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Experimental Studies |
1 From the Depts of Radiology (S.N.G., M.A., W.L.M., J.C.H., J.B.K.), Medical Oncology (K.E.S.), and Pathology (T.J.), Beth Israel Deaconess Med Ctr, Harvard Med School, 330 Brookline Ave, Boston, MA 02215; Dept of Cancer Biology, Dana Farber Cancer Institute, Boston, Mass (G.D.G.); Dept of Pharmaceutical Sciences, Bouve Coll of Health Sciences, Northeastern Univ, Boston, Mass (A.N.L., V.P.T.); and Dept of Radiology, Massachusetts Gen Hosp, Boston, Mass (G.S.G., E.F.H.). Received Apr 30, 2001; revision requested Jun 14; revision received Jul 30; accepted Sept 7. Supported in part by grants from Radionics. Address correspondence to S.N.G. (e-mail: sgoldber@caregroup.harvard.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: R3230 mammary adenocarcinoma 1.4–1.8-cm- diameter nodules were implanted subcutaneously in 132 female Fischer rats. Initially, tumors were treated with (a) conventional, monopolar RF (mean, 250 mA ± 25 [SD] at 70°C ± 1 for 5 minutes) ablation alone, (b) RF ablation followed by intravenous administration of 1 mg of liposomal doxorubicin, (c) RF ablation followed by intravenous administration of 1 mg of empty liposomes, (d) RF ablation and direct intratumoral administration of liposomal doxorubicin, or (e) no treatment. Subsequently, the dose (0.06–2.00 mg) of liposomal doxorubicin, the timing of administration (3 days before to 3 days after RF ablation), and the time of pathologic examination (0–72 hours after treatment) were varied.
RESULTS: Mean coagulation diameter for treated tumors follows: 6.7 mm ± 0.6, RF ablation alone; 11.1 mm ± 1.5, RF ablation and intravenous administration of empty liposomes (P < .05, compared with RF ablation alone); and 8.4 mm ± 1.1, RF ablation with intratumoral administration of liposomal doxorubicin (P < .05, compared with RF ablation alone). Maximal increased mean coagulation diameter (13.1 mm ± 1.5) was observed with a combination of liposomal doxorubicin and RF ablation (P < .001, for all comparisons). The increased coagulation for combination therapy developed over 48 hours after therapy. Coagulation diameter did not vary with the doxorubicin concentration range and was not dependent on the timing of administration of liposomal doxorubicin from 3 days before to 24 hours after RF ablation.
CONCLUSION: Intravenous administration of liposomal doxorubicin can improve RF ablation, since it increases coagulation diameter in solid tumors compared with RF ablation alone or a combination of RF ablation with administration of empty liposomes.
© RSNA, 2002
Index terms: Animals • Breast neoplasms, therapy, 00.32 • Chemotherapy • Hyperthermia • Radiofrequency (RF) ablation
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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In an attempt to overcome the limitations of current treatment, investigators have begun to experiment with a combination of therapies with RF ablation and chemotherapeutic adjuvants (14–17). In a previous study (16), the intratumoral injection of free unencapsulated doxorubicin into rat tumors significantly increased the region of induced coagulation necrosis compared with that induced with RF ablation alone or with doxorubicin chemotherapy alone. However, the maximal increase seen was only several millimeters, and a very narrow therapeutic window was identified for the timing of the intratumoral doxorubicin injection. Hence, it was postulated that improved methods of chemotherapeutic delivery might further improve this adjuvant combination therapy.
Recent advances in delivery of chemotherapeutic agents include the development of sterically stabilized liposomal carriers for compounds such as doxorubicin (18–20). Touted benefits for the use of these delivery systems (or carriers) include a prolonged circulation time, selective agent delivery through the leaky tumor endothelium, reduced systemic phagocytosis, and accompanying reduced toxicity profiles. Given these potentially advantageous characteristics, this study was conducted to determine whether a combination of RF ablation and a commercially available doxorubicin preparation that is encapsulated into polyethylene glycol–coated liposomes (doxorubicin hydrochloride liposome injection, Doxil; Alza Pharmaceuticals, Palo Alto, Calif) increases tumor destruction compared with RF ablation alone in an animal tumor model.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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Experiments were performed (M.A., J.C.H.) with a well-characterized (14,16,21) established R3230 mammary adenocarcinoma cell line (Ralph Weissleder, MD, PhD, Center for Molecular Imaging Research, Massachusetts General Hospital, Boston). Fresh tumor (approximately 1 cm in diameter) was initially harvested from a live carrier. Within 30 minutes of this tumor explantation, the tumor was homogenized with a tissue grinder (model 23; Kontes Glass, Vineland, NJ) by using an aseptic technique and was suspended in 7 mL of medium (RPMI 1640; INC Biomedicals, Aurora, Ill). In prior control experiments, we documented that this produces a concentration of approximately 1 x 107 tumor cells per 0.1 mL, with greater than 95% cellular viability.
With direct visualization, an 18-gauge needle was used to slowly inject 0.2–0.3 mL of the tumor suspension into the mammary fat pad of 132 female Fischer 344 rats, the strain of animals from which this tumor was initially derived. All animals (mean weight, 150 g ± 10 [SD]) were acquired from a single vendor (Taconic, Germantown, NY) at 8–9 weeks of age. To maximize the usable tumor yield of this model, one tumor was implanted within the mammary fat pad on each side of the abdomen in each animal, for a total of 264 tumor implantations. Animals were monitored, and tumor growth was measured every 3–4 days. Solid nonnecrotic 14–18-mm-diameter tumors depicted by using ultrasonography (US) were used for ablation studies. Tumors were grown for 14–24 days until the desired size was achieved. Although two tumors were implanted in each animal, variation in tumor size growth and in the development of cystic cavitation in larger tumors permitted only one tumor to be used in each animal. Thus, a total of 132 tumors were used in this study.
Overall Experimental Design
The study was performed as four separate experiments. In the first experiment, the effectiveness of a combination of intravenously administered liposomal doxorubicin and RF ablation was explored. In the second experiment, the pathologic changes observed during the time following therapy with a combination of RF ablation and liposomal doxorubicin were compared with the changes following RF ablation alone. In the third experiment, the effect of liposomal doxorubicin dose was studied in tumors being treated with this drug and RF ablation. In the fourth experiment, the effect of altering the timing between administration of chemotherapeutic agents and RF ablation was explored.
Experiment 1: assessment of effectiveness.—The experiment included a total of 52 tumors. Initially, eight tumors each were randomly assigned to each of six groups (n = 48). The groups included (a) RF ablation alone, (b) intravenous liposomal doxorubicin alone (0.5 mL of liposomal doxorubicin; total dose of 1 mg of doxorubicin), (c) intravenous injection of 0.5 mL of the empty liposome carrier, (d) RF ablation followed 15–30 minutes later by intravenous administration of 0.5 mL of liposomal doxorubicin, (e) RF ablation followed 15–30 minutes later by intravenous injection of 0.5 mL of the empty liposome carrier, and (f) no therapy. For these first experiments, the dose of liposomal doxorubicin was selected to contain an amount of doxorubicin (1 mg) previously demonstrated to induce maximum synergy with RF ablation when directly injected into this tumor model (16). Agents were injected slowly into the tail vein with a 27-gauge needle. As an additional control, four tumors were treated with direct intratumoral injection of 0.5 mL of liposomal doxorubicin immediately following RF ablation. Animals were sacrificed 48 hours after the last intervention. Tumors were excised, and pathologic examination was performed as described later.
Experiment 2: assessment of pathologic changes observed over time.—To determine the temporal effects of the combination of therapies that demonstrated the greatest effectiveness (ie, RF ablation and liposomal doxorubicin), an additional 24 tumors were examined. Twelve tumors treated with a combination of RF ablation and liposomal doxorubicin, with RF ablation followed 15–30 minutes later by intravenous administration of 0.5 mL of liposomal doxorubicin, and 12 tumors treated with RF ablation alone were examined immediately (within 15 minutes) and at 24 and 72 hours after therapy (n = 4 in each group). Included in the data analysis were 16 tumors from experiment 1 that had been treated with either a combination of RF ablation and liposomal doxorubicin or RF ablation alone and were analyzed 48 hours after therapy (total, n = 40). As an additional control experiment, four animals with four tumors were sacrificed 120 hours after being treated with RF ablation alone.
Experiment 3: dose effect studies.—The dose effect of the amount of intravenously administered liposomal doxorubicin was assessed (total, n = 20; including eight tumors treated with a 1-mg dose from experiment 1). Four tumors each were treated with 0.06 mg, 0.25 mg, and 2.00 mg of the doxorubicin dose 15–30 minutes after RF ablation. For these experiments, the lower doses of doxorubicin were achieved by diluting the liposomal doxorubicin concentration in physiologic saline to an injection volume of 0.5 mL. For the 2-mg dose, a total of 1 mL of liposomal doxorubicin was administered. For this phase, pathologic analysis was performed 48 hours after RF application.
Experiment 4: effect of altering the time between therapies.—For this last experiment, the time of administration of the liposomal doxorubicin was varied in relation to the RF application from 3 days before to 3 days after RF application (total, n = 48). In addition to the previously studied liposomal doxorubicin administered immediately after RF ablation (n = 8, from experiment 1), eight tumors each were treated with liposomal doxorubicin 72 and 24 hours before RF ablation and 24, 48, and 72 hours after the standardized course of RF ablation (n = 40). For these experiments, 0.5 mL of liposomal doxorubicin (1-mg doxorubicin dose) was administered. Pathologic examination was performed 48 hours after the last intervention.
RF Application
Conventional, monopolar RF was applied (M.A., J.C.H.) by using a 500-kHz RF generator (model 3E; Radionics, Burlington, Mass). To complete the RF circuit, the animal was placed on a standardized metallic grounding pad (Radionics). Contact was ensured by shaving the animal’s back and by liberally using electrolytic contact gel. Initially, the 1-cm tip of a 21-gauge electrically insulated electrode (SMK electrode; Radionics) was placed at the center of the tumor with US guidance. The distal 1-cm tip of this needle was not insulated to permit RF deposition. RF was applied for 5 minutes with the generator output titrated to maintain a mean tip temperature of 70°C ± 1 (90.4 mA ± 25.8; range, 48–160 mA).
This standardized method of RF application has been previously demonstrated to provide reproducible coagulation volume of approximately 50% of the tumor diameter (14,16,22). Thus, RF output was varied from animal to animal to maintain a constant uniform thermal dose of RF energy. A thermocouple at the tip of the RF electrode constantly measured the local ablation temperature, thereby enabling proper generator manipulation. Parameters of the RF ablation procedure, including tip temperature, tissue impedance, and applied current, were recorded at baseline and thereafter at 60-second intervals for the duration of RF application.
Liposome Carrier Construction
According to the manufacturer’s information of 1999 (Alza Pharmaceuticals, Palo Alto, Calif), the vehicle for doxorubicin in the specifically studied liposomal doxorubicin is a liposome that is approximately 100 nm and is coated with methoxypolyethylene glycol, or PEG, which affords steric stabilization. Control empty liposomes, which exactly mimick the lipid composition and content of this particular liposomal doxorubicin preparation, were formulated. All lipids were purchased (Avanti Polar Lipids, Alabaster, Ala). A lipid mixture of 6.38 mg of N-(carbonyl-methoxypolyethyleneglycol 2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine, 19.16 mg of fully hydrogenated soy phosphatidylcholine, and 6.38 mg of cholesterol was prepared by using solutions of individual lipids in organic solvents. Organic solvents were removed with vacuum.
The lipid film obtained was dispersed in 2 mL of 10 mmol/L (10 mM) of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, or HEPES, and 140 mmol/L (140 mM) of sodium chloride at pH 7.4 (HEPES buffered saline; Sigma, St Louis, Mo). Liposomes were formed with manual sequential extrusion of the crude lipid dispersion through 0.4 µm, 0.2 µm, and 0.1 µm polycarbonate filters by using a filter holder (Swindex; Millipore, Bedford, Mass) at 50°C. The lipid dispersion was forced through the filter by using a 0.5-mL syringe (Hamilton, Reno, Nev). Average liposome size was 124 nm (range, 120–160 nm) as verified with dynamic light scattering with a submicron particle size analyzer (Coulter N4 Plus; Beckman Coulter, Miami, Fla). On a physiologic level, this size was not appreciably different from the 108 nm (range, 94–130 nm) measured for the liposomal doxorubicin sample (23).
Pathologic Studies
After each experiment, animals were sacrificed with an overdose (0.2 mL/kg) of pentobarbital sodium (Nembutal; Abbott Laboratories, North Chicago, Ill). Tumors were excised and sectioned, and the extent of visible coagulation at gross pathologic examination was measured with calipers. Coagulation diameter, the longest measurement perpendicular to the inserted electrode (24), was determined by the consensus of two observers (M.A., S.N.G.) who were blinded to the treatment group at the time of measurement and who jointly measured and verified the findings. Apart from hematoxylin-eosin staining, histopathologic studies, with findings interpreted by one author (T.J.), included staining for mitochondrial enzyme activity with incubation of thin representative tissue sections for 30 minutes in 2% 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) (Sigma) at room temperature. This latter test is used to identify irreversible cellular injury during the early stages of RF-induced tissue necrosis (14,16).
Statistical Analysis
For all experiments, coagulation diameter was measured, and results were compared by using routine statistical analysis. All data are provided as the mean ± SD. One-way analysis of variance was performed for the comparisons reported. Pairwise t tests (
= .05, two-tailed test) on the basis of the least square means were subsequently performed only if the overall P value was considered to indicate a statistically significant difference.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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Differences in the type of thermal damage were observed when tumors treated with RF ablation and empty liposomes alone were compared with the tumors treated with RF ablation with or without doxorubicin. In the other treatment groups, RF ablation with or without doxorubicin produced uniform coagulation of one color; however, in the group treated with RF ablation with empty liposomes only (Fig 3a), a peripheral beige-tan zone surrounded the central whitish zone of coagulation. Additionally, for this group, coagulation was incomplete in the outer peripheral 2 mm of coagulated tumor, with streaky patches of TTC activity seen entering this zone. This finding differed from that in the other groups in which the region of coagulation (ie, induced tumor necrosis) at gross pathologic examination was within measurement error (<1 mm) of the results of TTC staining (ie, absent mitochondrial staining) in all cases.
Histopathologic analysis of the tumors treated with both doxorubicin and RF ablation demonstrated three zones, which were similar to those described for intratumoral injection of unencapsulated doxorubicin (Fig 2b). In the center of the tumor were largely intact cells with pyknotic, elongated, stream-like nuclei and dense cytoplasm (pattern A). These changes have been described as heat preservation or an electrocautery effect and have been previously reported (14,25) as a common finding after RF ablation alone. Surrounding this central area was a zone of increased coagulation that manifested frank coagulative necrosis, that is, an absence of nuclei and the presence of only ghost cells (pattern B). This region represented the increase in ablation compared with RF alone. Peripheral to this was normal-appearing, viable tumor (pattern C). In comparison, the coagulated focus in tumors treated with RF ablation predominantly demonstrated pattern A. Histologic abnormalities (combined zone of patterns A and B) corresponded in every case to the regions of absent TTC staining (ie, the region of absent mitochondrial enzyme function) to within a measurement error of less than 1 mm.
For all tumors treated with the empty liposomes and RF ablation, a zone of pattern A changes was seen in the center of the treatment zone. Surrounding this area (ie, in the peripheral 1–2-mm zone of absent mitochondrial enzyme activity) were predominantly pyknotic cells with dense, consolidated nuclei without elongated cellular or nuclear streaming (pattern D), with little frank coagulative necrosis. Additionally, clusters of apparently viable tumor cells were scattered throughout this peripheral coagulation zone (Fig 2b). Untreated controls and tumors treated with only liposomal doxorubicin had occasional scattered tiny (<1-mm) patches of necrosis but were otherwise characteristic of viable tumor throughout their entirety.
Experiment 2: Assessment of Pathologic Changes Observed over Time
For tumors treated with both liposomal doxorubicin and RF ablation therapy, the increase in observed coagulation diameter was progressive to 48 hours after RF ablation. Mean coagulation diameter was 6.6 mm ± 0.5 when animals were sacrificed immediately after ablation (P = .90, compared with that achieved with RF ablation alone) and 10.9 mm ± 1.0 when animals were sacrificed 24 hours after therapy. Histopathologic analysis immediately after RF ablation and liposomal doxorubicin administration revealed only RF ablation–induced coagulation (pattern A). At 24 hours, a combination of coagulative necrosis and dying cells with pyknotic nuclei in the zone surrounding the RF ablation–induced coagulation, similar to pattern D, was observed. Although mean coagulation diameter continued to increase to 48 hours (13.1 mm ± 1.5), no additional increase was observed at 72 hours (13.2 mm ± 0.4, P = .92). At both these times, the entire peripheral zone was composed of frank coagulative necrosis. In comparison, no change in mean coagulation diameter was observed for specimens obtained immediately after and at 24, 48, 72, and 120 hours after RF ablation without adjuvant therapy (6.6 mm ± 0.4, mean coagulation diameter for all groups).
Experiment 3: Dose Studies
In dose studies, with the range of medication studied, which was 0.06–2.00 mg of doxorubicin, the amount of liposomal doxorubicin administered 30 minutes after RF ablation did not significantly influence the overall coagulation diameter (Fig 4) or the histologic findings.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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In this study, the maximum coagulation diameter of 13.1 mm achieved with intravenous administration of liposomal doxorubicin 15–30 minutes after RF ablation was significantly greater than that achieved with direct intratumoral injection of liposomal doxorubicin or that achieved in prior studies (14) in the same model in which only 11.4 mm of coagulation diameter was achieved by using a combination of RF ablation and direct intratumoral injection of unencapsulated doxorubicin (P < .01). In addition to the increase in coagulation diameter observed compared with the coagulation diameter achieved with direct intratumoral injection, the use of an intravenous chemotherapeutic delivery route has several characteristics that would be potentially beneficial for its use in clinical practice. Most importantly, systemic intravenous administration of a chemotherapeutic agent offers a better chance for uniform delivery and deposition to the more peripheral portions of the tumor, compared with intratumoral injection strategies for which there is difficulty in achieving uniform diffusion and distribution of the agent throughout a targeted lesion (26).
The decrease in coagulation with liposomal doxorubicin compared with the coagulation with injection of free unencapsulated doxorubicin can likely be attributed to the decrease in diffusion of the larger liposome through the coagulated tumor tissue. Furthermore, given that the central zone is killed with RF ablation alone, the use of intravenous administration is more likely to provide optimal delivery of agents to the periphery where the synergistic effects of both therapies are needed.
The use of this particular liposomal delivery vehicle for administration of doxorubicin also permitted a greater window for optimal dose timing, which ranged from several days before to 24 hours after RF ablation, compared with direct intratumoral injection for which reduced coagulation was observed for administration of unencapsulated doxorubicin 6 hours after the RF ablation therapy (14). This difference was most pronounced after RF ablation, since a marked decrease in the effectiveness of intratumoral doxorubicin was observed within 6 hours after RF application. The known long intravascular circulating time of these liposomal preparations (19,20), coupled with the known increased vascular permeability of tumors treated with hyperthermia (27,28), is likely responsible for the maintenance of effectiveness for several days after administration. Likewise, it is also possible that the increased window of effectiveness after ablation is owing to the continuous exposure of the thermally damaged cells to doxorubicin rather than to a single exposure of these cells to an intratumoral injected dose.
In addition, several investigators have reported (17,18) preferential and improved doxorubicin uptake, as well as increased intratumoral retention for doxorubicin administered in the liposomal form. Alternatively, different mechanisms, such as the composition of the agents administered, may be responsible for the increases in observed coagulation, which will be explained later.
Findings in the experiments in this study also demonstrated increased tumor destruction when the empty liposomal carrier was administered in conjunction with RF heating. Although the effect was less pronounced and patchier than that observed when doxorubicin was administered, findings in this study suggest that the lipids and/or the polyethylene glycol coating that comprises the liposomal carrier are likely to have antitumoral activity when combined with RF heating. Findings of prior studies (29–31) demonstrated increased free-radical generation when lipids were administered in the presence of lower hyperthermic temperatures (41°C–45°C), and thus free-radical-mediated cytotoxic effects may be responsible for the increased coagulation.
Although the true mechanism of action requires further elucidation, it is likely that this observation can be further optimized and exploited through the careful study of the composition and size of future liposomal preparations. Regardless, the total increase in coagulation diameter observed with the combination of RF ablation and liposomal doxorubicin was not owing to the liposomes alone, because necrosis in the zone of increased coagulation was patchier and incomplete in the absence of doxorubicin.
The processes governing the increase in coagulation are complex and likely multifactorial. Monsky et al (17) demonstrated a sevenfold increase in doxorubicin deposition at 24 hours in RF ablation–treated R3230 rat breast tumors, compared with control unablated tumors in the same animals. They, therefore, postulated that hyperemia increased liposomal deposition in the zone surrounding the coagulation zone that had been treated with RF ablation. Thus, a component of the increased coagulation diameter observed is likely the increased delivery of doxorubicin to the peripheral zone of increased tumor destruction.
Such increases in delivery may also account for the relatively low doses of liposomal doxorubicin required to observe an effect compared with the reduced coagulation diameter observed with RF ablation combined with central intratumoral injection of doxorubicin. It is likely that it is more difficult to achieve sufficient doses of chemotherapeutic agents in the peripheral zone, which cannot be coagulated with RF ablation alone, when one relies on drug diffusion through the tumor from a central intratumoral injection rather than from intravascular delivery.
Dose-dependent differences in coagulation diameter were not observed with the dose range (0.06–2.00 mg of doxorubicin) of liposomal doxorubicin used in this study. This differs from the dose-dependent response curve (6.7–11.0 mm of coagulation diameter) observed for intratumoral injection of similar quantities of free unencapsulated doxorubicin in this model (16). While findings in this previous study (16) conclusively demonstrated synergism between RF heating and unencapsulated intratumoral doxorubicin, in view of the prior discussion, the newer results of this study suggest that very little doxorubicin may be needed to potentiate synergistic tumor destruction. One reason, which could also account for the lack of effect observed with liposomal doxorubicin or unencapsulated doxorubicin alone, is that the cell line used for the study was relatively resistant to doxorubicin, owing to a multidrug–resistant membrane protein that under normal conditions rapidly clears intracellular doxorubicin (32). RF heating could damage this pump and allow intracellular doxorubicin accumulation.
Alternatively, synergistic effects between the RF heating, the doxorubicin, and the additional lipid may very well reduce the amount of chemotherapeutic drug necessary to achieve cytotoxic effects (29). To help answer these questions, quantitation studies will be necessary to document the amount of doxorubicin truly delivered. This information will be particularly useful when researchers attempt to determine the doses of doxorubicin necessary to achieve optimal tumor destruction in clinical practice.
Future directions include the optimization of this liposomal doxorubicin preparation for clinical use. Clearly, confirmation of these findings in studies of other tumor types is warranted. Fortunately, the agent used in this study is both commercially available and already known to have some clinical effectiveness in the treatment of hepatoma and of neoplasms of the breast, ovary, and of other organs (33–35). Thus, a pilot clinical study with use of this agent in conjunction with RF ablation should be considered at this time. A better understanding of the underlying mechanisms through which synergistic effectiveness is achieved is also required to permit optimization of the most efficient liposomal chemotherapy system.
Components that must be studied include not only the composition, coating, charge, and size of the liposome but also the chemotherapeutic agent used. Additional optimization of the RF ablation protocol when used in conjunction with liposomal doxorubicin will also be required. Although thermal dosimetry curves are well known for RF heating alone (ie, that 4–6 minutes of heating at 50°C–55°C is required to induce coagulation) (22), these curves may be sufficiently altered by the presence of the liposomal doxorubicin so as to require different settings for optimal ablation.
Key limitations of this study include the limited generalization of results given the tumor model studied, the size of the ablated foci, the RF ablation technique, and the doxorubicin doses selected. Although this model was selected because it is a well-characterized, vascular, solid adenocarcinoma (14,21), it is possible that results will vary with other tumor types (ie, hepatocellular carcinoma) and in other orthotopic tumor sites (ie, the liver). Furthermore, while the 70°C tip temperature for RF application was optimal in this model, as it permitted the demonstration of synergy between the two methods, with alternative thermal ablation protocols destruction of the entire 1.5-cm tumor without combination therapy would have been possible. Hence, the size of the tumor model in this study precluded the ability to detect differences with higher RF tip temperatures. Additionally, it is extremely difficult to accurately assess overall volumetric changes in induced coagulation from extrapolation of a single diameter measurement.
Likewise, given these concerns, extrapolation of these results to larger more clinically relevant tumors must be made with caution. Nevertheless, findings in this study permit relative comparisons to be made and strongly support the validity of the overall approach of combining RF ablation and chemotherapy. Another limitation of this study is that only the short-term effects of a combination of RF ablation and liposomal doxorubicin therapy were measured, with the aim of assessing the effects of adjuvant liposomal doxorubicin on acute RF ablation–induced coagulation or tumor destruction. Because this was the primary end point of this study, the full effect of combination therapy may not have been fully assessed. Whereas findings of this and previous studies (16) have shown virtually no acute toxicity to doxorubicin alone in this model, toxicity is possible, and further anticipated study may demonstrate additional more chronic synergistic effects between the two therapies.
Practical application: Intravenous administration of a single dose of adjuvant liposomal doxorubicin can increase the extent of coagulation necrosis induced with RF ablation compared with that induced with either therapy alone or with RF ablation and direct intratumoral injection of liposomal doxorubicin in an animal tumor model. Thus, this clinically feasible technique could potentially improve minimally invasive strategies for ablating focal neoplasms of the liver, breast, and other organs in humans.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, S.N.G.; study concepts, S.N.G., G.D.G., J.B.K., V.P.T.; study design, S.N.G., K.E.S., W.L.M., J.B.K, G.D.G., V.P.T.; literature research, S.N.G., G.D.G., W.L.M.; experimental studies, S.N.G., J.C.H., M.A., A.N.L.; data acquisition, S.N.G., A.N.L., M.A., J.C.H., T.J., J.B.K.; data analysis/interpretation, S.N.G., G.S.G., M.A., T.J., J.B.K.; statistical analysis, S.N.G., G.S.G., E.F.H.; manuscript preparation, S.N.G., V.P.T.; manuscript definition of intellectual content, S.N.G., G.D.G., G.S.G., J.B.K.; manuscript editing, S.N.G., G.D.G., G.S.G., K.E.S., J.B.K., W.L.M., V.P.T.; manuscript revision/review and final version approval, all authors.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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G. D'Ippolito, M. Ahmed, G. D. Girnun, K. E. Stuart, J. B. Kruskal, E. F. Halpern, and S. N. Goldberg Percutaneous Tumor Ablation: Reduced Tumor Growth with Combined Radio-frequency Ablation and Liposomal Doxorubicin in a Rat Breast Tumor Model Radiology, July 1, 2003; 228(1): 112 - 118. [Abstract] [Full Text] [PDF]
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W. L. Monsky, J. B. Kruskal, A. N. Lukyanov, G. D. Girnun, M. Ahmed, G. S. Gazelle, J. C. Huertas, K. E. Stuart, V. P. Torchilin, and S. N. Goldberg Radio-frequency Ablation Increases Intratumoral Liposomal Doxorubicin Accumulation in a Rat Breast Tumor Model Radiology, September 1, 2002; 224(3): 823 - 829. [Abstract] [Full Text] [PDF]
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S. N. Goldberg, I. R. Kamel, J. B. Kruskal, K. Reynolds, W. L. Monsky, K. E. Stuart, M. Ahmed, and V. Raptopoulos Radiofrequency Ablation of Hepatic Tumors: Increased Tumor Destruction with Adjuvant Liposomal Doxorubicin Therapy Am. J. Roentgenol., July 1, 2002; 179(1): 93 - 101. [Abstract] [Full Text] [PDF]
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