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Notes: Abstract. Recent studies suggest a higher anti-tumour efficacy of internalizing monoclonal antibodies (MAbs) when labelled with Auger electron emitters, as compared with β-emitters. The aim of this study was to compare the anti-tumour efficacy and toxicity of the internalizing MAb, CO17-1A, labelled with Auger electron emitters (125I, 111In) versus conventional β–-emitters (131I, 90Y) in a colon cancer model, and to assess whether the residualizing radiometals may have therapeutic advantages over the conventionally iodinated conjugates. Biodistribution studies of 125I-, 111In- or 88Y-labelled CO17-1A were performed in nude mice bearing subcutaneous human colon cancer xenografts. For therapy, the mice were injected with either unlabelled or 125I-, 131I-, 111In- or 90Y-labelled CO17-1A IgG2a, whereas control groups were left untreated or were given a radiolabelled isotype-matched irrelevant antibody. The influence of internalization was assessed by comparing the results with those obtained with an anti-carcinoembryonic antigen (CEA) antibody which does not internalize to a relevant extent. The maximum tolerated activities (MTA) and doses (MTD) of each agent were determined. Myelotoxicity and potential second-organ toxicities, as well as tumour growth, were monitored. Bone marrow transplantation (BMT) was performed in order to enable dose intensification. Radiometals showed significantly better tumour-to-blood ratios than the respective iodinated conjugates. The MTAs of 131I- and 125I-CO17-1A without artificial support were 11.1 MBq (300 µCi) and 111 MBq (3 mCi), respectively; the MTA of the metals was reached at 4 MBq (100 µCi) for 90Y-, and at 85 MBq (2.3 mCi) for 111In-CO17-1A. Myelotoxicity was dose limiting in all cases. BMT enabled an increase in the MTA to 15 MBq (400 µCi) of 131I-labelled CO17-1A, to 4.4 MBq (120 µCi) of 90Y-labelled CO17-1A, and to 118 MBq (3.2 mCi) of 111In-labelled CO17-1A, while the MTA of 125I-CO17-1A had not been reached at 185 MBq (5 mCi) with BMT. Whereas no significant therapeutic effects were seen with unlabelled CO17-1A, tumour growth was retarded significantly with its radiolabelled forms. The therapeutic results were significantly (P〈0.01) better with both Auger electron emitters (125I and 111In) than with the β-emitters, and, in accordance with the biodistribution data, a trend towards better therapeutic results was found with radiometals (more complete remissions) as compared with radioiodine. In contrast, at equitoxic doses, no significant difference was observed in the therapeutic efficacy of 131I- versus 125I-labelled non-internalizing anti-CEA antibody, F023C5. These data suggest that, at equitoxic doses, the therapeutic efficacy of internalizing MAbs labelled with Auger electron emitters, such as 125I or 111In, is superior to that of internalizing MAbs labelled with conventional β-emitters. The lower toxicity of Auger electron emitters may be due to the short path length of their low-energy electrons, which can reach the nuclear DNA only if the antibody is internalized (as is the case in antigen-expressing tumour tissue, but not in the stem cells of the red marrow).

Notes: Abstract This study investigated whether reperfusion results in an increase of ultrastructurally determined myocardial injury in pig hearts. The left anterior descending coronary artery (LAD) was distally occluded in 12 pigs for 35–45 minutes and then reperfused for 3 hours. At the end of ischemia, as well as after 3 hours of reperfusion, one transmural biopsy was removed from the center of the risk region and subdivided into four specimens, representing the subendocardial (I), subendo-midmyocardial (II), subepi-midmyocardial (III), and subepicardial layers (IV). The degree of injury was assessed by electronmicroscopy and was scored as reversible (1), an almost equal mixture of reversible and irreversible (2), and totally irreversible (3) damage. In addition, infarct size was determined as the ratio of infarcted (tetrazolium stain) to ischemic (dye technique) myocardium. Infarct sizes ranged from 29.3% to 93% (mean 61.2%). The scores of injury of the four tissue layers before and after reperfusion did not differ significantly: layer I, 2.4 ± 0.8/2.3 ± 0.9; layer II, 2.2 ± 0.9/2.0 ± 0.9; layer III, 1.8 ± 0.9/2.0 ± 0.9; and layer IV, 1.6 ± 0.9/1.3 ± 0.6. The means of the four layers were almost identical at the end of ischemia (2.1 ± 0.8) and after 3 hours of reperfusion (2.0 ± 0.6). A linear regression analysis with 95% confidence limits of the score values before and after reperfusion indicated that maximally 25% of a mean final infarct size of about 50% may be due to lethal reperfusion injury. This study suggests that cell death in regional ischemia and reperfusion occurs predominantly during ischemia and not during reperfusion.

Notes: Summary The effect of intracoronary (IC) pretreatment with different calcium antagonists (diltiazem, nifedipine, verapamil) on the development of infarcts was investigated in two experimental series including 35 open-chest pigs. The left anterior descending coronary artery (LAD) was distally ligated for 75 minutes (series A) or for 45 minutes (series B) and was reperfused for 24 hours. Infarct size was determined as the ratio of infarcted myocardium (tetrazolium stain) to the risk region (dye technique). In series A, 20 pigs were pretreated immediately before occlusion with either IC diltiazem (n=5, 4 mg/2 min), IC nifedipine (n=5, 0.4 mg/2 min), IC verapamil (n=5, 1 mg/2 min), or isotonic sodium chloride solution (n=5). In series B, IC diltiazem (n=5, 4 mg/2 min), IC verapamil (n=5, 1 mg/2 min), or isotonic saline solution (n=5) were administered 8 minutes prior to ischemia. The IC infusion of all calcium antagonists (series A) depressed left ventricular peak pressure, diastolic blood pressure, and dp/dt max and increased heart rate and coronary venous oxygen saturation. The development of infarcts was significantly delayed by IC diltiazem and IC verapamil. Mean infarct sizes (series A) amounted to 62% in the diltiazem group, 88% in the nifedipine group, 40% in the verapamil group, and 94% in the control group. In series B, where a time period of 8 minutes elapsed between pretreatment and induction of ischemia, mean infarct sizes after 45 minutes of ischemia and 24 hours of reperfusion amounted to 47% in the diltiazem group, 4% in the verapamil group, and 76% in control experiments. The better protection of verapamil in series B can mainly be ascribed to its longer lasting regional depression compared to diltiazem. In conclusion, at the given drug concentrations, IC verapamil and IC diltiazem enhanced the ischemic tolerance to a greater extent than IC nifedipine (series A). When a time period of 8 minutes had elapsed between IC treatment and the onset of ischemia (series B), verapamil still exhibited a protective effect on the treated myocardium, which can mainly be ascribed to its long-lasting negative inotropic action.