| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Regular Articles |
1 University of Louvain Medical School, Unit of Pharmacology and Therapeutics (FATH 5349); 2 Cardiovascular Pathology Unit; 3 Biomedical Magnetic Resonance Unit and Medicinal Chemistry and Radiopharmacy Unit; and 4 Radiobiology and Radioprotection Unit, Brussels, Belgium
 |
ABSTRACT |
|---|
 Top ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Here, we showed that isolated tumor arterioles mounted in a pressure myograph have the ability, contrary to size-matched healthy arterioles, to contract in response to a transluminal pressure increase. This myogenic tone was exquisitely dependent on the endothelin-1 pathway because it was completely abolished by the selective endothelin receptor A (ETA) antagonist BQ123. This selectivity was additionally supported by the large increase in endothelin-1 abundance in tumors and the higher density of the ETA receptors in tumor vessels. We also documented by using laser Doppler microprobes and imaging that administration of the ETA antagonist led to a significant increase in tumor blood flow, whereas the perfusion in control healthy tissue was not altered. Finally, we provided evidence that acute administration of the ETA antagonist could significantly stimulate tumor oxygenation, as determined by electron paramagnetic resonance oximetry, and increase the efficacy of low-dose, clinically relevant fractionated radiotherapy.
Thus, blocking the tumor-selective increase in the vascular endothelin-1/ETA pathway led us to unravel an important reserve of vasorelaxation that can be exploited to selectively increase tumor response to radiotherapy.
|
INTRODUCTION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
We and others have reported that drugs like nitric oxide donors (10
, 11)
, nicotinamide (12)
, bradykinin agonist (13)
, and insulin (14)
, but also radiations and chemotherapeutic agents themselves (15, 16, 17)
, could modulate tumor blood flow, oxygenation, and permeability, thereby optimizing associated antitumor treatments. The validity of these adjuvant approaches to conventional chemo- and radiotherapy was usually verified a posteriori by documenting a better tumor response with very limited insights on the mechanisms of the tumor selectivity. Conversely, studies that did not look for a gain in treatment efficacy have identified the existence of tumor-specific vascular reactivity to various products including endothelin (18)
, endothelin agonist (19)
, angiotensin (20
, 21) , noradrenaline (22)
, hemoglobin A (23)
, and tumor necrosis factor 
(24)
.
We reasoned that the identification of vasomodulatory pathways truly selective of the tumor vasculature could arise from the ex vivo comparison of the intrinsic pharmacological reactivity of vessels issued either from tumors or from the tumor-hosting tissues. Indeed, the variety of chemokines and cytokines released by tumor cells are known to trigger regulatory processes within the tumor vasculature leading to phenotypic shift including escape from immunosurveillance and adaptation to hypoxia (2 , 25 , 26) . Therefore, it was very likely that the tumor microenvironment could also, directly or indirectly, induce profound alterations in the tumor vessel reactivity. Accordingly, using a myograph (originally dedicated to study the physiopathology of normal arterioles), we reported recently that the acetylcholine-induced nitric oxide-mediated vasodilation was dramatically altered in tumor arterioles (15) . Also, in the same study, we documented how ionizing radiations by reversing the lack of NO-mediated response of tumor vessels could increase the sensitivity of the tumor to further X-ray fractions (15) .
In the current study, our reflection started from the growing evidence that endothelin-1 production is increased in many tumor types where it plays crucial roles in proliferation and angiogenesis (27, 28, 29) . In these studies, however, there was no mention of the powerful vasoconstrictive effects of endothelin-1 (ET-1) and its potential action on the contractile tone of tumor vessels. Indeed, although ET-1 can induce vasodilation through activation of the endothelin receptor B (ETB), a powerful vasoconstriction is obtained when ET-1 interacts with the endothelin receptors A and B (ETA and ETB) located on smooth muscle cells. In this study, we therefore asked ourselves whether the tumor production of ET-1 could influence local vascular tone and whether blocking ET-1 signaling could have an impact on tumor blood flow and thereby be exploited to promote conventional antitumor therapy.
|
MATERIALS AND METHODS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
). The tumor diameters were tracked with an electronic caliper. When the tumor diameter reached 4.0 ± 0.5 mm, mice were sacrificed or randomly assigned to a treatment group. When indicated, they received an i.p. injection of the selective ETA antagonist BQ123 (0.5, 1, and 2 mg/kg; Sigma, Bornem, Belgium) or saline alone. Each procedure was approved by the local authorities according to national animal care regulations.
|
Myograph Assays.
Tumor saphenous arterioles and size-matched arterioles from healthy mice were dissected under a stereoscopic microscope and mounted on a 110P pressure myograph (DMT, Aarhus, Denmark). No macroscopic differences were detectable between the tumor and control arterioles (diameters of 284 ± 14 and 299 ± 17 µm, respectively; P > 0.1). Changes in the outer diameters were tracked and measured with the Myoview software (DMT). To evaluate the myogenic tone, isolated arterioles were left to recover for 45–60 min in no-flow condition (20 mm Hg; 37.5°C). Then, the pressure was increased by steps of 20 mm Hg (that were maintained for 15 min to allow arteriole response). For each pressure step, the active vessel diameter was determined in physiological salt solution buffer (NaCl 119 mM, KCl 4.7 mM, NaHCO3 25 mM, KH2PO4 1.18 mM, MgSO4 1.17 mM, EDTA 0.026 mM, glucose 5.5 mM, and CaCl2 1.6 mM); then the passive diameter of the same arteriole was measured in CaCl2-deprived physiological salt solution supplemented with 10 µM sodium nitroprusside and 2 mM EGTA. In some experiments, the active diameter was determined after a 60-min preincubation in the calcium-containing physiological salt solution buffer with BQ123 (1 µM).
For the establishment of the ET-1 dose-response curve, isolated arterioles were left to recover at physiological pressure for 45–60 min in no-flow condition in physiological salt solution medium (60 mm Hg, 37.5°C); additive doses of ET-1 (Sigma) were then delivered in the bathing medium. For each vessel used in this study, the ability of the vessels to contract upon application of a depolarizing KCl solution was verified at the end of the experiment and compared with a similar contraction performed at the very beginning of the experiment. If these two contractions differed by >10%, the experiment was disregarded.
Tumor Blood Flow Monitoring.
Tumor perfusion was measured with a Laser Doppler imager (Moor Instruments) and with Laser Doppler microprobes (Oxyflo; Oxford Optronix). Briefly, for the Laser Doppler imaging measurements, mice were anesthetized and fur was removed from the limbs using a depilatory cream. They were placed on a heating pad (37°C) to minimize variations in temperature. The average perfusions of the tumor-bearing leg and of the control leg were evaluated on the basis of colored histogram pixels. For the Oxyflo measurements, fiber-optic microprobes (Laser Doppler + thermocouple) were introduced into the tumor. Back scattering measurements were used to validate the absence of movement artifacts. A 10-min baseline of stable recordings was obtained before treatment administration through the catheterized tail vein; data were collected continuously at a sampling frequency of 20 Hz.
Electron Paramagnetic Resonance (EPR) Oximetry.
This real-time, O2-nonconsuming technique was used to track the changes in pO2 induced by BQ123 administration. EPR oximetry relies on the oxygen-dependent broadening of the EPR linewidth of a paramagnetic oxygen sensor preimplanted in the tumor. Accordingly, 50 µl of a suspension (100 mg/ml) of the O2-sensitive probe (charcoal wood powder, CX0670–1; EM Science, Gibbstown, NJ) were injected in the center of the tumor 24 h before X-ray irradiation, as described previously and validated (10
, 14
, 15) . The tumors of anesthetized mice were placed in the center of the surface coil. EPR spectra were recorded using an EPR spectrometer (Magnettech, Berlin, Germany) with a low frequency microwave bridge operating at 1.1 GHz and extended loop resonator.
Radiotherapy and Tumor Measurements.
Anesthetized TLT tumor-bearing mice were irradiated using the RT-250 device (Philips) for a dose delivery of 0.76 Gy/min. Mice were shielded with lead except for a 3-cm-diameter circular field where the tumor was centered. When indicated, mice received an i.p. injection of 1 mg/kg BQ123 or saline alone, 45-min before each dose delivery. Tumor-bearing and control legs were daily measured with an electronic caliper, the difference corresponding to the tumor diameter. Mean regrowth delays refer to the doubling of the tumor diameters.
Statistical Analyses.
Data are reported as mean ± SE; Student’s t test or two way ANOVA were used where appropriate. To determine synergism, we compared tumor doubling times using a nonparametric Mann-Whitney analysis; a generalized linear model with two-way ANOVA was also applied and led to similar results.
|
RESULTS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
). As shown in Fig. 1, B–D
, the different tumors were found to produce large amounts of ET-1 that were detectable both inside the tumor cells and in the extracellular space. Very low amounts of ET-1 were found in the healthy surrounding muscular tissues (see Fig. 1, B and C
) and in the necrotic core of the tumor (see Fig. 1D
). Importantly, the co-opted tumor vasculature was strongly labeled, revealing a 13-fold increase (P < 0.05; n = 15) in ET-1 in the vessel wall when compared with control size-matched arterioles (Fig. 1, E and F)
.
Differential Reactivity of Tumor Arterioles to ET-1.
To evaluate the vasomodulatory effects of the increased ET-1 concentrations in tumor arterioles, we isolated TLT-co-opted arterioles (see Fig. 1G
) and size-matched arterioles from healthy animals. These arterioles were mounted on a pressure myograph, and after pressurization and equilibration, exposed to increasing doses of ET-1. In arterioles from healthy mice, low ET-1 concentrations (10–13-10–10 M) were ineffective, whereas higher doses (10–9-10–7 M) dose-dependently constricted the vessels (Fig. 2A)
. By contrast, tumor-co-opted arterioles contracted with ET-1 concentrations as low as 10–11 M (Fig. 2A)
and reached a maximum at 10–8 M ET-1 (the maximum contraction was obtained at 10–7 M ET-1 in control vessels). Calculated EC50s were 0.40 nM and 2.01 nM (P < 0.05; n = 5) in tumor and in size-matched healthy arterioles, respectively. Immunoblots performed on carefully microdissected arterioles (cleaned from surrounding tissues) also revealed that the density of ETA (e.g., the ET-1 receptor mediating vasoconstriction) was increased by 5-fold in co-opted vessels versus healthy arterioles (Fig. 2B)
. Interestingly, when using total lysates from tumors, we failed to detect ETA receptor by immunoblotting suggesting a weaker density of this receptor in tumor cells than in vascular cells.
|
, and immunohistochemistry revealed that most of the ETB signal was concentrated in the endothelial layer of the arterioles (data not shown).
Tumor Arterioles Exhibit a Myogenic Tone Sensitive to an ETA Antagonist.
Because we have identified that tumor arterioles are chronically exposed to large amounts of ET-1 (see Fig. 1
) and are (remain) hyper-responsive to ET-1 (see Fig. 2
), we next examined whether intrinsic features of tumor arterioles were under the tonic control of this pathway. Accordingly, we examined the presence in tumor arterioles of a differential myogenic tone (i.e., the ability of arterioles to contract when the intraluminal pressure increases; Ref. 35
). Myogenic vasoconstriction is, indeed, thought to provide a level of basal tone that enables arterioles to respond to neurohumoral stimuli with the appropriate changes in vessel diameter.
Using a pressure myograph, we examined the response of isolated tumor-co-opted and control arterioles to step-by-step increases of the luminal pressure. Accordingly, the changes in the active diameter (measured in calcium-containing medium) and in the passive diameter (determined in a medium devoid of calcium) were consecutively tracked for each arteriole. In healthy mice, no myogenic tone was observed: both the active and the passive diameters increased similarly when the pressure raised (Fig. 3A)
. By contrast, tumor-co-opted arterioles were able to respond to the pressure increase by a vasoconstriction (detected as a lesser vasodilation) in calcium-containing, but not in calcium-deprived medium (Fig. 3B)
, thereby acknowledging the existence of an intrinsic myogenic tone.
|
; P < 0.01). In fact, the active diameter curve under ETA inhibition (Fig. 3B
, black triangles) was not different from the passive diameter curve (Fig. 3B
, open circles). As a control, we also demonstrated that ETA inhibition left unaffected the active diameter of size-matched arterioles from healthy mice (Fig. 3A)
.
ETA Inhibition Triggers a Tumor-Specific Increase in Blood Flow and Oxygenation.
We then investigated whether the BQ123-mediated abrogation of the myogenic tone (as elicited ex vivo) was correlated with an increased tumor perfusion in vivo. Accordingly, TLT tumor-bearing mice received a bolus i.p. injection of 1 mg/kg BQ123 or saline, and the perfusion of both the tumor-bearing and the control legs was monitored using a Laser Doppler imaging system. In BQ123-treated mice, we consistently observed an important increase in the blood flow of the tumor-bearing leg (Fig. 4A
, top panel, white circle), whereas the healthy opposite leg failed to show any significant changes in perfusion (Fig. 4A
, top panel, white arrows). Importantly, isovolemic saline i.p. injection barely increased the basal perfusion in the tumor-bearing leg (see Fig. 4A
, lower panels, and Fig. 4B
). We also used Laser Doppler needle probes directly introduced in the tumors to validate the results obtained with the imager. A similar increase in blood flow was observed after BQ123 administration (Fig. 4C)
.
|
shows that 60 min after administration of the ETA antagonist (but not of the saline solution), the tumor oxygenation was significantly increased over basal level (+174%; P < 0.01; n = 7). Of note, the measured pO2 corresponds to the mean value in a tumor volume of ±10 mm3 (i.e., the volume of charcoal dispersion as determined by histology) and, therefore, does not preclude more dramatic variations in specific regions of the tumor.
ETA Inhibition Radiosensitizes Tumors.
In various tumor models, improved tumor perfusion is associated with a net increase in tumor oxygenation, which may be exploited to increase the effectiveness of radiotherapy (10
, 14
, 15)
. Therefore, we tested the hypothesis that ETA inhibition could radiosensitize tumors. Accordingly, we daily determined the tumor diameters of mice receiving (or not) fractionated radiotherapy, and evaluated the effects of BQ123 administered 45 min before each radiation fraction (to have the maximum increase in pO2 at the time of X-ray exposure; see Fig. 4
). As shown in Fig. 5, A and B
, and Table 1
, when fractionated radiotherapy (5 x 2 Gy and 2 x 6 Gy) was combined to the BQ123 pretreatment, the overall benefit on tumor growth retardation was higher than the sum of the effects of the two treatments administered separately (P < 0.01; n = 8–11). Similar data were obtained with two other tumor models, namely Lewis Lung carcinoma tumors and Fibrosarcoma-II (data not shown); both tumor types overexpress ET-1 (see Fig. 1, C and D
) and arterioles issued from the former were shown to also exhibit myogenic tone (data not shown).
|
|
. Although limitations in BQ123 availability precluded additional exploration, it is noteworthy that with the higher dose (2 mg/kg), two mice (of 6) were in remission 5 weeks after treatment (see Fig. 5
legend). Of note, at each dose used in this study, BQ123 (two or five i.p. injections) only slightly restrained tumor growth by itself (see Fig. 5, A and B
, and Table 1
). |
DISCUSSION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The existence of a myogenic tone is almost impossible to quantitatively appreciate in vivo, because it requires the tracking of changes in vascular resistance in response to an increase in transmural pressure. Here, we used a unique experimental model specifically dedicated to this purpose, e.g., microdissected tumor vessels mounted in a myograph allowing step increases in pressure. This ex vivo mode of detection should not mask the in vivo importance of the myogenic tone in the autoregulation of blood flow by arterioles. Indeed, in normal vascular beds, spontaneous (oscillating) and pressure-induced variations in the muscular tone, known as vasomotion (36) and myogenic tone (35 , 37) , respectively, offer to the tissue circulation the intrinsic ability to maintain a relatively constant blood flow despite variations in blood pressure. In the case of tumors, such autoregulatory mechanisms are very likely to be needed to face the constant remodeling of tumor vascularization. Here, we have identified the implication of ET-1 as a trigger of the myogenic tone of tumor vessels. The signal transduction appears to transit through the smooth muscle-specific ETA receptor (the abundance of which is increased by 5-fold in tumor arterioles) because BQ123 (a specific ETA antagonist) completely abrogated the pressure-dependent development of vascular tone by tumor arterioles.
That the implication of the ET-1/ETA pathway in the development of a myogenic tone is specific of the tumor vascular bed was additionally authenticated by the increase in blood flow observed after treatment with BQ123 in tumors but not in control tissue from the same mouse (see Fig. 4
). Interestingly, ET-1 has been shown to exert its vasoconstrictive effects when applied from the adventitial side of the vessels (38
, 39)
, which in the case of ET-1-producing tumors is very likely to account for local (specific) effects. Moreover, we found an increased vascular ETA expression in tumor arterioles, which is also very likely to contribute to the observed myogenic tone. Exaggerated production of ET-1 has been reported previously to mediate similar increase in myogenic constriction in cerebral arteries exposed to oxidized low-density lipoprotein (40)
and arterioles isolated from hypertensive rats (41)
. Together with our study, these reports indicate that pathological states such as atherosclerosis, hypertension, and tumor growth can transform vessels devoid of myogenic tone in vessels prone to blood flow autoregulation. Of note, the phenotype shift can be considered as yet more dramatic for tumor vessels, because we used vessels with an external diameter of 300 µm, which is higher than the usually accepted diameter for resistance arterioles (<170 µm).
The observed ex vivo and in vivo vasodilating effects of BQ123 imply that functional smooth muscle cells are the target of this drug in tumor vessels. The presence of smooth muscle cells or mural cells on vessels is viewed as a hallmark of maturation (42) , and it is generally accepted that month/year-old human tumors are more likely to recruit pericytes on a larger proportion of their vasculature (versus rapidly growing mouse tumors). This suggests that functional tumor vessels constitute a yet more attractive target for selective vasomodulatory treatments in humans. Although additional studies are required to evaluate how our data can be extrapolated in the clinics, the tumor vessel selectivity of ETA antagonist treatment, as identified in mouse, offers strong bases for the establishment of an adjuvant strategy aiming to increase the effectiveness of conventional antitumor treatments (by acting on tumor blood flow and oxygenation). Adequately scheduled combination of these latter approaches with antiangiogenic drugs certainly represents a very attractive area of investigation for future cancer therapy development.
In this study, we provide evidence that acute administration of BQ123 (i.e., i.p. injection 45 min before local tumor irradiation) exerts profound effects on the efficacy of low-dose radiotherapy (5 x 2 Gy and 2 x 6 Gy). Importantly, these effects were shown to be ETA antagonist dose-dependent and obtained using clinically relevant schemes of fractionated radiation administration; a complete remission was even obtained in mice treated with the highest BQ123 dose tested in this study. Although a small effect of BQ123 alone was observed in the absence of irradiation (probably attributable to the antiproliferative effect of this drug; Refs. 27, 28, 29
), the combination of both irradiation and the ETA antagonist led to a synergistic effect in both irradiation protocols, increasing the tumor regrowth delay by >50% over the additive effects (see Table 1
). We additionally documented that the radiosensitizing effects of BQ123 were very likely to arise from the increase in tumor oxygenation directly associated with the elevation in tumor blood flow (see Fig. 4
).
The growing amounts of reports documenting the increase in ET-1 expression in various human tumors (reviewed in Ref. 29 ) indicate that this approach of blocking the ETA receptor opens very interesting perspectives in the treatment of many tumor types. Moreover, although we have here only documented the impact of modulating the ET-1/ETA transduction pathway for radiotherapy, it can be postulated that chemotherapy could also take advantage of a better tumor perfusion and drug delivery. Importantly, this study also confirmed the potential of the myograph assay to identify the existence of a differential reactivity in arterioles issued from animal tumors characterized by different environments (see also Refs. 15 , 33 ). This ex vivo pharmacological evaluation of tumor vessels could easily be extended to vessels isolated from human tumor biopsies, and thereby could lead to new insights on "provascular" adjuvant treatments susceptible to improve conventional anticancer treatments.
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
Note:P. Sonveaux and C. Dessy contributed equally to this work.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Requests for reprints: University of Louvain Medical School, Unit of Pharmacology and Therapeutics (FATH 5349), Brussels B-1200, Belgium. Phone: 32-2-764-5349; Fax: 32-2-764-9322; E-mail: feron{at}mint.ucl.ac.be
Received 5/ 8/03. Revised 2/18/04. Accepted 2/26/04.
|
REFERENCES |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  F. Frerart, P. Sonveaux, G. Rath, A. Smoos, A. Meqor, N. Charlier, B. F. Jordan, J. Saliez, A. Noel, C. Dessy, et al. The Acidic Tumor Microenvironment Promotes the Reconversion of Nitrite into Nitric Oxide: Towards a New and Safe Radiosensitizing Strategy Clin. Cancer Res., May 1, 2008; 14(9): 2768 - 2774. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. DeWever, F. Frerart, C. Bouzin, C. Baudelet, R. Ansiaux, P. Sonveaux, B. Gallez, C. Dessy, and O. Feron Caveolin-1 Is Critical for the Maturation of Tumor Blood Vessels through the Regulation of Both Endothelial Tube Formation and Mural Cell Recruitment Am. J. Pathol., November 1, 2007; 171(5): 1619 - 1628. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. A. Lee, E. B. Baek, K. S. Park, H. J. Jung, J. I. Kim, S. J. Kim, and Y. E Earm Mechanosensitive nonselective cation channel facilitation by endothelin-1 is regulated by protein kinase C in arterial myocytes Cardiovasc Res, November 1, 2007; 76(2): 224 - 235. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 O. Tredan, C. M. Galmarini, K. Patel, and I. F. Tannock Drug Resistance and the Solid Tumor Microenvironment J Natl Cancer Inst, October 3, 2007; 99(19): 1441 - 1454. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Sonveaux, I. I. Lobysheva, O. Feron, and T. J. McMahon Transport and Peripheral Bioactivities of Nitrogen Oxides Carried by Red Blood Cell Hemoglobin: Role in Oxygen Delivery Physiology, April 1, 2007; 22(2): 97 - 112. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. W. Dewhirst, I. C. Navia, D. M. Brizel, C. Willett, and T. W. Secomb Multiple Etiologies of Tumor Hypoxia Require Multifaceted Solutions Clin. Cancer Res., January 15, 2007; 13(2): 375 - 377. [Full Text] [PDF]
|
|
|
|
 |
|
 P. Martinive, J. De Wever, C. Bouzin, C. Baudelet, P. Sonveaux, V. Gregoire, B. Gallez, and O. Feron Reversal of temporal and spatial heterogeneities in tumor perfusion identifies the tumor vascular tone as a tunable variable to improve drug delivery. Mol. Cancer Ther., June 1, 2006; 5(6): 1620 - 1627. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Schwencke, R. C. Braun-Dullaeus, C. Wunderlich, and R. H. Strasser Caveolae and caveolin in transmembrane signaling: Implications for human disease Cardiovasc Res, April 1, 2006; 70(1): 42 - 49. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Ansiaux, C. Baudelet, G. O. Cron, J. Segers, C. Dessy, P. Martinive, J. De Wever, J. Verrax, V. Wauthier, N. Beghein, et al. Botulinum Toxin Potentiates Cancer Radiotherapy and Chemotherapy Clin. Cancer Res., February 15, 2006; 12(4): 1276 - 1283. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |
) and from transplantable liver tumor-bearing mice (
) were mounted on a pressure myograph and exposed to increasing doses of ET-1. Results are expressed as percentage of the maximal contraction obtained with 10–7 M ET-1. Sigmoidal fitting shows that the dose/effect curves for healthy and tumor vessels (R2 = 0.91 and 0.98, respectively) were significantly different (P < 0.01; n = 5); note that some SE are smaller than symbols; bars, ±SE. B, pools of arterioles from healthy and transplantable liver tumor-bearing mice were lysed (to obtain enough material) and were immunoblotted with endothelin receptor A (ETA) and endothelin receptor B (ETB) antibodies. Shown are representative immunoblots and a bar graph depicting the densitometric analysis of two different immunoblots (2 pools of 10 arterioles/condition).
; n = 10) or not (passive diameter, 
; n = 10). Saphenous arterioles were dissected from healthy mice (A) or were isolated from transplantable liver tumor (after co-option; B). In some experiments, arterioles were preincubated with the endothelin receptor A antagonist BQ123 (1 µM) in the calcium-containing medium (active diameter, 
; n = 3); ns, not significantly different; **, P < 0.01 between the indicated dose/effect curves); bars, ±SD.
; n = 7) or BQ123 (