METHOD FOR SCREENING THE RISK OF GASTRIC CANCER

Abstract: Method for screening the risk for gastric cancer using, in combination, the determination of serum pepsinogen I, gastrin-17 and the supporting determination of Helicobacter pylori antibodies from blood serum, in order to detect either atrophy of the corpus area, atrophy of the antrum area or atrophy of the mucosa of the whole stomach as well as a causative Helicobacter pylori infection, whereby the risk for gastric cancer can be evaluated and the necessary gastroscopy and follow-up can be planned.

Description: Method for screening the risk of gastric cancer Background of the invention In the following background information is presented re¬ lating to methods for screening the risk of gastric can¬ cer, primarily using pepsinogen I and gastrin-17 deter¬ mination from a blood sample. Although the occurrence of new cases of gastric cancer has diminished in the recent years, gastric cancer is still one of the most common malignancies. In Finland, appr. 250 to 300 new cases of cancer/one million peop- le/year are registered. In the age group of people above 50, there are an estimated 2350 cases of stomach cancer, which is about 3 per milie of the age group population (Finnish Cancer Registry - The Institute for Statistical and Epidemiological Cancer Research 1993). In addition to Finland, there is a high gastric cancer incidence in Ice¬ land, South America and especially in Japan. The prognosis of gastric cancer is usually poor, as there is no specific treatment. Presently the only possibility of successfully treating gastric cancer is its early de¬ tection and total removal surgically. Gastric cancer does not necessarily give any symptoms in its early stages. The late appearance of symptoms natu- rally delays the patient from seeking treatment. On the other hand, the clinical findings in the early stage of gastric cancer are often non-specific. The primary diag¬ nostic method for gastric cancer is presently gastroscopy and biopsies, cell and aspiration cytology associated therewith. As routine gastroscopies are carried out in order to examine symptoms, such as pain in the upper ab¬ domen or bleeding of the gastrointestinal tract, a symptomatic gastric cancer discovered in this manner is often already far advanced and thus inoperable. Attempts have also been made at improving primary diagnostics with various immunological methods, but no sufficiently speci¬ fic immunological method has been successfully developed. It is a primary object to find the means by which it would be possible to identify within the general popula¬ tion easily and with moderate costs those symptomless persons which might be suffering from gastric cancer in its initial stages. After identification these persons should immediately be examined by gastroscopy. At the same time those persons could be identified which exhibit premalignant gastric changes which need to be followed up. Gastric cancer can be preceded by a number of different gastric diseases or conditions (so called precancerous conditions), which are chronic atrophic gastritis, perni¬ cious anaemia, ventricular ulcer, gastric polyposis and the Menetrier disease (giant hypertrophic gastritis). Clearly identifiable changes of the mucosa are dysplasia and adenoma. The said conditions are associated with an appr. 4 to 5 fold relative cancer risk, as compared to the general population. It has been established that in almost all diseases the risk is mediated over chronic at- rophic gastritis. Chronic gastritis means a prolonged inflammatory con¬ dition of the gastric mucosa. The disease can coarsely be divided into the so-called superficial and the atrophic form. In superficial gastritis, the inflammatory cell in¬ filtration is concentrated below the surface epithelium. In case the inflammation progresses and diffuses between the specific gastric secretory glands, one refers to chronic atrophic gastritis. In such a case, the normal glandular structures of the gastric mucosa are at least partly substituted by etaplastic changes. The relative risk of gastric cancer in patients suffering from atrophic gastritis in the corpus area of the stomach, has been estimated, as calculated from the Finnish cancer statistics, to be about 4- to 5-fold as compared to persons having a healthy mucosa. In addition, there is a risk for falling ill with pernicious anaemia due to intrinsic factor deficiency and B12 vitamin absor¬ ption disturbance. In severe atrophy of the antrum area, the risk is even 18-fold. If atrophic changes appear both in the antrum and the corpus area (pangastritis) , the risk can increase to even 90-fold (Sipponen, Kekki, Haa- pakoski, Ihamaki & Siurala 1985). Screening for preliminary stages of gastric cancer by determination of pepsinogen and gastrin-17 in serum Stomach pepslnogens It is possible to electrophoretically distinguish 7 dif- ferent pepsinogens from the gastric mucosa in humans (Samloff 1969). Of these the five fastest form the immunologically uniform group of pepsinogen I. The other two form the pepsinogen II group. The group I pepsinogens are synthezised only in the main cells and the mucous secreting cells of the corpus area of the stomach. In contrast thereto, group II pepsinogens are formed in the glands over the whole stomach area and to some degree also in the upper part of the duodenum in the Brunner glands (Samloff & Liebman 1973; Weinstein, Lechango, Sa - loff et al 1977). In the serum of a healthy person the pepsinogen I concentration is approximately 6 times that of the pepsinogen II concentration (Samloff 1982). In at¬ rophic gastritis of the corpus area of the stomach the serum pepsinogen I concentration decreases, whereas the serum pepsinogen II concentration remains at the previous level. Thus, the serum pepsinogen I concentration fairly well reflects the number of pepsinogen secreting cells in the corpus area of the stomach, and their condition. The more serious the atrophic gastritis of the corpus area of the stomach is, the lower is the serum pepsinogen I concentration (Tamm, Villako, HSrkόnen & Karonen 1984; Kekki, Samloff, Varis & Ihamaki 1991). A low pepsinogen I concentration in the serum indicates severe atrophic cor¬ pus gastritis with a sensitivity of over 90 % and a spe¬ cificity of almost 100 % (Varis, Kekki, Harkόnen, Sippo- nen & Samloff 1991). In a Finnish study (Varis, Sipponen, Laxen, HarkOnen & Heinonen, still unpublished) wherein symptom-free smoking men over the age of 50 were screened for gastroscopical examination based on a low serum pepsinogen I concentra- tion, a neoplastic change was observed in 4.7 % of those that had undergone gastroscopy (5.8 % of the patients suffering from atrophic gastritis) and in 1 % a symptom- free precancerous condition (Table 1 and Table 2) was observed. In this study it was possible to identify, ba- sed on the low serum pepsinogen I test result, a number of gastric cancer incidences requiring immediate surgery and pre-cancerous conditions (dysplasia) requiring subse¬ quent gastroscopic following. At the same time it was possible to identify the population group which runs the risk of falling ill with pernicious anaemia and whose blood values should consequently be monitored in the fu¬ ture. Epidemiological studies show that only about 25 % of gas- trie cancer patients have severe atrophic corpus gastri¬ tis which can be verified based on a low serum pepsinogen I level (Sipponen, Kekki, Haapakoski; Ihamaki & Siurala 1985). In about 65 % the cancer is preceded by atrophy in the antrum area, which thus is not verifiable by pepsino- gen I determination. Table 1. Results from a study for screening gastric cancer in Fin¬ nish smoking men over the age of 50, based on a low serum pepsinogen I (S-PG I) level Screening result Number % of the % of those former gastroscopied Number examined 22431 Low S-PG I 2215 9.9 Gastroscopied 1347 60.8 Atrophic corpus gastritis 1092 81.1 Carcinoma 63 5.8 4.7 Table 2. Neoplastic (tumour like) changes of the gastric mucosa based on pepsinogen I determination in men over 50 years of age examined in Finland (see Table 1). Neoplastic type Number Moderate dysplasia (abnormal growth) 42 Severe dysplasia 7 Carcinoma 11 (initial 70%) Carcinoid tumour 3 Total number 63 Gastr±n of the antrum .area Gastrin is secreted in the gastrointestinal tract in at least three different forms, the immunoreactive activity of all these forms being measured when serum gastrin is determined (total serum gastrin). Gastrin subtypes are the so-called minigastrin (G-14), little gastrin (G-17) and big gastrin (G-34) (Gregory 1974). Physiologically most important are gastrin-17 and gastrin-34. The effect of gastrin-17 on the secretion of hydrochloric acid is 6 times that of gastrin-34 (Walsh, Isenberg, Ansfield & Maxwell 1976). Gastrin is secreted from the so-called G- cells, which appear both in antrum and in duodenum. The most important accelerators of gastrin secretion is the tonus of the vagus nerve and the protein degradation pro¬ ducts. The secretion of gastrin is slowed down by a pH decrease of below 2.5 (Walsh, Richardson & Fordtran 1975). The gastrin secreted from the antrum is to over 90 % of the gastrin-17 type, whereas the duodenal gastrin is primarily of the gastrin-34 type (Berson & Yalow 1971). In a fasting situation, primarily gastrin-34 is found in the serum, whereas after a meal the serum gast¬ rin is of the gastrin-17 type (Lamers, Harrison, Ippoliti & Walsh 1979). The secretion of gastrin-17 can also be studied using the so-called protein stimulation test. In such a test, a blood sample after fasting is taken in the morning, whereafter the patient eats a protein rich stan¬ dard meal and blood samples are taken at 15 minute inter¬ vals for two hours. The maximal increase is evident after appr. 20 minutes. In atrophic antrum gastritis the mucous membrane of the antrum is atrophied and thus its gastrin-17 secretion decreases and its concentration in the serum is reduced. A reduced gastrin-17 concentration in the serum would thus be an indicator of antrum atrophy and of an increa¬ sed risk for cancer in this area. In case the mucous mem¬ brane of the antrum is atrophied, there is a reduced res¬ ponse also in the protein stimulation test, which seems to be a more sensitive indicator of atrophy than the mere concentration determination. HelicoJacter pylori infection of the stomach Helicobacter pylori is a spiral shaped, gram-negative bacterium which thrives in the mucus in the immediate vicinity of the surface epithelial cells of the gastric mucosa and in the cell interstices. The bacterium appa¬ rently is transferred perorally from one person to the other. The effect of the bacterium on the gastric mucosa is an inflammation reaction, which is mediated over a complement by liberating strong inflammation mediator substances. After the acute stage, the inflammation is transformed into chronic gastritis. In patients suffering from chronic gastritis, in 70 to 90 % a Helicobacter py¬ lori infection can be established (Calam 1994). As Heli- cobacter pylori infection and chronic gastritis in the stomach are closely associated, it has been stipulated that this bacterial infection could be one etiological factor in the development of stomach cancer. It is for this reason possible that eradication of the Helicobater pylori bacteria in the initial stages of the infection, could prevent the development of atrophy associated with chronic gastritis, and thus reduce the cancer risk. Screening for gastric cancer using combined pepsinogen I - gastrin- 17 - Helicobacter pylori-antibody deter¬ mination in serum For the screening preferably a method can be used, accor¬ ding to which on a microplate simultaneously the serum pepsinogen I and gastrin-17 concentration and the Helico¬ bacter pylori antibodies can be determined. It is hereby possible to diagnose either corpus gastritis, antrum gastritis or pangastritis, as well as one cause of at¬ rophy, Helicobacter pylori infection. It is to be noted that in severe atrophic gastritis, no Helicobacter pylori bacteria can be found in the gastric mucosa, and also the antibodies in the serum have been normalized. For pepsinogen I determination the pepsinogen I antigen has been purified from the human gastric mucosa. It has been coupled by thiolation and protein-protein- conjugation to rabbit or sheep red blood cells and so rabbits or sheep have been immunized in the classical manner to produce antibodies to pepsinogen I. A polyclo- nal antibody to gastrin-17 has been produced with the same technique by coupling a [Leu 15 ]-gastrin-17 (Sigma S- 9145, [Leu 15 ]-gastrin-1) or -the gastrin-17 fragment 1-13 (Sigma G-6261) to rabbit autological red blood cells and immunizing the rabbits in a normal manner the rabbits to produce a specific antibody to gastrin-17. Polyclonal an- tibodies have been produced also with BSA-conjugates in the classical manner. A monoclonal gastrin-17 antibody has been produced in the classical manner in mouse with a [Leu 15 ]-gastrin-17-derivative, which is conjugated to thy- roglobulin. The specific antibodies have been purified with protein A-affinity chromatography or in some cases with pepsinogen I or gastrin-17 affinity chromatography. Pepsinogen I determination 1. The microplate wells are coated with a polyclonal an¬ tibody by incubating over night at + 4 β C. 2. The wells are emptied and washed with a washing solu¬ tion. 3. The sample is added at a suitable dilution, and incu- bated at the most one hour at + 37°C. 4. The wells are washed. 5. The enzyme labelled monoclonal antibody is added at a suitable dilution, and incubated for at the most one hour at +37 β C. 6. The wells are washed. 7. The substrate is added (chromogenic, fluorescent or luminescent substrate), and incubated maximally for 30 mins at room temperature. 8. The reaction is stopped and the absorbance, fluores¬ cence or luminescence is determined and compared to a calibration curve. The method can be speeded up by incubating the sample and the enzyme labelled monoclonal antibody simultaneously as a so-called one-step-ELISA-raethod. There are also other alternatives that can be used. Alternative 2 (competitive ELISA) 1. The sample and antibody are incubated on microplate wells, whereby the antigen of the sample couples to the antibody. 2. A known amount of labelled antigen is added, which competes with the antigen in the specimen for free anti¬ body. 3. The solution is transferred to a microplate well which has been coated with a second antibody, and incubated maximally for 1 hour. 4. Unbound material is washed away. 5. The substrate is added and incubated maximally for 30 minutes at room temperature. 6. The reaction is stopped and the results are evaluated by comparing to calibration curve. As an alternative, the antigens can be added simulta¬ neously and/or directly to a microplate well coated with a second antibody, but in such a case the sensitivity of the process is not as good. In this process, the competi¬ tion can be arranged also with labelled antibody. Gastrin-17 determination 1. The wells are coated with streptavidin. 2. An excess of gastrin-17 derivative labelled with biotin is added and incubated until equilibrium is reached . 3. The sample and the monoclonal antibody are added whereby the gastrin-17 in the specimen and the biotin labelled gastrin-17 compete for the antibody. The mixture is incubated for one hour at + 37 β C. 4. The wells are washed. 5. The enzyme labelled second antibody is added and incu¬ bated for appr. one hour. 6. The substrate (fluorescent or luminescent) is added and incubated for appr. 30 minutes at room temperature. 7. The reaction is stopped and the fluorescence or lu¬ minescence is read, and compared to a calibration curve. ffelicoiacter pylori determination For the determination of the Helicobacter pylori antibo¬ dies a number of commercial "kits" are available (e.g. Orion Pyloriset EIA-G, Pyloriset EIA-A, EIA 2G by Roche, Pyloristat by Whittaker Bioproducts). Antigens can be prepared from Helicobacter pylori bacteria in various ways (see Lelwala-Guruge, Nilsson, Ljungh, WadstrOm 1992) and they are also commercially available. The method we use for determining Helicobacter pylori antibodies is generally known and the antigen extracted from the bacte- ria with acidic glycine is attached by adsorption to the wells in a microplate. The second antibody (rabbit anti- human IgG) is labelled with enzyme (alkaline phosphatase and in some cases peroxidase). p-Nitrophenyl phosphate (adsorbance) or umbelliferyl-phosphate (fluorescence) is used as the enzyme substrate, whereby the absorbance (405 nm) or fluorescence (360 nm/460 nm) can be measured. Sensitivity of measurement In the determination of serum pepsinogen I the cut-off- value for atrophic gastritis is, according to our pre¬ vious studies, 20-30 μg/1 depending on the specificity and sensitivity agreed upon for the method in question, which corresponds to appr. 450 - 690 pmol/1 (Varis, Sip¬ ponen, Laxen, Harkonen & Heinonen, still unpublished). In a normal situation the gastrin-17 concentrations are in the range of 2 - 25 pmol/1. Thus, the serum gastrin-17 concentration is appr. 100 times smaller than that of pepsinogen I. As one measures even lower values in at¬ rophic antrum gastritis, a very high sensitivity of the developed method is required. In atrophy of the antrum area the cut-off value for serum gastrin-17 determination is in the range of 0.1 - 2 pmol/1. It is possible to reach a sufficiently high sensitivity with an enzyme la¬ bel and using, for example, luminescence measurement as a sensitive detection system. The sensitivity can be fur- ther increased by performing a so-called enzymatic recy¬ cling reaction which we have applied i.a. for the deter¬ mination of steroids (Harkonen, Adlercreutz & Groman 1974). Also in this case the product formed can be measu¬ red either using fluorescence technique or luminescence. For the Helicobacter pylori positiveness the cut-off ti- ter is 200 - 500. The use of the combination method for detecting atrophy of the mucosa in the various parts of the stomach is shown in the Table 3. Table 3. Combination method for serum pepsinogen I and gastrin-17 for detecting severe atrophic gastritis of the mucosa of the corpus area or the antrum area of the sto¬ mach, or of the whole stomach (pangastritis). Location of Serum Serum Increase of severe atrophy pepsino¬ gastrin- of serum gastrin in stomach gen I 17 17 (response) in μg/i pmol/1 protein stimula¬ tion Corpus < cut-off > upper normal or in- value reference creased response limit Antrum > cut-off < cut-off strongly reduced value value response Mucosa of the < cut-off at the reduced response whole stomach value lower limit (corpus and of reference antrum) value Reference values: Serum pepsinogen I 25 - 120 μg/1 Serum gastrin-17 2 - 25 pmol/1 Cut-off-values: Serum pepsinogen I 20 - 30 μg/1 Serum gastrin-17 0.1 - 2 pmol/1 According to the Table 3, when the serum pepsinogen I concentration is below the cut-off value, which according to the specificity of the method is in the range of appr. 20 - 30 μg/1, the atrophy is located in the corpus area of the stomach. If, on the other hand, the serum gastrin- 17 concentration is below the cut-off value, which depen- ding on the specificity of the method is in the range of 0.1 - 2 pmol/1, the atrophy is located in the antrum area of the stomach. In atrophy of the corpus area the gast¬ rin-17 value is above the upper limit of the reference values. Correspondingly in pangastritis, the serum pep¬ sinogen I concentration is below the cut-off value whe¬ reas the gastrin-17 concentration is at the lower limit of the reference values. The location of the atrophy can also be verified using the protein stimulation test, in which the serum gastrin-17 concentration is measured at the base line situation and after a protein rich standard meal. The response (increase of serum gastrin-17 as com¬ pared to the base line situation) is strongly reduced in atrophy of the antrum area only, and slightly decreased in atrophy of the mucosa of the whole stomach. On the other hand, if the mucosa of the antrum is healthy, but the corpus area is atrophied, the response is normal or increased. Literature Berson SA & Yalow, RS (1971) Nature of immunoreactive gastrin extracted from tissues of gastrointestinal tract. Gastroenterology 60:215-222 Calam, J (1994) Helicobacter pylori (Review) Eur. J. Clin Invest 24: 501-510 Gregory, RA (1974) The gastrointestinal hormones; a review of recent advances, J. Physiol. 241: 1-32 The Finnish Cancer Registry - The Institute for Statistical and Epidermiological Cancer Research (1993) Cancer Incidence in Finland 1991. Cancer Statistics of the National Research and Development Centre for Welfare and Health Harkδnen, M, Adlercreutz, H & Groman, EV (1974) Enzymatic techniques in steroid assay. J. Steroid Biochem. 5: 717-725 Kekki, M, Samloff, IM, Varis, K & Ihamaki, T (1991) Serum pepsinogen I and serum gastrin in the screening of severe atrophic corpus gastritis. Scand J Gast¬ roenterology 26 (suppl 186):109-116 Lamers, C, Harrison, A, Ippoliti, A & Walsh, J (1979) Molecular forms of circula¬ ting gastrin in normal subjects and duodenal ulcer patients. Gastroenterology 76: 1179 Lelwala-Guruge, J, Nilsson, I, jungh, A & Wadstrom. T (1992) Cell surface pro¬ teins of Helicobacter pylori as antigens in an ELISA and a comparison with three commercial ELISA. Scand J Infect Dis 24: 457-465 Samloff, JM & Liebman, WM (1972) Purification and immunochemical characteri¬ zation of group IT pepsinogens in human seminal fluid. Clin Exp Immunol 11:405- 414 Samloff, IM (1969) Slow moving protease and the seven pepsinogens. Electropho- retic demonstration of the existence of eight proteolytic fractions in human gastric mucosa. Gastroenterology 57:659-69 Samloff, IM (1982) Pepsinogens I and II: purification from gastric mucosa and radioimmuno-assay in serum. Gastroenterology 82:26-33 Sipponen, P, Kekki, M, Haapakoski, J. Ihamaki, T & Siurala, M (1985) Gastric cancer risk in chronic atrophic gastritis: statistical calculations of cross-sectional data. Int J Cancer 35:173-77 Tamm, A, Villako, H, Harkonen, M & Karonen, S-L (1984) Serum pepsinogen I and the state of gastric mucosa in an Estonian population sample. Scand. J. Gast- roenterol, 19: 1091-1094. Varis, K (1993) Secretorial function of the stomach (Mahan eritystoiminta) in the book Clinical gastroenterology (Kliininen gastroenterologia) editor (toim.) Mietti- nen, T, Seppala, K & Sivula, A., Duodecim, Jyvaskyla pp. 55-69 Varis, K, Kekki, M, Harkϋnen, M, Sipponen, P & Samloff, IM (1991) Serum pepsinogen I and serum gastrin in the screening of atrophic pangastritis with high risk of gastric cancer. Scand J Gastroenterology 26 (suppl 186): 117-123 Varis, K, Sipponen, P, Laxen, F, Harkonen, M & Heinonen O-P, julkaisematon tyό. Walsh, JH, Isenberg JI, Ansfield, J & Maxwell, V (1976) Clearance and acid- stimulating action of human big and little gastrins in duodenal ulcer subjects. J Clin Invest 57: 1125-1131 Walsh, JH, Richardson, CT & Fordtran, JS (1975) pH dependence of acid secretion and gastrin release in normal and ulcer subjects. J Clin Invest 55: 462-468 Weinstein, WM, Lechago, J. Samloff, IM et al. (1977) Pepsinogens in human gastric and esophageal glands (abstr). Clin Res 25:690

Claims: Claims 1. Method for screening the risk for gastric cancer from blood serum by detecting atrophy of the corpus or antrum area of the stomach, or atrophy of the mucosa of the who¬ le stomach, characterized in that the pepsinogen I and gastrin-17 concentrations are determined quantitatively from the serum and the values obtained are compared to the method specific cut-off value for the substance to be determined. 2. Method according to the claim 1, characterized in that the pepsinogen I and gastrin-17 concentration values ob¬ tained are compared also to the reference value of the substance to be determined. 3. Method according to the claim 1 or 2, characterized in that the serum gastrin-17 concentration is also measured using the protein stimulation test by measuring the said concentration at the base line situation and after a pro¬ tein rich standard meal. 4. Method according to the claim 1, 2 or 3, characterized in that a combined immunological pepsinogen I and gast- rin-17 method is used on a plastic, glass or cellulose support. 5. Method according to the claim 4, characterized in that the support is a microplate well. 6. Method according to any one of the claims 1 to 5, cha¬ racterized in that a detection method for absorbance, fluorescence or luminescence is used for the pepsinogen I and gastrin-17 determination. 7. Method according to any one of the claims 4 to 6, cha¬ racterized in that for the determination of the pepsino- gen I concentration, a polyclonal or monoclonal antibody to pepsinogen I is used. 8. Method according to any one of the claims 4 to 7, cha- racterized in that for the determination of the gastrin- 17 concentration, specific poly- or monoclonal antibody to gastrin-17 are used. 9. Method according to the claim 8, characterized in that a polyclonal antibody to gastrin-17 is obtained by im¬ munizing an animal, such as a rabbit or a lamb, with the gastrin fragment 1-13, [Leu 15 ]-gastrin-17 or using a gast- rin-17 antigen isolated from the stomach of an animal such as a pig. 10. Method according to the claim 8, characterized in that a monoclonal antibody has been produced in a mouse using the [Leu 15 ]-gastrin-17 antigen. 11. Method according to any preceding claim, characteri¬ zed in that is combined with a Helicobacter pylori anti¬ body determination. 12. Method according to any preceding claim, characteri- zed in that the pepsinogen I, gastrin-17 and Helicobacter pylori determination methods are combined to a kit-met¬ hod, wherein the determinationss are carried out simul¬ taneously on a microplate well using a method based on the ELISA technique, using polyclonal and monoclonal an- tibodies, as well as streptavidin-biotin-interaction, as well as sensitive detection methods based on absorption, fluorescence or luminescence.

Inventors: HAERKOENEN MATTI, HAERKOENEN, MATTI
Applicants: HAERKOENEN MATTI, LOCUS GENEX OY, HAERKOENEN, MATTI
Application year: 1995
Main classification: G01N33
IPC codes: A61B10, G01N33