Tad Konikowski

Experimental models for evaluation of radioactive tumor-localizing agents

Although subject to limitations, there is a need for carefully controlled laboratory studies using animal tumor models in research on tumor-localizing agents. This paper reviews the literature relating to the more important transplantable tumor systems, spontaneous or induced, as to origin, host, site, and radioactive agent used. The historical background of animal tumor models is discussed, including such technical aspects as source of tumor, techniques of transplantation, transplantation sites, and maintenance of transplants. Also, considered are the use of animal tumor models as predictive systems, expression of experimental results of quantitative studies of tissue uptake and comparative radionuclide tumor and distributional studies, and suggestions for future studies, such as the need of more intensive study of existing tumor models for a better understanding of the relationship between animal and human tumors, the need for the development of new tumor model systems, and for standardization of experimental protocols and procedures. A total of 48 t,mor models (26 in mice, 11 in rats, 7 in hamsters, 2 in rabbits, and 2 in dogs) are presented in seven tables dividing the models into tumors of epithelial tissue, connective tissue, hematopoietic tissues, melanin-forming tissue, neural tissues, undetermined site of origin or undifferentiated histologic pattern, and miscellaneous background. The use of animal tumor models in cancer research, which utilizes radionuclides, permits the investigator to do many things not permissible with human beings, but the extrapolation of animal results to human beings must be approached with caution, Although malignant disease, whether in animals or man, must be individualized, certain trends in animal studies can be observed. It is the goal of the laboratory investigator to be able to indicate to the clinician those trends or phenomena that, when repeatedly observed in animal model systems, may be applicable to an understanding of malignant disease in man.

Transplantable mouse neoplasm control by neutron capture therapy.

AFTER several years of effort based on the application of the principles of neutron capture therapy, we have empirically evolved a procedure which now can be added to the few effective treatments for established invasive transplantable neoplasms of animals. Previously, we discussed the biological utilization of thermal neutrons to generate alpha particles and lithium atom fragments from boron-10. We noted the pathways of these fragments are of cellular dimensions1–5, and how, in principle, one might thereby attain sharply localized intense effects. Our present observations on 611 neoplasms may serve to point towards achievement of these goals. In this communication we report the thermal neutron flux which must be incident on the skin over solid neoplasms 8 mm–17 mm in diameter to result in permanent regression after giving sodium pentaborate intravenously in a dose equivalent to 35 µg/g body weight of boron-10. Only a single treatment was required by this procedure.

Effects of varying boron-10 dose, thermal neutron fluence and reactor employed on results of neutron capture therapy of a transplantable mouse neoplasm

Abstract Data are presented comparing results from neutron capture therapy of a transplantable mouse neoplasm after doses of boron-10 equivalent to 25, 35 and 50 micrograms per gram body weight at comparable thermal neutron fluences; also data are presented comparing results with three differently designed nuclear reactors. In addition, in two of the studies to provide an extension of control data, data are presented of results obtained at very low thermal neutron fluences. Comments and data cover borate distribution among blood, neoplasm and muscle with a discernably different pattern emerging at the higher boron dose compared to the lower. The data reported are on 627 animals bearing neoplasms. From 50 to 79 per cent of treated animals, depending upon the specific study, showed complete and permanent (lifetime) regression of the neoplasm.

Long range effects of neutron capture therapy of cancer in mice—I Correlation between the time of intracellular residence of 10BNapentaborate and the regression of the tumor

Abstract In 1587 mice, each bearing a potentially lethal neoplasm implanted in the right thigh, the tumoricidal effects of a single exposure to a standard thermal neutron fluence, ranging from 1.41 to 1.67 x 10 12 /cm 2 , following an intravenous injection of sodium pentaborate of 35 ug l0 B/g observed body weight were observed. Observations were continued for the lifetime of the animal. Regression, measured by tumor diameter, began in every instance within a maximum of four days after treatment. After two weeks clear evidence of tumor growth resumption was apparent in some animals; however, in a majority, the disappearance of the tumor was complete and permanent. For each size of neoplasm studied, the percentage of tumor which permanently regressed rose to a maximum with increased residence time of boron in the tumor and then fell. The rise and fall of neoplasm regression do not parallel observed data on tumor borate concentration over the time-intervals observed. In neoplasms 8 mm dia., permanent regression occurred in 93% of the neoplasms when the borate intracellular-residence interval in the neoplasm was 7–11 min, fell to 74% in the 50 min residence interval and to 42% in the 88 min residence period. In neoplasms 9–11 mm dia., regression was 58% in the 7–11 min interval, rose to 86% in the 38–48 min period and thereafter fell to 19% in the 88–92 min residence interval. In animals with neoplasms 12–14 mm dia., regression was 22% in the 7–11 min interval, rose to 38% in the 50–60 min interval and fell to zero in the 74–80 min interval. The possible cellular mechanisms provoked by the reaction and their relationship to a calculated dose formulated on neutron fluence and boron-10 concentration will be explored in a subsequent communication.

Leukocyte labeling with technetium-99m

Abstract Erythrocyte labeling with 51Cr or 99mTc is a well-established procedure in nuclear medicine. The labeled cells are useful in the measurement of red cell mass, in erythrocyte survival studies, and in the localization of erythrocyte pools. Attempts to label the leukocyte with the same radionuclides have not been as successful. This study reports on various laboratory parameters of labeling leukocytes with 99mTc. Microgram quantities of stannous chloride are used in the labeling process to reduce 99mTc-pertechnetate to a lower valence state. Other reducing agents such as ferrous ion and penicillamine are not effective. Pertechnetate itself is only loosely bound to the leukocyte. An electrophoretic technique is used to determine labeling yield. Differences in labeling efficiency between the cells from normal donors and the cells from chronic myelocytic leukemia (CML) donors have been detected. Leukocytes from normal donors generally label with greater efficiency than leukocytes from CML donors, but subject age is probably a contributing factor, with cells from young normal donors labeling more like cells from CML donors. The leukocyte and erythrocyte can be labeled under identical conditions in about the same yield. Labeled leukocytes retain good viability and phagocytic capability. Although autoradiographic studies are not completely conclusive because of the poor radiation characteristics of 99mTc, it appears possible that the -Sn-99mTc label is on the surface of the cell and is not intracellular. The labeling process is being adapted to an aseptic process for future experimentation in animals and in human subjects.

An intercomparison of radiopharmaceutical kidney kinetics in the mouse

Abstract To satisfy partially the need for controlled intercomparative study in the same bio-system, the renal kinetics of ten radiopharmaceuticals were studied in the Yale-Swiss mouse. Time-course tissue distribution studies of the kidney, liver, blood and skin as well as blood and plasma renal clearance values, cumulative urinary excretion, whole body retention, and total body absorbed radiation doses are reported for 131 I-orthoiodohippurate sodium, 169 Yb-DTPA, 99 m Tc-Sn-DTPA, 113 In-DTPA, 99 m Tc-iron-ascorbic acid-DTPA, 67 Ga-iron-DTPA, 99 m Tc-iron-ascorbic acid, 197 Hg-chlormerodrin with and without meralluride predose, 67 Ga-chloride and 111 In-chloride. For kidney imaging, a rating order is reported based on biological distribution. Requirements for varying kidney functions are discussed. No single compound is clearly superior for renal studies, but insight is provided into important factors which must be considered in the selection of a useful agent for clinical renal function and imaging studies.

Differences in 111In uptake in mouse brain sarcoma based on form of administration

Abstract It has been shown that when 111 In is injected as the chloride, it largely binds to transferrin. We studied the biokinetics and distribution of three substances in mice bearing an in situ sarcoma-like brain tumor. The substances were 111 In-chloride at pH 1.5, 111 In bound to mouse serum proteins, and 111 In bound to transferrin (human). Standardized methods for determining tumor and tissue concentrations and renal clearance and whole body retention were used. For protein preparations, 111 In was incubated with mouse serum or transferrin (human), and then passed down a Sephadex G-25 column using total protein fractions. Tumor uptake of the 111 In-chloride was greater than uptake of the 111 In-serum protein or 111 In-transferrin from 1 to 4 hr. The brain uptakes of the three compounds were similar over 48 hr. There was more 111 In-chloride in the skin for all time periods after 1 hr; the muscle uptake of the 111 In-chloride was also greater than the other compounds over the first 6 hr. There were variations in blood concentrations of the three compounds over the first 4 hr, but the blood concentrations were the same after 6 hr. All left the blood faster than 131 I-iodinated human serum albumin. Considerably more of the 111 In-serum protein was found in the liver the first 2 hr. The urinary excretion patterns of the three compounds differed with the 111 In-chloride being excreted faster the first 2 hr, but slower over longer periods of time. Whole-body retention curves over 22 days for the three compounds were very similar, as were the estimated total body radiation doses. There are distinct differences in the biokinetics in the mouse of 111 In-chloride, 111 Inserum proteins (mouse), and 111 In-transferrin which indicate that all 111 In injections are not the same, and suggest that for tumor localization studies, the injection of the 111 In-chloride at pH 1.5 may be the best form of administration.