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The blood-brain tumor barrier (BTB) significantly limits delivery of therapeutic concentrations of chemotherapy to brain tumors. A novel approach to selectively increase drug delivery is pharmacologic modulation of signaling molecules that regulate BTB permeability, such as those in cGMP signaling. Here we show that oral administration of sildenafil (Viagra) and vardenafil (Levitra), inhibitors of cGMP-specific PDE5, selectively increased tumor capillary permeability in 9L gliosarcoma-bearing rats with no significant increase in normal brain capillaries. Tumor-bearing rats treated with the chemotherapy agent, adriamycin, in combination with vardenafil survived significantly longer than rats treated with adriamycin alone. The selective increase in tumor capillary permeability appears to be mediated by a selective increase in tumor cGMP levels and increased vesicular transport through tumor capillaries, and could be attenuated by iberiotoxin, a selective inhibitor for calcium-dependent potassium (K(Ca)) channels, that are effectors in cGMP signaling. The effect by sildenafil could be further increased by simultaneously using another BTB "opener", bradykinin. Collectively, this data demonstrates that oral administration of PDE5 inhibitors selectively increases BTB permeability and enhances anti-tumor efficacy for a chemotherapeutic agent. These findings have significant implications for improving delivery of anti-tumor agents to brain tumors.

Purpose: The blood-brain tumor barrier (BTB) significantly limits the delivery of chemotherapeutics to brain tumors. Nitric oxide (NO) is involved in the regulation of cerebral vascular permeability. We investigated the effects of NO donors, L-arginine and hydroxyurea, on BTB permeability in 9L gliosarcoma-bearing Fischer rats., Experimental Design: The rats implanted with 9L gliosarcoma were dosed orally with hydroxyurea and L-arginine. BTB permeability, defined by the unidirectional transport constant, Ki, for [14C]sucrose was measured. The expression of neural and endothelial NO synthase (NOS) in tumors and normal brain tissue was examined. Further, the levels of NO, L-citrulline, and cGMP in the tumor and normal brain tissue were measured., Results: Oral administration of l-arginine or hydroxyurea significantly increased BTB permeability when compared with the nontreated control. The selective effects were abolished by iberiotoxin, an antagonist of calcium-dependent potassium (KCa) channel that is a cGMP pathway effector. The expression of endothelial NOS, but not neural NOS, was higher in tumor vessels than in those of normal brain. Moreover, the levels of NO, L-citrulline, a byproduct of NO formation from L-arginine, and cGMP were enhanced in the tumor tissue by oral administration of L-arginine and/or hydroxyurea., Conclusions: Oral administration of L-arginine or hydroxyurea selectively increased tumor permeability, which is likely mediated by alteration in cGMP levels. The findings suggest that use of oral NO donors may be a strategy to enhance the delivery of chemotherapeutics to malignant brain tumors.

Purpose: Histone acetylation is one of the main mechanisms involved in regulation of gene expression. During carcinogenesis, tumor-suppressor genes can be silenced by aberrant histone deacetylation. This epigenetic modification has become an important target for tumor therapy. The histone deacetylation inhibitor, suberoylanilide hydroxamic acid (SAHA), can induce growth arrest in transformed cells. The aim of this study is to examine the effects of SAHA on gene expression and growth of glioblastoma multiforme (GBM) cells in vitro and in vivo., Experimental Design: The effect of SAHA on growth of GBM cell lines and explants was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. Changes of the cell cycle and relative gene expression were detected by fluorescence-activated cell sorting, real-time reverse transcription-PCR, and Western blotting. After glioma cells were implanted in the brains of mice, the ability of SAHA to decrease tumor growth was studied., Results: Proliferation of GBM cell lines and explants were inhibited in vitro by SAHA (ED50, 2x10(-6) to 2x10(-5) mol/L, 5 days). SAHA exposure of human U87 and T98G glioma cell lines, DA66 and JM94 GBM explants, as well as a murine GL26 GBM cell line resulted in an increased accumulation of cells in G2-M of the cell cycle. Many proapoptotic, antiproliferative genes increased in their expression (DR5, TNFalpha, p21WAF1, p27KIP1), and many antiapoptotic, progrowth genes decreased in their levels (CDK2, CDK4, cyclin D1, cyclin D2) as measured by real-time reverse transcription-PCR and/or Western blot after these GBM cells were cultured with SAHA (2.5x10(-6) mol/L, 1 day). Chromatin immunoprecipitation assay found that acetylation of histone 3 on the p21(WAF1) promoter was markedly increased by SAHA. In vivo murine experiments suggested that SAHA (10 mg/kg, i.v., or 100 mg/kg, i.p.) could cross the blood-brain barrier as shown by prominent increased levels of acetyl-H3 and acetyl-H4 in the brain tissue. Furthermore, the drug significantly (P<0.05) inhibited the proliferation of the GL26 glioma cells growing in the brains of mice and increased their survival., Conclusions: Taken together, SAHA can slow the growth of GBM in vitro and intracranially in vivo. SAHA may be a welcome addition for the treatment of this devastating disease.