A Novel Brachytherapy Agent for GBM

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DESCRIPTION (provided by applicant): Despite advances in surgery, chemotherapy, and radiation therapy, the average life span of a patient with glioblastoma multiforme (GBM) is about 15-months from time of diagnosis. Integrins are heterodimeric receptors found on the surface of GBM cells and angiogenic vasculature; they facilitate invasion into adjacent tissue. Normal brain tissue does not display activated integrins. Therapy for GBM based on integrin antagonism is most attractive, targeting both the neovasculature and the tumor itself. Our approach in this Phase I STTR is based on peptides known as disintegrins. Disintegrins bind with high affinity to a subset of human integrins involved in GBM and angiogenic endothelial cell invasion to inhibit tumor dissemination. The disintegrin we are studying, vicrostatin (VCN), is a recombinant single-chain peptide with all 10 cysteine residues involved in disulfide bond formation. We have shown that VCN has potent antitumor/antiangiogenic activity in breast, ovarian and prostate cancer. Advantages of VCN as GBM therapy: ability of VCN to disrupt the locomotor apparatus of the cell (actin cytoskeleton) and dramatically inhibit invasiveness of both GBM cells and angiogenic vasculature; minimal off-target effects due to lack of activated integrin expression in normal brain tissue; stable peptide enabling better penetration through the blood-tumor barrier; an exclusive recombinant production method that is robust, low cost and easily scalable; and stability of VCN to iodination with only a single tyrosine residue (Y51 in the amino acid sequence) iodinated. Since VCN is able to target integrins expressed on the luminal surface of GBM endothelium, 131I-VCN may be administered either intratumorally (i.t.) or intravenously (i.v.). Brachytherapy for malignant gliomas has been traditionally performed via invasive radioactive probes placed intracranially into the glioma. The use of 131I-VCN to selectively target integrins overexpressed on the angiogenic tumor endothelial cells and glioma cells will enable a novel non-invasive i.v. delivery modality with uniform distribution throughout the tumor. We propose two Specific Aims: In Aim 1 we will perform a dose-response study using 131I-VCN, delivered i.v. or i.t. to GBM in mouse models. 131I-VCN will deliver a dual effect by: (i) VCN integrin antagonistic activity, which blocks invasion of GBM and associated endothelial cells, and (ii) the brachytherapy effect from 131I. 131I- VCN binds specifically to GBM cells and associated angiogenic endothelial cells, but not to normal brain tissue, limiting the brachytherapy affect to the tumor. We will examine toxicity to normal brain, and the dose response on GBM progression. In Aim 2 we will examine combination of 131I-VCN (at optimal VCN and 131I dose) with antiangiogenic therapy or chemotherapy, and compare efficacy of the individual agents to their combination using GBM cells stereotactically implanted, as in Aim 1, with survival and tumor size as end points. We have assembled a unique team of experts including: a neurosurgeon, disintegrin/integrin specialist, molecular biologist, radiation oncologist, medical physicist, animal model specialist and biostatistician.