Phillip L. Hagan

Alterations in an indium-111 Fab′ under conditions of utilization

This study was conducted to investigate alterations that occur in an indium/111 Fab′ of a monoclonal antibody following its in vivo administration. Patients were infused with 111 In-Fab′ of the monoclonal antibody ZCE-025. Serum and urine specimens were collected from these patients. Starting materials, serum, urine and controls samples were studied by electrophoresis. Animal distribution studies were performed in normal Balb/c mice and, in some cases, nude mice bearing a carcinoembryonic antigen (CEA)/producing human colon tumour since the antibody targets CEA. The studies indicated that the molecule circulated almost totally intact for at least 4 h and to a considerable extent for 24 h, with some evidence for in vivo fragmentation by 24 h. Evidence was also obtained suggesting the formation of a high molecular weight species in some patients. Shortly after infusion, some of the 111In in the urine appeared as the intact Fab′, but within hours the majority migrated electro-phoretically as low molecular weight species. We conclude that while the majority of the 111In-Fab′ of this particular antibody remains intact and immunoreactive following its administration, the molecule is structurally changed to some degree shortly after its infusion into humans. Since each monoclonal antibody is unique, the degree and rapidity of degradation of its Fab′ in vivo could vary markedly from the above and possibly adversely effect its utility as a radiopharmaceutical.

The effect of parathyroid hormone on technetium-99m pyrophosphate distribution in rats

Sprague-Dawley rats were treated with varying quantities of parathyroid hormone for 1–3 days, then sacrificed at periods ranging from 1–6h after administration of 99mTc-pyrophosphate. Very little increase in bone accumulation of tracer occurred with this treatment. A small, but obvious decrease occurred in the blood levels of 99mTc-pyrophosphate and a smaller and less consistent decrease was affected in the muscle levels of the radiopharmaceutical. The overall result was an improvement in the bone/blood and bone/muscle ratios. It is suggested that the basis of the “supernormal” bone scan of hyperparathyroidism is achieved by this mechanism and that the increased bone uptake of other ions in response to parathyroid hormone is not shared by 99mTc-pyrophosphate.

RADIOIMMUNODETECTION STUDIES OF PROSTATE, COLON AND T-CELL LYMPHOMA TUMORS USING In-111 LABELED MONOCLONAL ANTITUMOR ANTIBODIES (In-111-MoAb); PRELIMINARY STUDIES

The purpose of these pilot studies was to determine if prostate carcinoma (PC), colon carcinoma (CC), and cutaneous T-Cell lymphoma (CTCL) could be detected using the In-111-MoAbs described below. Murine IgG MoAbs targeted against prostatic acid phosphatase (PAP), carcinoembryonic antigen (CEA), and an antibody that often recognizes CTCL (MAT-65) were labeled with In-111, and administered (Ad) intravenously to patients (PT) with PC, CC and CTCL respectively. One mg or less of MoAb was labeled with 1.5 – 5.0 mCI of In-111 in a total MoAb dose of 1–5 mg of anti-PAP, 0.5 mg of anti CEA, and 50 mg of MAT-65. All the MoAbs were infused over a two hour period. In one CTCL case, In-111-MoAb was Ad prior to, and a few weeks later, after a 50 mg dose of unlabeled MoAb. The infusion of In-111-MoAb followed a 50 mg infusion of unlabeled MoAb in the second CTCL case. Normal prostate tissue was visualized in 3 of 5 PT and 2 of the bone metastases imaged. Metastases from CC were visualized in 1 of 3 PTS. Outstanding definition of lymph nodes was achieved in CTCL, and the sequence of Ad markedly altered in the in-vivo kinetics of the In-111-MoAb. Some toxicity was observed in CTCL PTS, however, anti PAP and anti CEA were not toxic. We conclude that the above MoAbs will target tumor, and that further clinical trails with higher quantities of anti-PAP and CEA protein are warranted.

The effect of certain variables on the tumor and tissue distribution of tracers. IV. False carriers: ferric citrate.

The intravenous administration of Fe+3 -citrate (1.6 mg/kg body weight) was demonstrated to alter the concentration of carrier-free 67Ga and 54Mn in malignant and healthy tissues of the rat, Morris 7777 hepatoma model. When the Fe+3 was injected 2 hours before, simultaneously with, or 2 hours after 67Ga (and the rats sacrificed 4 hours after injection), the 67Ga in most normal tissues decreased, and the viable tumor concentrations increased by 135, 24, and 47%, respectively. Twenty-four hours after a simultaneous administration of Fe+3 and 67Ga, egress of 67Ga from the tumor was much less than from the healthy tissues. These changes resulted in significant improvements in viable tumor to background ratios, especially at 4 hours. These changes induced in the distribution of the two tracers by Fe+3 indicate that some kinetic characteristics are shared. This is discussed in the light of their response to carrier Ga and Mn. The use of Fe+3 shows promise as a means of improving tumor/background ratios for 68Ga and 52mMn, two short-lived positron emitters that can be used with positron scanners. Gallium-67 imaging may also be improved by these techniques. The Fe+3 increases excretion of 67Ga from the animal, and this could result in a lower radiation dose to a patient.

The distribution of cadmium-115m chloride, cobalt-57 bleomycin, iodine-125 human serum albumin, selenium-75 selenite and selenomethionine-75 in a rat hepatoma model: a comparison with gallium-67 citrate.

The distribution of cadmium-115m chloride, cobalt-57 bleomycin, selenium-75 selenite, selenium-75 selenomethionine and iodine-125 human serum albumin was investigated in rats bearing thigh implanted Morris 7777 hepatomas. Viable and nonviable tumor tissue were collected in order to determine the relative affinities of these radiopharmaceuticals for these tissues. Groups of animals were sacrificed at 4, 24, 48, 72 and 96 h following injection. Viable tumor-to-blood and muscle ratios for cadmium-115m chloride and cobalt-57 bleomycin were higher than those for gallium-67 bitrate at 4 h post-injection. The unusually high cobalt-57 bleomycin ratios for both viable and nonviable tumor were the result of very low muscle and blood values rather than high tumor uptake. Tumor-to-background ratios for iodine-125 human serum albumin, selenium-75 selenomethionine and selenium-75 selenite were inferior to those derived for cobalt-57 bleomycin or gallium-67 citrate. None of the agents included in this study compared well with gallium-67 citrate as a tumor localizing agent with the possible exception of cadmium-115m chloride and coblat-57 bleomycin at early time periods. As in most other radiopharmaceuticals studied in this model, a reversal occurred in the viable-to-nonviable tumor ratios as the time after injection increased.

Preparation and stability of 131I-tetracycline

Abstract A method for the iodination of tetracycline is presented which yields >85% labeling efficiency. The product is stable for a minimum of 72 hr and appears to retain tetracycline-like properties when studied in vivo . The critical factors in the synthesis are reaction temperature, acidity, and drying temperature. The data suggest that 131 I-TET can be studied as a tumor scanning agent without fear of product artifact.

RADIOIMMUNODETECTION OF MELANOMA USING In-111???96.5 MONOCLONAL ANTIBODY (In-111???96.5 MoAb)

The purpose of this study was to evaluate In-111–96.5 MoAb as a radiopharmaçeuticl (R) for the detection of melanoma (mel). The 96.5 MoAb targets a 97 kilodalton surface antigen on the mel cells. Labeling was by a bifunctional chelation technique, and resulted in 3–5 mCi of In-111 chelated to 1 mg of antibody (A). The R was administered (Ad) intravenously through a 30–120 minute period. Twenty-two studies were performed in 21 patients (PT), with one PT studied twice. In four PT, unlabeled A was Ad prior to the R. Other PT received from 2–19 mg of unlabeled A mixed with the R. Blood (B) was drawn at multiple times following the infusion to observe R kinetics, and to determine if serum chemistries indicated toxicity (tox). There was no evidence of tox from the R or carrier A. Increasing protein mass slowed the loss of In-111 from B, and appeared to improve lesion detection. 66% of the 73 lesions 1.5 cm or larger were detected. Eight metastases were detected which were not clinically suspected. Five metastases imaged were in the 0.5–1.0 cm size range. Two were scalp metastases, and three were lymph nodes in the anterior cervical triangle of the neck. Liver uptake was a major cause of failure of the R as lesions could not be resolved if they occurred in the liver. We conclude that In-111–96.5 MoAb shows promise as a R for the detection of mel, and warrants further study.

The effect of certain variables on the tumor and tissue distribution of tracers: VI. False-carrier effect, Part III, Fe.

Previous work has shown that Fe3+, when administered in the proper dose and time sequence, increases the tumor uptake of gallium-67 (67Ga) while decreasing its uptake by normal tissues. The purpose of this series of experiments was to examine further the postulate that the false carrier effect is mediated at the cellular as well as the vascular level, determine the lowest concentration of ionic Fe3+ that will induce near maximum tumor/background ratios (T/Bkg), determine the best technique for its administration, and decide whether Benadryl and dexamethasone could be used to offset side effects of the Fe3+ without altering tumor and tissue kinetics. Fe3+ altered tissue levels of 67Ga prior to changes in the blood. The threshold for initiation of the false-carrier effect varied to some extent from one organ to another. Tumor uptake of 67Ga was either enhanced or unaltered at 4 hours after injection; 0.3 mg Fe3+/kg administered 0.5 hour before and 2 hours after the 67Ga enhanced 4-hour T/Bkg by a factor of about ten. Twenty-four-hour ratios were improved (to a lesser extent than 4-hour), but decreased concentrations of 67Ga occurred in the tumor. Dexamethasone and Benadryl did not alter the outcome of the experiment. This technique should be useful for imaging with gallium-68 and the PET camera.

The effect of certain variables on the tumor and tissue distribution of tracers. III. Salicylates and vasoactive drugs.

Attempts were made to increase the viable tumor concentration of 54Mn and 67Ga in a rat hepatoma model by administering rat angiotensin, tolazoline, and salicylates. Salicylates increased the tumor concentrations of 54Mn and improved 65Mn viable tumor/background ratios. 67Ga was not affected by the salicylates. The salicylate effect appeared to be mediated by intracellular mechanisms rather than alterations in plasma protein binding. Rat angiotensin slightly increased the concentrations of 67Ga in the tumors but not enough to suggest that it would be useful clinically. Tolazoline did not increase tumor uptake of the tracers.

The effect of certain variables on the tumor and tissue distribution of tracers. II. Carrier effect: rapidity of onset and concentrations necessary for initiation and maximum response.

The smallest quantity of carrier Ga and Mn necessary to initiate and maximize a carrier effect was studied in the Morris 7777 rat hepatoma model. The quantity needed for a maximum response did not appear to adversely effect the rats. Not all tissues were equally affected at the same plasma concentrations. If carrier Ga was administered 2 hours following 67Ga injection and the rats sacrificed 30 minutes later, a dramatic change occurred in background activity, which was more pronounced in healthy than malignant tissues. Early viable and nonviable tumor/background ratios were improved by this technique. The data suggest that the use of carrier Ga and Mn might improve early lesion/background ratios in patients. This could be of use if tumor imaging were undertaken with 68Ga or 52mMn with positron detector systems.