Targeted toxin therapy for malignant astrocytoma

Tumor immunology, immunomics and targeted immunotherapy for central nervous system malignancies

Although the brain was traditionally considered as 'immunologically privileged', recent findings have implied an involvement of immune mechanisms in neurological disease and illness, including central nervous system (CNS) malignancies. In this review, we initially focus on aspects of the immune system critical for effective antitumor immunity, as an understanding of normal immunological functions and how they relate to tumor immunology will set a foundation for understanding the unique challenges facing the integration of neuro-oncology and neuroimmunology. We summarize current knowledge of immune responses in the 'immunologically quiescent' brain and its role in tumor immunology. We will then discuss the emerging field of 'immunomics' and recent advances in molecular technologies, such as DNA microarray, which are being applied to brain tumor antigen epitope discovery and patient stratification for brain cancer immunotherapy. This, in turn, should have significant importance for ultimately designing and developing efficient and focused strategies for anticancer immunotherapy. Finally, the current state of immune-based treatment paradigms and future directions will be discussed, paying particular attention to targeted antibody strategies, adoptive cellular immunotherapy, and tumor vaccine approaches that have been studied in clinical trials for CNS neoplasms.

Cerebral radiation necrosis: a review of the pathobiology, diagnosis and management considerations

Radiation therapy forms one of the building blocks of the multi-disciplinary management of patients with brain tumors. Improved survival following radiation therapy may come with a cost, including the potential complication of radiation necrosis. Radiation necrosis impacts the quality of life in cancer survivors, and it is essential to detect and effectively treat this entity as early as possible. Significant progress in neuro-radiology and molecular pathology facilitate more straightforward diagnosis and characterization of cerebral radiation necrosis. Several therapeutic interventions, both medical and surgical, may halt the progression of radiation necrosis and diminish or abrogate its clinical manifestations, but there are still no definitive guidelines to follow explicitly that guide treatment of radiation necrosis. We discuss the pathobiology, clinical features, diagnosis, available treatment modalities, and outcomes in the management of patients with intracranial radiation necrosis that follows radiation used to treat brain tumors.

Therapeutic window, a critical developmental stage for stem cell therapies

In children, cancers are the deadliest of diseases and second only to accidents as the leading cause of death. The deadliest of the brain cancers are the malignant gliomas. Approximately two-thirds of children can survive less malignant types of brain cancers, however, in ~67% of these survivors recurs under the current regimes of surgery followed by administration of high doses toxic drugs and exposure to high doses of radiation. Even more distressing is that fortunate survivors are generally left with life-long cognitive disabilities. A new medical approach is desperately needed. Stem cells, with their natural ability to seek out brain tumors, could be used to accurately deliver therapy directly to the cancer sparing normal tissues for suppression of tumor growth. Despite exciting initial reports, clinical potency of stem cell therapy in animal brain tumor models has to date proven disappointing. Attempts to extrapolate the animal study results to humans are stymied by the fact that stem cells are heterogeneous, resulting in differences in their efficacy. Indeed, therapeutic success relies on an effective strategy to select for a stem cell sub-population within some particular stage of the development at which they are competitive and capable of targeting brain tumors. To improve this during developmental path, concept of a 'therapeutic window' is proposed. The "therapeutic window" for stem cells or more specifically a "biochemical therapeutic window" can be determined from biochemical assays and a "biological therapeutic window" from biological assays or even a molecular window for genetic description. Taken together, we can use selective processes to generate more effective stem cells to treat cancers as is clearly needed today.

Use of ribosome-inactivating proteins from Sambucus for the construction of immunotoxins and conjugates for cancer therapy

The type 2 ribosome-inactivating proteins (RIPs) isolated from some species belonging to the Sambucus genus, have the characteristic that although being even more active than ricin inhibiting protein synthesis in cell-free extracts, they lack the high toxicity of ricin and related type 2 RIPs to intact cells and animals. This is due to the fact that after internalization, they follow a different intracellular pathway that does not allow them to reach the cytosolic ribosomes. The lack of toxicity of type 2 RIPs from Sambucus make them good candidates as toxic moieties in the construction of immunotoxins and conjugates directed against specific targets. Up to now they have been conjugated with either transferrin or anti-CD105 to target either transferrin receptor- or endoglin-overexpressing cells, respectively.

Gliomas in adults

BACKGROUND

Primary brain tumors are among the ten most common causes of cancer-related death. There is no screening test for them, but timely diagnosis and treatment improve the outcome. Ideally, treatment should be provided in a highly specialized center, but patients reach such centers only on the referral of their primary care physicians or other medical specialists from a wide variety of fields. An up-to-date account of basic knowledge in this area would thus seem desirable, as recent years have seen major developments both in the scientific understanding of these tumors and in clinical methods of diagnosis and treatment.

METHODS

Selective search of the pertinent literature (PubMed and Cochrane Library), including the guidelines of the German Societies of Neurosurgery, Neurology, and Radiotherapy.

RESULTS AND CONCLUSION

Modern neuroradiological imaging, in particular magnetic resonance imaging, can show structural lesions at high resolution and provide a variety of biological and functional information, yet it is still no substitute for histological diagnosis. Gross total resection of gliomas significantly improves overall survival. New molecular markers can be used for prognostication. Chemotherapy plays a major role in the treatment of various different kinds of glioma. The median survival, however, generally remains poor, e.g., 14.6 months for glio-blastoma.

Chemotherapy delivery issues in central nervous system malignancy: a reality check

PURPOSE

This review assesses the current state of knowledge regarding preclinical and clinical pharmacology for brain tumor chemotherapy and evaluates relevant brain tumor pharmacology studies before October 2006.

RESULTS

Chemotherapeutic regimens in brain tumor therapy have often emerged from empirical clinical studies with retrospective pharmacologic explanations, rather than prospective trials of rational chemotherapeutic approaches. Brain tumors are largely composed of CNS metastases of systemic cancers. Primary brain tumors, such as glioblastoma multiforme or primary CNS lymphomas, are less common. Few of these tumors have well-defined optimal treatment. Brain tumors are protected from systemic chemotherapy by the blood-brain barrier (BBB) and by intrinsic properties of the tumors. Pharmacologic studies of delivery of conventional chemotherapeutics and novel therapeutics showing actual tumor concentrations and biologic effect are lacking.

CONCLUSION

In this article, we review drug delivery across the BBB, as well as blood-tumor and -cerebrospinal fluid (CSF) barriers, and mechanisms to increase drug delivery to CNS and CSF tumors. Because of the difficulty in treating CNS tumors, innovative treatments and alternative delivery techniques involving brain/cord capillaries, choroid plexus, and CSF are needed.

Immunotherapy for patients with malignant glioma: from theoretical principles to clinical applications

Malignant gliomas are the most common type of primary brain tumor and are in great need of novel therapeutic approaches. Advances in treatment have been very modest, significant improvement in survival has been lacking for many decades and prognosis remains dismal. Despite 'gross total' surgical resections and currently available radio-chemotherapy, malignant gliomas inevitably recur due to reservoirs of notoriously invasive tumor cells that infiltrate adjacent and nonadjacent areas of normal brain parenchyma. In principle, the immune system is uniquely qualified to recognize and target these infiltrative pockets of tumor cells, which have generally eluded conventional treatment approaches. In the span of the last 10 years, our understanding of the cancer-immune system relationship has increased exponentially, and yet, we are only beginning to tease apart the intricacies of the CNS and immune cell interactions. This article reviews the complex associations of the immune system with brain tumors. We provide an overview of currently available treatment options for malignant gliomas, existing gaps in our knowledge of brain tumor immunology, and molecular techniques and targets that might be exploited for improved patient stratification and design of 'custom immunotherapeutics'. We will also examine major new immunotherapy approaches that are being actively investigated to treat patients with malignant glioma, and identify some current and future research priorities in this area.

Intracellular chemiluminescence activates targeted photodynamic destruction of leukaemic cells

Photodynamic therapy (PDT) involves a two-stage process. A light-absorbing photosensitiser (Ps) is endocytosed and then stimulated by light, inducing transfer of energy to a cytoplasmic acceptor molecule and the generation of reactive oxygen species that initiate damage to cellular membrane components and cytolysis. The expanded use of PDT in the clinic is hindered by the lack of Ps target-cell specificity and the limited tissue penetration by external light radiation. This study demonstrates that bioconjugates composed of transferrin and haematoporphyrin (Tf–Hp), significantly improve the specificity and efficiency of PDT for erythroleukemic cells by a factor of almost seven-fold. Fluorescence microscopy showed that the conjugates accumulate in intracellular vesicles whereas free Hp was mostly membrane bound. Experiments with cells deliberately exposed to Tf–Hp at <LD₁₀₀ doses showed that surviving cells did not develop resistance to subsequent treatments with the conjugate. Furthermore, we show that the compound luminol induces intracellular chemiluminescence. This strategy was then used to obviate the use of external radiation for Ps activation by incubating the cells with luminol either before or together with Tf–Hp. This novel chemical means of PDT activation induced cytotoxicity in 95% of cells. These combined approaches provide an opportunity to develop broader and more effective applications of PDT.

Efficacy of antiangiogenic targeted toxins against glioblastoma multiforme

OBJECT

Because the prognosis for patients with glioblastoma multiforme (GBM) remains poor, investigators have focused on developing new and more effective treatment modalities. Targeted toxins represent a new class of compounds composed of a potent protein toxin and a carrier ligand that will recognize cell surface antigens located on target tissue. A recombinant fusion protein was created that contains the translocation and catalytic portions of diphtheria toxin that are responsible for cell entry and killing, respectively, fused to the noninternalizing aminoterminal fragment portion of human plasminogen activator. This diptheria toxin-uPA fusion protein (DTAT) has the advantage over other fusion proteins of targeting malignant glioma cells and the endothelial cells of the neovasculature that express the urokinase-type plasminogen activator receptor (uPAR). Another protein, DTAT13, was synthesized to target uPAR on the neovasculature and the uPAR and interleukin-13 receptor-expressing GBM cells. The authors describe the in vitro and in vivo efficacy of DTAT and DTAT13 against GBM.

METHODS

The in vitro cytotoxicity of DTAT and DTAT13 was measured using cell proliferation assays. In vivo studies were performed in which DTAT, DTAT13, or a control protein was injected directly into GBM flank tumors in athymic nude mice. Tumor volume was assessed over time and analyzed using the Student t-test. The systemic organ effects of DTAT and DTAT13 were examined functionally and histologically in tumor-free C57BL/6 mice. In vitro, DTAT and DTAT13 were found to be highly potent and selective against U118MG, U87MG, and U373MG GBM cell lines and human umbilical vein endothelial cells. In vivo, DTAT and DTAT13 both caused a statistically significant (p < 0.05) regression of U87MG GBM flank tumors when administered every other day at 10 mg/day for five doses. No tumor regression was seen in control animals. Both DTAT and DTAT13 had little effect on histological findings in the liver, kidney, spleen, and lungs. Serum analysis did not demonstrate an effect on blood urea nitrogen levels, but liver alanine aminotransferase levels rose to statistically significant (p = 0.046) but not life-threatening levels. Also, DTAT13 was less toxic than DTAT in studies of mortality rates.

CONCLUSIONS

Both DTAT and DTAT13 might have potential for clinical application against GBM because of their ability to target both the tumor cells and neovasculature simultaneously with an absence of serious systemic side effects. The discovery that DTAT13 was less toxic than DTAT indicated that the bispecific fusion protein might target a broader subset of antigenetically diverse patients with tumors while reducing the systemic exposure to toxin that would be necessary if two agents were administered separately.

CEACAM6 as a novel target for indirect type 1 immunotoxin-based therapy in pancreatic adenocarcinoma

Immunotoxins are a potentially powerful approach for targeted anticancer therapy. We evaluated a novel immunotherapeutic strategy targeting the immunoglobulin superfamily member carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6). Using pancreatic adenocarcinoma as a model, we show that crosslinking CEACAM6 induces its cytoplasmic accumulation and that this effect can be utilized to increase the efficacy of antibody-mediated delivery of the ribosomal inhibitory protein saporin. Exposure of cells to anti-CEACAM6 antibody, followed by secondary saporin-conjugated immunoglobulin (IgG), induced marked cytotoxicity, via caspase-mediated apoptosis, in vitro. In an in vivo nude mouse xenograft model, this immunotherapeutic approach markedly suppressed pancreatic adenocarcinoma tumor growth and enhanced tumor apoptosis. Given the prevalence of CEACAM6 overexpression among human malignancies, immunological targeting of this tumor antigen may have therapeutic applicability.

Immunotoxin treatment targeted to the high-molecular-weight melanoma-associated antigen prolonging the survival of immunodeficient rats with invasive intracranial human glioblastoma multiforme

OBJECT

The aim of this study was to target immunotoxin treatment to the high-molecular-weight melanoma-associated antigen (HMW-MAA) and thereby examine any changes in the survival of immunodeficient rats with human glioblastoma multiforme (GBM).

METHODS

To target treatment specifically to human glioma cells, Pseudomonas exotoxin A (PE) was conjugated to the 9.2.27 antibody, which recognizes the HMW-MAA. Treatment of the antigen-positive glioma cell line U87MG with the resulting 9.2.27-PE caused cytotoxicity with a median inhibitory concentration of 1 ng/ml. Intratumoral 9.2.27-PE treatment of intracranial U87MG tumors in nude rats prolonged the survival of these animals by 43% compared with controls. In additional studies on the use of this targeted treatment, the authors precultured freshly dissected glioblastoma multiforme (GBM) biopsy tissue for 1 to 2 weeks. Inoculation of this tissue into the rat brain resulted in diffuse infiltrative gliomas. The markers glial fibrillary acidic protein and S100 protein were found to be expressed in the original biopsy specimens, as well as in the glioma xenografts in nude rat brains. Intratumoral immunotoxin treatment of such established tumors with 9.2.27-PE was effective and prolonged survival time from 30% to as high as 90% in animals with tumors originating from four different GBM specimens.

CONCLUSIONS

Targeted treatment of highly invasive GBMs proved effective, and these results emphasize the clinical relevance of this antigen as a target molecule for immunotoxin treatment of human GBMs.

Immunology and immunotherapy in neurosurgical disease

OBJECTIVE

For many years, the central nervous system (CNS) has been described as "immunologically privileged" and devoid of conventional immune reactivity. However, our more current understanding of neuroimmunology supports a different view. Although immune mechanisms within the CNS may behave differently from those located at peripheral anatomic sites, it is now widely accepted that biologically relevant immune responses can and do occur within the brain and that these responses can play important roles in CNS disease. The objective of this present review is to explore key aspects of recent insights into the cellular interactions involved in neuroimmunology, which may suggest more rational approaches to the immunotherapy of neurosurgical disorders.

CONCLUSION

Modern advances in molecular medicine and basic immunology have yielded a plethora of new data about CNS immunobiology. The design of effective immunotherapeutic strategies for CNS diseases requires a contemporary understanding of the basic tenets of how the immune system works. The current renaissance in this field may give neurosurgeons hope that, in the future, immunotherapy-based paradigms may be able to successfully treat neurosurgical diseases that are currently refractory to traditional therapies.

Convection-enhanced delivery in clinical trials

The poor prognosis associated with the current management of malignant gliomas has led investigators to develop alternative treatments such as targeted toxin therapy. The optimal method for administering these agents is under development but appears to be convection-enhanced delivery (CED).

The direct intratumoral infusion of targeted toxins was first performed in nude mouse flank tumor models of human malignant glioma. After the demonstration of in vivo efficacy, these potent cytotoxic compounds were tested in Phase I and Phase II clinical trials.

Using a high-flow microinfusion technique, volumes of up to 180 ml were infused by CED through catheters placed directly into brain tumors. Minor systemic toxicity was seen in the form of hepatic enzyme elevation. Neural toxicity manifested as seizure activity and hemiparesis resulted from peritumoral edema that followed the completion of the infusion. Peritumoral toxicity was believed to be more related to the concentration of the infused immunotoxin than to the infusion volume. In approximately half of patients treated with CED a stable disease course, a partial response, or a complete response was demonstrated in some clinical trials.

Targeted toxin therapy has clinical efficacy in patients with malignant gliomas. Convection-enhanced delivery appears to represent an effective method for administering these agents in patients with malignant brain tumors.

Leptomeningeal metastases

LM is an increasingly common neurologic complication of cancer with variable clinical manifestations. Although there are no curative treatments, currently available therapies can preserve neurologic function and potentially improve quality of life. Further research into the mechanisms of leptomeningeal metastasis will elucidate molecular and cellular pathways that may allow identification of potential targets to interrupt this process early or to prevent this complication. Animal models are needed to further define the pathophysiology of LM and to provide an experimental system to test novel treatments [242-245]. There is an urgent need to develop new drug-based or radiation-based treatments for patients with LM. Randomized clinical trials are the appropriate study design to determine the efficacy of new treatments for LM. However, surrogate markers for response must be developed to facilitate the identification of effective regimens. Survival is not the optimal end point for such studies as most patients who develop this complication already have advanced, incurable cancer. Prevention of or delay in neurologic progression is one objective that has been utilized in recent randomized trials in patients with LM, and this end point deserves further attention. Although the development of LM represents a poor prognostic marker in patients with cancer it is important for physicians to recognize the symptoms and signs of the disease and establish the diagnosis as early in the disease course as possible. This may provide an opportunity for effective intervention that can improve quality of life, prevent further neurologic deterioration and, for a subset of patients, improve survival.

Targeting cancer cells with transferrin conjugates containing the non-toxic type 2 ribosome-inactivating proteins nigrin b or ebulin l

Nigrin b and ebulin l are type 2 ribosome-inactivating proteins (RIPs) with 10(4) times less cellular and in vivo toxicity than ricin that are currently being considered for the construction of anti-cancer conjugates. Here we provide evidence that both RIPs can be used for the construction of conjugates directed to a target such as the transferrin receptor (TfR), which is over-expressed in cancer cells. Nigrin b- and ebulin l-transferrin conjugates were constructed with no substantial reduction in the translational inhibitory molecular activity of either RIPs. Conjugation with transferrin decreased the IC(50) of the proteins from 3 x 10(-7)M (nigrin b) and 1.5 x 10(-8)M (ebulin l) to 3.5 x 10(-10)M in HeLa cells. Thus, both conjugates could be considered as useful tools for targeting TfR-over-expressing cancer cells.

Activity of anti-epidermal growth factor receptor monoclonal antibody C225 against glioblastoma multiforme

OBJECTIVE

Overexpression of epidermal growth factor receptor (EGFR) in glioblastoma multiforme (GBM) secondary to EGFR gene amplification is associated with a more aggressive tumor phenotype and a worse clinical outcome. The purpose of this study was to analyze whether blocking this receptor with the anti-EGFR chimeric monoclonal antibody C225 would decrease proliferation and increase apoptosis in GBM cells.

METHODS

EGFR expression and amplification were analyzed for seven human GBM cell lines. These lines were then exposed to different concentrations of C225 for 48 hours, 72 hours, and 7 days, after which time cytotoxicity, apoptosis, and vascular endothelial growth factor expression were assessed in vitro. Two EGFR-amplified human GBM were implanted in the flanks of nude mice, and the animals received C225 twice per week intraperitoneally for 5 weeks. Tumor volumes and survival times were compared with those of sham-treated mice.

RESULTS

EGFR gene amplification was demonstrated in three of the primary GBM lines. C225 treatment produced significant cytotoxicity in all three EGFR-amplified GBM lines, but not in unamplified lines. Flow cytometry demonstrated increased apoptosis in C225-treated, EGFR-amplified GBM lines, but not in unamplified lines. There was a decrease in vascular endothelial growth factor expression in all GBM lines with exposure to C225. Tumor-bearing mice treated with C225 experienced significant inhibition of tumor growth as well as a 200% increase in median survival.

CONCLUSION

Blocking EGFR in GBM cells that overexpress this receptor significantly changes tumor cell biology by promoting apoptosis while decreasing proliferation and vascular endothelial growth factor expression. This approach holds great promise for the treatment of patients with GBMs.

New systems for delivery of drugs to the brain in neurological disease

The restricted or regulated entry of most blood-borne substances into the brain has been recognised for more than a century. The blood-brain barrier (BBB)-shielding function provided by endothelial cells is important in the treatment of neurological diseases because this exclusion of foreign substances also restricts entry of many potentially therapeutic agents into the brain. The recent identification of several neuroactive proteins of potential therapeutic value has highlighted the crucial need for effective and safe transcapillary delivery methods to the brain. One promising method is delivery through brain capillaries by augmentation of pinocytotic vesicles delivery systems that use this cellular mechanism are in development. Recent investigations in animal models show that large molecules of neurotherapeutic potential can be conjugated to peptidomimetic ligands, which bind to selected peptide receptors, and are then internalised and transported in small vesicles across the cytoplasmic brain capillary barrier. These conjugates have been shown to remain functionally active and effective in animal models of neurological disease.

Non-cytotoxic therapies for malignant gliomas

Malignant gliomas cause 2% of cancer deaths in western countries, and even the most intensive combinations of radiotherapy and chemotherapy cannot be curative. New chemotherapeutic drugs and alternative therapeutic modalities are strongly needed. Huge efforts are directed towards the development of innovative strategies for targeting and mending the specific molecular alterations in tumor cells (translational research). This review aims to summarize the most promising lines of investigational research in the field of neuro-oncology, such as non-cytotoxic drugs, immunotoxins, inhibitors of angiogenesis and gene therapy approaches, which will probably offer new therapy options for brain tumor patients.

Changing boundaries in the treatment of malignant gliomas

Malignant gliomas are still among the most lethal and difficult tumors to treat; even the most intensive combinations of radio- and chemotherapy are not curative and yield only a modest impact on survival for most of these patients, as long-term survivors are less than 10%. There is a major need for new chemotherapeutic drugs and alternative therapeutic modalities. This review aims to define the best standard treatment in the common clinical practice and also summarizes the most promising lines of investigational research in the field of neuro-oncology, which will probably offer new and long-awaited valid therapy options for brain tumor patients.

Sensitization of human malignant glioma cell lines to tumor necrosis factor-induced apoptosis by cisplatin

Most tumors, including gliomas, are resistant to tumor necrosis factor (TNF) cytotoxicity unless protein or RNA synthesis is inhibited. We investigated the effects of the combined use of TNF-alpha and cisplatin (CDDP) on cultured malignant glioma cells, T98G, U373MG, A172, and U87MG. All glioma cell lines were sensitive to treatment with CDDP but resistant to TNF-alpha during 24 h-incubation. The combined use of CDDP and TNF-alpha had synergistic effects on T98G and U87MG but not on U373MG and A172 cells. Sequential treatments showed that only pretreatment with CDDP for 2 h followed by TNF-alpha for 22 h was synergistic on cell cytotoxicity. Annexin V-flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling assay showed that TNF-alpha can induce apoptosis in cells treated with CDDP. Although only sensitive cell lines express transcripts for p75 TNF receptor 2, changes in TNF receptors were not found to contribute to the susceptibility to TNF-alpha. The production of interleukin-6, a representative cytoprotective cytokine, from glioma cells stimulated by TNF-alpha was suppressed by the combined use of actinomycin D, but not CDDP. Our results indicate that CDDP can sensitize glioma cells to TNF-alpha-induced apoptosis by a mechanism other than blocking the cytoprotective protein production.