab. The biodistribution of ¹⁷⁷Lu-tetraxetan-tetulomab did not change significantly when the protein dose was varied from 0.01 to 1 mg/kg. Dosimetry calculations showed that the absorbed radiation doses to normal tissues and tumor in mice were not significantly different for ¹⁷⁷Lu-tetraxetan-tetuloma b and ¹⁷⁷Lu-tetraxetan-rituximab. The absorbed radiation doses were extrapolated to human absorbed radiation doses. These extrapolated absorbed radiation doses to normal tissues for ¹⁷⁷Lu-tetraxetan-tetulomab at an injection of 40 MBq/kg were significantly lower than the absorbed radiation doses for 15 MBq/kg Zevalin, suggesting that higher tumor radiation dose can be reached with ¹⁷⁷Lu-tetraxetan-tetulomab in the clinic.

A novel anti-CD37 antibody-drug conjugate with multiple anti-tumor mechanisms for the treatment of B-cell malignancies

CD37 has gathered renewed interest as a therapeutic target in non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL); however, CD37-directed antibody-drug conjugates (ADCs) have not been explored. Here, we identified a novel anti-CD37 antibody, K7153A, with potent in vitro activity against B-cell lines through multiple mechanisms including apoptosis induction, antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and complement-dependent cytotoxicity. The antibody was conjugated to the maytansinoid, DM1, a potent antimicrotubule agent, via the thioether linker, N-succinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC), and the resulting ADC, IMGN529, retained the intrinsic antibody activities and showed enhanced cytotoxic activity from targeted payload delivery. In lymphoma cell lines, IMGN529 induced G2/M cell cycle arrest after internalization and lysosomal processing to lysine-N(ε)-SMCC-DM1 as the sole intracellular maytansinoid metabolite. IMGN529 was highly active against subcutaneous B-cell tumor xenografts in severe combined immunodeficient mice with comparable or better activity than rituximab, a combination of cyclophosphamide, vincristine, and prednisone, or bendamustine. In human blood cells, CD37 is expressed in B cells at similar levels as CD20, and IMGN529 resulted in potent and specific depletion of normal and CLL B cells. These results support evaluation of the CD37-targeted ADC, IMGN529, in clinical trials in patients with B-cell malignancies including NHL and CLL.

Glycovariant anti-CD37 monospecific protein therapeutic exhibits enhanced effector cell-mediated cytotoxicity against chronic and acute B cell malignancies

TRU-016 is a SMIP(TM) (monospecific protein therapeutic) molecule against the tetraspanin transmembrane family protein CD37 that is currently in Phase 2 trials in Chronic Lymphocytic Leukemia (CLL) and Non-Hodgkin Lymphoma (NHL). In an attempt to enhance the ADCC function of SMIP-016, the chimeric version of TRU-016, SMIP-016(GV) was engineered with a modification in a glycosylation site in the Fc domain. The wild-type and glycovariant SMIP proteins mediate comparable Type I antibody-like direct cytotoxicity in the presence of anti-human Fc crosslinker and show a similar tyrosine phosphorylation pattern post-treatment. However, NK cells stimulated with the SMIP-016(GV) exhibit enhanced activation and release 3-fold more interferon-γ compared with SMIP-016. SMIP-016(GV) shows enhanced ADCC function against cells expressing CD37 with NK cell effectors derived from both normal and CLL-affected individuals. Enhanced ADCC is observed against CLL cells and is sustained at concentrations of SMIP-016(GV) as low at 5E(-6) µg/mL on cells expressing minimal CD37 antigen. In support of the biological relevance of this, SMIP-016(GV) mediates effective ADCC against primary acute lymphoblastic leukemia (ALL) cells with low surface expression of CD37. Collectively, these data suggest potential use of the novel therapeutic agent SMIP-016(GV) with enhanced effector function for B cell malignancies, including CLL and ALL therapy.

Targeting tetraspanins in cancer

INTRODUCTION

Tetraspanins are a family of small proteins that cross the membrane four times and form complexes by interacting between themselves and with a variety of transmembrane and cytosolic proteins, building a network of interactions referred to as tetraspanin web or tetraspanin enriched microdomains (TEMs). These domains provide a signaling platform involved in many important cellular functions and malignant processes.

AREAS COVERED

The authors describe the methods and the rationale for targeting tetraspanins in the therapy of cancer in this review.

EXPERT OPINION

Targeting tetraspanins in cancer may be a promising therapy due to the importance of tetraspanins in several steps of tumor formation, communication with the environment, dissemination, and metastasis.

Radioimmunotherapy in mantle cell lymphoma

Mantle cell lymphoma (MCL), though characterized by the chromosomal translocation t(11; 14) (q13; q32), is a heterogeneous disease. Often termed an aggressive lymphoma in the U.S., but included in indolent lymphoma trials in Europe, MCL is not curable with standard immuno-chemotherapy. There is no single standard initial therapy for this disease. Although standard lymphoma therapies yield high response rates, relapse is inevitable. Unmet needs in MCL include better induction therapy, consolidation treatments to prolong first remission and better therapeutic options for relapsed disease. In this review, we evaluate the role of radioimmunotherapy (RIT) in MCL, a novel strategy combining monoclonal antibodies with radioisotopes to deliver radiation directly to tumour tissue, both in the frontline and relapsed setting.

Using antibodies to target cancer therapeutics

INTRODUCTION

Over a half a century ago, radiolabeled antibodies were shown to localize selectively in tissues based on the expression of unique antigens. Antibodies have since become the de facto targeting agent, even inspiring the development of non-antibody compounds for targeting purposes.

AREAS COVERED

In this article, we review various aspects of how antibodies are transforming the way cancer is being detected and treated, with the growing demand for unconjugated and many new antibody conjugates. While unconjugated antibodies continue to garner most of the attention, interest in new antibody drug conjugates and immunotoxins has expanded over the past few years. However, there continues to be active research with new radioimmunoconjugates for imaging and therapy, particularly with α-emitters, as well as antibody-targeted cytokines and other biological response modifiers.

EXPERT OPINION

The increasing number of new agents being developed and tested clinically suggests that antibody-targeted compounds will have an expanding role in the future.

Clinical radioimmunotherapy--the role of radiobiology

Conventional external-beam radiation therapy is dedicated to the treatment of localized disease, whereas radioimmunotherapy represents an innovative tool for the treatment of local or diffuse tumors. Radioimmunotherapy involves the administration of radiolabeled monoclonal antibodies that are directed specifically against tumor-associated antigens or against the tumor microenvironment. Although many tumor-associated antigens have been identified as possible targets for radioimmunotherapy of patients with hematological or solid tumors, clinical success has so far been achieved mostly with radiolabeled antibodies against CD20 ((131)I-tositumomab and (90)Y-ibritumomab tiuxetan) for the treatment of lymphoma. In this Review, we provide an update on the current challenges aimed to improve the efficacy of radioimmunotherapy and discuss the main radiobiological issues associated with clinical radioimmunotherapy.

A novel Fc-engineered monoclonal antibody to CD37 with enhanced ADCC and high proapoptotic activity for treatment of B-cell malignancies

The tetraspanin CD37 is widely expressed in B-cell malignancies and represents an attractive target for immunotherapy with mAbs. We have chimerized a high-affinity mouse Ab to CD37 and engineered the CH2 domain for improved binding to human Fcγ receptors. The resulting mAb 37.1 showed high intrinsic proapoptotic activity on malignant B cells accompanied by homotypic aggregation. Furthermore, the Ab-mediated high Ab-dependent cell-mediated cytotoxicity (ADCC) on lymphoma and primary CLL cells. mAb 37.1 strongly depleted normal B cells as well as spiked B-lymphoma cells in blood samples from healthy donors as well as malignant B cells in blood from CLL patients. In all assays, mAb 37.1 was superior to rituximab in terms of potency and maximal cell lysis. A single dose of mAb CD37.1 administered to human CD37-transgenic mice resulted in a reversible, dose-dependent reduction of peripheral B cells. In a Ramos mouse model of human B-cell lymphoma, administration of mAb 37.1 strongly suppressed tumor growth. Finally, a surrogate Fc-engineered Ab to macaque CD37, with in vitro proapoptotic and ADCC activities very similar to those of mAb 37.1, induced dose-dependent, reversible B-cell depletion in cynomolgus monkeys. In conclusion, the remarkable preclinical pharmacodynamic and antitumor effects of mAb 37.1 warrant clinical development for B-cell malignancies.

The Role of Nuclear Medicine in the Treatment of Non-Hodgkin's Lymphoma (NHL)

The emergence of radioimmunotherapy (RIT) provides a new therapeutic approach in which monoclonal antibodies directed against tumor-specific antigens are used to target therapeutic radioisotopes to sites of disseminated disease. The target cell is eliminated and adjacent tumor cells, to which antibody has not bound, are also killed. To date, 90Y-ibritumomab tiuxetan and 131I-tositumomab are the only FDA-approved, and most extensively studied, radioimmunoconjugates for RIT of non-Hodgkin's lymphoma (NHL). Both 90Y-ibritumomab tiuxetan and 131I-tositumomab utilize an anti-CD20 monoclonal antibody to target radioactivity to malignant B-cells. 90Y-ibritumomab tiuxetan emits pure therapeutic beta radiation, permitting outpatient treatment. The high energy of the beta particles emitted by 90Y (2.3 MeV) achieves a wide-ranging crossfire effect. Approximately 90% of the energy is deposited within 5 mm of the radiation source, which kills not only antibody-bound cells but also neighboring malignant cells within a diameter of up to 12 mm. In addition, the half-life of 90Y matches the in vivo biological half-life of the monoclonal antibody (64 h), with negligible excretion of 90Y in urine. With 90Y-ibritumomab tiuxetan, hematological adverse events correlate with the degree of bone marrow involvement and the bone marrow reserve, rather than with dosimetric parameters, and doses to normal organs and red marrow are well below the accepted limits of 20 Gy to normal organs and 3 Gy to red marrow. A dosing schedule based on patient weight and baseline platelet counts has therefore been developed, and dosimetry is not routinely required. 131I, the isotope used in tositumomab RIT, emits both therapeutic beta radiation and highly penetrating gamma emissions. The lower energy of the beta particles emitted by 131I (0.6 MeV) achieves a crossfire effect of up to 2 mm in diameter, which is used to treat tumors. The gamma radiation emitted by 131I allows both dosimetry and biodistribution studies to be performed; such studies are important because the rate of 131I-tositumomab clearance varies among individuals. Therefore, dosimetry must be performed in each patient before the therapeutic dose of 131I-tositumomab is administered. Similarly, because of this variability in 131I clearance, the dosage of 131I-tositumomab is calculated accordingly for each patient. 131I-tositumomab is a substrate for dehalogenases, which decouple the radioisotope from the antibody moiety, resulting in free, circulating 131I, which can accumulate in the thyroid. Patients who receive 131I-tositumomab therapy are usually hospitalized in radioprotection wards, and are treated by specially trained hospital staff. The administration of RIT requires an integrated team approach, involving nuclear medicine (or, in some countries, radiation oncology), hematology-oncology, nursing, radiopharmacy and radiation safety personnel. Effective collaboration between all members of the RIT team is essential to treatment success, and understanding the properties of these novel agents will facilitate their safe and effective administration.

Recombinant bispecific monoclonal antibodies prepared by the dock-and-lock strategy for pretargeted radioimmunotherapy

The selective delivery of therapeutic radionuclides is a promising approach for treating cancer. Antibody-targeted radionuclides are of particular interest, with 2 products approved for the treatment of certain forms of non-Hodgkin lymphoma. However, for many other cancers, radioimmunotherapy has been ineffective, being limited by prolonged exposure to the highly radiosensitive bone marrow. An alternative approach, known as pretargeting, separates radionuclide from the antibody, allowing the radiation to be delivered on a small molecule that can quickly and efficiently migrate into the tumor, and then rapidly clear from the body with minimal retention in tissues. Several pretargeting methods have been developed that differ in the way they selectively capture the radionuclide. This review focuses on the development of a novel form of bispecific monoclonal antibody (bsMAb) pretargeting that uses a unique radiolabeled hapten-peptide system that can be modified to bind numerous therapeutic and imaging radionuclides. Together with a specialized recombinant humanized bsMAb prepared with by a technique known as the Dock-and-Lock method, this pretargeting procedure has been examined in many different animal models, showing a high level of sensitivity and specificity for localizing tumors, and improved efficacy with less hematologic toxicity associated with directly radiolabeled IgG. The bsMAb is a tri-Fab structure, having 2 binding arms for the tumor antigen and 1 capable of binding a hapten-peptide. Preclinical studies were preformed to support the clinical use of a bsMAb and a hapten-peptide bearing a single DOTA moiety (IMP-288). A phase 0 trial found an (131)I-tri-Fab bsMAb, TF2, that targets carcinoembryonic antigen was stable in vivo, quickly clears from the blood, and localizes known tumors. The first-in-patient pretargeting experience with the (111)In-IMP-288 also observed rapid clearance and low tissue (kidney) retention, as well as localization of tumors, providing initial promising evidence for developing these materials for radioimmunotherapy.

Genomewide DNA methylation analysis reveals novel targets for drug development in mantle cell lymphoma

Mantle cell lymphoma (MCL) is a mostly incurable malignancy arising from naive B cells (NBCs) in the mantle zone of lymph nodes. We analyzed genomewide methylation in MCL patients with the HELP (HpaII tiny fragment Enrichment by Ligation-mediated PCR) assay and found significant aberrancy in promoter methylation patterns compared with normal NBCs. Using biologic and statistical criteria, we further identified 4 hypermethylated genes CDKN2B, MLF-1, PCDH8, and HOXD8 and 4 hypomethylated genes CD37, HDAC1, NOTCH1, and CDK5 when aberrant methylation was associated with inverse changes in mRNA levels. Immunohistochemical analysis of an independent cohort of MCL patient samples confirmed CD37 surface expression in 93% of patients, validating its selection as a target for MCL therapy. Treatment of MCL cell lines with a small modular immunopharmaceutical (CD37-SMIP) resulted in significant loss of viability in cell lines with intense surface CD37 expression. Treatment of MCL cell lines with the DNA methyltransferase inhibitor decitabine resulted in reversal of aberrant hypermethylation and synergized with the histone deacetylase inhibitor suberoylanilide hydroxamic acid in induction of the hypermethylated genes and anti-MCL cytotoxicity. Our data show prominent and aberrant promoter methylation in MCL and suggest that differentially methylated genes can be targeted for therapeutic benefit in MCL.

Improving the treatment of non-Hodgkin lymphoma with antibody-targeted radionuclides

Radioimmunotherapy of non-Hodgkin lymphoma comprises a (90)Y- or (131)I-labeled murine anti-CD20 IgG, but both agents also include a substantial dose of unlabeled anti-CD20 IgG given immediately before the radioconjugate to reduce its uptake in the spleen (primary normal B-cell antigen sink); this extends its plasma half-life and improves tumor visualization. Thus, these treatments combine an effective anti-CD20 radioconjugate with an unconjugated anti-CD20 antibody that is also therapeutically active, but the large anti-CD20 IgG predose ( approximately 900 mg) may diminish the tumor localization of the radioimmunoconjugate (eg, 10-35 mg). We have examined alternative approaches that enhance radionuclide targeting and improve antitumor responses. One uses a (90)Y-labeled anti-CD22 IgG (epratuzumab) combined with an antibody therapy regimen of a humanized anti-CD20 IgG (veltuzumab). Pretargeted radionuclide therapy using a trivalent, humanized, recombinant bispecific anti-CD20 antibody with a (90)Y-hapten-peptide is another highly effective method that is also less toxic than directly radiolabeled IgG. Finally, all approaches benefit from the addition of a consolidation-dosing regimen of the anti-CD20 IgG antibody. This article reviews these various options and discusses how some fundamental changes could potentially enhance the response and duration from radionuclide-targeted therapy.

Targeting of tetraspanin proteins--potential benefits and strategies

The tetraspanin transmembrane proteins have emerged as key players in malignancy, the immune system, during fertilization and infectious disease processes. Tetraspanins engage in a wide range of specific molecular interactions, occurring through the formation of tetraspanin-enriched microdomains (TEMs). TEMs therefore serve as a starting point for understanding how tetraspanins affect cell signalling, adhesion, morphology, motility, fusion and virus infection. An abundance of recent evidence suggests that targeting tetraspanins, for example, by monoclonal antibodies, soluble large-loop proteins or RNAi technology, should be therapeutically beneficial.

A re-examination of radioimmunotherapy in the treatment of non-Hodgkin lymphoma: prospects for dual-targeted antibody/radioantibody therapy

Antibody-based therapies, both unconjugated antibodies and radioimmunotherapy, have had a significant impact on the treatment of non-Hodgkin lymphoma. Single-agent rituximab is an effective therapy, but it is being increasingly used with combination chemotherapy to improve the objective response and its duration. The approved anti-CD20 radioimmunoconjugates ((90)Y-ibritumomab tiuxetan or (131)I-tositumomab) have had encouraging results, with trials now seeking to incorporate a radioimmunoconjugate in various settings. However, new preclinical data raise important questions concerning current radioimmunoconjugate treatment regimens and ways to improve them. In radioconjugate therapy, nearly 900 mg of the unlabeled anti-CD20 IgG antibody is predosed to the patient before the anti-CD20 antibody conjugated to either (90)Y or (131)I is given. Combining an unconjugated anti-CD20 antibody therapy with a radioimmunoconjugate binding to a noncompeting antigen might improve responses by allowing optimal uptake of each agent. Preclinical models have indicated that careful consideration should be given to predosing when using competing antibodies, but that consolidation anti-CD20 therapy enhances the efficacy of radioimmunoconjugate therapy. New technologies, such as pretargeted radioimmunotherapy, also hold promise by reducing toxicity without sacrificing efficacy, and consideration should be given to fractionating or giving multiple radioimmunoconjugate treatments. This perspective discusses how these issues could affect current and future clinical trials.

Myeloablative 131I-tositumomab radioimmunotherapy in treating non-Hodgkin's lymphoma: comparison of dosimetry based on whole-body retention and dose to critical organ receiving the highest dose

Myeloablative radioimmunotherapy using (131)I-tositumomab (anti-CD20) monoclonal antibodies is an effective therapy for B-cell non-Hodgkin's lymphoma. The amount of radioactivity for radioimmunotherapy may be determined by several methods, including those based on whole-body retention and on dose to a limiting normal organ. The goal of each approach is to deliver maximal myeloablative amounts of radioactivity within the tolerance of critical normal organs.

METHODS

Records of 100 consecutive patients who underwent biodistribution and dosimetry evaluation after tracer infusion of (131)I-tositumomab before radioimmunotherapy were reviewed. We assessed organ and tissue activities over time by serial gamma-camera imaging to calculate radiation-absorbed doses. Organ volumes were determined from CT scans for organ-specific dosimetry. These dose estimates helped us to determine therapy on the basis of projected dose to the critical normal organ receiving a maximum tolerable radiation dose. We compared organ-specific dosimetry for treatment planning with the whole-body dose-assessment method by retrospectively analyzing the differences in projected organ-absorbed doses and their ratios.

RESULTS

Mean organ doses per unit of administered activity (mGy/MBq) estimated by both methods were 0.33 for liver and 0.33 for lungs by the whole-body method and 1.52 for liver and 1.74 for lungs by the organ-specific method (P=0.0001). The median differences between methods were 0.92 mGy/MBq (range, 0.36-2.2 mGy/MBq) for lungs, 0.82 mGy/MBq (range, 0.28-1.67 mGy/MBq) for liver, and -0.01 mGy/MBq (range, -0.18-0.16 mGy/MBq) for whole body. The median ratios of the treatment activities based on limiting normal-organ dose were 5.12 (range, 2.33-10.01) for lungs, 4.14 (range, 2.16-6.67) for liver, and 0.94 (range, 0.79-1.22) for whole body. We found substantial differences between the dose estimated by the 2 methods for liver and lungs (P=0.0001).

CONCLUSION

Dosimetry based on whole-body retention will underestimate the organ doses, and a preferable approach is to evaluate organ-specific doses by accounting for actual radionuclide biodistribution. Myeloablative treatments based on the latter approach allow administration of the maximum amount of radioactivity while minimizing toxicity.

Lym-1-induced apoptosis of non-Hodgkin's lymphomas produces regression of transplanted tumors

Lym-1 was one of the first antibodies to be used successfully for the radioimmunotherapy of the human malignant lymphomas. This antibody, which recognizes the HLA-DR10 antigen preferentially expressed in B-cell lymphomas, was recently shown to induce apoptosis upon binding to lymphoma cells. In this study, Lym-1-induced apoptosis was studied to identify the potential molecular pathways of programmed cell death and to demonstrate the clinical potential of this antibody in the treatment of the human malignant lymphomas. Immunofluorescence microscopy revealed that Lym-1 stained focal areas of the cell surface, consistent with the fact that the HLA-DR10 antigen is associated with lipid rafts, a known prerequisite for apoptosis signaling. Likewise, Annexin V/propidium iodide staining and TUNEL assays demonstrated that both murine Lym-1 and chimeric Lym-1 induced both early and late apoptosis, respectively, unlike anti-CD20 rituximab. Furthermore, Lym-1 was found to produce a rapid loss of mitochondrial membrane potential and mitochondrial release of cytochrome C 14 hours post-Lym-1 treatment. Although it was found to activate caspase-3, inhibitors of caspase pathways showed that the Lym-1-induced apoptosis in lymphoma cell lines is independent of caspase induction. Finally, treatment studies in vivo demonstrated that, compared with murine anti-CD20 (2B8), Lym-1 was more effective in inducing the regression of human lymphoma xenografts. Based upon these results, chimeric Lym-1 should be especially effective in treating lymphoma patients, as, in addition to being able to elicit immune effector functions such as chimeric anti-CD20, it can also induce apoptosis directly upon cell binding.

Current results and future applications of radioimmunotherapy management of non-Hodgkin's lymphoma

Monoclonal antibodies labeled with radionuclides have become an important therapeutic tool in the treatment of patients with non-Hodgkin's lymphomas (NHL). At the present time, their use in the US is approved for patients with rituximab-resistant, low-grade, follicular or transformed NHL. Encouraging responses seen in the relapsed and refractory patients have prompted their evaluation in earlier disease or in other histologic sub-types either alone or in combination with conventional chemotherapy. Additionally, they have been included as preparative regimens for stem cell transplant protocols within the context of clinical trials. This review discusses the latest clinical trials and future directions of radioimmunoconjugates in the treatment of NHL, with emphasis on US Food and Drug Administration (FDA) approved radioimmunoconjugates, namely 131I-tositumomab and 90Y-ibritumomab tiuxetan.

Preclinical and clinical evaluation of epratuzumab (anti-CD22 IgG) in B-cell malignancies

The vast majority of non-Hodgkin's lymphomas are of B-cell phenotype. Development of unlabeled or radiolabeled therapeutic monoclonal antibodies against the cell surface antigen, CD20, has revolutionized the treatment of these malignancies. It is clear that antibodies targeting other B-cell-specific molecules, such as CD22, also offer potential therapeutic benefit. Epratuzumab is a humanized anti-CD22 monoclonal, which has undergone preclinical and phase I/II clinical evaluation in patients with indolent or aggressive lymphoma. Data suggest that this agent is well tolerated, and can induce tumor regressions. Trials are currently evaluating its safety and activity in combination with rituximab (chimeric anti-CD20) and standard chemotherapy are ongoing. Initial results suggest that these regimens have acceptable toxicity, and that epratuzumab warrants further evaluation as an adjunct to standard lymphoma treatment regimens.

Targeting CD37-positive lymphoid malignancies with a novel engineered small modular immunopharmaceutical

CD37 is a lineage-specific B-cell antigen that to date has been neglected as an attractive therapeutic target. To exploit this, novel CD37-specific small modular immunopharmaceuticals (CD37-SMIP) that include variable regions linked to modified human IgG(1) hinge, CH(2), and CH(3) domains were designed. The lead CD37-SMIP molecule induces potent apoptosis in the presence of a cross-linker, and antibody-dependent cellular cytotoxicity against B-cell leukemia/lymphoma cell lines and primary chronic lymphocytic leukemia (CLL) cells superior to therapeutic antibodies used in these diseases. The CD37-SMIP-dependent ADCC function in vitro was mediated by natural killer (NK) cells but not naive or activated monocytes. Significant in vivo therapeutic efficacy was demonstrated in a SCID mouse xenograft leukemia/lymphoma model. Depletion of NK cells in this mouse model resulted in diminished efficacy further supported the in vivo importance of NK cells in SMIP therapy. These findings provide strong justification for CD37 as a therapeutic target and introduce small modular immunopharmaceuticals as a novel class of targeted therapies for B-cell malignancies.

Epratuzumab in the therapy of oncological and immunological diseases

B cells play an important role in the pathogenesis of certain lymphomas and leukemias, as well as many autoimmune diseases. Antagonistic B-cell antibodies are thus gaining an increasing role in the management of these diseases. The first antibody target in this regard was CD20, with the development and introduction of rituximab in the management of B-cell malignancies, as well as rheumatoid arthritis. A second candidate target is CD22. The first antagonistic antibody to this B-cell marker, epratuzumab, appears to function, in contrast to CD20 antibodies, more by modulation of B cells rather than by their high depletion in circulation. Originally developed for the treatment of non-Hodgkin's lymphoma, epratuzumab has now been found to be effective, with a very good safety profile, in two prototype autoimmune diseases: systemic lupus erythematosus and primary Sjögren's syndrome. Recent studies have demonstrated the activity and safety of epratuzumab in non-Hodgkin's lymphoma patients who have relapsed or are refractive to conventional therapy, including rituximab, and has also shown good activity in follicular and diffuse large B-cell lymphoma in combination with rituximab. As such, this new investigative antibody may have a significant market potential owing to the multitude of diseases and patients who may benefit from a CD22, B-cell antibody immunotherapy that is complementary to the known effects and role of CD20 antibodies, but can usually be administered within 1 h and depletes approximately 50% of circulating B cells.

Radioimmunotherapeutic strategies in autologous hematopoietic stem-cell transplantation for malignant lymphoma

High-dose therapy followed by autologous hematopoietic stem-cell transplantation is the preferred therapy for relapsed chemotherapy-sensitive aggressive non-Hodgkin lymphoma, and may play a role in the treatment of high-risk first-remission aggressive lymphomas, mantle-cell lymphomas and relapsed follicular lymphomas. The primary cause of failure of this approach is disease recurrence despite initial responses. Traditional high-dose regimens have relied upon myeloablative combinations of chemotherapy with or without total body irradiation. In the Western world, over 90% of lymphomas are of B-cell origin, and the vast majority of those that come to transplant remain CD20-positive. The development of radioimmunotherapeutic approaches targeting this antigen allows for either dose escalation with stem-cell support, or the addition of targeted therapy to conditioning regimens either as a replacement for total body irradiation or in addition to myeloablative chemotherapy regimens. Results to date with yttrium-90 ibritumomab tiuxetan (Zevalin) and I-131 tositumomab (Bexxar) suggest that the addition of radioimmunoconjugate therapy to conventional conditioning regimens results in a toxicity profile similar to that seen with chemotherapy conditioning alone. Demonstration of improved disease control will ultimately require phase-III studies, though preliminary results are promising.

Iodine-131 tositumomab (Bexxar) in a radiation oncology environment

Iodine-131 (I-131) tositumomab (Bexxar; GlaxoSmithKline, Research Triangle Park, NC) is one of two recently approved radiolabeled antibodies directed against the CD20 surface antigen found on normal B cells and in more than 95% of B cell non-Hodgkin's lymphoma. The compound itself is formulated as an IgG2a immunoglobulin radiolabeled with the mixed beta/gamma emitter I-131. Multicenter clinical trials have repeatedly shown impressive clinical responses (20-40% complete response rates and 60-80% overall response rates) in the patient groups for whom this treatment is indicated. Treatment-related toxicity is generally extremely mild and typically involves only reversible hematopoietic suppression and (in some cases) a risk of treatment-induced hypothyroidism. Owing to the radiation safety concerns necessitated by the clinical use of this targeted radiopharmaceutical, it is important for radiation oncology departments wishing to participate in the care of these patients to establish methodologies and standard operating procedures for safe and efficient departmental use. This summary reviews the pertinent background information related to the current clinical experience with I-131 tositumomab and highlights some of the major opportunities for the participation of radiation oncology in the patient evaluation and treatment process. I-131 tositumomab provides an excellent example of the way in which the increasingly important new field of "targeted therapy" intersects with the practice of clinical radiotherapy. The author contends that it will be worth the time and effort involved in establishing a firm basis for the development of a comprehensive program for systemic targeted radiopharmaceutical therapies (STaRT) within the radiation medicine domain.

Radioinmunoterapia en los linfomas no Hodgkin: desarrollo histórico y estado actual

Radioimmunotherapy treatment for lymphoma is a novel targeted therapeutic approach. Several years of development of radioimmunotherapeutic compounds came to fruition in February of 2002 when 90Y-ibritumomab tiuxetan (Zevalin, Y2B8) was approved in the USA and later in Europe, for the treatment of relapsed or refractory, low grade or transformed B-cell lymphoma in the USA. 90Y-ibritumomab tiuxetan utilizes a monoclonal anti-CD20 antibody to deliver beta-emitting yttrium-90 to the malignant B-cells. Clinical trials have demonstrated its efficacy, with observed clinical responses in the 80 % range. This product has become available in Europe, with simplified administration, for the treatment of relapsed follicular lymphoma. A similar anti-CD20 radiotherapeutic compound, 131I-tositumomab, was subsequently approved in the USA. Promising studies exploring expanded applications of radioimmunotherapy as consolidation, as part of transplant, or in other histologic types have been recently completed or are under way. Radioimmunotherapy has been shown to be an effective and clinically relevant complementary therapeutic approach for patients with lymphoma, bringing the Nuclear Medicine into lymphoma therapeutics.

Cancer radioimmunotherapy with alpha-emitting nuclides

In lymphoid malignancies and in certain solid cancers such as medullary thyroid carcinoma, somewhat mixed success has been achieved when applying radioimmunotherapy (RIT) with beta-emitters for the treatment of refractory cases. The development of novel RIT with alpha-emitters has created new opportunities and theoretical advantages due to the high linear energy transfer (LET) and the short path length in biological tissue of alpha-particles. These physical properties offer the prospect of achieving selective tumoural cell killing. Thus, RIT with alpha-emitters appears particularly suited for the elimination of circulating single cells or cell clusters or for the treatment of micrometastases at an early stage. However, to avoid non-specific irradiation of healthy tissues, it is necessary to identify accessible tumoural targets easily and rapidly. For this purpose, a small number of alpha-emitters have been investigated, among which only a few have been used for in vivo preclinical studies. Another problem is the availability and cost of these radionuclides; for instance, the low cost and the development of a reliable actinium-225/bismuth-213 generator were probably determining elements in the choice of bismuth-213 in the only human trial of RIT with an alpha-emitter. This article reviews the literature concerning monoclonal antibodies radiolabelled with alpha-emitters that have been developed for possible RIT in cancer patients. The principal radio-immunoconjugates are considered, starting with physical and chemical properties of alpha-emitters, their mode of production, the possibilities and difficulties of labelling, in vitro studies and finally, when available, in vivo preclinical and clinical studies.

Radioimmunotherapy for Non-Hodgkin's Lymphoma

Non-Hodgkin's lymphoma (NHL) is the most common hematological malignancy in the United States with a rapidly increasing incidence. Most follicular NHL is indolent but incurable, whereas the more aggressive varieties do respond to therapy. Most patients with follicular NHL who transform to an aggressive NHL are very difficult to treat successfully. Treatment options have included chemotherapy, radiation, immunotherapy with monoclonal antibodies, alone or in combination, and hematopoietic stem cell transplantation. The efficacy of monoclonal antibodies is augmented when they are combined with a radioisotope like iodine-131 or yttrium-90. There have been a number of studies done in recent years studying the efficacy of this form of therapy, i.e., radioimmunotherapy (RIT) in patients with NHL. This review attempts to integrate the information from the various clinical trials done using RIT in patients with relapsed/refractory or newly diagnosed NHL and in hematopoietic stem cell transplantation. It also includes updates on the use of RIT in elderly patients and in patients with significant bone marrow involvement among other recent advances made in this field.

Radioimmunotherapy using 131I-rituximab in patients with advanced stage B-cell non-Hodgkin’s lymphoma: initial experience

PURPOSE

The aim of this study was to evaluate the safety, toxicity and therapeutic response of non-myeloablative radioimmunotherapy using 131I-rituximab in previously heavily treated patients with B-cell non-Hodgkin's lymphoma (B-NHL).

METHODS

Nine patients with relapsed, refractory or transformed B-NHL received ten radioimmunotherapies. Patients had a median of 5 (range 2-7) prior standard therapies. Four patients had received prior high-dose chemotherapy followed by autologous stem cell transplantation, and eight had received prior rituximab therapy. Histopathology consisted of four mantle cell, one follicular and four diffuse large B-cell lymphomas. Rituximab, a monoclonal chimeric anti-CD20 antibody (IDEC-C2B8), was labelled with 131I using the Iodogen method. The administered activity (2,200+/-600 MBq) was based on a dosimetrically calculated 45 cGy total-body radiation dose. All patients received an infusion of 2.5 mg/kg of rituximab prior to administration of the radiopharmaceutical.

RESULTS

No acute adverse effects were observed after the administration of 131I-rituximab. Radioimmunotherapy was safe in our patient group and achieved one complete response ongoing at 14 months and two partial responses progressing at 12 and 13 months after treatment. One partial responder was re-treated with radioimmunotherapy and achieved an additional progression-free interval of 7 months. Four non-responders with bulky disease died 4.8+/-2.0 months after therapy. Three patients had an elevated serum lactate dehydrogenase (LDH) level prior to radioimmunotherapy and none of the patients responded. Of two patients who received radioimmunotherapy as an additional treatment after salvage chemotherapy, one continues to be disease-free at 9 months and one relapsed at 5 months' follow-up. Reversible grade 3 or 4 haematological toxicity occurred in seven of nine patients. Median nadirs were 35 days for platelets, 44 days for leucocytes and 57 days for erythrocytes.

CONCLUSION

Radioimmunotherapy with 131I-rituximab in previously heavily treated B-NHL patients was safe and well tolerated, and four out of ten therapies induced responses. Radioimmunotherapy was less efficient in patients with bulky disease and elevated LDH. Severe haematological toxicity in seven patients did not cause significant clinical problems. Radioimmunotherapy seems to be an additional therapeutic option in carefully selected therapy-refractory B-NHL patients.

Development of 131I-tositumomab

The median survival for patients with advanced indolent non-Hodgkin's lymphoma (NHL) has remained at 7 to 8 years since the 1960s. Targeted treatment using radioimmunotherapy (RIT), radiolabeled monoclonal antibodies directed against tumor-specific antigens, is an attractive option for this patient population, combining the advantages of an active biologic therapy with low dose-rate irradiation of an inherently radiosensitive tumor. Two anti-CD20 RIT agents have now been approved for the treatment of refractory NHL: 90Y-ibritumomab tiuxetan (Zevalin; Biogen Idec Inc, San Diego, CA, and Schering AG, Berlin, Germany) is approved in both the United States and Europe, and 131I-tositumomab (Bexxar; Corixa Corp, Seattle, WA) is approved only in the United States. This article discusses the development of 131I-tositumomab. Because 131I-labeled antibody clearance varies significantly among patients, prescription of 131I-tositumomab activity must be based on a calculated total-body dose derived from quantitative whole-body imaging. The maximum tolerated total-body dose has been established at 75 cGy in patients with adequate bone marrow reserves and less than 25% bone marrow involvement by lymphoma (65 cGy in patients with mild thrombocytopenia; 45 cGy in patients who have received stem cell transplantation). In a phase III trial, overall response rate (ORR) and complete response (CR) rate were significantly higher following 131I-tositumomab than following the patient's last qualifying chemotherapy (ORR, 65% v 28%; P <.001; CR, 20% v 3%; P <.001). 131I-tositumomab has also been shown to be effective in patients who are refractory to rituximab (ORR, 70%; CR, 32%) and as first-line therapy in patients with NHL (ORR, 97%; CR, 63%). The major side effects of 131I-tositumomab are hematologic. In the phase III study, 20% of patients experienced grade 4 neutropenia and 22% experienced grade 4 thrombocytopenia. Myelodysplastic syndromes or secondary acute myeloid leukemia have been reported in 8.4% of patients with chemotherapy-refractory disease treated with 131I-tositumomab, but have not been observed to date in patients receiving 131I-tositumomab as first-line therapy. Future progress in NHL management is likely to include RIT as part of a multi-modality approach; trials are planned or currently underway to investigate the combination of RIT with chemotherapy regimens.