Biomedical subjects

D J Chaplin

Publications and source records attributed to D J Chaplin.

At least 37 records · Page 2Linked to original sources

PubMed1998

Tumour radiosensitization by high-oxygen-content gases: influence of the carbon dioxide content of the inspired gas on PO2, microcirculatory function and radiosensitivity.

PURPOSE: To measure the effects of breathing high-oxygen-content gases, with a CO2 fraction of between 0 and 10%, on tumour radiosensitivity, blood flow and oxygenation. METHODS AND MATERIALS: The murine sarcoma F was used, implanted subcutaneously (s.c.) in syngeneic CBA mice. We assessed the induced changes in tumour microregional blood flow and oxygenation using laser Doppler flowmetry, and pO2 histography, respectively. Radiation response was determined using an in vivo-in vitro clonogenic assay 18-20 h post treatment. RESULTS: The results show that the level of radiosensitization achieved is dependent on both the CO2 content of the inspired gas and the duration of gas breathing. No radiosensitization was evident following inhalation of 90% O2 + 10% CO2. All other gases elicited radiosensitization; however, that achieved with 100% O2 disappeared at the extended preirradiation breathing time of 45 min. At this time, radiosensitization was maintained for gases containing 1%, 2.5%, or 5% CO2. Changes in oxygenation, as measured by PO2 electrodes, did indicate improved oxygenation status during inhalation of the gases. However, the time-course and extent of the changes did not mirror accurately the changes in radiosensitization. All the gases with a CO2 content of 2.5% or greater induced a 10-20% reduction in microregional blood flow, with no change evident following inhalation of 100% O2 or 99% O2 + 1% CO2. CONCLUSIONS: The data imply that the decreased radiosensitization seen at extended breathing times of oxygen is unrelated to blood flow changes. The fact that radiosensitization is seen with extended breathing times of gases containing 2.5% and 5% CO2, despite blood flow decreases, is indicative of other overriding physiological changes, perhaps related to oxygen utilisation. The studies overall indicate that, at least in the tumour investigated, radiosensitization is not affected if the CO2 content of the inspired gas is reduced from 5% to 2.5%, or even 1%. Further evaluation of the radiosensitizing effects of such gas mixtures is now warranted. In addition, comparison with recent studies of other tumour types, where carbogen has been shown to improve tumour blood flow, suggests that this may be a tumour-specific phenomenon. Based on these data, further effort is required to elucidate the physiological mechanisms that determine these blood flow changes.

Administration, Inhalation↗

PubMed1998

Modification of tumor blood flow: current status and future directions.

Suboptimal drug distribution and hypoxia, which can contribute to treatment failure, are a direct consequence of the spatial and temporal heterogeneity in perfusion that occurs in solid tumors. Therefore, improvements in tumor blood flow have wide-ranging therapeutic importance. Paradoxically, controlled decreases in tumor blood flow can also be exploited and, if permanent, induce extensive tumor cell death on their own. We review the current knowledge of the factors controlling tumor blood flow with emphasis on the roles of the endogeneous vasodilator nitric oxide and the endogenous vasoconstrictor endothelin-1. The potential importance and application of approaches that irreversibly damage vascular function, so-called vascular targeting, are also discussed. Emphasis is given to the drug-based approaches to vascular targeting that are now entering clinical evaluation. There is no doubt that increased understanding of the processes that determine blood flow in tumors, coupled with the availability of techniques to monitor blood flow noninvasively in the clinic, will enable strategies for selectively modifying tumor blood flow to be transferred from the laboratory to the clinical setting.

Antineoplastic Agents↗

PubMed1998

Microenvironmental control of gene expression: implications for tumor angiogenesis, progression, and metastasis.

Low oxygen tension (hypoxia) is an important prognostic factor in cancer treatment because it affects tumor formation and malignant progression. Many genes governing these complex processes have been found to be oxygen regulated. This article reviews the present knowledge of hypoxia-inducible gene expression and how this affects angiogenesis, progression, and metastasis. Of particular importance are hypoxia-regulated transcription factors because they can modulate expression of countless different genes. Additional genes analyzed in some detail include those encoding angiogenic growth factors, factors controlling blood flow, and those involved in metastasis. Although hypoxia is generally perceived as a hindrance to cancer therapy, it is possibly exploitable because severe oxygen deficiency is tumor specific. Strategies aimed at using the presence of hypoxia in solid tumors include oxygen sensitive chemotherapy and gene therapy.

Angiogenesis Inducing Agents↗

PubMed1998

Magnetic resonance imaging and spectroscopy of combretastatin A4 prodrug-induced disruption of tumour perfusion and energetic status.

The effects of combretastatin A4 prodrug on perfusion and the levels of 31P metabolites in an implanted murine tumour were investigated for 3 h after drug treatment using nuclear magnetic resonance imaging (MRI) and spectroscopy (MRS). The area of regions of low signal intensity in spin-echo images of tumours increased slightly after treatment with the drug. These regions of low signal intensity corresponded to necrosis seen in histological sections, whereas the expanding regions surrounding them corresponded to haemorrhage. Tumour perfusion was assessed before and 160 min after drug treatment using dynamic MRI measurements of gadolinium diethylenetriaminepentaacetate (GdDTPA) uptake and washout. Perfusion decreased significantly in central regions of the tumour after treatment. This was attributed to disruption of the vasculature and was consistent with the haemorrhage seen in histological sections. The mean apparent diffusion coefficient of water within the tumour did not change, indicating that there was no expansion of necrotic regions during the 3 h after drug treatment. Localized 31P-MRS showed that there was decline in cellular energy status in the tumour after treatment with the drug. The concentrations of nucleoside triphosphates within the tumour fell, the inorganic phosphate concentration increased and there was a significant decrease in tumour pH for 80 min after drug treatment. The rapid, selective and extensive damage caused to these tumours by combretastatin A4 prodrug has highlighted the potential of the agent as a novel cancer chemotherapeutic agent. We have shown that the response of tumours to treatment with the drug may be monitored non-invasively using MRI and MRS experiments that are appropriate for use in a clinical setting.

Animals↗

PubMed1998

The effect of oxygen and carbon dioxide on tumor cell endothelin-1 production.

Endothelin-1 (ET-1) is produced by some tumor cells, but the dependence of this production on pO2 and pCO2, conditions relevant within the tumor microenvironment, has not been described. HT29 colon adenocarcinoma cells and DU145 prostate carcinoma cells produce similar amounts of ET-1 in vitro under normal cell culture conditions of 21% O2/5% CO2 (normoxia). Exposure of HT29 cells to either 2% O2 or 0.2% O2 significantly reduced ET-1 production compared to cells in normoxia. In contrast, production of ET-1 by DU145 cells was usually unaffected by hypoxia and was even slightly increased in cells exposed to 2% O2 in HEPES-buffered EMEM (HEPES-EMEM). Exposure of cells to either 2.2% CO2 or 7.1% CO2 had no effect on the production of ET-1 by cells in bicarbonate-buffered EMEM (EMEM). However, in HEPES-EMEM, ET-1 production by both cell lines was reduced in 7.1% CO2. A slight reduction in ET-1 produced by DU145 cells was also observed in 2.2% CO2. These results illustrate that changes in ET-1 production by tumor cells in response to hypoxia and hypercapnia are tumor-dependent. It is clear that the production of ET-1 by tumor cells under normal culture conditions may not accurately reflect production within the tumor microenvironment. A greater insight into the in vivo situation, however, may be possible by modifying the cell culture conditions.

Adenocarcinoma↗

PubMed1998

Involvement of oxygen free radicals in ischaemia-reperfusion injury to murine tumours: role of nitric oxide.

Ischaemia-reperfusion (I/R) injury is a model system of oxidative stress and a potential anti-cancer therapy. Tumour cytotoxicity follows oxygen radical damage to the vasculature which is modulated by tumour production of the vasoactive agent, nitric oxide (NO.). In vivo hydroxylation of salicylate, to 2,3- and 2,5-dihydroxybenzoate (DHBs), was used to measure the generation of hydroxyl radicals (OH.) following temporary vascular occlusion in two murine tumours (with widely differing capacity to produce NO.) and normal skin. Significantly greater OH. generation followed I/R of murine adenocarcinoma CaNT tumours (low NO. production) compared to round cell sarcoma SaS tumours (high NO. production) and normal skin. These data suggest that tumour production of NO. confers resistance to I/R injury, in part by reducing production of oxygen radicals and oxidative stress to the vasculature. Inhibition of NO synthase (NOS), during vascular reperfusion, significantly increased OH. generation in both tumour types, but not skin. This increase in cytotoxicity suggests oxidative injury may be attenuation by tumour production of NO.. Hydroxyl radical generation following I/R injury correlated with vascular damage and response of tumours in vivo, but not skin, which indicates a potential therapeutic benefit from this approach.

Adenocarcinoma↗

PubMed1998

Antineoplastic agents 393. Synthesis of the trans-isomer of combretastatin A-4 prodrug.

The (E)-stilbene isomer (2a) of the (Z)-combretastatin A-4 prodrug (1b) was efficiently prepared from (E)-combretastatin A-4 by a reaction sequence employing phosphorylation (dibenzyl chlorophosphite), cleavage (trimethyliodosilane) of the benzyl ester and reaction of the resulting phosphoric acid with sodium methoxide. The sodium phosphate product (2c) was also found to be an important side-product, presumably from iodine-catalyzed isomerization, when the analogous synthetic route was used to obtain the combretastatin A-4 prodrug (1b). The phosphoric acid precursor of prodrug 1b derived from (Z)-combretastatin A-4 (1a) was converted into a series of metal cation and ammonium cation salts to evaluate effects on human cancer cell growth, antimicrobial activities and solubility behavior.

Animals↗

PubMed1997

Human tumor blood flow is enhanced by nicotinamide and carbogen breathing.

Perfusion insufficiency and the resultant hypoxia are recognized as important mechanisms of resistance to anticancer therapy. Modification of the tumor microenvironment to increase perfusion and oxygenation of tumors may improve on the efficacy of these treatments. Using laser Doppler probes to measure microregional RBC flux, this study examines the influence of nicotinamide and carbogen on human tumor perfusion. Ten patients with advanced cancers were studied. Nicotinamide (80 mg/kg) was given p.o., and 60 min later, up to six probes were inserted into the tumor. Readings were taken for 1 h, followed by 10 min of carbogen breathing and 10 additional min of breathing room air. Results were compared with those from a similar group of eight control patients who were not given nicotinamide, but who breathed carbogen. In 44 microregions analyzed, 33 (73%) showed perfusion fluctuations of 50% or more, and 20 (44%) by 100% or more. This compared with the control group in whom 62% and 27% of microregions varied by 50% or more and 100% or more, respectively. Perfusion increases outweighed decreases by 30% with nicotinamide and 20% in the controls. On breathing carbogen, patients pretreated with nicotinamide showed an increase in tumor perfusion of 17% at 5 min and 22% at 10 min, compared with only 0% and 1% in the control group. Pretreatment with nicotinamide made little difference to the random blood flow fluctuations seen in controls. However, when carbogen was introduced, tumor perfusion increased compared with the control group. This may have important therapeutic implications by improving response to treatment and allowing better delivery of systemically administered agents.

Administration, Inhalation↗

PubMed1997

Vascular response of tumour and normal tissues to endothelin-1 following antagonism of ET(A) and ET(B) receptors in anaesthetised rats.

Modification of blood flow by endothelin-1 (ET-1) was examined in the s.c. HSN fibrosarcoma and compared to normal tissues of anaesthetised CBH/CBi rats. The ET receptor subtypes involved in the response were investigated using the ET(A) and ET(B) receptor antagonists BQ-610 and BQ-788, respectively. Blood flow and vascular resistance were determined using the uptake of radiolabelled iodo-antipyrine (125I-IAP). BQ-610 or BQ-788 was infused for 30 min prior to blood flow determination. ET-1 was administered 15 min into the infusion time. BQ-610 and BQ-788 infused alone did not modify any vascular parameters. Tumour blood flow increased slightly following ET-1, contrasting with most normal tissues, in which blood flow was reduced. Vascular resistance increased in all tissues, including the tumour. Neither antagonist significantly modified the ET-1-induced changes in tumour blood flow or vascular resistance, whereas in the majority of normal tissues BQ-610 attenuated and BQ-788 potentiated the vascular resonse to ET-1. Our results show that the HSN tumour vasculature is only weakly responsive to ET- 1 and antagonism of its effects by BQ-610 and BQ-788. This contrasts with the majority of normal tissues, in which ET- 1 induces an intense vasoconstriction.

Animals↗

PubMed1997

Combretastatin A-4, an agent that displays potent and selective toxicity toward tumor vasculature.

Selective induction of vascular damage within tumors represents an emerging approach to cancer treatment. Histological studies have shown that several tubulin-binding agents can induce vascular damage within tumors but only at doses approximating the maximum tolerated dose, which has limited their clinical applicability. In this study, we show that the combretastatin A-4 prodrug induces vascular shutdown within tumors at doses less than one-tenth of the maximum tolerated dose. In vitro studies indicate that a short drug exposure results in profound long-term antiproliferative/cytotoxic effects against proliferating endothelial cells but not cells that are quiescent prior to and during drug exposure. Vascular shutdown, within experimental and human breast cancer models in vivo following systemic drug administration, was demonstrated with a reduction in functional vascular volume of 93% at 6 h following drug administration and persisted over the next 12 h, with corresponding histology consistent with hemorrhagic necrosis resulting from vascular damage. These actions against tumor vasculature and the broad therapeutic window demonstrate the clinical potential of these drugs and warrant further study to elucidate the mechanisms responsible for the antivascular effects of combretastatin A-4.

Adenocarcinoma↗

PubMed1997

Inhibition of nitric oxide synthase induces a selective reduction in tumor blood flow that is reversible with L-arginine.

The effect of i.v. administration of the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NNA) on tumor blood flow compared with normal tissue blood flow was studied in anesthetized BD9 rats bearing subcutaneous P22 carcinosarcomas. Blood flow was measured by the tissue uptake of radiolabeled iodoantipyrine. The reversibility of blood flow changes was tested by subsequent administration of L-arginine, the natural substrate for NOS. The effect of L-NNA was compared to that of the imidazolineoxyl N-oxide C-PTIO, a carboxyl derivative of 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide and a nitric oxide scavenger. Drug-induced changes in mean arterial blood pressure (MABP) were monitored and used to calculate relative drug-induced changes in tissue vascular resistance. Heart rate was measured from blood pressure traces. L-NNA significantly decreased heart rate and increased MABP in a dose-dependent manner. Significant dose-dependent reductions in blood flow with L-NNA were observed in tumor, skeletal muscle, spleen, and skin overlying the tumor. No significant effect was found for normal skin, brain, heart, kidney, and small intestine. At 1 mg/kg, the effect of L-NNA was selective for the tumor, with a significant decrease in tumor blood flow to 0.45 of the control level and no significant effect in any of the normal tissues. Higher doses did not produce any further reduction in tumor blood flow, presumably due to an increase in tumor perfusion pressure arising from the increase in MABP at these doses. Vascular resistance was increased to some extent in all of the tissues studied but, overall, was greatest in the tumor. At 1 mg/kg, there was a 2-2.5-fold increase in tumor vascular resistance but no significant increase in any of the normal tissues. At the highest dose used (10 mg/kg), the increases in vascular resistance in the skeletal muscle and spleen were equivalent to that in the tumor. Administration of L-arginine 15 min after L-NNA completely reversed the decrease in tumor blood flow observed for 1 mg/kg L-NNA alone. In contrast to the effect of L-NNA, constant i.v. infusion of C-PTIO had no effect on tumor or normal tissue blood flow. These results indicate that nitric oxide is important for maintaining a vasodilatory tone in tumors and that inhibition of NOS may provide a means for enhancing therapeutic regimens that would benefit from a selective reduction in tumor blood flow.

Animals↗

PubMed1997

Nicotinamide as a radiosensitizer in tumours and normal tissues: the importance of drug dose and timing.

BACKGROUND AND PURPOSE: Nicotinamide is a radiation sensitizer currently undergoing clinical testing. This was an experimental study to determine the importance of drug dose and time interval between drug administration and irradiation for radiosensitization. MATERIALS AND METHODS: Nicotinamide (50-500 mg/kg) was injected intraperitoneally into CDFI or C3H mice and drug plasma pharmacokinetics were determined by HPLC. Radiosensitization was measured in tumours and normal tissues after local irradiation. The tumours were a C3H mammary carcinoma, the KHT sarcoma and the SCCVII carcinoma. Tumour response was assessed using either growth delay (C3H) or clonogenic survival (KHT/SCCVII). Normal tissue toxicities evaluated included early responding skin (development of moist desquamation of the foot) and late responding bladder (reservoir function estimated by cystometry) and lung (ventilation rate measured by plethysmography). RESULTS: All nicotinamide peak plasma concentrations were seen within 30 min after injection. Irradiating tumours at peak times resulted in enhancement ratios (ERs) of 1.27 (C3H), 1.75 (KHT) and 1.45 (SCCVII) with high nicotinamide doses and 1.27 (C3H), 1.28 (KHT) and 1.36 (SCCVII) after giving clinically relevant doses (100-200 mg/kg). Lower ERs were observed when the time interval between drug injection and irradiation was increased beyond the peak time. Irradiating normal tissues at peak times after injecting 100-200 mg/kg nicotinamide gave ERs of 1.20 (skin), 0.90 (bladder) and 1.02 (lung). CONCLUSIONS: Clinically achievable doses of nicotinamide will enhance tumour radiation damage while having minimal effects in normal tissues, but for the best tumour effect radiation should be given at the time of peak plasma drug concentrations.

Animals↗

PubMed1997

The relationship between extracellular lactate and tumour pH in a murine tumour model of ischaemia-reperfusion.

We have studied the relationship between extracellular lactate (LACTe) and extracellular pH (pHe) in murine tumours after vascular occlusion (clamping) followed by reperfusion. In tumours occluded at ambient room temperature, LACTe, measured by microdialysis, increased linearly with time and correlated strongly with the acidification of the extracellular compartment (r=0.97, P<0.03, n=4). Significant decrease in LACTe was evident following removal of occlusion at room temperature and is consistent with vascular reperfusion. Occlusion at 35 degrees C, i.e. to maintain tumour temperature during occlusion, resulted in an initial increase in LACTe, which mirrored a rapid reduction in pHe. However further reductions in pHe occurred without increase in LACTe. During vascular occlusion, tumour adenine nucleotide pool decreased and AMP accumulated. AMP subsequently decreased in the 35 degrees C group and this may contribute to the observed differences in accumulation of LACTe, and capacity to recover from vascular occlusion, between the two treatment groups. These data show that extracellular lactate concentration is a good predictor for tumour pH when adequate energy sources are available within the tumour. However, under conditions of more severe stress, resulting in abolition of primary energy stores and cell death, the pHe continues to decline in the absence of a corresponding accumulation of extracellular lactate. This emphasizes the fact that other processes, apart from lactate production, can contribute to reduction in extracellular pH.

Adenocarcinoma↗

PubMed1997

Metabolic and clonogenic consequences of ischaemia reperfusion insult in solid tumours.

Tumour cell survival is intimately related to blood vessel function and so the tumour vasculature represents a novel target for cancer therapy. We have investigated a murine tumour model in which a metal clamp was used to occlude the vascular supply temporarily and then removed to allow reperfusion. This allows the study of ischaemia-reperfusion as a model system for investigating tumour response to metabolic and oxidative stress. Recent studies have shown that prolonged reduction of tumour blood flow results in a deterioration of the hypoxic and acidic microenvironment found within tumours which leads to cytotoxicity. This cytotoxicity is dramatically enhanced if these cells are subsequently reperfused. It was the aim of the present study to determine the relative contribution of cytotoxicity occurring during the ischaemic period and that occurring during reperfusion. Although significant reductions in tumour energy status were induced during the clamping period itself, these were poorly correlated with the degree of tumour cytotoxicity. Relative vascular perfusion, measured using a radiolabelled tracer, remained significantly depressed below the control value following clamp removal. The degree of recovery of perfusion was also dependent upon the clamp duration. Relative tumour perfusion at 1 h after clamp removal was 70.1 +/- 14.6 and 50.5 +/- 6.3% of control values after a 1 or 3 h clamp, respectively, and showed no significant further increase when measured at 24 h after clamp removal. Tumour cytotoxicity following ischaemia reperfusion insult was modulated by administering the anti-oxidant enzymes superoxide dismutase or catalase intravenously just before clamp removal. These enzymes are restricted to the vascular compartment, where it is proposed that they modulate the concentration of oxygen free radicals released during reperfusion and by neutrophil oxidative burst. Reperfusion injury to the tumour was enhanced by administration of an inhibitor of nitric oxide synthase, nitro-L-arginine, probably owing to enhanced neutrophil adhesion and oxidative burst. Conversely, reperfusion injury to the tumour was reduced by administration of a nitric oxide donor, diethylamine nitric oxide. The murine model reported in this paper shows that ischaemia-reperfusion damage mediated by oxygen free radical formation provides a model system for investigating tumour response to oxidative stress at the level of the vascular endothelium.

Animals↗

PubMed1997

Nicotinamide reduces tumour interstitial fluid pressure in a dose- and time-dependent manner.

Nicotinamide radiosensitizes a number of experimental tumours, and increases blood flow and mean pO2 in some tumours. It has been suggested that nicotinamide reduces tumour interstitial fluid pressure (IFP), thereby reducing transient vessel non-perfusion and acute hypoxia, and radiosensitizing tumours. To test this hypothesis, tumour IFP, transient vessel non-perfusion, and radiosensitivity after nicotinamide administration were examined in the murine carcinoma NT. Nicotinamide at doses of 500 and 1000 mg kg-1 significantly reduced tumour IFP within 20 min of administration, with recovery to control values by 60-80 min; 100 mg kg-1 had no effect. The percentage of previously non-perfused vessels that became perfused 20 min after administering 1000 mg kg-1 of nicotinamide significantly exceeded the percentage that became perfused within 20 min in the absence of nicotinamide. By 90 min after nicotinamide administration, this differential effect was abolished. The correlation in the time courses of reduced IFP and increased vessel perfusion after nicotinamide administration suggest that decreased IFP may accompany vessel reperfusion. However, 1000 mg kg-1 of nicotinamide radiosensitized the NT carcinoma 80 min after administration, whilst no radiosensitization was seen within 10 min. Thus it is unlikely that increased vessel perfusion is the sole mechanism of nicotinamide-induced radiosensitization in this tumour.

Adenocarcinoma↗

PubMed1997

Measurement of tumor oxygenation: a comparison between polarographic needle electrodes and a time-resolved luminescence-based optical sensor.

A novel oxygen sensor which does not rely on electrochemical reduction has been used to measure the oxygenation of the murine sarcoma F in a comparative study with an existing polarographic electrode that is available commercially. The prototype luminescence sensor yielded an oxygen distribution comparable with readings made using a pO2 histograph. The percentage of regions detected that had a pO2 less than 5 mm Hg was 79 and 75 using the Eppendorf pO2 histograph and the luminescence fiber optic sensor, respectively. These values were compatible with a measured radiobiologically hypoxic fraction of 67% in this tumor. The polarographic method detected more regions with a pO2 of 2.5 mm Hg or less (69%) compared with the optical sensor (50%) (P < 0.05). This could reflect differences in the oxygen use of the sensing devices. This initial assessment indicates the potential of a fiber-optic-based oxygen-monitoring system. Such a system should have several advantages including monitoring temporal oxygen changes in a given microregion and use with NMR procedures.

Animals↗

PubMed1997

Targeting gene therapy to cancer: a review.

In recent years the idea of using gene therapy as a modality in the treatment of diseases other than genetically inherited, monogenic disorders has taken root. This is particularly obvious in the field of oncology where currently more than 100 clinical trials have been approved worldwide. This report will summarize some of the exciting progress that has recently been made with respect to both targeting the delivery of potentially therapeutic genes to tumor sites and regulating their expression within the tumor microenvironment. In order to specifically target malignant cells while at the same time sparing normal tissue, cancer gene therapy will need to combine highly selective gene delivery with highly specific gene expression, specific gene product activity, and, possibly, specific drug activation. Although the efficient delivery of DNA to tumor sites remains a formidable task, progress has been made in recent years using both viral (retrovirus, adenovirus, adeno-associated virus) and nonviral (liposomes, gene gun, injection) methods. In this report emphasis will be placed on targeted rather than high-efficiency delivery, although those would need to be combined in the future for effective therapy. To date delivery has been targeted to tumor-specific and tissue-specific antigens, such as epithelial growth factor receptor, c-kit receptor, and folate receptor, and these will be described in some detail. To increase specificity and safety of gene therapy further, the expression of the therapeutic gene needs to be tightly controlled within the target tissue. Targeted gene expression has been analyzed using tissue-specific promoters (breast-, prostate-, and melanoma-specific promoters) and disease-specific promoters (carcinoembryonic antigen, HER-2/neu, Myc-Max response elements, DF3/MUC). Alternatively, expression could be regulated externally with the use of radiation-induced promoters or tetracycline-responsive elements. Another novel possibility that will be discussed is the regulation of therapeutic gene products by tumor-specific gene splicing. Gene expression could also be targeted at conditions specific to the tumor microenvironment, such as glucose deprivation and hypoxia. We have concentrated on hypoxia-targeted gene expression and this report will discuss our progress in detail. Chronic hypoxia occurs in tissue that is more than 100-200 microns away from a functional blood supply. In solid tumors hypoxia is widespread both because cancer cells are more prolific than the invading endothelial cells that make up the blood vessels and because the newly formed blood supply is disorganized. Measurements of oxygen partial pressure in patients' tumors showed a high percentage of severe hypoxia readings (less than 2.5 mmHg), readings not seen in normal tissue. This is a major problem in the treatment of cancer, because hypoxic cells are resistant to radiotherapy and often to chemotherapy. However, severe hypoxia is also a physiological condition specific to tumors, which makes it a potentially exploitable target. We have utilized hypoxia response elements (HRE) derived from the oxygen-regulated phosphoglycerate kinase gene to control gene expression in human tumor cells in vitro and in experimental tumors. The list of genes that have been considered for use in the treatment of cancer is extensive. It includes cytokines and costimulatory cell surface molecules intended to induce an effective systemic immune response against tumor antigens that would not otherwise develop. Other inventive strategies include the use of internally expressed antibodies to target oncogenic proteins (intrabodies) and the use of antisense technology (antisense oligonucleotides, antigenes, and ribozymes). This report will concentrate more on novel genes encoding prodrug activating enzymes, so-called suicide genes (Herpes simplex virus thymidine kinase, Escherichia coli nitroreductase, E. (ABSTRACT TRUNCATED)

Animals↗

PubMed1996

A comparative study of tumour blood flow modification in two rat tumour systems using endothelin-1 and angiotensin II: influence of tumour size on angiotensin II response.

Tumour blood flow modification following i.v. administration of angiotensin II (AT II, 0.19 nmol kg-1 min-1) or endothelin-1 (ET-1, 1 nmol kg-1) was compared in the P22 carcinosarcoma-bearing BD9 rat and the HSN fibrosarcoma-bearing CBH/CBi rat using the tissue uptake of radiolabelled iodoantipyrine. Results were compared with a range of normal tissues. HSN tumour blood flow was unmodified by either peptide, whereas P22 tumour blood flow was unmodified by ET-1 but was reduced to 80% of the control flow by AT II. Both peptides reduced absolute blood flow in the skin overlying the tumour, in contralateral skin, skeletal muscle, kidney and small intestine, whereas blood flow to the brain and heart was significantly increased by ET-1 and unmodified by AT II. Both peptides significantly increased vascular resistance (mean arterial blood pressure / tissue blood flow) in all normal tissues and both tumours, thus demonstrating the existence of vascular receptors for these 2 vasomodifiers, and the capacity of the vessels to respond to receptor activation. Dependency of response on tumour size was examined in the P22 tumour. In contrast to that in small P22 tumours (1.22 +/- 0.06 g), blood flow to large P22 tumours (7.18 +/- 0.25 g) was unmodified by AT II. Vascular resistance was equally increased in both tumour groups, thus illustrating little difference in the vascular response to AT II in the size range examined. Results show that the 2 rat tumours responded directly to ET-1 and AT II, but do not indicate any advantage of ET-1 over AT II in tumour blood flow modification. However, the existence of tumour vascular endothelin receptors suggests that the advent of less toxic and more controllable receptor ligands may make endothelin receptors of value in the modification of tumour blood flow.

Angiotensin II↗