Permeability of human brain tumor to 99mTc-gluco-heptonate and 99mTc-albumin. Implications for monoclonal antibody therapy

[Superselective intra-arterial administration of bevacizumab with blood-brain barrier disruption in patients with recurrent malignant gliomas: case report and literature review]

Glioblastoma multiforme is characterized by persistent recurrent course despite surgical, radio- and chemotherapeutic treatment. The outcomes of superselective intra-arterial administration of bevacizumab with blood-brain barrier disruption in patients with recurrent glioblastoma have been published. The authors reported significant increase in overall survival (up to 2.5 years). We report treatment of recurrent glioblastoma in a young patient with progressive course of disease despite 4 previous neurosurgical interventions, radiotherapy and first-line chemotherapy. Superselective intra-arterial administration of bevacizumab with blood-brain barrier disruption made it possible to achieve clinical response and improve neurological status.

Magnesium therapy improves outcome in Streptococcus pneumoniae meningitis by altering pneumolysin pore formation

BACKGROUND AND PURPOSE

Streptococcus pneumoniae is the most common cause of bacterial meningitis in adults and is characterized by high lethality and substantial cognitive disabilities in survivors. Here, we have studied the capacity of an established therapeutic agent, magnesium, to improve survival in pneumococcal meningitis by modulating the neurological effects of the major pneumococcal pathogenic factor, pneumolysin.

EXPERIMENTAL APPROACH

We used mixed primary glial and acute brain slice cultures, pneumolysin injection in infant rats, a mouse meningitis model and complementary approaches such as Western blot, a black lipid bilayer conductance assay and live imaging of primary glial cells.

KEY RESULTS

Treatment with therapeutic concentrations of magnesium chloride (500 mg·kg^-1 in animals and 2 mM in cultures) prevented pneumolysin-induced brain swelling and tissue remodelling both in brain slices and in animal models. In contrast to other divalent ions, which diminish the membrane binding of pneumolysin in non-therapeutic concentrations, magnesium delayed toxin-driven pore formation without affecting its membrane binding or the conductance profile of its pores. Finally, magnesium prolonged the survival and improved clinical condition of mice with pneumococcal meningitis, in the absence of antibiotic treatment.

CONCLUSIONS AND IMPLICATIONS

Magnesium is a well-established and safe therapeutic agent that has demonstrated capacity for attenuating pneumolysin-triggered pathogenic effects on the brain. The improved animal survival and clinical condition in the meningitis model identifies magnesium as a promising candidate for adjunctive treatment of pneumococcal meningitis, together with antibiotic therapy.

Targeted signal-amplifying enzymes enhance MRI of EGFR expression in an orthotopic model of human glioma

Epidermal growth factor receptor (EGFR) imaging in brain tumors is essential to visualize overexpression of EGFRvIII variants as a signature of highly aggressive gliomas and to identify patients that would benefit from anti-EGFR therapy. Seeking imaging improvements, we tested a novel pretargeting approach that relies on initial administration of enzyme-linked anti-EGFR monoclonal antibodies (mAb; EMD72000) followed by administration of a low-molecular-weight paramagnetic molecule (diTyr-GdDTPA) retained at the site of EGFR mAb accumulation. We hypothesized that diTyr-GdDTPA would become enzyme activated and retained on cells due to binding to tissue proteins. In support of this hypothesis, mAb-enzyme conjugates reacted with both membrane-isolated wild-type (wt) EGFR and EGFRvIII, but they bound primarily to EGFRvIII-expressing cells and not to EGFRwt-expressing cells. In vivo analysis of magnetic resonance (MR) tumor signal revealed differences in MR signal decay following diTyr-GdDTPA substrate administration. These differences were significant in that they suggested differences in substrate elimination from the tissue which relied on the specificity of the initial mAb binding: a biexponential signal decay was observed in tumors only upon preinjection with EGFR-targeted conjugates. Endpoint MRI in this setting revealed detailed images of tumors which correlated with immunohistochemical detection of EGFR expression. Together, our findings suggest an improved method to identify EGFRvIII-expressing gliomas in vivo that are best suited for treatment with therapeutic EGFR antibodies.

Safety and maximum tolerated dose of superselective intraarterial cerebral infusion of bevacizumab after osmotic blood-brain barrier disruption for recurrent malignant glioma. Clinical article

OBJECT

The authors assessed the safety and maximum tolerated dose of superselective intraarterial cerebral infusion (SIACI) of bevacizumab after osmotic disruption of the blood-brain barrier (BBB) with mannitol in patients with recurrent malignant glioma.

METHODS

A total of 30 patients with recurrent malignant glioma were included in the current study.

RESULTS

The authors report no dose-limiting toxicity from a single dose of SIACI of bevacizumab up to 15 mg/kg after osmotic BBB disruption with mannitol. Two groups of patients were studied; those without prior bevacizumab exposure (naïve patients; Group I) and those who had received previous intravenous bevacizumab (exposed patients; Group II). Radiographic changes demonstrated on MR imaging were assessed at 1 month postprocedure. In Group I patients, MR imaging at 1 month showed a median reduction in the area of tumor enhancement of 34.7%, a median reduction in the volume of tumor enhancement of 46.9%, a median MR perfusion (MRP) reduction of 32.14%, and a T2-weighted/FLAIR signal decrease in 9 (47.4%) of 19 patients. In Group II patients, MR imaging at 1 month showed a median reduction in the area of tumor enhancement of 15.2%, a median volume reduction of 8.3%, a median MRP reduction of 25.5%, and a T2-weighted FLAIR decrease in 0 (0%) of 11 patients.

CONCLUSIONS

The authors conclude that SIACI of mannitol followed by bevacizumab (up to 15 mg/kg) for recurrent malignant glioma is safe and well tolerated. Magnetic resonance imaging shows that SIACI treatment with bevacizumab can lead to reduction in tumor area, volume, perfusion, and T2-weighted/FLAIR signal.

Monoclonal antibody therapy with rituximab for acute lymphoblastic leukemia

Significant advances have been achieved in the treatment of acute lymphoblastic leukemia (ALL) with the incorporation of targeted therapy agents. Targeting leukemia surface antigens with monoclonal antibodies is another promising strategy. This article comprehensively reviews available data regarding the use of rituximab for the treatment of Burkitt-type leukemia/lymphoma and CD20-positive precursor B-cell ALL. The incorporation of rituximab into frontline chemotherapy regimens for Burkitt-type leukemia/lymphoma appears to improve outcome. Preliminary data regarding the use of rituximab in frontline therapy for CD20- positive precursor B-cell ALL suggest its use may also be beneficial, particularly for the younger subsets.

The efficacy of rituximab in high-grade pediatric B-cell lymphoma/leukemia: a review of available evidence

PURPOSE OF REVIEW

This review evaluates whether rituximab has efficacy in high-grade pediatric B-cell lymphoma/leukemia. Current pediatric protocols for CD20+ B-cell lymphoma/leukemia significantly improve survival, but with major morbidity. To assess whether rituximab has efficacy in very high-grade pediatric disease, all published data on rituximab therapy for Burkitt's lymphoma/B acute lymphoblastic leukaemia (B-ALL) and pediatric patients with relapsed/refractory large B-cell lymphoma were reviewed.

RECENT FINDINGS

Three trials in adult Burkitt's/B-ALL showed a significant survival advantage when rituximab was added to standard chemotherapy. Minimal pediatric data have been published, but 19 children with mature B-cell lymphoma/B-ALL received rituximab, alone or in combination with chemotherapy, as salvage therapy, after failure of intensive chemotherapy. Fifteen of 19 (79%) responded, 12 (63%) remained alive in continuous complete remission at 5+ to 48+ months of follow-up. Two patients were alive in partial remission. Five patients died, four of progressive disease. Only one patient had no response to rituximab.

SUMMARY

Rituximab has demonstrated efficacy in Burkitt's disease in adults. Although positive reporting bias is suspected, it appears that rituximab, even as monotherapy, has efficacy in heavily pretreated pediatric patients with high-grade B-lymphoma/B-ALL. Rituximab use can be justified in a prospective controlled chemotherapy dose-reduction study.

Albumin marks pseudopodia of astrocytoma cells responding to hepatocyte growth factor or serum

It is well accepted that dysfunction in the blood brain barrier (BBB) allows permeation of albumin from the bloodstream into astrocytic brain tumors, especially glioblastomas, the most aggressive astrocytomas. In vitro, bovine serum albumin (BSA) aids functional cell assays by maintaining cytokines and growth factors in solution and delivering its cargo of fatty acids. Earlier, we showed that BSA was prominent in lysates prepared from pseudopodia formed by U87 astrocytoma cells. The present studies investigated the association of albumin with pseudopodia formed by U87 and LN229 astrocytoma cells. With hepatocyte growth factor (HGF) stimulation, cell migration was enhanced and BSA, especially its dimerized form, was prominent in pseudopodia compared to unmigrated cells on one-dimensional gels and immunoblots. When lysates were equalized for levels of glyceraldehyde-3-phosphate dehydrogenase, the rise for BSA levels in pseudopodia vs migrated cells was comparable or greater than levels noted for established pseudopodial proteins, beta-actin and ezrin. The increase for dimerized BSA in pseudopodia compared to unmigrated cells was greater than the rise in levels of beta-actin, ezrin, HGF, and phosphorylated Met when pseudopodia were harvested from filters with 1 mum pores using either cell line. Fluorescein (F)-labeled BSA co-localized with HGF on actin-rich cellular protrusions and with CM-DiI labeled pseudopodial plasma membranes. The F-BSA highlighted small, individual pseudopodial profiles more so than complex pseudopodial networks (reticulopodia) or unmigrated cells. Labeled human serum albumin also decorated pseudopodia preferentially. Albumin's association with pseudopodia may help to explain its selective accumulation in astrocytomas in vivo. The leaky BBB permits serum albumin to enter the microenvironment of astrocytomas thus allowing their invasive cells contact with serum albumin as a source of fatty acids that would be useful for remodeling cell membranes in pseudopodia. Thus, albumin potentially aids and marks invasion as it accumulates in these tumors.

Practices and Pitfalls of Mouse Cancer Models in Drug Discovery

Mouse models of cancer are critical tools for elucidating mechanisms of cancer development, as well as for assessment of putative cancer therapies. However, there are ongoing concerns about the value of mouse cancer models for predicting therapeutic efficacy in humans. This chapter reviews the most commonly used transplanted tumor models, including subcutaneous and orthotopic tumors in mice. It also reviews commonly utilized in vivo study endpoints. Even small improvements in predictive value achieved through careful selection of models and endpoints have the potential to have large impacts on productivity and overall drug development costs.

Imaging of central nervous system lymphomas with iodine-123 labeled rituximab

Most patients with primary central nervous system (CNS) lymphoma (PCNSL) relapse after initial response to chemotherapy or the combination of chemotherapy and irradiation. Thus, novel treatment regimens for relapsed PCNSL are needed. As the majority of PCNSL are B-cell neoplasms expressing the CD20 antigen, treatment with the chimeric monoclonal antibody (MAb) rituximab might be reasonable. Nevertheless, the potential efficacy of intravenous rituximab in PCNSL seems to be limited as MAbs are high molecular weight proteins, which might be unable to pass the blood brain barrier. Thus, we performed dosimetric measurements with iodine-123 (123I)-rituximab to evaluate rituximab uptake in PCNSL after systemic intravenous administration. We analyzed four patients with PCNSL receiving a preinfusion of 250 mg/m2 rituximab followed by 200-500 MBq of the gamma-emitter 123I-rituximab. Single photon emission computed tomography (SPECT) was performed 1, 24 and 48 h after administration of the radio-immunoconstruct. Only one patient showed a very weak or questionable uptake of 123I-rituximab into tumor tissue which was ninefold lower compared with the blood-pool accumulation. These data suggest that systemic MAb-based radio-immunotherapy is not feasible in patients with PCNSL because a sufficient activity in the tumor will be associated with severe hematotoxicity. If an uptake of therapeutic rituximab doses into PCNSL can be achieved remains questionable.

BR96-DOX immunoconjugate targeting of chemotherapy in brain tumor models

An immunoconjugate of doxorubicin (adriamycin) and a tumor-specific monoclonal antibody, BR96-DOX (now SGN-15) targets chemotherapy to cells that express the LewisY antigen. This immunoconjugate is internalized into lysosomes in antigen-expressing cells, with release of free doxorubicin after hydrolysis of the acid-labile linker. We review our studies using BR96-DOX in a human small-cell lung carcinoma intracerebral xenograft model in nude rats. We have found that the immunoconjugate is effective against intracerebral tumors when delivery is enhanced with osmotic disruption of the blood-brain barrier (BBB). Enhanced delivery of BR96-DOX with BBB opening can work together with radiotherapy to increase antitumor efficacy, which is maximally effective if immunoconjugate is administered prior to radiotherapy. In heterogeneous brain tumors, enhanced delivery of BR96-DOX significantly reduced tumor volumes, but local release of doxorubicin by targeting antigen expressing cells shows modest cytotoxicity against adjacent non-expressor cells. Although BR96-DOX is not effective against glioma cells tested, it does provide a model for drug-immunoconjugate therapy of gliomas. Our studies in a rat brain tumor model point out the importance of optimized delivery, antigenic heterogeneity, and bystander effect for brain tumor therapy. We review additional studies of drug-mAb immunoconjugates pertinent to the treatment of gliomas.

Intraventricular and intravenous treatment of a patient with refractory primary CNS lymphoma using rituximab

The treatment of primary central nervous system lymphoma (PCNSL) with chemo- and radiotherapy is efficient in terms of tumor response. However, time to tumor progression often is of short duration and leptomeningeal relapse is common. We present a 66-year-old man in third relapse of a CD20-positive PCNSL. After treatment with intravenous and intraventricular administration of the chimeric anti-CD20 monoclonal antibody rituximab, a total clearing of lymphoma cells in the cerebrospinal fluid (CSF) was achieved. There was no change in the size of the parenchymal tumor mass but there was slight improvement of clinical symptoms after therapy. Rituximab infusions (375 mg/m2) were first given systemically on days 1 and 8. Intraventricular injections of rituximab via Ommaya reservoir were given on days 16 (10 mg), 17 (40 mg), 24 (25 mg) and 25 (25 mg). Reversible side effects such as nausea, chills and hypotension were observed only immediately after intraventricular administration of 40 mg rituximab. Antibody levels in CSF were measured at 7 timepoints during and after the treatment period. These data suggest that intraventicular treatment with rituximab is safe and feasible with a potential activity on leptomeningeal tumor manifestation. Efficacy and pharmacokinetics of rituximab in PCNSL should be investigated in future trials.

Enhancing effect of electric stimulation on cytotoxicity of anticancer agents against rat and human glioma cells

Electropermeabilization, or electroporation, has been used to deliver genes or drugs into the cytoplasm through micropores in the cell membrane caused by electric stimulation. The cytotoxic effect of a combination of anticancer agents with electric stimulation on rat C6 and human T98G glioma cells was examined in vitro. Electric pulses of 100 microsec square waves (eight cycles at 1 Hz) at various electric fields were delivered to C6 or T98G glioma cell suspensions in combination with several anticancer agents. Cell growth was evaluated 48-72 h after treatment. Measurement of cell lysis by electric stimulation was used to assess the optimum field strength for electroporation. Electric stimulation enhanced significantly the cytotoxicity of bleomycin to both C6 and T98G cells by more than 1000-fold using an electric field of 1750 V/cm for C6 cells and 1000 V/cm for T98G cells. The enhancement disappeared when bleomycin concentration was reduced to 100 pg/ml. The cytotoxicity of carboplatin was weakly but significantly enhanced by electric stimulation when a high dose of carboplatin was used. However, there was no enhancement of the cytotoxicity of nimustine hydrochloride (ACNU), etoposide, and vincristine. These results indicate that the combination of bleomycin and electroporation is the most potent candidate for electrochemotherapy in vivo.

Antitumour activity of an immunoconjugate composed of anti-human astrocytoma monoclonal antibody and neocarzinostatin

Neocarzinostatin (NCS) linked to the thiol group on the hinge region of the Fab' fragment of GA-17, a murine monoclonal antibody reacting with tyrosine-specific phosphorylated antigens, which are exclusively expressed on the cell surface of human astrocytomas, was evaluated for in vivo activity. GA-17-NCS immunoconjugates significantly suppressed the growth of human malignant glioma cell line U87-MG subcutaneous xenografts in nude mice until day 50 when administered intravenously into the tail vein. Disulphide- and thioether-linked GA-17-NCS were nearly equipotent immunoconjugates, but thioether-linked GA-17-NCS was more effective than disulphide-linked conjugates with 250 U/kg NCS content on day 50 (P < 0.05). Thioether-linked GA-17-NCS was significantly more effective on day 50 than free NCS with 500 U/kg or 250 U/kg NCS content (P < 0.05, P < 0.01, respectively). These results suggest that GA-17-NCS may prove useful in the treatment of human malignant gliomas.

A new model of systemic drug rescue based on permeability characteristics of the blood-brain barrier in intracerebral abscess-bearing rats

✓The authors report the results of their investigation of a systemic drug rescue method using antibody to a therapeutic drug based on the differential permeability of the blood-brain barrier to low- and high-molecular-weight compounds. Rats bearing intracerebral abscesses initially received systemic [125I]-gentamicin (Mr 462) followed 60 minutes later by specific gentamicin antiserum (immune group) or normal rabbit serum (nonimmune group). Animals receiving antigentamicin immunoglobulin G (IgG, Mr 150,000) demonstrated 90% binding of serum gentamicin. Immunoprecipitation of serum samples with protein A-Sepharose demonstrated that the increased binding of gentamicin in immune animals was due to antigen binding with antigentamicin IgG. By contrast, the percent of gentamicin bound to antibody within the brain did not differ between immune and nonimmune groups, implying that high-molecular-weight IgG was excluded from the brain and brain lesion. Significant differences in gentamicin deliveries were noted in the abscess, brain around the abscess, brain distant from the abscess, and normal brain areas. In contrast, analysis of comparable brain areas demonstrated no significant differences in gentamicin delivery between immune and nonimmune animals, indicating that the systemic presence of gentamicin antibody did not alter central nervous system delivery of unbound drug. These findings suggest the possibility of a drug rescue method using antidrug IgG, based on the differential permeability of the blood-brain barrier to drug versus antibody. While the present work was developed in a brain abscess model, the drug rescue method may also be applicable in the management of intracerebral tumors.

Preclinical and phase I studies of monoclonal antibodies in melanoma: application to boron neutron capture therapy of melanoma

Monoclonal antibodies (MAbs) provide an attractive method of selectively localizing sufficient boron atoms around tumour cells to capture neutrons. Assuming that 10(8)-10(10) 10B atoms are needed for one capture event and that 10(3)-10(4) atoms can be coupled to each antibody molecule, then 10(5)-10(6) antibody molecules gathered on an individual cell will destroy that cell. Binding to normal tissues, on the other hand, would need to be at least 20-fold less than that to tumour tissues to avoid toxic effects of neutrons on surrounding tissues. Preclinical studies in animals show that several MAbs may bind to melanoma cells in sufficient quantities in vitro to localize the required amount of Boron per cell. Whether this will occur in vivo, however, may depend not only on antigen density but a variety of other properties of the tumour cells and MAbs. These include the Ig class and affinity of the antibody and whether the antibody is internalized into the tumour cell. The ratio of uptake between tumour and normal tissue is governed by such factors as the percentage of tumour cells within a tumour expressing the antigen and whether the MAb react with normal tissues. Use of Fab or F(ab)2 preparations of the MAb may increase the uptake ratio by preventing uptake of MAb by cells with Fc receptors. In contrast to preclinical animal studies, tumour/normal tissue uptake ratios in phase I studies in humans have been disappointingly low.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological and biochemical strategies for the identification of brain tumor-associated antigens

Various strategies have been used to identify and characterize the antigens associated with human brain tumors. These approaches have included the raising of polyclonal and monoclonal antibodies against tumor antigens and, more recently, efforts toward the direct biochemical identification of such proteins. This review summarizes the progress made in this area, suggests reasons for the broad antigenic cross-reactivity and heterogeneity revealed by these studies, and proposes additional methods for deciphering the complex antigenic composition of human brain tumors.

Magnetic resonance imaging of gadolinium-labeled monoclonal antibody polymers directed at human T lymphocytes implanted in canine brain

Two different murine monoclonal anti-human T cell antibodies, that were coupled to gadolinium (Gd), bind specifically to human T lymphocyte cells implanted in canine brain. This binding was at a concentration of Gd sufficient to detect the implanted cells and to distinguish them from the surrounding brain tissue with magnetic resonance imaging (MRI) at a field strength of 1.5 Tesla. These Gd-labeled immunoglobulin preparations did not bind bovine T cells at a concentration sufficient to be detected on MRI. A protein solution containing the immunoglobulins (100 micrograms), gelatin (2 mg), and bovine serum albumin (2.5 mg) was reacted with the dianhydride of diethylenetriaminepentaacetic acid (DTPA); the DTPA serves as a metal chelator and as a protein crosslinking agent. The DTPA-protein complex was reacted with Gd chloride. There were approximately 10 DTPA residues per protein molecule in the modified protein mixture. Isolated human or bovine monocytes (approximately 12 million cells) were implanted in the brains of anesthetized dogs in a volume of 40 microliters. The blood-brain barrier was then disrupted by the intra-arterial injection of hyperosmotic mannitol, and the Gd-labeled antibodies were injected through a catheter placed at the branch of the internal and external carotid arteries. The brains were imaged 48 to 72 hours later. The MRI scans revealed a markedly decreased T1 relaxation time with a high signal intensity (TE = 25 msec, TR = 200 msec) related to the human T cell implants. There was no evidence of decreased T1 at the site of the bovine T cells. Neither control murine gamma globulin coupled to Gd-DTPA nor anti-human T cell antibodies uncoupled to Gd modified the MRI contrast of the human T cells in the brain.

Chemotherapy administered in conjunction with osmotic blood-brain barrier modification in patients with brain metastases

Clinical experience in seven patients with systemic malignancies (breast, lung and testicular) metastatic to the central nervous system treated with chemotherapy given in association with reversible osmotic blood-brain barrier modification is reviewed. A combination chemotherapy regimen including intra-arterial methotrexate, intravenous cytoxan and oral procarbazine in conjunction with intra-arterial mannitol infusions was successfully carried out with minimal toxicity. The results in these patients demonstrate some therapeutic efficacy to the increased drug delivery achieved with this technique. Although suggestive, additional studies will be required to confirm that barrier modification is a key parameter in such efficacy.