Ectopic Hormone Production by Malignant Tumors

Transcription

1 ANNALS O F CLINICAL AND LABORATORY SCIENCE, Vol. 9, No. 4 Copyright 1979, Institute for Clinical Science, Inc. Ectopic Hormone Production by Malignant Tumors IRW IN J. H O LLA N D ER, M.D. and GONZALO E. APONTE, M.D. Department o f Pathology, Jefferson Medical College o f Thomas Jefferson University, Philadelphia, PA ABSTRACT M alignant tum ors of nonendocrine tissues may produce ectopic hormones. The most likely m echanism is depression of genes which code for hormones. Ectopic hormones are invariably peptides, and each is identical to some peptide product of an endocrine gland. However, the majority of ectopic hormones occur as biologically inactive precursors or subunits and therefore rem ain occult unless they are specifically sought. W hen appropriate assays are made for such inactive forms, it is found that ectopic production of hormone-like peptides occurs frequently. Clinical syndromes result only in the relatively rare patients in whom a biologically active form is synthesized in large quantities. Laboratory research in this area improves our understanding of genetic control mechanisms in neoplasia. Ectopic hormones may be of lim ited use in diagnosis of cancer, especially when m ultiple m arkers are m easured sim ultaneously. Introduction To most of us, the ectopic synthesis of hormones by malignant tumors brings to m ind a rare p a tie n t w hose vigorous w orkup by an e n th u siastic en d o crin ologist m erite d a case rep o rt. T he phenom enon is neither new nor all that rare, but our awareness of it has increased w ith the advent of radioim m unoassay tech n iq u es w hich have im proved the sensitivity and availability of hormone m easurem ents. Recent work has greatly advanced our understanding of ectopic horm ones and has indicated that they may provide a tool for exploring the molecular biology of neoplasia. E ctopic horm one production is synthesis of a hormone by tissues which do not norm ally produce that hormone. This definition implies, of course, that all of the normal sites of origin of the hormone are know n, b u t this assum ption conceals complexities to which we will return later. The organ in which the ectopic synthesis occurs may or may not have an endocrine function in healthy persons. In the great majority of cases, it is tissue not considered endocrine until neoplasia endows it w ith that capacity. The four glycopeptide hormones are human chorionic gonadotrophin (HCG), luteinizing horm one (LH), follicle stim u lating horm one (FSH) and thyrotropin /79/ $01.20 Institute for Clinical Science, Inc.

2 ECTOPIC HORMONES 269 stim ulating horm one (TSH). They are each composed of an alpha chain and a b e ta chain w hich lack biologic effect w hen separated but which, when bound as a dimer, form a biologically active molecule. The alpha chains of all four are nearly identical, and the biological and imm unological specificity of these hormones is conferred by their beta chains. In addition to the peptide structures, each hormone has a carbohydrate com ponent w hich, if rem oved, leaves a m olecule which retains immunologic reactivity in assays but is of greatly reduced biological potency because of an enormous decrease in m etabolic half-life.9 Until quite recently, HCG could be assayed only as the sum of HCG and LH because the beta chains of these two hormones are sufficiently sim ilar to cause im m unologic cross-reaction. T he production of small amounts of HCG had escaped detection because it could not be separated from the relatively large normal levels of LH. T he fairly recent developm ent of the so-called beta-subunit assay which is highly specific for HCG was the technical advance which made possible much of the current understanding of the ectopic production of this hormone. The Special Role of Placental Hormones One of the first problem s encountered in considering ectopic hormones is how to prove that they are synthesized ectopically by tum ors rath er than produced eutopically at a normal site of origin. The most elegant and definitive m ethods are a dem onstration of an arteriovenous gradient in hormone concentration across the tumor or in vitro production of hormone by tumor explants. These studies, while optimal, are rarely done. D irect analysis of tum or tissue for horm one is somewhat more practical, but it cannot distinguish genuine synthesis of hormone by tumor from mere concentration or trapping of horm one in tum or tissue. In m ost cases, of course, plasm a hormone concentrations are the only data available. Since most hormones are subject to a negative-feedback-physiologic regulation, production of ordinary quantities of hormone ectopically succeeds only in shutting off eutopic synthesis, and the net result is a non-diagnostic blood level in the normal range. The diagnosis ofectopic production by this approach m ust often wait until the plasma hormone concentration clearly exceeds normal levels, which lowers the rate of detection to the point where this phenom enon becomes a m edical curiosity. Placental hormones such as HCG and hum an placental lactogen (HPL) assume special im portance as ectopic products because they are not found in the sera of healthy non-pregnant persons and are not subject to any feedback-loop control, so that they are almost specific for cancer when present in serum in any m easurable quantity. W ith the great sensitivity allow ed by this low level of significant production, the placental hormones are found early and relatively frequently, and much of the most interesting and important recent research in ectopic hormone production has cen tered about these horm ones.12 These placental hormones are not to be confused with fetal proteins, such as alpha fetoprotein or carcinoembryonic antigen, which are normally present in sera of healthy adults in small quantities. G enetic D erepression The m echanism of polypeptide production by nonendocrine tumors has been the subject of controversy ever since the phenom enon was first described. One theory has been that it is part of the chaos of malignancy, in which a peptide corresponding to the active site of a hormone is fortuitously synthesized by an occasional tumor. T here is now m uch evidence, how ever, that ectopic synthesis is not ran

3 270 HOLLANDER AND APONTE dom, and th at it is of very basic significance in tumor biology. An hypothesis term ed genetic d e re pression explains the observations in a much more satisfactory way than does any previous theory. Essentially, it states that all tissues contain the same genetic information in the nuclei of all cells, but much of it is repressed as cellular and tissue differentiation advances. In the neoplastic process, some of these repressed genes may be activated, leading to production of norm al peptides by tissues other than their natural sources. If this theory is true, then ectopic hormones should all be polypeptides and never steroids or thyroid hormones, and this is in fact what has been found. All ectopic horm ones w h ich have b e e n studied are peptides. In those patients who have appeared to produce steroid or thyroid hormones ectopically, the tumor makes only the tropic hormone, which is a peptide, while the steroid or thyroid hormones are secondary products of eutopic origin. To believe otherwise would be to ignore what is known from ultrastructure and biochem istry, since all nucleated cells possess the organelles and enzymes for making peptides, but only certain cells in the body have the long and complex pathw ays necessary for steroid synthesis. A dditional su p p o rt for this theory comes from the finding that those ectopic hormones which have been isolated and characterized are structurally identical to eutopic hormones and their precursors and subunits. Not only the active site but an entire polypeptide is faithfully duplicated by the tumor. Such fidelity would be most unlikely if ectopic hormones arise from chaos, but it is the expected result if their origin lies in genetic derepression.11 The association of certain tumors with ectopic production of one hormone much m ore freq u en tly than others, such as squam ous cell carcinom a and parathorm one, suggests that derepression of deoxyribonucleic acid (DNA) in m alignancy may have an elem ent of selectivity. This has fostered an additional hypothesis in which there is a hierarchy of availability for derepression of DNA, ranging from DNA w hich is inaccessible through various degrees of reversible repression to DNA which is actively coding m essenger ribonucleic acid (RNA). In this theory, the synthesis of ectopic hormones by tumors is governed by DNA which is in those m iddle levels of reversible repression, and the frequency with which a peptide is synthesized ectopically should correlate with the ease of derepression of the DNA which codes for it.18 R esearch using tissu e c u ltu res of m alignant tumors has made significant contributions to our understanding of the m echanism of ectopic horm one production. The well-known HeLa cell line was derived from a carcinoma of the uterine cervix and has been m aintained in cell culture for over 25 years. HeLa cells have been dem onstrated to secrete the alpha subunit of HCG ectopically in significant amounts, and the fact that alpha subunit was synthesized by all of the HeLa cell strains studied by one laboratory suggests that transcription of this peptide may be relatively easily derepressed.7 Variability in expression of this d erep ressed genetic inform ation has b een elegantly dem onstrated in another cell culture system. In 1971 a subcutaneous metastasis was excised from a 45-year-old man with an HCG-producing bronchogenic carcinom a. A num ber of clonal strains from single cells of this tumor, designated ChaGo, were established in long-term tissue cultures. Secretion of HCG and its subunits into the culture media of three of these clones has been m easured and was found to be un b alanced in all three but in very different ratios of alpha to beta to complete HCG in each. The remarkable aspect of these data is that the three hormone-producing clones were all derived from that single lesion, so that even in one man s tumor the

4 ECTOPIC HORMONES 271 individual cells express their repressed genetic inform ation in heterogeneous fashion.15 T he regulatory m echanism s for hormone production may differ betw een ectopic and eutopic sites. Sodium butyrate induces HCG and HCG-alpha synthesis in the two nontrophoblastic cell lines HeLa and ChaGo but represses synthesis in several cell cultures of trophoblastic tumors.3 It has been generally assumed that ectopic protein production is intrinsically less efficient than eutopic synthesis, and the occasional p a tie n t in whom high serum levels of hormone cause clinical symptoms if sustained long enough is accounted for by the sheer enormity of his kilograms of tumor relative to the size of endocrine glands. This belief has been questioned by work in which one particular clone of ChaGo has been shown to secrete alpha subunit at a rate exceeding that of the m ost active know n choriocarcinom a clone, representing ectopic production more efficient than eutopic synthesis u n d e r com parable in vitro conditions.6 Universal Ectopic Hormones Ectopic synthesis of prohormones or of subunits should not be view ed as exceptions to the apparent rule that ectopic horm ones are identical to the eutopic product. These precursors and fragments are normally present in the glands which synthesize the hormones and are equally as natural as the circulating active horm one. T he re la te d enzym e system s necessary to com plete the synthesis of the active form o f th e horm one (e.g., hydrolysis of prohorm one, assem bly of subunits, addition of carbohydrate) are not likely to be well developed in tumor tissue, leading to production of peptides which are replicas of biologically inactive forms of horm ones.17 In fact, ectopic synthesis of these inactive precursors and subunits appears to be much more common than production of com plete active horm ones. The great majority of these cases ordinarily go undetected because no symptoms are produced and the assays used clinically show nothing amiss. H ow ever, research workers using appropriate methodology have detected this kind of ectopic hormone production so frequently that one group has stated boldly that ectopic protein synthesis is a universal concomitant of neoplasia. 10 In their well-known study, Gewirtz and Yalow5 found big A C T H (adrenocorticotrophic hormone, a prohormone) in tissue extracts of almost all lung cancers they studied, regardless ofhistologic type. Normal tissues contained no immunoreactive big A CTH in their assay system. Carrying this idea m uch further, O dell10 and his group have reported the presence of m easurable q u an tities of A C TH, b e ta -lip o tro p in (beta-m SH, melanocyte stimulating hormone), HCG and alpha glycopeptide even in normal lung, colon and liv e r as w ell as in neoplasms of these and other organs. The ACTH and beta-m SH activities w ere greater in tumors than in normal tissues, w hile the quantities of the other hormones were similar in both. This work suggests that the genetic material coding for these hormones is not completely suppressed even in norm al nonendocrine tissue and is relatively less suppressed in neoplastic tissue. There is other evidence that ectopic hormone production, at least of HCG, is not lim ited to malignancy. The presence of HCG has been dem onstrated in tissue extracts of normal testis2 and in extracts of colon and liver in male patients who died of non-neoplastic disease.19 Occasional laboratories have reported HCG in serum of patients w ith non-neoplastic gastrointestinal diseases17 and benign nontrophoblastic gynecologic conditions,13 although these findings in serum have not been w idely confirmed. A likely in terpre

5 272 HOLLANDER AND APONTE tation is that the peptide portion of HCG is produced in most or all human cells, normal and neoplastic, but it is either not secreted into blood or it is secreted but degraded very quickly, since HCG of nontrophoblastic origin has m uch less carbohydrate com ponent than placental HCG.9 The unanswered question is w hether it is the neoplastic process per se or merely the increased cell replication rate found in neoplasms which correlate with the quantity of peptide secreted.10 This greatly com plicates the basic definition of ectopic synthesis, since eutopic production of HCG, and possibly of other hormones, is not truly restricted to what we regard as the normal sites. It goes on at a very low level in many tissues, perhaps in all. It may be more realistic to think of ectopic synthesis as an occult process b e coming manifest rather than as a function acquired de novo. This concept is the correlate, on the tissue level, of the theory of genetic derepression. Ectopic Hormones as Tumor Markers It is tim e to turn from theoretical to practical m atters and to consider putting ectopic hormones to work as blood tests for cancer. As m entioned previously, because the ectopic and eutopic products are indistinguishable, the only hormones of diagnostic promise are those which are entirely absent from serum of healthy persons, namely, the placental hormones. For purposes of clinical diagnosis, th eir presence can be ignored in extracts of normal tissues and in sera of some patients with certain non-m alignant disorders, since m ention is made now only of practical serum markers and the great majority of people have no detectable circulating placental hormones. For HCG, the one m ost extensively studied in this context, only a tantalizing minority of cancer patients have hormone in their sera, so that a positive testis significant but a negative one is not. Cancers of th e liver, stom ach a n d pancreas have relatively high incidences of ectopic synthesis of HCG detectable in serum (21 percent, 22 percen t and 33 percent, respectively, in one large series).17 In another series of patients with bronchogenic and gastrointestinal carcinom as, only 17 percent had detectable plasma HCG, and the great majority of those had only modest quantities.4 In breast cancer, 36 percent of pre-operative patients and 48 percent of patients w ith metastatic disease had HCG in their sera, and these women may have a less favorable prognosis than w om en w ithout HCG. In patients with HCG, the level generally rose and fell with clinical relapse or remission. However, the quantitative range of HCG levels was small, so th at c lin ic a l u tility for th e ra p e u tic monitoring or for estimation of prognosis is lim ited.16 One hope for increasing the diagnostic sensitivity of ectopic horm ones is to screen for a battery of selected markers. In one series of patients, sim ultaneous determinations were made of HCG and two other placental polypeptides known to be produced ectopically by nontrophoblastic tumors, hum an placental lactogen and the placental isoenzym e of alkaline phosphatase. It was found that these processes were discordant, that is, that the marker peptides w ere secreted independently w ith o u t a d isc e rn ib le p a tte rn. O n a theoretical level, this implies that ectopic protein synthesis is not controlled by a single m echanism. In a more practical vein, it means that diagnostic yield rises when m ultiple markers are m easured.14 This series was very sm all and was intended only to establish the discordance of m arker production. It appears that larger and more definitive studies along these lines have not yet been reported. Ectopic Hormones and Tumor Immunology Having considered the theoretical and the practical, a b rief fling with speculation is allow ed. C ould an ectopic horm one

6 ECTOPIC HORMONES 273 have a function to perform? One avenue that has been explored is the relation of HCG to lymphocyte activity. It has been shown in lymphocyte culture that HCG inhibits the response of lymphocytes to phytohem agglutinin in a reversible and noncytotoxic m anner.1 This work was done in reference to the failure of maternal lymphocytes to reject fetal trophoblast, and the horm one concentrations required for this effect, while attained locally in trophoblast, are above the range associated with ectopic HCG. However, a possible relevance to nontrophoblastic malignancy is provided by work in which immunoperoxidase technique was used to demonstrate and localize HCG in tissue sections of a broad variety of cancers.8 There was a tendency for accum ulation of HCG at the tum or cell surface, which would yield a high local concentration in a critical site in w hich it m ight be potentially effective in inhibiting T-cell action. By this technique, HCG was dem onstrable in 25 of 28 nontrophoblastic m alignancies, and the percentage of tumor cells staining for it ranged from 10 to 15 percent up to 90 to 95 percent. At this point there is not enough data to accept this as the means by which tumor cells are sheltered from immune surveillance, but it is an in triguing possibility. Conclusion The production of ectopic hormones by malignant tumors is detected frequently if appropriate methods are employed. The capacity to synthesize hormones extends beyond endocrine organs. It exists in partially repressed form in many tissues and is expressed more fully w hen malignancy develops. T he p e p tid e s se c re te d by tumors are normal products of normal genes, but they are more often hormonally inactive precursors or subunits than complete active horm ones. At the present time, the use of ectopic hormones in the clinical diagnosis of cancer appears lim ited. In the research setting, how ever, this phenom enon has an important role in improving our understanding of neoplasia. References 1. A d c o c k, E. W., T e a s d a l e, F., A u g u s t, C. S., C ox, S., M e s c h ia, G,, B a t t a g l i a, F. C., and N a u g h t o n, M. A.: Human chorionic gonadotropin: Its possible role in maternal lymphocyte suppression. Science 181: , B r a u n s t e in, G. D., R a s o r, J., and W a d e, M. E.: Presence in normal human testes of a chorionic-gonadodropin-like substance distinct from human luteinizing hormone. New Eng. J. Med. 293: , C h o u, J., R o b in s o n, J. C., and W a n g, S.: Effects of sodium butyrate on synthesis of human chorionic gonadotropin in trophoblastic and non-trophoblastic tumors. Nature 268: , G a il a n i, S., M in g C h u, T., N u s s b a u m, A., O s t r a n d e r, M., and C h r i s t o f f, N.: Human chorionic gonadotrophins (HCG) in nontrophoblastic neoplasms. Cancer 38: , G e w i r t z, G. and Ya l o w, R. S.: Ectopic ACTH production in carcinoma of the lung. J. Clin. Invest. 53: , L ie b lic h, J. M., W e in t r a u b, B. D., K r a u t h, G. H., K o h l e r, P. O., R a b so n, A. S., and R o s e n, S. W.: Ectopic and eutopic secretion of chorionic gonadotropin and its subunits in vitro: Comparison of clonal strains from carcinomas of lung and placenta. J. Nat. Cancer Inst. 56: , L ie b lic h, J. M., W e in t r a u b, B. D., R o s e n, S. W., C h o u, J. Y., and R o b in so n, J. C.: HeLa cells secrete a subunit of glycoprotein trophic hormones. Nature 260: , M c M a n u s, L. M., N a u g h t o n, M. A., and M a r t in e z - H e r n a n d e z, A.: Human chorionic gonadotropin in human neoplastic cells. Cancer Res. 36: , O d e l l, W. O.: Glycopeptide hormones and neoplasms. New Eng. J. Med. 297: , O d e l l, W., W o l f s e n, A., Y o s h im o t o, Y., W e itz m a n, R., F is h e r, D., and H ir o s e, F.: Ectopic peptide synthesis: A universal concomitant of neoplasia. Trans. Assoc. Amer. Phys. 13: , OMENN, G. S.: Pathobiology of ectopic hormone production by neoplasms in man. Pathobiol. Ann. 3: , R o s e n, S. W., W e in t r a u b, B. D., V a itu k a - i t is, J. L., S u ssm a n, H. H., H e r s h m a n, J. M., and MUGGIA, F. M.: Placental proteins and their subunits as tumor markers. Ann. Int. Med. 82:71-83, R u t a n e n, E. M. and S e p p a l a, M.: The HCGbeta subunit radioimmunoassay in nontrophoblastic gynecologic tumors. Cancer 4 1 : , S u s s m a n, H. H., W e i n t r a u b, B. D., an d R o se n, S. W.: R ela tio n sh ip o f e cto p ic p lacen tal

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