Characterization and Magnetic Resonance Imaging of a Rat Model of Human B-Cell Central Nervous System Lymphoma

Zanubrutinib delays selinexor resistance evolution in biopsy sample-derived primary central nervous system lymphoma models

Primary central nervous system lymphoma (PCNSL) is a rare and aggressive lymphoma of the brain with poor prognosis. The scarcity of cell lines established using PCNSL makes it difficult to conduct preclinical studies on new drugs. We aimed to explore the effect of selinexor combined with zanubrutinib in PCNSL using established PCNSL cells and an orthotopic PCNSL model. Primary PCNSL cells were successfully cultured. Selinexor inhibited proliferation, induced G1 phase arrest, and promoted apoptosis, however, induced drug resistance in PCNSL. Selinexor combined with zanubrutinib had a synergistic effect on PCNSL and prevented the onset of selinexor resistance in PCNSL by inhibiting AKT signaling. Moreover, selinexor combined with zanubrutinib notably slowed tumor growth and prolonged survival compared to that of the control. Overall, the addition of zanubrutinib to selinexor monotreatment had a synergistic effect in vitro and prolonged survival in vivo.

Understanding the molecular pathogenesis of primary central nervous system lymphoma by experimental animal models

Primary central nervous system lymphoma (PCNSL) is a rare and invasive diffuse large B cell lymphoma confined in central nervous system (CNS). The effort to press forward the translational progress has been frustrated by the insufficient understanding of immunophenotype of CNS and tumor genetic alterations of PCNSL, and the lack of validated diagnostic biomarkers. Researchers now have a variety of PCNSL animal models at their disposal that resemble the morphology and immunophenotype of PCNSL, however, a careful and detailed re-examination of these animal models is needed to clarify the differences in genetic alterations, migration capability, and immune status. In this review, we present the knowledge about the phenotypic and genotypic features of PCNSL tumor cells, and compile the preclinical animal models of PCNSL with regard to various injection sites, cell origins, recipient animals, and immune status, and elaborate on the tropism and migration of tumor cells and novel therapeutic strategies for PCNSL. We envisage that the selection of suitable animal models will serve as a well-defined preclinical system to understand the molecular pathogenesis of PCNSL, thereby galvanizing the development of novel and potent therapeutic approaches.

Blood-Brain Barrier Alterations and Edema Formation in Different Brain Mass Lesions

Differential diagnosis of brain lesion pathologies is complex, but it is nevertheless crucial for appropriate clinical management. Advanced imaging methods, including diffusion-weighted imaging and apparent diffusion coefficient, can help discriminate between brain mass lesions such as glioblastoma, brain metastasis, brain abscesses as well as brain lymphomas. These pathologies are characterized by blood-brain barrier alterations and have been extensively studied. However, the changes in the blood-brain barrier that are observed around brain pathologies and that contribute to the development of vasogenic brain edema are not well described. Some infiltrative brain pathologies such as glioblastoma are characterized by glioma cell infiltration in the brain tissue around the tumor mass and thus affect the nature of the vasogenic edema. Interestingly, a common feature of primary and secondary brain tumors or tumor-like brain lesions characterized by vasogenic brain edema is the formation of various molecules that lead to alterations of tight junctions and result in blood-brain barrier damage. The resulting vasogenic edema, especially blood-brain barrier disruption, can be visualized using advanced magnetic resonance imaging techniques, such as diffusion-weighted imaging and apparent diffusion coefficient. This review presents a comprehensive overview of blood-brain barrier changes contributing to the development of vasogenic brain edema around glioblastoma, brain metastases, lymphomas, and abscesses.

Benefits and limitations of nanomedicine treatment of brain cancers and age-dependent neurodegenerative disorders

The treatment of central nervous system (CNS) malignancies, including brain cancers, is limited by a number of obstructions, including the blood-brain barrier (BBB), the heterogeneity and high invasiveness of tumors, the inaccessibility of tissues for early diagnosis and effective surgery, and anti-cancer drug resistance. Therapies employing nanomedicine have been shown to facilitate drug penetration across the BBB and maintain biodistribution and accumulation of therapeutic agents at the desired target site. The application of lipid-, polymer-, or metal-based nanocarriers represents an advanced drug delivery system for a growing group of anti-cancer chemicals. The nanocarrier surface is designed to contain an active ligand (cancer cell marker or antibody)-binding structure which can be modified to target specific cancer cells. Glioblastoma, ependymoma, neuroblastoma, medulloblastoma, and primary CNS lymphomas were recently targeted by easily absorbed nanocarriers. The metal- (such as transferrin drug-loaded systems), polymer- (nanocapsules and nanospheres), or lipid- (such as sulfatide-containing nanoliposomes)-based nano-vehicles were loaded with apoptosis- and/or ferroptosis-stimulating agents and demonstrated promising anti-cancer effects. This review aims to discuss effective nanomedicine approaches designed to overcome the current limitations in the therapy of brain cancers and age-dependent neurodegenerative disorders. To accent current obstacles for successful CNS-based cancer therapy, we discuss nanomedicine perspectives and limitations of nanodrug use associated with the specificity of nervous tissue characteristics and the effects nanocarriers have on cognition.

Efficacy of Boron Neutron Capture Therapy in Primary Central Nervous System Lymphoma: In Vitro and In Vivo Evaluation

Background: Boron neutron capture therapy (BNCT) is a nuclear reaction-based tumor cell-selective particle irradiation method. High-dose methotrexate and whole-brain radiation therapy (WBRT) are the recommended treatments for primary central nervous system lymphoma (PCNSL). This tumor responds well to initial treatment but relapses even after successful treatment, and the prognosis is poor as there is no safe and effective treatment for relapse. In this study, we aimed to conduct basic research to explore the possibility of using BNCT as a treatment for PCNSL. Methods: The boron concentration in human lymphoma cells was measured. Subsequently, neutron irradiation experiments on lymphoma cells were conducted. A mouse central nervous system (CNS) lymphoma model was created to evaluate the biodistribution of boron after the administration of borono-phenylalanine as a capture agent. In the neutron irradiation study of a mouse PCNSL model, the therapeutic effect of BNCT on PCNSL was evaluated in terms of survival. Results: The boron uptake capability of human lymphoma cells was sufficiently high both in vitro and in vivo. In the neutron irradiation study, the BNCT group showed a higher cell killing effect and prolonged survival compared with the control group. Conclusions: A new therapeutic approach for PCNSL is urgently required, and BNCT may be a promising treatment for PCNSL. The results of this study, including those of neutron irradiation, suggest success in the conduct of future clinical trials to explore the possibility of BNCT as a new treatment option for PCNSL.

Emerging insights into origin and pathobiology of primary central nervous system lymphoma

Primary central nervous system lymphoma (PCNSL) is an aggressive cancer typically confined to the brain, eyes, leptomeninges and spinal cord, without evidence of systemic involvement. PCNSL remains a challenge for scientists and clinicians due to insufficient biological knowledge, a lack of appropriate animal models and validated diagnostic biomarkers. We summarize recent findings on genomic, transcriptomic and epigenetic alterations identified in PCNSL. These findings help to define pathobiology of the disease and delineate defects in B cell differentiation. Evidence from genomic and transcriptomic studies helps to separate PCNSL from other hematological malignancies, improves diagnostics and reveals new therapeutic targets for treatment. Discovery of the CNS lymphatic system may be instrumental in better understanding the origin of the disease. We critically assess the attempts to model PCNSL in rodents, and conclude that there is a lack of a genetic/transgenic model that adequately mimics pathogenesis of the disease. Contribution of the tumor microenvironment in tumorigenesis and aggressiveness of PCNSL remains understudied. Assessing heterogeneity of immune infiltrates, cytokine profiling and molecular markers, may improve diagnostics and put forward new therapeutic strategies.

[18F]Fludarabine-PET as a promising tool for differentiating CNS lymphoma and glioblastoma: Comparative analysis with [18F]FDG in human xenograft models

This paper investigated whether positron emission tomography (PET) imaging with [¹⁸F]fludarabine ([¹⁸F]FDB) can help to differentiate central nervous system lymphoma (CNSL) from glioblastoma (GBM), which is a crucial issue in the diagnosis and management of patients with these aggressive brain tumors. Multimodal analyses with [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG), magnetic resonance imaging (MRI) and histology have also been considered to address the specificity of [¹⁸F]FDB for CNSL. Methods: Nude rats were implanted with human MC116 lymphoma-cells (n = 9) or U87 glioma-cells (n = 4). Tumor growth was monitored by MRI, with T2-weighted sequence for anatomical features and T1-weighted with gadolinium (Gd) enhancement for blood brain barrier (BBB) permeability assessment. For PET investigation, [¹⁸F]FDB or [¹⁸F]FDG (~11 MBq) were injected via tail vein and dynamic PET images were acquired up to 90 min after radiotracer injection. Paired scans of the same rat with the two [¹⁸F]-labelled radiotracers were investigated. Initial volumes of interest were manually delineated on T2w images and set on co-registered PET images and tumor-to-background ratio (TBR) was calculated to semi-quantitatively assess the tracer accumulation in the tumor. A tile-based method for image analysis was developed in order to make comparative analysis between radiotracer uptake and values extracted from immunohistochemistry staining. Results: In the lymphoma model, PET time-activity curves (TACs) revealed a differential response of [¹⁸F]FDB between tumoral and healthy tissues with average TBR varying from 2.45 to 3.16 between 5 to 90 min post-injection. In contrast, [¹⁸F]FDG demonstrated similar uptake profiles for tumoral and normal regions with TBR varying from 0.84 to 1.06 between these two time points. In the glioblastoma (GBM) model, the average TBRs were from 2.14 to 1.01 for [¹⁸F]FDB and from 0.95 to 1.65 for [¹⁸F]FDG. Therefore, inter-model comparisons showed significantly divergent responses (p < 0.01) of [¹⁸F]FDB between lymphoma and GBM, while [¹⁸F]FDG demonstrated overlap (p = 0.04) between the groups. Tumor characterization with histology (based mainly on Hoechst and CD79), as well as with MRI was overall in better agreement with [¹⁸F]FDB-PET than [¹⁸F]FDG with regard to tumor selectivity. Conclusions: [¹⁸F]FDB-PET demonstrated considerably greater specificity for CNSL when compared to [¹⁸F]FDG. It also permitted a more precise definition of target volume compared to contrast-enhanced MRI. Therefore, the potential of [¹⁸F]FDB-PET to distinguish CNSL from GBM is quite evident and will be further investigated in humans.

Delivery of chemotherapeutics across the blood-brain barrier: challenges and advances

The blood-brain barrier (BBB) limits drug delivery to brain tumors. We utilize intraarterial infusion of hyperosmotic mannitol to reversibly open the BBB by shrinking endothelial cells and opening tight junctions between the cells. This approach transiently increases the delivery of chemotherapy, antibodies, and nanoparticles to brain. Our preclinical studies have optimized the BBB disruption (BBBD) technique and clinical studies have shown its safety and efficacy. The delivery of methotrexate-based chemotherapy in conjunction with BBBD provides excellent outcomes in primary central nervous system lymphoma (PCNSL) including stable or improved cognitive function in survivors a median of 12 years (range 2-26 years) after diagnosis. The addition of rituximab to chemotherapy with BBBD for PCNSL can be safely accomplished with excellent overall survival. Our translational studies of thiol agents to protect against platinum-induced toxicities led to the development of a two-compartment model in brain tumor patients. We showed that delayed high-dose sodium thiosulfate protects against carboplatin-induced hearing loss, providing the framework for large cooperative group trials of hearing chemoprotection. Neuroimaging studies have identified that ferumoxytol, an iron oxide nanoparticle blood pool agent, appears to be a superior contrast agent to accurately assess therapy-induced changes in brain tumor vasculature, in brain tumor response to therapy, and in differentiating central nervous system lesions with inflammatory components. This chapter reviews the breakthroughs, challenges, and future directions for BBBD.

Systems biology of primary CNS lymphoma: from genetic aberrations to modeling in mice

Primary lymphoma of the central nervous system (CNS, PCNSL) is a specific diffuse large B cell lymphoma entity arising in and confined to the CNS. Despite extensive research since many decades, the pathogenetic mechanisms underlying the remarkable tropism of this peculiar malignant hematopoietic tumor remain still to be elucidated. In the present review, we summarize the present knowledge on the genotypic and phenotypic characteristics of the tumor cells of PCNSL, give an overview over deregulated molecular pathways in PCNSL and present recent progress in the field of preclinical modeling of PCNSL in mice. With regard to the phenotype, PCNSL cells resemble late germinal center exit IgM+IgD+ B cells with blocked terminal B cell differentiation. They show continued BCL6 activity in line with ongoing activity of the germinal center program. This together with the pathways deregulated by genetic alterations may foster B cell activation and brisk proliferation, which correlated with the simultaneous MYC and BCL2 overexpression characteristic for PCNSL. On the genetic level, PCNSL are characterized by ongoing aberrant somatic hypermutation that, besides the IG locus, targets the PAX5, TTF, MYC, and PIM1 genes. Moreover, PCNSL cells show impaired IG class switch due to sμ region deletions, and PRDM1 mutations. Several important pathways, i.e., the B cell receptor (BCR), the toll-like receptor, and the nuclear factor-κB pathway, are activated frequently due to genetic changes affecting genes like CD79B, SHIP, CBL, BLNK, CARD11, MALT1, BCL2, and MYD88. These changes likely foster tumor cell survival. Nevertheless, many of these features are also present in subsets of systemic DLBLC and might not be the only reasons for the peculiar tropism of PCNSL. Here, preclinical animal models that closely mimic the clinical course and neuropathology of human PCNSL may provide further insight and we discuss recent advances in this field. Such models enable us to understand the pathogenetic interaction between the malignant B cells, resident cell populations of the CNS, and the associated inflammatory infiltrate. Indeed, the immunophenotype of the CNS as well as tumor cell characteristics and intracerebral interactions may create a micromilieu particularly conducive to PCNSL that may foster aggressiveness of tumor cells and accelerate the fatal course of disease. Suitable animal models may also serve as a well-defined preclinical system and may provide a useful tool for developing new specific therapeutic strategies.

Mechanisms of intracerebral lymphoma growth delineated in a syngeneic mouse model of central nervous system lymphoma

Primary lymphoma of the central nervous system (PCNSL) is defined as lymphoma of the diffuse large B-cell type confined to the CNS. To understand the effects of the CNS microenvironment on the malignant B cells and their interactions with the cells of the target organ, we analyzed a syngeneic mouse model. Transplantation of BAL17 cells into the frontal white matter of syngeneic BALB/c mice induced lymphomas with major clinical and neuropathologic features that parallel those of human PCNSL, including an angiocentric growth pattern in the brain parenchyma and tropism for the inner and outer ventricular system. Seven cycles of repeated isolation of lymphoma cells from the CNS and their intracerebral reimplantation induced genotypic and phenotypic alterations in resulting BAL17VII cells; the affected genes regulate apoptosis and are of the JAK/STAT pathway. Because lymphoma growth of BAL17VII cells was significantly accelerated, that is, shortening the time to death of the mice, these data indicate that prolonged stay of the lymphoma cells in the CNS was associated with worse outcome. These findings suggest that the CNS microenvironment fosters aggressiveness of lymphoma cells, thereby accelerating the lethal course of PCNSL.

[Management of primary central nervous system lymphoma]

Primary CNS lymphoma is the malignant brain tumor whose prognosis has improved the most the two past decades. The majority of the patients achieve a complete remission with treatment and a substantial minority may hope to be cured. The treatment includes high-dose methotrexate polychemotherapy combined or not with whole brain radiotherapy (WBRT). Elderly patients who are exposed to a high risk of treatment induced neurotoxicity need a specific management avoiding or defering WBRT. In young patients, the main questions concerning the treatment are the role of consolidation WBRT and intensive chemotherapy with peripheral blood stem cell rescue in the initial treatment of PCNSL. As recently shown, national and international collaborative efforts make now possible randomized trials for this rare disease, which would contribute to better define the treatment strategy. New insights in PCNSL tumorigenesis would help to better understand the heterogeneity of outcome and to develop efficient targeted therapies.

Imaging and therapy with rituximab anti-CD20 immunotherapy in an animal model of central nervous system lymphoma

PURPOSE

To evaluate the effect of rituximab monoclonal antibody (mAb) on MRI tumor volumetrics and efficacy in a rat model of central nervous system (CNS) lymphoma when delivery to the brain was optimized with osmotic blood-brain barrier disruption (BBBD).

EXPERIMENTAL DESIGN

Female nude rats with intracerebral MC116 human B-cell lymphoma xenografts underwent baseline MRI and were randomized into 5 groups (n = 6 per group): (i) BBBD saline control; (ii) methotrexate with BBBD; (iii) rituximab with BBBD; (iv) rituximab and methotrexate with BBBD; and (v) intravenous rituximab. Tumor volumes were assessed by MRI at 1 week, and rats were followed for survival.

RESULTS

BBBD increased delivery of yttrium-90-radiolabeled mAb in the model of CNS lymphoma. Control rats showed 201 ± 102% increase in tumor volume on MRI 1 week after entering the study and median 14-day survival (range: 6-33). Tumor growth on MRI was slowed in the methotrexate treatment group, but survival time (median: 7 days; range: 5-12) was not different from controls. Among 17 evaluable rats treated with rituximab, 10 showed decreased tumor volume on MRI. All rituximab groups had increased survival compared with control, with a combined median of 43 days (range: 20-60, P < 0.001). There were no differences by route of delivery or combination with methotrexate.

CONCLUSIONS

Rituximab was effective at decreasing tumor volume and improving survival in a model of CNS lymphoma and was not affected by combination with methotrexate or by BBBD. We suggest that rituximab warrants further study in human primary CNS lymphoma.

Epstein-Barr virus-associated primary central nervous system lymphomas in immunocompetent elderly patients: analysis for latent membrane protein-1 oncogene deletion and EBNA-2 strain typing

Epstein-Barr virus (EBV) has been implicated in the pathogenesis of primary central nervous system lymphomas (PCNLs) in immunocompetent hosts. To investigate the role of EBV in the pathogenesis of PCNLs in immunocompetent hosts, this study assessed six PCNL cases (elderly male immunocompetent patients; age ≥60 years) histologically and immunohistochemically, and an EBV genetic study was performed. Histologically, all cases were diagnosed as diffuse large B-cell lymphoma with extensive necrosis. In all six cases, PCNL cells showed immunohistochemical positivity for latent membrane protein 1 (LMP-1) and Epstein-Barr nuclear 2 (EBNA2). Lymphoma cells also showed positive signals for EBV-encoded small RNAs (EBERs) on in-situ hybridization. EBV subtyping-PCR analysis demonstrated that one case was EBNA 2B type and the other five cases were EBNA 2A type, and two cases were EBV wild-type and four cases showed 30-bp LMP-1 deletion by PCR analysis. It is therefore possible that LMP gene deletion or EBNA-2 strain type are important in the tumorigenesis of EBV-positive PCNLs. In addition, EBV-positive PCNLs in immunocompetent hosts may be related to immunological deterioration derived from the aging process.

Primary central nervous system lymphoma: an update

PURPOSE OF REVIEW

The purpose of the present review is to present an overview of the recent findings in diagnostic procedures, treatment outcomes and biological advances in primary central nervous system lymphoma (PCNSL).

RECENT FINDINGS

Recent imaging techniques are helpful in the diagnosis of atypical presentations of PCNSL and are likely to represent useful tools for patient follow-up. Knowledge of the biology of PCNSL is still fragmentary, but an increasing amount of data support the biological specificity of this disease with the identification of specific molecular alterations in PCNSL and specific interactions of lymphoma cells with the CNS microenvironment. The origin of the malignant cell is still unknown. Improvement of the therapeutic results along with numerous phase II studies clearly highlight a few important issues that need to be unequivocally answered and stress the need for the development of multicentric comparative studies. Attempts to decrease treatment-related toxicity on the CNS without impacting the disease control are ongoing.

SUMMARY

The standard of care for PCNSL has definitively switched toward a curative objective. Considerable cooperative efforts are being made and will hopefully result in both a better understanding of the disease and significant therapeutic outcomes.

Cyclophosphamide enhances human tumor growth in nude rat xenografted tumor models

The effect of the immunomodulatory chemotherapeutic agent cyclophosphamide (CTX) on tumor growth was investigated in primary and metastatic intracerebral and subcutaneous rat xenograft models. Nude rats were treated with CTX (100 mg/kg, intraperitoneally) 24 hours before human ovarian carcinoma (SKOV3), small cell lung carcinoma (LX-1 SCLC), and glioma (UW28, U87MG, and U251) tumor cells were inoculated subcutaneously, intraperitoneally, or in the right cerebral hemisphere or were infused into the right internal carotid artery. Tumor development was monitored and recorded. Potential mechanisms were further investigated. Only animals that received both CTX and Matrigel showed consistent growth of subcutaneous tumors. Cyclophosphamide pretreatment increased the percentage (83.3% vs 0%) of animals showing intraperitoneal tumors. In intracerebral implantation tumor models, CTX pretreatment increased the tumor volume and the percentage of animals showing tumors. Cyclophosphamide increased lung carcinoma bone and facial metastases after intra-arterial injection, and 20% of animals showed brain metastases. Cyclophosphamide transiently decreased nude rat white blood cell counts and glutathione concentration, whereas serum vascular endothelial growth factor was significantly elevated. Cyclophosphamide also increased CD31 reactivity, a marker of vascular endothelium, and macrophage (CD68-positive) infiltration into glioma cell-inoculated rat brains. Cyclophosphamide may enhance primary and metastatic tumor growth through multiple mechanisms, including immune modulation, decreased response to oxidative stress, increased tumor vascularization, and increased macrophage infiltration. These findings may be clinically relevant because chemotherapy may predispose human cancer subjects to tumor growth in the brain or other tissues.

Efficacy and MRI of rituximab and methotrexate treatment in a nude rat model of CNS lymphoma

To determine the efficacy of methotrexate and/or rituximab in a CNS lymphoma model and to evaluate MRI modalities for monitoring efficacy, we inoculated female athymic nude rats (rnu/rnu) intracerebrally with human MC116 B-lymphoma cells. Between days 16 and 26, rats were randomized to receive intravenous (IV) treatment with (1) saline (controls, n = 15), (2) methotrexate 1,000 mg/m(2) (n = 6), (3) rituximab 375 mg/m(2) (n = 6), or (4) rituximab plus methotrexate (n = 6). T2/fluid-attenuated inversion recovery (FLAIR) and gadolinium contrast-enhanced T1 MRI sequences were performed prior to and 1 week after treatment. IV rituximab gave an objective tumor response in four of six animals (>50% reduction in tumor volume comparing pre- and posttreatment T2/FLAIR MRI) and resulted in stable disease (50%-125% of baseline) in another animal. The percent change in tumor volume on T2/FLAIR images was significantly different in the control versus rituximab group (p = 0.0051). IV methotrexate slowed tumor growth, compared to controls, but only one of six animals had an objective response. In untreated controls, tumor histological volumes correlated well with T2/FLAIR or contrast-enhanced T1 images (r = 0.877). In the treatment groups, T2/FLAIR correlation was good, but the gadolinium-enhanced T1 MRI was not significantly correlated with histology (r = 0.19). The MC116 CNS lymphoma model seems valuable for preclinical testing of efficacy and toxicity of treatment regimens. IV rituximab was highly effective, but methotrexate was only minimally effective. T2/FLAIR was superior to contrast-enhanced T1 for monitoring efficacy.

Strategies to advance translational research into brain barriers

There is a paucity of therapies for most neurological disorders--from rare lysosomal storage diseases to major public health concerns such as stroke and Alzheimer's disease. Advances in the targeting of drugs to the CNS are essential for the future success of neurotherapeutics; however, the delivery of many potentially therapeutic and diagnostic compounds to specific areas of the brain is restricted by the blood-brain barrier, the blood-CSF barrier, or other specialised CNS barriers. These brain barriers are now recognised as a major obstacle to the treatment of most brain disorders. The challenge to deliver therapies to the CNS is formidable, and the solution will require concerted international efforts among academia, government, and industry. At a recent meeting of expert panels, essential and high-priority recommendations to propel brain barrier research forward in six topical areas were developed and these recommendations are presented here.