Top down or bottom up? Competing management structures in the morphogenesis of colorectal neoplasms

Sporadic Polyps of the Colorectum

Colorectal polyps are common, and their diagnosis and classification represent a major component of gastrointestinal pathology practice. The majority of colorectal polyps represent precursors of either the chromosomal instability or serrated neoplasia pathways to colorectal carcinoma. Accurate reporting of these polyps has major implications for surveillance and thus for cancer prevention. In this review, we discuss the key histologic features of the major colorectal polyps with a particular emphasis on diagnostic pitfalls and areas of contention.

Combination Chemotherapy of Multidrug-resistant Early-stage Colon Cancer: Determining Optimal Dose Schedules by High-performance Computer Simulation

The goal of this project was to utilize mechanistic simulation to demonstrate a methodology that could determine drug combination dose schedules and dose intensities that would be most effective in eliminating multidrug resistant cancer cells in early-stage colon cancer. An agent-based model of cell dynamics in human colon crypts was calibrated using measurements of human biopsy specimens. Mutant cancer cells were simulated as cells that were resistant to each of two drugs when the drugs were used separately. The drugs, 5-flurouracil and sulindac, have different mechanisms of action. An artificial neural network was used to generate nearly two hundred thousand two-drug dose schedules. A high-performance computer simulated each dose schedule as a in silico clinical trial and evaluated each dose schedule for its efficiency to cure (eliminate) multidrug resistant cancer cells and its toxicity to the host, as indicated by continued crypt function. Among the dose schedules that were generated, 2430 dose schedules were found to cure all multidrug resistant mutants in each of the 50 simulated trials and retained colon crypt function. One dose schedule was optimal; it eliminated multidrug resistant cancer cells with the minimum toxicity and had a time schedule that would be practical for implementation in the clinic. These results demonstrate a procedure to identify which combination drug dose schedules could be most effective in eliminating drug resistant cancer cells. This was accomplished using a calibrated agent-based model of a human tissue, and a high-performance computer simulation of clinical trials.

Temporal and spatial changes of cells positive for stem-like markers in different compartments and stages of human colorectal adenoma-carcinoma sequence

Considerable evidence supports the idea that stem-like cells may play an essential role during the development of colorectal cancer (CRC). To accomplish this aim, we use immunohistochemistry (IHC) and double IHC with different potential stem-like markers, anti-musashi (Msi), anti-CD133, anti- LGR5 and anti-ALDH1 to examine the presentation of stem-like cells in different compartments including adenoma/CRC epithelium, transitional crypts and tumor stroma in colorectal adenoma and CRC. The results showed that cells positive for stem-like markers were remarkably increased in number and frequently observed in the adenoma/CRC epithelium, transitional crypts and tumor stroma. Notably, the population of cells positive for stem-liker markers was expanded from the base to the middle part of the transitional crypt in both adenoma and CRC tissues, reflecting that stem-like cells are likely involved in the process of colorectal tumorigenesis. Counting results showed that the grading scores of cells positive for LGR5 and ALDH1 in the adenoma/CRC epithelium were significantly increased relative with the control epithelium, and associated with the degree of dysplasia in the adenoma and node involvement in the CRC (all P < 0.05). In addition, the density of cells positive for stem-like markers in the adenomatous/cancerous stroma was also increased and paralleled an increase in the density of proliferative stromal cells labeled by PCNA, which were primarily identified as vimentin positive fibroblasts. Our results have revealed a changed temporal and spatial presentation of stem-like markers in different stages of human colorectal adenoma-carcinoma sequence, which might be a hallmark of the adenoma-carcinoma transition.

Surface-bound galectin-4 regulates gene transcription and secretion of chemokines in human colorectal cancer cell lines

One long-term complication of chronic intestinal inflammation is the development of colorectal cancer. However, the mechanisms linking inflammation to the colorectal tumorigenesis are poorly defined. Previously, we have demonstrated that galectin-4 is predominantly expressed in the luminal epithelia of the gastrointestinal tract, and its loss of expression plays a key role in the colorectal tumorigenesis. However, the mechanism by which galectin-4 regulates inflammation-induced tumorigenesis is unclear. Here, we show that galectin-4 secreted by the colorectal cancer cell lines was bound to the cell surface. Neutralization of surface-bound galectin-4 with anti-galectin-4 antibody resulted in increased cell proliferation with concomitant secretion of several chemokines into the extracellular medium. Neutralization of the surface-bound galectin-4 also resulted in the up-regulation of transcription of 29 genes, several of which are components of multiple inflammation signaling pathways. In an alternate experiment, binding of recombinant galectin-4 protein to cell surface of the galectin-4-negative colorectal cancer cells resulted in increased p27, and decreased cyclin D1 and c-Myc levels, leading to cell cycle arrest and apoptosis. Together, these data demonstrated that surface-bound galectin-4 is a dual function protein-down-regulating cell proliferation and chemokine secretion in galectin-4-expressing colorectal cancer cells on one hand and inducing apoptosis in galectin-4-negative colorectal cancer cells on the other hand.

Multiscale Model of Colorectal Cancer Using the Cellular Potts Framework

Colorectal cancer (CRC) is one of the major causes of death in the developed world and forms a canonical example of tumorigenesis. CRC arises from a string of mutations of individual cells in the colorectal crypt, making it particularly suited for multiscale multicellular modeling, where mutations of individual cells can be clearly represented and their effects readily tracked. In this paper, we present a multicellular model of the onset of colorectal cancer, utilizing the cellular Potts model (CPM). We use the model to investigate how, through the modification of their mechanical properties, mutant cells colonize the crypt. Moreover, we study the influence of mutations on the shape of cells in the crypt, suggesting possible cell- and tissue-level indicators for identifying early-stage cancerous crypts. Crucially, we discuss the effect that the motility parameters of the model (key factors in the behavior of the CPM) have on the distribution of cells within a homeostatic crypt, resulting in an optimal parameter regime that accurately reflects biological assumptions. In summary, the key results of this paper are 1) how to couple the CPM with processes occurring on other spatial scales, using the example of the crypt to motivate suitable motility parameters; 2) modeling mutant cells with the CPM; 3) and investigating how mutations influence the shape of cells in the crypt.

A Big Bang model of human colorectal tumor growth

What happens in the early, still undetectable human malignancy is unknown because direct observations are impractical. Here we present and validate a “Big Bang” model, whereby tumors grow predominantly as a single expansion producing numerous intermixed sub-clones that are not subject to stringent selection, and where both public (clonal) and most detectable private (subclonal) alterations arise early during growth. Genomic profiling of 349 individual glands from 15 colorectal tumors revealed the absence of selective sweeps, uniformly high intra-tumor heterogeneity (ITH), and sub-clone mixing in distant regions, as postulated by our model. We also verified the prediction that most detectable ITH originates from early private alterations, and not from later clonal expansions, thus exposing the profile of the primordial tumor. Moreover, some tumors appear born-to-be-bad, with sub-clone mixing indicative of early malignant potential. This new model provides a quantitative framework to interpret tumor growth dynamics and the origins of ITH with significant clinical implications.

Single-molecule genomic data delineate patient-specific tumor profiles and cancer stem cell organization

Substantial evidence supports the concept that cancers are organized in a cellular hierarchy with cancer stem cells (CSC) at the apex. To date, the primary evidence for CSCs derives from transplantation assays, which have known limitations. In particular, they are unable to report on the fate of cells within the original human tumor. Because of the difficulty in measuring tumor characteristics in patients, cellular organization and other aspects of cancer dynamics have not been quantified directly, although they likely play a fundamental role in tumor progression and therapy response. As such, new approaches to study CSCs in patient-derived tumor specimens are needed. In this study, we exploited ultradeep single-molecule genomic data derived from multiple microdissected colorectal cancer glands per tumor, along with a novel quantitative approach to measure tumor characteristics, define patient-specific tumor profiles, and infer tumor ancestral trees. We show that each cancer is unique in terms of its cellular organization, molecular heterogeneity, time from malignant transformation, and rate of mutation and apoptosis. Importantly, we estimate CSC fractions between 0.5% and 4%, indicative of a hierarchical organization responsible for long-lived CSC lineages, with variable rates of symmetric cell division. We also observed extensive molecular heterogeneity, both between and within individual cancer glands, suggesting a complex hierarchy of mitotic clones. Our framework enables the measurement of clinically relevant patient-specific characteristics in vivo, providing insight into the cellular organization and dynamics of tumor growth, with implications for personalized patient care.

Long-term feeding of various fat diets modulates azoxymethane-induced colon carcinogenesis through Wnt/beta-catenin signaling in rats

The Wnt signaling pathway plays an essential role in carcinogenesis, and the amount of fat intake and composition of dietary fatty acids are crucial factors for colon carcinogenesis. We investigated whether various dietary fats affected the Wnt signaling pathway of colon tumorigenesis in azoxymethane (AOM)-treated rats. Male Sprague-Dawley rats were given intraperitoneal injections of AOM and supplemented with 10% corn, olive, beef, and fish oil for 44 wk. Aberrant crypt foci (ACF) and tumors were examined at 12 and 44 wk. Normal appearing colon mucosal proliferation and apoptosis were evaluated by 5-bromo-2'-deoxyuridine (BrdU) incorporation and percentages of fragmented DNA, respectively. Expressions of beta-catenin, cyclin D(1), Wnt2, Wnt3, and Wnt5a of normal appearing colon mucosa were analyzed by Western blot analysis. Long-term dietary corn oil and beef tallow increased ACF, tumor incidence, and tumor numbers in AOM-treated rats. In contrast, both olive and fish oil inhibited them. Dietary corn oil and beef tallow increased BrdU incorporation and the expression of cytosolic beta-catenin and cyclin D(1) and decreased apoptosis in the colon mucosa. Expressions of Wnt2 and Wnt3 in rats fed with beef tallow and Wnt5a in rats fed with corn oil increased with or without AOM-treatment. BrdU-incorporated cells were often observed at the tops of crypts in rats fed with beef tallow, whereas this was not observed in rats fed with the other diet. Long-term high intake of corn oil and beef tallow enhanced cell proliferation through Wnt signaling and modulated the distribution of proliferating cells, which might contribute to promoting effects in colon tumorigenesis.

The morphogenetic code and colon cancer development

The initiating genetic lesion in sporadically occurring cancers is impossible to identify. The existence of rare inherited cancer syndromes has helped to uncover some of the mutations that can initiate tumorigenesis. Most of these initiating lesions affect genes belonging to morphogenetic signaling pathways. We review the evidence that the cellular fate of individual epithelial cells in the adult is nonautonomous and depends on extrinsic information, just like cells in a developing embryo. Cancer stem cells need to disrupt these extrinsic restraints to gain an autonomous clonal proliferative advantage over neighboring stem cells.

Bottom-up cell proliferation with cyclin A and p27Kip1 expression in ulcerative colitis-associated dysplasia

To analyze the cell kinetics of ulcerative colitis (UC)-associated dysplasia, cyclin A, cyclin D1, cyclin E, cdk2, cdk4, p21(Waf1), and p27(Kip1) were immunohistochemically examined, in comparison with sporadic tubular adenomas. Immunohistochemical labeling indices for each marker in formalin-fixed paraffin-embedded tissue sections were assessed in a total of 23 low-grade dysplasias, 27 high-grade dysplasias, and 14 invasive adenocarcinomas associated with UC. For comparison, 21 sporadic tubular adenomas with low-grade dysplasia, 33 with high-grade dysplasia, and 21 invasive adenocarcinomas were also examined. In UC-associated dysplasias, cyclin A and p27(Kip1) were located in the lower parts of the crypts and p21(Waf1) in the upper regions. In tubular adenomas, cyclin A, cdk4, p27(Kip1), and p21(Waf1) were all expressed in the upper parts of the crypts. The expression levels of cyclin D1, cyclin E, and cdk2 were low. The cell proliferation zone in UC-associated dysplasia is located towards the bases of the crypts with the strong expression of cyclin A and p27(Kip1), in contrast to tubular adenomas, which have their cell proliferation zone in the upper parts of neoplastic crypts. It is considered that tumorigenesis with UC-associated dysplasia is of the bottom-up type, related to altered expression of cyclin A and p27(Kip1).

Stem cell relationships and the origin of gastrointestinal cancer

Gastrointestinal stem cells have the capacity for long-term self-replication and the ability to give rise to all other epithelial cell lineages. These properties make them essential since they maintain tissue homeostasis by regulating cell turnover depending on the current demand. However, they are also important players in the earliest stages of gastric and colonic cancer, as they form a target for mutations to accumulate and lead to the development of the malignant phenotype. Due to the lack of reliable markers, gastrointestinal stem cells are difficult to define and characterise. This limits the knowledge about their number and position within the gastric gland and the intestinal crypt, respectively, and consequently about the clonal structure of these units. Therefore, the morphological events of early gastrointestinal carcinoma formation and expansion are hotly debated. In this review we summarize the properties of gastrointestinal stem cells and illuminate their role in the development of the earliest lesions in the gastric and colonic mucosa. We also resume current opinions about the morphological pathways and the clonality of these neoplasias and the subsequent mechanism of spread within the adjacent tissues.

EGF receptor transactivation mediates ANG II-stimulated mitogenesis in intestinal epithelial cells through the PI3-kinase/Akt/mTOR/p70S6K1 signaling pathway

The role of epidermal growth factor receptor (EGFR) tyrosine kinase and its downstream targets in the regulation of the transition from the G0/G1 phase into DNA synthesis in response to ANG II has not been previously investigated in intestinal epithelial IEC-18 cells. ANG II induced a rapid and striking EGFR tyrosine phosphorylation, which was prevented by selective inhibitors of EGFR tyrosine kinase activity (e.g., AG-1478) or by broad-spectrum matrix metalloproteinase (MMP) inhibitor GM-6001. Pretreatment of these cells with either AG-1478 or GM-6001 reduced ANG II-stimulated DNA synthesis by approximately 50%. To elucidate the downstream targets of EGFR, we demonstrated that ANG II stimulated phosphorylation of Akt at Ser473, mTOR at Ser2448, p70S6K1 at Thr389, and S6 ribosomal protein at Ser(235/236). Pretreatment with AG-1478 inhibited Akt, p70S6K1, and S6 ribosomal protein phosphorylation. Inhibition of phosphatidylinositol (PI)3-kinase with LY-294002 or mTOR/p70S6K1 with rapamycin reduced [3H]thymidine incorporation by 50%, i.e., to levels comparable to those achieved by addition of either AG-1478 or GM-6001. Utilizing Akt small-interfering RNA targeted to Akt1 and Akt2, Akt protein knockdown dramatically inhibited p70S6K1 and S6 ribosomal protein phosphorylation. In contrast, AG-1478 or Akt gene silencing exerted no detectable inhibitory effect on ANG II-induced extracellular signal-regulated kinase 1/2 phosphorylation in IEC-18 cells. Taken together, our results demonstrate that EGFR transactivation mediates ANG II-stimulated mitogenesis through the PI3-kinase/Akt/mTOR/p70S6K1 signaling pathway in IEC-18 cells.

Cytoskeletal network in colon cancer: from genes to clinical application

Colorectal cancer arises from well-defined sequential steps characterised by distinct genetic events. Abnormalities in the expression and functional activity of cell adhesion molecules are implicated in the development and progression of the majority of colorectal cancers. Intercellular (e.g. E-cadherin/catenin complex) and cell-matrix (e.g. integrins) adhesion molecules are more than just cementing substances but regulate cell polarity, differentiation, proliferation, migration and invasion. Many of these cellular events are mediated through their intimate association with the actin cytoskeletal network. A dynamic actin cytoskeleton characterises normal epithelial cells and polymerisation and depolymerisation of actin filaments enables cell shape to change during migration and mitosis. In colorectal cancer, cells lose actin cytoskeletal organisation and normal cell adhesion when they become invasive. Future investigations should allow the unravelling of new cytoskeletal network functions in tumour biology and may lead to the development of novel therapeutic strategies based on the manipulation of its associated molecules.

The gastrointestinal stem cell

The longevity of adult stem cells, and their potential for vast tissue regeneration, makes them a focal point of current research and debate, with future aspirations for the use of stem cells in the treatment of a number of human pathological conditions. Due to the rapid rate of cell turnover in the gastrointestinal tract, the stem cells of this tissue are amongst the most assiduous in the body, although they remain unidentified to this day due to their immature, undifferentiated phenotype. However, our knowledge of the mechanisms regulating gastrointestinal stem cell function is evolving, with the identification of putative cellular markers and the elucidation of signalling pathways which regulate cell behaviour in the normal and neoplastic gastrointestinal tract. This review describes the fundamental properties of the gastrointestinal stem cell including: (i) their number, location and origins, (ii) their primary function of deriving gastrointestinal cell lineages and maintaining tissue homeostasis, (iii) the acquisition of gastrointestinal cell lineages from adult stem cells of extraneous tissues and the consequences of this in a therapeutic context, and (iv) the genetic and morphological phenomena surrounding neoplastic transformation in the gastrointestinal tract.

A novel immunohistochemical method to estimate cell-cycle phase distribution in archival tissue: implications for the prediction of outcome in colorectal cancer

An immunohistochemical method for assessing cell-cycle phase distribution in colorectal resection specimens would enable phase data to be incorporated into diagnostic algorithms for the estimation of prognosis and response to adjuvant chemotherapy in colorectal cancer. In contrast to flow cytometry, an immunohistochemical method would also allow the phase distribution to be examined within morphologically heterogeneous regions of neoplasms. Paraffin sections of normal colon (n = 25), colonic adenoma (n = 15), and colonic adenocarcinoma (n = 30) were analysed by immunohistochemistry using antibodies against markers of cell-cycle entry, Mcm-2 and Ki67, and putative markers of the cell-cycle phase, cyclins D1 and E (putative markers of G1 phase), cyclin A (S phase), cytoplasmic cyclin B1 (G2 phase), and phosphohistone H3 (M phase). The phase specificity of each marker was assessed by examining the degree of co-expression of adjacent phase markers using double-antibody fluorescence confocal microscopy and by comparison with flow cytometric analysis performed on adjacent tissue sections. The S-phase specificity of detectable cyclin A was also assessed in combination with in situ DNA replication using fluorescence confocal microscopy. All cells expressing phase markers co-expressed Mcm-2. Adjacent phase markers were not significantly co-expressed, confirming the relative specificity of these markers in tissue sections of colon. Cell-cycle phase distribution, calculated by immunohistochemistry, compared well with phase analyses obtained by flow cytometry. No cells expressed cyclin A in the absence of active DNA replication. The S-phase labelling index, as defined by detectable cyclin A expression, showed a positive correlation with the Mcm-2 labelling index and increased in the progression from normal colon to adenocarcinoma. In conclusion, a combination of these cell-cycle phase markers can be used to calculate the distribution of cells throughout each phase of the cell cycle in colorectal tissue sections. Detectable cyclin A can be used as a surrogate marker of S phase and may be of value in predicting prognosis and response to adjuvant therapy.