Biomedical subjects

Randy Burd

Publications and source records attributed to Randy Burd.

11 recordsLinked to original sources

PubMed2006

Effect of simultaneous inhibition of epidermal growth factor receptor and cyclooxygenase-2 in HER-2/neu-positive breast cancer.

PURPOSE: HER-2/erbB2/neu is overexpressed in 25% to 30% of all invasive breast cancers and is associated with an aggressive course and reduced survival. HER-2/erbB2/neu breast tumors are frequently associated with up-regulation of cyclooxygenase (COX)-2 and activation of the epidermal growth factor receptor (EGFR) pathway, which promote enhanced cell growth and resistance to apoptosis. This study investigated whether simultaneously blocking both EGFR and COX-2 pathways with ZD1839 and celecoxib, respectively, would be more effective in inhibiting cell growth and inducing apoptosis than either agent alone. EXPERIMENTAL DESIGN: The effects of ZD1839, celecoxib, and their combination on cell survival, cell cycle progression, and apoptosis were determined in NMF11.2 mouse mammary tumor cells. We also investigated the potential downstream EGFR-activated pathways that are altered by simultaneous inhibition of COX-2 and EGFR. RESULTS: Celecoxib alone and ZD1839 alone produced a concentration- and time-dependent inhibition of cell survival. Both agents combined produced supra-additive inhibitory effects on cell survival and apoptosis compared with either agent alone. This effect was associated with increased cleaved poly(ADP-ribose)polymerase and reduced protein expression of bcl-2. Phosphorylation of extracellular signal-regulated kinase 1/2 was partially blocked by ZD1839 and celecoxib alone and was completely blocked by the combination of both agents. The enhanced proapoptotic effects of the combined agents were also associated with decreased phosphorylation of Akt and increased phosphorylation of p38. CONCLUSIONS: These findings show that both COX-2 and EGFR are important targets for inhibiting survival and inducing apoptosis in breast cancer. The data suggest a potential cross-talk between COX-2 and EGFR signaling in breast cancer cells overexpressing HER-2/erbB2/neu.

Animals↗

PubMed2006

Malignant transformation of immortalized HaCaT keratinocytes through deregulated nuclear factor kappaB signaling.

Previous studies addressing functional aspects of nuclear factor kappaB (NF-kappaB) activation in normal and transformed keratinocytes revealed complex and seemingly contradictory roles of this transcription factor in this cell type. In normal skin, NF-kappaB signaling seems to inhibit squamous cell carcinoma development whereas, in squamous cell carcinoma themselves, deregulated NF-kappaB expression and/or signaling is frequently observed. To further investigate this paradox, we focused on NF-kappaB activation as it relates to the transformed phenotype of immortalized but nontumorigenic human keratinocytes (HaCaT cells). We observed that NF-kappaB activity contributed to survival and growth of cultured HaCaT keratinocytes as shown by use of pharmacologic NF-kappaB inhibitors, RNA interference, and inducible overexpression of a dominant interfering IkappaB construct. NF-kappaB activation was largely provided through interaction with extracellular matrix components because preventing cell attachment by forced suspension culture markedly reduced NFkappaB signaling associated with cell death (anoikis); conversely, anoikis was partially reversed by NF-kappaB activation induced either by tumor necrosis factor-alpha treatment or by overexpressing the NF-kappaB p65 subunit in HaCaT cells. Furthermore, overexpression of NF-kappaBp65 in HaCaT cells induced colony formation in soft agar and tumorigenicity in nude mice. In summary, as opposed to normal keratinocytes, immortalized HaCaT keratinocytes provide a cellular context in which deregulated NF-kappaB signaling supports multiple malignant traits in vitro and in vivo.

Animals↗

PubMed2005

Effect of the tumor vascular-damaging agent, ZD6126, on the radioresponse of U87 glioblastoma.

PURPOSE: The effect of ZD6126 on tumor oxygen tension and tumor growth delay in combination with ionizing radiation was examined in the human U87 glioblastoma tumor model. Resistance to ZD6126 treatment was investigated with the nitric oxide synthase inhibitor, l-N(G)-nitroarginine methyl ester (hydrochloride; l-NAME/active form, l-NNA). METHODS: U87 human xenografts were grown in athymic nude mice. ZD6126 was given with or without l-NNA. Tumor oxygen tension was measured using the Oxford Oxylite (Oxford, England) fiberoptic probe system. Tumor volume was determined by direct measurement with calipers and calculated by the formula [(smallest diameter(2) x widest diameter)/2]. RESULTS: Multiple doses of ZD6126 treatment (three doses) had a significant effect on tumor growth delay, reducing the average daily tumor growth rate from 29% to 16%. When given 1 hour before radiation, ZD6126 caused an acute increase in hypoxia in U87 tumors, and reduced tumor growth delay compared with that of radiation alone. The combination of ZD6126 given after radiation, either as a single dose or in multiple doses, had greater or similar antitumor activity compared with radiation alone. Twenty-four hours after administration, a single dose of ZD6126 induced little (10 +/- 8%) necrosis in U87 xenografts. l-NNA, when given in combination with ZD6126, significantly enhanced the effectiveness of ZD6126 in inducing tumor necrosis. CONCLUSIONS: Our observation that ZD6126-induced tumor hypoxia can decrease radiation response when ZD6126 is given prior to radiation indicates the importance of scheduling. Our findings suggest that the optimal therapeutic benefit of ZD6126 plus radiation in human glioblastoma may require multiple dosing in combination with a nitric oxide synthase inhibitor, to be scheduled following radiotherapy.

Angiogenesis Inhibitors↗

PubMed2005

Factors controlling oxygen utilization.

We demonstrate, theoretically, that oxygen diffusion distance is related to the metabolic rate of tumors (QO2) as well as the oxygen tension. The difference in QO2 rate between tumors can vary by as much as 80-fold. Inhibition of oxygen utilization by glucose or chemical inhibitors can improve the diffusion distance. Combining respiratory inhibitors with increased availability of oxygen will further improve the oxygen diffusion distance for all tumors. A simple means for inhibiting oxygen consumption is the use of glucose (the Crabtree effect). The inhibition of tumor oxygen utilization by glucose occurs in R323OAc mammary carcinoma and 9L glioma cells. However, stimulation of oxygen consumption is observed with glucose in the Q7 hepatoma cell line. MIBG, a known inhibitor of oxygen utilization, blocks oxygen consumption in 9L, but is weakly inhibitory with the Q7. Q7 tumor cells demonstrate an anomalous behavior of glucose and MIBG on oxygen consumption. Our results clearly demonstrate the necessity for comparing effects of different agents on different tumor cells. Generalizations cannot be made with respect to the choice of inhibitor for in vivo use. Our work shows that oxygen consumption also can be inhibited with malonate and chlorosuccinate. These substrates may be effective in vivo, where glucose is low and glutamine is the major substrate. Our results indicate that information about individual tumor substrate-linked metabolic controls may be necessary before attempting to inhibit oxygen utilization in vivo for therapeutic benefit.

3-Iodobenzylguanidine↗

PubMed2004

Improving tumor response to radiotherapy by targeting angiogenesis signaling pathways.

Radiotherapy is one of the most widely used treatments for cancer; however, the development of tumor radioresistance is an ongoing problem. Agents that target tumor angiogenesis are being used in combination with radiotherapy to improve the therapeutic index without a clear understanding of how these agents may affect radiosensitization. This article discusses recently published studies that may shed some light on the underlying signaling mechanisms that are involved in the interactions of antiangiogenic agents with ionizing radiation.

Angiogenesis Inhibitors↗

PubMed2004

Protocols for simulating the thermal component of fever: preclinical and clinical experience.

An increase in body temperature in association with inflammation or infection has been evolutionarily conserved in all cold and warm-blooded vertebrates and even in several invertebrates thus far examined. This change in temperature is strongly correlated with survival from infection in many animal models. Although the means by which body temperature is increased and maintained differs between cold- versus warm-blooded species, there are strong similarities in terms of the magnitude of temperature change and its duration. Despite these intriguing observations and significant biological sequelae, temperature manipulation is rarely considered in the context of most experimental immunological investigations. We have hypothesized that the thermal microenvironment plays a critical role in regulating events in the immune response and that an increase in ambient temperature can serve as a natural trigger or "danger signal" to the immune system. To examine the direct effects of fever-like temperatures on immunological parameters, we have designed and characterized protocols for performing whole body heating of mice and humans in vivo, and heating of cultured cells in vitro. Our studies have now progressed to the development of therapeutic uses of fever-range hyperthermia in combination with other therapies. This chapter describes the experimental procedures that have been developed for these studies and summarizes several of the immunologically relevant effects that we have noticed following mild heat treatments in vivo and in vitro.

Animals↗

PubMed2004

Cyclooxygenase (COX)-2-dependent effects of the inhibitor SC236 when combined with ionizing radiation in mammary tumor cells derived from HER-2/neu mice.

Cyclooxygenase (COX)-2-derived prostaglandins (PGs) are thought to contribute to tumor growth and resistance to radiation therapy. COX-2 protein expression is increased in many tumors including those of the breast. COX-2-derived PGs have been shown to protect cells from radiation damage. This study evaluated the role of COX-2-derived PG in radiation treatment by using the NMF11.2 mammary tumor cell line originally obtained from HER-2/neu mice that overexpress HER-2/neu. We determined whether the effects of the COX-2 inhibitor SC236 on cell growth, radiation-induced PGE2 production and COX expression, cell cycle redistribution, and vascular endothelial growth factor (VEGF) were acting through COX-2-dependent mechanisms. The NMF11.2 cells expressed both COX-1 and COX-2 protein and mRNA. The radiation treatment alone led to a dose-dependent increase in the levels of COX-2 mRNA and COX-2 protein, which was associated with an increase in the production of PGE2 and prostacyclin (PGI2). Treating NMF11.2 cells with high concentrations (20 microM) of SC236 for 48 h reduced the radiation-induced increase in COX-2 activity and also decreased cell growth. SC236 (20 microM) increased the accumulation of the cells in the radiosensitive G2-M phase of the cell cycle. However, a low concentration (5 microM) of SC236 was adequate to reduce COX-2 activity. The lower concentration of SC236 (5 microM) also decreased cell growth after a longer incubation period (96 h) and, in combination with a 2 or 5 Gy dose, led to an accumulation of cells in G2-M phase. Restoring PG to control values in cells treated with 5 microM SC236 prevented the growth inhibition and G2-M cell cycle arrest. Radiation treatment of NMF11.2 cells also increased VEGF protein expression and VEGF secretion in a dose-dependent manner, which was blocked in those cells pretreated with 20 microM SC236 but not in those pretreated with 5 microM SC236. These findings indicate that the COX-2 inhibitor SC236 reduced cell growth and arrested cells in the G2-M phase of the cell cycle by mechanisms that are both dependent and independent of PG production while its effects on VEGF appear to be independent of COX-2.

Animals↗

PubMed2003

Effect of mild hyperglycemia +/- meta-iodo-benzylguanidine on the radiation response of R3230 Ac tumors.

The effects of glucose or meta-iodo-benzylguanidine (MIBG) on oxygen utilization (QO2) of several tumor cell lines were studied using a Clark-type electrode chamber. For in vivo studies, rats bearing R3230 Ac rat mammary adenocarcinomas were utilized. To evaluate changes in tumor oxygenation induced by glucose or MIBG, intratumoral pO2 and skeletal muscle pO2 were measured using Eppendorf Histography. To find the effect of mild hyperglycemia (i.p., 1 g/kg) +/- MIBG (i.p., 20 mg/kg) on the radiation response, a growth delay assay was used. Glucose alone produced a approximately 20% inhibition of QO2 in several tumor cells we tested except Q7 tumor cells. MIBG inhibited QO2 in R3230 Ac tumors. The median tumor pO2 for glucose + MIBG was increased from 5.3 mm Hg to 13.8 mm Hg. We hypothesized that combined treatment with glucose + MIBG significantly enhanced radiation-induced tumoricidal effects on R3230 Ac tumors, mainly due to reduction in QO2 and increase in tumor pO2.

3-Iodobenzylguanidine↗

PubMed2003

Tumor oxygenation and acidification are increased in melanoma xenografts after exposure to hyperglycemia and meta-iodo-benzylguanidine.

Tumor oxygen tension and extracellular pH (pH(e)) are physiological parameters that can be manipulated to improve current cancer therapies. Many human tumors consist of cells that are chronically exposed to low pH(e). Exposure of tumor cells in culture to glucose decreases oxygen consumption (oxygen sparing or Crabtree effect), and while this effect is absent in low pH-adapted tumor cells, it can be restored by combining the respiratory inhibitor meta-iodo-benzylguanidine (MIBG) with glucose (Burd et al., Cancer Res. 61, 5630-5635, 2001). The effects of hyperglycemia and MIBG on tumor oxygen tension and on pH(e) were investigated in human melanoma xenografts in SCID mice. An oral gavage of 1 M glucose (2 g/kg) increased the average blood glucose concentration from <140 mg/dl to approximately 400 mg/dl. Although tumor pH(e) decreased from pH 6.7 to pH 6.5 (P < 0.01) after about 60 min, no change in tumor oxygen tension was observed. However, when oral glucose and MIBG (15 mg/kg) were administered together, oxygen tension increased from 2.8 mmHg to approximately 17 mmHg, and tumor pH(e) decreased from pH 6.7 to pH 6.3 (P < 0.01) after about 115 min. In conclusion, administration of glucose together with MIBG increases tumor oxygen tension and also increases the magnitude and duration of acidification. Hyperglycemia plus MIBG has the potential to improve response to radiation therapy as well as to hyperthermia and some chemotherapies.

Animals↗

PubMed2003

Tumor response to ionizing radiation combined with antiangiogenesis or vascular targeting agents: exploring mechanisms of interaction.

Recent preclinical studies have suggested that radiotherapy in combination with antiangiogenic/vasculature targeting agents enhances the therapeutic ratio of ionizing radiation alone. Because radiotherapy is one of the most widely used treatments for cancer, it is important to understand how best to use these two modalities to aid in the design of rational patient protocols. The mechanisms of interaction between antiangiogenic/vasculature targeting agents and ionizing radiation are complex and involve interactions between the tumor stroma and vasculature and the tumor cells themselves. Vascular targeting agents are aimed specifically at the existing tumor vasculature. Antiangiogenic agents target angiogenesis or the new growth of tumor vessels. These agents can decrease overall tumor resistance to radiation by affecting both tumor cells and tumor vasculature, thereby breaking the codependent cycle of tumor growth and angiogenesis. The hypoxic microenvironment of the tumor also contributes to the mechanisms of interactions between antiangiogenic/vasculature targeting agents and ionizing radiation. Hypoxia stimulates up-regulation of angiogenic and tumor cell survival factors, giving rise to tumor proliferation, radioresistance, and angiogenesis. Preclinical evidence suggests that antiangiogenic agents reduce tumor hypoxia and provides a rationale for combining these agents with ionizing radiation. Optimal scheduling of combined treatment with these agents and ionizing radiation will ultimately depend on understanding how tumor oxygenation changes as tumors regress and regrow during exposure to these agents. This review article explores the complex interactions between antiangiogenic/vasculature targeting agents and radiation and offers insight into the mechanisms of interaction that may be responsible for improved tumor response to radiation.

Angiogenesis Inhibitors↗

PubMed2002

Regulation of intracellular pH in human melanoma: potential therapeutic implications.

Melanoma cells in vivo maintain intracellular pH (pHi) in a viable range despite an extracellular tumor pH (pHe) that is typically below 7.0. In general, three families of transporters are capable of removing metabolic protons, but the specific transporters responsible for the maintenance of pHi at low pHe in melanomas have not been identified. Although the transporters exist in most cells, an inhibitor would be predicted to have selectivity for cells located in an acidic tumor bed because cells in that environment would be expected to have transporters chronically activated. In this report, the levels and extent of expression of the Na+/H+ exchanger (NHE-1) and two of the H+-linked monocarboxylate transporters (MCTs) were evaluated in three melanoma cell lines. The effects of inhibitors of each transporter were tested at an extracellular pH (pHe) of 7.3, 6.7, or 6.5 in melanoma cells that were grown at pHe 7.3 or 6.7. The activity of MCT isoform 1 (MCT-1) was up-regulated in three melanoma cell lines at low pHe, but that of NHE-1 was not. Furthermore, NHE-1 activity was lower in the melanomas than in other normal and malignant cell lines that were tested. Reverse transcription-PCR using primers specific for MCT-1, MCT-4, and NHE-1 showed that expression of none of these transporters was reproducibly up-regulated at the level of transcription when cells were grown at pHe 6.7 instead of pHe 7.3. Ex vivo experiments using DB-1 human melanoma xenografts grown in severe combined immunodeficient mice found that MCT-1 and not NHE-1 was a major determinant of DB-1 tumor cell pHi. Taken together, the data indicate that MCTs are major determinants of pH regulation in melanoma. In contrast, keratinocytes and melanocytes under low pHe conditions relied on NHE-1. Inhibitors of MCTs thus have great potential to improve the effectiveness of chemotherapeutic drugs that work best at low pHi, such as alkylating agents and platinum-containing compounds, and they should be selective for cells in an acidic tumor bed. In most tissues, it is proposed that the NHE-1 could compensate for an inhibited MCT to prevent acidification, but in melanoma cells this did not occur. Therefore, MCT inhibitors may be particularly effective against malignant melanoma.

Animals↗