Molecular advances to treat cancer of the brain.

Malignant primary and metastatic brain tumours continue to be associated with poor prognosis. Nevertheless, recent advances in molecular medicine, specifically in the strategies of gene therapy, targeting tumour cells, anti-angiogenesis and immunotherapy, have created novel tools that may be of therapeutic value. To date, gene therapy trials have not yet demonstrated clinical efficacy because of inherent defects in vector design. Despite this, advances in adenoviral technology, namely the helper-dependent adenoviral constructs (gutless) and the uncovering of brain parenchymal cells as effective and necessary targets for antitumour benefits of adenoviral-mediated gene transfer, suggest that developments in vector design may be approaching the point of clinical utility. Targeting tumour cells refers to strategies that destroy malignant but spare normal cells. A new assortment of oncolytic viruses have emerged, capable of specific lysis of cancer tissue while sparing normal cells and propagating until they reach the tumour borders. Furthermore, peptides have been transformed into bullets that specifically seek and destroy cancer cells. The concept of tumour angiogenesis has been challenged by new but still very controversial findings that tumour cells themselves may form blood channels. These results may lead to the redirecting of the molecular targets toward anti-angiogenesis in some tumours including glioblastoma multiform. Unfortunately, our knowledge regarding the immunological ignorance of the tumour is still limited. Even so, newly discovered molecules have shed light on novel pathways leading to the escape of the tumour from the immune system. Finally, significant limitations in our current experimental tumour models may soon be overcome by firstly, the development of models of reproducible organ-specific tumours in non-inbred animals and secondly applying genomics to individualize therapy for a particular tumour in a specific patient.

Gene transfer into brain parenchyma elicits antitumor effects.

Gene therapy strategies for cancer currently aim at targeting gene delivery to the malignant cell. In a mouse model of intracerebral Lewis lung carcinoma (3LL), adenoviral vectors transduce not only 3LL cells but also brain parenchymal cells including endothelial cells, neurons, microglia, and astrocytes in vivo. Furthermore, transgene expression persists longer in brain than in tumor. Transfer of IFN-gamma into brain parenchymal cells rather than tumor is both necessary and sufficient to generate antitumor therapeutic benefits. Therefore, parenchymal cells represent an effective and necessary target for delivery of genes that render the brain uninhabitable by the tumor.

Demyelination but no cognitive, motor or behavioral deficits after adenovirus-mediated gene transfer into the brain.

Adenovirus-mediated gene transfer of interferon gamma (AdIFN) elicits rejection of intracerebral Lewis lung carcinoma. In this system, gene transfer into brain parenchymal cells is both necessary and sufficient to generate the antitumor response. Despite persistent parenchymal inflammation and demyelination, wild-type mice injected intracerebrally with either AdIFN or beta-galactosidase adenovirus (AdBGAL) perform as well as non-injected animals in behavioral, memory, and motor tests. Both AdIFN and AdBGAL elicit demyelination whose incidence rises sharply when the lowest effective dose of AdIFN is exceeded. Therefore, transfer of interferon gamma into brain parenchyma does not seem to elicit detectable cognitive, behavioral or motor deficits. Furthermore, gene transfer into the brain, by adenoviral vectors currently in clinical trials, is associated with a narrow therapeutic window where the incidence of demyelination rises sharply soon after the effective dose is achieved. Gene Therapy (2000) 7, 2094-2098.

Gene transfer of IFN-gamma into established brain tumors represses growth by antiangiogenesis.

The experiments in this paper were designed to examine the therapeutic effects of adenoviral-mediated gene transfer of IFN-gamma into a mouse model of an established metastatic brain tumor. Temperature-sensitive replication-defective adenovirus was generated for gene transfer of IFN-gamma (AdIFN) and beta-galactosidase (AdBGAL) cDNAs in vivo. In this model, treatment with AdIFN elicits prolonged survival times and brain tumor rejection. Evidence against an immune-mediated response accounting for this result include: 1) absence of a memory immune response upon challenge, 2) lack of antitumor effects at sites distal to inoculation of AdIFN, and 3) preservation of the therapeutic effects of AdIFN in scid and beige mice and in inducible NO synthase (iNOS) knockouts. High concentrations of IFN-gamma do not inhibit tumor growth in vitro making it unlikely that the antitumor effect of this treatment acts directly on the growth of the tumor cells. However, gene transfer of IFN-gamma inhibits neovascularization of the tumor in a 3LL-Matrigel assay in vivo, and AdIFN induces apoptosis of endothelial cells in vivo, supporting the idea that AdIFN represses tumor growth by inhibiting angiogenesis. The substantial non-immune-mediated therapeutic benefits of AdIFN in animals paves the way for devising novel strategies for treating human brain tumors.

Priming in the brain, an immunologically privileged organ, elicits anti-tumor immunity.

A crucial question in the study of tumor neuro-immunology concerns the capacity of the central nervous system to initiate and execute an immune response. In a 100% fatal rat malignant glioma model, genetically modified tumors secreting INF-gamma intracerebrally generate an immune response resulting in a substantial increase in survival time, tumor rejection and specific systemic immunity. Tumors modified to secrete IL-2 alone do not change the biologic behavior of transfected gliomas. INF-gamma induces elevated expression of major-histocompatibility-complex-class-I and -class-II molecules in microglia throughout the brain and invokes enhanced tumor infiltration by CD4, CD8 and NK cells. These findings demonstrate successful immunization against a central-nervous-system tumor by direct priming in the brain with a live growth-competent tumor vaccine.

Response of primary leptomeningeal melanoma to intrathecal recombinant interleukin-2. A case report.

BACKGROUND: Primary leptomeningeal melanomas are rare tumors that originate in the leptomeninges and are associated with a poor prognosis and no response to radiation and chemotherapy. These tumors rarely metastasize outside the central nervous system. Recombinant interleukin-2-(rIL-2) is a cytokine that activates natural killer cells and lymphokine-activated killer cells, augments their antitumor effects, and recruits and activates cytotoxic T lymphocytes. We have hypothesized that rIL-2 may prolong disease free survival in a patient with primary leptomeningeal melanoma. METHODS: The patient was treated with intrathecal rIL-2 via lumbar puncture daily for 5 days, the weekly for 5 weeks. To investigate whether rIL-2 induced a favorable clinical response, the following parameters were monitored: survival, neurologic status, cerebrospinal fluid (CSF) analysis, visual fields, and magnetic resonance imaging (MRI) of the lumbosacral spine. RESULTS: The patient is still alive and disease free 15 months after receiving rIL-2, and his neurologic status remains unchanged. The CFS glucose concentration, undetectable prior to therapy, has become normal. Repeated cytologic examinations of CSF were negative for malignant cells. The visual field examinations have remained unchanged. MRI scans of the lumbosacral spine have shown the development of arachnoiditis, but no recurrence of the mass lesion. CONCLUSIONS: The tumor response in this patient, as measured by remarkable disease free survival and normalization of the CSF glucose concentration, illustrates the potential benefits of intrathecal rIL-2 in the treatment of patients with this otherwise rapidly fatal disease.