Glycoprotein Nonmetastatic Melanoma Protein B, a Potential Molecular Therapeutic Target in Patients with Glioblastoma Multiforme

Abstract

Purpose: More brain tumor markers are required for prognosis and targeted therapy. We have identified and validated promising molecular therapeutic glioblastoma multiforme (GBM) targets: human transmembrane glycoprotein nonmetastatic melanoma protein B (GPNMB wt ) and a splice variant form (GPNMB sv , a 12-amino-acid in-frame insertion in the extracellular domain). Experimental Design: We have done genetic and immunohistochemical evaluation of human GBM to determine incidence, distribution, and pattern of localization of GPNMB antigens in brain tumors as well as survival analyses. Results: Quantitative real-time PCR on 50 newly diagnosed GBM patient tumor samples indicated that 35 of 50 GBMs (70%) were positive for GPNMB wt+sv transcripts and 15 of 50 GBMs (30%) were positive for GPNMB sv transcripts. Normal brain samples expressed little or no GPNMB mRNA.We have isolated and characterized an anti-GPNMB polyclonal rabbit antiserum (2640) and two IgG2b monoclonal antibodies (mAb; G11 and U2). The binding affinity constants of the mAbs ranged from 0.27 Â 10 8 to 9.6 Â 10 8 M À1 measured by surface plasmon resonance with immobilized GPNMB, or 1.7 to 2.1 Â 10 8 M À1 by Scatchard analyses with cellexpressed GPNMB. Immunohistochemical analysis detected GPNMB in a membranous and cytoplasmic pattern in 52 of 79 GBMs (66%), with focal perivascular reactivity in f27%. Quantitative flow cytometric analysis revealed GPNMB cell surface molecular density of 1.1 Â 10 4 to 7.8 Â 10 4 molecules per cell, levels sufficient for mAb targeting. Increased GPNMB mRNA levels correlated with elevated GPNMB protein expression in GBM biopsy samples. Univariate and multivariate analyses correlated expression of GPNMB with survival of 39 GBM patients using RNA expression and immunohistochemical data, establishing that patients with relatively high mRNA GPNMB transcript levels (wt+sv and wt), >3-fold over normal brain, as well as positive immunohistochemistry, have a significantly higher risk of death (hazard ratios, 3.0, 2.2, and 2.8, respectively). Conclusions: Increased mRNA and protein levels in GBM patient biopsy samples correlated with higher survival risk; as a detectable surface membrane protein in glioma cells, the data indicate that GPNMB is a potentially useful tumor-associated antigen and prognostic predictor for therapeutic approaches with malignant gliomas or any malignant tumor that expresses GPNMB.Glioblastoma multiforme (GBM) accounts for f50% of all primary brain tumors in adults and is usually rapidly fatal (1). Despite recent advances in surgery and radiotherapy and the development of chemotherapeutic reagents, the clinical outcome for most GBM patients is unsatisfactory. Although a recent study showed, for the first time, a meaningful survival benefit associated with chemotherapy using an innovative, temozolomide-based chemoradiation approach (2), the median progression-free survival among patients treated with this regimen was only 7.9 months, whereas the overall survival was only 14.6 months (2). Thus, effecti...

Role of MicroRNA-150 and Glycoprotein Nonmetastatic Melanoma Protein B in Angiogenesis during Hyperoxia-Induced Neonatal Lung Injury

“…GPNMB has been shown to have angiogenic properties (36,37). Furthermore, induction of GPNMB has been associated with several cancers, where it helps with tumor invasion by reducing apoptosis and promoting endothelial recruitment (42). These studies lead us to speculate as to whether hyperoxia-induced GPNMB in neonatal lungs contributes to angiogenesis or has any protective roles in cellular injury.…”

Glycoprotein non-metastatic melanoma protein B as a predictive prognostic factor in clear-cell renal cell carcinoma following radical nephrectomy

“…Gpnmb is a transmembrane glycoprotein that is expressed in various types of cancer and promotes the migration, invasion and metastasis of tumor cells. This protein is also highly expressed in several aggressive types of cancer, including melanoma (a cancer with high propensity for metastasizing to bone), glioma and breast cancer (24)(25)(26)(27). Finally, the ectopic expression of Gpnmb is sufficient to enhance invasive phenotypes in vitro and metastatic capabilities in vivo (28).…”

Gpnmb/osteoactivin, an attractive target in cancer immunotherapy

“…First, it is highly expressed at the surface of cancer cells [1], but is predominantly expressed intracellularly in normal cells, such as macrophages or melanocytes [2,3].This expression pattern makes Gpnmb/OA particularly attractive for antibody-based therapies because, as a target, it would be more readily accessible in cancer cells than in normal cells, thereby reducing potential complications owing to bystander effects. It is also highly expressed in several aggressive cancers, including melanoma (a cancer with high affinity to metastasize to bone) [1], glioma [4,5] and breast cancer [6]. Finally, ectopic expression of Gpnmb/OA, or its murine orthologue OA, in glioma, hepatocellular carcinoma and breast cancer cells is sufficient to enhance invasive phenotypes in vitro and metastasis capabilities in vivo [4,6,7].…”

“…In addition to its diverse roles in normal cells, aberrant Gpnmb/OA expression had been linked to various pathological disorders such as glaucoma [18], kidney disease [19][20][21] and osteoarthritis [22]. Gpnmb/OA was also expressed at higher levels in several malignant human tissues, such as hepatocellular carcinoma [7], glioma [4,5], melanoma [1,23] and breast cancer cells [6,24], relative to corresponding normal tissue.…”