Discussion of Doctor Greenstein's Paper*

SIDNEY WEINHOUSE

(Lankenau Ho,pital Research Institute and The Insiituiefor Cancer Research, Philad4phia, Pa.)

Dr. Greenstein in his scholarly and thoughtful and processes are integrated to produce the func. review has provided a theme which is indeed a tioning cell. fundamental one in biologyâ€”that of biochemical The harmonious activities of the functioning uniformity versus heterogeneity. I have been cell may be compared with the musical structure of deeply impressed by the great deal of evidence a beautiful symphony. Suppose we had befoi@e us that can be collected to show that, biochemically, all the various elements of music which made up the cancer cell is a distinctive cell type. Though the symphony but did not have the actual score. the cancer cell may or may not retain certain char We could classify the notes into so many of each acteristics of its non-neoplastic ancestor, in its notes of the scale, and we could subclassify these enzymatic characteristics it apparently resembles into half-, quarter-, eighth-, and sixteenth-notes. its sisters and cousins more than its parent. What After careful analysis of such data we would know I may call the Greenstein Hypothesis, that in the a great deal about the ingredients of a symphony. neoplastic transformation there is a convergence of Possibly by pursuing this study further we might enzyme activities to a common pattern, is one of even find that by and large all symphonies have the few experimentally conceived generalizations the same content of these various musical com in the cancer field. The possibility that cancer ponents ! I do not think I need pursue this simile cells, which have in common an autonomous further. growth and invasiveness, also have common en It seems likely that we could learn a great deal zymic characteristics offers the cancer researcher about the biochemical nature of neoplasia by ex the hope that, by digging deeply enough into the amining which activities are lost when a cell be operations of the tumor cell, he may learn enough comes cancerous, and which are retained. !Jnfor to control or destroy it without comparable harm tunately, this approach has not led anywhere as to the host. This hypothesis also offers the hope yet. Perhaps the best examples of such compari â€˜thata single, selective lethal agent may be found sons are those between the liver cell and its neo which will act against all malignant neoplasms. plastic counterpart in the primary tumor induced Dr. Greenstein has been careful to point out an by the feeding of carcinogens. Despite the reten other side to this story. In a sense, any generaliza tion of sufficient morphologic resemblance to be tion concerning the biochemical uniformity of can recognizable to the pathologist as a hepatic cell, cer cells must be regarded with skepticism as long the hepatoma cell has undergone a variety of as we are unable to explain biochemically those enzymatic changes. Referring to Dr. Greenstein's differences which we know exist between different book (4, p. 350) we find marked decreases of tumors. We are confronted with tumor cells catalase, arginase, and cystine desulfurase activi varying greatly in morphology, growth rate, trans ties. There are also almost complete losses in such plantability, and other properties; and, as will be metabolic functions as the synthesis of urea (3) shown in the rest of this program, in resistance to and ketone bodies (3, 6) and the storage of gly the action of chemical agents. Possibly these tu cogen (6). As far as we can tell at present, these mors look alike to us because biochemically we see changes occur abruptly with onset of the tumor shadows and not images. We know a great deal and are not gradual changes occurring during the now about the composition of cell components, preneoplastic period. Apparently there has sprung and we are beginning to learn something about up an entirely new cell type within the framework their transformations inside the cell; but we know of the liver cell, like the wolf in sheep's clothing. relatively little as yet about how these components If it is a normal liver cell which becomes neo plastic, is the metabolism altered before cell divi a Presentedat the meetingof the ScientificReviewCorn rnittee of the American Cancer Society, held at the Westchester sion occurs, or does cell division bring about the Country Club, Rye, N.Y., March 23-25, 1956. altered metabolism? In considering these alterna 654

Downloaded from cancerres.aacrjournals.org on October 1, 2021. © 1956 American Association for Cancer Research. WEn@iious1@â€”DÃ£cussion: Biologieal Characteri4ics of Cancer 655 tives we must keep in mind that it is not cell divi I would like to take a more partisan stand. sion per se which we are discussing, but a particu The Warburg theory (8), enunciated some 30 lar cancerous type of cell division, since the re years ago, proposed that cancer originates when a generating liver, though growing rapidly, pre non-neoplastic cell adopts an anaerobic metabolism sumably retains all of its metabolic functions. A as a means of survival after injury to its respira corollary question is : Are all of the biochemical tory system. It is presumed that the tumor is initi activities which are absent in the fully grown tu ated by a damaged respiration, which persists as a mor lost with the first cell division, or are they lost characteristic feature of the neoplastic condition. gradually with successive cell divisions? I know of In a recent paper entitled, â€œOnthe Origin of the no categorical answer to this question. However, Cancer Cell,â€• published in Naturwinenachaften Dr. Greenstein has collected numerous examples (9) and reprinted in Science (10), Warburg reiter in his book (4, pp. 352, 358) which show clearly ates this hypothesis and claims further support for that primary tumors may more closely resemble it on the basis of experiments with ascites tumor their tissues of origin than late generation trans cells. I shall leave it to biologists to appraise this plants. With successive transplantation, tumors theory in its general aspects. My remarks will be gradually lose certain distinguishing features char restricted to his basic biochemical premise, acteristic of their tissue of origin, and along with namely, that cancer cells have a damaged respira these changes they become increasingly malignant, tion. as exemplified by ease in transplantation. The con In a comprehensive review of this subject in vergence in biochemical properties of late genera 1939, Burk (1) first pointed out the essentially fal tion transplants seems due, at least in part, to lacious reasoning behind this hypothesis. More gradual loss of distinguishing functional activities. recently Schmidt (7) and I (11) reviewed this topic May not the absence of certain enzyme activities independently in the light of modern findings and in the primary tumor also be the result of stepwise concluded similarly that there is no sound experi loss of single activities during successive cell divi mental basis for the belief that oxidative metabo sions? It is possible to imagine that the tumor, in lism in tumors is impaired. I would like to point its race toward eventual annihilation of its host out the various reasons for this conclusion. It is and itself, probably taxes own enzymatic capac recognized by all, including Warburg, that, despite ities. Before the cell can fulfil all of its synthetic their high glycolysis, oxygen consumption in tu capabilities, it divides and yields two daughter mors is not quantitatively diminished; by and cells. These likewise may divide before their capa large a representative group of tumors absorb oxy bilities are fuffilled, and ultimately a cell type may gen about as rapidly as a comparable group of result which retains only those activities needed non-neoplastic tissues. This may be clearly seen by for cell division. Like the stripped-down racing referring to the early, extensive tables of data col car, the rapidly dividing cancer cell may have lected by Burk (1) and has been amply confirmed dropped those characteristics which distinguish in more recent studies, including our own (11). An one cell type from another and retained only those early statement by Warburg, illustrative of his activities necessary for survival. Thus, tumors of views concerning the relationship between the the most varied origin may converge to a common high aerobic and anaerobic glycolysis of tumor pattern of biochemical behavior by following a cells and their oxygen consumption, is the follow common pattern of gradual enzyme loss through ing (8, p. 139): successive cell divisions. Whether or not this ex â€œWedetermined the Meyerhof quotient for car planation of the Greenstein hypothesis is correct, cinoma tissue, lactic acid bacteria, embryonic tis a study of those enzymic and metabolic capacities sue and a number of other glycolyzing tissues, and which are retained in common by tumors may tell as a rule obtained the same mean values as Meyer us much about the biochemical factors concerned hof. As a rule 1 mol. of breathed oxygen, just as in with the neoplastic process. muscle, causes the disappearance of lâ€”@mol.lactic I would now like to turn to another problem acid. This result . . . proves that the influence of which has been with the tumor biochemist for the the respiration on the cleavage metabolism in the past 30 years. This is the perennial question of carcinoma-cell is normal. . . . Although in the tu respiration and glycolysis. Dr. Greenstein has al mor every oxygen molecule breathed is just as ef ready summarized this subject in his review. How fective as in muscleâ€”the Meyerhof Quotient is ever, I feel a further elaboration might be appro equal in the two casesâ€”yet the respiration does priate in view of Warburg's recent publications. In not cause the glycolysis to disappear. The respira his judicial manner, Dr. Greenstein has presented tion of the carcinoma tissue is too small in corn the Warburg view without prejudice for or against. parison with its glycolytic power.â€•

Thus, according to Warburg, the Meyerhof support such a concept. Effects of inhibitors such Quotient (a quantitative expression of the Pasteur as fluoride ion or dinitrophenol are similar in neo Effect) is normal in carcinoma, and the respiration plastic and non-neoplastic tissues (l@), and data of is also not different; but respiration is damaged be other investigators (11, p. 3@1)indicate that oxida cause glycolysis occurs in oxygen. Warburg's con tive phosphorylation occurs in tumor mitochon clusion that tumors have a damaged respiration is dna in the same manner that this process occurs in thus not based on an experimentally established their noncancerous counterparts. quantitative impairment in oxygen consumption, Another pertinent illustration of the inadequacy or on a deviation in the Pasteur Effect, but only on of the Warburg concept is that it fails to consider its failure to eliminate the high aerobic glycolysis. that a large part of the respiration of cancer cells Though Warburg still states categorically that may be due to fatty acid oxidation. Though it

â€œ. . . the respiration of all cancer cells is dam seems fairly certain now that animal tissues gen aged . . .â€œ(10,p. 309), he has given no clearer jus erally, including the neoplastic, use fatty acids as a tification now for this view than he did @6years metabolic fuel, nowhere in Warburg's writings is ago. In Table 1 of his paper (10) he shows that, there any consideration of the possible role played whereas liver, kidney, and embryo have Qo,'s of by fatty acids in the respiration of cells.

â€” 15, the ascites tumor has a Qo, of â€”7. On these Another weakness of the Warburg hypothesis is grounds he concludes that the tumor cannot utilize that it does not fit in with what we have learned in sufficient oxygen for its needs and thus requires recent years of chemical mechanisms of glycolysis fermentative energy. On the assumption that each and respiration. Again, Warburg states, â€œWeneed mole of lactic acid formed from glucose yields one to know no more of respiration and fermentation mole of ATP and each mole of oxygen consumed here than that they are energy producing reac gives rise to 7 moles of ATP, he calculated that the tions. . . .â€œThisattitude may have been justified tumor obtains more than half of its potential @,5yearsago when little was known of their chemi phosphate-bond energy by glycolysis, whereas the cal nature. At present we recognize that they are three non-neoplastic tissues obtain theirs mainly not â€œindependentmetabolic processesâ€•but are in by respiration. Accepting these results at their face timately related. To assume that respiration and value, it is still necessary to ask why some normal glycolysis are separately activated, alternate tissues manage to survive without glycolysis, with means of cellular energy production, it is indeed Qo,'s of â€”3 to â€”6; also, why some tumors gly necessary to ignore all that has been learned of colyze highly with Qo,'s as high as â€”10to â€”@0(1, their chemical mechanisms. pp. 438â€”441). It is also pertinent to ask why cer According to our present conceptions, the major tam non-neoplastic tissues, with moderate to high pathway of oxidation of glucose to carbon dioxide oxygen uptakes, as, for example, brain, retina, in animal cells, whether normal or neoplastic, in kidney medulla, and intestinal mucosa, glycolyze volves its conversion to pyruvic acid by way of the as highly as many tumors (s). It is evident now, as Embden-Meyerhof process, oxidative decarboxyl it was earlier, that all tumors produce large ation of pyruvic acid to acetyl coenzyme A, and amounts of lactic acid, but so do many noncan condensation of acetyl coenzyme A with oxalacetic cerous tissues; and, just as noncancer tissues dis acid to enter the citric acid cycle. Down to the play a wide diversity in oxygen uptake, so do tu pyruvic acid stage, respiration and fermentation mors. follow a common pathway. The extent to which Perhaps the most damaging evidence against pyruvic acid, a common intermediary in both res the Warburg hypothesis has been obtained in piration and glycolysis, competes for electrons held isotope tracer studies (11, p. 303). The results of by the pyridine nucleotides with those factors such studies leave no doubt of the ability of mis which transport electrons to oxygen; viz., the cellaneous tumors to convert glucose (and fatty flavoproteins and cytochromes should be a crucial acids) to carbon dioxide at rates similar in magni factor in determining the degree of aerobic glycoly tude to those exhibited by non-neoplastic tissues s's. (7, 11). It is difficult to imagine a type of respira If there is a disturbance in respiration which tory disturbance not involving either a diminution leads to an accumulation of lactic acid, it can only in oxygen consumption or a loss in the ability to occur at or beyond the pyruvic acid stage and must convert glucose and fatty acids to CO2. be due either to some aberration in carbon trans Warburg suggests in the present paper that per port through the citric acid cycle or to some â€œbot haps the respiratory impairment may involve an tieneckâ€• in electron transport. Many enzymatic inability to couple oxidation with phosphoryla and isotope tracer studies have fully established tion. Here again, the available evidence does not that the citric acid cycle operates in tumors (11, p.

811). Though cytochromes are reportedly low in ous tissues and that they employ the same mecha tumors (4, p. 404), as are also some of the B vita nisms for their oxidation. Undeniably, certain tu mins involved in electron transport (4, p. 408), the mors differ from certain normal tissues in activities generally unimpaired oxygen consumption already of certain individual enzymes, but such differ referred to clearly indicates that electrons reach ences, though known for many years, have not as oxygen about as readily in tumors as in other tis yet been demonstrated as rate-determining in sues. Thus, the available evidence indicates to me over-all metabolic processes. that high glycolysis occurs despite quantitatively and qualitatively normal occurrence of carbon and REFERENCES electron transport. This can only mean that glu 1. Bmix, D. A ColloquialConsiderationofthe Pasteurand cose catabolism is so rapid in tumors that the nor Nec-Pasteur Effects. Cold Spring Harbor Symposium on mal channels for disposal of pyruvic acid are over Quantitative Biologj, 7:420-59, 1939. loaded. Many possibilities which do not involve 2. DlcxzNs, F. In: J. B. Su@sm and K. Mniascx (eds.), The Enzymes,2(1): 624-83. New York:AcademicPress, disturbances in respiration exist for explaining this 1955. high glucose catabolism. My colleagues and I are S. Dicxzr@rs,F.,and WEIL.MALTInRnE,H.The Metabolism now attempting to unravel the multiplicity of fac of Normal and Tumor Tissue. Cancer Research, 3:78-87, tors concerned with lactic acid production in the 1943. 4. GasuwsTaur,J. P. Biochemistryof Cancer.2d ed. New intact cell. York:AcademicPress,1954. I do not wish to minimize the significance of the 5. Guunr, S. Fat Metabolism, pp. 138-49. Baltimore: Johns high aerobic and anaerobic glycolysis of tumor tis Hopkins Press, 1954. sue. It is conceivable that glycolytic activity, 6. Msmas, G.; FRIEDMANN,B.;and Wjrnuiousz, S. Fatty though not resulting from a faulty respiration, Acid Metabolism. VIII. Acetate Metabolism in Vitro dur jug Hepatocarcinogenesis by p-Dimethylaminoasobenaene. may play a special role in the neoplastic process. Cancer Research, 16:57-62, 1956. Data are available from the field of lipid metabo 7. Scminvr, C. 6. Biological Oxidation and Glycolysis in Tn. lism, for example, which suggest that some phase more.Kiln. Wchnschr.,33:409â€”19,1955. of glucose catabolism in liver is coupled with fatty 8. W&niiuno,0.The MetabolismofTumours(translatedby acid synthesis (5). The close association of lactic F. Dzc@zi@s).London:ArnoldConstable,1930. 9. - . tYberdieEntatehungderKrebszellen.Naturwis acid production with the neoplastic process, and senschaften, 42:401â€”6, 1955. - with growth in general, makes this phenomenon a 10. - . On the Originof CancerCells.Science,123:309â€” worthy subject of study. As far as I am aware, 14, 1956. there is no concrete evidence in support of War 11. Wzniuousu, S. OxidativeMetabolismof NeoplasticTis burg's basic premise that the high glycolysis of tu sues. Adv. Cancer Research, 3:269-325,1955. 12. Wz@Nza,C.E., and Wwusouaz, S. Metabolismof Nec mors is due to a faulty respiration. All the avail plastic Tissue. VII. Effects of Dinitrophenol and Fluoride able evidence indicates that tumors as a class on Glucose Oxidation in Tumor Homogenates. Cancer Re oxidize the same metabolic fuels as do noncancer search, 15:407â€”503, 1955.

Sidney Weinhouse

Cancer Res 1956;16:654-657.

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