Showing papers on "In vivo published in 1975"

Tumorigenicity of virus-transformed cells in nude mice is correlated specifically with anchorage independent growth in vitro.

Abstract: Clonal isolates of mouse 3T3 cells and primary rat embryo cells, recovered nonselectively after infection by simian virus 40 (SV40), have been tested for tumorigenicity in the immune-deficient nude mice in order to determine the cellular growth properties in vitro specifically correlated with neoplastic growth in vivo. In addition, mouse 3T3 cells transformed by murine sarcoma virus (MuSV, Kirsten strain), and revertants isolated from cells fully transformed by either SV40 or MuSV were also studied. Results suggest that the single cellular property consistently associated with tumorigenicity in nude mice is the acquisition by virus-transformed cells of the ability to proliferate in vitro in the absence of anchorage. Other cellular parameters of virus-induced transformation, such as lack of sensitivity to high cell density and the capacity to grow in low serum concentration, are dissociable from cellular tumorigeneicity. This conclusion is supported further by the demonstration that specific selection in vivo for tumorigenic cells from anchorage-dependent cells results in the isolation of anchorage-independent cells. Conversely, a single-step selection in vitro for anchorage-independent cells from nontumorigenic cells results in a simultaneous selection of highly tumorigenic subclones.

Differences in corticosterone and dexamethasone binding to rat brain and pituitary

Abstract: In an attempt to relate binding of 3H-corticosterone and 3H-dexamethasone to their respective potencies in blocking pituitary-adrenal activity, cytosol binding in vitro and cell nuclear binding both in vivo and in tissue slices in vitro were studied in hippocampus, hypothalamus, and anterior pituitary of adrenalectomized rats. It was found that the extremely potent glucocorticoid dexamethasone has a different pattern of binding than corticosterone in the brain and in the anterior pituitary. 1) In cytosol, differences in the estimated binding capacities in a particular tissue for 3H-corticosterone and 3H-dexamethasone and different rates of inactivation in the ability to bind the two steroids are observed. 2) For 3H-corticosterone, cytosol binding in hippocampus is higher than that in hypothalamus, and cell nuclear binding follows the same pattern. For 3H-dexamethasone, cytosol binding is again higher in the hippocampus than in hypothalamus but cell nuclear binding in the two structures is not significantly different. With respect to the anterior pituitary, binding to cell nuclei is higher for 3H-dexamethasone, while the binding to cytosol macromolecules is higher for 3H-corticosterone. 3) In vivo and in vitro cell nuclear binding for both steroids showed the same pattern among the three tissues, but in vivo data showed more distinctly the preference of 3H-dexamethasone for the anterior pituitary and the preference of 3H-corticosterone for the hippocampus. 4) When labeled in tissue slices, cell nuclear radioactivity appears to be bound to macromolecules. 5) Steroid metabolism does not occur in slices during 60 min in vitro at 25 C and cannot account for the observed tissue differences in binding. The existence of more than one population of corticosteroid-binding sites in brain and in anterior pituitary is suggested. The results are consistent with the view that the dexamethasone blockade of stress-induced ACTH release is mediated by the anterior pituitary, while the high specificity of cotricosterone binding in the hippocampus implies a specific but as yet undetermined effect of the hormone in this brain area, an effect which may not be directly related to regulation of ACTH secretion.

Genetic variation of in vitro cytolytic activity and in vivo rejection potential of non-immunized semi-syngeneic mice against a mouse lymphoma line.

Abstract: Spleens of normal young mice of certain genotypes contain lymphocytes that can kill strain A-derived YAC-1 and some other in vitro-grown Moloney lymphoma lines in a 51Cr-release cytotoxic test. We have previously shown that mouse strains can be classified as high or low reactors in this test. F(1) hybrids between low- and high-reactive strains are high-reactive. In the present study, strain-A mice and eight different A F(1) hybrids were tested in parallel for their spleen-cell-mediated killing effect in vitro and their ability to reject graded numbers of YAC ascites or in vitro cultivated cells in vivo. There was a clear correlation between in vitro cytotoxicity and in vivo rejection in all tested genotypes. In segregating (A times C57Bl) times A backcross mice, in vivo rejection of YAC cells was H-2 linked. This is in line with the earlier backcross analysis of the in vitro cytotoxicity, suggesting a polygenic control with at least one H-2 linked factor.

Genes required for cytotoxicity against virus-infected target cells in k and d regions of h-2 complex.

Abstract: EVIDENCE is mounting that in mice, certain specific immunological effector functions of thymus-derived (T) lymphocytes are efficient only when donors of T cells and the cells with which they interact have at least a part of the H-2 gene complex in common1–8. Examples include T helper function in vivo and in vitro1–3, cytotoxicity mediated by T cells against virus-infected4–6 or TNP-modified7 target cells in vitro, immunopathology mediated by T cells4, or protection against bacterial8 and viral infection6 in vivo. This requirement for H-2 compatibility has been studied in detail by measuring the cytotoxicity of T cells from donors immunised with either lymphocytic choriomeningitis (LCM) or ectromelia virus using target cells infected with the homologus virus.

Direct effects of ethanol on the nervous system.

Abstract: Neurophysiological, neurochemical and behavioral studies of the effects of ethanol on the nervous system have so far failed to identify specific, direct, primary mechnisms of action that may account for the typical pattern of alcohol intoxication in vivo. Electroencephalogram and evoked response studies indicate biphasic effects in the intact subject, which may correlate better with the level of arousal than with a specific drug action. Effects on spinal reflexes are also biphasic, probably representing the net result of direct influence on resting membrane potential, primary afferent depolarization, and neurotransmitter release. With the exception of its inhibitory effect on release of oxytocin, vasopressin and possibly other hypothalamic peptides, ethanol does not appear notably different in its spectrum of effects from a wide range of other hypnotics, anesthetics and minor tranquilizers. Interpretation of the findings is complicated by the fact that functional alteration of any given neuronal system by ethanol in vivo may reflect a) direct local action of ethanol on the cells under study, b) change in the input to those cells because of an action elsewhere in the nervous system, c) effects of ethanol metabolites, or d) indirect consequences of decreased blood flow, oxygen or metabolite supply, hormonal action, or hypothermia, due to disturbances of homeostasis in the whole body as a result of deep intoxication. To date, attempts to circmvent b, c and d by the study of brain tissue in vitro have shown consistent effects of ethanol only at concentrations well above those that are meaningful in vivo. Relatively specific patterns of action of different drugs in vivo may prove to be largely dependent on their customary rates and routes of administration, and on summation of minor differences in the dose-response curves with different types of neuron, even though the basic types of molecular action may be essentially similar.

Activity of vitamin A analogues in cell cultures of mouse epidermis and organ cultures of hamster trachea.

Abstract: FIFTY years after the discovery that vitamin A controls cel differentiation in epithelial tissues the mechanism involved is still unknown. The recent introduction of two-cell and organ culture systems, involving serum-free medium, for the assay of vitamin A activity in vitro may help. One assay uses epidermal cell cultures derived from mouse skin1 and the other uses tracheal organ cultures from vitamin A-deficient hamsters2. In both, the observed cellular response depends on the addition of vitamin A, which induces a marked increase in the cellular RNA of the skin cultures and a change from the production of keratin to the production of cilia and mucus in the tracheal organ cultures. We have now investigated the Biological activity of seven analogues of natural vitamin A ester (β-retinyl acetate) and vitamin A acid (β-retinoic acid), in line with the common practice of assaying physiological and pharmacological actions of vitamins, hormones and drugs using structural analogues of a parent compound. In the analogues we used, the 5,6-cyclohexenyl ring system of natural vitamin A is modified substantially. Although data obtained in vivo show that modification of the ring portion of the molecule can reduce growth-promoting activity3–5, we found that several vitamin A analogues with alterations in the ring, including a shift of the 5,6-double bond of the cyclohexene ring to the 4,5-position and replacement of the cyclohexene ring with substituted aromatic and cyclopentene rings, have substantial activity in the skin and tracheobronchial assays. Because of the sensitivity of the two assays it is now possible to assay vitamin A activity in the 10−9–10−10M range (30–300 pg ml−1). Moreover, there is excellent correlation between the results of the two assays in terms of the evaluation of Biol.ogical activity of new analogues.

Suppression of tumour growth in mice by a drug–antibody conjugate using a novel approach to linkage

Abstract: THE possibility of using cytotoxic drugs linked to tumour-specific antibodies as a form of cancer chemotherapy has been revived recently. In theory the antibodies would selectively transport the drugs to the target tumour site. The demonstration by Ghose et al.1,2 and also by Flechner3 that chlorambucil and antibody combined produce an augmented antitumour effect can, however, be explained by an additive or synergistic effect of drugs and antibody uncombined, since there is a high probability of in vivo dissociation4–6. Although this synergistic drug–antibody effect has been studied in detail7–9, the original aim of preparing a stable drug–antibody conjugate has also been pursued and evidence of in vivo tumour suppression has been obtained with covalent conjugates of rabbit antitumour immunoglobulin (Ig) and alkylating agents10,11. In these studies, direct conjugation of the drugs with Ig was carried out using a water-soluble carbodiimide. Successful tumour suppression was, however, dependent on using large amounts of linked material since severe limitations are imposed on the degree of drug substitution by the physico-chemical changes induced in the immunoglobulin by linkage. These changes are reflected in loss of antibody activity and poor water solubility of the preparations thus limiting the clinical potential of complexes in this form. Here we describe a method of overcoming these problems. Instead of direct substitution of the drugs on the Ig, an intermediate carrier molecule is heavily substituted and the drug carrier then linked to Ig. By minimising interference with the chemical structure of Ig in this linkage step, a conjugate is produced with both a high concentration of drug and little loss of antibody activity. This conjugate has proved effective in suppressing tumour growth in mice.

The heart as a target organ in systemic allergic reactions: comparison of cardiac analphylaxis in vivo and in vitro.

Abstract: The purpose of this investigation was to define and quantitatively evaluate cardiac anaphylaxis in vivo. Guinea pigs, passively sensitized with graded amounts of rabbit antipenicilloyl antibody, were anesthetized, ventilated, and challenged intravenously with a constant amount of antigen (anaphylaxis in vivo). In other experiments, guinea pig hearts were excised, perfused in a Langendorff apparatus, and challenged (analphylaxis in vitro). During in vivo anaphylaxis, sinus rate increased 10-30 beats/min, conduction arrhythmias occurred in 15 of 22 experiments, and ventricular fibrillation was seen in 8 of 22 experiments. Tachycardia and arrhythmias began approximately 20 seconds after antigen administration and were accompanied, but not preceded, by respiratory and pressor changes. During in vitro anaphylaxis, sinus rate increased 70-110 beats/min, coronary flow rate decreased 2-22%, conduction arrhythmias occurred in 21 of 31 experiments, and ventricular ectopic activity was seen in 13 of 31 experiments. Tachycardia and arrhythmias began approximately 15 seconds after antigen administration. Sinus tachycardia, atrioventricular conduction block, increased ventricular automaticity, and histamine release were characteristic features of cardiac anaphylaxis in vivo and in vitro. Both in vivo and in vitro, the intensity of the cardiac reaction depended on the amount of antibody used in passive sensitization. Our results clearly indicate that the heart reacts as a target organ in systemic anaphylaxis of the guinea pig.

Blocking the formation of N-nitroso compounds with ascorbic acid in vitro and in vivo.

Abstract: N-Nitroso compounds (NO-compounds) , such as nitrosamines and nitrosamides, are produced by the reaction of nitrite with nitrogen compounds. The formation of these compounds in vitro and in vivo was recently reviewed.l Kinetic studies showed that differences of up to 200,000 X occur in the ease of nitrosation of various nitrogen compounds, as measured by the kinetic rate constants. The most readily nitrosated classes of compounds are the weakly basic secondary amines (e.g. morpholine, piperazine, and N-methylaniline) , tertiary enamines (e.g. aminopyrine), N-alkylureas, and N-alkylcarbamates. Nitrite occurs in nitrite-preserved meat and fish, spoiled foods (where nitrate is reduced by bacterial action), and human saliva (which has about 10. mg NaNOJliter) . Amines, ureas, and carbamates occur widely as food constituents, food additives, drugs, and/or pesticides. More than 100 NO-compounds have been found to induce tumors in rodents, in the stomach, liver, esophagus, lungs, nervous system and pancreas. Many of these tumors are similar to tumors in man, where they show wide geographic and temporal variations in incidence, suggesting that they are induced by chemical agents. Hence the possibility arises that these tumors are induced in man by NO-compounds. These could reach the body from external sources, food and cigarette smoke, for example, or be formed in vivo, especially, since nitrosation is acid-catalyzed, in the stomach. The latter situation has been produced in rats and mice, where feeding nitrite together with amines or u r e a has given rise to acute liver damage and tumors of various organs. The concentration of NO-compounds so far determined in food is usually small, <0.1 mg/kg, and it remains to be established whether NO-compounds present a significant risk to human populations. However, populations exposed to high levels of nitrate (which could be reduced to nitrite) appear to show raised incidences of gastric and liver cancer.'. In conclusion, the points briefly reviewed here indicate that involvement of NO-compounds in the etiology of human cancer is a real possibility. Therefore, it would be useful to be able to prevent the formation of NOcompounds in food and in vivo. Since a number of readily nitrosated drugs are administered orally in largc doses, their possible nitrosation in vivo is particularly disturbing. Among such drugs are piperazine, phenmetrazine, aminopyrine, ethambutol, and (possibly) oxytetracycline (OTC) and disulfiram. Many other drugs have yielded NO-derivatives, but often only under extreme

Mechanism of the suppressive effect of interferon on antibody synthesis in vivo.

Abstract: Mouse interferon preparations significantly suppress the in vivo antibody response to sheep red blood cells (SRBC), a thymus-dependent antigen, and to Salmonella typhimurium lipopolysaccharide (LPS), a thymus-independent antigen. It is also possible to effect the late responses of antigen sensitive “memory” cells observed during secondary immunization by administration of interferon prior to primary immunization. The immunosuppressive activity of interferon was time- and dose-dependent. Maximum suppression was produced when animals were given 1.5 × 10 5 units of interferon between 4 and 48 hr before antigenic stimulation. These findings suggested that interferon affects some early event(s) in the process of antibody synthesis which might be related to the general inhibitory effect of interferon on rapidly dividing cells and viral m -RNA translation. In addition, the use of nonadherent spleen cell cultures from interferontreated mice, immunized in vitro with a thymus-independent antigen, indicated that in this situation the inhibitory effect of interferon was due to an action on B lymphocytes. A variety of soluble “suppressive” factors are secreted by T cells as a consequence of activation by mitogens or specific antigens in vitro. Since T cells are recognized as one of the sources of interferon, it is suggested that interferon should be investigated as a suppressor T cell-produced lymphokine which can regulate B cell expression.

Comparison between macrophage activation and enhancement of nonspecific resistance to tumors by mycobacterial immunoadjuvants

Abstract: It has repeatedly been observed that various bacterial preparations could increase the host's resistance to tumors. It has also been shown that after nonspecific activation by BCG (bacillus Calmette-Guerin), peritoneal macrophages could inhibit in vitro the growth of neoplastic target cells. In the present study a fraction extracted from Myobacterium smegmatis and referred to as interphase material was tested in view of measuring its ability to activate macrophages in vitro and in vivo. This preparation was previously shown to protect mice against a syngeneic leukemia and to increase the immune response of the guinea pig. Other water-soluble adjuvants devoid of demonstrable antitumor activity in vivo were also assayed. The results argue in favor of a correlation between adjuvant activity and the capacity of activating macrophages. Moreover, interphase material administered in vivo consistently induced stronger and more persistent stimulations of macrophages than the other preparations assayed.

In Vitro Metabolism and Microsome-mediated Mutagenicity of Dialkylnitrosamines in Rat, Hamster, and Mouse Tissues

Abstract: Summary Rates of conversion of 14C-labeled dimethyl- and diethyl-nitrosamine by rat and hamster tissue slices to 14CO2 and/or into mutagenic reactants were measured using Salmonella typhimurium G-46 or TA 1530 and fortified tissue fractions in vitro. A correlation between the CO2 production from dimethyl- or diethylnitrosamine in liver or lung and the organ distribution of induced tumors in vivo was observed. As an exception, hamster lung, which is a major target organ in diethylnitrosamine carcinogenesis, did not convert this nitrosamine into metabolites mutagenic for S. typhimurium TA 1530, although the 14CO2 production in vitro was even higher than in hamster liver. The effect of pretreating rats, hamsters, and mice with phenobarbitone on the mutation frequency produced by dimethyl- or diethylnitrosamine in in vitro assays was determined. The relationship between the site of metabolic activation, mutagenicity, and carcinogenicity of the dialkylnitrosamines and the effect of enzyme inducers are discussed.

The specific cytotoxic effects of daunomycin conjugated to antitumor antibodies.

Abstract: Daunomycin was covalently bound to immunoglobulins by periodate oxidation as described in the preceding paper. Conjugates were prepared with immunoglobulins directed against either of two mouse lymphoid tumors or with nonspecific immunoglobulins. These conjugates were tested for their toxic effects on various tumor target cells as measured either by their inhibition of RNA synthesis or by their reduction of the growth of the tumor cells after transplantation. We found that the drug preferentially affected the target cells that the antibody to which it was attached could recognize. These daunomycin-antibody conjugates are therefore sufficiently toxic and selective in their effects to be potentially useful in in vivo therapeutic studies.

An isolated guinea pig heart preparation with in vivo like features.

Abstract: Hemodynamic and metabolic characteristics of an isolated guinea pig heart preparation perfused with a pyruvate fortified Krebs-Ringer-bicarbonate solution are described. The preparation is stable for more than 90 min with respect to coronary flow, heart rate, left ventricular pressure,dP/dt, oxygen consumption, and myocardial high energy phosphate levels. The changes in coronary flow induced by alterations of perfusion pressure, ischemia, and hypoxia resemble those seen under in vivo conditions. The preparation also exhibits concentration dependent and reproducible changes in coronary resistance upon administration of adenosine and papaverine. The in vivo like features of this preparation can be mainly attributed to the use of pyruvate as additional and preferentially utilized substrate. The preparation appears to be suitable for quantitative studies of myocardial metabolism and heart function as well as for investigations of the coronary system.

An Assay for Erythropoietin in Vitro at the Milliunit Level

Abstract: A method is described for the assay of erythropoietin using primary cultures of adult rat bone marrow cells. Either total labeled iron uptake by the cells or hematin synthesis from labeled iron may be used as the measure of erythropoietin action. The method is useful in the range 0.001 to 0.010 U, where the log response is linear with the log dose, and can be carried out in 2 working days. This method has the disadvantage of detecting asialoerythropoietin which has no activity in vivo. (Endocrinology 97: 315, 1975)

Effects of canine distemper virus infection on lymphoid function in vitro and in vivo.

Abstract: In the present study, the immunodepressive effects of canine distemper virus (CDV) infection of dogs on two parameters of lymphocyte function, namely phytomitogen-induced cellular proliferation and skin allograft rejection, were investigated. Infection of susceptible gnotobiotic dogs with virulent R252-CDV resulted in a depression of peripheral blood lymphocyte mitogen response as measured by (3H)thymidine incorporation for up to 10 weeks after inoculation. This effect coincided with the appearance of viral antigen by immunofluorescence in leukocytes but persisted after the virus was no longer detectable. Loss of mitogen reactivity was seen in all infected dogs. However, when these same CDV-infected dogs were challenged with foreign skin allografts, no significant retention of grafts over controls was observed despite the depressed lymphocyte activity. Considering the in vitro and in vivo data it was concluded that, although immunodepressive effects of CDV were demonstrated in vitro, paralled in vivo experiments indicated that less than complete suppression of immune functions occurs during the course of CDV infection.

Correlation of in vivo collagen degradation rate with in vitro measurements.

Abstract: The rate of in vitro enzymatic degradation of various materials based on collagen has been determined by a novel mechanochemical method, and has been compared with the extent of degradation resulting from subcutaneous implantation in guinea pigs. In vitro data correlate well with in vivo data. It is suggested that the simple in vitro method described is an effective means of screening a large number of materials based on collagen for their ability to resist degradation during implantation in animals.

Biochemically differentiated mouse glial lines carrying a nervous system specific cell surface antigen (NS-1).

Abstract: Six biochemically differentiated clonal lines have been established from a transplantable glioma (tg26) of the C57BL/6 inbred mouse strain. Antibodies have been previously raised against G26 tumor cells, which define a cell surface component(s), NS-1 (nervous system antigen-1), found exclusively in the nervous system. NS-1 concentrations approximate the levels of the original G26 tumor when the clonal lines are grown as clonal tumors in vivo, but are reduced when the cells are grown in vitro. NS-1 concentrations are further reduced in vitro upon incubation of the cells with 1 mM dibutyryl 3:5-cyclic AMP. H-2 histocompatibility antigen concentration, in contrast, is unaffected by dibutyryl cAMP. In addition to expressing NS-1, the neuroectodermal origin of these cell lines is further confirmed by their synthesis of the nervous system specific acidic protein S-100 and by the high specific activity of the enzyme 2:3-cyclic nucleotide 3-phosphohydrolase. In addition, they respond to catecholamines by the elevation of intracellular 3:5-cyclic AMP levels. Whereas expression of S-100 protein is high under in vitro conditions but negligible after one passage in vivo, 2:3-cyclic nucleotide 3-phosphohydrolase is not detectable in vitro but becomes detectable again in vivo. The two membrane-bound constituents, NS-1 and 2:3-cyclic nucleotide 3-phosphohydrolase, therefore seem to be subjected to different regulatory mechanisms from that of the soluble, intracellular S-100 protein.

The role of c3 as an opsonin in the early stages of infection.

Abstract: In order to investigate the role of C3 in host defense in vivo, normal AKR/J mice, genetically deficient in C5, were depleted of serum C3 by the injection of purified cobra venom factor (CoVF). Concurrent with their C3 depletion, their serum opsonizing activity decreased to a level less than 20% of normal. When these mice were challenged with an intraperitoneal injection of pneumococci 2 hr after the CoVF treatment, the LD50 was from 30 to 80 times lower than the LD50 in saline-treated control animals. When the CoVF was given only 6 hr after the pneumococcal challenge, the LD50 was the same as in the control mice. If the pneumococci were first preopsonized in vitro and then injected into CoVF-treated animals, the LD50 was the same as that in control animals. These experiments demonstrate that C3 plays a significant role in vivo in the host's defense against infection and that a major part of that role is through its action as an opsonin. Furthermore, these experiments demonstrate that the role of C3 is most significant during the early stages of bacterial invasion.

In vivo testing of hypoxic radiosensitizers using the KHT murine tumour assayed by the lung-colony technique.

Abstract: The KHT transplantable tumour of C3H mice has been used as a model tumour for the in vivo study of hypoxic cell sensitizers. Eleven sensitizers comprising four nitrofuran five nitrobenzene and two nitroimidazole derivatives, which have been shown to be effective on hypoxic mammalian cells in vitro, have been investigated. Two of these compounds, metronidazole (2-methyl-5-nitroimidazole-1 ethanol) and tinidazole (ethy1 [2-(2′-methyl-5′-nitro-1′- imidazolyl) ethyl] sulfone), showed signs of hypoxic cell-sensitization in vivo when given systemically by intraperitoneal injections. In addition, preliminary testing of the nitrobenzene NDPP (p-nitro-3-dimethyl-propriophenone hydrochloride) indicated that when it was injected directly into the tumour and irradiation was completed within ten minutes after injection, appreciable sensitization was obtained. More detailed studies indicated that both metronidazole at 1,500 mg/kg and tinidazole at 750 mg/kg given intraperitoneally gave an enhancement ratio of ...

Antibodies against mouse ovaries and their effect on fertilization in vitro and in vivo in the mouse.

Abstract: The specificity and mechanism of the effect of heteroimmune antibodies against mouse ovaries in fertilization in vitro and in vivo were investigated. Mouse ovarian homogenate supernatant was prepared for immunization of rabbits. The resultant serum was absorbed by normal mouse serum and by the sediment of mouse liver spleen and kidney tissue homogenate and was termed specific immune serum. The antisera were tested by indirect immunofluorescence using pig antirabbit immunoglobulin G labeled with fluorescein isothiocyanate. All tissues (spleen kidney liver lung uterus heart ovary) tested in mice aged 10-16 weeks with the immune nonabsorbed serum gave positive results. The specific immune serum gave reactions in the zona pellucida only in ovarian sections and in live oocytes. Rabbit heteroimmune antiserum had no effect on the dispersion of cumulus and corona radiata cells by the spermatozoa. The administration in vitro of antiovarian antibodies seemed to be a block to sperm penetration through the zona pellucida. Sperm penetration was blocked when antibodies were administered 39-15 hours before human chorionic gonadotropin was injected.

In vitro evaluation of in vivo brain tumor chemotherapy with 1,3-bis(2-chloroethyl)-1-nitrosourea.

Abstract: An in vitro colony formation assay was used to determine the efficacy of in vivo therapy with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) on a rat brain tumor. The fraction of clonogenic cells surviving in vivo therapy was determined by a comparison between the in vitro colony-forming capacity of cells derived from previously treated and untreated tumors. With this intracerebral solid tumor a direct correlation was found between the surviving fraction of cells and animal survival, implying that the in vitro assay system is a reliable test of therapeutic effect. The BCNU dose-response curve was exponential up to a dose of 0.75 times the LD/sub 10/ dose with little additional cell kill noted at higher drug levels. This plateau does not appear to represent a resistant subpopulation of cells, since retreatment of tumors derived from cells surviving an LD/sub 10/ dose were as sensitive to BCNU as those with no prior drug exposure. Instead, it may represent, at least in part, failure of the drug to reach and/or enter cells in all parts of solid tumors. On the average BCNU doses of 0.75 times the LD/sub 10/ dose or greater resulted in slightly more than a 3-log cell kill and doubled the life-span formore » our tumor-bearing animals. The finding that an increase in animal life-span requires at least a 1-log tumor cell kill indicates that survival studies with intracranial tumor models may be insensitive to single courses or many chemotherapeutic agents with modest but significant antitumor activity. (auth)« less