The biology of colorectal cancer. Implications for pretreatment and follow-up management

The biology of colorectal cancer is discussed in terms of multistage carcinogenesis. Colorectal cancer evolves through the stepwise acquisition of mutations at certain critical genetic loci, many of which have been identified recently. The earliest step in the neoplastic pathway is a shift of proliferation from the normally restricted zone at the base of the colonic crypt and the retention of cells capable of proliferation at the top of the colonic crypt. This appears to be mediated by a mutation in the APC gene. The adenoma, a collection of benign neoplastic cells, is the first pathologically recognizable neoplastic lesion. Adenomas may grow or involute. Additional genetic lesions, such as a mutation in the Ki-ras gene, contribute to the growth and progressive dysplasia of the adenoma. Critical lesions in the p53 gene appear to be responsible for malignant transformation and the appearance of genetic instability of the neoplastic cell, which greatly increases the likelihood that additional genetic events will occur that contribute to a progressively more aggressive neoplastic phenotype. Genetic and phenotypic diversity develop within the primary malignant tumor, and metastasis occurs as a consequence of a complex series of events. Opportunities for detection and therapeutic intervention in colorectal neoplasia are discussed in this framework.

Genetics, natural history, tumor spectrum, and pathology of hereditary nonpolyposis colorectal cancer: an updated review

Hereditary nonpolyposis colorectal cancer (HNPCC) dates to Warthin's description of family G, which he began studying in 1895. Warthin's observations were not fully appreciated until 1966 when two families with an autosomal dominant inheritance pattern of nonpolyposis colorectal cancer (CRC) and endometrial cancer were described. This condition was first termed the "cancer family syndrome" and was later renamed HNPCC. Some have proposed that HNPCC consists of at least two syndromes: Lynch syndrome I, with hereditary predisposition for CRC having early (approximately 44 years) age of onset, a proclivity (70%) for the proximal colon, and an excess of synchronous and metachronous colonic cancers and Lynch syndrome II, featuring a similar colonic phenotype accompanied by a high risk for carcinoma of the endometrium. Transitional cell carcinoma of the ureter and renal pelvis and carcinomas of the stomach, small bowel, ovary, and pancreas also afflict some families. Current estimates indicate that HNPCC may account for as much as 6% of the total CRC burden. There are no known premonitory phenotypic signs or biomarkers of cancer susceptibility in the Lynch syndromes. This report will summarize current knowledge, with emphasis on the manner in which this knowledge can be employed effectively for diagnosis and management of HNPCC.

Post-translational processing of gastrin in neoplastic human colonic tissues

Gastrin has been postulated to stimulate proliferation in colorectal neoplasms. Although gastrin mRNA has been demonstrated to be present in colon cancer cell lines, the intact peptide had not been recovered from human colorectal neoplasms. We demonstrate that gastrin and its precursors are present in both colorectal neoplasia and adjacent normal-appearing colonic mucosa. In colonic tissue, the glycine-extended precursor form of the peptide is over 10-fold more abundant than the amidated gastrin, and progastrin is more than 700-fold more abundant. In contrast, amidated gastrin in the human antrum is the predominant form of gastrin by a factor of 10. Furthermore, the ratio of gastrin precursors to gastrin is significantly increased in neoplastic colonic mucosa when compared with normal colonic tissue. These data suggest that the processing of gastrin is unique in the human colon and that further differences in processing occur in neoplastic colonic tissue.

Transforming growth factor alpha protection against drug-induced injury to the rat gastric mucosa in vivo

This study was designed to determine whether transforming growth factor alpha (TGF alpha) protects rat gastric mucosa against ethanol- and aspirin-induced injury. Systemic administration of TGF alpha dose-dependently decreased 100% ethanol-induced gastric mucosal injury; a dose of 50 micrograms/kg delivered intraperitoneally 15 min before ethanol decreased macroscopic mucosal injury by > 90%. At the microscopic level, TGF alpha prevented deep gastric necrotic lesions and reduced disruption of surface epithelium. Pretreatment with orogastric TGF alpha (200 micrograms/kg) only partially (40%) decreased macroscopic ethanol damage. Intraperitoneal administration of TGF alpha at a dose of 10 micrograms/kg, which does not significantly inhibit gastric acid secretion, decreased aspirin-induced macroscopic damage by > 80%. TGF alpha protection does not seem to be mediated by prostaglandin, glutathione, or ornithine decarboxylase-related events, as evidenced by lack of influence of the inhibition of their production. Pretreatment with the sulfhydryl blocking agent N-ethylmaleimide partially abolished (40%) the protective effect of TGF alpha. In addition, systemic administration of TGF alpha resulted in a two-fold increase in tyrosine phosphorylation of phospholipase C-gamma 1 and in a time- and dose-dependent increase in levels of immunoreactive insoluble gastric mucin; these events occurred in a time frame consistent with their participation in the protective effect of TGF alpha.

Regulation of canine gastric mucin synthesis and phospholipid secretion by acid secretagogues

Key components of the mucous gel include the glycoprotein mucin and surface-active phospholipids. In the present study, mucin production and release of the surface-active phospholipid phosphatidylcholine (PC) into the medium were measured with an isolated canine mucous cell culture system. Stimulation of glycoprotein synthesis in response to 10(-4) mol/L histamine (160% +/- 9% of control, P < 0.01), 10(-6) mol/L gastrin (129% +/- 7%, P < 0.01), and 10(-6) mol/L carbamylcholine (129% +/- 7%, P < 0.01) was observed by metabolic labeling, whereas prostaglandin E2 (PGE2) had no effect. The effect of histamine was blocked by the H2 receptor antagonist cimetidine but not the H1 receptor antagonist diphenhydramine (P < 0.01). Activators of adenylate cyclase and cyclic adenosine monophosphate analogs significantly stimulated mucin synthesis (P < 0.05). A 7.8% +/- 1.7% increase in mucin above basal levels after 24 hours was observed with a solid-phase immunoassay in control wells, whereas histamine, gastrin, and carbamylcholine increased total mucin by 14% +/- 0.7%, 17% +/- 4.3%, and 20.4% +/- 4%, respectively (all P < 0.01), and PGE2 had no significant effect. PC release was stimulated by the administration of histamine, carbamylcholine, gastrin (108%-110% of control, P < or = 0.05), and PGE2 (120% of control, P < 0.01). The acid secretagogues histamine, gastrin, and carbamylcholine stimulated mucin synthesis and PC release. PGE2 has no direct role in the synthesis of canine gastric mucin but stimulates release of surface-active phospholipids. The mechanisms responsible for acid secretion provide for the coordinated production of the primary layer of defense against the injurious effects of low pH.

Effect of sucralfate on components of mucosal barrier produced by cultured canine epithelial cells in vitro

The mucous gel maintains a neutral microclimate at the epithelial cell surface, which may play a role in both the prevention of gastroduodenal injury and the provision of an environment essential for epithelial restitution and regeneration after injury. Enhancement of the components of the mucous barrier by sucralfate may explain its therapeutic efficacy for upper gastrointestinal tract protection, repair, and healing. We studied the effect of sucralfate and its major soluble component, sucrose octasulfate (SOS), on the synthesis and release of gastric mucin and surface active phospholipid, utilizing an isolated canine gastric mucous cells in culture. We correlated these results with the effect of the agents on mucin synthesis and secretion utilizing explants of canine fundus in vitro. Sucralfate and SOS significantly stimulated phospholipid secretion by isolated canine mucous cells in culture (123% and 112% of control, respectively). Indomethacin pretreatment significantly inhibited the effect of sucralfate, but not SOS, on the stimulation of phospholipid release. Administration of either sucralfate or SOS to the isolated canine mucous cells had no effect upon mucin synthesis or secretion using a sensitive immunoassay. Sucralfate and SOS did not stimulate mucin release in the canine explants; sucralfate significantly stimulated the synthesis of mucin, but only to 108% of that observed in untreated explants. No increase in PGE2 release was observed after sucralfate or SOS exposure to the isolated canine mucous cells. Our results suggest sucralfate affects the mucous barrier largely in a qualitative manner. No increase in mucin secretion or major effect on synthesis was noted, although a significant increase in surface active phospholipid release was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple tumor suppressor genes in multistep carcinogenesis

One of the most exciting areas of molecular oncology is the convergence of two independent lines of evidence suggesting involvement of multiple tumor suppressor genes in a given type of cancer. First, epidemiology and somatic cell genetics indicate the presence of multiple tumor suppressor genes in each of several malignancies. Second, cancers often lose multiple chromosomal regions during tumor progression. We will use two tumors, colorectal cancer and Wilms tumor, to illustrate the questions that multiple tumor suppressor genes raise.

Colon cancer genetics

The terms "hereditary," "sporadic," and "familial" colorectal cancer (CRC) suggest a knowledge of causation; however, current understanding of CRC does not permit categorization of differing CRC risks in accord with their cause per se. Despite these serious shortcomings, these terms are defined operationally on the basis of a family history of cancer, and when available, additional phenotypic information. The sporadic type occurs in the absence of a family history of CRC in a first-degree relative. The familial type occurs when at least one first-degree relative has CRC. Both these categories require the exclusion of hereditary CRC. In the case of hereditary CRC, this type is defined as a family history of CRC occurring in a pattern that indicates autosomal-dominant inheritance, which also may involve certain phenotypic signs (depending on the specific disorder, i.e., florid adenomatous polyps, benign and malignant extracolonic lesions, cancer of unusually early onset, and multiple primary cancer, particularly synchronous and metachronous CRC). Although this operational classification does not produce etiologically homogeneous groups, it is believed to have pragmatic utility with respect to planning targeted surveillance and management strategies. Because of the distinctive natural history of CRC in hereditary syndromes, it is of paramount clinical importance to identify hereditary CRC when it does occur. Even in patients with no evidence of hereditary CRC syndrome, their family history may be second only to age in determining the best CRC screening program for those who are asymptomatic. In an attempt to provide a perspective on the clinical evaluation of CRC risk, research was reviewed on pathologic features and biomarkers that may be related to CRC causes, especially the genetic basis of CRC susceptibility. The long-term objective of studies on the genetic epidemiology of CRC is primary and secondary prevention through development of targeted management and surveillance recommendations (based on an understanding of CRC causation) that is relevant to hereditary, familial, and sporadic CRC.

Role of prostaglandin E2 in cholinergic-mediated glycoprotein synthesis in canine antrum

We studied the mechanism of cholinergic stimulation of mucin synthesis in canine antral explants, including the role of PGE2 as an intermediate messenger. Isolated antral mucosa was incubated with 10(-5) M carbachol (Cb), 10(-5) M indomethacin (IND), 10(-5) M pirenzepine (PZ), 10(-5) M Cb + 10(-5) M PZ, 10(-5) M Cb + 10(-5) M IND, and 10(-5) M IND + PGE2 (10(-8), 10(-7) and 10(-6) M) in the presence or absence of [3H]glucosamine. After 24 hr, total glycoprotein synthesis was quantitated by Sepharose-4B chromatography and by 10% TCA/1% PTA precipitation with lipid extraction. PGE2 released into the media was measured by radioimmunoassay (RIA). Cb significantly increased total glycoprotein synthesis and produced a significant increase in PGE2 release. The increase in glycoprotein synthesis and the release of PGE2 was blocked by the addition of muscarinic antagonist PZ. The addition of IND significantly inhibited glycoprotein synthesis and almost entirely suppressed PGE2 secretion. IND also inhibited the effect of Cb on glycoprotein synthesis and PGE2 release. Moreover, PGE2 (10(-6) and 10(-7) M) significantly increased the glycoprotein synthesis in the canine stomach. This suggests the coordinate participation of PGE2-releasing cell population in modulation of glycoprotein synthesis in gastric mucosa.

Eicosanoid production by the human gastric cancer cell line AGS and its relation to cell growth

Eicosanoids have the ability to stimulate or inhibit the proliferation of epithelial cells, and they have been shown to modulate the growth characteristics of certain tumor cell lines. In addition, many epithelial cells have the ability to produce eicosanoids, which may then serve as autocrine growth factors. We have measured the eicosanoids produced by the human stomach cell line AGS using reverse-phase high-performance liquid chromatography. AGS cells were incubated with [3H]arachidonic acid and stimulated to release eicosanoids by the calcium ionophore A23187. Unlike its counterpart from the normal stomach, the AGS tumor cell line produced prominent amounts of the leukotrienes D4, C4, and B4; 6-keto-prostaglandin F1 alpha; thromboxane B2; hydroxyeicosatetraenoic acids; and smaller amounts of other prostaglandins in response to A23187. Under basal condition (in the absence of calcium ionophore), hydroxyeicosatetraenoic acid was produced in greatest relative amount compared with the other eicosanoids. To elucidate the potential autacoid role of these agents, exogenous eicosanoids were added to AGS cells, and proliferation was measured. Prostaglandins D2 and E2 suppressed the growth of AGS cells in a dose-dependent manner. On the other hand, leukotrienes D4 and C4 had a dose-dependent proliferative effect on cell growth. The lipoxygenase inhibitor nordihydroguaiaretic acid (10(-6), 10(-5) M) and hydrocortisone (10(-5) M) had dose-dependent suppressive effects on growth, whereas indomethacin (10(-6) M and 10(-5) M) had no effect. These results suggest that AGS cells preferentially metabolize arachidonic acid through the 5-lipoxygenase pathway, which results in the production of growth-stimulatory autocoids. Agents that selectively block this arm of eicosanoid metabolism might be useful therapeutic agents in the treatment of certain gastrointestinal cancers.

Lectin reactivities as intermediate biomarkers in premalignant colorectal epithelium

Normal colonic epithelial cells undergo maturation as they traverse the crypt to the lumenal surface. The binding of lectins to goblet cell mucins and other glycoconjugates changes as the cells migrate and differentiate. Additional stepwise modifications in glycoconjugate expression occur in premalignant and malignant neoplasms that may be detected by lectin binding studies. The lectins Dolichos biflorus agglutinin (DBA) and soybean agglutinin (SBA) have been developed as markers of differentiation in normal-appearing colonic epithelium. Using a quantitative biometric system to score tissues, reduced levels of lectin binding have been found in rectal tissue from patients with familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer. The lectin Amaranthus caudatus agglutinin (ACA) binds to a cytoplasmic glycoconjugate expressed at the base of the colonic crypt and serves as a possible proliferation marker in the distal, but not proximal, colon. ACA binding increases in tandem with increased levels of proliferation (using BrdU incorporation) in neoplastic tissues. Binding by the peanut lectin (PNA) occurs late in the adenoma-to-carcinoma sequence--in larger adenomas and in cancers--and serves as a marker of advancing neoplasia. Lectins identify the stepwise changes that occur during normal differentiation, proliferation and in advancing neoplasia. By selecting the appropriate probe, biomarkers may be developed for early, intermediate, and late events in colorectal cancer.

Synthesis and prostaglandin E2-induced secretion of surfactant phospholipid by isolated gastric mucous cells

Lipids, particularly surface-active phospholipids, have been proposed to provide an important protective barrier in the gastric mucosa. The predominant surface-active phospholipid in the pulmonary surfactant complex is dipalmitoylphosphatidylcholine. To determine whether the gastric epithelium synthesizes and secretes this phospholipid, primary cultures of canine gastric mucous cells isolated by counterflow elutriation were studied. During the 24-hour period of culture, the gastric mucous cells incorporated 3H-choline into phosphatidylcholine, with dipalmitoylphosphatidylcholine representing 13.8% +/- 0.6% of the phosphatidylcholine synthesized. When mucous cell preparations with greater chief cell contamination were studied, they incorporated significantly less precursor into dipalmitoylphosphatidylcholine. Administration of prostaglandin E2, a cytoprotective agent, to the cultured mucous cells for 1 hour led to a significant increase in phosphatidylcholine release, reaching a maximum of 120.4% +/- 4.2% (P less than 0.001) at 10(-6) mol/L. No significant stimulation of phospholipid release by prostaglandin E2 was seen in the fractions containing a greater proportion of chief cells. To further establish the relationship between mucin and phospholipid secretion, two gastric cancer cell lines, Hs746T and KATO III, were studied. Using immunocytochemical and biochemical techniques, mucin synthesis and secretion were confirmed by these cell lines. The Hs746T cells were significantly more active in the secretion of both mucin and phospholipid than the KATO III cells. The Hs746T line secreted 5.7-fold more mucin and 7.3-fold more phospholipid than KATO III cells during a 24-hour period of culture. The association between mucin and phospholipids in an aqueous solution was also studied. Purified mucin in the concentration of 0.5-2 mg/mL of glycoprotein led to a significant dose-dependent increase in phospholipid solubility, suggesting the formation of a glycoprotein-phospholipid complex. The current studies indicate that the gastric mucous cell is the source of surfactant phospholipids as well as mucin. The synthesis and release of mucin and phospholipid are functions of the mucous cell that play a critical role in the primary defense of gastric epithelium.

Use of the lectin from Amaranthus caudatus as a histochemical probe of proliferating colonic epithelial cells

A newly isolated lectin, Amaranthus caudatus agglutinin (also called amaranthin or ACA), which binds to the Thomsen-Friedenreich antigen (T-antigen) and its sialylated variants, was used as a histochemical probe for proliferating cells in sections of human colonic tissues. Binding inhibition studies revealed that ACA binds to different sites on histological sections when compared to peanut agglutinin, which also recognizes the T-antigen. ACA bound selectively to the cells at the base of the colonic crypt [46 +/- 4% (SEM) of glands] which is the zone of proliferation in this tissue and preferentially labeled cytoplasmic and apical membrane glycoconjugates. Only 7 +/- 2% of the upper portions of the colonic crypts were labeled (P less than 0.001 compared to the base), and this was largely a result of extensive labeling in 2 of 23 samples studies. A marked increase in histochemical labeling by ACA was seen in adenomatous polyps and adenocarcinomas of the colon, in which 82 +/- 7 and 97 +/- 2% of the glandular units were labeled, respectively. Transitional mucosa and connective tissue adjacent to cancers were also labeled by ACA. Neuraminidase studies indicated that removal of sialic acid residues enhanced binding by peanut agglutinin, but not ACA, to glycoconjugates in cancer specimens. Specimens of colonic tissue from patients with familial adenomatous polyposis (FAP) were examined with ACA; 83 +/- 7% of adenomatous glands and 60 +/- 7% of glands in flat, normal-appearing tissue were labeled. Colonic tissues from persons at 50% risk for hereditary nonpolyposis colorectal cancer (HNPCC), FAP, and normal colons were studied and given "weighted average" labelling scores that ranged from 0-400 to accommodate variable intensity and distribution of labeling. Normal colons had a weighted average score of 65 +/- 33; FAP tissues had a score of 224 +/- 76 (P less than 0.001 compared to normal colon) and HNPCC tissues had a score of 74 +/- 70 (P less than 0.05 compared to normal colon). A group of five HNPCC cases had scores of 203 +/- 43 (P less than 0.001 compared to normal colon). ACA labels glycoconjugates in the proliferative region of normal human colonic epithelium and neoplastic lesions of the colon. The results of FAP and HNPCC tissues suggest that it may be useful for identifying foci of abnormal proliferation in familial colorectal cancer syndromes.

Abnormalities of lectin histochemistry in familial polyposis coli and hereditary nonpolyposis colorectal cancer

A transformation in the composition of colonic glycoconjugates has been described in adenomas, carcinomas, and certain premalignant conditions. These changes have been detected histochemically by the labeling patterns of fluorescein-conjugated lectins, which bind specific carbohydrate structures on fixed tissue sections. This study was performed to determine whether abnormal lectin binding patterns are present in tissues from patients genetically predisposed to colonic neoplasms and whether these patterns could be used as phenotypic markers for inheritance of the genotype. Lectin staining patterns of 22 colectomy specimens from patients with familial polyposis coli (FPC) and rectal biopsy specimens from 47 patients at risk for hereditary nonpolyposis colorectal cancer (HNPCC) (also known as Lynch syndromes I and II) were compared with rectal biopsy specimens from 27 sex-matched controls. The fluorescein-conjugated lectins included the agglutinins derived from peanut, Dolichos biflorus, Ulex europeus, and wheat germ (including the succinylated derivative). Using a technique for quantitating lectin binding on the tissue sections that provided a score from 0 to 400, labeling with certain lectins was found to vary slightly as a function of age and sex. Histologically normal mucosa from patients with FPC bound significantly less wheat germ agglutinin but significantly more U. europeus and succinylated wheat germ agglutinins than controls. Adenomas and dysplastic flat mucosa from the colectomy specimens of patients with FPC showed significantly less binding with D. biflorus, succinylated wheat germ, and wheat germ agglutinins than controls. Rectal tissues from patients at risk for HNPCC were found to bind significantly less peanut agglutinin and D. biflorus agglutinin than controls. Of interest, staining of the tissues by peanut and wheat germ lectins increased as a function of patient age; the control subjects were older than the patients with familial colon cancer, which could possibly account for the observations made with these two lectins. These results provide evidence that the premalignant colonic epithelium in familial polyposis and the hereditary nonpolyposis colon cancer syndromes may be biologically different and indicate that glycoconjugate modifications are early events in the evolution of the neoplastic phenotype.

Characterization of mucous cell synthetic functions in a new primary canine gastric mucous cell culture system

Mucin is a critical component of the protective layer secreted by gastrointestinal mucous cells. A detailed understanding of the molecular processing of gastric mucin and the physiology of its secretion has been limited by the lack of an adequate model for their study. We have developed a primary culture system of canine gastric mucous cells that has permitted us to study their synthetic and secretory functions. It was found that [3H]glucosamine used for metabolic labeling studies was incorporated into both mucin and lipid components of gastric mucus. To measure mucin with this model, a new immunoassay was developed to quantitate canine gastric mucin. Mucin was purified from the canine stomach, a polyclonal antibody was generated, and an enzyme-linked immunosorbent assay for gastric mucin was established. Mast cells were frequent contaminants of the gastric mucous cell preparation, and two methods were developed to limit their contamination. A new culture system has been developed for the study of gastric mucous cells. These cells synthesize and secrete both mucin and phospholipids. This system will permit us to study the molecular processing of mucin and the physiology of its production and release.

The carbohydrate composition of mucin in colonic cancer

Mucins synthesized in colonic cancer are known to be different from those in the normal colon; however, the biochemical differences between these mucins have not been defined. We have purified mucins from samples of nonneoplastic (normal) human colon and colon cancer and found that the carbohydrate content of the cancer-associated mucins is 48% of that in the normal colon, including significant reductions in galactose, N-acetylglucosamine, N-acetylgalactosamine, and fucose. By subjecting the mucins to alkaline degradation, we determined that there are 19% fewer oligosaccharide chains per milligram of cancer-associated colonic mucin than there are in mucins from normal colons. We also found a reduction in mean oligosaccharide chain length in cancer-associated mucin (5.83 carbohydrate residues per chain) compared with those derived from normal colons (10.2 residues). Total and individual amino acid contents were greater in cancer-associated mucins, with the exception of three amino acids (threonine, serine, and proline), two of which represent the O-linked glycosylation sites for glycoproteins. Thus, mucins are aberrantly glycosylated in colon cancer, both in terms of the number and mean chain length of the oligosaccharide moiety. Because of their relative abundance in colonic tissue, mucins appear to be useful molecular species in the study of the derangements in protein glycosylation that occur during neoplasia.

Analysis of cancer-associated colonic mucin by ion-exchange chromatography: evidence for a mucin species of lower molecular charge and weight in cancer

Cancer-associated mucins in the colon are antigenically distinct and glycosylated differently from their normal counterparts. Mucin-rich glycoconjugate preparations were made from nine non-neoplastic colons, seven colon cancers, and two different xenografts from mucin-producing human colon cancer cell lines, and radiolabeled with 3H. The preparation was applied to a DEAE-cellulose ion-exchange column, and eluted with a discontinuous ascending NaCl gradient resulting in seven discrete fractions or 'species'. Over half of the 3H-labeled glycoconjugates from specimens of non-neoplastic colonic epithelium eluted in fraction V (eluted with 0.25 NaCl). Significantly less of the 3H-labeled glycoconjugates from specimens of colon cancer eluted in fraction V (34%, P less than 0.0005), and there were significant increases in glycoconjugates eluted in fractions IV (P less than 0.008), III (P less than 0.0005), and II (P less than 0.028). Additional samples were prepared without the radiolabeling procedures, chromatographed on a DEAE-cellulose ion-exchange column, and analyzed for monosaccharide content. Each of the fractions contained the monosaccharides expected in mucin-type glycoproteins, but only sialic acid was differentially expressed in the seven fractions or 'species', occurring principally in the more charged species. However, differences in sialic acid content were not sufficient to explain the differences in retention on the ion-exchange column, nor were differences in O-acetylation of the mucins. Mucin-type glycoconjugates from colon cancers are relatively less charged than those from the normal colon, and elute at lower ionic strengths. Of interest, cancer-associated mucins appear to be of lower molecular weight than their normal counterparts. Additional studies of oligosaccharide and apomucin structure will be required to explain the molecular basis of these differences in charge.

Searching for the face of neoplasia

Modifications of blood group antigens are known to occur in neoplastic tissues of the gastrointestinal tract. We had used lectins, naturally occurring proteins used as molecular probes of carbohydrate structure, to identify a marker of premalignant epithelium in the colon. We used a similar approach to study metaplastic and neoplastic epithelium in the upper gastrointestinal tract, with an emphasis on Barrett's esophagus. The carbohydrate structures (i.e., the glycoconjugates) present faithfully reflected the morphological features, rather than the anatomical location, of each tissue. Of note, only minor modifications in carbohydrate structure were seen in low-grade dysplasia, whereas more distinct changes were seen in high-grade dysplasia and adenocarcinoma. This approach provides insight into the biochemistry and metabolism occurring with disordered maturation of the epithelial cell. The aim of this type of investigation is to develop sensitive markers of earlier neoplasia in the gastrointestinal tract.

Assay of lectin binding sites in colon cancer-associated mucins: comparison of fluorescence microscopy with a quantitative chromatographic technique

We have developed a technique for quantitation of binding of fluorescent lectins to glycoconjugates in specimens of tumors derived from cultured human colorectal cancer cells. Tumor cells were injected subcutaneously into nude mice, giving rise to xenografts that resemble primary human colorectal cancers. The tumors were extracted with saline and were subjected to dialysis and lyophilization. Standardized amounts of the tumor extract were then incubated with fluorescent lectins and subjected to gel permeation liquid chromatography to separate lectin bound to high molecular weight glycoproteins from free (unbound) lectin, and were quantitated using a spectrofluorometer. This assay permitted quantitative measurement of the lectin bound to high molecular weight glycoconjugates such as mucin. The results of this assay were compared with the standard histochemical assessment of tissue labeling by fluorescent lectins. A close correlation between the two techniques was found, especially when little or no labeling was present. Greater variations were observed at higher levels of labeling. The quantitative assay confirms that lectins bind to high molecular weight mucin-type glycoconjugates on fixed sections of tumors, and supports the use of semi-quantitative histochemical assessments of tissue labeling.

Quantitation of lectin binding sites in human colon mucins by use of peanut and wheat germ agglutinins

We have developed a novel method for quantitation of lectin binding sites in mucins derived from colon tissues. Binding of peanut agglutinin and wheat germ agglutinin was measured in extracts from normal and malignant human colon epithelium. Binding of wheat germ agglutinin was used as an estimate of the total mucin present in the tissue extract. Peanut agglutinin was found to bind to mucin from normal colon, but at levels that may be difficult to appreciate by fluorescence microscopy. The yield of mucin extracted from colon cancer was more variable than that from normal colon, and the binding ratio of peanut agglutinin to wheat germ agglutinin was greater in extracts from tumors than in normal tissues. Our findings confirm the histological observation that peanut agglutinin binds more avidly to mucins from colon cancer than to those from normal colon. The finding of peanut agglutinin binding sites in mucins front normal colon was not expected. The quantitative technique may have detected small numbers of binding sites not readily appreciable by fluorescence microscopy. Alternatively, the chromatographic method for measuring lectin binding may be sufficiently sensitive to detect nonspecific binding of the lectin to terminal galactose residues other than the Thomsen-Friedenreich antigen.

Glycoconjugate expression in normal, metaplastic, and neoplastic human upper gastrointestinal mucosa

Glycoconjugate structure in upper gastrointestinal epithelium was studied using five lectins to determine the relationship between aberrant differentiation and glycoconjugate expression. Specimens of normal esophagus, stomach, and duodenum were examined and compared with specimens of columnar metaplasia in the esophagus (Barrett's esophagus) and specimens of adenocarcinoma of the esophagus and stomach. Specific terminal glycoconjugate structures were found for the esophagus, stomach, and duodenum. Minor differences were found between the antral and fundic gland mucosae, reflecting their respective cell populations. In biopsies of Barrett's esophagus, gastric-type columnar metaplasia expressed glycoconjugates indistinguishable from those in the normal stomach. In specialized-type columnar metaplasia, a more restricted expression of glycoconjugates was seen resembling the normal duodenum. The presence of low grade dysplasia in Barrett's esophagus associated with adenocarcinoma had no impact on glycoconjugate expression. However, a distinctive difference in glycosylation was seen in high grade dysplasia of the columnar-lined esophagus and in adenocarcinoma of the esophagus and stomach. Barrett's esophagus is a morphological mosaic in which the glycoconjugate expression resembles that seen in the normal stomach and duodenum. However, in high grade dysplasia and carcinoma, variable deletion of glycoconjugate expression can be found.

Glycoconjugates in the colons of New World monkeys with spontaneous colitis. Association between inflammation and neoplasia

A spontaneously occurring experimental model of chronic colitis has been described in three closely related species of New World monkeys. One species, Saguinus oedipus oedipus, has the additional feature of developing adenocarcinoma of the colon in this setting. Pathological and lectin histochemistry studies were undertaken in 50 such colonic specimens to determine if pathological or histochemical features were associated with the concomitant development of cancer. Chronic inflammation was found in all of the colons examined, and 14% had features of acute inflammation, which was significantly associated with those animals that developed cancer. An oncofetal glycoconjugate structure has been defined in human colons by the ability to bind peanut lectin. A similar glycoconjugate, probably a mucin, was expressed in the colons of 65% of these animals. A marked degree of expression of the mucin was significantly associated with those animals that developed cancer. A highly significant association was found between the presence of acute inflammation and the expression of the mucin. These studies demonstrate similarities in glycoconjugate expression between the human colon and the New World monkey model of spontaneous colitis. A form of mucin is expressed in these animals that is highly associated with both the presence of acute inflammation and the development of cancer elsewhere in the colon. In addition, an association between acute inflammatory activity and neoplasia was found, suggesting a potential etiologic linkage between the two.