Cancer research
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Comparative Study
Urea as a recovery marker for quantitative assessment of tumor interstitial solutes with microdialysis.
Microdialysis is a technique that enables measurement of extracellular concentrations of unbound analytes. A small probe with a semipermeable membrane is implanted in tissue and constantly perfused. Small analytes in the interstitial fluid diffuse into the perfusate and are collected. ⋯ There was no effect of hyperglycemia on tumor blood flow. Urea appears to be a useful low molecular weight relative recovery marker for tumor microdialysis. In combination with the determination of relative diffusivity between urea and the solute of interest, this calibration method may allow for quantitative measurements of tumor metabolites and unbound drugs.
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Immunotherapy targeting for the induction of a T-cell-mediated antitumor response in patients with renal cell carcinoma (RCC) appears to hold significant promise. Here we describe a novel RCC vaccine strategy that allows for the concomitant delivery of dual immune activators: G250, a widely expressed RCC associated antigen; and granulocyte/macrophage-colony stimulating factor (GM-CSF), an immunomodulatory factor for antigen-presenting cells. The G250-GM-CSF fusion gene was constructed and expressed in Sf9 cells using a baculovirus expression vector system. ⋯ All FP-modulated peripheral blood mononuclear cell cultures with antitumor activity showed an up-regulated CD3+CD4+ cell population. These results suggest that GM-CSF-G250 FP is a potent immunostimulant with the capacity for activating immunomodulatory DCs and inducing a T-helper cell-supported, G250-targeted, and CD8+-mediated antitumor response. These findings may have important implications for the use of GM-CSF-G250 FP as a tumor vaccine for the treatment of patients with advanced kidney cancer.
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Modulation of thiol levels may alter both the efficacy and toxicity of chemotherapeutic agents. We investigated cytoenhancement, using L-buthionine-[S,R]-sulfoximine (BSO) to reduce cellular glutathione levels prior to intracarotid alkylator administration. We also evaluated chemoprotection against chemotherapy-induced systemic toxicity when the thiol agents N-acetylcysteine (NAC) and sodium thiosulfate were administered into the descending aorta to limit brain delivery. ⋯ Thus, BSO depleted brain and brain tumor glutathione but thereby increased chemotherapy-induced myelosuppression. Surprisingly, although NAC was found to readily cross the blood-brain barrier when given into the carotid artery, aortic infusion of NAC resulted in minimal exposure to the central nervous system (CNS) vasculature because of rapid clearance. As a result, aortic infusion of NAC to perfuse bone marrow and minimize myelosuppression and toxicity to visceral organs could be performed without interfering with the CNS cytotoxicity of intracarotid alkylators, even after BSO depletion of CNS glutathione.
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In the first Phase I clinical trials of endostatin as an antiangiogenic therapy for cancer, the protein was administered as an i.v. bolus for approximately 20-30 min each day. This protocol was based on experimental studies in which animals were treated by s.c. bolus once a day. However, it was not clear in the previous studies whether this schedule could be maximized further. ⋯ Additional experiments using a human pancreatic cancer model in severe combined immunodeficient mice showed that there was a significant decrease in the microvessel density between the treatment groups and the control group. These data show that continuous administration of human endostatin results in sustained systemic concentrations of the protein leading to: (a) increased efficacy manifested as increased tumor regression; and (b) an 8-10-fold decrease in the dose required to achieve the same antitumor effect as the single daily bolus administration of endostatin. On the basis of this approach, an additional clinical trial has been designed and initiated and is under way in two countries.
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Many oncogenes induce expression of vascular endothelial growth factor (VEGF), a key factor in tumor angiogenesis. Phosphatidylinositol 3'-kinase (PI3K)/Akt is a common signaling pathway for oncogenes and tumor suppressor genes and is involved in VEGF regulation. Because hypoxia is a major stimulus for VEGF production, we examined the effects of LY294002, a selective PI3K inhibitor, on hypoxia-inducible factor (HIF)-1alpha and HIF-2alpha expression and on endogenous VEGF responses to hypoxia. ⋯ This effect was blocked by PI3K inhibitor, demonstrating one mechanism for ras synergy with hypoxia-mediated induction of genes. The decreased HIF-1alpha expression was not dependent on VHL interaction because a renal carcinoma cell line with VHL mutation and constitutive high HIF-1alpha expression also showed down-regulation of HIF-1alpha after treatment with LY294002. These results have implications for the use of PI3K inhibitors to inhibit synergistic effects of hypoxia with a wide range of common oncogenes.