Multicenter phase II study of iodine-131 tositumomab for chemotherapy-relapsed/refractory low-grade and transformed low-grade B-cell non-Hodgkin's lymphomas

A Critical Analysis of the FDA's Omics-Driven Pharmacodynamic Biomarkers to Establish Biosimilarity

Demonstrating biosimilarity entails comprehensive analytical assessment, clinical pharmacology profiling, and efficacy testing in patients for at least one medical indication, as required by the U.S. Biologics Price Competition and Innovation Act (BPCIA). The efficacy testing can be waived if the drug has known pharmacodynamic (PD) markers, leaving most therapeutic proteins out of this concession. To overcome this, the FDA suggests that biosimilar developers discover PD biomarkers using omics technologies such as proteomics, glycomics, transcriptomics, genomics, epigenomics, and metabolomics. This approach is redundant since the mode-action-action biomarkers of approved therapeutic proteins are already available, as compiled in this paper for the first time. Other potential biomarkers are receptor binding and pharmacokinetic profiling, which can be made more relevant to ensure biosimilarity without requiring biosimilar developers to conduct extensive research, for which they are rarely qualified.

Individualization of Radionuclide Therapies: Challenges and Prospects

Simple Summary

Currently, patient-specific treatment plans and dosimetry calculations are not routinely performed for radionuclide therapies. In external beam radiotherapy, it is quite the opposite. As a result, a small fraction of patients receives optimal radioactivity. This conservative approach provides “radiation safety” to healthy tissues but delivers a lower than indicated absorbed dose to the tumors, resulting in a lower response rate and a higher disease relapse rate. Evidence shows that better and more predictable outcomes can be achieved with patient-individualized dose assessment. Therefore, the incorporation of individual planning into radionuclide therapies is a high priority for nuclear medicine physicians and medical physicists alike. Internal dosimetry is used in tumor therapy to optimize the absorbed dose to the target tissue. The main reasons for the difficulties in incorporating patients’ internal dosimetry into routine clinical practice are discussed. The article presents the prospects for the routine implementation of personalized radionuclide therapies.

Abstract

The article presents the problems of clinical implementation of personalized radioisotope therapy. The use of radioactive drugs in the treatment of malignant and benign diseases is rapidly expanding. Currently, in the majority of nuclear medicine departments worldwide, patients receive standard activities of therapeutic radiopharmaceuticals. Intensively conducted clinical trials constantly provide more evidence of a close relationship between the dose of radiopharmaceutical absorbed in pathological tissues and the therapeutic effect of radioisotope therapy. Due to the lack of individual internal dosimetry (based on the quantitative analysis of a series of diagnostic images) before or during the treatment, only a small fraction of patients receives optimal radioactivity. The vast majority of patients receive too-low doses of ionizing radiation to the target tissues. This conservative approach provides “radiation safety” to healthy tissues, but also delivers lower radiopharmaceutical activity to the neoplastic tissue, resulting in a low level of response and a higher relapse rate. The article presents information on the currently used radionuclides in individual radioisotope therapies and on radionuclides newly introduced to the therapeutic market. It discusses the causes of difficulties with the implementation of individualized radioisotope therapies as well as possible changes in the current clinical situation.

Theragnostics before we found its name

Theragnostics embraces "gnosis" and "prognosis" and concerns a treatment strategy which combines diagnostics with therapeutics. The birth of what we call today theragnostics can be traced in 1936, with the proposal of radioiodine, the first radiopharmaceutical approved in 1951 by FDA, in USA, as 131I sodium iodide. In 1957, 89Sr was also approved as first therapeutic radiotracer for skeletal metastases, followed in the subsequent years by 186Rh, 153Sm and, more recently, 223Ra, the first alpha emitter clinically utilized, allowing curative results and not only a palliative effect. Proposed in first eighties as [131I] Metaiodobenzylguanidine (MIBG), the theragnostic couple 123I/131I MIBG is still used in neural crest tumors, while, starting from partially unsatisfactory results in 70's, models based on antibodies for radioimmunoscintigraphy/radioimmunotherapy have been subsequently upgraded thanks to the introduction of monoclonal antibodies and other significant biological and technical improvements. The "Theragnostics called with this name" can be dated to early 90's with the first proposal of the somatostatin model, actually widely operating in neuroendocrine tumors with radio-chelates usable for diagnosis and therapy. Since then, many investigators are working on new theragnostics agents, also outside of the nuclear medicine, based on peptides, antibodies and other tools to find new models applicable in the clinical practice. The fast growth is stimulated by the interest of big pharma. Theragnostic concepts are the roots of nuclear medicine and new great goals are soon to be achieved in the direction of an increasing precision and tailored medicine.

The α-emitter astatine-211 targeted to CD38 can eradicate multiple myeloma in a disseminated disease model

Minimal residual disease (MRD) has become an increasingly prevalent and important entity in multiple myeloma (MM). Despite deepening responses to frontline therapy, roughly 75% of MM patients never become MRD-negative to ≤10-5, which is concerning because MRD-negative status predicts significantly longer survival. MM is highly heterogeneous, and MRD persistence may reflect survival of isolated single cells and small clusters of treatment-resistant subclones. Virtually all MM clones are exquisitely sensitive to radiation, and the α-emitter astatine-211 (211At) deposits prodigious energy within 3 cell diameters, which is ideal for eliminating MRD if effectively targeted. CD38 is a proven MM target, and we conjugated 211At to an anti-CD38 monoclonal antibody to create an 211At-CD38 therapy. When examined in a bulky xenograft model of MM, single-dose 211At-CD38 at 15 to 45 µCi at least doubled median survival of mice relative to untreated controls (P < .003), but no mice achieved complete remission and all died within 75 days. In contrast, in a disseminated disease model designed to reflect low-burden MRD, 3 studies demonstrated that single-dose 211At-CD38 at 24 to 45 µCi produced sustained remission and long-term survival (>150 days) for 50% to 80% of mice, where all untreated mice died in 20 to 55 days (P < .0001). Treatment toxicities were transient and minimal. These data suggest that 211At-CD38 offers the potential to eliminate residual MM cell clones in low-disease-burden settings, including MRD. We are optimistic that, in a planned clinical trial, addition of 211At-CD38 to an autologous stem cell transplant (ASCT) conditioning regimen may improve ASCT outcomes for MM patients.

Radioimmunotherapy in Non-Hodgkin's Lymphoma: Retrospective Adverse Event Profiling of Zevalin and Bexxar

The development of monoclonal antibodies has dramatically changed the outcome of patients with non-Hodgkin’s lymphoma (NHL), the most common hematological malignancy. However, despite the satisfying results of monoclonal antibody treatment, only few NHL patients are permanently cured with single-agent therapies. In this context, radioimmunotherapy, the administration of radionuclides conjugated to monoclonal antibodies, is aimed to augment the single-agent efficacy of immunotherapy in order to deliver targeted radiation to tumors, particularly CD20+ B-cell lymphomas. Based on evidence from several trials in NHL, the radiolabeled antibodies ⁹⁰Y-ibritumomab tiuxetan (Zevalin, Spectrum Pharmaceuticals) and ¹³¹I-tositumomab (Bexxar, GlaxoSmithKline) received FDA approval in 2002 and 2003, respectively. However, none of the two radioimmunotherapeutic agents has been broadly applied in clinical practice. The main reason for the under-utilization of radioimmunotherapy includes economic and logistic considerations. However, concerns about potential side effects have also been raised. Driven by these developments, we performed retrospective analysis of adverse events reporting Zevalin or Bexxar, extracted from the FDA’s Adverse Event Reporting System (FAERS) and the World Health Organization’s VigiBase repository. Our results indicate that the two radioimmunotherapeutic agents have both related and distinct side effect profiles and confirm their known toxicological considerations. Our work also suggests that computational analysis of real-world post-marketing data can provide informative clinical insights. While more prospective studies are necessary to fully characterize the efficacy and safety of radioimmunotherapy, we expect that it has not yet reached its full therapeutic potential in modern hematological oncology.

Combining Biology and Chemistry for a New Take on Chemotherapy: Antibody-Drug Conjugates in Hematologic Malignancies

PURPOSE OF REVIEW

This review is about the antibody-drug conjugate (ADC), a form of drug delivery consisting of a monoclonal antibody, linker, and cytotoxic payload. We summarize the history of ADC development, highlighting the three FDA-approved ADCs currently available.

RECENT FINDINGS

Gemtuzumab ozogamicin is a CD33-targeted ADC linked to calicheamicin. It is approved for CD33+ AML in the first line or the relapsed or refractory (R/R) setting. Brentuximab vedotin is a CD30-targeted ADC bound to MMAE. It is approved for the treatment of certain R/R CD30+ lymphomas. Recently, it has been approved for first line therapy with chemotherapy in advanced HL. Inotuzumab ozogamicin is a CD22-directed ADC attached to calicheamicin indicated for the treatment of adults with R/R B cell precursor ALL. Three ADCs have been approved for the treatment of various hematologic malignancies. We discuss the pertinent human trials that led to FDA approval. We include our perspectives about drug resistance, toxicities, and future development.

Novel Methods to Improve the Efficiency of Radioimmunotherapy for Non-Hodgkin Lymphoma

Radioimmunotherapy (RIT) is a novel strategy for treating non-Hodgkin lymphoma (NHL). Several studies have shown the promising results of using RIT in NHL, which have led to FDA approval for two RIT agents in treating low grade NHL. In spite of these favorable results in low-grade NHL, most of the aggressive or relapsed/refractory NHL subjects experience relapses following RIT. Although more aggressive treatments such as myeloablative doses of RIT followed by stem cell transplantation appear to be able to provide a longer survival for some patients these approaches are associated with significant treatment-related adverse events and challenging to deliver in most centers. Therefore, it seems reasonable to develop treatment approaches that enhance the efficiency of RIT, while reducing its toxicity. In this paper, novel methods that improve the efficiency of RIT and reduce its toxicity through various mechanisms are reviewed. Further clinical development of these methods could expand the NHL patient groups eligible for receiving RIT, and even extend the use of RIT to new indications and disease groups in future.

Nanomedicines for the treatment of hematological malignancies

Hematological malignancies (HM) are a collection of malignant transformations originating from cells in the primary or secondary lymphoid organs. Leukemia, lymphoma, and multiple myeloma comprise the three major types of HM. Current treatment consists of bone marrow transplantation, radiotherapy, immunotherapy and chemotherapy. Although, many chemotherapeutic drugs are clinically available for the treatment of HM, the use of these agents is limited due to dose-related toxicity and lack of specificity to tumor tissue. Moreover, the poor pharmacokinetic profile of most of the chemotherapeutics requires high dosage and frequent administration to maintain therapeutic levels at the target site, both increasing adverse effects. This underlines an urgent need for a suitable drug delivery system to improve efficacy, safety, and pharmacokinetic properties of conventional therapeutics. Nanomedicines have proven to enhance these properties for anticancer therapeutics. The most extensively studied nanomedicine systems are lipid-based nanoparticles and polymeric nanoparticles. Typically, nanomedicines are small sub-micron sized particles in the size range of 20-200 nm. The biocompatible and biodegradable nature of nanomedicines makes them attractive vehicles to improve drug delivery. Their small size allows them to extravasate and accumulate at malignant sites passively by means of the enhanced permeability and retention (EPR) effect, resulting from rapid angiogenesis and inflammation. Moreover, the specificity to the target tissue can be further enhanced by surface modification of nanoparticles. This review describes currently available therapies as well as limitations and potential advantages of nanomedicine formulations for treatment of various types of HM. Additionally, recent investigational and approved nanomedicine formulations and their limited applications in HM are discussed.

Use of 18F FDG PET and the short temporal response of Hodgkin's disease to RIT

Radioimmunotherapy (RIT) has been available for some time to treat patients with non-Hodgkin's lymphoma, but its use in Hodgkin's lymphoma has been less available, partly because of the need to find an appropriate antibody. A new radioiodinated chimeric antibody directed against the CD25 epitope (¹³¹I basiliximab) seems promising, but assessment of response has been difficult. ¹⁸F-fluorodeoxyglucose-positron emission tomography (¹⁸F-FDG-PET) has become a standard method by which the response of Hodgkin's disease to chemotherapy is both predicted and assessed with well-understood criteria of response. The aim of this study is to determine ¹⁸F-FDG-PET can be used to assess response to RIT. Pre- and post-treatment ¹⁸F-FDG-PET imaging was performed in a series of 13 patients with advanced Hodgkin's disease who had failed conventional therapy and had been enrolled on a compassionate use program for treatment with ¹³¹I basiliximab. The ¹³¹I basiliximab was given at an activity of 1200MBq/m² with one patient receiving 2 cycles and the rest a single cycle. The ¹⁸F-FDG-PET studies were compared using the “Deauville” criteria and by comparing the maximum standardized uptake value (SUVmax) of target tumors before and 4 and 8 weeks after treatment. All patients survived long enough for their initial ¹⁸F-FDG-PET-computed tomography scan at 4 weeks after their ¹³¹I basiliximab therapy. One out of ten patients with “Deauville” Grade 4 or 5 response died during the 6-month follow-up period. Two out of three patients with a “Deauville” Grade 2 or 3 response died in the follow-up period. The mean SUVmax pretreatment was 11.9 (±4.7); at 4-week posttreatment, the mean SUVmax was significantly lower at 6.5 (±5.8) (P = 0.02). At 8 weeks, the mean SUVmax was 8.8 (±7.0), which was not significantly different from the pretreatment level. ¹⁸F-FDG-PET imaging is able to predict the short-term response to treatment of Hodgkin's disease by RIT, and an initial poor response appears to predict poor outcome. Early changes in ¹⁸F-FDG-PET uptake did not predict sustained response and by 8 weeks all but one patient had recurrent disease.

Cutaneous Adverse Events of Targeted Therapies for Hematolymphoid Malignancies

The identification of oncogenic drivers of liquid tumors has led to the rapid development of targeted agents with distinct cutaneous adverse event (AE) profiles. The diagnosis and management of these skin toxicities has motivated a novel partnership between dermatologists and oncologists in developing supportive oncodermatology clinics. In this article we review the current state of knowledge of clinical presentation, mechanisms, and management of the most common and significant cutaneous AEs observed during treatment with targeted therapies for hematologic and lymphoid malignancies. We systematically review according to drug-targeting pathway the cutaneous AE profiles of these drugs, and offer insight when possible into whether pharmacologic target versus immunologic modulation primarily underlie presentation. We include discussion of tyrosine kinase inhibitors (imatinib, dasatinib, nilotinib, bosutinib, ponatinib), blinatumomab, ibrutinib, idelalisib, anti-B cell antibodies (rituximab, ibritumomab, obinutuzumab, ofatumumab, tositumomab), immune checkpoint inhibitors (nivolumab, pembrolizumab), alemtuzumab, brentuximab, and proteasome inhibitors (bortezomib, carfilzomib, ixazomib). We highlight skin reactions seen with antiliquid but not solid tumor agents, draw attention to serious cutaneous AEs that might require therapy modification or cessation, and offer management strategies to permit treatment tolerability. We emphasize the importance of early diagnosis and treatment to minimize disruptions to care, optimize prognosis and quality of life, and promptly address life-threatening skin or infectious events. This evolving partnership between oncologists and dermatologists in the iterative characterization and management of skin toxicities will contribute to a better understanding of these drugs' cutaneous targets and improved patient care.

Addressing the Immunogenicity of the Cargo and of the Targeting Antibodies with a Focus on Demmunized Bacterial Toxins and on Antibody-Targeted Human Effector Proteins

Third-generation immunotoxins are composed of a human, or humanized, targeting moiety, usually a monoclonal antibody or an antibody fragment, and a non-human effector molecule. Due to the non-human origin of the cytotoxic domain, these molecules stimulate potent anti-drug immune responses, which limit treatment options. Efforts are made to deimmunize such immunotoxins or to combine treatment with immunosuppression. An alternative approach is using the so-called “human cytotoxic fusion proteins”, in which antibodies are used to target human effector proteins. Here, we present three relevant approaches for reducing the immunogenicity of antibody-targeted protein therapeutics: (1) reducing the immunogenicity of the bacterial toxin, (2) fusing human cytokines to antibodies to generate immunocytokines and (3) addressing the immunogenicity of the targeting antibodies.

Targeted Cancer Therapy Using Radiolabeled Monoclonal Antibodies

Radioimmunotherapy (RIT) combines the advantages of targeted radiation therapy and specific immunotherapy using monoclonal antibodies. RIT can be used either to target tumor cells or to specifically suppress immunocompetent host cells in the setting of allogeneic transplantation. The choice of radionuclide used for RIT depends on its distinct radiation characteristics and the type of malignancy or cells targeted. Beta-emitters with their lower energy and longer path length are more suitable to target bulky, solid tumors whereas α-emitters with their high linear energy transfer and short path length are better suited to target hematopoietic cells (normal or malignant). Different approaches of RIT such as the use of stable radioimmunoconjugates or of pretargeting strategies are available. Encouraging results have been obtained with RIT in patients with hematologic malignancies. The results in solid tumors are somewhat less favorable but new strategies for patients with minimal residual disease using adjuvant and locoregional treatment are evolving. This report outlines basic principles of RIT, gives an overview of available radionuclides and radioimmunoconjugates, and discusses clinical results with special emphasis on their use in hematologic malignancies including use in conditioning regimens for bone marrow transplantation.

Consolidative Radioimmunotherapy After Chemoimmunotherapy in Patients With Histologic Transformation of Indolent Non-Hodgkin Lymphoma

INTRODUCTION

Histologic transformation (HT) of indolent non-Hodgkin lymphomas is an event that results in considerable morbidity and mortality. The introduction of chemoimmunotherapy regimens has resulted in an improvement in the management of this disease, and consolidation of responses with autologous stem cell transplantation appears efficacious. Many patients are not eligible for high-dose therapy, however. Radioimmunotherapy (RIT) has demonstrated single-agent efficacy in HT and can be used safely as consolidation after chemoimmunotherapy. For these reasons, RIT consolidation after chemoimmunotherapy induction has been our standard treatment approach at the University of Rochester for patients with HT who were ineligible for autologous stem cell transplantation.

PATIENTS AND METHODS

A retrospective cohort study was performed to describe the clinical outcomes of these patients. Twenty-one patients were identified who received RIT consolidation. The Kaplan-Meier method was used to estimate the distributions of overall survival and progression-free survival. Comparisons were made between patients with pathologic HT and the combination of clinical HT and composite lymphoma using the log-rank test to compare survival curves.

RESULTS

The median overall survival of the cohort was 84 months, and progression-free survival was 38 months. The major toxicity was myelosuppression, and 2 deaths were attributed to therapy. One case of therapy-related acute myeloid leukemia was noted.

CONCLUSION

In a population of patients ineligible for high-dose therapy with autologous stem cell support, consolidation of response to chemoimmunotherapy with RIT was well tolerated and should be considered in patients with disease responsive to induction therapy.

Advancing radioimmunotherapy and its future role in non-Hodgkin lymphoma

Radioimmunotherapy is an effective treatment modality with an acceptable toxicity profile in both indolent B-cell non-Hodgkin lymphoma and histologic transformation. Its ease of administration from a patient's perspective sets it apart from chemoimmunotherapy regimens. It has demonstrated efficacy in a range of different treatment scenarios. Despite its promise as a treatment modality, radioimmunotherapy has been seldom used, and one of the previously available agents is now off the market. Radioimmunotherapy has shown impressive activity in both the relapsed and upfront settings in follicular lymphoma, histologic transformation, as consolidation after chemotherapy, and in conjunction with high-dose chemotherapy and autologous stem cell support. Future efforts should focus on its optimal employment in the upfront setting for follicular lymphoma as well as further investigation of the promising activity in histologic transformation.

Antibody-mediated delivery of therapeutics for cancer therapy

INTRODUCTION

Antibody-conjugated therapies (ACTs) combine the specificity of monoclonal antibodies to target cancer cells directly with highly potent payloads, often resulting in superior efficacy and/or reduced toxicity. This represents a new approach to the treatment of cancer. There have been highly promising clinical trial results using this approach with improvements in linker and payload technology. The breadth of current trials examining ACTs in haematological malignancies and solid tumours indicate the potential for clinical impact.

AREAS COVERED

This review will provide an overview of ACTs currently in clinical development as well as the principles of antibody delivery and types of payloads used, including cytotoxic drugs, radiolabelled isotopes, nanoparticle-based siRNA particles and immunotoxins.

EXPERT OPINION

The focus of much of the clinical activity in ACTs has, understandably, been on their use as a monotherapy or in combination with standard of care drugs. This will continue, as will the search for better targets, linkers and payloads. Increasingly, as these drugs enter routine clinical care, important questions will arise regarding how to optimise ACT treatment approaches, including investigation of resistance mechanisms, biomarker and patient selection strategies, understanding of the unique toxicities of these drugs, and combinatorial approaches with standard therapies as well as emerging therapeutic agents like immunotherapy.

Astatine-211 conjugated to an anti-CD20 monoclonal antibody eradicates disseminated B-cell lymphoma in a mouse model

α-Emitting radionuclides deposit a large amount of energy within a few cell diameters and may be particularly effective for radioimmunotherapy targeting minimal residual disease (MRD). To evaluate this hypothesis, (211)At-labeled 1F5 monoclonal antibody (mAb) (anti-CD20) was studied in both bulky lymphoma tumor xenograft and MRD animal models. Superior treatment responses to (211)At-labeled 1F5 mAb were evident in the MRD setting. Lymphoma xenograft tumor-bearing animals treated with doses of up to 48 µCi of (211)At-labeled anti-CD20 mAb ([(211)At]1F5-B10) experienced modest responses (0% cures but two- to threefold prolongation of survival compared with negative controls). In contrast, 70% of animals in the MRD lymphoma model demonstrated complete eradication of disease when treated with (211)At-B10-1F5 at a radiation dose that was less than one-third (15 µCi) of the highest dose given to xenograft animals. Tumor progression among untreated control animals in both models was uniformly lethal. After 130 days, no significant renal or hepatic toxicity was observed in the cured animals receiving 15 µCi of [(211)At]1F5-B10. These findings suggest that α-emitters are highly efficacious in MRD settings, where isolated cells and small tumor clusters prevail.

Exposure levels associated with Na(131)I thyroid cancer patients: correlation with initial activity and clinical physical parameters

Initial radiation exposure levels X (0) at 1 m from the navel of thyroid cancer patients were measured for 165 individuals at the time of ingestion. Some 61 patients had previously signed informed consent so only those patients could be assayed with regard to body parameters. While the activity was in the stomach, resultant X (0) values were seen to be linearly correlated with the total (131)I activity (A) given orally. Yet large differences in X (0) were seen; e.g., at A = 7.4 GBq, variations of a factor of four were found between the largest and smallest exposure rates. Correlation analyses were performed between normalized rate X (0)A-1 and several patient physical parameters. These included age, sex, height, weight, and BMI (body mass index). Only weight and BMI had significant linear correlation (p < 0.05) with normalized exposure rate. In the former case, the correlation coefficient ρ (weight) was -0.296 (p = 0.02). Using BMI as the independent variable, ρ (BMI) was -0.386 (p = 0.0021). With further analysis of the BMI variation, 95% confidence intervals could be determined at various BMI levels. For example, at 28 kg m(-2), the normalized rate varied between 0.039 and 0.0446 μGy h(-1) MBq(-1)-approximately a ±6.5% variation on the mean value of 0.0419 μGy h(-1) MBq(-1) at this BMI. Given such clinical information, differences in normalized exposure rate can be reduced to values on the order of ±10% or less for BMI values over the clinically relevant interval 20 to 40 kg m(-2).

Tumor-Absorbed Dose Predicts Progression-Free Survival Following (131)I-Tositumomab Radioimmunotherapy

The study aimed at identifying patient-specific dosimetric and nondosimetric factors predicting outcome of non-Hodgkin lymphoma patients after (131)I-tositumomab radioimmunotherapy for potential use in treatment planning.

METHODS

Tumor-absorbed dose measures were estimated for 130 tumors in 39 relapsed or refractory non-Hodgkin lymphoma patients by coupling SPECT/CT imaging with the Dose Planning Method (DPM) Monte Carlo code. Equivalent biologic effect was calculated to assess the biologic effects of nonuniform absorbed dose including the effects of the unlabeled antibody. Evaluated nondosimetric covariates included histology, presence of bulky disease, and prior treatment history. Tumor level outcome was based on volume shrinkage assessed on follow-up CT. Patient level outcome measures were overall response (OR), complete response (CR), and progression-free survival (PFS), determined from clinical assessments that included PET/CT.

RESULTS

The estimated mean tumor-absorbed dose had a median value of 275 cGy (range, 94-711 cGy). A high correlation was observed between tracer-predicted and therapy-delivered mean tumor-absorbed doses (P < 0.001; r = 0.85). In univariate tumor-level analysis, tumor shrinkage correlated significantly with almost all of the evaluated dosimetric factors, including equivalent biologic effect. Regression analysis showed that OR, CR, and PFS were associated with the dosimetric factors and equivalent biologic effect. Both mean tumor-absorbed dose (P = 0.025) and equivalent biologic effect (P = 0.035) were significant predictors of PFS whereas none of the nondosimetric covariates were found to be statistically significant factors affecting PFS. The most important finding of the study was that in Kaplan-Meier curves stratified by mean dose, longer PFS was observed in patients receiving mean tumor-absorbed doses greater than 200 cGy than in those receiving 200 cGy or less (median PFS, 13.6 vs. 1.9 mo for the 2 dose groups; log-rank P < 0.0001).

CONCLUSION

A higher mean tumor-absorbed dose was significantly predictive of improved PFS after (131)I-tositumomab radioimmunotherapy. Hence tumor-absorbed dose, which can be estimated before therapy, can potentially be used to design radioimmunotherapy protocols to improve efficacy.

Phase 1 study of radiosensitization using bortezomib in patients with relapsed non-Hodgkin lymphoma receiving radioimmunotherapy with 131I-tositumomab

Radioimmunotherapy (RIT) is effective treatment for indolent non-Hodgkin lymphomas (NHLs), but response durations are usually limited, especially in aggressive NHL. We hypothesized that administration of bortezomib as a radiosensitizer with RIT would be tolerable and improve efficacy in NHL. This phase 1 dose-escalation study evaluated escalating doses of bortezomib combined with 131I-tositumomab in patients with relapsed/refractory NHL. Twenty-five patients were treated. Treatment was well tolerated, with primarily hematologic toxicity. The maximum tolerated dose (MTD) was determined to be 0.9 mg/m2 bortezomib, in combination with a standard dose of 75 cGy 131I-tositumomab. Sixteen patients responded (64%), including 44% complete responses (CRs), with 82% CR in patients with follicular lymphoma (FL). At a median follow-up of 7 months, median progression-free survival was 7 months, and seven of 11 patients with FL remained in remission at a median of 22 months. In conclusion, bortezomib can be safely administered in combination with 131I-tositumomab with promising response rates.

The status of radioimmunotherapy in CD20+ non-Hodgkin's lymphoma

Rituximab, the CD20-directed antibody, has become a standard component of treatment regimens for patients with B cell non-Hodgkin's lymphoma (NHL). The use of rituximab has resulted in greatly improved response and survival rates with less toxicity relative to standard chemotherapeutic regimes. However, relapse and recurrence is common, particularly in indolent varieties which remain incurable, requiring alternate therapeutic options. The subsequent coupling of β-emitting isotopes such as (131)I and (90)Y to anti-CD20 monoclonal antibodies (mAbs), including rituximab, has been steadily growing over the last decade and demonstrates even greater therapeutic efficacy with more durable responses. (177)Lutetium-labelled rituximab offers a number of convenient advantages over (131)I and (90)Y anti-CD20 mAbs for treatment of NHL, and a number of alpha-emitting isotopes lie at the frontier of consolidation therapy for residual, micrometastatic disease.

Prolonged progression-free survival and preserved quality of life in the Canadian prospective study of tositumomab and iodine(131)-tositumomab for previously treated, rituximab-exposed, indolent non-Hodgkin lymphoma

Radioimmunotherapy offers a unique treatment modality for indolent non-Hodgkin lymphoma (iNHL). We report 5-year outcomes and quality of life (QoL) in tositumomab and iodine(131)-tositumomab (TST/I(131)-TST) treated patients with iNHL previously treated with rituximab. Ninety-three patients with ≥ 2 lines of therapy, responding to last treatment, were enrolled at 12 Canadian centers. Median age, disease duration and number of prior therapies (#PTx) were 59 years, 4.9 years and 5, respectively. Outcomes were response rate (43.0%), median progression-free survival (mPFS) (12.0 months), 5-year PFS (27%) and median overall survival (OS) (59.8 months). In responders, median response duration and mPFS were not reached. Improvements in QoL were seen by week 7. In univariate and multivariate analyses, hemoglobin, disease bulk and body surface area (BSA) predicted OS, whereas lactate dehydrogenase (LDH), bulk, BSA and #PTx predicted PFS. Most common adverse events (AEs) were fatigue and nausea. Two cases of myelodysplastic syndrome (MDS) were reported. TST/I(131)-TST was associated with durable responses, and prolonged OS and PFS in heavily pretreated iNHL.

Predictive patient-specific dosimetry and individualized dosing of pretargeted radioimmunotherapy in patients with advanced colorectal cancer

PURPOSE

Pretargeted radioimmunotherapy (PRIT) with bispecific antibodies (bsMAb) and a radiolabeled peptide reduces the radiation dose to normal tissues. Here we report the accuracy of an (111)In-labeled pretherapy test dose for personalized dosing of (177)Lu-labeled IMP288 following pretargeting with the anti-CEA × anti-hapten bsMAb, TF2, in patients with metastatic colorectal cancer (CRC).

METHODS

In 20 patients bone marrow absorbed doses (BMD) and doses to the kidneys were predicted based on blood samples and scintigrams acquired after (111)In-IMP288 injection for individualized dosing of PRIT with (177)Lu-IMP288. Different dose schedules were studied, varying the interval between the bsMAb and peptide administration (5 days vs. 1 day), increasing the bsMAb dose (75 mg vs. 150 mg), and lowering the peptide dose (100 μg vs. 25 μg).

RESULTS

TF2 and (111)In/(177)Lu-IMP288 clearance was highly variable. A strong correlation was observed between peptide residence times and individual TF2 blood concentrations at the time of peptide injection (Spearman's ρ = 0.94, P < 0.0001). PRIT with 7.4 GBq (177)Lu-IMP288 resulted in low radiation doses to normal tissues (BMD <0.5 Gy, kidney dose <3 Gy). Predicted (177)Lu-IMP288 BMD were in good agreement with the actual measured doses (mean ± SD difference -0.0026 ± 0.028 mGy/MBq). Hematological toxicity was mild in most patients, with only two (10 %) having grade 3-4 thrombocytopenia. A correlation was found between platelet toxicity and BMD (Spearman's ρ = 0.58, P = 0.008). No nonhematological toxicity was observed.

CONCLUSION

These results show that individual high activity doses in PRIT in patients with CEA-expressing CRC could be safely administered by predicting the radiation dose to red marrow and kidneys, based on dosimetric analysis of a test dose of TF2 and (111)In-IMP288.

High dose chemotherapy with autologous stem cell transplant for patients with transformed B-cell non-Hodgkin lymphoma in the rituximab era

High dose chemotherapy with autologous stem cell transplant (HD-ASCT) is a recommended procedure for patients with transformed indolent B-cell lymphoma from the pre-rituximab era. In this retrospective single-center study, we present our experience with HD-ASCT in patients with histologically verified transformed indolent B-cell lymphoma in the rituximab era. Forty-two patients were included, of whom 28 with chemosensitive disease proceeded to HD-ASCT. Twenty patients (71%) achieved a complete response (CR) and five (18%) a partial response (PR) after HD-ASCT. With a median observation time of 49 months for the survivors, the median progression-free survival (PFS) and overall survival (OS) for patients with HD-ASCT were 39 months and 57 months, respectively. Patients who were rituximab-naive at transformation had a significantly better OS compared to patients previously treated with rituximab, both in the whole patient cohort and among the HD-ASCT-treated patients (p = 0.036 and p = 0.039, respectively). Furthermore, male sex influenced survival negatively, whereas time from diagnosis to transformation was positively associated with survival, both with borderline significance, in HD-ASCT-treated patients. In conclusion, HD-ASCT remains an effective treatment for transformed indolent lymphomas in the rituximab era.

Toxicity of targeted therapeutic agents in lymphoma and management: part 1: monoclonal antibodies and radioimmunotherapy

SUMMARY This two-part review strives to comprehensively characterize common toxicities associated with targeted therapies in lymphoma and their management. Current targeted therapies for lymphoma include monoclonal antibodies, radioimmunotherapy and histone deacteylase inhibitors. New drugs that are expected to significantly alter the therapeutic landscape include PI3K, Bruton’s tyrosine kinase and BCL2 inhibitors. This manuscript focuses on the toxicities and associated management recommendations of monoclonal antibodies and radioimmunotherapy. In the second part of this review, we will focus on the toxicities and management pertaining to targeted therapeutic agents including histone deacteylase, PI3K/AKT and Bruton’s tyrosine kinase and BCL2 inhibitors.

Rates and outcomes of follicular lymphoma transformation in the immunochemotherapy era: a report from the University of Iowa/MayoClinic Specialized Program of Research Excellence Molecular Epidemiology Resource

PURPOSE

This study sought to characterize transformation incidence and outcome for patients with follicular lymphoma (FL) in a prospective observational series begun after diffusion of rituximab use.

PATIENTS AND METHODS

Patients with newly diagnosed FL were prospectively enrolled onto the University of Iowa/Mayo Clinic Specialized Program of Research Excellence Molecular Epidemiology Resource from 2002 to 2009. Patients were actively followed for re-treatment, clinical or pathologic transformation, and death. Risk of transformation was analyzed via time to transformation by using death as a competing risk.

RESULTS

In all, there were 631 patients with newly diagnosed grade 1 to 3a FL who had a median age at enrollment of 60 years. At a median follow-up of 60 months (range, 11 to 110 months), 79 patients had died, and 60 patients developed transformed lymphoma, of which 51 were biopsy proven. The overall transformation rate at 5 years was 10.7%, with an estimated rate of 2% per year. Increased lactate dehydrogenase was associated with increased risk of transformation. Transformation rate at 5 years was highest in patients who were initially observed and lowest in patients who initially received rituximab monotherapy (14.4% v 3.2%; P = .021). Median overall survival following transformation was 50 months and was superior in patients with transformation greater than 18 months after FL diagnosis compared with patients with earlier transformation (5-year overall survival, 66% v 22%; P < .001).

CONCLUSION

Follicular transformation rates in the immunochemotherapy era are similar to risk of death without transformation and may be lower than reported in older series. Post-transformation prognosis is substantially better than described in older series. Initial management strategies may influence the risk of transformation.

Pruritus in patients treated with targeted cancer therapies: systematic review and meta-analysis

BACKGROUND

Pruritus has been anecdotally described in association with targeted cancer therapies. The risk of pruritus has not been systematically ascertained.

OBJECTIVE

A systematic review and meta-analysis of the literature was conducted for axitinib, cetuximab, dasatinib, erlotinib, everolimus, gefitinib, imatinib, ipilimumab, lapatinib, nilotinib, panitumumab, pazopanib, rituximab, sorafenib, temsirolimus, tositumomab, vandetanib, and vemurafenib.

METHODS

Databases from PubMed, Web of Science (January 1998 through July 2012), and American Society of Clinical Oncology abstracts (2004 through 2012) were searched. Incidence and relative risk of pruritus were calculated using random- or fixed-effects model.

RESULTS

The incidences of all-grade and high-grade pruritus were 17.4% (95% confidence interval 16.0%-19.0%) and 1.4% (95% confidence interval 1.2%-1.6%), respectively. There was an increased risk of all-grade pruritus (relative risk 2.90 [95% confidence interval 1.76-4.77, P < .001]) and variation among different drugs (P < .001).

LIMITATIONS

The reporting of pruritus may vary, resulting from concomitant medications, comorbidities, and underlying malignancies. We found a higher incidence of pruritus in patients with solid tumors, concordant with those targeted therapies with the highest pruritus incidences.

CONCLUSION

There is a significant risk of developing pruritus in patients receiving targeted therapies. To prevent suboptimal dosing and decreased quality of life, patients should be counseled and treated against this untoward symptom.

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.

Prediction of therapy tumor-absorbed dose estimates in I-131 radioimmunotherapy using tracer data via a mixed-model fit to time activity

BACKGROUND

For individualized treatment planning in radioimmunotherapy (RIT), correlations must be established between tracer-predicted and therapy-delivered absorbed doses. The focus of this work was to investigate this correlation for tumors.

METHODS

The study analyzed 57 tumors in 19 follicular lymphoma patients treated with I-131 tositumomab and imaged with SPECT/CT multiple times after tracer and therapy administrations. Instead of the typical least-squares fit to a single tumor's measured time-activity data, estimation was accomplished via a biexponential mixed model in which the curves from multiple subjects were jointly estimated. The tumor-absorbed dose estimates were determined by patient-specific Monte Carlo calculation.

RESULTS

The mixed model gave realistic tumor time-activity fits that showed the expected uptake and clearance phases even with noisy data or missing time points. Correlation between tracer and therapy tumor-residence times (r=0.98; p<0.0001) and correlation between tracer-predicted and therapy-delivered mean tumor-absorbed doses (r=0.86; p<0.0001) were very high. The predicted and delivered absorbed doses were within ± 25% (or within ± 75 cGy) for 80% of tumors.

CONCLUSIONS

The mixed-model approach is feasible for fitting tumor time-activity data in RIT treatment planning when individual least-squares fitting is not possible due to inadequate sampling points. The good correlation between predicted and delivered tumor doses demonstrates the potential of using a pretherapy tracer study for tumor dosimetry-based treatment planning in RIT.

Radioimmunotherapy for B-cell non-hodgkin lymphomas

BACKGROUND

Radioimmunotherapy (RIT) is a safe and effective therapeutic option for patients with indolent B-cell non-Hodgkin lymphomas (NHL), in both up-front and relapsed/refractory settings. Two approved agents (90Y-ibritumomab tiuxetan and 131I-tositumomab) are available in the United States. Both target CD20 with similar clinical outcomes but with unique clinical considerations and radiation precautions due to the use of varying radioisotopes.

METHODS

This paper reviews the available evidence for these approved RIT agents and examines the recently published and ongoing clinical trials of potential novel indications for aggressive B-cell NHL.

RESULTS

A pretreatment biodistribution evaluation required before administering the 90Y-ibritumomab tiuxetan therapeutic dose has been removed, which once limited its usage. The potential clinical applications of RIT include relapsed/refractory indolent B-cell NHL, diffuse large B-cell lymphoma, indolent lymphoma in the front-line setting, and mantle cell lymphoma. Multiple novel RIT agents are in preclinical and clinical development, and the addition of radiosensitizers or external-beam radiotherapy may act in synergy with RIT for both indolent and aggressive lymphomas. The risk of treatment-related myelodysplastic syndrome does not appear to be higher in patients treated with RIT over those receiving chemotherapy alone.

CONCLUSIONS

RIT is a safe, effective, and significantly underutilized therapy for patients with B-cell NHL, and many studies have demonstrated the efficacy of 90Y-ibritumomab tiuxetan and 131I-tositumomab for relapsed/refractory indolent B-cell lymphomas. Continued research to establish its efficacy for other lymphoma subtypes is warranted.

Advances in immuno-positron emission tomography: antibodies for molecular imaging in oncology

Identification of cancer cell-surface biomarkers and advances in antibody engineering have led to a sharp increase in the development of therapeutic antibodies. These same advances have led to a new generation of radiolabeled antibodies and antibody fragments that can be used as cancer-specific imaging agents, allowing quantitative imaging of cell-surface protein expression in vivo. Immuno-positron emission tomography (immunoPET) imaging with intact antibodies has shown success clinically in diagnosing and staging cancer. Engineered antibody fragments, such as diabodies, minibodies, and single-chain Fv (scFv) -Fc, have been successfully employed for immunoPET imaging of cancer cell-surface biomarkers in preclinical models and are poised to bring same-day imaging into clinical development. ImmunoPET can potentially provide a noninvasive approach for obtaining target-specific information useful for titrating doses for radioimmunotherapy, for patient risk stratification and selection of targeted therapies, for evaluating response to therapy, and for predicting adverse effects, thus contributing to the ongoing development of personalized cancer treatment.

Superior long-term outcome of patients with early transformation of non-Hodgkin lymphoma undergoing stem cell transplantation

In this study, we discuss the results of patients with transformed lymphoma (TL) undergoing stem cell transplantation (SCT). Because of the paucity of literature on the treatment of TL, deciding on the optimal evidence-based treatment is a challenge. Herein, our results indicate that patients with early transformation may benefit the most from SCT.

BACKGROUND

Transformed non-Hodgkin's lymphoma arising from follicular lymphoma (TL) carries a poor prognosis with a median survival time after transformation reported to be approximately 1 year.

PATIENTS AND METHODS

Fifty-one consecutive patients with TL received SCT between January 2000 and December 2010 (autologous SCT, n = 44, allogeneic SCT, n = 7).

RESULTS

Thirty-six (70.5%) patients had an early transformation, defined as histologic evidence of transformation at the time of initial diagnosis or transformation within 1 year of follicular lymphoma. Fifteen patients had early stage disease (29%) and 36 (71%) had advanced stage disease on presentation. At the time of analysis, 37 patients were alive with an estimated 5-year overall survival (OS) and event free survival (EFS) of 61.8% and 45%, respectively. OS and EFS were not significantly different between types of transplant procedure. The major cause of transplant failure was disease recurrence, with estimated 2-year relapse rate of 37.4%. Importantly, early transformation was independently associated with improved OS (hazard ratio [HR] 3.29; P = .028) and EFS (HR 2.49; P = .029).

CONCLUSION

Our results indicate that an aggressive transplant approach should be considered first in patients with TL and emphasize the need to incorporate novel strategies (eg, immunomodulation) early post-SCT to prevent relapses as disease recurrence remains the major cause of failure in heavily pretreated patients.

Antibody delivery of drugs and radionuclides: factors influencing clinical pharmacology

The therapeutic rationale of antibody conjugates is the selective delivery of a cytotoxin to tumor cells via binding and internalization of the monoclonal antibodies to a specific cell-surface antigen, thereby enhancing the therapeutic index of the cytotoxin. The key structural and functional components of an antibody conjugate are the antibody, the linker and the cytotoxin (chemical or radionuclide) with each component being critical for the successful development of the conjugate. Considerable efforts have been made in understanding the pharmacokinetics, pharmacodynamics, tissue distribution, metabolism and pharmacologic effects of these complex macromolecular entities. The purpose of this article is to discuss the properties and various structural components of antibody conjugates that influence their clinical pharmacology.

Modification of a motel-type room to accommodate patients receiving radioiodine therapy: reduction of environmental exposure

Patients receiving ¹³¹I-based therapies are generally restricted in leaving the medical institution. In the U.S., the U.S. Nuclear Regulatory Commission (U.S. NRC) has developed the rule that a ≤ 7 mR h⁻¹ reading at 1 m from the patient (or 33 mCi) is sufficient to allow unrestricted release. Because of home situations and other constraints, it is preferable that a patient-specific release level be determined by the radiation safety staff. Locally, the City of Hope has instituted a general release criterion of ≤ 2 mR h⁻¹ at 1 m. While contributing to a reduction in public exposure, this as low as reasonably achievable (ALARA) approach is difficult to justify on a cost basis due to the expense of maintaining the radioactive individual in a hospital room. Instead, it was determined that a motel-type room already on the campus be modified to allow the patient to remain on-site until at or below a locally permitted release level. By adding lead to the bathroom area and sealing the tile surfaces, the room may be converted for less than $5,000. Daily cost for the patient is $65. In comparing the use of this facility for thyroid cancer patients from 2006 to 2010, it was found that the public exposure at 1 m was reduced by approximately 70% as compared to release at the 7 mR h level. In addition, controlling the release reduces the likelihood of a radiation incident in the public environment such as on public transportation or in a hotel.

Ofatumumab monotherapy in rituximab-refractory follicular lymphoma: results from a multicenter study

New treatments are required for rituximab-refractory follicular lymphoma (FL). In the present study, patients with rituximab-refractory FL received 8 weekly infusions of ofatumumab (CD20 mAb; dose 1, 300 mg and doses 2-8, 500 or 1000 mg; N = 116). The median age of these patients was 61 years, 47% had high-risk Follicular Lymphoma International Prognostic Index scores, 65% were chemotherapy-refractory, and the median number of prior therapies was 4. The overall response rate was 13% and 10% for the 500-mg and 1000-mg arms, respectively. Among 27 patients refractory to rituximab monotherapy, the overall response rate was 22%. The median progression-free survival was 5.8 months. Forty-six percent of patients demonstrated tumor reduction 3 months after therapy initiation, and the median progression-free survival for these patients was 9.1 months. The most common adverse events included infections, rash, urticaria, fatigue, and pruritus. Three patients experienced grade 3 infusion-related reactions, none of which were considered serious events. Grade 3-4 neutropenia, leukopenia, anemia, and thrombocytopenia occurred in a subset of patients. Ofatumumab was well tolerated and modestly active in this heavily pretreated, rituximab-refractory population and is therefore now being studied in less refractory FL and in combination with other agents in various B-cell neoplasms. The present study was registered at www.clinicaltrials.gov as NCT00394836.

Brentuximab Vedotin (SGN-35)

Brentuximab vedotin (SGN-35) is an antibody-drug conjugate (ADC) directed against the CD30 antigen expressed on Hodgkin lymphoma and anaplastic large cell lymphoma. SGN-35 consists of the cAC10 chimerized IgG1 monoclonal antibody SGN30, modified by the addition of a valine-citrulline dipeptide linker to permit attachment of the potent inhibitor of microtubule polymerization monomethylauristatin E (MMAE). In phase II trials, SGN-35 produced response rates of 75% in patients with Hodgkin lymphoma (n = 102) and 87% in patients with anaplastic large cell lymphoma (n = 30). Responses to SGN-35 might be related not only to the cytotoxic effect due to release of MMAE within the malignant cell but also to other effects. First, SGN-35 may signal malignant cells through CD30 ligation to deliver an apoptotic or proliferative response. The former would amplify the cytotoxicity of MMAE. A proliferative signal delivered in the context of MMAE intoxication could enhance cell death. Second, the efficacy of SGN-35, particularly in Hodgkin lymphoma, might be attributed to its effect on the tumor microenvironment. Diffusion of free MMAE from the targeted tumor cells could result in a bystander effect that kills the normal supporting cells in close proximity to the malignant cells. The elimination of T regulatory cells that inhibit cytotoxic effector cells and elimination of cells that provide growth factor support for Hodgkin/Reed-Sternberg cells could further enhance the cytotoxic activity of SGN-35. Here we review the biology of SGN-35 and the clinical effects of SGN-35 administration.

Targeted radionuclide therapy

Targeted radiotherapy is an evolving and promising modality of cancer treatment. The killing of cancer cells is achieved with the use of biological vectors and appropriate radionuclides. Among the many advantages of this approach are its selectiveness in delivering the radiation to the target, relatively less severe and infrequent side effects, and the possibility of assessing the uptake by the tumor prior to the therapy. Several different radiopharmaceuticals are currently being used by various administration routes and targeting mechanisms. This article aims to briefly review the current status of targeted radiotherapy as well as to outline the advantages and disadvantages of radionuclides used for this purpose.

Pretargeted radioimmunotherapy using genetically engineered antibody-streptavidin fusion proteins for treatment of non-hodgkin lymphoma

PURPOSE

Pretargeted radioimmunotherapy (PRIT) using streptavidin (SAv)-biotin technology can deliver higher therapeutic doses of radioactivity to tumors than conventional RIT. However, "endogenous" biotin can interfere with the effectiveness of this approach by blocking binding of radiolabeled biotin to SAv. We engineered a series of SAv FPs that downmodulate the affinity of SAv for biotin, while retaining high avidity for divalent DOTA-bis-biotin to circumvent this problem.

EXPERIMENTAL DESIGN

The single-chain variable region gene of the murine 1F5 anti-CD20 antibody was fused to the wild-type (WT) SAv gene and to mutant SAv genes, Y43A-SAv and S45A-SAv. FPs were expressed, purified, and compared in studies using athymic mice bearing Ramos lymphoma xenografts.

RESULTS

Biodistribution studies showed delivery of more radioactivity to tumors of mice pretargeted with mutant SAv FPs followed by (111)In-DOTA-bis-biotin [6.2 ± 1.7% of the injected dose per gram (%ID/gm) of tumor 24 hours after Y43A-SAv FP and 5.6 ± 2.2%ID/g with S45A-SAv FP] than in mice on normal diets pretargeted with WT-SAv FP (2.5 ± 1.6%ID/g; P = 0.01). These superior biodistributions translated into superior antitumor efficacy in mice treated with mutant FPs and (90)Y-DOTA-bis-biotin [tumor volumes after 11 days: 237 ± 66 mm(3) with Y43A-SAv, 543 ± 320 mm(3) with S45A-SAv, 1129 ± 322 mm(3) with WT-SAv, and 1435 ± 212 mm(3) with control FP (P < 0.0001)].

CONCLUSIONS

Genetically engineered mutant-SAv FPs and bis-biotin reagents provide an attractive alternative to current SAv-biotin PRIT methods in settings where endogenous biotin levels are high.

Comparison of I-131 radioimmunotherapy tumor dosimetry: unit density sphere model versus patient-specific Monte Carlo calculations

High computational requirements restrict the use of Monte Carlo algorithms for dose estimation in a clinical setting, despite the fact that they are considered more accurate than traditional methods. The goal of this study was to compare mean tumor absorbed dose estimates using the unit density sphere model incorporated in OLINDA with previously reported dose estimates from Monte Carlo simulations using the dose planning method (DPMMC) particle transport algorithm. The dataset (57 tumors, 19 lymphoma patients who underwent SPECT/CT imaging during I-131 radioimmunotherapy) included tumors of varying size, shape, and contrast. OLINDA calculations were first carried out using the baseline tumor volume and residence time from SPECT/CT imaging during 6 days post-tracer and 8 days post-therapy. Next, the OLINDA calculation was split over multiple time periods and summed to get the total dose, which accounted for the changes in tumor size. Results from the second calculation were compared with results determined by coupling SPECT/CT images with DPM Monte Carlo algorithms. Results from the OLINDA calculation accounting for changes in tumor size were almost always higher (median 22%, range -1%-68%) than the results from OLINDA using the baseline tumor volume because of tumor shrinkage. There was good agreement (median -5%, range -13%-2%) between the OLINDA results and the self-dose component from Monte Carlo calculations, indicating that tumor shape effects are a minor source of error when using the sphere model. However, because the sphere model ignores cross-irradiation, the OLINDA calculation significantly underestimated (median 14%, range 2%-31%) the total tumor absorbed dose compared with Monte Carlo. These results show that when the quantity of interest is the mean tumor absorbed dose, the unit density sphere model is a practical alternative to Monte Carlo for some applications. For applications requiring higher accuracy, computer-intensive Monte Carlo calculation is needed.

Treatment options for transformed lymphoma: incorporating allogeneic stem cell transplantation in a multimodality approach

Transformed non-Hodgkin lymphoma (TL) arising from follicular lymphoma carries a poor prognosis, and the median survival time after transformation is approximately 10 to 12 months. Standard chemotherapy and radioimmunotherapy have offered promising responses; however, the duration of response does not appear to last long. Several studies evaluating the role of autologous stem cell transplantation (auto-SCT) as a salvage regimen have been reported, and a subset of patients benefit from this modality of treatment. With an improvement in supportive care, outcome after allogeneic stem cell transplantation (allo-SCT) has been improved significantly over past decades; however, very limited data are available for TL. In the era of emerging novel therapies, the actual timing, optimal conditioning regimens, and long-term impact of the type of stem cell transplantation (auto-SCT vs allo-SCT) is unclear. This review addresses the approaches to the management of patients with TL.