Active efflux of Dasatinib from the brain limits efficacy against murine glioblastoma: broad implications for the clinical use of molecularly targeted agents.

The importance of the blood-brain barrier in preventing effective pharmacotherapy of glioblastoma has been controversial. The controversy stems from the fact that vascular endothelial cell tight junctions are disrupted in the tumor, allowing some systemic drug delivery. P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) efflux drugs from brain capillary endothelial cells into the blood. We tested the hypothesis that although the tight junctions are "leaky" in the core of glioblastomas, active efflux limits drug delivery to tumor-infiltrated normal brain and consequently, treatment efficacy. Malignant gliomas were induced by oncogene transfer into wild-type (WT) mice or mice deficient for Pgp and BCRP (knockout, KO). Glioma-bearing mice were orally dosed with dasatinib, a kinase inhibitor and dual BCRP/PgP substrate that is being currently tested in clinical trials. KO mice treated with dasatinib survived for twice as long as WT mice. Microdissection of the tumor core, invasive rim, and normal brain revealed 2- to 3-fold enhancement in dasatinib brain concentrations in KO mice relative to WT. Analysis of signaling showed that poor drug delivery correlated with the lack of inhibition of a dasatinib target, especially in normal brain. A majority of human glioma xenograft lines tested expressed BCRP or PgP and were sensitized to dasatinib by a dual BCRP/Pgp inhibitor, illustrating a second barrier to drug delivery intrinsic to the tumor itself. These data show that active efflux is a relevant obstacle to treating glioblastoma and provide a plausible mechanistic basis for the clinical failure of numerous drugs that are BCRP/Pgp substrates.

Superior efficacy of tumor cell vaccines grown in physiologic oxygen.

PURPOSE: Atmospheric oxygen (∼20% O(2)) has been the universal condition employed to culture tumor cells used as vaccine antigen. We tested the hypothesis that reducing oxygen tension would increase the efficacy of tumor cell lysate vaccines. EXPERIMENTAL DESIGN: GL261 glioma cells and EMT6 breast carcinoma cells were grown in 5% or 20% O(2). Syngeneic tumor-bearing mice were vaccinated with these tumor cell lysates mixed with CpG oligodeoxynucleotides as an adjuvant. Tumor infiltrating T cells and apoptotic GL261 cells were quantified by immunohistochemistry. Tumor-reactive immunoglobulin was detected by Western blot. Ovalbumin and gp100-derived peptides were mixed with GL261 lysates as marker antigens to detect changes in presentation of exogenous antigen on MHC class I in vitro, and in vivo following adoptive transfer of gp100-specific CD8(+) T cells. RESULTS: Mice bearing orthotopic glioma and breast carcinoma survived significantly longer when vaccinated with 5% O(2) lysates. Antigen-specific CTL activation was significantly enhanced following stimulation with lysates derived from GL261 cells grown in 5% O(2) versus 20% O(2) through a mechanism that involved enhanced cross-presentation of exogenous antigen on MHC I. Vaccination with 5% O(2) GL261 cell lysates caused a significant increase in CTL proliferation, tumoricidal function, and trafficking into brain tumor sites, whereas 20% O(2) lysate vaccines predominantly evoked an antibody response. CONCLUSIONS: Tissue culture oxygen functions as an "immunologic switch" by dictating the cellular and humoral immune responses elicited by tumor cell lysates. These results have profound implications for cancer vaccines that utilize tumor cells as the source of antigen.

Anti-tumor immune response correlates with neurological symptoms in a dog with spontaneous astrocytoma treated by gene and vaccine therapy.

Gene therapy and vaccination have been tested in malignant glioma patients with modest, albeit encouraging results. The combination of these therapies has demonstrated synergistic efficacy in murine models but has not been reported in large animals. Gemistocytic astrocytoma (GemA) is a low-grade glioma that typically progresses to lethal malignancy despite conventional therapies. Until now there has been no useful animal model of GemA. Here we report the treatment of a dog with spontaneous GemA using the combination of surgery, intracavitary adenoviral interferon gamma (IFNgamma) gene transfer, and vaccination with glioma cell lysates mixed with CpG oligodeoxynucleotides. Surgical tumor debulking and delivery of Ad-IFNgamma into the resection cavity were performed. Autologous tumor cells grew slowly in culture, necessitating vaccination with allogeneic tumor lysate in four of the five vaccinations. Transient left-sided blindness and hemiparesis occurred following the fourth and fifth vaccinations. These neurological symptoms correlated with a peak in the levels of tumor-reactive IgG and CD8(+) T cells measured in the blood. All symptoms resolved and this dog remains tumor-free over 450 days following surgery. This case report preliminarily demonstrates the feasibility of treating dogs with spontaneous glioma using immune-based therapy and warrants further study using this therapeutic approach.

Expression of Grb2 distinguishes classical Hodgkin lymphomas from primary mediastinal B-cell lymphomas and other diffuse large B-cell lymphomas.

Growth factor receptor-bound protein 2 is an adaptor molecule that mediates B-cell receptor (BCR) signaling pathways, but the expression of growth factor receptor-bound protein 2 in lymphoma tissues has not been reported. We sought to characterize growth factor receptor-bound protein 2 protein expression in reactive tonsillar tissues and lymphoma tissues obtained from diagnostic biopsies of classical Hodgkin lymphoma, primary mediastinal large B-cell lymphoma, diffuse large B-cell lymphoma, nodular lymphocyte predominant Hodgkin lymphoma, and 20 low-grade B-cell lymphomas. Growth factor receptor-bound protein 2 expression was assessed in tissues by immunohistochemistry and in lymphoma cell lines by immunoblotting. In reactive lymphoid tissues, growth factor receptor-bound protein 2 was expressed in the cytoplasm of B-cells and histiocytes but not T-cells. Strong, cytoplasmic growth factor receptor-bound protein 2 expression was seen in the neoplastic cells of follicular lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma, splenic marginal zone lymphoma, primary mediastinal large B-cell lymphoma, diffuse large B-cell lymphoma, and nodular lymphocyte predominant Hodgkin lymphoma. In contrast, only 10% of the classical Hodgkin lymphomas showed growth factor receptor-bound protein 2 expression in the neoplastic cells. Growth factor receptor-bound protein 2 protein expression was detected by Western blotting in all lymphoma cell lines tested with higher levels in primary mediastinal large B-cell lymphoma compared with classical Hodgkin lymphoma cell lines. These findings support a role for growth factor receptor-bound protein 2 in the diagnostically challenging workup of classical Hodgkin lymphoma versus primary mediastinal large B-cell lymphoma and warrant further studies to evaluate the biologic significance of growth factor receptor-bound protein 2 in the pathogenesis of classical Hodgkin lymphoma.