UNCLASSIFIED . . . M .: monto ................... ... . .. : WS V . if we VP . t . . ' 722 . i . . +ry ORNU-P- ryor. -4 6th IBM Medical Symposium cpu!. Poughkeepsie and Brookhaven Laboratory, N. Y. October 5-9, 1964 CURRENT TRENDS IN CANCER RESEARCH ВУ Arthur C. Upton, M.D. Biology Division Oak Ridge National Laboratory Oak Ridge, Tennessee *Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. RE . . Running hend: Send proof to: Dr. Arthur C. Upton Biology Division Oak Ridge National Laboratory P. 0. Box Y Oak Ridge, Tennessee 37831 . - 2 . . . . . . . i ** The breadth and depth of cancer research are greater today than ever before, reflecting the rapid development of contemporary biology and medicine. An exhaustive review of the field is outside the scope of this report, which will attempt instead merely to survey a few of the highlights among recent contributions and current trends. Molecular biology. Although cancer includes many forms of neoplasia, it is clear that all involve an unexplained transformation of the neoplastic cell toward uncontrolled growth. Recent advances in cancer biochemistry (Table 1) and molecular biology provide new clues and new approaches to an understanding of cell division, its control, and the nature of the "neoplastic transformation" (Kalckar, 1964; Pardee, 1964; Heidelberger, 1964). It is evident now that the "resting" stage of the division cycle is a misnomer in that a "resting" cell must carry out an extensive series of synthetic reactions before it can enter mitosis (see Mazia, 1963). The use of autoradiographic methods with isotopically labelled metabolites has helped to define the steps involved in cell division, and to enable detailed analysis of the cell generation cycle (see Prescott, 1963). As a result, it 18 now possible to pinpoint the action of factors influencing cell division at various stages of the cycle (e.8., see Dewey and Humphrey, 1963). This approach should contribute greatly toward elucidation of the mechanisms controlling growth and differentiation and of the effects of carcinogenic and carcinostatic agents. Kinetics of growth and turnover of neoplastic cells. The autoradiographic approach has provided quantitative data on the kinetics of growth and turnover reas: of cancer cells. These data have helped to explain hitherto puzzling differences between neoplastic and normal tissues, as well as between a es different neoplasms (Mendelsohn, 1963), The evidence indicates that cancer is not necessarily associated with abnormally rapid cell division, cells in certain neoplasms dividing no faster than their normal. counterparts (Cronkite et al., 1960; Gafosto et al., 1960). From this, it can be inferred that the accumulation of neoplastic cells in excessive numbers may in certain instances reflect their defective removal, through faulty maturation or elimination, rather than their overproduction. It has also been noted that all the cells in a seemingly homogeneous tumor do not multiply at the same rate and that the overall average growth rate of such cells is not constant with time (Mendelsohn, 1963). These differences call for a new measure of sophistication in our attitude toward the development, progression, treatment, and recurrence of cancer. Chromosome analysis. Cytogenetic technics have come to be fruitfully applied to human and animal tumors only recently, despite their usefulness in the hands of plant cytologists for decades. It is too early to conclude .. what such technics will ultimately tell us about cancer, but already they .. have revealed that neoplastic cells tend to undergo random and progressive aneuploidization with the passage of time, the severity of the chromosome change tending to parallel the progression of the neoplasm (see Hauschka, 1963; Ford and Clarke, 1963). The stemline at any one moment in a particular tumor usually consists of cells having only one or a few types of aberration. Although the precise chromosomal abnormality varies from tumor to tumor, with few exceptions, a growing number of neoplasms have been found to be associated with specific types of chromosomal changes (see Upton, 1963; Makino, 1963; Wald et al.. , 1964). These findings point to the individuality of neoplasms and their clonal nature (Ford and Clarke, 1963). - . . -- . ... . - The association between alteration of a particwar chromosome and a - . N HL given type of neoplasm is consistent with the somatic mutation hypothesis O .. of carcinogenesis (i.e., that the neoplastic transformation results from .... . . . genetic or chromosomal changes within the cell), but the possibility that ........ - - the chromosomal change 18 a result, rather than the cause, of the neoplasu has not yet been excluded (see Upton, 1964). .......... It is noteworthy in this connection thut the frequency of chromosomal aberrations in human and animal cells has been observed to rise with age and ......................... with irradiation (Jacote et al., 1963; Bender and Gooch, 1963; Curtis, 1963), in accordance with expectations from radiobiological studies with simpler organisms. Such aberrations have been found, moreover, to persist indefinitely.in non-dividing cells, possibly throughout the life of the affected individual (Buckton et al., 1962; Curtis, 1963). The implications of these findings for carcinogenesis, senescence, and immunological memory have stimulated new lines of investigation, which are most promising. Tumor progression. The characteristically long time required for the diritto development of a neoplasm, either in the presence or absence of known exposure Vinavertiràtipark moeite mi sono valamint to a carcinogenic stimulus, has been interpreted to indicate that a succession of changes are necessary to cause neoplastic transformation (see Burch, 1962; Doll, 1963). Further support for this view has come from studies of tumor initiation, promotion, and progression, which demonstrate a series of , i ning tablishment discrete stages in the induction and evolution of certain types of malignancy ment eti Dom (Furth, 1953; Foulds, 1963). Although the biological basis of this step-wise progression is yet to be established, its multistage nature has significant implications for the etiology, variability, and therapy of neoplasms. Involved in neoplastic progression is a complex interaction of intrinsic and extrinsic factors, which include homeostatic mechanisms hitherto unrecognized. The latter comprise intracellular, as well as systemic, systems capable of repairing lesions at various levels of organization, down to the DNA molecule 1teelt (see Setlow and Carrier, 1964). Through the action of such reparative processes, lesions otherwise leading to mutations, chromosome aberrations, neoplasia, and cell death may be largely arrested or repaired (see Upton, 1964). The action of a carcinogen may depend, therefore, less on its initial molecular effects within the cell than on the final macromolecular lesion remaining after metabolic efforts toward adaptation. Consequently, the cancer biologist must now analyze the action of a carcinogenic agent in terms of its quantitative effects at the molecular, genetic and cellular levels, as well as at the tissue level. Such an approach muist, furthermore, allow for systemic effects of diverse kinds; e.g., (1) the carcinogeric action of certain chemicals results entirely from their metabolic breakdown products, and these may be formed elsewhere in the body than at the site of neoplasia; (2) the induction of thymic lymphoid tumors in the mouse, üy chemicals .or radiation, appears to involve injury of the bone marrow in addition to the thymus and "activation" of a latent leukemia virus present elsewhere in the body as well as in the thymus and marrow (Upton, 1964). Cancer viruses. The dramatic recent advances in tumor virology point up the complexity of the interaction between intrinsic and extrinsic factors in oncogenesis. For example, it was the use of the newborn, as opposed to the adult, animal as the assay system that demonstrated the transmissibility of spontaneous and radiation-induced murine leukemias. with cell-free filtrates (see Gross, 1961) and has since led to the discovery of a rapidly growing series of oncogenic viruses and to the presence of carcinogenic activity in viruses bitherto associated only with non--neoplastic infections (see Upton, 1963). Not only have new tumor viruses been found in astonishing numbers but the range of host cells that may be susceptible to a given virus has been recognized to be broader, thar formerly suspected, most notably in the case of the polyoma virus which is oncogenic for many organs of the mouse as well as for other rodents (see Gross, 1961). It seems increasingly likely, therefore, that a virus tumorigenic for man will ultimately be found. Although the mechanisms of viral carcinogenesis are still obscure, a virus is apparently required only to initiate the neoplastic transformation and need not remain in the tumor cell, at least in a detectable form, to maintain the neoplastic state (Kaplan, 1962; Dulbecco, 1963). Whether the virus in such instances acts directly on the genome of the cell or on other targets is not known, but chromosome breakage has been suggested as a possible basis for the oncogenic action of certain viruses (Vogt and Dulbecco, 1963; Wald et al., 1964). In other instances, notably in the case of what is presumed to be an RNA virus, homology between the viral RNA and the host cell DNA has been interpreted as evidence that viral information may be integrated into the genome of the cell, thereby constituting a basis for neoplastic transformation (Temin, 1964). Whatever the mechanisms of viral oncogenesis, the possible role of viruses can no longer be neglected in any studies of neoplasia. Such studies are complicated, moreover, by the possibility that oncogenic viruses may be transmitted vertically from generation to generation across the placenta or even via the zygote (see Gross, 1961; Walburg et al., 1964). Immunclogical studies. The recogniiion that virus-induced tumors in many instances contain antigens specific for the causative virus (Habel, 1962; Pope and Rowe, 1964; Old, Boyse and Stockert, 1964; Klein and Klein, 1964) has rekindled the hope that immunological means may ultimately be found to prevent or destroy such growths, even in those cases where the antigen is not present in the virus itself but only in the induced tumor cells. By the same token, although the antigenic diversity of chemically induced growths sets them apart from viral neoplasms (Prehn, 1962; old et al., 1962), the antigenicity of chemically induced tumors for their primary hosts is thought, to account for the greater inducibility of such neoplasms in neonatally tiymectomized animals than in animals with an intact immune system (Miller et al., 1963, 1964; Maisin, 1964; Malmgren et al., 1964). With the refinement of immunologic technics, the possible role of cell surface antigens in normal regulation of growth and differentiation is being actively explored (see Abercrombie, 1962). The importance of surface phenomena, whether immunological or not, is implied by experiments on plastic film tumorigenesis, which indicate that interference with interaction between 6 adjacent cells is carcinogenic under certain circumstances (Oppenheimer et al., 1958), and by the loss of contact inhibition which often accompanies transformation of cells by oncogenic viruses in vitro (Vogt, 1964). Another category of studies having to do with immunity in relation to cancer concern the autoimune phenomena and immunological depression . 1 i . frequently encountered in individuals with advance malignancy (see Burnet, - th 1964). 3 - n " S iin.' Cancer epidemiology. Although the pathogenesis of neoplasia remains largely obscure, many cases of cancer that might otherwise have developed have been prevented already through elimination or control of carcinogenic factors in the environment (Hueper, 1961). With the accelerating modification of the environment by modern technology, the identification of carcinogenic hazards becomes, however, ever more important and difficult. To cope with this problem, toxicological studies in experimental animals are being intensified and epidemiological studies in human populations are being expended. In both approaches, improvements in experimental čechnic are needed, especially in relation to the cocarcinogenic effects of multiple agents and the estimation of risks at low levels of exposure to carcinogen. Further clues to environmental carcinogens are being sought in analysis of geographic differences in cancer rates (Stewart, 1964), although such differences are usually complicated by other variables, such as genetic variations, which are difficult to assess. Cancer therapy. Despite the absence o. a "breakthrough", the outlook of the patient with malignant disease is gradually improving, thanks to w.. 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Science 143:810-813, 1964. . 4 y Table 1 Fifty Years of Cancer Biochemistry 1913-1963 Period Cancer Biochemistry General Biochemistry 1913-1923 Enzyme differences 1918, 3' RNA-tides 1918, Fructose 6-P 1922, Glucose 6-P 1923–1933 Aerobic glycolysis (respiratory defect) 1924, Slice technic 1929, ATP 1930, Deoxyribose 1933, Glycolytic schenie 1933–1943 1934-35, TPN, DPN Aerobic glycolysis (respiratory defect) . 1936, Homogenate technic 1937, Citric cycle 1939, Oxidative phosphorylation Convergence 1950, Alternative pathways 1951, 5' RNA-tides 1952, Pentose cycle . 1953-1963 Catabolic deletion (alternative pathways) MUPN 1953, DNA structure 1956, Feedback 1957, Repression 1961, Messenger RNA 1962, Regulatory sites TA 1963- Feedback deletion A . . (From Potter 906h Thomas r I .. VER 2 . ? ,, 1 TE 2 -SI - DATE FILMED | 1 / 21 65 ANA A . 7 # 1 22 7 TL SV ... " CMS 1 ." - - - -* . . - LEGAL NOTICE T ', . Ei This report was prepared as an account of Government sponsored work. 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