Chapter 24 / Biological Modifiers 405 24 Biological Modifiers Alexander Mason, Steven Toms, and Aleck Hercbergs Summary Conventional multimodailty therapies have not altered the dismal prognosis of glioblastoma which has prompted alternative investigational approaches utilising biological modifiers of response.We review here interferon alpha (IFN-D) and beta (IFN-E), interleukin-2 (IL-2), tumor necrosis factor-D TNF, interleukin 4 (IL-4) , monoclonal antibodies to EGFR, EGFRvIII and radio- labeled anti-tenascin monoclonal antibody. A current novel approach is exploitation of some of the biological consequences of thyroid hormone deprivation on tumor biology. In a preliminary Phase I/II trial significant improvement in survival and tumor regression rates in recurrent high grade glioma patients were observed following propylthiouracil induced mild (chemical) hypothyroidism combined with high dose tamoxifen.The background to this approach is reviewed. Key Words: glioblastoma; biological modifiers; hypothyroidism; tamoxifen INTRODUCTION Despite advances in surgical resection, computer assisted radiation therapy, and novel chemotherapeutic agents, survival for malignant glioma remains poor. The 2-yr survival of glioblastoma multiforme (GBM), the most malignant form of glioma, remains less than 20%. In light of poor outcomes with more traditional therapies, a number of alternatives have been explored. Immunotherapy has had some success against tumors such as melanoma and renal cell carcinoma. Cell-based immunotherapy and vaccine trials will be the subject of other chapters. In this chapter we will focus on the role of biological response modifiers in the treatment of malignant glioma Biological response modifiers may be defined as any naturally occurring substance, such as cytokine or hormone, that may be used to influence tumor growth. These substances may directly induce cell death, alter growth rates, or augment the body’s own immune response. Malignant gliomas are the most common primary brain tumor in adults and the current prognosis for patients with glioma remains poor. Despite mainstay treatment options including surgery, radiation, and chemotherapy, the estimated 2-yr survival remains less than 20% (1). One strategy in the spectrum of treatment options involves activation of the host immunologic response to destroy malignant glioma cells. Cytokines have been extensively studied as a vehicle of in vitro and in vivo immunologic activation and will be the focus of this chapter. TUMOR NECROSIS FACTOR FAMILY The cytokine tumor necrosis factor-D (TNF-D) was discovered by Carswell et al. in 1975 and has been shown to have cytotoxic effects in vitro and in vivo on tumor cells (2). TNF-D From: Current Clinical Oncology: High-Grade Gliomas: Diagnosis and Treatment Edited by: G. H. Barnett © Humana Press Inc., Totowa, NJ 405 406 Part V / Mason, Toms, and Hercbergs is produced by macrophages, monocytes and has also been shown to be produced by activated microglial and glioma cells (3). It has been shown to inhibit lipoprotein lipase (4), simulate granulocytes and the proliferation of fibroblasts, and has antiviral activity and endothelial cytotoxicity that varies by cell type (5). Tumor response to TNF-D is quite variable in that it inhibits growth and causes apoptosis in several tumor cell lines, but can stimulate growth in others (3,6–8). Additionally, this cytokine enhances major histocompatability complex (MHC) expression in glioma lines (9) and induces the production of intercellular adhesion molecule- 1 in glioblastoma cell lines (10). In recent years, the TNF family of cytokines - Dhas been extensively studied in association with apoptosis in human malignant glioma cell. TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family that rapidly triggers apoptosis in various types of tumors (11). TRAIL preferentially triggers apoptosis in glioma cell lines vs normal stromal/ endothelial cells (12). TRAIL is characterized by activation of capase-8 caspase –3, DNA fragmentation and apoptosis in >50% of glioma cell lines (13). Its selective induction of apoptosis in glioma but not in primary cultures of normal astrocytes suggests the possibility of tumor suppression in vivo. Unfortunately, TNF-D induces apoptosis in human hepatocyte cultures, implying that it may be a poor choice for systemic use. Local, intratumoral admin- istration with convection-enhanced delivery (12,14) or with genetically modified stem cell delivery of TNF-D may play a role in the future. Another member of the TNF-D family that exerts strong antiglial activity is the CD95 ligand. Certain human glioma cell lines express CD95, also known as Fas/APO-1, and using an endogenous pathway, undergo apoptosis when exposed to antibodies to this ligand (15). The cytotoxicity of this endogenous pathway was shown to significantly increase when exposed to exogenous cytokines such as TNF-D, IFN- E, Il-1, and Il-8 (15). Like TNF-D there is concern that CD95 ligand immunotherapy given systemically may lead to liver failure (16). It has been proposed in the recent literature that Taxol works synergistically with CD95 to sensitize glioma cells to the CD95 ligand, and may reduce systemic toxic effects (177). Recombinant human TNF-D has been used systemically with mixed responses (18,19). Yoshida administered the cytokine intra-arterially in 20 cases of malignant gliomas with a reported 20% response rate and minimal side effects (5). Recent detailed examination of ultra- structural sequelae of intra-arterial TNF- D administrated in an experimental rat model dem- onstrated necrotizing effects on tumor vascular endothelium, thus suggesting another mechanism of the anti-tumoral effect of TNF- D (20). Interleukin-1 [IL-1], a key pro-inflammatory cytokine which initiates the production of a variety of other cytokines, has been found to increase the immune response to glioma (21). Convection-enhanced delivery (CED) has been investigated as a means to overcome the problem of weak tumor response to systemically administered IL-1. The effect of intratumoral delivery of interleukin (IL)-1 and interferon (IFN)- (IFN-D) by CED on tumor immune cell invasion in a rat glioma model demonstrated that intratumoral cytokine infusion using CED leads to strong tumor invasion with macrophages and lymphocytes suggesting a tumor spe- cific immune response. Survival ongoing studies are yet to be reported. INTERLEUKIN-2 Interleukin-2 (IL-2), originally called T-cell growth factor, is a potent, well-studied 15.5 kDa cytokine that is important in the generation of anti-tumor immunity. When T-helper cells are exposed to tumor antigens, they release small quantities of IL-2. This acts locally to activate Chapter 24 / Biological Modifiers 407 cytotoxic T-cells and natural killer (NK) cells that mediate systemic tumor cell destruction (22). It has been shown that intravenous, intralymphatic, or intralesional administration of IL-2 has produced responses in several types of cancer such as renal cell carcinoma and melanoma, but that systemic routes of therapy can cause severe side effects such as hypoten- sion, bradycardia, and extreme fatigue (22). Additionally, long-term central administration of IL-2 in rat model has neurotoxic consequences associated with elevated IL-2 central nervous system (CNS) levels (23). Nonetheless, IL-2 therapy by systemic, local, or genetic means has been an intriguing target of study because of its potent effect on the immune system and encouraging impact on gliomas in preclinical testing. The immunoregulatory effects of IL-2 are complex and varied. IL-2 is a growth factor that stimulates the proliferation of cytotoxic T-cells, helper T-cells, NK cells, and LAK cells, all of which can participate in the host’s response to tumor cells (24,25). Although there is a decreased immune response in vivo to glioma cells because of poor antigen presentation and the release of suppressor factors (26), effector cells such as cytotoxic T-cells or NK cells have been shown to be activated by IL-2, causing a more effective lytic process in certain glial- tumor lines (27–29). Clinically, methods of combining tumor antigens and genetically modi- fied cytokine-producing tumor cells (i.e., tumor vaccine) have had mixed successes (30,31). Autologous dendritic cell (DC) vaccines have attracted attention for the treatment of gliomas with or without IL-2 or other cytokine activation (32,33). DC vaccines have attracted attention for the treatment of gliomas, as survival time was elongated in patients with malignant gliomas and other brain tumors (33,34). These will be covered in more detail in the chapter on cellular immunotherapy. Because of the relative immunologic isolation of glial tumors within the CNS, blunted immune response and the systemic toxicity of IL-2, experiments using local and regional delivery of IL-2 by means of direct injection, polymer-based IL-2, or gene transfer has been examined. In small clinical studies using direct tumor bed injection of activated NK cells and IL-2, no significant effect on prognosis was seen (35). A variety of genetically modified viruses have been examined as vectors for secreting IL-2 locally. In one approach, replication- deficient herpes simplex virus (HSV) with a mutated thymidine kinase produced tumor cell death locally (36). In another study, IL-2 was secreted in low levels from cells with their tumorgenicity removed (“package cells”), and such cytokine release induced a long-lasting protective immune response against challenge with a tumorigenic dose of tumor cells (38). Although there have been mixed results, the injection of cytokine secreting allogenic tumor cells into a tumor bed is hypothesized to induce an anti-tumor immune response capable of prolonging survival (22,39). Although preclinical studies with IL-2 gene therapy have been promising (21), there have been limited clinical trials (22,39). INTERLEUKIN-4 The cytokine interleukin 4 (IL-4) was first described in 1982 as a B-cell stimulator with activating and growth factor potential (41). It also has been associated with T-cell activation, and can be inactivated by IFN-JJ.