A validated quantitative assay to detect occult micrometastases by reverse transcriptase-polymerase chain reaction of guanylyl cyclase C in patients with colorectal cancer

Therapeutic opportunities in colon cancer: Focus on phosphodiesterase inhibitors

Despite novel technologies, colon cancer remains undiagnosed and 25% of patients are diagnosed with metastatic colon cancer. Resistant to chemotherapeutic agents is one of the major problems associated with treating colon cancer which creates the need to develop novel agents targeting towards newer targets. A phosphodiesterase is a group of isoenzyme, which, hydrolyze cyclic nucleotides and thereby lowers intracellular levels of cAMP and cGMP leading to tumorigenic effects. Many in vitro and in vivo studies have confirmed increased PDE expression in different types of cancers including colon cancer. cAMP-specific PDE inhibitors increase intracellular cAMP that leads to activation of effector molecules-cAMP-dependent protein kinase A, exchange protein activated by cAMP and cAMP gated ion channels. These molecules regulate cellular responses and exert its anticancer role through different mechanisms including apoptosis, inhibition of angiogenesis, upregulating tumor suppressor genes and suppressing oncogenes. On the other hand, cGMP specific PDE inhibitors exhibit anticancer effects through cGMP dependent protein kinase and cGMP dependent cation channels. Elevation in cGMP works through activation of caspases, suppression of Wnt/b-catenin pathway and TCF transcription leading to inhibition of CDK and survivin. These studies point out towards the fact that PDE inhibition is associated with anti-proliferative, anti-apoptotic and anti-angiogenic pathways involved in its anticancer effects in colon cancer. Thus, inhibition of PDE enzymes can be used as a novel approach to treat colon cancer. This review will focus on cAMP and cGMP signaling pathways leading to tumorigenesis and the use of PDE inhibitors in colon cancer.

Split tolerance permits safe Ad5-GUCY2C-PADRE vaccine-induced T-cell responses in colon cancer patients

BACKGROUND

The colorectal cancer antigen GUCY2C exhibits unique split tolerance, evoking antigen-specific CD8⁺, but not CD4⁺, T-cell responses that deliver anti-tumor immunity without autoimmunity in mice. Here, the cancer vaccine Ad5-GUCY2C-PADRE was evaluated in a first-in-man phase I clinical study of patients with early-stage colorectal cancer to assess its safety and immunological efficacy.

METHODS

Ten patients with surgically-resected stage I or stage II (pN0) colon cancer received a single intramuscular injection of 10¹¹ viral particles (vp) of Ad5-GUCY2C-PADRE. Safety assessment and immunomonitoring were carried out for 6 months following immunization. This trial employed continual monitoring of both efficacy and toxicity of subjects as joint primary outcomes.

RESULTS

All patients receiving Ad5-GUCY2C-PADRE completed the study and none developed adverse events greater than grade 1. Antibody responses to GUCY2C were detected in 10% of patients, while 40% exhibited GUCY2C-specific T-cell responses. GUCY2C-specific responses were exclusively CD8⁺ cytotoxic T cells, mimicking pre-clinical studies in mice in which GUCY2C-specific CD4⁺ T cells are eliminated by self-tolerance, while CD8⁺ T cells escape tolerance and mediate antitumor immunity. Moreover, pre-existing neutralizing antibodies (NAbs) to the Ad5 vector were associated with poor vaccine-induced responses, suggesting that Ad5 NAbs oppose GUCY2C immune responses to the vaccine in patients and supported by mouse studies.

CONCLUSIONS

Split tolerance to GUCY2C in cancer patients can be exploited to safely generate antigen-specific cytotoxic CD8⁺, but not autoimmune CD4⁺, T cells by Ad5-GUCY2C-PADRE in the absence of pre-existing NAbs to the viral vector.

TRIAL REGISTRATION

This trial (NCT01972737) was registered at ClinicalTrials.gov on October 30th, 2013. https://clinicaltrials.gov/ct2/show/NCT01972737.

Adoptive Cell Transfer: Is it a Promising Immunotherapy for Colorectal Cancer?

The last decade has witnessed significant advances in the adoptive cell transfer (ACT) technique, which has been appreciated as one of the most promising treatments for patients with cancer. Utilization of ACT can enhance the function of the immune system or improve the specificity and persistence of transferred cells. Various immune cells including T lymphocytes, natural killer cells, dendritic cells, and even stem cells can be used in the ACT despite their different functional mechanisms. Colorectal cancer (CRC) is among the most common malignancies and causes millions of deaths worldwide every year. In this review, we discuss the status and perspective of the ACT in the treatment of CRC.

The expansion of targetable biomarkers for CAR T cell therapy

Biomarkers are an integral part of cancer management due to their use in risk assessment, screening, differential diagnosis, prognosis, prediction of response to treatment, and monitoring progress of disease. Recently, with the advent of Chimeric Antigen Receptor (CAR) T cell therapy, a new category of targetable biomarkers has emerged. These biomarkers are associated with the surface of malignant cells and serve as targets for directing cytotoxic T cells. The first biomarker target used for CAR T cell therapy was CD19, a B cell marker expressed highly on malignant B cells. With the success of CD19, the last decade has shown an explosion of new targetable biomarkers on a range of human malignancies. These surface targets have made it possible to provide directed, specific therapy that reduces healthy tissue destruction and preserves the patient's immune system during treatment. As of May 2018, there are over 100 clinical trials underway that target over 25 different surface biomarkers in almost every human tissue. This expansion has led to not only promising results in terms of patient outcome, but has also led to an exponential growth in the investigation of new biomarkers that could potentially be utilized in CAR T cell therapy for treating patients. In this review, we discuss the biomarkers currently under investigation and point out several promising biomarkers in the preclinical stage of development that may be useful as targets.

Expression of guanylyl cyclase C in tissue samples and the circulation of rectal cancer patients

Guanylyl cyclase C (GCC) is a transmembrane surface receptor restricted to intestinal epithelial cells, from the duodenum to the rectum. We compared GCC expression in tumors and normal rectal tissues, and investigated the relation between GCC expression and metastasis and long-term survival of rectal cancer patients. Based on the UICC classification, 42 rectal cancer patients in this study were classified as stage I, 48 patients as stage II, and 90 patients as stage III. Overexpression of GCC was observed in 80 rectal tumors as compared to matched normal tissues, where no strong staining of GCC was observed. An association between GCC mRNA in the circulation and tumor emboli in vessels, CK20 mRNA, distant organ metastasis, and survival status was observed in 100 rectal cancer patients. Univariate Cox regression analysis indicated that tumor emboli in vessels, lymph node metastasis, mesenteric root lymph node metastasis and GCC mRNA correlated with 5-year disease-free survival (DFS); while lymph node metastasis, GCC mRNA, and CK20 mRNA strongly correlated with 5-year overall survival (OS). In a multivariate Cox regression model, GCC mRNA level and mesenteric root lymph node metastasis associated with DFS, while GCC mRNA levels associated with OS. Quantification of GCC expression in circulation is a valuable biomarker for assessing tumor burden and predicting outcome in rectal cancer patients.

Detection of Circulating Tumor Cells Using Microfluidics

Metastasis is the main cause of death in cancer patients worldwide. During metastasis, cancer cells detach from the primary tumor and invade distant tissue. The cells that undergo this process are called circulating tumor cells (CTCs). Studies show that the number of CTCs in the peripheral blood can predict progression-free survival and overall survival and can be informative concerning the efficacy of treatment. Research is now concentrated on developing devices that can detect CTCs in the blood of cancer patients with improved sensitivity and specificity that can lead to improved clinical evaluation. This review focuses on devices that detect and capture CTCs using different cell properties (surface markers, size, deformability, electrical properties, etc.). We also discuss the process of tumor cell dissemination, the biology of CTCs, epithelial-mesenchymal transition (EMT), and several challenges and clinical applications of CTC detection.

A monomethyl auristatin E-conjugated antibody to guanylyl cyclase C is cytotoxic to target-expressing cells in vitro and in vivo

Guanylyl cyclase C (GCC) is a cell-surface protein that is expressed by normal intestinal epithelial cells, more than 95% of metastatic colorectal cancers (mCRC), and the majority of gastric and pancreatic cancers. Due to strict apical localization, systemically delivered GCC-targeting agents should not reach GCC in normal intestinal tissue, while accessing antigen in tumor. We generated an investigational antibody-drug conjugate (TAK-264, formerly MLN0264) comprising a fully human anti-GCC monoclonal antibody conjugated to monomethyl auristatin E via a protease-cleavable peptide linker. TAK-264 specifically bound, was internalized by, and killed GCC-expressing cells in vitro in an antigen-density-dependent manner. In GCC-expressing xenograft models with similar GCC expression levels/patterns observed in human mCRC samples, TAK-264 induced cell death, leading to tumor regressions and long-term tumor growth inhibition. TAK-264 antitumor activity was generally antigen-density-dependent, although some GCC-expressing tumors were refractory to TAK-264-targeted high local concentrations of payload. These data support further evaluation of TAK-264 in the treatment of GCC-expressing tumors.

Prime-Boost Immunization Eliminates Metastatic Colorectal Cancer by Producing High-Avidity Effector CD8+ T Cells

Heterologous prime-boost immunization with plasmid DNA and viral vector vaccines is an emerging approach to elicit CD8+ T cell-mediated immunity targeting pathogens and tumor Ags that is superior to either monotherapy. Yet, the mechanisms underlying the synergy of prime-boost strategies remain incompletely defined. In this study, we examine a DNA and adenovirus (Ad5) combination regimen targeting guanylyl cyclase C (GUCY2C), a receptor expressed by intestinal mucosa and universally expressed by metastatic colorectal cancer. DNA immunization efficacy was optimized by i.m. delivery via electroporation, yet it remained modest compared with Ad5. Sequential immunization with DNA and Ad5 produced superior antitumor efficacy associated with increased TCR avidity, whereas targeted disruption of TCR avidity enhancement eliminated GUCY2C-specific antitumor efficacy, without affecting responding T cell number or cytokine profile. Indeed, functional TCR avidity of responding GUCY2C-specific CD8+ T cells induced by various prime or prime-boost regimens correlated with antitumor efficacy, whereas T cell number and cytokine profile were not. Importantly, although sequential immunization with DNA and Ad5 maximized antitumor efficacy through TCR avidity enhancement, it produced no autoimmunity, reflecting sequestration of GUCY2C to intestinal apical membranes and segregation of mucosal and systemic immunity. Together, TCR avidity enhancement may be leveraged by prime-boost immunization to improve GUCY2C-targeted colorectal cancer immunotherapeutic efficacy and patient outcomes without concomitant autoimmune toxicity.

A survey of physician receptivity to molecular diagnostic testing and readiness to act on results for early-stage colon cancer patients

Background

We sought to assess physician interest in molecular prognosic testing for patients with early stage colon cancer, and identify factors associated with the likelihood of test adoption.

Methods

We identified physicians who care for patients with early-stage (pN0) colon cancer patients, mailed them a survey, and analyzed survey responses to assess clinician receptivity to the use of a new molecular test (GUCY2C) that identifies patients at risk for recurrence, and clinician readiness to act on abnormal test results.

Results

Of 104 eligible potential respondents, 41 completed and returned the survey. Among responding physicians, 56 % were receptive to using the new prognostic test. Multivariable analyses showed that physicians in academic medical centers were significantly more receptive to molecular test use than those in non-academic settings.

Forty-one percent of respondents were ready to act on abnormal molecular test results. Physicians who viewed current staging methods as inaccurate and were confident in their capacity to incorporate molecular testing in practice were more likely to say they would act on abnormal test results.

Conclusions

Physician receptivity to molecular diagnostic testing for early-stage colon cancer patients is likely to be influenced by practice setting and perceptions related to delivering quality care to patients.

Trial registration

ClinicalTrials.gov Identifier: NCT01972737

GUCY2C-directed CAR-T cells oppose colorectal cancer metastases without autoimmunity

Adoptive T-cell therapy (ACT) is an emerging paradigm in which T cells are genetically modified to target cancer-associated antigens and eradicate tumors. However, challenges treating epithelial cancers with ACT reflect antigen targets that are not tumor-specific, permitting immune damage to normal tissues, and preclinical testing in artificial xenogeneic models, preventing prediction of toxicities in patients. In that context, mucosa-restricted antigens expressed by cancers exploit anatomical compartmentalization which shields mucosae from systemic antitumor immunity. This shielding may be amplified with ACT platforms employing antibody-based chimeric antigen receptors (CARs), which mediate MHC-independent recog-nition of antigens. GUCY2C is a cancer mucosa antigen expressed on the luminal surfaces of the intestinal mucosa in mice and humans, and universally overexpressed by colorectal tumors, suggesting its unique utility as an ACT target. T cells expressing CARs directed by a GUCY2C-specific antibody fragment recognized GUCY2C, quantified by expression of activation markers and cytokines. Further, GUCY2C CAR-T cells lysed GUCY2C-expressing, but not GUCY2C-deficient, mouse colorectal cancer cells. Moreover, GUCY2C CAR-T cells reduced tumor number and morbidity and improved survival in mice harboring GUCY2C-expressing colorectal cancer metastases. GUCY2C-directed T cell efficacy reflected CAR affinity and surface expression and was achieved without immune-mediated damage to normal tissues in syngeneic mice. These observations highlight the potential for therapeutic translation of GUCY2C-directed CAR-T cells to treat metastatic tumors, without collateral autoimmunity, in patients with metastatic colorectal cancer.

Prognostic Value of Molecular Detection of Lymph Node Metastases After Curative Resection of Stage II Colon Cancer: A Systematic Pooled Data Analysis

BACKGROUND

We aimed to clarify the prognostic value of guanylyl cyclase C (GCC) lymph node ratio (LNR) status as a predictor of recurrence in untreated stage IIA colon cancer on the basis of pooled individual data from previous studies.

METHODS

Patients were classified according to predefined GCC LNR risk groups (low, LNR ≤ 0.1; intermediate, 0.1 < LNR ≤ 0.2; high, LNR > 0.2). Outcomes included time to recurrence, disease-free survival, and overall survival. Stratified log-rank tests and multivariate Cox models assessed the association between outcomes and GCC lymph node status.

RESULTS

The final data set contained 553 patients with stage IIA colon cancer with a median of 18 lymph nodes examined after resection; 65 patients (11.8%) had recurrence. Overall, 109 patients (19.7%) were classified high risk on the basis of GCC LNR. In multivariate analysis, high GCC LNR value (> 0.2) was a significant predictor of cancer recurrence (hazard ratio [HR], 3.18; 95% confidence interval [CI], 1.77-5.71; P < .001) and lower disease-free survival (HR, 2.40; 95% CI, 1.60-3.62; P < .001) and overall survival (HR, 2.12; 95% CI, 1.35-3.33; P = .001).

CONCLUSION

Patients considered at high risk on the basis of their GCC LNR status have significantly inferior outcomes compared to those with low GCC LNR values, particularly among those traditionally considered to be at low risk for recurrence.

GUCY2C lysosomotropic endocytosis delivers immunotoxin therapy to metastatic colorectal cancer

The emergence of targeted cancer therapy has been limited by the paucity of determinants which are tumor-specific and generally associated with disease, and have cell dynamics which effectively deploy cytotoxic payloads. Guanylyl cyclase C (GUCY2C) may be ideal for targeting because it is normally expressed only in insulated barrier compartments, including intestine and brain, but over-expressed by systemic metastatic colorectal tumors. Here, we reveal that GUCY2C rapidly internalizes from the cell surface to lysosomes in intestinal and colorectal cancer cells. Endocytosis is independent of ligand binding and receptor activation, and is mediated by clathrin. This mechanism suggests a design for immunotoxins comprising a GUCY2C-directed monoclonal antibody conjugated through a reducible disulfide linkage to ricin A chain, which is activated to a potent cytotoxin in lysosomes. Indeed, this immunotoxin specifically killed GUCY2C-expressing colorectal cancer cells in a lysosomal- and clathrin-dependent fashion. Moreover, this immunotoxin reduced pulmonary tumors>80% (p<0.001), and improved survival 25% (p<0.001), in mice with established colorectal cancer metastases. Further, therapeutic efficacy was achieved without histologic evidence of toxicity in normal tissues. These observations support GUCY2C-targeted immunotoxins as novel therapeutics for metastatic tumors originating in the GI tract, including colorectum, stomach, esophagus, and pancreas.

The paracrine hormone for the GUCY2C tumor suppressor, guanylin, is universally lost in colorectal cancer

BACKGROUND

Although colorectal cancer is a disease characterized by sequential accumulation of mutations in epithelial cells, mechanisms leading to genomic vulnerability contributing to tumor initiation remain undefined. GUCY2C has emerged as an intestine-specific tumor suppressor controlling epithelial homeostasis through circuits canonically disrupted in cancer. Surprisingly, the GUCY2C tumor suppressor is universally overexpressed by human colorectal cancer cells. This apparent paradox likely reflects silencing of GUCY2C through loss of its paracrine hormone guanylin. Here, we quantified expression of guanylin mRNA and protein in tumors and normal epithelia from patients with colorectal cancer.

METHODS

Guanylin mRNA was quantified in tumors and normal adjacent epithelia from 281 patients by the reverse transcriptase-polymerase chain reaction. Separately, the guanylin protein was quantified by immunohistochemistry in 54 colorectal tumors and 30 specimens of normal intestinal epithelium.

RESULTS

Guanylin mRNA in colorectum varied more than a 100-fold across the population. Guanylin mRNA was reduced 100- to 1,000-fold in >85% of tumors compared with matched normal adjacent mucosa (P < 0.001). Loss of guanylin mRNA was greatest in tumors from patients <50 years old (P < 0.005) and with the highest expression in normal adjacent mucosa (Spearman correlation coefficient = 0.61; P < 0.001). In a separate validation cohort, guanylin protein was detected in all 30 normal colorectal mucosa specimens, but in none of 54 colorectal tumors.

CONCLUSIONS

Colorectal cancer may initiate as a disease of paracrine hormone insufficiency through loss of guanylin expression, silencing the GUCY2C tumor suppressor and disrupting homeostatic mechanisms regulating colorectal epithelia cells.

IMPACT

Intestinal tumorigenesis may be prevented by oral GUCY2C hormone replacement therapy.

Molecular testing for lymph node metastases as a determinant of colon cancer recurrence: results from a retrospective multicenter study

PURPOSE

Recurrence risk assessment to make treatment decisions for early-stage colon cancer patients is a major unmet medical need. The aim of this retrospective multicenter study was to evaluate the clinical utility of guanylyl cyclase C (GCC) mRNA levels in lymph nodes on colon cancer recurrence.

METHODS

The proportion of lymph nodes with GCC-positive mRNA (LNR) was evaluated in 463 untreated T3N0 patients, blinded to clinical outcomes. One site's (n = 97) tissue grossing method precluded appropriate lymph node assessment resulting in post hoc exclusion. Cox regression models tested the relationship between GCC and the primary endpoint of time to recurrence. Assay methods, primary analyses, and cut points were all prespecified.

RESULTS

Final dataset contained 366 patients, 38 (10%) of whom had recurrence. Presence of four or more GCC-positive lymph nodes was significantly associated with risk of recurrence [hazard ratio (HR) = 2.46, 95% confidence interval (CI), 1.07-5.69, P = 0.035], whereas binary GCC LNR risk class (HR = 1.87, 95% CI, 0.99-3.54, P = 0.054) and mismatch repair (MMR) status (HR = 0.77, 95% CI, 0.36-1.62, P = 0.49) were not. In a secondary analysis using a 3-level GCC LNR risk group classification of high (LNR > 0.20), intermediate (0.10 < LNR ≤ 0.20), and low (LNR ≤ 0.10), high-risk patients had a 2.5 times higher recurrence risk compared with low-risk patients (HR = 2.53, 95% CI, 1.24-5.17, P = 0.011).

CONCLUSIONS

GCC status is a promising prognostic factor independent of traditional histopathology risk factors in a contemporary population of patients with stage IIa colon cancer not treated with adjuvant therapy, but GCC determination must be performed with methodology adapted to the tissue procurement and fixation technique.

Current status of gene expression profiling to assist decision making in stage II colon cancer

The decision regarding adjuvant therapy for patients with stage II colon cancer remains a challenge. In contrast to stage III colon cancer, for which compelling clinical data support the use of adjuvant chemotherapy, the clinical benefit of systemic therapy in unselected patients with stage II disease is modest at best. Risk stratification based on clinicopathologic features and DNA mismatch repair status is commonly used in adjuvant therapy decisions, but these factors do not have a desired level of precision in identifying patients at high risk. Recently, gene expression platforms have been developed to further define risk and to assist in therapeutic decision making for patients with stage II disease. This review describes those platforms that are furthest along in clinical development, in an effort to place their potential clinical application in context.

Tumor radiation therapy creates therapeutic vaccine responses to the colorectal cancer antigen GUCY2C

PURPOSE

Radiation therapy (RT) is thought to produce clinical responses in cancer patients, not only through direct toxicity to cancer cells and supporting tumor stroma cells, but also through activation of immunologic effectors. More recently, RT has potentiated the local and systemic effects of cancer immunotherapy (IT). However, combination regimens that maximize immunologic and clinical efficacy remain undefined.

METHODS AND MATERIALS

We evaluated the impact of local RT on adenoviral-mediated vaccination against the colorectal cancer antigen GUCY2C (Ad5-GUCY2C) in a murine subcutaneous tumor model using mouse CT26 colon cancer cells (CT26-GUCY2C). Immune responses were assessed by ELISpot, and clinical responses were assessed by tumor size and incidence.

RESULTS

The specific sequence of tumor-directed RT preceding Ad5-GUCY2C IT transformed inactive therapeutic Ad5-GUCY2C vaccination into a curative vaccine. GUCY2C-specific T cell responses were amplified (P<.05), tumor eradication was maximized (P<.01), and tumor volumes were minimized (P<.001) in mice whose tumors were irradiated before, compared with after, Ad5-GUCY2C vaccination. The immunologic and antitumor efficacy of Ad5-GUCY2C was amplified comparably by unfractionated (8 Gy × 1), or biologically equivalent doses of fractionated (3.5 Gy × 3), RT. The antitumor effects of sequential RT and IT (RT-IT) depended on expression of GUCY2C by tumor cells and the adenoviral vaccine vector, and tumor volumes were inversely related to the magnitude of GUCY2C-specific T cell responses. Moreover, mice cured of CT26-GUCY2C tumors by RT-IT showed long-lasting antigen-dependent protection, resisting tumors formed by GUCY2C-expressing 4T1 breast cancer cells inoculated 50 days after CT26 cells.

CONCLUSIONS

Optimal sequencing of RT and IT amplifies antigen-specific local and systemic immune responses, revealing novel acute and long-term therapeutic antitumor protection. These observations underscore the importance of modality sequence optimization before the initiation of clinical trials of RT and IT to maximize immune and antitumor responses.

Intestinal GUCY2C prevents TGF-β secretion coordinating desmoplasia and hyperproliferation in colorectal cancer

Tumorigenesis is a multistep process that reflects intimate reciprocal interactions between epithelia and underlying stroma. However, tumor-initiating mechanisms coordinating transformation of both epithelial and stromal components are not defined. In humans and mice, initiation of colorectal cancer is universally associated with loss of guanylin and uroguanylin, the endogenous ligands for the tumor suppressor guanylyl cyclase C (GUCY2C), disrupting a network of homeostatic mechanisms along the crypt-surface axis. Here, we reveal that silencing GUCY2C in human colon cancer cells increases Akt-dependent TGF-β secretion, activating fibroblasts through TGF-β type I receptors and Smad3 phosphorylation. In turn, activating TGF-β signaling induces fibroblasts to secrete hepatocyte growth factor (HGF), reciprocally driving colon cancer cell proliferation through cMET-dependent signaling. Elimination of GUCY2C signaling in mice (Gucy2c(-/-)) produces intestinal desmoplasia, with increased reactive myofibroblasts, which is suppressed by anti-TGF-β antibodies or genetic silencing of Akt. Thus, GUCY2C coordinates intestinal epithelial-mesenchymal homeostasis through reciprocal paracrine circuits mediated by TGF-β and HGF. In that context, GUCY2C signaling constitutes a direct link between the initiation of colorectal cancer and the induction of its associated desmoplastic stromal niche. The recent regulatory approval of oral GUCY2C ligands to treat chronic gastrointestinal disorders underscores the potential therapeutic opportunity for oral GUCY2C hormone replacement to prevent remodeling of the microenvironment essential for colorectal tumorigenesis.

Translating colorectal cancer prevention through the guanylyl cyclase C signaling axis

Colorectal cancer (CRC) is a major public health concern, ranking among the leading causes of cancer death in both men and women. Because of this continued burden there is a clear need for improved treatment, and more importantly prevention of this disease. In recent years there is significant evidence to support the hypothesis that guanylyl cyclase C (GCY2C) is a tumor suppressor in the intestine, and that the loss of hormone ligands for this receptor is an important step in the disease process. Thus, ligand replacement therapy has been proposed as a strategy to prevent CRC. Until recently this strategy was not clinically plausible; however, the recent regulatory approval of linaclotide (LINZESS™, Forest Laboratories and Ironwood Pharmaceuticals, Inc.), an oral GUCY2C ligand, has raised the possibility of utilizing this strategy clinically to prevent CRC.

Evidence-based Guidelines for Precision Risk Stratification-Based Screening (PRSBS) for Colorectal Cancer: Lessons learned from the US Armed Forces: Consensus and Future Directions

Colorectal cancer (CRC) is the third most common cause of cancer-related death in the United States (U.S.), with estimates of 143,460 new cases and 51,690 deaths for the year 2012. Numerous organizations have published guidelines for CRC screening; however, these numerical estimates of incidence and disease-specific mortality have remained stable from years prior. Technological, genetic profiling, molecular and surgical advances in our modern era should allow us to improve risk stratification of patients with CRC and identify those who may benefit from preventive measures, early aggressive treatment, alternative treatment strategies, and/or frequent surveillance for the early detection of disease recurrence. To better negotiate future economic constraints and enhance patient outcomes, ultimately, we propose to apply the principals of personalized and precise cancer care to risk-stratify patients for CRC screening (Precision Risk Stratification-Based Screening, PRSBS). We believe that genetic, molecular, ethnic and socioeconomic disparities impact oncological outcomes in general, those related to CRC, in particular. This document highlights evidence-based screening recommendations and risk stratification methods in response to our CRC working group private-public consensus meeting held in March 2012. Our aim was to address how we could improve CRC risk stratification-based screening, and to provide a vision for the future to achieving superior survival rates for patients diagnosed with CRC.

Molecular staging of node negative patients with colorectal cancer

Metastatic disease is the principle cause of death from colorectal cancer. In that context, the most significant indicator of overall survival and therapeutic response to adjuvant chemotherapy is the presence of metastatic tumor cells in regional lymph nodes. Although histopathologic analysis of lymph nodes is central to all colorectal cancer staging paradigms, its prognostic and predictive value is limited. Indeed, about 30% of patients with histopathology-negative lymph nodes (pN0) die from metastatic disease, reflected by microscopic lymph node metastases that are overlooked by standard techniques. These unrecognized tumor cells are especially important when considering racial disparities in outcomes in colorectal cancer patients, where blacks with lymph node-negative disease have the largest discrepancies in outcomes, with more than 40% excess mortality compared to Caucasian patients. However, the significance of tumor cells in regional lymph nodes remains uncertain, and approximately 50% of colorectal cancer patients with nodal metastases detected by histopathology remain free of recurrent disease. Accurate identification of occult metastases in regional lymph nodes, and defining their value as prognostic markers of recurrence risk and predictive markers of response to adjuvant chemotherapy remains one challenge in the management of colorectal cancer patients. Guanylyl cyclase C (GUCY2C), a receptor which is expressed primarily in intestinal cells normally, but is universally over-expressed by colorectal cancer cells, has been validated to detect prognostically significant occult metastases using quantitative RT-PCR (RT-qPCR). Biomarker validation was achieved through a prospective, multicenter, blinded clinical trial. In that trial, occult tumor burden estimated across all regional lymph nodes by GUCY2C RT-qPCR predicted clinical outcomes, identifying node-negative patients with a low (near zero) risk, and those with >80% risk, of developing disease recurrence. Moreover, there was disproportionately higher occult tumor burden in black, compared to white, patients which contributes to racial disparities in outcomes in colorectal cancer. The diagnostic paradigm quantifying occult tumor burden using GUCY2C qRT-PCR is positioned to reduce racial disparities in colorectal cancer mortality.

Guanylyl cyclase C as a biomarker in colorectal cancer

While histologic assessment of nodes is a component of all colon cancer staging paradigms, approximately 30% of patients with histology-negative nodes (pN0) die of disseminated disease reflected by occult nodal metastases. Undetected metastases are particularly important when considering racial disparities in colon cancer, where black subjects with pN0 disease exhibit the greatest differences in outcomes, with >40% excess mortality. Recently, guanylyl cyclase C (GCC), a protein normally restricted to intestinal cells, but universally expressed by colorectal cancer cells, was validated for detecting occult metastases. Indeed, occult tumor burden across regional lymph nodes estimated by GCC quantitative reverse transcription PCR identifies pN0 patients with near zero risk, and those with >80% risk, of unfavorable outcomes. Disproportionately high occult tumor burden in black patients underlies racial disparities in stage-specific mortality. These studies position the platform encompassing quantification of occult tumor burden by GCC quantitative reverse transcription PCR for translation, as a detect-treat paradigm to reduce racial disparities in colon cancer mortality.

Molecular profiling for stage II colon cancer

SUMMARY Although nearly 80% of patients with stage II colon cancer are cured by surgery alone, 20% will relapse. One major challenge is to identify individuals who will derive enough benefit from adjuvant therapy to balance the risks, costs and inconvenience. Existing markers, such as microsatellite instability, are predictive and prognostic, but only apply to a small number of patients. Novel technologies that include molecular profiling are emerging tools that may help to identify patients at high risk for recurrence or predict who will derive a greater benefit from adjuvant treatment. This article reviews molecular markers in stage II colon cancer and their potential role in identification of high-risk patients.

Detection of circulating tumor cells in peripheral blood of colorectal cancer patients without distant organ metastases

PURPOSE

Recently, the detection of circulating tumor cells (CTCs) in peripheral blood has become an important tool for the non-invasive assessment of micrometastases and to predict clinical outcome. The objective of this study was to investigate if the presence of CTCs in peripheral blood influences the prognosis in colorectal cancer (CRC) patients without distant organ metastases.

METHODS

The GCC mRNA and CK20 mRNA levels in peripheral blood and the serum levels of CEA of 92 CRC patients without distant organ metastasis were analyzed by quantitative RT-PCR and ELISA, respectively. Its associations with overall survival (OS) and disease-free survival (DFS) rates were analyzed.

RESULTS

Univariate analyses showed that lower OS and DFS rates were significantly associated with GCC and CK20 mRNA levels, the presence of lymph node metastases, the presence of mesenteric root lymph node metastases, and the presence of tumor emboli in vessels (p < 0.05), but not with CEA levels. Multivariate analyses showed a significant association between 1) OS and GCC mRNA levels and differentiation types and 2) DFS and the presence of tumor emboli in the vessels. Kaplan-Meier curves showed that DFS was significantly associated with the presence of poorly differentiated cells, the presence of mesenteric root lymph node metastases having received prior chemotherapy, and the presence of tumor emboli in vessels.

CONCLUSION

The detection of CTCs in peripheral blood may be useful for the prediction of clinical outcome in CRC patients without distant organ metastases.

GC-C gene silencing inhibits the growth of subcutaneously implanted gastric tumors in nude mice

AIM: To study the effect of GC-C gene silencing on the biological behaviors of subcutaneously implanted gastric tumors and to explore the possible mechanisms involved.

METHODS: Non-transfected SGC-7901 cells (SGC-7901 group), SGC-7901 cells transfected cell with an empty plasmid (PRNA group), and those transfected with a shRNA targeting the GC-C gene (GC-C-shRNA group) were subcutaneously inoculated into nude mice. Then, the histologically intact xenograft tissues were subcutaneously transplanted to nude mice to observe the condition of nude mice and determine the rate of tumor survival and growth velocity. The levels of GC-C mRNA and protein were determined by RFQ-PCR and Western blot, respectively. The heteromorphism and necrosis of tumor cells were observed after HE staining. The expression of CXCR4 protein was detected by Western blot and immunohistochemistry.

RESULTS: The rate of tumor survival and the condition of nude mice did not differ significantly among the three groups. Compared to the SGC-7901 group and PRNA group, the tumors grew more slowly and became smaller in the GC-C-shRNA group (all P < 0.05). The reduced rate of tumor growth velocity and volume in the GC-C-shRNA group were 33.7% and 33.2%, respectively, and GC-C gene silencing efficiency was 66.8% and 64.4%, respectively (P < 0.05). The expression of GC-C protein decreased by 50.0% and 49.6%, respectively (P < 0.05), and the degree of tumor heteromorphism and necrosis and expression of CXCR4 protein in the GC-C-shRNA group decreased obviously (all P < 0.05).

CONCLUSION: GC-C gene silencing slows the growth velocity of gastric tumors in vivo possibly in a CXCR4-dependent manner.

GUCY2C molecular staging personalizes colorectal cancer patient management

While the most significant prognostic and predictive marker in the management of colorectal cancer patients is cancer cells in regional lymph nodes, approximately 30% of patients whose lymph nodes are ostensibly free of tumor cells by histopathology ultimately develop recurrent disease reflecting occult metastases. Molecular techniques utilizing highly specific markers and ultra-sensitive detection technologies have emerged as powerful staging platforms to establish prognosis and predict responsiveness to chemotherapy in colorectal cancer patients. This review describes the evolution of the tumor suppressor GUCY2C as a prognostic and predictive molecular biomarker that quantifies occult tumor burden in regional lymph nodes for staging patients with colorectal cancer.

Molecular staging individualizing cancer management

Although the most important prognostic and predictive marker in colorectal cancer is tumor cells in lymph nodes, approximately 30% of patients who are node-negative die from occult metastases. Molecular staging employing specific markers and sensitive detection technologies has emerged as a powerful platform to assess prognosis in node-negative colon cancer. Integrating molecular staging into algorithms that individualize patient management will require validation and the definition of relationships between occult tumor cells, prognosis, and responses to chemotherapy.

Analytic lymph node number establishes staging accuracy by occult tumor burden in colorectal cancer

BACKGROUND AND OBJECTIVES

Recurrence in lymph node-negative (pN0) colorectal cancer suggests the presence of undetected occult metastases. Occult tumor burden in nodes estimated by GUCY2C RT-qPCR predicts risk of disease recurrence. This study explored the impact of the number of nodes analyzed by RT-qPCR (analytic) on the prognostic utility of occult tumor burden.

METHODS

Lymph nodes (range: 2-159) from 282 prospectively enrolled pN0 colorectal cancer patients, followed for a median of 24 months (range: 2-63), were analyzed by GUCY2C RT-qPCR. Prognostic risk categorization defined using occult tumor burden was the primary outcome measure. Association of prognostic variables and risk category were defined by multivariable polytomous and semi-parametric polytomous logistic regression.

RESULTS

Occult tumor burden stratified this pN0 cohort into categories of low (60%; recurrence rate (RR) = 2.3% [95% CI 0.1-4.5%]), intermediate (31%; RR = 33.3% [23.7-44.1%]), and high (9%; RR = 68.0% [46.5-85.1%], P < 0.001) risk of recurrence. Beyond race and T stage, the number of analytic nodes was an independent marker of risk category (P < 0.001). When >12 nodes were analyzed, occult tumor burden almost completely resolved prognostic risk classification of pN0 patients.

CONCLUSIONS

The prognostic utility of occult tumor burden assessed by GUCY2C RT-qPCR is dependent on the number of analytic lymph nodes.

Epitope-targeted cytotoxic T cells mediate lineage-specific antitumor efficacy induced by the cancer mucosa antigen GUCY2C

Guanylyl cyclase C (GUCY2C) is the index cancer mucosa antigen, an emerging class of immunotherapeutic targets for the prevention of recurrent metastases originating in visceral epithelia. GUCY2C is an autoantigen principally expressed by intestinal epithelium, and universally by primary and metastatic colorectal tumors. Immunization with adenovirus expressing the structurally unique GUCY2C extracellular domain (GUCY2C(ECD); Ad5-GUCY2C) produces prophylactic and therapeutic protection against GUCY2C-expressing colon cancer metastases in mice, without collateral autoimmunity. GUCY2C antitumor efficacy is mediated by a unique immunological mechanism involving lineage-specific induction of antigen-targeted CD8(+) T cells, without CD4(+) T cells or B cells. Here, the unusual lineage specificity of this response was explored by integrating high-throughput peptide screening and bioinformatics, revealing the role for GUCY2C-directed CD8(+) T cells targeting specific epitopes in antitumor efficacy. In BALB/c mice vaccinated with Ad5-GUCY2C, CD8(+) T cells recognize the dominant GUCY2C(254-262) epitope in the context of H-2K(d), driving critical effector functions including interferon gamma secretion, cytolysis ex vivo and in vivo, and antitumor efficacy. The ability of GUCY2C to induce lineage-specific responses targeted to cytotoxic CD8(+) T cells recognizing a single epitope mediating antitumor efficacy without autoimmunity highlights the immediate translational potential of cancer mucosa antigen-based vaccines for preventing metastases of mucosa-derived cancers.

Occult tumor burden contributes to racial disparities in stage-specific colorectal cancer outcomes

BACKGROUND

There are differences in outcomes in blacks compared with whites with lymph node-negative (pN0) colorectal cancer. Recurrence in pN0 patients suggests the presence of occult metastases undetected by conventional approaches. This study explores the association of racial differences in outcomes with occult tumor burden in regional lymph nodes.

METHODS

Lymph nodes (range, 2-159) from 282 prospectively enrolled pN0 colorectal cancer patients followed for a median of 24 months (range, 2-63 months) were subjected to molecular analysis. Occult tumor burden was estimated by quantifying the expression of GUCY2C, a biomarker for metastatic colorectal cancer cells. Risk categories defined using occult tumor burden was the primary outcome measure. Association of prognostic variables and risk were defined by multivariate polytomous logistic regression.

RESULTS

Occult tumor burden stratified this cohort of 259 whites and 23 blacks into categories with low (60%; recurrence rate [RR] = 2.3%; 95% confidence interval [CI], 0.1%-4.5%), intermediate (31%; RR = 33.3%; 95% CI, 23.7%-44.1%), and high (9%; RR = 68.0%; 95% CI, 46.5%-85.1%; P < .001) risk. Blacks compared with whites exhibited 4-fold greater occult metastases in individual lymph nodes (P < .001). Multivariate analysis revealed that race (P = .02), T stage (P = .02), and number of lymph nodes collected (P = .003) were independent prognostic markers of risk category. Blacks compared with whites were more likely to harbor levels of occult tumor burden, associated with the highest recurrence risk (adjusted odds ratio = 5.08; 95% CI, 1.69-21.39; P = .007).

CONCLUSIONS

Racial disparities in stage-specific outcomes in colorectal cancer are associated with differences in occult tumor burden in regional lymph nodes.

Lymph node CEA and MUC2 mRNA as useful predictors of outcome in colorectal cancer

The aim was to explore the utility for staging and prognostic impact of carcinoembryonic antigen (CEA), cytokeratin 20 (CK20), guanylyl cyclase C (GCC), CUB (complement protein subcomponents C1r/C1s, urchin embryonic growth factor, and bone morphogenic protein 1) containing domain protein 1 (CDCP1) and mucin 2 (MUC2) mRNA levels in mesenteric lymph nodes of colorectal cancer (CRC) patients. Lymph nodes were collected at surgery and bisected; one half was subjected to biomarker mRNA analysis using real-time quantitative RT-PCR and the other half to routine histopathology. Lymph nodes from 174 CRC patients and 24 controls were analyzed. The median follow-up time was 59 (range 17-131) months. Cut-off levels were defined by analyzing quintiles by Cox regression model. CEA mRNA showed the best discriminating power between patients with recurrence in CRC after surgery and patients who were apparently disease-free (p = 0.015). The risk of recurrence for the CEA(+) patients was 4.6 times greater than for the CEA(-) patients (p < 0.0001). The other biomarkers gave lower hazard ratios. Cumulative survival analysis demonstrated that the average survival time was 99 months for CEA(-) patients compared to 39 months for CEA(+) patients, a difference of 60 months (p < 0.0001). Six to nine percent of the Stage I and Stage II patients [H&E(-)] had CEA(+), CK20(+), GCC(+) and/or MUC2(+) lymph nodes. Two of these patients died from recurrent CRC. Low lymph node MUC2/CEA mRNA ratio identified patients with high risk for recurrence (p = 0.011). Thus, quantitative reverse transcriptase-polymerase chain reaction of CEA mRNA is a sensitive method to identify tumor cells in lymph nodes of CRC patients and, in combination with MUC2 mRNA, allows improved prediction of clinical outcome.

Contrast-enhanced ultrasound imaging of sentinel lymph nodes after peritumoral administration of Sonazoid in a melanoma tumor animal model

OBJECTIVES

The purpose of this study was to compare lymphosonography (ie, contrast-enhanced ultrasound imaging [US] after interstitial injection of a US contrast agent) for the detection of sentinel lymph nodes (SLNs) in swine with naturally occurring melanoma tumors to lymphoscintigraphy using blue dye-guided surgical dissection as the reference standard. Also, we sought to determine if lymphosonography can be used to characterize SLNs.

METHODS

Sixty-three swine with 104 melanomas were evaluated. Contrast-specific US was performed after peritumoral injection (1 mL dose) of Sonazoid (GE Healthcare, Oslo, Norway). Lymphoscintigraphy was performed after peritumoral injections of technetium Tc 99m sulfur colloid. Peritumoral injection of 1% Lymphazurin (Ben Venue Labs, Inc, Bedford, OH) was used to guide SLN resection. The accuracy of SLN detection with the two imaging modalities was compared using the McNemar test. The SLNs were qualitatively and quantitatively characterized as benign or malignant based on the lymphosonography results with histopathology and RNA analyses used as the reference standards.

RESULTS

Blue dye-guided surgery identified 351 SLNs. Lymphosonography detected 293 SLNs and 11 false-positives, while lymphoscintigraphy detected 231 SLNs and 20 false-positives. The accuracy of SLN detection was 81.8% for lymphosonography, which was significantly higher than the 63.2% achieved with lymphoscintigraphy (P < .0001). The accuracy of lymphosonography for SLN characterization was 80%. When the size of the enhanced SLN was taken into consideration to characterize SLNs, the accuracy was 86%.

CONCLUSIONS

Lymphosonography is statistically better than lymphoscintigraphy for the detection of SLNs in this animal model. The ability to use lymphosonography as a means to characterize SLNs as benign or malignant is limited.

Occult tumor burden predicts disease recurrence in lymph node-negative colorectal cancer

PURPOSE

Lymph node involvement by histopathology informs colorectal cancer prognosis, whereas recurrence in 25% of node-negative patients suggests the presence of occult metastasis. GUCY2C (guanylyl cyclase C) is a marker of colorectal cancer cells that identifies occult nodal metastases associated with recurrence risk. Here, we defined the association of occult tumor burden, quantified by GUCY2C reverse transcriptase-PCR (RT-PCR), with outcomes in colorectal cancer.

EXPERIMENTAL DESIGN

Lymph nodes (range: 2-159) from 291 prospectively enrolled node-negative colorectal cancer patients were analyzed by histopathology and GUCY2C quantitative RT-PCR. Participants were followed for a median of 24 months (range: 2-63). Time to recurrence and disease-free survival served as primary and secondary outcomes, respectively. Association of outcomes with prognostic markers, including molecular tumor burden, was estimated by recursive partitioning and Cox models.

RESULTS

In this cohort, 176 (60%) patients exhibited low tumor burden (Mol(Low)), and all but four remained free of disease [recurrence rate 2.3% (95% CI, 0.1-4.5%)]. Also, 90 (31%) patients exhibited intermediate tumor burden (Mol(Int)) and 30 [33.3% (23.7-44.1)] developed recurrent disease. Furthermore, 25 (9%) patients exhibited high tumor burden (Mol(High)) and 17 [68.0% (46.5-85.1)] developed recurrent disease (P < 0.001). Occult tumor burden was an independent marker of prognosis. Mol(Int) and Mol(High) patients exhibited a graded risk of earlier time to recurrence [Mol(Int), adjusted HR 25.52 (11.08-143.18); P < 0.001; Mol(High), 65.38 (39.01-676.94); P < 0.001] and reduced disease-free survival [Mol(Int), 9.77 (6.26-87.26); P < 0.001; Mol(High), 22.97 (21.59-316.16); P < 0.001].

CONCLUSION

Molecular tumor burden in lymph nodes is independently associated with time to recurrence and disease-free survival in patients with node-negative colorectal cancer.

Cure and curse: E. coli heat-stable enterotoxin and its receptor guanylyl cyclase C

Enterotoxigenic Escherichia coli (ETEC) associated diarrhea is responsible for roughly half a million deaths per year, the majority taking place in developing countries. The main agent responsible for these diseases is the bacterial heat-stable enterotoxin STa. STa is secreted by ETEC and after secretion binds to the intestinal receptor guanylyl cyclase C (GC-C), thus triggering a signaling cascade that eventually leads to the release of electrolytes and water in the intestine. Additionally, GC-C is a specific marker for colorectal carcinoma and STa is suggested to have an inhibitory effect on intestinal carcinogenesis. To understand the conformational events involved in ligand binding to GC-C and to devise therapeutic strategies to treat both diarrheal diseases and colorectal cancer, it is paramount to obtain structural information on the receptor ligand system. Here we summarize the currently available structural data and report on physiological consequences of STa binding to GC-C in intestinal epithelia and colorectal carcinoma cells.

Bacterial heat-stable enterotoxins: translation of pathogenic peptides into novel targeted diagnostics and therapeutics

Heat-stable toxins (STs) produced by enterotoxigenic bacteria cause endemic and traveler’s diarrhea by binding to and activating the intestinal receptor guanylyl cyclase C (GC-C). Advances in understanding the biology of GC-C have extended ST from a diarrheagenic peptide to a novel therapeutic agent. Here, we summarize the physiological and pathophysiological role of GC-C in fluid-electrolyte regulation and intestinal crypt-villus homeostasis, as well as describe translational opportunities offered by STs, reflecting the unique characteristics of GC-C, in treating irritable bowel syndrome and chronic constipation, and in preventing and treating colorectal cancer.

Can colorectal cancer be prevented or treated by oral hormone replacement therapy?

Guanylyl cyclase C (GCC) is the receptor specifically expressed by intestinal cells for the paracrine hormones guanylin and uroguanylin and diarrheagenic bacterial heat-stable enterotoxins. This tissue-specific receptor coordinates lineage-dependent regulation of epithelial homeostasis, and its disruption contributes to intestinal tumorigenesis. It coordinates regenerative and metabolic circuits by restricting the cell cycle and proliferation and programming metabolic transitions central to organizing the dynamic crypt-surface axis. Further, mice deficient in GCC signaling are more susceptible to colon cancer induced by Apc mutations or the carcinogen azoxymethane. Moreover, guanylin and uroguanylin are gene products most commonly lost, early, in colon cancer in animals and humans. The role of GCC as a tumor suppressing receptor regulating proliferation and metabolism, together with the universal loss of guanylin and uroguanylin in tumorigenesis, suggests a model in which colorectal cancer is a paracrine hormone deficiency syndrome. In that context, activation of GCC reverses the tumorigenic phenotype by limiting growth of colorectal cancer cells by restricting progression through the G1/S transition and reprogramming metabolic circuits from glycolysis to oxidative phosphorylation, limiting bioenergetic support for rapid proliferation. These observations suggest a pathophysiological hypothesis in which GCC is a lineage-dependent tumor suppressing receptor coordinating proliferative homeostasis whose dysregulation through hormone loss contributes to neoplasia. The correlative therapeutic hypothesis suggests that colorectal cancer is a disease of hormone insufficiency that can be prevented or treated by oral supplementation with GCC ligands.

Radiometallated peptides targeting guanylate cyclase C and the urokinase-type plasminogen activator receptor

Research is currently underway worldwide into the development of receptor-specific radiopharmaceuticals for the imaging and treatment of cancer. The successful clinical development of radiolabeled somatostatin analogs for imaging and treatment of cancers overexpressing somatostatin receptors has catalyzed further preclinical investigation of other radiolabeled peptides for molecular imaging and peptide-receptor radiotherapy, including such well-studied peptide vectors as cholecystokinin, neurotensin, bombesin and RGD peptides. Within this larger context, this article will focus on the current status of two more recent additions to the list of molecular imaging targets – guanylate cyclase C, a specific marker for colorectal cancer, and the urokinase plasminogen activator receptor, a cell-surface receptor overexpressed in diverse cancer types.

Colorectal cancer is a paracrine deficiency syndrome amenable to oral hormone replacement therapy

The most commonly lost gene products in colorectal carcinogenesis include the paracrine hormones guanylin and uroguanylin, the endogenous ligands for guanylyl cyclase C (GCC), the intestinal receptor for diarrheagenic bacterial enterotoxins. Recently, GCC-cGMP signaling has emerged as a principal regulator of proliferation, genetic integrity and metabolic programming in normal human enterocytes and colon cancer cells. Elimination of GCC in mice produced hyperplasia of the proliferating compartment associated with increases in rapidly cycling progenitor cells, and reprogrammed enterocyte metabolism, with a shift from oxidative phosphorylation to glycolysis. In addition, in colons of mice carrying mutations in Apc (Apc(Min) (/+)) or exposed to the carcinogen azoxymethane, elimination of GCC increased tumor initiation and promotion by disrupting genomic integrity and releasing cell cycle restriction. These previously unrecognized roles for GCC as a fundamental regulator of intestinal homeostasis and as an intestinal tumor suppressor suggest that receptor dysregulation reflecting paracrine hormone insufficiency is a key event during the initial stages of colorectal tumorigenesis. Together with the uniform over-expression of GCC in human tumors, these novel roles for GCC underscore the potential of oral replacement with GCC ligands for targeted prevention and therapy of colorectal cancer.

Selection of optimal reference genes for normalization in quantitative RT-PCR

Background

Normalization in real-time qRT-PCR is necessary to compensate for experimental variation. A popular normalization strategy employs reference gene(s), which may introduce additional variability into normalized expression levels due to innate variation (between tissues, individuals, etc). To minimize this innate variability, multiple reference genes are used. Current methods of selecting reference genes make an assumption of independence in their innate variation. This assumption is not always justified, which may lead to selecting a suboptimal set of reference genes.

Results

We propose a robust approach for selecting optimal subset(s) of reference genes with the smallest variance of the corresponding normalizing factors. The normalizing factor variance estimates are based on the estimated unstructured covariance matrix of all available candidate reference genes, adjusting for all possible correlations. Robustness is achieved through bootstrapping all candidate reference gene data and obtaining the bootstrap upper confidence limits for the variances of the log-transformed normalizing factors. The selection of the reference gene subset is optimized with respect to one of the following criteria: (A) to minimize the variability of the normalizing factor; (B) to minimize the number of reference genes with acceptable upper limit on variability of the normalizing factor, (C) to minimize the average rank of the variance of the normalizing factor. The proposed approach evaluates all gene subsets of various sizes rather than ranking individual reference genes by their stability, as in the previous work. In two publicly available data sets and one new data set, our approach identified subset(s) of reference genes with smaller empirical variance of the normalizing factor than in subsets identified using previously published methods. A small simulation study indicated an advantage of the proposed approach in terms of sensitivity to identify the true optimal reference subset in the presence of even modest, especially negative correlation among the candidate reference genes.

Conclusions

The proposed approach performs comprehensive and robust evaluation of the variability of normalizing factors based on all possible subsets of candidate reference genes. The results of this evaluation provide flexibility to choose from important criteria for selecting the optimal subset(s) of reference genes, unless one subset meets all the criteria. This approach identifies gene subset(s) with smaller variability of normalizing factors than current standard approaches, particularly if there is some nontrivial innate correlation among the candidate genes.

Analytical performance of a qRT-PCR assay to detect guanylyl cyclase C in FFPE lymph nodes of patients with colon cancer

Up to 30% of patients with stage II (pN0) colon cancer develop recurrences, suggesting that the presence of lymph node (LN) metastases escaped detection at histopathologic staging. A simple way to overcome this limitation and to improve staging accuracy is to use reverse transcription-polymerase chain reaction (RT-PCR) to examine a larger fraction or an entire specimen. The Guanylyl cyclase C (GCC) gene is uniquely expressed in apical cells of the gastrointestinal tract. Its expression in colon cancer cells and metastases is conserved. Therefore, detection of GCC mRNA in LNs has been shown to be indicative of the presence of colon cancer metastases. As the current processing of LNs involves formalin fixation and paraffin embedding, we developed a method for extracting RNA from formalin-fixed paraffin-embedded LN specimens and detecting GCC mRNA by quantitative RT-PCR. The assay has a dynamic range of 5 logs, an average amplification efficiency of 98.4% (95% confidence interval, 96.6-100.3), a reaction linearity of 0.998 (95% confidence interval, 0.997-0.999), and also intraplate and interplate CVs of <1% and <5%, respectively. The test specificity was 98% with LNs collected from patients affected by conditions other than colon cancer (n=380). Sensitivity was 97% for patients with stage III colon cancer (n=34), whereas 35% of patients with stages I and II disease (n=51) had at least 1 GCC mRNA-positive LN. The high specificity of GCC mRNA suggests that routine utilization of the quantitative RT-PCR test has the potential to improve the detection of colon cancer metastases in LNs.

The hormone receptor GUCY2C suppresses intestinal tumor formation by inhibiting AKT signaling

BACKGROUND & AIMS

GUCY2C is the intestinal receptor for the paracrine hormones guanylin and uroguanylin that converts guanosine-5'-triphosphate to cyclic guanosine monophosphate (cGMP). It functions as a tumor suppressor; its loss disrupts intestinal homeostasis and promotes tumorigenesis. We investigated the effects of GUCY2C loss on intestinal cell proliferation, metabolism, signaling, and tumorigenesis in mice.

METHODS

Intestinal cell proliferation and metabolism were examined in Gucy2c(-/-) and colon cancer cells by microscopy, immunoblot, and functional analyses. Microarray analyses compared gene expression profiles of intestine cell from Gucy2c(-/-) and wild-type mice. v akt murine thymoma viral oncogene homolog (AKT) regulation and signaling were examined, and the role of AKT in GUCY2C-dependent tumorigenesis was defined in Gucy2c(-/-)Akt1(-/-) mice.

RESULTS

The size and number of intestinal crypts increased in Gucy2c(-/-) mice; the associated epithelial cells showed accelerated proliferation, increased glycolysis, and reduced oxidative phosphorylation, which was reversed by oral administration of cGMP. Conversely, activating guanylyl cyclase C in human colon cancer cells delayed cell-cycle progression, decreased DNA synthesis and colony formation, reduced glycolysis, and increased mitochondrial adenosine triphosphate production. AKT signaling pathways were activated in intestines of Gucy2c(-/-) mice, associated with increased AKT phosphorylation. Disruption of AKT activity, pharmacologically or genetically, reduced DNA synthesis, proliferation, and glycolysis, and increased mitochondrial biogenesis. Intestinal tumorigenesis increased after administration of azoxymethane to Gucy2c(-/-) mice, compared with wild-type mice, but was eliminated in Gucy2c(-/-)Akt1(-/-) mice.

CONCLUSIONS

GUCY2C is a tumor suppressor that controls proliferation and metabolism of intestinal epithelial cells by inactivating AKT signaling. This receptor and its ligands, which are paracrine hormones, might be novel candidates for anticolorectal cancer therapy.

Molecular staging estimates occult tumor burden in colorectal cancer

Tumor cells in regional lymph nodes are a key prognostic marker of survival and predictive marker of response to adjuvant chemotherapy in colorectal cancer. However, clinicopathologic techniques to detect lymph node metastases remain imperfect, and approximately 30% of patients with lymph nodes negative by histology (pN0) develop recurrent disease, reflecting occult metastases that escape detection. These observations underscore an unmet clinical need for accurate approaches to identify occult nodal metastases in colorectal cancer patients. GUCY2C is a receptor whose expression normally is restricted to intestinal epithelial cells, but is universally overexpressed by colorectal cancer cells. A prospective, multicenter, blinded clinical trial established the prognostic utility of GUCY2C qRT-PCR to detect occult nodal metastases in pN0 colorectal cancer patients. Molecular staging revealed that approximately 13% of pN0 patients were free of cancer cells, while approximately 87% had GUCY2C results that suggested occult metastases. The presence of occult nodal metastases was the most powerful independent predictor of time to recurrence and disease-free survival. These observations establish the utility of molecular detection of occult nodal metastases for assessing prognostic risk in pN0 colorectal cancer patients. Advancing GUCY2C into staging paradigms in clinical laboratories will require validation in independent patient populations, definition of the relationship between the quantity of occult tumor metastases and risk, and determination of the utility of GUCY2C qRT-PCR to identify pN0 patients who might benefit from adjuvant chemotherapy.

GCC signaling in colorectal cancer: Is colorectal cancer a paracrine deficiency syndrome?

Guanylyl cyclase C (GCC) is the receptor expressed by intestinal cells for the paracrine hormones guanylin and uroguanylin that coordinate mucosal homeostasis and its silencing contributes to intestinal transformation. It orchestrates proliferative and metabolic circuits by limiting the cell cycle and programming metabolic transitions central to regeneration along the crypt-villus axis. Mice deficient in GCC are more susceptible to colon cancer induced by germline mutations or carcinogens. Moreover, guanylin and uroguanylin are the most commonly lost gene products in colon cancer. The role of GCC as a tumor suppressor and the universal loss of its hormones in transformation suggest a paradigm in which colorectal cancer is a disease of paracrine hormone insufficiency. Indeed, GCC signaling reverses the tumorigenic phenotype of human colon cancer cells by regulating proliferation and metabolism. These data suggest a pathophysiological hypothesis in which GCC is a tumor suppressor coordinating proliferative homeostasis whose silencing through hormone loss initiates transformation. The correlative therapeutic hypothesis suggests that colorectal cancer is a disease of hormone insufficiency that can be prevented or treated by oral hormone replacement therapy employing GCC ligands.

GUCY2C reverse transcriptase PCR to stage pN0 colorectal cancer patients

The most important prognostic marker of survival and predictive marker of response to adjuvant chemotherapy in colon cancer patients is tumor cells in regional lymph nodes. Despite their importance, standard techniques to assess nodal metastases remain imperfect, as approximately 30% of patients with histology-negative lymph nodes (pN0) die of recurrent disease, reflecting occult metastases that escape detection. These observations highlight the clinical need for novel, accurate approaches to detect occult lymph node metastases in patients with colon cancer. GUCY2C is a biomarker whose expression normally is restricted to intestinal cells, but is near universally overexpressed by colorectal cancer cells. Recently, a prospective, multicenter, blinded clinical trial demonstrated for the first time that the prognostic utility of GUCY2C quantitative reverse transcriptase (qRT)-PCR to detect occult lymph node metastases in pN0 colorectal cancer patients. Molecular staging revealed that approximately 13% of pN0 patients were free of tumor cells, while approximately 87% had GUCY2C results that suggested occult metastases. The presence of occult lymph node metastases was the strongest independent predictor of time to recurrence and disease-free survival. These observations establish the utility of molecular detection of occult lymph node metastases for estimating prognostic risk in pN0 colorectal cancer patients. Advancing this molecular diagnostic into staging paradigms in clinical laboratories will require validation in independent patient populations, definition of the relationship between the quantity of occult tumor metastases and risk, and determination of the utility of GUCY2C qRT-PCR to identify pN0 patients who might benefit from adjuvant chemotherapy.

Expression of the intestinal biomarkers Guanylyl cyclase C and CDX2 in poorly differentiated colorectal carcinomas

Guanylyl cyclase C, a receptor for bacterial diarrheagenic enterotoxins, is expressed selectively by intestinal epithelium and is an endogenous downstream target of CDX2. The expression of Guanylyl cyclase C is preserved throughout the adenoma/carcinoma sequence in the colorectum. Detection of Guanylyl cyclase C expression by reverse transcriptase-polymerase chain reaction is currently being validated as a technique to identify occult lymph node metastases in patients with colorectal cancer and for circulating cells in the blood for postoperative surveillance. Although Guanylyl cyclase C is widely expressed by well-differentiated colorectal cancer, its expression in poorly differentiated colorectal cancer has not been evaluated. A tissue microarray was created from 69 archival specimens including 44 poorly differentiated, 15 undifferentiated or medullary, and 10 signet ring cell colorectal carcinomas. Matched normal colonic mucosa was used as a positive control. Immunohistochemical staining for Guanylyl cyclase C and CDX2 was evaluated as positive or negative based on at least a 10% extent of staining. Of the 69 tumor samples, 75%, 47%, and 90% of the poorly differentiated, medullary, and signet ring cell tumors were positive for Guanylyl cyclase C and 75%, 40% and 90% of these subsets were positive for CDX2, respectively. There was excellent correlation between Guanylyl cyclase C and CDX2 expression on a case-per-case basis (P < .0001). There was also a statistically significant difference in the Guanylyl cyclase C staining pattern between medullary carcinomas and poorly differentiated, not otherwise specified (P = .05). Immunopositivity for Guanylyl cyclase C was greater than 95% in a separately stained microarray series of well/moderately differentiated colorectal carcinomas. In conclusion, Guanylyl cyclase C expression is lost in a quarter of poorly differentiated and half of undifferentiated colorectal carcinomas. Therefore, the utility of Guanylyl cyclase C expression as a diagnostic marker for colorectal carcinoma may be questionable in poorly differentiated colorectal neoplasms.

Previstage GCC colorectal cancer staging test: a new molecular test to identify lymph node metastases and provide more accurate information about the stage of patients with colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and a leading cause of death for both men and women in North America. The staging of the CRC at the time of diagnosis is the single most important prognostic factor in determining recurrence and survival. Until 2008, accurate evaluation of CRC stages I and II was based on examination of regional lymph nodes (LNs) under a microscope to identify cancer cells. This method can detect one cancer cell in 200 normal cells, but analyzes only a fraction of the available tissue from the LN (less than 0.1%). Up to 30% of patients assessed by traditional histopathology methods as having stage II disease (negative LNs) experience a recurrence of their cancer. Previstage GCC Colorectal Cancer Staging Test, a new molecular diagnostic test, is able to identify patients at high risk of recurrence by examining their LNs for guanylyl cyclase C (GCC). GCC is a marker found in cells lining the lumen of the gastrointestinal tract. The expression of GCC is conserved in CRC and metastatic disease. Using an ultrasensitive quantitative reverse transcription (RT)-PCR, the test interrogates a patient's LN tissues to identify GCC levels consistent with metastatic (stage III) disease. The technology employed in Previstage GCC is nearly 100,000 times more sensitive than microscopic staging methods. This molecular diagnostic test allows a more thorough examination of LNs and has an analytic sensitivity of 92% and a specificity of 98%. Such a test can be used to overcome the limitations of staging by traditional histopathology alone.

Guanylyl cyclase C in colorectal cancer: susceptibility gene and potential therapeutic target

Colorectal cancer is one of the leading causes of tumor-related morbidity and mortality worldwide. While mechanisms underlying this disease have been elucidated over the past two decades, these molecular insights have failed to translate into efficacious therapy. The oncogenomic view of cancer suggests that terminal transformation reflects the sequential corruption of signal transduction circuits regulating key homeostatic mechanisms, whose multiplicity underlies the therapeutic resistance of most tumors to interventions targeting individual pathways. Conversely, the paucity of mechanistic insights into proximal pathophysiological processes that initiate and amplify oncogenic circuits preceding accumulation of mutations and transformation impedes development of effective prevention and therapy. In that context, guanylyl cyclase C (GCC), the intestinal receptor for the paracrine hormones guanylin and uroguanylin, whose early loss characterizes colorectal transformation, has emerged as a component of lineage-specific homeostatic programs organizing spatiotemporal patterning along the crypt-surface axis. Dysregulation of GCC signaling, reflecting hormone loss, promotes tumorigenesis through reprogramming of replicative and bioenergetic circuits and genomic instability. Compensatory upregulation of GCC in response to hormone loss provides a unique translational opportunity for prevention and treatment of colorectal tumors by hormone-replacement therapy.

Lineage-specific T-cell responses to cancer mucosa antigen oppose systemic metastases without mucosal inflammatory disease

Cancer mucosa antigens are emerging as a new category of self-antigens expressed normally in immunologically privileged mucosal compartments and universally by their derivative tumors. These antigens leverage the established immunologic partitioning of systemic and mucosal compartments, limiting tolerance opposing systemic antitumor efficacy. An unresolved issue surrounding self-antigens as immunotherapeutic targets is autoimmunity following systemic immunization. In the context of cancer mucosa antigens, immune effectors to self-antigens risk amplifying mucosal inflammatory disease promoting carcinogenesis. Here, we examined the relationship between immunotherapy for systemic colon cancer metastases targeting the intestinal cancer mucosa antigen guanylyl cyclase C (GCC) and its effect on inflammatory bowel disease and carcinogenesis in mice. Immunization with GCC-expressing viral vectors opposed nascent tumor growth in mouse models of pulmonary metastasis, reflecting systemic lineage-specific tolerance characterized by CD8(+), but not CD4(+), T-cell or antibody responses. Responses protecting against systemic metastases spared intestinal epithelium from autoimmunity, and systemic GCC immunity did not amplify chemically induced inflammatory bowel disease. Moreover, GCC immunization failed to promote intestinal carcinogenesis induced by germ-line mutations or chronic inflammation. The established role of CD8(+) T cells in antitumor efficacy, but CD4(+) T cells in autoimmunity, suggests that lineage-specific responses to GCC are particularly advantageous to protect against systemic metastases without mucosal inflammation. These observations support the utility of GCC-targeted immunotherapy in patients at risk for systemic metastases, including those with inflammatory bowel disease, hereditary colorectal cancer syndromes, and sporadic colorectal cancer.