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Ann Thorac Surg 2002;74:893-898
© 2002 The Society of Thoracic Surgeons
a Department of Thoracic and Vascular Surgery, University of Antwerp, Antwerp, Belgium
b Department of Oncology and Radiotherapy, Catholic University of Leuven, Leuven, Belgium
* Address reprint requests to Dr Van Schil, MD, Department of Thoracic and Vascular Surgery, University Hospital Antwerp (UZA), Wilrijkstraat 10, B-2650 Edegem, Belgium
e-mail: paul.van.schil{at}uza.be
Presented at the Thirty-eighth Annual Meeting of The Society of Thoracic Surgeons, Fort Launderdale, FL, Jan 2830, 2002.
| Abstract |
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Methods. ILuP with 0.5 mg MN was performed in Wag- Rij rats for 30 minutes either by a single-pass system (SP) (fixed concentration) (n = 10) or by reperfusion (RP) (bolus injection) (n = 10). In a separate experiment, rats were perfused with blood as the perfusate. In a third experiment, tumor levels were compared between SP, RP, or intravenous therapy with a dose of 0.5 mg. For induction of pulmonary metastases, 0.5 x106 single adenocarcinoma cells were injected intravenously and therapy was given on day 30. For comparison of drug concentrations, unpaired Students t test was applied. Statistical significance was accepted at p less than 0.05.
Results. Lung perfusion studies were succesfully performed without systemic leakage. Temperature of perfusate and rats was 34°C to 37°C. A significantly higher hematocrit (mean 27.9) compared with buffered starch (mean 2.5) did not result in higher MN lung levels or lower wet-to-dry ratio. Tumor levels were significantly higher after ILuP compared with intravenous therapy. However, no difference in tumor and lung levels was seen between single-pass and reperfusion.
Conclusions. Both ILuP techniques resulted in significantly higher MN lung levels than after intravenous therapy. Because no difference was seen between single-pass and recirculating perfusion, MN can be injected as a bolus into the closed perfusion circuit.
| Introduction |
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| Material and methods |
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Tumor
The CC531S tumor cell line was used for assessment of MN levels in lung metastases. This cell line was derived from a chemically induced adenocarcinoma of the colon of a WAG rat. CC531S was cultured in complete medium and maintained by serial passage. Complete medium consisted of RPMI 1640 medium, supplemented with 10% heat-activated fetal bovine serum (FBS; both from Life Technologies, Merelbeke, Belgium), 2 mmol/L glutamine, 50 mg/mL streptomycin, and 50 U/mL penicillin [3].
Induction of lung metastases
CC531S cells were prepared for injection by dispersal with a solution of 0.25% ethylinediamine tetraacetic acid (EDTA) and 0.05% trypsin in Hanks balanced salt solution (HBSS). Cell viability was determined with a tryptan blue exclusion method using a hemocytometer [8]. Because the original technique for induction of lung metastases resulted in small pulmonary metastases not suitable for pharmacokinetic analysis, a new model was developed. Ten rats were injected with only 500,000 CC531S adenocarcinoma cells in 1 mL of RPMI 1640 into the left femoral vein. Half of the rats were killed on day 15 and half on day 30. On day 15, only a few tumor nodules were visible, which were still too small for selective excision. However, on day 30, large metastases were visible macroscopically as separate nodules, easy to excise for further analysis.
Blood
To perfuse the lung with buffered hetastarch (BHE) enriched with red blood cells, many rats need to be sacrificed for one experiment because only 6 mL/100 g whole blood can be retrieved from a single rat. Because red blood cells (RBC) seem to be of surprising uniformity in all mammals [11], we were not restricted to the use of rodent RBCs, and washed rabbit erytrocytes were chosen to enrich the perfusate. Rabbit blood was drawn directly from the left ventricle of living rabbits after systemic heparinization. The red cells were processed within a few hours, using sterile techniques to remove plasma, white cells, and platelets. The blood was spun at 3,500 g for 10 minutes and the supernatant plasma was removed. The cells were diluted with 0.9% saline and spun in the same way as in the first process. The RBCs were then diluted with BHE solution to a hematocrit of around 30%. Thereafter, leukocytes were removed through a commercially available leukocyte filter.
Technique of single-pass isolated left lung perfusion (SP) and isolated left lung reperfusion (RP)
Single-pass isolated left lung perfusion (SP) was performed according to the technique as described by Hendriks and associates [12]. Briefly, anesthesia was induced with isoflurane. Rats were intubated by translaryngeal illumination and connected to the ventilator. Isoflurane was titrated between 0.5% and 1.5% according to muscle relaxation, heart rate, and pupil size. Ventilation was accomplished with a volume-controlled ventilator at a rate of 75 strokes/minute and a tidal volume of 10 mL/kg. After a left thoracotomy, the lung and rib retractors were placed anteriorly and the hilum was dissected free. The bronchus was deprived from its surrounding tissue in order to exclude the bronchial arterial flow to the lung. After clamping the pulmonary artery and vein with curved microclips, a 16-G Angiocath was placed through the chest wall. A PE-10 perfusion catheter was introduced into the chest through the Angiocath and secured by a 4/0 silk tie after insertion into the pulmonary artery. Perfusate was delivered through this catheter. In addition, a pulmonary venotomy was performed and two venous catheters (PE-90) were placed into the superior and inferior pulmonary veins to collect the venous effluent. In the case of single-pass perfusion, the effluent is discarded at the venous side. With isolated left lung reperfusion, the venous effluent is collected into the warm water bath, and from this bath reinfused into the pulmonary artery (Fig 1).
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In all experiments, animals were perfused on the left side for 25 minutes at a rate of 0.5 mL/min, followed by a 5-minute washout with buffered hetastarch (BHE) at 0.5 mL/min.
Melphalan (Alkeran, 50 mg/vial; Wellcome, Waterloo, Belgium) perfusate solutions were prepared by reconstituting lyophilized powder in the supplied diluent and performing appropriate dilutions with BHE before the experiments.
Experiment 1: single-pass isolated lung perfusion versus isolated lung reperfusion with buffered starch and red blood cells as perfusates
Twenty-eight rats were randomized into four groups. Group 1 (n = 10) and group 3 (n = 4) had SP with 0.5 mg of MN, whereas group 2 (n = 10) and group 4 (n = 4) had RP with 0.5 mg of MN. Whereas groups 1 and 2 had BHE as the perfusate, this was BHE enriched with red blood cells (RBHE) for groups 3 and 4. During perfusion, pulmonary effluent samples were collected at 5-minute intervals throughout the perfusion for groups 1 and 2. At the completion of a 25-minute MN perfusion and 5-minute BHE washout, the left lung was removed and frozen at -70°C for later analysis.
Experiment 2: determination of melphalan levels within the lung metastases
Twelve rats were randomized into three groups (n = 4 each). On day 0, all rats received 500,000 CC531S adenocarcinoma cells in the left femoral vein. On day 30, group 1 had SP with 0.5 mg of MN and group 2 had RP with 0.5 mg of MN. Group 3 received 0.5 mg of intravenous MN. The left lungs of groups 1 and 2 were perfused for 25 minutes with BHE as the perfusate followed by a 5-minute BHE washout. Thirty minutes after the onset of therapy, pulmonary metastases in all groups were separated from normal lung tissue and frozen at -70°C for later analysis.
Melphalan processing and measurement
Gas chromatography-mass spectrometry, as described by De Boeck and associates, was used for measuring melphalan levels in lung tissue and serum [13]. P-[Bis(2-chloroethyl)amino]-phenylacetic acid methyl ester was used as an internal standard. Samples were extracted over trifunctional C18 silica columns.
Statistical analysis
All data are presented as mean ± standard deviation (SD). Comparison between groups was done by an unpaired Students t test. Significance was defined as p less than 0.05.
| Results |
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Experiment 1
The temperature of the reservoir and the rats was not significantly different between groups (Table 1).
Hematocrit levels were significantly lower for groups 1 and 2 (BHE perfusate) compared with groups 3 and 4 (RBC-BHE perfusate). No significant difference was seen in wet-to-dry ratios between the groups (Table 1).
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| Comment |
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Since the early 1980s, the technique of isolated lung perfusion has been tested with success in large animals like dogs and pigs [4, 16, 17]. Later, rat models were developed for tumor efficacy studies with different chemotherapeutic agents. Numerous agents like tumor necrosis factor, FUDR, cisplatin, and doxorubicin have been tested with success in these rat models, and single-pass left lung perfusion was the only technique used [18]. A single-pass system was selected as a procedure for technical reasons and because this method facilitates drug kinetic studies by ensuring a constant drug concentration in the perfusate. Technically seen, it is very demanding to cannulate the pulmonary veins of the rat and even more difficult to restore the venotomies after perfusion in the case of survival experiments. Therefore, no cannulation is performed in the single-pass technique, but the effluent is discarded by a suction catheter and closure of the small venotomy is accomplished by pressure after the procedure [19].
Weksler and associates showed in their rat model of ILuP that the perfusate doxorubicin concentration and duration of perfusion were the only factors determining the final lung concentration of doxorubicin. The dose of doxorubicin, and the total amount and rate of perfusion were not important in determining the final lung doxorubicin concentration [20]. They did not investigate these values in a model of pulmonary metastases. Their studies were finalized by a phase I dose-escalating trial of ILuP with doxorubicin [21]. For this clinical study, a recirculating perfusion system was preferred because it minimizes the amount of perfusate and drug needed, vascular isolation becomes more complete, and greater flexibility is obtained in regulation of the perfusion environment [22]. The drug was added to the circuit as a bolus and not as a constant concentration. The fact that drug concentration was crucial in the rat experiments for the final lung concentration might explain the large variations in perfusate and lung levels of doxorubicin between patients receiving the same amount of drug [21]. It also shows the difficulty of calculating the amount of drug to give each patient. In contrast with isolated limb perfusion, where doses are calculated by the amount of water displaced by the limb [10], no such value is available for lung perfusion studies.
In our laboratory, a rat model of isolated single-lung perfusion was developed, and experiments with melphalan were extensively performed in preparation of human clinical trials since 1995. These animal experiments showed low operative mortality and negligible long-term injury to the lungs [7, 8]. We have shown that ILuP with melphalan results in significantly higher final lung melphalan levels compared with a high intravenous injection of melphalan [7]. Studies of experimental pulmonary metastases showed statistically significant eradication of experimental sarcoma and carcinoma metastases in rats undergoing isolated single-lung perfusion with melphalan compared with intravenous therapy [79]. In preparation of a clinical phase I dose-escalating trial of isolated lung perfusion with melphalan, a number of questions were unanswered. First, it is unknown how the dose should be calculated because lung mass can be very different between two patients. No value such as limb volume for isolated limb perfusion is available for the lung. Second, in all clinical studies performed so far, a closed circuit was used in order to lessen the amount of perfusate needed and to control values like flow, air leakage and temperature. In these studies, the drug was given as a bolus into the circuit proximal to the pulmonary artery (a dose), but not offered to the lung as a constant concentration. However, Weksler and associates demonstrated that drug concentration was crucial for the final lung concentration of doxorubicin [20]. For melphalan these values were not known. In this study, both lung and tumor MN levels were determined, as no correlation had been made between normal lung and tumor tissue. Tumor MN levels were significantly higher in the single-pass group compared with MN levels in the intravenous group. However, there was no significant difference between the single-pass and reperfusion group, and a steady state was reached after 15 minutes. So, not the concentration but the total amount of drug was critical for the final lung concentration, which is in contrast with rat studies of doxorubicin [20]. In this way, it seems that a bolus of MN into the circuit will result in the same final lung and tumor levels compared with a single-pass perfusion with a fixed concentration. A higher concentration within the lung was achieved compared with the tumor. In the reperfusion group, a higher concentration was reached in the tumor compared with the single-pass group, but the difference was not significant.
So far, both experimental and clinical studies are only available for doxorubicin. Although doxorubicin has proven to be a superior agent for isolated lung perfusion studies compared with intravenous therapy, the clinical dose-escalating study was disappointing, and for the highest dose, important side-effects were seen [21]. Putnam and associates showed that smaller dose increases can result in lower morbidity [23]. The highest dose used by Burt and associates, 80 mg/kg, was twice the lower dose, whereas Putnam and associates included a dose of 60 mg/kg without any morbidity. These two studies show that pharmacokinetics will behave totally differently from the three compartment model described for intravenous administration of chemotherapy. These dose-escalating studies should be performed for every agent that was promising in animal studies. The human isolated lung model described by Linder and associates extrapolates animal studies into the human situation, and provides useful pharmacokinetic information before starting phase I dose-escalating trials [24].
No significant differences in wet-to-dry ratios were seen between the groups in our experimental study (mean of all groups, 6.5 ± 0.5). Because both the pulmonary veins were cannulated, the wet-to-dry ratios were higher compared with the results obtained by Weksler and associates [20]. In our previous work, we used BHE as the perfusate fluid of choice based on the experiments by Weksler and associates [20]. These experiments did not investigate the addition of RBCs within the perfusate. However, it is possible that these RBCs will act as a better carrier for melphalan [25] and will diminish the amount of pulmonary edema during perfusion. In addition, RBCs will decrease anoxia-induced pulmonary damage. Despite these hypotheses, no significantly higher MN levels were reached with RBCs within the perfusate compared with BHE, and no difference was seen in the amount of pulmonary edema. Therefore, BHE will remain the perfusate fluid of choice for both laboratory and clinical studies.
In conclusion, no difference in final lung concentration was seen between single-pass left lung perfusion and isolated left lung reperfusion. The single-pass left lung perfusion acted as a model to deliver a fixed concentration of drug to the lung. This was compared with recirculating isolated lung perfusion as a model of a closed circuit, in which a bolus of melphalan was injected at a certain time point. The total amount of drug delivered in the two models was identical. In addition, the administration of RBCs to the perfusate did not increase the final lung concentration, and the amount of pulmonary edema was not statistically significant. These findings will simplify isolated lung perfusion with melphalan because buffered starch will be the perfusate of choice and melphalan can be injected as a bolus into the circuit, after stabilization of the main values, such as temperature, flow, and leakage. Dose-escalating phase I studies will determine wether melphalan is a useful agent in the setting of isolated lung perfusion.
| Acknowledgments |
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| Discussion |
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DR HENDRIKS: Well, although not the aim of this study, different techniques can increase the uptake. The agent best known to increase the uptake of melphalan is TNF, but we could not test this agent because it is not delivered to us anymore for free. So it was beyond the budget. Regarding your second question, our results are quite similar to the experiments with doxorubicin in pigs, where no difference was found between the single-pass and the reperfusion technique. I know the trend was towards statistical significance, but because of the spread in the values, it was not reached. We are now expanding the groups in rats and have also added experiments in human lungs to exclude a possible difference between the two techniques.
DR W. ROY SMYTHE (Houston, TX): I enjoyed your presentation. Have you looked at biological correlates of the effect of chemotherapy in a single-pass versus a recirculation model? It may be that you reach a saturation level of drug with either method, but biologically, there may be a greater effect on the tumor cells with recirculation. Have you looked at biologic correlates of effect? Have you looked at measures of apoptosis, DNA adducts, or other variables?
DR HENDRIKS: We are performing a similar experiment regarding the saturation level that will be finished pretty soon and sent for publication. Regarding biologic correlates of effect, no, we did not investigate that.
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