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Published online before print May 23, 2006, 10.1148/radiol.2401050788
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(Radiology 2006;240:82-89.)
© RSNA, 2006

Experimental Studies

Improved Tumor Destruction with Arsenic Trioxide and Radiofrequency Ablation in Three Animal Models1

Andrew Hines-Peralta, MD, Vikas Sukhatme, MD, PhD, Meredith Regan, ScD, Sabina Signoretti, PhD, Zheng-jun Liu, MD and S. Nahum Goldberg, MD

1 From the Laboratory for Minimally Invasive Tumor Therapy, Department of Radiology (A.H., Z.j.L., S.N.G.), and Department of Medicine, Renal Division (V.S.), Beth Israel Deaconess Medical Center, 1 Deaconess Rd, WCC 308B, Boston, MA 02215; Department of Biostatistics and Computational Biology, Dana Farber Cancer Institute and the Renal Cancer Program of the Dana Farber/Harvard Cancer Center, Boston, Mass (M.R.); Department of Medical Oncology, Dana Farber Cancer Institute, Boston, Mass (S.S.); and Harvard Medical School, Boston, Mass (A.H., V.S., M.R., S.S., Z.j.L., S.N.G.). Received May 9, 2005; revision requested July 7; revision received August 18; final version accepted September 14. Supported by National Cancer Institute Dana Farber/Harvard Cancer Center Renal Cancer SPORE grant 1 P50 CA10194-01. Address correspondence to S.N.G. (e-mail: sgoldber{at}caregroup.harvard.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Purpose: To assess the extent of tumor blood flow reduction that is achievable with arsenic trioxide (As2O3) and the effect of As2O3 on radiofrequency (RF)-induced coagulation.

Materials and Methods: All animal protocols and experiments were approved by an institutional animal care and use committee before the start of the study. Experiments were conducted in three tumor models: intrarenal VX2 sarcoma in 27 rabbits, RCC 786-0 human renal cell carcinoma in 24 nude mice, and R3230 mammary adenocarcinoma in 40 rats. One dose (0–7.5 mg per kilogram of body weight) of As2O3 was administered (intraperitoneally in rodents, intravenously in rabbits) 1, 6, or 24 hours before standardized RF ablation, which was performed by using a 1-cm active tip, with mean temperatures of 70°C ± 2 (standard deviation) for 5 minutes in rodents and 90°C ± 2 for 6 minutes in rabbits. Laser Doppler flowmetry was used to quantify changes in blood flow, which were compared with diameters of induced tumor coagulation. Comparisons between groups were performed by using Student t tests or analysis of variance. The strengths of correlations between As2O3, tumor blood flow, and RF-induced coagulation were assessed by using linear and higher-order regression models and reported as R2 computations.

Results: Administration of As2O3 significantly (P < .05) reduced blood flow and increased tumor destruction in all tumor models. In VX2 sarcoma tumors, 1 mg/kg As2O3 reduced mean tumor blood flow to 46% ± 13 of the normal value. The mean resultant coagulation (1.1 cm ± 0.1) was significantly greater than that achieved with RF ablation alone (0.6 cm ± 0.1, P < .01). In RCC 786-0 and R3230 tumors, 5 mg/kg As2O3 reduced mean tumor blood flow to 57% ± 6 and 46% ± 6 of normal, respectively, increasing mean ablation extent to 0.8 cm ± 0.1 for both models, compared with those achieved with the control treatment (0.6 cm ± 0.1 and 0.5 cm ± 0.1, respectively; P < .05 for both comparisons). Dose studies revealed correlations between drug dose, tumor blood flow, and RF-induced coagulation in all three tumor models (R2 = 0.60–0.79). Maximal RF synergy was observed 1 hour after As2O3 administration.

Conclusion: As2O3 administration represents a transient noninvasive method of reducing tumor blood flow during RF ablation, enabling larger zones of tumor destruction in multiple tumor models.

© RSNA, 2006


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Image-guided radiofrequency (RF) tumor ablation induces tumor necrosis by means of direct heating of tumor cells to temperatures above 50°C for short durations (<15 minutes) with use of needle electrodes (1). This minimally invasive procedure continues to gain attention as a viable treatment option for the focal destruction of solid tumors because it has potential advantages compared with surgical resection, including reduced morbidity, outpatient therapy, and ability to treat poor surgical candidates (2,3). Initially, RF ablation was used to treat hepatic malignancies because of the substantial morbidity associated with hepatic resection (3–7). The favorable outcomes of using RF ablation, however, have now fueled the expansion of this technique to include treatment of neoplasms at other sites, including kidneys (8), breasts (9), bone (10), and lungs (11).

A major obstacle to the wide-scale adoption of this potentially advantageous treatment option is the inability to reliably create adequate volumes of complete tumor destruction (2). RF ablation can be effective for the destruction of small (<3 cm) tumors (12), but success in destroying index tumors larger than 3.5 cm in diameter has been less robust (4–7).

The difficulty in treating moderate to large tumors is often attributed to the powerful heat-sink effect of tumor blood flow, which draws heat away from the tumor site (13,14). Because tumor destruction with RF relies on the exposure of the entire tumor volume to cytotoxic temperatures that induce tumor coagulation and necrosis, perfusion-mediated tissue cooling can substantially limit the size and uniformity of tumor destruction (13,14). For this reason, the treatment of even small vascular tumors, such as centrally located renal cell carcinoma, with RF ablation may be challenging (8). Accordingly, surgical and angiographic techniques that decrease tumor blood flow, such as the Pringle maneuver (ie, vascular clamping of portal inflow at surgery) and chemoembolization, have been shown to yield significantly larger volumes of cellular destruction (15,16). These maneuvers, however, are disadvantageous in that they require invasive procedures, which negate some of the purported benefit of minimally invasive therapy. Thus, concomitant administration of a minimally invasive adjuvant antivascular pharmaceutical agent that suppresses the heat-sink effect of tumor blood flow would be of considerable clinical interest.

Arsenic trioxide has been shown to have antivascular properties (17–19). It has been proposed as a possible pharmaceutical alternative that potentiates RF ablation by reducing tumor blood flow (20). The purpose of this study was to assess the extent of tumor blood flow reduction that is achievable with arsenic trioxide and the effect of arsenic trioxide on RF-induced coagulation.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Overall Experimental Design
Experiments were conducted in three tumor models: (a) VX2 sarcoma in the kidneys of 27 New Zealand white rabbits (Milbrook Breeding Laboratories, Amherst, Mass), (b) RCC 786-0 human renal cell carcinoma in the subcutaneous tissue of 24 nude mice (Fisher Scientific, Pittsburgh, Pa), and (c) R3230 adenocarcinoma in the mammary tissue of 40 rats (Fisher Scientific). One tumor was implanted in each animal. In a blinded fashion, a single bolus dose (0–7.5 mg per kilogram of body weight) of arsenic trioxide (Sigma Pharmaceuticals, St Louis, Mo) was administered by two authors (A.H. and Z.j.L., with 3 and 8 years experience, respectively). These authors quantified the resultant decreases in intratumoral blood flow by using laser Doppler flowmetry 1 hour after the arsenic trioxide administration. They then performed RF ablation by using a 1-cm active tip with a mean temperature of 70°C ± 2 (standard deviation) for 6 minutes in the rodents and by using this tip with a mean temperature of 90°C ± 2 for 5 minutes in the rabbits.

In addition, a second cohort of animals that received 5 mg/kg arsenic trioxide was randomly assigned to be treated with RF ablation 6 or 24 hours after the administration for assessment of the dependency of arsenic effectiveness for RF ablation on time. The diameters of coagulation were measured in a blinded fashion (by A.H., Z.j.L., S.S., and S.N.G.), compared, and then correlated with tumor blood flow reduction and arsenic trioxide administration.

Animal Models and Tumor Preparation
All animal protocols were approved by our institutional animal care and use committee.

Intrarenal VX2 sarcoma in New Zealand white rabbits.—The in vivo rabbit intrarenal VX2 carcinoma model has been used previously to determine the effects of minimally invasive tumor ablation and has well-characterized tumor vascularity (20). Tumors were harvested and implanted, as described by Horkan et al (20), by two authors (A.H. and Z.j.L.). Tumor growth was monitored with ultrasonography (US) every 3–4 days after the implantation (by Z.j.L., with 8 years experience with this technique). Solid nonnecrotic tumors 1.5–2.0 cm in diameter (approximate incubation, 10–14 days) were used. The rabbits were intubated before all RF ablations. Their heart rate, pulse oximetry values, and body temperature were monitored throughout. The kidney was accessed percutaneously for tumor implantation and by means of open laparotomy for blood flow monitoring and RF ablation.

Intramammary R3230 adenocarcinoma in Fisher 344 rats.—R3230 mammary adenocarcinoma is a well-characterized cell line previously used to identify changes in tumor coagulation from RF ablation (21). Animal care and tumor preparation were performed (by A.H. and Z.j.L.) as described by Goldberg et al (21). The animals were monitored every 3–4 days to measure tumor growth. Solid nonnecrotic tumors (as determined at US) 14–18 mm in diameter were used for the ablation studies. Tumors were grown for 14–24 days until the desired size was achieved.

Subcutaneous RCC 786-0 human renal cell carcinoma in nude mice.—This model was chosen for experimentation because of the marked interest in RF ablation for treatment of renal cell carcinoma (8). Tumor harvesting was performed as described earlier, with the exception that tumor resuspension was performed in 4 mL of RPMI 1640 medium (INC Biomedicals, Aurora, Ill) to obtain adequate tumor concentration. For tumor implantation, female nude mice with a mean weight of 25 g ± 5 (standard deviation) were injected subcutaneously with 2 x 106 cells (approximately 0.1 mL by volume). Solid nonnecrotic tumors (as determined at US) 10–12 mm in diameter were used for the ablation studies. All animals were anesthetized with ketamine and xylazine and monitored by institutional animal care and use committee–approved veterinary personnel during all procedures.

Arsenic Trioxide Administration
Arsenic trioxide was constituted and diluted in phosphate-buffered saline to a concentration of 1–10 mg/mL. Phosphate-buffered saline by itself was used as the control agent. For the rat R3230 (40 tumors, five per dose group) and mouse RCC 786-0 (24 tumors, three per dose group) experiments, a one-time arsenic trioxide dose was administered intraperitoneally (A.H., Z.j.L.) in six blinded and randomized dose groups: (a) 0 mg/kg (control), (b) 1.00 mg/kg, (c) 2.50 mg/kg, (d) 3.75 mg/kg, (e) 5.00 mg/kg, and (f) 7.50 mg/kg. For the rabbit VX2 tumor (n = 27, four tumors in all except one dose group, in which there were three tumors) experiments, arsenic trioxide was administered intravenously (A.H., Z.j.L.) in five blinded and randomized dose groups: (a) 0 mg/kg (control), (b) 0.2 mg/kg, (c) 1.0 mg/kg, (d) 2.5 mg/kg, and (e) 5.0 mg/kg. In our experience, the median lethal dose of arsenic trioxide in rat R3230 and nude mouse RCC 786-0 tumor models has been approximately 15 mg/kg. For this reason, doses higher than 7.5 mg/kg were not administered in these two models and doses higher than 5 mg/kg were not administered in the rabbit intrarenal VX2 model. One rabbit randomly assigned to receive 0.2 mg/kg died during anesthesia induction and did not receive arsenic trioxide or RF ablation; thus, there were four tumors in all except the 0.2 mg/kg group, in which there were three tumors.

In a separate cohort of animals, all three tumor models were randomly assigned to be treated with a one-time arsenic trioxide dose of 5 mg/kg either 6 or 24 hours before RF ablation. We compared these results with those of the 5 mg/kg arsenic trioxide administration at 1 hour before RF ablation to establish the duration of the effect of arsenic trioxide on RF-induced coagulation.

Blood Flow Measurement
Tumor blood flow was measured by using laser Doppler flowmetry (A.H. and Z.j.L., both with 3 years laser Doppler flowmetry experience), a technique that has been validated for accurate measurement of tumor microcirculatory blood flow, including that in VX2 and other tumor models (22). The microcirculatory blood flow in the tumors and in the renal parenchyma was measured as described by Horkan et al (20). Continuous laser Doppler flowmetry recordings were initiated 15 minutes before the arsenic trioxide administration to obtain baseline perfusion measurements. Blood flow was again recorded 1 hour after the arsenic trioxide administration, immediately before RF ablation. Laser Doppler flowmetry was not performed in the animals that were treated with RF ablation 6 or 24 hours after arsenic trioxide administration.

RF Ablation
A 500-kHz RF generator (CC-1; ValleyLab, Boulder, Colo) was used to apply conventional monopolar RF energy. This generator was selected because it is available for clinical use and is capable of monitoring impedance, tip temperature, and other parameters of the ablation. RF energy was applied for 6 minutes in the rabbits and for 5 minutes in rodents, with the generator output titrated to maintain a designated tip temperature: a mean temperature of 90°C ± 2 (standard deviation) for the rabbits and of 70°C ± 2 for the rodents. RF ablation was performed, as described previously by Horkan et al (20), by two authors (A.H. and Z.j.L., with 3 and 8 years experience with this technique, respectively).

Histopathologic Examinations
The animals were euthanized immediately after RF ablation with pentobarbital (Fatal Plus, 0.25 mL/kg; Vortech Pharmaceuticals, Dearborn, Mich). Staining was performed to assess mitochondrial enzyme activity by incubating thin representative tissue sections in 2% 2,3,5-triphenyltetrazolium chloride (Fisher Scientific, Fairlawn, NJ) for 30 minutes. The absence of mitochondrial enzyme activity has been shown to accurately reflect irreversible cellular injury induced by percutaneous tumor ablation (23). With this assessment method, viable tissue with intact mitochondrial enzyme activity is stained red, while ablated tissue does not have a red color. Gross measurements of tumor destruction were performed on both the 2,3,5-triphenyltetrazolium chloride–stained and the nonstained sections, and the extent of visible coagulation was measured with calipers. The coagulation diameter (ie, longest measurement perpendicular to the inserted electrode) in all tissue samples was determined in a blinded fashion by three authors (A.H., Z.j.L., and S.S., with 3, 8, and 10 years experience, respectively). Histopathologic examinations of all samples were also performed (by S.S.) by using hematoxylin-eosin staining. All pathologic and histopathologic analyses were performed at the Beth Israel Deaconess/Dana Farber Cancer Institute Renal Cancer Program Core.

Statistical Analyses
For all experiments, every treatment protocol involved at least three animals and the results were reported as means ± standard deviations. In each animal, one tumor was implanted and used for analysis. The coagulation diameter perpendicular to the RF electrode (ie, on the short axis) and the blood flow were considered outcome measures for all statistical analyses (23). The Student t test (two-tailed) was used for comparisons between two separate groups, while a paired t test was used for comparisons of paired data—for example, the comparison between tumor blood flow and normal parenchyma blood flow. A P value of .05 indicated a significant difference. Analysis of variance was performed with statistical software (Origin 6.1; OriginLab, Northampton, Mass) to assess significant differences when three or more groups were being compared.

Multivariable regression analyses, including linear and higher-order models, were performed by using Origin 6.1, with arsenic trioxide dose and tumor blood flow used as predictive variables of coagulation diameter. Higher-order regressions were performed by using the outcome measure (coagulation diameter or blood flow) as the dependent variable and predicting the results by using a function of the independent variable (ie, arsenic trioxide dose). The strengths of these best-fit regression curves were reported as R2 computations. All statistical analyses were performed by three authors (M.R., S.N.G., and A.H., with 10, 12, and 3 years experience, respectively).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Effect of Arsenic Trioxide on Blood Flow
In all three tumor models, dose-dependent decreases in tumor blood flow were observed after arsenic trioxide administration. One hour after arsenic trioxide administration in the rabbits with implanted intrarenal VX2 tumors, laser Doppler flowmetry revealed a potent effect of 1.0 mg/kg and higher doses. With the 1.0 mg/kg dose, the mean tumor blood flow decreased significantly to 46% ± 13 (standard deviation) of the baseline value (P < .01 for comparison with control dose value); this was significantly greater than the blood flow decreases observed in the normal kidney parenchyma (to mean of 62% ± 15 of baseline, P < .05) (Fig 1). Decreases in blood flow were best described as an exponential decay function (for tumor, R2 = 0.80; for normal kidney parenchyma, R2 = 0.55), with no continued blood flow decreases observed at higher doses (Fig 1). With the control dose, blood flow decreased to a mean of 94% ± 7 of the baseline for the tumors and to a mean of 93% ± 11 of the baseline for the normal kidney parenchyma, owing to the effects of general anesthesia.


Figure 1
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  		Figure 1: Graph illustrates arsenic trioxide dose versus blood flow in intrarenal VX2 tumors and normal kidneys. Preferential dose-dependent reduction in the tumor vasculature blood flow was noted.

 
In the R3230 mammary adenocarcinomas in rats, significant decreases in blood flow following a sigmoidal dose response curve (R2 = 0.88) were observed: Mean tumor blood flow decreased to 46% ± 6 of the baseline after administration of 5.0 mg/kg arsenic trioxide (P < .01 for comparison with control) (Fig 2). Blood flow decreases in the RCC 786-0 tumors in nude mice followed a similar sigmoidal response curve (R2 = 0.97): Mean tumor blood flow decreased to 57% ± 6 of the baseline after administration of 5.0 mg/kg arsenic trioxide (P < .01 for comparison with control). Mean blood flow in the control R3230 and RCC tumors did not decrease significantly (to 93% ± 7 and 94% ± 6, respectively).


Figure 2
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  		Figure 2: Graph illustrates arsenic trioxide dose versus tumor blood flow in the three tumor models. Increasing the arsenic trioxide dose led to a progressive decrease in blood flow in all tumor models. Differences in the sensitivity of blood flow to arsenic trioxide were observed on a tumor-by-tumor basis. RCC = renal cell carcinoma.

 
Effect of Arsenic Trioxide on Tumor Coagulation
The extent of RF-induced tumor coagulation was significantly greater in all three tumor models after arsenic trioxide administration. Dose-dependent increases in RF-induced coagulation that corresponded to the dose-related changes in blood flow were observed (Fig 3). In the intrarenal VX2 tumors, the synergy of arsenic trioxide and RF-induced coagulation was observed at doses of 1.0 mg/kg and higher: The mean diameter of coagulation was 1.1 cm ± 0.1, almost double that achieved with the control dose: 0.6 cm ± 0.1 (P < .01). This logarithmic relationship (R2 = 0.70) indicated that further gains in coagulation with the higher doses were only nominal.


Figure 3
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  		Figure 3: Graph illustrates tumor coagulation (assessed in terms of coagulation diameter) induced by RF ablation performed 1 hour after arsenic trioxide administration. Dose-dependent curves were demonstrated in all three tumor models, with varying sensitivity to arsenic trioxide dose. RCC = renal cell carcinoma.

 
In the R3230 tumors, arsenic trioxide administration led to significant gains in the extent of RF-induced coagulation at concentrations near 5.0 mg/kg: The mean diameter of coagulation was 0.8 cm ± 0.1, which was significantly greater than that achieved with the control dose: 0.5 cm ± 0.1 (P < .05). The mean coagulation diameter measured after administration of 5 mg/kg arsenic trioxide in the mice with RCC 786-0 tumors, 0.8 cm ± 0.1, also was significantly greater than that achieved with the control dose: 0.6 cm ± 0.1 (P < .05) (Fig 4). In the R3230 and RCC tumors, arsenic trioxide had a sigmoidal relationship with RF-induced coagulation (R2 = 0.75 for both R3230 and RCC 786-0 tumors).


Figure 4
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  		Figure 4: Gross pathologic specimens of RF-induced coagulation in RCC 786-0 tumors treated with RF ablation only (left) and with RF ablation and arsenic trioxide (right). Arrows point to areas where a significantly (P < .05) larger zone of coagulation resulted from RF ablation performed 1 hour after administration of 5 mg/kg arsenic trioxide.

 
Correlation between Blood Flow Decreases and Coagulation Increases
Regression analyses revealed linear correlations between blood flow changes and coagulation in all three tumor models (for VX2 tumors, R2 = 0.75; for R3230 tumors, R2 = 0.79; for RCC 786-0 tumors, R2 = 0.60). In addition, these regression curves exhibited nearly identical slopes (Fig 5), with only small differences in amplitude. Specifically, for the R3230 and RCC 786-0 tumors, both of which were treated with RF ablation at a mean tip temperature of 70°C ± 2, the regression curves, including slopes and amplitudes, were nearly identical (P > .8, goodness-of-fit {chi}2 analysis). In the VX2 tumors, for which RF ablation was performed at a higher tip temperature (mean, 90°C ± 2), the amplitude (ie, coagulation) was greater, but with a slope (ie, relationship to blood flow) of 6.2 x 10–3, similar to the slopes for the R3230 (5.8 x 10–3) and RCC 786-0 (4.3 x 10–3) tumors (Fig 5).


Figure 5
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  		Figure 5: Graph illustrates tumor blood flow versus RF-induced tumor coagulation diameter. A linear correlation between these variables was demonstrated in all tumor models. RCC = renal cell carcinoma.

 
Effect of Arsenic Trioxide Duration
The greatest effect of arsenic trioxide with RF ablation was observed when the agent was administered 1 hour before the ablation (Fig 6). After 6 hours, the combined effect of arsenic trioxide and RF ablation began to diminish, with smaller zones of RF-induced coagulation created compared with those created 1 hour after the arsenic trioxide administration (Fig 6). Twenty-four hours after the arsenic trioxide administration, the extent of RF-induced coagulation returned to nearly the baseline level.


Figure 6
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  		Figure 6: Graph illustrates the effect of the interval between arsenic trioxide administration and RF ablation on the resultant coagulation diameter. The maximal effect was seen 1 hour after the arsenic trioxide administration; this finding suggests a transient nature of the synergistic effect. RCC = renal cell carcinoma.

 
Histopathologic Findings
The appearance of the intrarenal VX2 tumors treated with a 5 mg/kg or lower dose of arsenic trioxide—including those examined 1, 6, and 24 hours after administration of the agent—did not differ substantially from that of the control tumors (those treated with 0 mg/kg) on the hematoxylin-eosin–stained sections. Specifically, no evidence of reduced tumor vascularity, intravascular thrombosis, or foci of increased necrosis was seen in the tumor regions subjected to arsenic trioxide therapy (Fig 7). Similarly, the hematoxylin-eosin–stained sections of R3230 and RCC 786-0 tumors treated with arsenic trioxide doses of 5 mg/kg or less did not reveal appreciable histologic differences from the control samples. Stained sections of R3230 and RCC tumors treated with a 10 mg/kg dose showed areas of central necrosis 24 hours after the agent was administered, as previously described (17).


Figure 7
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  		Figure 7: Histopathologic sections of RCC 786-0 and VX2 tumors. Similar degrees of tumor vascularity are seen in, A, control agent–treated, and, B, 5 mg/kg arsenic trioxide–treated RCC 786-0 tumors 24 hours after treatment. C, Section of VX2 tumor treated with 5 mg/kg arsenic trioxide also shows numerous patent blood vessels (arrows) 6 hours after arsenic trioxide administration. (Hematoxylin-eosin stain; original magnification, x20.)

 
The histopathologic samples of all RF-ablated tumors that were pretreated with up to 5 mg/kg arsenic trioxide revealed tissue changes that were consistent with the 2,3,5-triphenyltetrazolium chloride–stained coagulation in the RF ablation–treated zone only, with normal-appearing tumor tissue beyond this zone. These samples did not differ substantially from the samples of tumors treated with RF ablation alone, except in the diameter of central coagulation; these findings are consistent with the gross-specimen observations (Fig 4).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 References
 
The results reported in our study confirm the hypothesis proposed in earlier studies (20) that arsenic trioxide can substantially enhance RF ablation. Multiple mechanisms underlying this effect have been described and include apoptotic activation in leukemia cells and induced preferential vascular shutdown in solid malignancies (17,18,24). Arsenic also has antivascular and thermosensitizing properties that have prompted investigations of the use of this element in combination with radiation and hyperthermia (18,19,25).

The results of our experiments establish a clear dose-dependent synergy between arsenic trioxide and RF-induced coagulation in three tumor models—a finding that, to our knowledge, had not yet been reported. Furthermore, our work demonstrates an acute but transient nature of arsenic-triggered decreases in tumor blood flow, as documented with laser Doppler flowmetry. This transient decrease was evidenced by the linear associations between tumor blood flow reduction and RF-induced coagulation that were nearly superimposable in two of the three tumor models. Since RF ablation of the VX2 tumors was performed at a mean tip temperature of 90°C ± 2, as opposed to the mean tip temperature of 70°C ± 2 used to treat the RCC 786-0 and R3230 tumors, greater coagulation was expected and was observed. These linear relationships of similar slope reinforce prior reports documenting a direct relationship between reduced perfusion-mediated tissue cooling and extent of RF-induced coagulation (13,16,20). Also, the tight correlations suggest that a primary mechanism of the arsenic potentiation of RF-induced tumor destruction is probably related to the potent antivascular properties of this element.

Nonetheless, the mechanisms responsible for the transient decreases in tumor blood perfusion observed with arsenic trioxide administration are not clearly understood and require further study. In our study, we observed central tumor necrosis after administration of 10 mg/kg arsenic trioxide, which is consistent with previous study findings demonstrating the inducement of central necrosis and vessel thrombosis (17,18). Given that the effects we observed at lower concentrations were transient and maximal at 1 hour—when no tissue necrosis or vessel thrombosis was noted—other physiologic mechanisms may be responsible for the observed effects. Consequently, arsenic may regulate tumor blood flow in a manner that has not yet been characterized, the elucidation of which may shed light in the field of tumor perfusion.

Our statistical analyses were limited by the small sample sizes of the tumor groups due to animal research restrictions. Because of the large number of groups needed to establish the duration and dose dependency of arsenic effectiveness with RF ablation, we often used a small number of animals (three to five) to establish initial mean values and value variances. Given the inherent variance in biologic systems, larger group sizes are necessary to refine and further clarify the gross trends identified in our study.

Our study was limited also by the lack of an additional method of confirming the changes in blood flow registered with laser Doppler flowmetry. The laser Doppler flowmeter measures changes in blood flow at a single site in the tumor, although these changes may be variable in a given tumor. The global tumor effects of arsenic remain unclear. Furthermore, laser Doppler flowmetry is not adequate for observing changes in blood flow for longer than several hours, because animal movement can cause relocation of the Doppler site and consequently unreliable results. For these reasons, a secondary method of blood flow analysis such as computed tomography or magnetic resonance perfusion imaging would be helpful for assessing the changes in blood flow that occur more than 1 hour after the arsenic trioxide administration.

The one-time arsenic trioxide dose that is appropriate for human investigations is not yet known. In our experimental studies, the optimal dose ranged between 1 and 5 mg/kg and was probably dependent on both the tumor type and the animal model. Furthermore, translational dosing from animals to humans can be further complicated by additional factors, including surface area–to-weight ratio, renal clearance, fat composition, and other variables (26). For treatment of leukemia, the approved dose regimen is 0.15 mg/kg arsenic trioxide administered daily for several weeks; in terms of treatment of solid tumors, however, initial investigation has involved assessment of only a one-time dose (26). It is unknown whether smaller arsenic concentrations administered daily affect tumor blood flow, but the accumulation of arsenic trioxide and other agents composed of arsenic in tissue suggests that this might be a worthy investigation (27). The investigation of dose regimens similar to those already approved also may be prudent in facilitating a rapid adoption of this potentially beneficial therapy for clinical use.

Practical applications: The identification of transient and perhaps reversible pathways that regulate tumor blood flow is desired for increasing the coagulation induced by not only RF ablation but also other image-guided thermal ablation therapies (2). The preferential reduction in tumor blood flow, as opposed to the blood flow in the surrounding parenchyma, as observed in the intrarenal VX2 tumors in our study, may further enhance RF ablation when greater blood flow in the surrounding tissue might help prevent unwanted thermal injury to adjacent structures. Arsenic trioxide therapy may be useful also when it is combined with other drugs such as doxorubicin, the antitumor effects of which are improved with hypoxia (28). In addition, further elucidation of the underlying mechanism of this apparently preferential reduction in blood flow may enable the development of new drug targets for some cancers.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
References
 


   FOOTNOTES
 

Abbreviations: RF = radiofrequency

Authors stated no financial relationship to disclose.

Author contributions: Guarantor of integrity of entire study, S.N.G.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, A.H., V.S., S.N.G.; experimental studies, A.H., V.S., S.S., Z.j.L., S.N.G.; statistical analysis, A.H., M.R., Z.j.L., S.N.G.; and manuscript editing, A.H., V.S., M.R., S.N.G.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 

  1. Goldberg SN, Dupuy DE. Image-guided radiofrequency tumor ablation. I. Challenges and opportunities. J Vasc Interv Radiol 2001;12:1021–1032.
  2. Dupuy DE, Goldberg SN. Image-guided radiofrequency tumor ablation. II. Challenges and opportunities. J Vasc Interv Radiol 2001;12:1135–1148.[Medline]
  3. Curley SA, Izzo F, Delrio P, et al. Radiofrequency ablation of unresectable primary and metastatic hepatic malignancies: results in 123 patients. Ann Surg 1999;230:1–8.[CrossRef][Medline]
  4. Solbiati L, Livraghi T, Goldberg SN, et al. Percutaneous radio-frequency ablation of hepatic metastases from colorectal cancer: long-term results in 117 patients. Radiology 2001;221(1):159–166.[Abstract/Free Full Text]
  5. Lencioni R, Cioni D, Crocetti L, et al. Early-stage hepatocellular carcinoma in patients with cirrhosis: long-term results of percutaneous image-guided radiofrequency ablation. Radiology 2005;234(3):961–967.[Abstract/Free Full Text]
  6. Tateishi R, Shiina S, Teratani T, et al. Percutaneous radiofrequency ablation for hepatocellular carcinoma: an analysis of 1000 cases. Cancer 2005;103(6):1201–1209.[CrossRef][Medline]
  7. Livraghi T, Meloni F, Goldberg SN, Lazzaroni S, Solbiati L, Gazelle GS. Hepatocellular carcinoma: radio-frequency ablation of medium and large lesions. Radiology 2000;214:761–768.[Abstract/Free Full Text]
  8. Hines-Peralta A, Goldberg SN. Review of radiofrequency ablation for renal cell carcinoma. Clin Cancer Res 2004;10(18 pt 2):6328S–6334S.[Abstract/Free Full Text]
  9. Jeffrey SS, Birdwell RL, Ikeda DM, et al. Radiofrequency ablation of breast cancer: first report of an emerging technology. Arch Surg 1999;134:1064–1068.[Abstract/Free Full Text]
  10. Dupuy DE, Safran H, Mayo-Smith WW, Goldberg SN. Radiofrequency ablation of painful osseous metastases [abstract]. Radiology 1998;209(P):389.
  11. Sewell PE Jr, Vance RB, Wang YD. Assessing radiofrequency ablation of non-small cell lung cancer with positron emission tomography (PET) [abstract]. Radiology 2000;217(P):334.
  12. Lu DS, Yu NC, Raman SS, et al. Radiofrequency ablation of hepatocellular carcinoma: treatment success as defined by histologic examination of the explanted liver. Radiology 2005;234(3):954–960.[Abstract/Free Full Text]
  13. Chang I, Mikityansky I, Wray-Cahen D, Pritchard WF, Karanian JW, Wood BJ. Effects of perfusion on radiofrequency ablation in swine kidneys. Radiology 2004;231(2):500–505.[Abstract/Free Full Text]
  14. Goldberg SN, Hahn PF, Tanabe KK, et al. Percutaneous radiofrequency tissue ablation: does perfusion-mediated tissue cooling limit coagulation necrosis? J Vasc Interv Radiol 1998;9(1):101–111.[Medline]
  15. Yamasaki T, Kurokawa F, Shirahashi H, Kusano N, Hironaka K, Okita K. Percutaneous radiofrequency ablation therapy for patients with hepatocellular carcinoma during occlusion of hepatic blood flow: comparison with standard percutaneous radiofrequency ablation therapy. Cancer 2002;95(11):2353–2360.[CrossRef][Medline]
  16. Shen P, Fleming S, Westcott C, Challa V. Laparoscopic radiofrequency ablation of the liver in proximity to major vasculature: effect of the Pringle maneuver. J Surg Oncol 2003;83(1):36–41.[CrossRef][Medline]
  17. Lew YS, Brown SL, Griffin RJ, Song CW, Kim JH. Arsenic trioxide causes selective necrosis in solid murine tumors by vascular shutdown. Cancer Res 1999;59:6033–6037.[Abstract/Free Full Text]
  18. Griffin RJ, Lee SH, Rood KL, et al. Use of arsenic trioxide as an antivascular and thermosensitizing agent in solid tumors. Neoplasia 2000;2:555–560.[CrossRef][Medline]
  19. Griffin RJ, Monzen H, Williams BW, Park H, Lee SH, Song CW. Arsenic trioxide induces selective tumour vascular damage via oxidative stress and increases thermosensitivity of tumours. Int J Hyperthermia 2003;19(6):575–589.[CrossRef][Medline]
  20. Horkan C, Ahmed M, Liu Z, et al. Radiofrequency ablation: effect of pharmacologic modulation of hepatic and renal blood flow on coagulation diameter in a VX2 tumor model. J Vasc Interv Radiol 2004;15(3):269–274.[Medline]
  21. Goldberg SN, Girnan GD, Lukyanov AN, et al. Percutaneous tumor ablation: increased necrosis with combined radiofrequency and intravenous liposomal doxorubicin in a rat breast tumor model. Radiology 2002;222:797–804.[Abstract/Free Full Text]
  22. Yanagibashi K, Imamura M, Tobe T. Evaluation of microcirculation in the tumor-bearing liver of rabbits by laser-Doppler flowmetry. Nippon Geka Hokan 1992;61:3–18.[Medline]
  23. Liszczak TM, Hedley-Whyte ET, Adams JF, et al. Limitations of tetrazolium salts in delineating infarcted brain. Acta Neuropathol (Berl) 1984;65:150–157.[CrossRef][Medline]
  24. Roboz GJ, Dias S, Lam G, et al. Arsenic trioxide induces dose- and time-dependent apoptosis of endothelium and may exert an antileukemic effect via inhibition of angiogenesis. Blood 2000;96(4):1525–1530.[Abstract/Free Full Text]
  25. Lew YS, Kolozsvary A, Brown SL, Kim JH. Synergistic interaction with arsenic trioxide and fractionated radiation in locally advanced murine tumor. Cancer Res 2002;62(15):4202–4205.[Abstract/Free Full Text]
  26. Shen ZX, Chen GQ, Ni JH, et al. Use of arsenic trioxide (As2O3) in the treatment of acute promyelocytic leukemia (APL). II. Clinical efficacy and pharmacokinetics in relapsed patients. Blood 1997;89:3354–3360.
  27. Lin CJ, Wu MH, Hsueh YM, Sun SS, Cheng AL. Tissue distribution of arsenic species in rabbits after single and multiple parenteral administration of arsenic trioxide: tissue accumulation and the reversibility after washout are tissue-selective. Cancer Chemother Pharmacol 2005;55(2):170–178.[CrossRef][Medline]
  28. Kruskal JB, Hlatky L, Hahnfeldt P, Teramoto K, Stokes KR, Clouse ME. In vivo and in vitro analysis of the effectiveness of doxorubicin combined with temporary arterial occlusion in liver tumors. J Vasc Interv Radiol 1993;4(6):741–747.[Medline]



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