Concepts in radiotherapy and immunotherapy: Anti-CD20 mechanisms of action and targets

Physiological Considerations for Modeling in vivo Antibody-Target Interactions

The number of therapeutic antibodies in development pipelines is increasing rapidly. Despite superior success rates relative to small molecules, therapeutic antibodies still face many unique development challenges. There is often a translational gap from their high target affinity and specificity to the therapeutic effects. Tissue microenvironment and physiology critically influence antibody-target interactions contributing to apparent affinity alterations and dynamic target engagement. The full potential of therapeutic antibodies will be further realized by contextualizing antibody-target interactions under physiological conditions. Here we review how local physiology such as physical stress, biological fluid, and membrane characteristics could influence antibody-target association, dissociation, and apparent affinity. These physiological factors in the early development of therapeutic antibodies are valuable toward rational antibody engineering, preclinical candidate selection, and lead optimization.

Emerging Preclinical and Clinical Applications of Theranostics for Nononcological Disorders

Studies in nuclear medicine have shed light on molecular imaging and therapeutic approaches for oncological and nononcological conditions. Using the same radiopharmaceuticals for diagnosis and therapeutics of malignancies, the theranostics approach, has improved clinical management of patients. Theranostic approaches for nononcological conditions are recognized as emerging topics of research. This review focuses on preclinical and clinical studies of nononcological disorders that include theranostic strategies. Theranostic approaches are demonstrated as possible in the clinical management of infections and inflammations. There is an emerging need for randomized trials to specify the factors affecting validity and efficacy of theranostic approaches in nononcological diseases.

New targeted therapies for indolent B-cell malignancies in older patients

Molecularly targeted agents have become an established component of the treatment of indolent B-cell malignancies (iNHL). iNHL disproportionately affects older adults, so treatments that have excellent tolerability and efficacy across multiple lines of therapy are in demand. The numbers and classes of targeted therapies for iNHL have proliferated rapidly in recent years; classes of agents that show promise for older patients with iNHL include anti-CD20 antibodies, phosphatidyl-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway inhibitors, immunomodulators, proteasome inhibitors, epigenetic modulators, and immunotherapies. Here, we review the proposed mechanisms of action, efficacy, and tolerability of novel agents for iNHL, with an emphasis on their applicability to older patients.

Cancer dormancy: lessons from a B cell lymphoma and adenocarcinoma of the prostate

Cancer dormancy delineates a situation in which residual tumor cells persist in a patient with no apparent clinical symptoms. Although the precise mechanisms underlying cancer dormancy have not been explained, experimental models have provided some insights into the factors that might be involved in the induction and maintenance of a tumor dormant state. The authors of the present chapter studied a murine B cell lymphoma that can be made dormant when interacting with antibodies directed against the idiotype on its immunoglobulin Ig receptor. This experimental model of antibody-induced dormancy enabled the isolation and characterization of dormant lymphoma cells. The results indicated that anti-Ig antibodies activate growth-inhibiting signals that induced cycle arrest and apoptosis. This process appeared to be balanced by the growth of the tumor cells such that the tumor did not expand. In contrast, antibodies against HER-2expressed on prostate adenocarcinoma (PAC) cells were not growth inhibitory. However, an immunotoxin (IT) prepared by conjugating HER-2 to the A-chain of ricin (RTA) was internalized by PAC cells, followed by induction of cycle arrest and apoptotic death. Infusion of HER-2-specific IT into PAC-bearing immunodeficient mice did not eradicate the tumor but retained it dormant over an extended period of time. Hence, certain aspects of signaling receptors expressed on cancer can be manipulated by antibodies to induce and maintain a tumor dormant state.

Combined therapy with rituximab plus cyclophosphamide/vincristine/prednisone for Sjogren's syndrome-associated B-cell non-Hodgkin's lymphoma

Sjogren's syndrome (SS) is characterized by an increased risk of developing non-Hodgkin's lymphoma (NHL). Optimal treatment for NHL-complicating SS is not clearly established. NHL, which expresses the CD20 antigen on tumor cell surfaces, is a disease entity candidate to treatment with anti-CD20 monoclonal antibodies. We report clinical and immunological data of a patient with SS and NHL who was treated with a regimen consisting of cyclophosphamide/vincristine/prednisone (CVP) plus rituximab. A 68-year-old women had a 26-year history of SS and autoimmune thyroiditis. The clinical course of SS was complicated with severe splenomegaly. An increased percentage of CD19+ B cells (up to 30%) was detected in peripheral blood during follow-up. Clonal rearrangement of immunoglobulin heavy chain was detected. Low-grade B marginal zone lymphoma was diagnosed (peripheral blood immunophenotype: CD19+CD20+CD23+sIg+Kappa; bone marrow immunophenotype: 25% lymphocytes; CD19+CD20+CD79A/BCL2+). She received a total of six cycles of CVP plus rituximab (375 mg/m2). Therapy was well tolerated, and B lymphocytes were depleted from the peripheral blood. Splenomegaly normalized. No evidence of neoplastic infiltration was detected in bone marrow after completion of therapy, while certain symptoms of SS (sicca and arthralgia) improved with treatment. CVP plus rituximab proved effective in a patient with SS with NHL.

Present and future drug treatments for chronic kidney diseases: evolving targets in renoprotection

At present, there are no specific cures for most of the acquired chronic kidney diseases, and renal transplantation is limited by organ shortage, therefore present efforts are concentrated on the prevention of progression of renal diseases. There is robust experimental and clinical evidence that progression of chronic nephropathies is multifactorial; however, intraglomerular haemodynamic changes and proteinuria play a key role in this process. With a focus on renoprotection, we first examine more established therapies--such as those that modulate the renin-angiotensin-aldosterone system--that can be used for the treatment of proteinuric renal diseases. We then discuss examples of novel drugs and biologics that might be used to target the inflammatory and profibrotic process, and glomerular injury, highlighting results from recent clinical trials.

Computational model predicts effective delivery of 188-Re-labeled melanin-binding antibody to metastatic melanoma tumors with wide range of melanin concentrations

Metastatic melanoma is almost always deadly and new methods of treatment are urgently needed. Recently, we established the feasibility of radioimmunotherapy (RIT) for experimental melanoma in mice using a 188-rhenium (188Re)-labeled monoclonal antibody (mAb) 6D2 (IgM) to melanin. Our objective was to determine the effects of varying tumor melanin concentration and of different diffusivities and lymphatic clearance rates of the normal tissue, on the absorbed dose to the tumor in simulated therapy, in preparation for a clinical trial of RIT for melanoma. Using finite element analysis (FEA), we created a pharmacokinetic model that describes melanin-targeting RIT of a melanoma micrometastasis (1.3-mm radius) imbedded in normal tissue (14.3-mm radius). Our method incorporates antibody plasma kinetics, transcapillary transport, interstitial diffusion, and lymphatic clearance. Michaelis-Menten kinetics was used to model mAb binding to tumor melanin for melanin concentrations of 76, 7.6, 0.76, 0.076, and 0.0076 micromol/l. An absorbed dose was calculated, after accounting for direct and crossfire irradiation, on the basis of a 7.4-GBq intravenous dose of 188Re-6D2. The results showed that penetration of mAb into the tumor was inversely proportional to tumor melanin concentration. Decreased diffusivity and increased lymphatic clearance of the surrounding normal tissue decreased the dose to the tumor. The formation of mAb-melanin complex was remarkably similar within a 1000-fold range of melanin concentration, resulting in total doses of 2840, 2820, 2710, and 1990 cGy being delivered to tumors with melanin concentrations of 76, 7.6, 0.76, and 0.076 micromol/l, respectively. In conclusion, RIT of metastatic melanoma can be effective over a wide range of tumor melanin concentrations. The results can be useful in the design of a clinical trial of melanin-targeting RIT in patients with metastatic melanoma.

Radioimmunotherapy for non-Hodgkin's lymphoma

OBJECTIVES

To describe the rationale for radioimmunotherapy as a treatment of non-Hodgkin's lymphoma. To present the similarities and differences in the two radioimmunotherapies and the nursing implications in caring for patients receiving these agents.

DATA SOURCES

Published literature and review of published clinical trials.

CONCLUSION

Radiolabeled monoclonal antibodies bind to specific antigens and provide a means of targeting tumor cells with cytotoxic radioactivity. The infusion of radiolabeled monoclonal antibodies requires an understanding of antibody therapy, radiation therapy, and principles of time, distance, and shielding.

IMPLICATIONS FOR NURSING PRACTICE

As the use of radioimmunotherapy grows, nurses must be aware of the background for, logistics of, and follow-up required for patients receiving this form of radiation treatment.

Thrice-Weekly Low-Dose Rituximab Decreases CD20 Loss via Shaving and Promotes Enhanced Targeting in Chronic Lymphocytic Leukemia

Treatment of chronic lymphocytic leukemia (CLL) patients with standard dose infusion of rituximab (RTX), 375 mg/m2, induces clearance of malignant cells from peripheral blood after infusion of 30 mg of RTX. After completion of the full RTX infusion, substantial recrudescence of CLL cells occurs, and these cells have lost > 90% of CD20. To gain insight into mechanism(s) of CD20 loss, we investigated the hypothesis that thrice-weekly low-dose RTX (20 or 60 mg/m2) treatment for CLL over 4 wk would preserve CD20 and enhance leukemic cell clearance. During initial infusions in all 12 patients, the first 30 mg of RTX promoted clearance of > 75% leukemic cells. Four of six patients receiving 20 mg/m2 RTX retained > or = 50% CD20, and additional RTX infusions promoted further cell clearance. However, four of six patients receiving 60 mg/m2 had CD20 levels < 20% baseline 2 days after initial infusions, and additional RTX infusions were less effective, presumably due to epitope loss. Our results suggest that when a threshold RTX dose is exceeded, recrudesced RTX-opsonized cells are not cleared, due to saturation of the mononuclear phagocytic system, but instead are shaved of RTX-CD20 complexes by acceptor cells. Thrice-weekly low-dose RTX may promote enhanced clearance of circulating CLL cells by preserving CD20.

The emerging role of rituximab in organ transplantation

Long-term acceptance of solid organ allografts remains a challenge. While many acute rejection episodes can be treated, new mechanisms of allograft damage are now being defined especially in kidney transplantation. Unexpected clusters of CD20(+) cells have been discovered in renal biopsies performed for clinical rejection. C4d deposition is now routinely seen in refractory rejection. Despite the rapid introduction of new immunosuppressive agents in transplantation, the search for an efficacious anti-B-cell agent remains. With novel mechanisms of allograft damage now being defined, it is important to consider how an anti-B-cell agent might fit into an immunosuppressive regimen. Rituximab is a high-affinity CD20 specific antibody that depletes the B-cell compartment by inducing cellular apoptosis. Thus, it is a rational choice for therapy in transplantation to abrogate B-cell mediated events. In this review, we will discuss the mechanisms of action of rituximab, and its use in for a variety of indications in solid organ transplantation. There are emerging case reports that show that rituximab may be an effective agent to treat antibody-mediated rejection, and post-transplant lymphoproliferative disorder. Rituximab has been frequently cited as an important adjunct therapy in desensitization protocols for highly sensitized transplant recipients as well as recipients of ABO incompatible transplants. Rituximab demonstrates promise in this regard and warrants additional consideration in prospective clinical trials.

Ex Vivo-activated Human Macrophages Kill Chronic Lymphocytic Leukemia Cells in the Presence of Rituximab: Mechanism of Antibody-dependent Cellular Cytotoxicity and Impact of Human Serum

Antibody-dependent cellular cytotoxicity (ADCC) is one of the mechanisms of tumor killing during antibody (Ab) immunotherapy, and a role for myeloid cells as effectors has been observed in several models. We are developing immunotherapy approaches based on administration of large numbers of ex vivo interferon-gamma-activated macrophages to cancer patients. With a quantitative assay measuring killing of nonproliferating tumor cells, we evaluated whether, in physiologic conditions, these macrophages synergize with the anti-CD20 Ab rituximab for killing primary B-cell chronic lymphocytic leukemia (B-CLL) cells. ADCC reached levels of 70% to 80% at effector to target ratios as low as 1:1. Macrophage recruitment by Ab-opsonized tumor cells did not result in enhanced cytokine secretion, suggesting that the cytokine shower observed in rituximab-treated patients is not caused by macrophage activation, and that cytokines have no role in CLL killing. We observed that uptake of tumor material by macrophages was not directly correlated to tumor killing. Nonetheless, experiments in the presence of cytochalasin D showed that ADCC occurred mainly by phagocytosis. Tumor killing was largely mediated by Fc gammaRI and inhibited by increasing concentration of serum. Importantly, complement deposition on B-CLL cells did not seem to enhance macrophage ADCC in this model, as complement-depleted and complement-repleted human plasmas exerted comparable inhibition.

The Shaving Reaction: Rituximab/CD20 Complexes Are Removed from Mantle Cell Lymphoma and Chronic Lymphocytic Leukemia Cells by THP-1 Monocytes

Clinical investigations have revealed that infusion of immunotherapeutic mAbs directed to normal or tumor cells can lead to loss of targeted epitopes, a phenomenon called antigenic modulation. Recently, we reported that rituximab treatment of chronic lymphocytic leukemia patients induced substantial loss of CD20 on B cells found in the circulation after rituximab infusion, when rituximab plasma concentrations were high. Such antigenic modulation can severely compromise therapeutic efficacy, and we postulated that B cells had been stripped (shaved) of the rituximab/CD20 complex by monocytes or macrophages in a reaction mediated by FcgammaR. We developed an in vitro model to replicate this in vivo shaving process, based on reacting rituximab-opsonized CD20(+) cells with acceptor THP-1 monocytes. After 45 min at 37 degrees C, rituximab and CD20 are removed from opsonized cells, and both are demonstrable on acceptor THP-1 cells. The reaction occurs equally well in the presence and absence of normal human serum, and monocytes isolated from peripheral blood also promote shaving of CD20 from rituximab-opsonized cells. Tests with inhibitors and use of F(ab')(2) of rituximab indicate transfer of rituximab/CD20 complexes to THP-1 cells is mediated by FcgammaR. Antigenic modulation described in previous reports may have been mediated by such shaving, and our findings may have profound implications for the use of mAbs in the immunotherapy of cancer.

The pharmacokinetics of rituximab following an intravitreal injection

Rituximab is a monoclonal antibody directed against the CD20 B-cell antigen and is approved for the treatment of B-cell lymphoma. We investigated the pharmacokinetics of rituximab following intravitreal administration to assess the feasibility of treating primary intraocular lymphoma. Intravitreal injections of rituximab 0.1 ml (1 mg) were performed in rabbits. Drug concentrations in the aqueous and vitreous humor were measured at intervals from 2 to 17 days after administration. The half-life of the total amount of rituximab in the two compartments was calculated to be 4.7 days. The aqueous and vitreous humor drug levels decayed in parallel maintaining an average ratio of approximately seven. Fitting the data to a two-compartment model yielded a clearance from the aqueous humor of 1.2 microl/min. The clearance was less than the reported rate of aqueous humor outflow indicating that elimination by this route could have been sufficient to account for the disappearance of the drug from the eye. The duration of time over which sustained levels of rituximab were achieved suggest that intravitreal administration warrants further investigation as an approach to treating vitreous and anterior chamber infiltrates in patients with primary intraocular lymphoma.