Iodine-131-anti-B1 radioimmunotherapy for B-cell lymphoma

Radiochemistry: A Hot Field with Opportunities for Cool Chemistry

Recent Food and Drug Administration (FDA) approval of diagnostic and therapeutic radiopharmaceuticals and concurrent miniaturization of particle accelerators leading to improved access has fueled interest in the development of chemical transformations suitable for short-lived radioactive isotopes on the tracer scale. This recent renaissance of radiochemistry is paired with new opportunities to study fundamental chemical behavior and reactivity of elements to improve their production, separation, and incorporation into bioactive molecules to generate new radiopharmaceuticals. This outlook outlines pertinent challenges in the field of radiochemistry and indicates areas of opportunity for chemical discovery and development, including those of clinically established (C-11, F-18) and experimental radionuclides in preclinical development across the periodic table.

Methods for Engineering Binders to Multi-Pass Membrane Proteins

Numerous potential drug targets, including G-protein-coupled receptors and ion channel proteins, reside on the cell surface as multi-pass membrane proteins. Unfortunately, despite advances in engineering technologies, engineering biologics against multi-pass membrane proteins remains a formidable task. In this review, we focus on the different methods used to prepare/present multi-pass transmembrane proteins for engineering target-specific biologics such as antibodies, nanobodies and synthetic scaffold proteins. The engineered biologics exhibit high specificity and affinity, and have broad applications as therapeutics, probes for cell staining and chaperones for promoting protein crystallization. We primarily cover publications on this topic from the past 10 years, with a focus on the different formats of multi-pass transmembrane proteins. Finally, the remaining challenges facing this field and new technologies developed to overcome a number of obstacles are discussed.

Radioimmunotherapy of Non-Hodgkin B-cell Lymphoma: An update

Systemic radioimmunotherapy (RIT) is arguably the most effective and least toxic anticancer treatment for non-Hodgkin lymphoma (NHL). In treatment-naïve patients with indolent NHL, the efficacy of a single injection of RIT compares with that of multiple cycles of combination chemotherapy. However, 20 years following the approval of the first CD20-targeting radioimmunoconjugates ⁹⁰Y-Ibritumomab-tiuxetan (Zevalin) and ¹³¹I-tositumomab (Bexxar), the number of patients referred for RIT in western countries has dramatically decreased. Notwithstanding this, the development of RIT has continued. Therapeutic targets other than CD20 have been identified, new vector molecules have been produced allowing for faster delivery of RIT to the target, and innovative radionuclides with favorable physical characteristics such as alpha emitters have been more widely available. In this article, we reviewed the current status of RIT in NHL, with particular focus on recent clinical and preclinical developments.

Use of imaging-based dosimetry for personalising radiopharmaceutical therapy of cancer

Theranostics - i.e., the combination of molecular imaging and radiopharmaceutical therapy of cancer targeting a common biological feature - is a rapidly expanding field owing the recent successes of novel radiopharmaceutical therapies, such as ¹⁷⁷Lu-based prostate-specific membrane antigen radioligand therapy of prostate cancer and peptide receptor radionuclide therapy of neuroendocrine tumours. Despite the ongoing technical developments in imaging-based dosimetry, the existence of tumour absorbed dose-efficacy and organ absorbed dose-toxicity relationships, as well as the high interpatient variability in absorbed doses per unit activity, radiopharmaceutical therapies are still mostly administered in a fixed-activity, one-size-fits-all fashion. This is at odds with the principles of radiation oncology, where the absorbed doses to tissues are prescribed and their delivery is carefully planned and controlled for each individual patient to maximise the clinical benefits. There is a growing body of clinical evidence that dosimetry-based radiopharmaceutical therapy allows to safely optimise tumour irradiation, which translates into improved clinical outcomes. In this narrative review, we will present the reported prospective clinical experience to date on the use of imaging-based dosimetry to personalise radiopharmaceutical therapies.

Epitope Mapping of an Anti-CD20 Monoclonal Antibody (C20Mab-60) Using Enzyme-Linked Immunosorbent Assay

CD20 is a glycosylated transmembrane protein and is expressed on normal B cells and B cell malignancies. Therapeutic antibodies against CD20 are developed and used in clinic. The understanding of antibody-antigen binding by revealing the epitope is essential for future application to antibody technology. Previously, we developed an anti-human CD20 monoclonal antibody, C₂₀Mab-60 (IgG_2a, kappa), using the Cell-Based Immunization and Screening (CBIS). C₂₀Mab-60 can be used for flow cytometry, Western blot, and immunohistochemical analyses. In this study, we examined the critical epitope of C₂₀Mab-60 using enzyme-linked immunosorbent assay (ELISA) with synthesized peptides. We performed ELISA with deletion mutants, and C₂₀Mab-60 reacted to the 160-179 amino acids sequence of CD20. Next, we analyzed the reaction to 20 point mutants, and C₂₀Mab-60 did not recognize the alanine-substituted peptides of N171A, P172A, S173A, and E174A. The results indicate that the binding epitope of C₂₀Mab-60, developed by CBIS, includes Asn171, Pro172, Ser173, and Glu174 of CD20.

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.

FDG PET/CT parameters and correlations with tumor-absorbed doses in a phase 1 trial of 177Lu-lilotomab satetraxetan for treatment of relapsed non-Hodgkin lymphoma

Purpose

¹⁷⁷Lu-lilotomab satetraxetan targets the CD37 antigen and has been investigated in a first-in-human phase 1/2a study for relapsed non-Hodgkin lymphoma (NHL). Tumor dosimetry and response evaluation can be challenging after radioimmunotherapy (RIT). Changes in FDG PET/CT parameters after RIT and correlations with tumor-absorbed doses has not been examined previously in patients with lymphoma. Treatment-induced changes were measured at FDG PET/CT and ceCT to evaluate response at the lesion level after treatment, and correlations with tumor-absorbed doses were investigated.

Methods

Forty-five tumors in 16 patients, with different pre-treatment and pre-dosing regimens, were included. Dosimetry was performed based on multiple SPECT/CT images. FDG PET/CT was performed at baseline and at 3 and 6 months. SUV_max, MTV, TLG, and changes in these parameters were calculated for each tumor. Lesion response was evaluated at 3 and 6 months (PET_3months and PET_6months) based on Deauville criteria. Anatomical changes based on ceCT at baseline and at 6 and 12 months were investigated by the sum of perpendiculars (SPD).

Results

Tumor-absorbed doses ranged from 35 to 859 cGy. Intra- and interpatient variations were observed. Mean decreases in PET parameters from baseline to 3 months were ΔSUV_max-3months 61%, ΔMTV_3months 80%, and ΔTLG_3months 77%. There was no overall correlation between tumor-absorbed dose and change in FDG PET or ceCT parameters at the lesion level or significant difference in tumor-absorbed doses between metabolic responders and non-responders after treatment.

Conclusion

Our analysis does not show any correlation between tumor-absorbed doses and changes in FDG PET or ceCT parameters for the included lesions. The combination regimen, including cold antibodies, may be one of the factors precluding such a correlation. Increased intra-patient response with increased tumor-absorbed doses was observed for most patients, implying individual variations in radiation sensitivity or biology.

Trial registration

ClinicalTrials.gov Identifier (NCT01796171). Registered December 2012

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-020-05098-x.

Phase 2 Study of Iodine-131 Tositumomab Plus Chemotherapy in Patients With Previously Untreated Mantle-Cell Lymphoma

BACKGROUND

Mantle-cell lymphoma (MCL) is sensitive to radiotherapy, and the CD20 antigen is relatively highly expressed in MCL. Therefore, radioimmunotherapy using radiolabeled anti-CD20 monoclonal antibodies has the potential to treat MCL. The objective of this study was to investigate the efficacy, pharmacokinetics, and safety of tositumomab (TST) and iodine-131 tositumomab (I-131 TST) followed by 6 cycles of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) in patients with previously untreated MCL (ClinicalTrials.govNCT00022945).

PATIENTS AND METHODS

In this phase 2 open-label study, patients received dosimetric (day 0: 450 mg TST, then 35 mg I-131 TST [5 mCi]) and therapeutic (between days 7 and 14: 450 mg TST, then an individualized dose of I-131 TST [65-75 cGy]) TST/I-131 TST, with CHOP treatment commencing approximately 13 weeks after the therapeutic dose. The primary end point was the MCL response rate to treatment; secondary end points included confirmed complete response rate and total body residence time.

RESULTS

Twenty-six patients were enrolled, and 25 were included in the intent-to-treat population. The overall unconfirmed response rate was 84%, and the confirmed complete response rate was 44%. The median progression free-survival was 27.6 months. The median total body residence time was 94.5 hours. No new or unexpected safety signals were identified.

CONCLUSION

Patients with previously untreated MCL who received radioimmunotherapy with TST/I-131 TST followed by CHOP had a high response rate and a long duration of response, indicating that radioimmunotherapy is a therapeutic option in this patient population.

Image-guided mathematical modeling for pharmacological evaluation of nanomaterials and monoclonal antibodies

While plasma concentration kinetics has traditionally been the predictor of drug pharmacological effects, it can occasionally fail to represent kinetics at the site of action, particularly for solid tumors. This is especially true in the case of delivery of therapeutic macromolecules (drug-loaded nanomaterials or monoclonal antibodies), which can experience challenges to effective delivery due to particle size-dependent diffusion barriers at the target site. As a result, disparity between therapeutic plasma kinetics and kinetics at the site of action may exist, highlighting the importance of target site concentration kinetics in determining the pharmacodynamic effects of macromolecular therapeutic agents. Assessment of concentration kinetics at the target site has been facilitated by non-invasive in vivo imaging modalities. This allows for visualization and quantification of the whole-body disposition behavior of therapeutics that is essential for a comprehensive understanding of their pharmacokinetics and pharmacodynamics. Quantitative non-invasive imaging can also help guide the development and parameterization of mathematical models for descriptive and predictive purposes. Here, we present a review of the application of state-of-the-art imaging modalities for quantitative pharmacological evaluation of therapeutic nanoparticles and monoclonal antibodies, with a focus on their integration with mathematical models, and identify challenges and opportunities. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Diagnostic Tools > in vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Biodistribution and Dosimetry of Indigenously Produced 131I-Rituximab in B-Cell Lymphoma: Pilot Study Estimating Patient-Specific Dose Comparing 2 Different Dosimetric Methods

Cost containment through indigenous production of radioimmunotherapy agents for non-Hodgkin lymphoma (NHL) would be a pivotal step toward wider clinical availability, especially in developing countries. We examined the biodistribution and dosimetry of indigenously developed and radiolabeled ¹³¹I-rituximab, using the monoclonal antibody of chimeric origin, in patients with B-cell lymphoma for potential use in radioimmunotherapy. Methods: This prospective study included 13 patients with B-cell NHL who underwent low-dose diagnostic scanning for dosimetric and biodistribution studies. Soon after rituximab infusion, a diagnostic dose of radioiodinated rituximab was administered. Serial planar whole-body γ-camera images were taken soon afterward and on days 1, 2, 4, and 6. A source of ¹³¹I with known activity was used as a reference standard for dosimetry calculations. Results: The patient-specific administered dose that would give a whole-body absorbed radiation dose of 75 cGy, calculated by the MIRD schema, ranged from 3,095.42 to 6,330.33 MBq (83.66-171.09 mCi), with a mean of 3,986.01 ± 863.95 MBq (107.73 ± 23.35 mCi) and a median of 3,697.41 MBq (99.93 mCi). The mean residence time was 69.54 h. Within the first 48 h at least 50% of the injected activity was cleared, and by 144 h at least 80% was cleared. The patient-specific administered dose that would give a whole-body absorbed radiation dose of 75 cGy, calculated by mean residence time and activity-hours, ranged from 2,654.75 to 6,210.45 MBq (71.75-167.85 mCi), with a mean of 3,576.42 ± 927.59 MBq (96.66 ± 25.07 mCi) and a median of 3,421.02 MBq (92.46 mCi). With respect to organ-specific dosimetry, the mean absorbed doses to organs (apart from blood pool [3.77 Gy] and spleen [4.02 Gy]) were 0.97 Gy to the lungs, 0.69 Gy to the liver, and 0.7 Gy to the kidneys. Conclusion: The indigenous product had kinetics similar to commercial radiopharmaceuticals, with the advantage of a lower human antimouse antibody response because of the pharmaceutical's being a chimeric antibody rather than a murine antibody. Hence, clinical administration was safe. In none of the organs did dose-limiting radiation exposure occur at the proposed therapeutic dose.

Radiolabeled Anti-Adenosine Triphosphate Synthase Monoclonal Antibody as a Theragnostic Agent Targeting Angiogenesis

INTRODUCTION

The potential of a radioiodine-labeled, anti-adenosine triphosphate synthase monoclonal antibody (ATPS mAb) as a theragnostic agent for simultaneous cancer imaging and treatment was evaluated.

METHODS

Adenosine triphosphate synthase monoclonal antibody was labeled with radioiodine, then radiotracer uptake was measured in 6 different cancer cell lines. In vivo biodistribution was evaluated 24 and 48 hours after intravenous injection of ¹²⁵I-ATPS mAb into MKN-45 tumor-bearing mice (n = 3). For radioimmunotherapy, 18.5 MBq ¹³¹I-ATPS mAb (n = 7), isotype immunoglobulin G (IgG) (n = 6), and vehicle (n = 6) were injected into MKN-45 tumor-bearing mice for 4 weeks, and tumor volume and percentage of tumor growth inhibition (TGI) were compared each week.

RESULTS

MKN-45 cells showed the highest in vitro cellular binding after 4 hours (0.00324 ± 0.00013%/μg), which was significantly inhibited by unlabeled ATPS mAb at concentrations of greater than 0.4 μM. The in vitro retention rate of ¹²⁵I-ATPS mAb in MKN-45 cells was 64.1% ± 1.0% at 60 minutes. The highest tumor uptake of ¹²⁵I-ATPS mAb in MKN-45 tumor-bearing mice was achieved 24 hours after injection (6.26% ± 0.47% injected dose [ID]/g), whereas tumor to muscle and tumor to blood ratios peaked at 48 hours. The 24-hour tumor uptake decreased to 3.43% ± 0.85% ID/g by blocking with unlabeled ATPS mAb. After 4 weeks of treatment, mice receiving ¹³¹I-ATPS mAb had significantly smaller tumors (679.4 ± 232.3 mm³) compared with control (1687.6 ± 420.4 mm³, P = .0431) and IgG-treated mice (2870.2 ± 484.1 mm³, P = .0010). The percentage of TGI of ¹³¹I-ATPS mAb was greater than 50% during the entire study period (range: 53.7%-75.9%).

CONCLUSION

The specific binding and antitumor effects of radioiodinated ATPS mAb were confirmed in in vitro and in vivo models of stomach cancer.

Phase I/II Trial of Anticarcinoembryonic Antigen Radioimmunotherapy, Gemcitabine, and Hepatic Arterial Infusion of Fluorodeoxyuridine Postresection of Liver Metastasis for Colorectal Carcinoma

OBJECTIVES

Report the feasibility, toxicities, and long-term results of a Phase I/II trial of ⁹⁰Y-labeled anticarcinoembryonic antigen (anti-CEA) (cT84.66) radioimmunotherapy (RIT), gemcitabine, and hepatic arterial infusion (HAI) of fluorodeoxyuridine (FUdR) after maximal hepatic resection of metastatic colorectal cancer to the liver.

METHODS

Patients with metastatic colorectal cancer to the liver postresection or ablation to minimum disease were eligible. Each cohort received HAI of FUdR for 14 days on a dose escalation schedule. The maximum HAI FUdR dose level planned was 0.2 mg/kg/day, which is the standard dose for HAI FUdR alone. On day 9, ⁹⁰Y-cT84.66 anti-CEA at 16.6 mCi/m² as an i.v. bolus infusion and on days 9-11 i.v. gemcitabine at 105 mg/m² were given. Patients could receive up to three cycles every 6 weeks of protocol therapy. Four additional cycles of HAI FUdR were allowed after RIT.

RESULTS

Sixteen patients were treated on this study. A maximum tolerated dose of 0.20 mg/kg/day of HAI FUdR combined with RIT at 16.6 mCi/m² and gemcitabine at 105 mg/m² was achieved with only 1 patient experiencing grade 3 reversible toxicity (mucositis). After surgery, 10 patients had no evidence of visible disease and remained without evidence of disease after completion of protocol therapy. The remaining 6 patients demonstrated radiological visible disease after surgery and after protocol therapy 2 patients had a CR, 1 patient had PR, 2 had stable disease, and 1 had progression. With a median follow-up of 41.8 months (18.7-114.6), median progression free survival was 9.6 months. Two patients demonstrated long-term disease control out to 45+ and 113+ months.

CONCLUSION

This study demonstrates the safety, feasibility, and potential utility of HAI FUdR, RIT, and systemic gemcitabine. The trimodality approach does not have higher hematologic toxicities than seen in prior RIT-alone studies. Future efforts evaluating RIT in colorectal cancer should integrate RIT with systemic and regional therapies in the minimal tumor burden setting.

Initial Experience with Tositumomab and I-131-Labeled Tositumomab for Treatment of Relapsed/Refractory Hodgkin Lymphoma

PURPOSE

To determine the maximum tolerated dose (MTD) of [¹³¹I]tositumomab in patients with refractory/recurrent Hodgkin lymphoma (HL) and to preliminarily determine if [¹³¹I]tositumomab has activity against HL and if positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]DG) performed 6 weeks post-therapy predicted 12-week response.

PROCEDURES

Separate dose-finding studies were performed for patients with and without prior transplant. A single therapeutic total body radiation dose (TBD) of [¹³¹I]tositumomab was administered. TBD was escalated/de-escalated based on dose-limiting hematologic toxicity (DLT) using a modified continual reassessment method. [¹⁸F]DG-PET/CT scans were performed at baseline and 6 and 12 weeks post therapy.

RESULTS

Twelve patients (nine classical HL, three lymphocyte-predominant [LP] HL) completed two dosing levels (n = 3 each) in the post-transplant (55 cGy, 79 cGy) and no transplant (75 cGy, 87 cGy) groups. Hematologic toxicities were common and transient. Twelve weeks after [¹³¹I]tositumomab, 10 patients progressed and two with LPHL achieved complete response. [¹⁸F]DG-PET/CT at 6 weeks post therapy appeared more predictive than CT at 6 weeks of a response at 12 weeks.

CONCLUSIONS

Tositumomab and [¹³¹I]tositumomab was well-tolerated in patients with relapsed/refractory HL. Complete responses in LPHL support a therapeutic effect in this subtype. Early metabolic response assessments by [¹⁸F]DG-PET in HL after radioimmunotherapy appear to be more predictive than purely anatomic assessments.

Autologous hematopoietic cell transplantation: an update for clinicians

High-dose chemotherapy followed by transplantation of autologous hematopoietic progenitor cells has a proven track record of safety and efficacy in hematological malignancies and select solid tumors. The near-universal use of peripheral blood stem cells as source for autografts, routine growth factor support, and antimicrobial prophylaxis post transplantation has improved the safety of this procedure. However, the advent of highly active novel therapies in the last few years warrants reappraisal of the role of autologous transplantation in the therapeutic armamentarium of malignant disorder. This review summarizes the current role of autologous transplantation for hematological malignancies, discusses modern standards for patient selection, and highlights long-term care issues of transplant survivors from an internist's perspective. Role of tumor purging in autologous transplantation, novel transplant conditioning regimens, and post-transplant therapies to prevent disease relapse are reviewed.

Radioimmunotherapy: a specific treatment protocol for cancer by cytotoxic radioisotopes conjugated to antibodies

Radioimmunotherapy (RIT) represents a selective internal radiation therapy, that is, the use of radionuclides conjugated to tumor-directed monoclonal antibodies (including those fragments) or peptides. In a clinical field, two successful examples of this treatment protocol are currently extended by ⁹⁰Y-ibritumomab tiuxetan (Zevalin) and ¹³¹I-tositumomab (Bexxar), both of which are anti-CD20 monoclonal antibodies coupled to cytotoxic radioisotopes and are approved for the treatment of non-Hodgkin lymphoma patients. In addition, some beneficial observations are obtained in preclinical studies targeting solid tumors. To date, in order to reduce the unnecessary exposure and to enhance the therapeutic efficacy, various biological, chemical, and treatment procedural improvements have been investigated in RIT. This review outlines the fundamentals of RIT and current knowledge of the preclinical/clinical trials for cancer treatment.

Delivery of an miR155 inhibitor by anti-CD20 single-chain antibody into B cells reduces the acetylcholine receptor-specific autoantibodies and ameliorates experimental autoimmune myasthenia gravis

MicroRNA-155 (miR155) is required for antibody production after vaccination with attenuated Salmonella. miR155-deficient B cells generated reduced germinal centre responses and failed to produce high-affinity immunoglobulin (Ig)G1 antibodies. In this study, we observed up-regulation of miR155 in the peripheral blood mononuclear cells (PBMCs) of patients with myasthenia gravis (MG), and miR155 was also up-regulated in torpedo acetylcholine receptor (T-AChR)-stimulated B cells. We used an inhibitor of miR155 conjugated to anti-CD20 single-chain antibody to treat both the cultured B cells and the experimental autoimmune MG (EAMG) mice. Our results demonstrated that silencing of miR155 by its inhibitor impaired the B cell-activating factor (BAFF)-R-related signalling pathway and reduced the translocation of nuclear factor (NF)-κB into the nucleus. Additionally, AChR-specific autoantibodies were reduced, which may be related to the altered amounts of marginal zone B cells and memory B cells in the spleens of EAMG mice. Our study suggests that miR155 may be a promising target for the clinical therapy of MG.

Myeloablative anti-CD20 radioimmunotherapy +/- high-dose chemotherapy followed by autologous stem cell support for relapsed/refractory B-cell lymphoma results in excellent long-term survival

Background

Radioimmunotherapy (RIT) has been used to treat relapsed/refractory CD20+ Non-Hodgkin lymphoma (NHL). Myeloablative anti-CD20 RIT followed by autologous stem cell infusion (ASCT) enables high radiation doses to lymphoma sites. We performed a phase I/II trial to assess feasibility and survival.

Methods

Twenty-three patients with relapsed/refractory NHL without complete remission (CR) to salvage chemotherapy were enrolled to evaluate RIT with Iodine-131 labelled rituximab (¹³¹I-rituximab) in a myeloablative setting. Biodistribution and dosimetric studies were performed to determine ¹³¹I activity required to induce a total body dose of 21-27Gy to critical organs. In 6/23 patients RIT was combined with high-dose chemotherapy. 8/23 patients received a sequential high-dose chemotherapy with a second ASCT. The median follow-up is 9.5 years.

Results

6.956-19.425GBq of ¹³¹I was delivered to achieve the limiting organ dose to lungs or kidneys. No grade III/IV non-hematologic toxicity was seen with RIT alone. Significant grade III/IV toxicity (mucositis, fever, infection, one therapy related death) was observed in patients treated with RIT combined with high-dose chemotherapy. The overall response rate was 87% (64% CR). The median progression-free (PFS) and overall survival (OS) is 47.5 and 101.5 months. An international prognostic index score >1 was predictive for OS.

Conclusion

Myeloablative RIT with ¹³¹I-rituximab followed by ASCT is feasible, well-tolerated and effective in high risk CD20+ NHL. Combination of RIT and high-dose chemotherapy increased toxicity significantly. Long-term results for PFS and OS are encouraging.

Personalized dosimetry of 131I-rituximab radioimmunotherapy of non-hodgkin lymphoma defined by pharmacokinetics in bone marrow and blood

PURPOSE

To report a comparison of SPECT/CT technique with standard blood-based dosimetry methodology in a cohort of non-Hodgkin lymphoma (NHL) patients treated with 131I-rituximab anti-CD20 chimeric monoclonal antibody.

METHODOLOGY

Red marrow uptake was measured directly using serial quantitative whole-body imaging in conjunction with SPECT/CT in a cohort of 23 patients undergoing routine 131I-rituximab radioimmunotherapy of NHL. Absorbed dose measurements were then compared with radiation doses calculated using standard peripheral blood counting methodology.

RESULTS

Activity clearance from whole body of 88.7 hours measured by imaging 131I-rituximab was significantly slower (p<0.001) than the mean effective half-life clearance of 60.8 hours calculated from the sampling peripheral blood. The mean activity concentrations in bone marrow measured using SPECT/CT, and by blood sampling, extrapolated to the time of administration, were, however, concordant. The absorbed self-dose in red marrow, measured using imaging, was 1.02 Gy compared with the dose (0.81 Gy) calculated from blood sampling. Neutrophil toxicity correlated with absorbed dose by SPECT/CT imaging (p=0.01), whereas the blood sampling method demonstrated no correlation with any parameters of hematological toxicity.

CONCLUSION

Radiation dose to red marrow from 131I-rituximab is inherently underestimated by standard indirect peripheral blood counting methods. Personalized marrow dosimetry by quantitative gamma imaging more accurately predicts of hemopoietic myelotoxicity by direct measurement of the bone marrow activity concentration of 131I-rituximab.

Monoclonal antibodies in conditioning regimens for hematopoietic cell transplantation

Monoclonal antibodies are increasingly being incorporated in conditioning regimens for autologous or allogeneic hematopoietic cell transplantation (HCT). The benefit of adding rituximab to autologous HCT regimens is purportedly related to in vivo purging of clonal B cells. Randomized trials comparing the addition (or not) of rituximab to high-dose therapy regimens are lacking. No benefit of standard-dose radioimmunotherapy-based regimens for autografting in aggressive lymphomas was seen in a randomized controlled study. The incorporation of rituximab into allogeneic HCT regimens aims to improve responses while reducing nonrelapse mortality resulting from acute graft-versus-host disease. The optimal dose and administration schedule of rituximab in this setting are unknown, and potentially serious complications from increased infections owing to prolonged (and profound) cytopenias or persistent hypogammaglobulinemia are of concern. Radioimmunotherapy-based conditioning for allografting holds promise as a modality to optimize tumor control and synergize adoptive immunotherapy effects, but it remains experimental at this time. The addition of alemtuzumab to allogeneic HCT regimens is associated with prolonged lymphopenia and impaired immune reconstitution, high relapse rates, and serious infections. The optimal dose and schedule of alemtuzumab to avoid prolonged immune paresis remain elusive. It is anticipated that additional monoclonal antibodies will soon become available that can be incorporated into HCT regimens after safety and clinical efficacy are demonstrated.

An update on radioimmunotherapy for lymphoma

SUMMARY Radioimmunotherapy is a promising treatment for B-cell lymphoma. 90Y-ibritumomab tiuxetan (Zevalin®) and 131I-tositumomab (Bexxar®) combine the potent antilymphoma effect of radiation with the specificity of antibody targeting. They have shown efficacy in follicular lymphoma in the setting of relapsed or refractory disease as consolidation regimens after first-line therapy, and in the front-line setting as single agents. Given their tolerability, they are actively being investigated as therapies or adjuncts for elderly patients with relapsed or high-risk diffuse large B-cell lymphoma. They have been added to autologous and allogeneic stem cell transplant preparatory regimens in early clinical trials with acceptable safety and efficacy. Early concerns over excess rates of treatment-related myelodysplastic syndrome and acute myelogenous leukemia have not come to fruition, but these questions remain to be fully answered. Ultimately, these are promising treatments for a variety of B-cell lymphomas. They are also models for the development of new radioimmunotherapies.

Dosimetric considerations in radioimmunotherapy and systemic radionuclide therapies: a review

Radiopharmaceutical therapy, once touted as the “magic bullet” in radiation oncology, is increasingly being used in the treatment of a variety of malignancies; albeit in later disease stages. With ever-increasing public and medical awareness of radiation effects, radiation dosimetry is becoming more important. Dosimetry allows administration of the maximum tolerated radiation dose to the tumor/organ to be treated but limiting radiation to critical organs. Traditional tumor dosimetry involved acquiring pretherapy planar scans and plasma estimates with a diagnostic dose of intended radiopharmaceuticals. New advancements in single photon emission computed tomography and positron emission tomography systems allow semi-quantitative measurements of radiation dosimetry thus allowing treatments tailored to each individual patient.

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.

Cancer radioimmunotherapy

Targeting of radionuclides with antibodies, or radioimmunotherapy, has been an active field of research spanning nearly 50 years, evolving with advancing technologies in molecular biology and chemistry, and with many important preclinical and clinical studies illustrating the benefits, but also the challenges, which all forms of targeted therapies face. There are currently two radiolabeled antibodies approved for the treatment of non-Hodgkin lymphoma, but radioimmunotherapy of solid tumors remains a challenge. Novel antibody constructs, focusing on treatment of localized and minimal disease, and pretargeting are all promising new approaches that are currently under investigation.

Cancer immunotherapy

Cancer immunotherapy consists of approaches that modify the host immune system, and/or the utilization of components of the immune system, as cancer treatment. During the past 25 years, 17 immunologic products have received regulatory approval based on anticancer activity as single agents and/or in combination with chemotherapy. These include the nonspecific immune stimulants BCG and levamisole; the cytokines interferon-α and interleukin-2; the monoclonal antibodies rituximab, ofatumumab, alemtuzumab, trastuzumab, bevacizumab, cetuximab, and panitumumab; the radiolabeled antibodies Y-90 ibritumomab tiuxetan and I-131 tositumomab; the immunotoxins denileukin diftitox and gemtuzumab ozogamicin; nonmyeloablative allogeneic transplants with donor lymphocyte infusions; and the anti-prostate cancer cell-based therapy sipuleucel-T. All but two of these products are still regularly used to treat various B- and T-cell malignancies, and numerous solid tumors, including breast, lung, colorectal, prostate, melanoma, kidney, glioblastoma, bladder, and head and neck. Positive randomized trials have recently been reported for idiotype vaccines in lymphoma and a peptide vaccine in melanoma. The anti-CTLA-4 monoclonal antibody ipilumumab, which blocks regulatory T-cells, is expected to receive regulatory approval in the near future, based on a randomized trial in melanoma. As the fourth modality of cancer treatment, biotherapy/immunotherapy is an increasingly important component of the anticancer armamentarium.

Pharmacokinetics and dosimetry of (111)In/(188)Re-labeled PEGylated liposomal drugs in two colon carcinoma-bearing mouse models

PEGylated liposomes are important drug carriers for nanomedicine cancer therapy. PEGylated liposomes can encapsulate radio- and chemo-drugs and passively target tumor sites via enhanced permeability and retention effect. This study estimated the pharmacokinetics and dosimetry after administration of radio-chemotherapeutics ((111)In-labeled vinorelbine [VNB]-encapsulated liposomes, InVNBL, and (188)Re-labeled doxorubicin [DXR]-encapsulated liposomes, ReDXRL) for radionuclide therapy in two colon carcinoma-bearing mouse models. A C26 colon carcinoma tumor/ascites mouse model and a subcutaneous solid tumor-bearing mouse model were employed. Biodistribution studies of InVNBL and ReDXRL after intraperitoneal administration in tumor/ascites-bearing mice (protocol A) and intravenous administration in subcutaneous solid tumor-bearing mice (protocol B) were performed. The radiation dose to normal tissues and tumors were calculated based on the results of distribution studies in mice, using the OLINDA/EXM program. The cumulated activities in most organs after administration of InVNBL in either the tumor/ascites-bearing mice (protocol A) or the subcutaneous solid tumor-bearing mice (protocol B) were higher than those of ReDXRL. Higher tumor-to-normal-tissues absorption dose ratios (T/NTs) were observed after administration of InVNBL than those of ReDXRL for protocol A. The T/NTs for the liver, spleen, and red marrow after injection of InVNBL for protocol B were similar to those of ReDXRL. The critical organ was found to be red marrow, and thus the red marrow absorption dose defined the recommended maximum administration activity of these liposomal drugs. Characterization of pharmacokinetics and dosimetry is needed to select the appropriate radiotherapeutics for specific tumor treatment applications. The results suggest that InVNBL is a promising therapeutic agent, which is as good as ReDXRL, in two mouse tumor models.

Development and evaluation of a model-based downscatter compensation method for quantitative I-131 SPECT

PURPOSE

The radionuclide 131I has found widespread use in targeted radionuclide therapy (TRT), partly due to the fact that it emits photons that can be imaged to perform treatment planning or posttherapy dose verification as well as beta rays that are suitable for therapy. In both the treatment planning and dose verification applications, it is necessary to estimate the activity distribution in organs or tumors at several time points. In vivo estimates of the 131I activity distribution at each time point can be obtained from quantitative single-photon emission computed tomography (QSPECT) images and organ activity estimates can be obtained either from QSPECT images or quantification of planar projection data. However, in addition to the photon used for imaging, 131I decay results in emission of a number of other higher-energy photons with significant abundances. These higher-energy photons can scatter in the body, collimator, or detector and be counted in the 364 keV photopeak energy window, resulting in reduced image contrast and degraded quantitative accuracy; these photons are referred to as downscatter. The goal of this study was to develop and evaluate a model-based downscatter compensation method specifically designed for the compensation of high-energy photons emitted by 131I and detected in the imaging energy window.

METHODS

In the evaluation study, we used a Monte Carlo simulation (MCS) code that had previously been validated for other radionuclides. Thus, in preparation for the evaluation study, we first validated the code for 131I imaging simulation by comparison with experimental data. Next, we assessed the accuracy of the downscatter model by comparing downscatter estimates with MCS results. Finally, we combined the downscatter model with iterative reconstruction-based compensation for attenuation (A) and scatter (S) and the full (D) collimator-detector response of the 364 keV photons to form a comprehensive compensation method. We evaluated this combined method in terms of quantitative accuracy using the realistic 3D NCAT phantom and an activity distribution obtained from patient studies. We compared the accuracy of organ activity estimates in images reconstructed with and without addition of downscatter compensation from projections with and without downscatter contamination.

RESULTS

We observed that the proposed method provided substantial improvements in accuracy compared to no downscatter compensation and had accuracies comparable to reconstructions from projections without downscatter contamination.

CONCLUSIONS

The results demonstrate that the proposed model-based downscatter compensation method is effective and may have a role in quantitative 131I imaging.

Radioimmunotherapy for NHL: Experience of90Y-Ibritumomab Tiuxetan in Clinical Practice

Radioimmunotherapy (RIT) is a novel treatment modality that combines the benefits of radiotherapy and immunotherapy, enabling multiple sites of disseminated disease to be treated simultaneously and effectively, while minimizing toxicity to normal tissues. 90Y-ibritumomab tiuxetan consists of the anti-CD20 monoclonal antibody (MAb) ibritumomab covalently linked to tiuxetan for chelation of 90Y for therapy. Early work established that a dose of 14.8 MBq/kg (0.4 mCi/kg) is safe and effective in patients with < 25% bone marrow involvement and adequate marrow reserves, as is a dose of 11.1 MBq/kg (0.3 mCi/kg) in patients with mild thrombocytopenia (platelet counts 100 x 10(9)-150 x 10(9)/l). To date, 5 clinical trials using 90Y-ibritumomab tiuxetan have been reported, one of which assessed the efficacy in rituximab-refractory patients with follicular non-Hodgkin's lymphoma (NHL) histology. Within the 54 follicular lymphoma patients, an overall response (OR) rate of 74% and a complete response (CR) rate of 15% were achieved, despite patients having received a median of 4 prior therapies and 73% having tumors > or = 5 cm in diameter. In addition, a major phase III randomized trial directly compared 90Y-ibritumomab tiuxetan with the unlabeled anti-CD20 MAb rituximab. Results from the randomized trial demonstrated that OR and CR rates were significantly higher with 90Y-ibritumomab tiuxetan, compared with rituximab (OR rate 80% vs. 56%, P = 0.002; CR rate 30% vs. 16%, P = 0.004). Time to progression (TTP) was 11.2 vs. 10.1 months (P = 0.173). Treatment was generally well tolerated; the primary toxicity associated with 90Y-ibritumomab tiuxetan therapy is reversible myelosuppression, which correlates with the degree of bone marrow involvement at baseline. In an integrated analysis of safety data from 5 90Y-ibritumomab tiuxetan studies, only 7% of patients were hospitalized due to infection during the treatment period. In addition, 90Y-ibritumomab tiuxetan therapy was not shown to increase the risk of developing secondary malignancies (myelodysplastic syndrome/acute myeloid leukemia), or preclude subsequent therapy upon relapse. Current investigations are focussing on the potential role of 90Y-ibritumomab tiuxetan earlier in the treatment algorithm, including as single-agent therapy for relapsed diffuse large B-cell lymphoma patients not eligible for transplantation, and consolidation treatment for low-grade NHL patients after first-line, alkylating agent-based therapy.

Bio-effect model applied to 131I radioimmunotherapy of refractory non-Hodgkin's lymphoma

PURPOSE

Improved data collection methods have improved absorbed dose estimation by tracking activity distributions and tumor extent at multiple time points, allowing individualized absorbed dose estimation. Treatment with tositumomab and (131)I-tositumomab anti-CD20 radioimmunotherapy (BEXXAR) yields a cold antibody antitumor response (cold protein effect) and a radiation response. Biologically effective contributions, including the cold protein effect, are included in an equivalent biological effect model that was fit to patient data.

METHODS

Fifty-seven tumors in 19 patients were followed using 6 single proton emission computed tomography (SPECT)/CT studies, 3 each post tracer (5 mCi) and therapy (∼100 mCi) injections with tositumomab and (131)I-tositumomab. Both injections used identical antibody mass, a flood dose of 450 mg plus 35 mg of (131)I tagged antibody. The SPECT/CT data were used to calculate absorbed dose rate distributions and tumor and whole-body time-activity curves, yielding a space-time dependent absorbed dose rate description for each tumor. Tumor volume outlines on CT were used to derive the time dependence of tumor size for tracer and therapy time points. A combination of an equivalent biological effect model and an inactivated cell clearance model was used to fit absorbed dose sensitivity and cold effect sensitivity parameters to tumor shrinkage data, from which equivalent therapy values were calculated.

RESULTS

Patient responses were categorized into three groups: standard radiation sensitivity with no cold effect (7 patients), standard radiation sensitivity with cold effect (11 patients), and high radiation sensitivity with cold effect (1 patient).

CONCLUSION

Fit parameters can be used to categorize patient response, implying a potential predictive capability.

I-131 tositumomab

IMPORTANCE OF THE FIELD

Follicular lymphoma (FL) is a subgroup of B-cell Non-Hodgkin's lymphomas (NHL) that account for 15 - 30% of all lymphomas. I-131 tositumomab is a radiommunoconjugate of (131)I and the anti-CD20 monoclonal antibody tositumomab. It is one of two available radioimmunoconjugates for the treatment of recurrent, refractory, or transformed FL.

AREAS COVERED IN THIS REVIEW

This review describes the clinical pharmacology of I-131 tositumomab, dosing and administration guidelines, and the key clinical trials providing evidence of its efficacy and safety in patients with FL, transformed, or other aggressive B-NHL, in combination with chemotherapy, or its incorporation in transplant conditioning regimens. This review also covers safety and regulatory concerns regarding the use of I-131 tositumomab.

WHAT THE READER WILL GAIN

This review critically appraises the clinical trials behind approval of I-131 tositumomab as a second-line agent for FL and also outlines the data supporting its use in the upfront setting.

TAKE HOME MESSAGE

I-131 tositumomab is a safe and effective option for patients with recurrent, refractory, or transformed FL and carries promise in the upfront treatment of FL, aggressive B-NHL, and as a transplant conditioning regimen.

Comparative dosimetric evaluation of nanotargeted (188)Re-(DXR)-liposome for internal radiotherapy

A dosimetric analysis was performed to evaluate nanoliposomes as carriers of radionuclides ((188)Re-liposomes) and radiochemotherapeutic drugs [(188)Re-doxorubicin (DXR)-liposomes] in internal radiotherapy for colon carcinoma, as evaluated in mice.

METHODS

Pharmacokinetic data for (188)Re-N, N-bis (2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA), (188)Re-liposome, and (188)Re-DXR-liposome were obtained for the estimation of absorbed doses in tumors and normal organs. Two colon carcinoma mouse models were employed: subcutaneous growing solid tumor and malignant ascites pervading tumor models. Radiation-dose estimates for normal tissues and tumors were calculated by using the OLINDA/EXM program. An evaluation of a recommended maximum administered activity (MAA) for the nanotargeted drugs was also made.

RESULTS

Mean absorbed doses derived from (188)Re-liposome and (188)Re-DXR-liposome in normal tissues were generally similar to those from (188)Re-BMEDA in intraperitoneal and intravenous administration. Tissue-absorbed dose in the liver was 0.24-0.40 and 0.17-0.26 (mGy/MBq) and in red marrow was 0.033-0.050 and 0.038-0.046 (mGy/MBq), respectively, for (188)Re-liposome and (188)Re-DXR-liposome. Tumor-absorbed doses for the nanotargeted (188)Re-liposome and (188)Re-DXR-liposome were higher than those of (188)Re-BMEDA for both routes of administration (4-26-fold). Dose to red marrow defined the recommended MAA.

CONCLUSIONS

Our results suggest that radionuclide and chemoradiotherapeutic passive targeting delivery, using nanoliposomes as the carrier, is feasible and promising in systemic-targeted radionuclide therapy.

Dose intensified molecular targeted radiotherapy for cancer-lymphoma as a paradigm

Although most patients with locoregional cancer are cured by surgery, radiotherapy, chemotherapy, and combinations thereof, those with distant metastases are not despite systemic chemotherapy. These patients respond to local radiotherapy but generally need systemic therapy. Non-Hodgkin's lymphoma (NHL) provides a paradigm for the role of molecular targeted radiotherapy (MTRT) because these patients have multifocal disease in most cases. Although patients with NHL achieve remissions after multiple cycles of chemotherapy, less than one half of those with aggressive NHL are cured and almost none of those with low grade NHL. Furthermore, NHL, like other cancers, becomes chemoresistant, yet remains responsive to radiotherapy. MTRT, radiation targeted by molecules, is a good strategy for the treatment of multifocal and radiosensitive cancers. Radioimmunotherapy (RIT) is an MTRT approach using MAbs, or parts thereof, to target the radionuclide that delivers radiation. Two anti-CD20 monoclonal antibodies (MAbs), one labeled with (111)In for imaging or (90)Y for therapy and a second labeled with (131)I for imaging and therapy, have proven effective and safe for MTRT for NHL patients. The importance of the radiation is demonstrated in the data from the randomized pivotal trial of (90)Y-ibritumomab; response rates were distinctly better in the (90)Y-ibritumomab arm than in the rituximab arm. Furthermore, the efficacy of (131)I-tositumomab was greater than that of the same MAb alone in another pivotal trial. Although hematologic toxicity is dose limiting for MTRT, febrile neutropenia is uncommon. MTRT is also not associated with mucositis, hair loss, or persistent nausea or vomiting, unlike chemotherapy. Randomized trials of MTRT in different strategies have not been conducted, but there is evidence of better outcomes, particularly for strategies that provide dose intensification, such as pretargeted MTRT, multiple dosing ("fractionation"), and MTRT with stem cell transplantation (SCT). Pretargeted RIT separates delivery of the targeting molecule from radionuclide delivery, provides dose escalation, and is more effective than direct one-step RIT, although more complicated to implement. Improved drugs and strategies for MTRT have documented potential for better patient outcomes. Smaller radionuclide carriers, such as those used for pretargeted MTRT, should be incorporated into the management of patients with NHL and other cancers soon after the patients have proven incurable. Expected improvements using better drugs, strategies, and combinations with other drugs seem likely to make MTRT integral in the management of many patients with cancer and likely to lead to cures of NHL.

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.

Improving the efficacy of radioimmunotherapy for non-Hodgkin lymphomas

Approximately 66,000 Americans develop non-Hodgkin lymphoma (NHL) each year. Although the use of unlabeled antibodies such as rituximab has significantly improved survival when combined with standard chemotherapy regimens, approximately two-thirds of lymphoma patients eventually develop disease recurrence and die of their disease. Novel treatments are urgently needed to cure these patients. One strategy involves the use of radiolabeled immunoconjugates that specifically localize radiation delivery to sites of lymphoma while minimizing toxicity to normal tissues. A growing number of studies support the contention that radiolabeled antibody therapy can improve overall survival of lymphoma patients and lead to durable remissions, with probable cures, in many patients. Various approaches for enhancing the effectiveness of radioimmunoconjugates have been studied, including: use in newly diagnosed lymphoma patients, combination with chemotherapy or other monoclonal antibodies, use with hematopoietic stem cell transplantation, multistep pretargeting strategies to further minimize toxicity, and simultaneous targeting of multiple B-cell antigens. This article summarizes the current knowledge supporting the use of radioimmunotherapy, an underused but effective treatment modality in NHL patients.

Use of integrated SPECT/CT imaging for tumor dosimetry in I-131 radioimmunotherapy: a pilot patient study

Integrated systems combining functional (single-photon emission computed tomography; SPECT) imaging with anatomic (computed tomography; CT) imaging have the potential to greatly improve the accuracy of dose estimation in radionuclide therapy. In this article, we present the methodology for highly patient-specific tumor dosimetry by utilizing such a system and apply it to a pilot study of 4 follicular lymphoma patients treated with I-131 tositumomab. SPECT quantification included three-dimensional ordered-subset expectation-maximization reconstruction and CT-defined tumor outlines at each time point. SPECT/CT images from multiple time points were coupled to a Monte Carlo algorithm to calculate a mean tumor dose that incorporated measured changes in tumor volume. The tumor shrinkage, defined as the difference between volumes drawn on the first and last CT scan (a typical time period of 15 days) was in the range 5%-49%. The therapy-delivered mean tumor-absorbed dose was in the range 146-334 cGy. For comparison, the therapy dose was also calculated by assuming a static volume from the initial CT and was found to underestimate this dose by up to 47%. The agreement between tracer-predicted and therapy-delivered tumor-absorbed dose was in the range 7%-21%. In summary, malignant lymphomas can have dramatic tumor regression within days of treatment, and advanced imaging methods allow for a highly patient-specific tumor-dosimetry calculation that accounts for this regression.

Listeriolysin O as cytotoxic component of an immunotoxin

Monoclonal antibodies (mAbs) have been developed over the past years as promising anticancer therapeutics. The conjugation of tumor specific mAbs with cytotoxic molecules has been shown to improve their efficacy dramatically. These bifunctional immunotoxins, consisting of covalently linked antibodies and protein toxins, possess considerable potential in cancer therapy. Many of them are under investigation in clinical trials. As a result of general interest in new toxic components, we describe here the suitability of the bacterial protein Listeriolysin O (LLO) as cytotoxic component of an immunotoxin. Unique characteristics of LLO, such as its acidic pH optimum and the possibility to regulate the cytolytic activity by cysteine-oxidation, make LLO an interesting toxophore. Oxidized LLO shows a substantially decreased cytolytic activity when compared with the reduced protein as analyzed by hemolysis. Both oxidized and reduced LLO exhibit a cell-type-unspecific toxicity in cell culture with a significantly higher toxicity of reduced LLO. For cell-type-specific targeting of LLO to tumor cells, LLO was coupled to the dsFv fragment of the monoclonal antibody B3, which recognizes the tumor-antigen Lewis Y. The coupling of LLO to dsFv-B3 was performed via cysteine-containing polyionic fusion peptides that act as a specific heterodimerization motif. The novel immunotoxin B3-LLO could be shown to specifically eliminate antigen positive MCF7 cells with an EC(50) value of 2.3 nM, whereas antigen negative cell lines were 80- to 250-fold less sensitive towards B3-LLO.

Follicular lymphoma: a historical overview

Lymphoma was first described in 1862 and follicular lymphoma in 1925. Initially considered a benign disorder, and named Brill - Symmers disease after the authors of the original papers, it was rapidly recognized as a malignancy with a variable but often indolent course. Most of its clinical features were described by the early 1940s. Despite discussion about its cell of origin, and in contrast to many other lymphoma subtypes, follicular lymphoma could always be accurately recognized and diagnosed using light microscopy morphological features. B-cell origin was demonstrated in the 1970s and the important role of t(14;18) and bcl-2 gene rearrangement in the pathogenesis of follicular lymphoma was established shortly thereafter. The etiology of follicular lymphoma, the reason for marked geographic variation in its incidence, the role of alternative molecular pathways in its pathogenesis, and the cause for its variable clinical behavior all remain unknown. Several observations suggest an important role for the normal immune response in regulating the clinical behavior of follicular lymphoma. From the earliest descriptions, radiation therapy was shown to be very effective in follicular lymphoma, but not curative. Combination chemotherapy was tested in the 1970s, but despite high rates of response, there was only minimal impact on survival. Interferon combined with anthracycline based chemotherapy was the first treatment to improve survival, but was not widely adopted in the USA. Randomized studies have shown an impact of autologous transplantation on progression free survival. Allogeneic transplantation is a curative therapy, but is too toxic for widespread application. Targeted therapies, particularly rituximab have revolutionized the treatment of follicular lymphoma. A convergence of technological and biological advances will likely lead to further dramatic progress in the next decade. For the first time consistent improvements in survival of follicular lymphoma are reported.

In vitro characterization of (177)Lu-radiolabelled chimeric anti-CD20 monoclonal antibody and a preliminary dosimetry study

PURPOSE

(131)I- and (90)Y-labelled anti-CD20 antibodies have been shown to be effective in the treatment of low-grade, B-cell non-Hodgkin's lymphoma (NHL). However, the most appropriate radionuclide in terms of high efficiency and low toxicity has not yet been established. In this study we evaluated an immunoconjugate formed by the anti-CD20 antibody rituximab and the chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). DOTA-rituximab was prepared as a kit formulation and can be labelled in a short time (<20 min) with either (177)Lu or (90)Y.

MATERIALS AND METHODS

Immunoconjugates with different numbers of DOTA molecules per rituximab were prepared using p-SCN-Bz-DOTA. In vitro immunoreactivity and stability were tested and preliminary dosimetric results were acquired in two patients.

RESULTS

The immunological binding properties of DOTA-rituximab to the CD20 antigen were found to be retained after conjugation with up to four chelators. The labelled product was stable against a 10(5) times excess of diethylenetriaminepentaacetic acid (DTPA, 37 degrees C, 7 days). Two patients with relapsed NHL were treated with 740 MBq/m(2) body surface (177)Lu-DOTA-rituximab. Scintigraphic images showed specific uptake at tumour sites and acceptable dosimetric results. The mean whole-body dose was found to be 314 mGy. The administration of (177)Lu-DOTA-rituximab was tolerated well.

CONCLUSION

Our results show that DOTA-rituximab (4:1) can be labelled with (177)Lu with sufficient stability while the immunoconjugate retains its immunoreactivity. (177)Lu-DOTA-rituximab is an interesting, well-tolerated radiolabelled antibody with clinical activity in a low dose range, and provides an approach to the efficient treatment with few side effects for patients with relapsed NHL.

Update on the rational use of tositumomab and iodine-131 tositumomab radioimmunotherapy for the treatment of non-Hodgkin's lymphoma

Targeted radioimmunotherapy in non-Hodgkin’s B-cell lymphoma (NHL) offers an efficacious therapy and minimal toxicity compared to conventional chemotherapy. Iodine 131 tositumomab (¹³¹I-TST) is a murine monoclonal antibody against the CD20 cell surface protein and is directly covalently conjugated to ¹³¹I, a radioactive β and γ emitter. While initially approved for use in relapsed, refractory, or transformed low grade B-cell NHL, investigational uses with promising results include autologous stem cell transplant, intermediate grade NHL, and the frontline management of indolent NHL. This review summarizes the ¹³¹I-TST literature on mechanism of action, treatment indications, treatment delivery, efficacy, investigational uses, and future prospects.

Pretargeted versus directly targeted radioimmunotherapy combined with anti-CD20 antibody consolidation therapy of non-Hodgkin lymphoma

We determined whether therapeutic responses using a bispecific antibody that pretargeted (90)Y-hapten-peptide radioimmunotherapy or a directly radiolabeled, humanized, (90)Y-anti-CD20 IgG (veltuzumab) could be improved by combining these treatments with unlabeled humanized antibodies against CD22 (epratuzumab), CD74 (milatuzumab), or veltuzumab.

METHODS

Nude mice bearing established subcutaneous Ramos human Burkitt lymphoma were treated with antibodies alone or in combination with pretargeted radioimmunotherapy (PT-RAIT) or radioimmunotherapy, and tumor growth was monitored. Biodistribution studies examined the effect that predosing with unlabeled veltuzumab had on radioimmunotherapy and PT-RAIT targeting.

RESULTS

None of the unconjugated antibodies was effective against established and rapidly growing xenografts, but PT-RAIT, at approximately 30% of its maximum tolerated dose, and radioimmunotherapy alone, at its maximum tolerated dose, were able to arrest growth and even entirely ablate tumors in some animals. Only combinations with veltuzumab improved therapeutic responses, most significantly when a veltuzumab regimen (weekly, 1.0 mg followed by 3 x 0.5 mg) was initiated 1 wk after PT-RAIT or (90)Y-veltuzumab. Biodistribution data indicated that when unlabeled veltuzumab (1.0 or 0.25 mg) was administered in advance of the radiolabeled veltuzumab or bispecific antibody injection, tumor uptake was significantly reduced ((111)In-veltuzumab, 47% and 25%, respectively; (111)In-hapten-peptide, 74% and 49%, respectively). Despite an approximately 50% decrease in radioactivity uptake in the tumor, antitumor responses were not diminished significantly for (90)Y-veltuzumab, and in the case of PT-RAIT responses were improved. However, higher amounts of predosed veltuzumab reduced the effects of PT-RAIT.

CONCLUSION

These studies suggest that administering unlabeled anti-CD20 IgG therapy after the radioactivity dose provides the best efficacy and that the amount of unlabeled anti-CD20 IgG administered as a predose to anti-CD20-targeted radionuclide therapy should be minimized.

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.

New insights into the mechanisms of action of radioimmunotherapy in lymphoma

The exquisite sensitivity of haematological malignancies to targeted radiation alongside the impressive results achieved by the pioneers in this field suggests that radioimmunotherapy is likely to be a productive area for future clinical research. Recent experimental work has demonstrated that the combination of targeted radiation and antibody effector mechanisms are critical to long-term clearance of tumour. This review provides the background of clinical and biological insights into the mechanisms of action of radioimmunotherapy.

Immunotherapy of lymphomas with T cells modified by anti-CD20 scFv/CD28/CD3zeta recombinant gene

One of the approaches to make anti-CD20 antibody more efficient is to express this antibody on the surface of T cells. scFv from anti-CD20 antibody has been expressed on T cell surface to bind to CD20 positive cells and CD3zeta has been expressed as a fusion partner to transduct signals. T cells grafted with this chimeric scFv/CD3zeta were able to redirect grafted T cells to an MHC/Ag-independent antitumor response. To test the effects of CD28 signal on the cellular activation and antitumor effectiveness of chimeric scFv/CD3zeta modified T cells, we constructed a recombinant anti-CD20 scFv/CD28/CD3zeta gene in a retroviral vector. T cells expressing anti-CD20 scFv/CD28/CD3zeta specifically lysed CD20 positive target tumor cells and secreted not only IFN-gamma but also IL-2 after binding to their target cells. Our data indicate that CD3 and CD28 signalling can be delivered in one molecule, which is sufficient for complete T cell activation without exogenous B7/CD28 costimulation.