Showing papers in "Cancer Research in 1968"

Surface IgM-kappa Specificity on a Burkitt Lymphoma Cell In Vivo and in Derived Culture Lines

Abstract: Summary An exceptional Burkitt lymphoma patient, a 16-year-old boy, yielded tumor biopsy cells and derived tissue culture lines that displayed a strong surface accumulation of IgM heavy and kappa light chain specificities judged by direct membrane fluorescence and cytotoxicity tests. This property was maintained unchanged in the course of more than 5 months of serial passage in vitro . A fourth biopsy, obtained from the patient after massive necrosis had been induced in the tumor by cytosine arabinoside chemotherapy, did not show this property at either the biopsy stage or in the derived cell line. The possibility that the neoplastic transformation of lymphoid cells may have afflicted a cell specialized to carry immunoglobulin on its surface may be considered. The phenomenon has to be distinguished from immunoglobulin coating in vivo seen with certain biopsy samples from this and other patients. The latter type of coating can be of IgM, IgG, or IgA nature and disappears rapidly on cultivation in vitro .

The Establishment of a Cell Line of Human Hormone-synthesizing Trophoblastic Cells in Vitro

Abstract: A human hormone-synthesizing trophoblastic cell system has been established in vitro and may prove to be the first functional human embryonic cell line in continuous culture. Chorionic gonadotropin hormone produced by these cultures serve as a marker for identification of the trophoblastic cell. No interruption in this property nor change in cytologic display has occurred during 1.5 years in continuous culture. The continued proliferation of the undifferentiated cytotrophoblast is being stabilized in serial cultivation.

Inhibition of mammalian DNA polymerase by the 5'-triphosphate of 1-beta-d-arabinofuranosylcytosine and the 5'-triphosphate of 9-beta-d-arabinofuranoxyladenine.

Abstract: Summary The 5′-triphosphate of 1-β-d-arabinofuranosylcytosine (ara-CTP) was tested as a substrate or inhibitor of polynucleotide synthesis using mammalian polymerases. The compound did not replace deoxycytidine triphosphate (dCTP) as substrate for DNA polymerase and did not replace cytidine triphosphate as substrate for RNA polymerase. The compound was found to inhibit DNA synthesis catalyzed by DNA polymerase; the inhibition appeared to be competitive with dCTP. No inhibition of RNA polymerase was observed. Further studies indicate that the inhibition of mammalian DNA polymerase by the 5′-triphosphate of 9-β-d-arabinofuranosyladenine (ara-ATP) is also competitive with the corresponding deoxytriphosphate. The data on the mode of action of 1-β-d-arabinofuranosylcytosine and of 9-β-d-arabinofuranosyladenine have been summarized, and the present status of hypotheses on these mechanisms have been discussed. The data are consistent with the view that ara-CTP and ara-ATP act in animal cells via their respective triphosphates to inhibit the animal cell DNA polymerase, although ara-ATP, but not ara-CTP, may also act by inhibiting ribonucleotide reductase.

Inhibition of Ribonucleoside Diphosphate Reductase by Hydroxyurea

Abstract: Hydroxyurea, a compound which inhibits the growth of rapidly proliferating tissues in animals and man, is known to inhibit DNA synthesis, and studies in crude systems have indicated that it does so by preventing the reduction of ribonucleotides to deoxyribonucleotides. This study demonstrates hydroxyurea-induced inhibition of the reduction of ribonucleotides by a highly purified enzyme system from Escherichia coli B. The inhibition (70% at 3 × 10-3 m under standard incubation conditions) is dependent on the concentration of hydroxyurea and on the duration of exposure of the enzyme to hydroxyurea. The effect of hydroxyurea is specific for protein B2 of the ribonucleoside diphosphate reductase system. The inhibition of enzymatic activity is apparently irreversible, although there is negligible irreversible binding of 14C-labeled hydroxyurea to the enzyme protein.

Production of embryonal serum alpha-globulin by hepatomas: review of experimental and clinical data.

Abstract: It was demonstrated in 1963 that transplantable mouse and rat hepatomas synthesize and secrete into the blood a specific a-globulin of embryonic sera, «(-globulin (1, 6, 7). It was shown further that the same phenomenon of elaboration of embryonic serum a-globulin by hepatomas could be obtained by primary liver tumors of rats (20), mice (2, 23), and hu man beings (33, 34). An important aspect of the problem is the possibility of using a [-globulin appearance in the blood of patients for diag nosis of hepatomas in the clinic. The experimental data obtained in mice did not suggest such a possibility, since a rglobulin was revealed only in 25% of chemically induced primary liver tumors and this protein could be also demonstrated by liver regeneration. The detection of a {-globulin in clinical cases might, however, be of certain value in differential diagnosis of hepatocellular carcinoma. Thus, Tatarinov (33), who was the first to find this globulin in cases of human hepatoma, was unable to detect it either in cases of cholangioma and secondary localization of other tumors in liver or in noncancerous diseases accom panied by liver regeneration, such as cirrhosis and hepatitis. He regularly revealed «(-globulin in the blood of patients with hepatocellular liver cancer. Immunochemical diagnosis, as dis tinct from clinical, was in full coincidence with autopsy data. By 1966 Tatarinov et al. (33, 34, 36, 37) described 6 cases of arglobulin appearance in primary hepatomas on the back ground of numerous negative controls. One additional case was described by Czech investigators (25). This suggests that the arglobulin test is both more regular and more specific in hu man hepatomas than in experimentally induced tumors, at least in mice. The main findings reported by Tatarinov have been con firmed and extended by 2 separate groups: ours, in collabora tion with the Institute of Experimental and Clinical Oncology of the USSR Academy of Medical Sciences (3, 10, 36), and by Grabar's group in Villejuif and Dakar (38). The results

A Serum Alkaline Phosphatase Isoenzyme of Human Neoplastic Cell Origin

Abstract: Summary In the course of a study of serum phosphatase isoenzymes in cancer patients, a patient with bronchogenic carcinoma was discovered, whose serum contained an alkaline phosphatase which was indistinguishable from placental alkaline phosphatase. The same enzyme was demonstrated in high concentration in the neoplasm and its metastases. This single case demonstrates the possibility that elevated serum alkaline phosphatase in patients with metastatic cancer can be of neoplastic rather than of hepatic and osseous origin.

A method for the experimental induction of bronchogenic carcinoma.

Abstract: Summary A methodology for the experimental induction of bronchogenic carcinoma in conditions related to those of human exposure to respiratory carcinogens is described. Animal of choice is the hamster. Polynuclear hydrocarbon carcinogens are prepared as suspensions of fine crystalline particles and attached to a finely particulated inert dust which acts as a carrier; the mixed dust is suspended in saline and administered by intratracheal instillation. Penetration and distribution patterns are described. No necrosis and no chronic inflammatory reactions other than phagocytosis are induced. Repeated intratracheal instillations of benzo[a]pyrene with hematite dust induce up to 100% incidences of respiratory tract tumors, mostly bronchogenic carcinomas. The morphology of these tumors appears very close to that of human lung cancer; squamous cell carcinomas are the most frequent type followed by anaplastic carcinomas and by a few adenocarcinomas. The experimental model presented here appears adequate for studies on factors involved in the pathogenesis of cancer of the lung.

Uptake and Retention of Daunomycin by Mouse Leukemic Cells as Factors in Drug Response

Abstract: Summary Survival of mice bearing different transplantable tumors and treated with Daunomycin was compared with the capacity of the tumor cells for uptake of the drug in vitro and for drug uptake and retention in vivo . The data obtained indicate that the ability of these cells to retain Daunomycin in vivo was a determinant of drug response.

Cellular Location of Carcinoembryonic Antigens of the Human Digestive System

Abstract: Summary Earlier studies revealed that all adenocarcinomata of the human digestive system, arising from entodermally derived epithelium, contain identical tumor-specific antigens. Further investigations showed that similar constituents are present in embryonic and fetal gut, pancreas, and liver in the first two trimesters of gestation. These components have, thus, been named carcinoembryonic antigens (CEA) of the human digestive system. Serologic testing demonstrated that the sera of the majority of patients suffering from nonmetastatic digestive system cancer contain specific anti-CEA antibodies, which disappear from the circulation following metastatic dissemination of the tumor. These findings led to experiments, described in this report, which were designed to localize the CEA sites of the digestive system cancer cell. Immunofluorescent studies of tumor tissue sections and agglutination reactions with cultured explanted cells of digestive system cancers indicated that the CEA are associated with the tumor cell surface. This observation is discussed in the light of the significance of the human anti-CEA antibody response.

Direct implantation and serial transplantation of human acute lymphoblastic leukemia in hamsters, SB-2.

Abstract: Summary Human acute lymphoblastic leukemia cells have been established as a serially transplantable lymphosarcoma in newborn Syrian hamsters by the direct inoculation of cells from the peripheral blood of a boy in the terminal stages of lymphosarcoma The experimental neoplasm, currently in its 70th serial passage, is metastatic and occasionally progresses to frank leukemia In later passages, it has become transplantable in the newborn hamster every 10–12 days Immunofluorescence evidence indicates that it is still composed of human cells after continued passage in the experimental host Cytogenetic examination shows the cells to be of male human karyotype Electron-microscopic examination reveals them to be free of morphologically recognizable virus

Toxicology and carcinogenic action of pyrrolizidine alkaloids

Abstract: Summary The studies of the hepatoxic and hepatocarcinogenic pyrrolizidine alkaloids (PA) have shown that ( a ) The conventional testing for toxicity and its evaluation on the basis of death occurring a few days after dosing is meaningless for carcinogenic agents. ( b ) A single dose of a water-soluble substance, the main part of which is metabolized and excreted in a few hours after ingestion and which does not cause immediately obvious illness, can induce tumors that become apparent a long time after its administration. The induction of tumors appears to resemble a ripening process, which can be accelerated by repeated dosage of the same or of certain other compounds (and presumably could also be delayed). ( c ) The first impact of a carcinogenic agent on a cell is the inhibition of its division, possibly through interference with a “mitotic factor.” ( d ) The very young are more susceptible than adults to PA9s; if ingested by lactating females, the latter may remain unscathed, while the suckling young will suffer the ill effects and may develop tumors when still very young. ( e ) The elimination of the toxin in the milk may be a factor in the greater resistance of the lactating female to such agents. ( f ) Sexual hormones affect the response to PA9s, adult males are more susceptible than adult females to these hepatotoxins. ( g ) The hepatotoxic entity is probably a product formed from pyrrolizidine alkaloids in the course of their metabolism in the liver and possibly also in other tissues. The effects of age, sex, diet, and animal species may thus be related to the concomitant variations in the metabolism of PA9s. ( h ) Hepatotoxic PA9s induce in primates mainly pulmonary and venoocclusive lesions. ( i ) Man is also susceptible to the hepatotoxic PA9s. Vascular lesions described as Chiari9s syndrome in South Africa and as “venoocclusive disease” in Jamaica have been correlated with the ingestion of PA9s.

Streptozotocin: depression of mouse liver pyridine nucleotides.

Abstract: Summary A single intravenous diabetogenic dose of Streptozotocin, 200 mg/kg, produced a 24-hour depression of oxidized and reduced nicotinamide adenine dinucleotide (NAD and NADH) content in mouse liver. This was followed by a gradual return to normal coenzyme concentrations by the end of 48 hours. Intraperitoneal nicotinamide, 500 mg/kg, administered ten minutes prior to Streptozotocin protected animals against NAD depression for approximately 16 hours. Animals receiving nicotinamide alone showed significantly higher liver NAD values than the combination treatment group. It was found that 1-methyl-1-nitrosourea, the nondiabetogenic but antileukemic moiety of the Streptozotocin molecule, could produce a similar dose-related depression of NAD, while Alloxan did not. The serum half-life of Streptozotocin after an intravenous injection, 200 mg/kg, was approximately 5 minutes, with no drug measurable by two hours. Streptozotocin was detectable in the acid-soluble fraction of liver for 20 hours, and it was found that nicotinamide pretreatment did not significantly alter the drug uptake by this organ. Using prevention of diabetes as the criterion of toxicity modification, a schedule of small serial administrations of nicotinamide over a 24-hour period was shown to be more effective than the injection of the total dose just prior to Streptozotocin. It is suggested that Streptozotocin is inhibiting synthesis of pyridine nucleotides.

Induction of increased benzpyrene hydroxylase activity by flavones and related compounds.

Abstract: Summary A study of relationships between the structure of flavones, flavanones, and chalcones and their capacity to induce increased 3,4-benzpyrene (BP) hydroxylase activity in the liver and lung of the rat has been carried out. Appropriate halogenation increases inducing activity. In the compounds studied, hydroxylation reduces inducing capacity, but the corresponding methoxy compounds are active. Two naturally occurring polymethoxy flavones, tangeretin and nobiletin, have been found to be active inducers of BP hydroxylase activity.

On the Nature of a Transport Alteration Determining Resistance to Amethopterin in the L1210 Leukemia

Abstract: The uptake of amethopterin-3H by L1210 leukemia cells appears to be mediated, probably, via an active transport mechanism. Uptake occurred against a concentration gradient, was temperature dependent, required a readily available source of energy, exhibited a pH optimum of 7.6 and conformed to Michaelis-Menten kinetics. The maximum intracellular concentration of unbound amethopterin-3H accumulated at equilibrium was 8-fold the external concentration. Both folate and H2-folate compete with amethopterin-3H for the same system, but to a limited degree. The rate of transport was reduced 4-fold in cells of a subline (XVI4) resistant to amethopterin, 6-mercaptopurine and 5-fluorouracil. Kinetic analysis revealed an increase in the Michaelis constant ( Km ) for the system in these resistant cells, suggesting an alteration in the binding properties of a carrier component as the basis for the impairment. A second subline (XVI4a) was derived directly from the original subline XVI4 and was characterized by the absence of the subtelocentric chromosome and an elevated dihydrofolate reductase. The rate of transport in cells of this chromosomal variant was normal, although the Km for the system was increased as in cells of subline XVI4. Maximum intracellular accumulation of unbound amethopterin-3H by cells of subline XVI4a was greater than 11-fold the external concentration.

A comparison of ultrastructural changes in rat liver due to chemical carcinogens.

Abstract: Summary A wide range of nonspecific and reversible ultrastructural responses occur in liver cells following acute and chronic exposure to hepatocarcinogens Although most changes do not occur to a uniform extent in all cells in acute and chronic experiments, nor do they persist indefinitely after withdrawal of the carcinogen, nucleolar abnormalities and disturbance in the ribosome-ergastoplasm relationship are the most consistent alterations in acute and chronic intervals and in the tumor cells themselves None of the carcinogens used produced tumors with ultrastructural features sufficiently characteristic to distinguish them from those produced by other carcinogens Despite the limitations of sampling and methods of electron microscopy, it would appear from a morphologic point of view that, following administration of hepatocarcinogens, nucleolar abnormalities at the level of synthesis and assembly of ribosomal precursors probably are equal in importance to changes in the ribosome-ergastoplasm complex in the cytoplasm

Tumor-specific transplantation antigens: G. H. A. Clowes memorial lecture.

Abstract: Summary Tumor-specific transplantation antigens capable of inducing rejection responses of variable strength in genetically compatible (syngeneic) hosts, have been demonstrated in most experimental tumors studied by sensitive assay systems with graded challenge inoculum doses. The reactions are particularly clear-cut in tumors induced by chemical carcinogens and oncogenic viruses, but they could also be demonstrated in a number of “spontaneous” tumors of unknown origin. Antigenic cross-reactivity is the rule for tumors induced by a given virus, whereas chemically induced neoplasms tend to show individually distinct antigenic specificity. This opens new avenues of approach for studies on the phenotype of the neoplastic cell. Provided due regard is given to the passenger virus problem, the demonstration of antigenic cross-reactivity in unknown systems may give new clues with regard to possible etiologic relationships. The existence of tumor-specific transplantation antigens raises the paradoxical question of how antigenic tumor cells can grow out in spite of host responses. Neonatal thymectomy increases the incidence of certain chemically and virally induced tumors, indicating that immunologic surveillance normally eliminates potentially neoplastic cells in a fraction of the cases. Its failure in others may be related to the immune status of the primary autochthonous host. This is quite different for different systems; documented situations include full and apparently specific tolerance (demonstrated for certain vertically transmitted oncogenic RNA viruses in their natural hosts, particularly some murine leukemia agents and the mammary tumor agent); nonspecific immunodepression (shown for certain chemical carcinogens), sometimes with a superimposed component of specific antigenic paralysis (indicated for mouse methylcholanthrene-induced sarcomas); nonspecific immunodepression due to aging; and a curious state of inertia characterized by the absence of both tolerance and sensitization (exemplified by most DNA virus-induced tumors or by the Schmidt-Ruppin variant of the Rous agent). This inertia is most liable to be influenced by immunologic reinforcement, although the risk of enhancement must be taken into consideration. The possible therapeutic significance of tumor-specific immune responses still remains to be clarified, but there is good reason to believe that immune responses may contribute to the inhibition of disseminated tumor cells and thus reduce the risk of recurrence, at least in certain systems.

Toxicology of Cycasin

Abstract: These compounds are extractable from seeds and roots of cycad plants Cycads are ancient gymnospermous plants which are con sidered an intermediate form in plant evolution from ferns to flowering plants. Study of fossils indicates that cycads were distributed widely throughout the world in the early mesozoic period, i.e., about 200 million years ago. The cycads which can be found today are essentially limited to the tropical and subtropical zones around the globe (8, 51). Although this review emphasizes recent developments in cycad research, it is important to realize that toxic properties of seeds and roots of cycads were known to populations which used them as food long before the toxic principles were identified. Strikingly similar methods for removing the poison were apparently employed by these populations. In the course of our studies with cycads, we have examined samples of cycad flour prepared by several families on Guam for human consumption and have found it nontoxic and noncarcinogenic in experimental animals (61). Apparently the methods em ployed by these people removed the greater part, if not all, of the poison from the seeds. An extensive literature review of the chemistry and toxicity of cycads is available and contains accounts of the uses of cycads as food and medicines (58). The paper has been subdivided into five sections, reviewing the following aspects of cycad toxicity: (a) isolation of toxic principle, (b) neurotoxicity, (c) carcinogenicity, (d) metabolic conversion of cycasin to MAM in vivo, and (e) biologic effects. The review closes with several general comments, including suggestions for important work to be done in the future.

The Teratogenicity of Cyclophosphamide in Mice

Abstract: Summary Cyclophosphamide, administered intraperitoneally to time-dated pregnant Swiss Webster mice on gestational Days 9 through 14 in a dosage of 20 mg/kg, resulted in increased numbers of resorptions and a variety of teratogenic effects. Gross examination of fetuses revealed cleft palate, exencephaly, digital defects, and kinky tail. Skeletal anomalies included polydactyly, syndactyly, ectrodactyly, adactyly, fusion of the long bones, curvature of the long bones, and missing ribs. Soft tissue malformations included open eyes, aphakia, microphakia, hydronephrosis, and hydrocephalus. Dosages of 5 and 10 mg/kg resulted in increased resorption and decreased growth rates in a dose-related manner but produced no discernible anomalies. Fetal mortality curves were biphasic, with the highest peak occurring on administration Days 9 and 10 and a second peak on Days 13 and 14.

The occurrence and metabolism of alkyl and alk-1-enyl ethers of glycerol in transplantable rat and mouse tumors.

Abstract: SUMMARY Thirteen transplantable animal tumors have been quantita tively analyzed for their glyceryl alkyl and alk-1-enyl ethers in the neutral lipid and phospholipid fractions. The data ob tained demonstrate that the quantity of glyceryl ethers in the neutral lipid fraction of tumors is significantly higher than that found in normal tissues. The amount of ether-linked phospholipids is also higher in tumors than in most normal tissues. Radioactivity from intraperitoneal injections of palmitic acid-l-14C was incorporated into both the ether-linked aliphatic moiety (13-25% of the total glyceryl ether diester activity) and the esterified fatty acids of glyceryl ether diesters isolated from Ehrlich ascites cells. Labeling of the glyceryl ether diesters also occurred when fatty alcohols-14C and triglycerides-14C were administered to mice bearing the ascites cells; radio activity from acetate-2-14C, glucose-14C, and 3H20 was not incorporated into the glyceryl ether diesters. The specific ac tivity of the triglycA©ride fraction was always higher than that of the glyceryl ether diesters found in Ehrlich ascites cells after injections of palmitic acid-l-14C. In similar experiments, the specific activities of the alk-1-enyl ethers were always higher than the specific activities of the alkyl ethers in the neutral lipid fraction, but these specific activities were essentially the same in the phospholipid fraction.

The mutagenic action of caffeine in higher organisms.

Abstract: Caffeine is a purine, l, 3, 7-trimethyl xanthine. Since it is consumed in great quantities by man, the question concerning whether it is a mutagen for man is of great significance. There is now good evidence that caffeine is mutagenic not only in bacteria (4, 5, 7, 9,18), fungi (6,41), and plants (11, 12), but equally mutagenic in Drosophila melanogaster [2, 16, 25, 29; negative reports, (40)], in mice [Kuhlmann and Ostertag 1968, unpublished; negative report, (15); ambiguous results, (3)], as well as in human cells in vitro (24, 26, 28; Jacobson, unpublished). There is some evidence that caffeine inhibits dark repair in bacteria (38) as well as in mammalian cells (33; Jacobson, C., unpublished). Caffeine is teratogenic in mice if high doses are applied (17). There is no evidence that caffeine is involved in carcinogenesis. We have good evidence from studies with Drosophila melanogaster that caffeine also causes somatic damage by breakage of chromosomes in somatic cells (29). By analogy with the action of radiation, which causes the same type of somatic damage (23; Ostertag, unpublished data), we have good reason to assume that caffeine induces premature aging in Drosophila.

Immunologic, Virologic, and Pathologic Studies of Regression of Autochthonous Moloney Sarcoma Virus-induced Tumors in Mice

Abstract: Summary Adult mice inoculated with murine sarcoma virus (Moloney) (MSV) developed tumors which ultimately regressed, whereas newborn or preirradiated hosts died with nonregressing tumors. Regression of autochthonous tumors was preceded, accompanied, and followed by the production of circulating antibody capable of neutralizing the oncogenicity of MSV and by the development of resistance to the transplantation of syngeneic Moloney sarcoma cells. The regressing tumors exhibited degenerative changes, were progressively infiltrated with mononuclear cells, and ultimately exhibited a relatively low content of MSV. By contrast, tumors induced in immunologically hyporesponsive hosts grew progressively, were not infiltrated with mononuclear cells, and contained abundant MSV at all times. These mice had oncogenic MSV in plasma and spleen and no virus-neutralizing activity in the serum. It is suggested that a specific immunologic response is operative in the rejection of MSV-induced tumors by the autochthonous host and is manifested by tumor regression. Evidence is discussed for the view that the rejection may be largely mediated by a cellular, rather than a humoral, response. Finally, these results, coupled with analogous studies in the Rous sarcoma and Shope papilloma systems, suggest that rejection of antigenic autochthonous tumors, of microscopic if not macroscopic size, by an immunologically reactive host may represent a more general phenomenon in nature than was previously suspected.

Cross-resistance to the Transplantation of Syngeneic Friend, Moloney, and Rauscher Virus-induced Tumors

Abstract: Summary Immunofluorescence data are presented which confirm the previously reported cytotoxic antibody studies suggesting that Friend, Moloney, and Rauscher (FMR) virus-induced lymphomas possess similar surface antigens, not shared by Gross lymphomas. It is not known, however, whether the antigenic relationship demonstrable serologically is, or should necessarily be, demonstrable by transplantation studies. To determine if tumors induced by FMR and Gross virus share transplantation antigens, C57BL/6 mice were pretreated with either infectious FMR viruses, FMR lymphomas, or a Gross lymphoma and challenged with syngeneic FMR and Gross lymphomas. Mice pretreated with any one infectious FMR virus or its induced lymphoma became resistant to the transplantation of all FMR lymphomas, but not to the Gross lymphoma. Immunization with the Gross lymphoma failed to induce resistance to the transplantation of the FMR lymphomas, but also failed to induce resistance to itself. The results strongly suggest that FMR lymphomas possess related or identical transplantation antigens.

Modes of uptake of methotrexate by normal and leukemic human leukocytes in vitro and their relation to drug response.

Abstract: Characteristics of Methotrexate transport by normal and leukemic human leukocytes were measured in vitro . At high external drug levels (≧20 µm) drug uptake by all cell types was temperature-insensitive, nonsaturable, and nonconcentrative. The steady-state cell/medium drug distribution ratio was about 0.03. During clinical treatment with Methotrexate, plasma drug levels generally reach 0.2 µm. At this lower drug level: ( a ) A temperature-sensitive and saturable mode of transport was demonstrable in all cell types except small lymphocytes. In normal granulocytes the steady-state drug distribution ratio reached 0.2. ( b ) Leukemic cell types showed a wide variation in capacity for uptake of the drug, and an association was seen between this capacity and clinical response to the drug.

Growth characteristics of a mouse plasma cell tumor

Abstract: Summary A quantitative spleen-colony assay was developed and used to evaluate the growth characteristics of the Adj. PC-5 colony-forming units (CFU). There was a positive correlation between the number of colonies per spleen and the number of tumor cells injected, which is compatible with the assumption that each colony arises from one malignant cell. At 21 days, each colony contains 8.4 ± 2.1 × 107 cells, but less than 4.4% of these are tumor stem cells with the proliferative capacity to form a colony. The growth rate of tumor CFU was estimated in the spleen (CFU TD = 20 ± 4 hours) and femoral marrow (CFU TD = 29 ± 5 hours). A survival TD of 36 ± 2 hours was estimated from the survival of mice injected with graded numbers of tumor cells as an indication of the growth rate of the total tumor. The proliferative capacity of the tumor CFU was completely suppressed during a 10-hour exposure to vinblastine in vivo. This result suggests that the majority of tumor CFU have a TG of less than 10 hours. All of the tumor CFU appear to be in cell cycle, for no detectable tumor CFU survived a 10-hour exposure to vinblastine, and 70% of these cells were killed by a 20-minute exposure to tritiated thymidine in vitro. Based on these findings, a model is proposed for the growth kinetics of this tumor. The model states that a small fraction of the tumor population is composed of cells in a short generation cycle with unlimited proliferative capacity (i.e., tumor stem cells). The remaining tumor cells lack the proliferative capacity to form a colony. This model for the Adj. PC-5 tumor is compared with that of a transplantable AKR lymphoma, and the chemotherapeutic implications are discussed.

The combined effect of hydroxyurea and x-rays on Chinese hamster cells in vitro

Abstract: Summary Hydroxyurea inhibits DNA synthesis in Chinese hamster cells and is selectively toxic for cells actually in DNA synthesis (i.e., in S phase) at the time of exposure to the drug. Synchronized cells in G 1 inhibited from entering S by hydroxyurea show a complex response to X-radiation. Cells become steadily more sensitive for a period of about 4 hr and then recover about a normal G 1 sensitivity in approximately a further 4 hr. They never achieve the high survival level normally found for uninhibited cells in late S, but they will reach this level quite rapidly if the hydroxyurea is removed prior to exposure. The sensitization is, therefore, completely reversible. Hydroxyurea has no effect if present only during exposure at room temperature. Additional sensitization is obtained if the drug is present after exposure which increases for a period of about 4 hr. This postirradiation sensitization is independent of the time in the cycle at which irradiation takes place. These results with synchronized populations enable the effects of hydroxyurea on asynchronous populations to be predicted. The most sensitive condition occurs when irradiation is given about 4 hr after the administration of hydroxyurea and the drug is kept on subsequently. The results indicate that hydroxyurea in combination with X-rays can be a most effective toxic agent for Chinese hamster cells. If these results are applicable to in vivo situations, combination therapy with hydroxyurea given systemically and X-rays delivered locally to tumors may be most effective. However, in view of some of the problems in tumor control that cannot be evaluated in vitro , experiments with suitable animal tumor systems are needed.

Regulation of cell reproduction.

Abstract: With each complete turn of the cell through its life cycle, all of the structural elements and functional capacities of the nucleus and cytoplasm undergo a doubling. All of these events, such as mitochondrion and ribosome production, formation of new membranes, doubling in the capacities for glycolysis and lipid metabolism, chromosome reproduction, etc., must be pre cisely interrelated and coordinated through a variety of reg ulatory mechanisms that assure balanced cell growth and cell function. These integration mechanisms are the central element of growth, and the lack of specific information about their physiologic or molecular bases puts a serious limit on our understanding of cell reproduction. New mitochondria, for example, are produced by fission of the old (28, 29), but how mitochondrial growth and fission are continuously adjusted to the pace of all the other component parts of cell growth is unknown. In a general sense the regulation of the growth and production of a subcellular part must be tied into its func tional contribution to the cell; for example, mitochondrial in crease must somehow be linked to function through some such condition as the concentration of ATP, ADP, diphosphopyridine nucleotide (reduced) or triphosphopyridine nucleotide (reduced) etc. Such specific information on the relation be tween function and growth is still not available for any cellular organelle or part. Relatively little attention is given at present to problems of cytoplasmic growth and reproduction because the pace of cell progress through the life cycle appears to be governed principally by the nuclear events of chromosome replication and segregation; all other growth activities are ultimately geared directly or remotely to the accomplishment of the chromosomal processes. The explanations of how the cell cycle is driven forward, of the regulation of cell cycle progress, or of how reproduction of cells is controlled within an organism all hinge primarily on successful analysis of the regulation of chromosome replication and segregation. The subdivision of the cell life cycle into G1( S, G2, and D (or M) reflects this attitude, since these subsections are defined by what the chromosomes are doing or aren't doing rather than