Guanylyl cyclase C: a molecular marker for staging and postoperative surveillance of patients with colorectal cancer

The Role of the Tumor Microenvironment and Treatment Strategies in Colorectal Cancer

Colorectal cancer (CRC) has the second highest mortality rate among all cancers worldwide. Surgery, chemotherapy, radiotherapy, molecular targeting and other treatment methods have significantly prolonged the survival of patients with CRC. Recently, the emergence of tumor immunotherapy represented by immune checkpoint inhibitors (ICIs) has brought new immunotherapy options for the treatment of advanced CRC. As the efficacy of ICIs is closely related to the tumor immune microenvironment (TME), it is necessary to clarify the relationship between the immune microenvironment of CRC and the efficacy of immunotherapy to ensure that the appropriate drugs are selected. We herein review the latest research progress in the immune microenvironment and strategies related to immunotherapy for CRC. We hope that this review helps in the selection of appropriate treatment strategies for CRC patients.

GUCY2C as a biomarker to target precision therapies for patients with colorectal cancer

Introduction

Colorectal cancer (CRC) is one of the most-deadly malignancies worldwide. Current therapeutic regimens for CRC patients are relatively generic, based primarily on disease type and stage, with little variation. As the field of molecular oncology advances, so too must therapeutic management of CRC. Understanding molecular heterogeneity has led to a new-found promotion for precision therapy in CRC; underlining the diversity of molecularly targeted therapies based on individual tumor characteristics.

Areas covered

We review current approaches for the treatment of CRC and discuss the potential of precision therapy in advanced CRC. We highlight the utility of the intestinal protein guanylyl cyclase C (GUCY2C), as a multi-purpose biomarker and unique therapeutic target in CRC. Here, we summarize current GUCY2C-targeted approaches for treatment of CRC.

Expert opinion

The GUCY2C biomarker has multi-faceted utility in medicine. Developmental investment of GUCY2C as a diagnostic and therapeutic biomarker offers a variety of options taking the molecular characteristics of cancer into account. From GUCY2C-targeted therapies, namely cancer vaccines, CAR-T cells, and monoclonal antibodies, to GUCY2C agonists for chemoprevention in those who are at high risk for developing colorectal cancer, the utility of this protein provides many avenues for exploration with significance in the field of precision medicine.

Monoclonal antibodies and chimeric antigen receptor (CAR) T cells in the treatment of colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of cancer deaths worldwide. Besides common therapeutic approaches, such as surgery, chemotherapy, and radiotherapy, novel therapeutic approaches, including immunotherapy, have been an advent in CRC treatment. The immunotherapy approaches try to elicit patients` immune responses against tumor cells to eradicate the tumor. Monoclonal antibodies (mAbs) and chimeric antigen receptor (CAR) T cells are two branches of cancer immunotherapy. MAbs demonstrate the great ability to completely recognize cancer cell-surface receptors and blockade proliferative or inhibitory pathways. On the other hand, T cell activation by genetically engineered CAR receptor via the TCR/CD3 and costimulatory domains can induce potent immune responses against specific tumor-associated antigens (TAAs). Both of these approaches have beneficial anti-tumor effects on CRC. Herein, we review the different mAbs against various pathways and their applications in clinical trials, the different types of CAR-T cells, various specific CAR-T cells against TAAs, and their clinical use in CRC treatment.

CAR-T cells for Colorectal Cancer: Target-selection and strategies for improved activity and safety

Chimeric antigen receptor-T (CAR-T) cell immunotherapy is a novel method that is genetically engineered to recruit T cells against malignant disease. Administration of CAR-T cells has led to progress in hematological malignancies, and it has been proposed for solid tumors like colorectal cancer (CRC) for years. However, this method was not living up to expectations for the intrinsic challenges posed to CAR-T cells by solid tumors, which mainly due to the lacking of tumor-restricted antigens and adverse effects following treatment. New approaches are proposed to overcome the multiple challenges to alleviate the difficult situation of CAR-T cells in CRC, including engineering T cells with immune-activating molecules, regional administration of T cell, bispecific T cell engager, and combinatorial target-antigen recognition. In this review, we sum up the current stage of knowledge about target-selection, adverse events like on/off-tumor toxicity, the preclinical and clinical studies of CAR-T therapy, and the characteristics of strategies applied in CRC.

Two distinct GUCY2C circuits with PMV (hypothalamic) and SN/VTA (midbrain) origin

Guanylyl cyclase C (GUCY2C) is the afferent central receptor in the gut-brain endocrine axis regulated by the anorexigenic intestinal hormone uroguanylin. GUCY2C mRNA and protein are produced in the hypothalamus, a major center regulating appetite and metabolic homeostasis. Further, GUCY2C mRNA and protein are expressed in the ventral midbrain, a principal structure regulating hedonic reward from behaviors including eating. While GUCY2C is expressed in hypothalamus and midbrain, its precise neuroanatomical organization and relationship with circuits regulating satiety remain unknown. Here, we reveal that hypothalamic GUCY2C mRNA is confined to the ventral premammillary nucleus (PMV), while in midbrain it is produced by neurons in the ventral tegmental area (VTA) and substantia nigra (SN). GUCY2C in the PMV is produced by 46% of neurons expressing anorexigenic leptin receptors, while in the VTA/SN it is produced in most tyrosine hydroxylase-immunoreactive neurons. In contrast to mRNA, GUCY2C protein is widely distributed throughout the brain in canonical sites of PMV and VTA/SN axonal projections. Selective stereotaxic ablation of PMV or VTA/SN neurons eliminated GUCY2C only in their respective canonical projection sites. Conversely, specific anterograde tracer analyses of PMV or VTA/SN neurons confirmed distinct GUCY2C-immunoreactive axons projecting to those canonical locations. Together, these findings reveal two discrete neuronal circuits expressing GUCY2C originating in the PMV in the hypothalamus and in the VTA/SN in midbrain, which separately project to other sites throughout the brain. They suggest a structural basis for a role for the GUCY2C-uroguanylin gut-brain endocrine axis in regulating homeostatic and behavioral components contributing to satiety.

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.

TCR Retrogenic Mice as a Model To Map Self-Tolerance Mechanisms to the Cancer Mucosa Antigen GUCY2C

Characterizing self-tolerance mechanisms and their failure is critical to understand immune homeostasis, cancer immunity, and autoimmunity. However, examination of self-tolerance mechanisms has relied primarily on transgenic mice expressing TCRs targeting well-characterized, but nonphysiologic, model Ags, such as OVA and hemagglutinin. Identifying TCRs directed against bona fide self-antigens is made difficult by the extraordinary diversity of TCRs and the low prevalence of Ag-specific clones (<10-100 naive cells per organism), limiting dissection of tolerance mechanisms restricting immunity to self-proteins. In this study, we isolated and characterized TCRs recognizing the intestinal epithelial cell receptor and colorectal cancer Ag GUCY2C to establish a model to study self-antigen-specific tolerance mechanisms. GUCY2C-specific CD4+ effector T cells were isolated from immunized, nontolerant Gucy2c -/- mice. Next-generation sequencing identified GUCY2C-specific TCRs, which were engineered into CD4+ T cells in vitro to confirm TCR recognition of GUCY2C. Further, the generation of "retrogenic" mice by reconstitution with TCR-transduced hematopoietic stem cells resulted in normal CD4+ T cell development, responsiveness to immunization, and GUCY2C-induced tolerance in recipient mice, recapitulating observations in conventional models. This retrogenic model can be employed to define self-tolerance mechanisms restricting T and B cell responses to GUCY2C to optimize colorectal cancer immunotherapy without autoimmunity.

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.

Consistent expression of guanylyl cyclase-C in primary and metastatic gastrointestinal cancers

BACKGROUND

The transmembrane receptor guanylate cyclase-C (GCC) has been found to be expressed in colorectal cancers. However, limited data are available on GCC protein expression in non-colorectal gastrointestinal tumors and few studies have reported whether GCC protein expression was consistently preserved in synchronous primary and metastatic cancer tissues.

METHODS

GCC protein status was assessed by immunohistochemistry in tumor specimens from individuals (n = 627) with gastrointestinal tumors, including esophageal (n = 130), gastric (n = 276), pancreatic (n = 136), and colorectal (n = 85) primary and metastatic tumors. Tissue specimens consisted of tissue microarrays containing esophageal, gastric, pancreatic tumors, and whole-slide tissue sections from colorectal cancer patients with matching primary and metastatic tumors.

RESULT

Among the evaluated esophageal, gastric, and pancreatic tumors, the frequency of GCC positivity at the protein level ranged from 59% to 68%. GCC was consistently expressed in primary and matched/synchronous metastatic lesions of colorectal cancer tissues derived from the same patients.

CONCLUSION

This observational study demonstrated the protein expression of GCC across various gastrointestinal malignancies. In all cancer histotypes, GCC protein localization was observed predominantly in the cytoplasm compared to the membrane region of tumor cells. Consistent immunohistochemistry detection of GCC protein expression in primary colorectal cancers and in their matched liver metastases suggests that the expression of GCC is maintained throughout the process of tumor progression and formation of metastatic disease.

The Heat-Stable Enterotoxin Receptor, Guanylyl Cyclase C, as a Pharmacological Target in Colorectal Cancer Immunotherapy: A Bench-to-Bedside Current Report

Cancer immunotherapy is becoming a routine treatment modality in the oncology clinic, in spite of the fact that it is a relatively nascent field. The challenge in developing effective immunotherapeutics is the identification of target molecules that promote anti-tumor efficacy across the patient population while sparing healthy tissue from damaging autoimmunity. The intestinally restricted receptor guanylyl cyclase C (GUCY2C) is a target that has been investigated for the treatment of colorectal cancer and numerous animal, and clinical studies have demonstrated both efficacy and safety. Here, we describe the current state of GUCY2C-directed cancer immunotherapy and the future directions of this work.

Preclinical Evaluation of a Replication-Deficient Recombinant Adenovirus Serotype 5 Vaccine Expressing Guanylate Cyclase C and the PADRE T-helper Epitope

There is an unmet need for improved therapeutics for colorectal cancer, the second leading cause of cancer mortality worldwide. Adjuvant chemotherapy only marginally improves survival in some patients and has no benefit in others, underscoring the clinical opportunity for novel immunotherapeutic approaches to improve survival in colorectal cancer. In that context, guanylate cyclase C (GUCY2C) is an established biomarker and therapeutic target for metastatic colorectal cancer with immunological characteristics that promote durable antitumor efficacy without autoimmunity. Preliminary studies established non-replicating human type 5 adenovirus (Ad5) expressing GUCY2C as safe and effective to induce GUCY2C-specific immune responses and antitumor immunity in mice. This study characterized the biodistribution, immunogenicity, and safety of a vector expressing GUCY2C fused with the human CD4⁺ T helper cell epitope PADRE (Ad5-GUCY2C-PADRE) to advance this vaccine into clinical trials in colorectal cancer patients. Ad5-GUCY2C-PADRE levels were highest in the injection site and distributed in vivo primarily to draining lymph nodes, the liver, spleen and, unexpectedly, to the bone marrow. Immune responses following Ad5-GUCY2C-PADRE administration were characterized by PADRE-specific CD4⁺ T-cell and GUCY2C-specific B-cell and CD8⁺ T-cell responses, producing antitumor immunity targeting GUCY2C-expressing colorectal cancer metastases in the lungs, without acute or chronic autoimmune or other toxicities. Collectively, these data support Ad5-GUCY2C-PADRE as a safe and effective vaccination strategy in preclinical models and position Ad5-GUCY2C-PADRE for Phase I clinical testing in colorectal cancer patients.

CAR-T cell therapy in gastrointestinal tumors and hepatic carcinoma: From bench to bedside

The chimeric antigen receptor (CAR) is a genetically engineered receptor that combines a scFv domain, which specifically recognizes the tumor-specific antigen, with T cell activation domains. CAR-T cell therapies have demonstrated tremendous efficacy against hematologic malignancies in many clinical trials. Recent studies have extended these efforts to the treatment of solid tumors. However, the outcomes of CAR-T cell therapy for solid tumors are not as remarkable as the outcomes have been for hematologic malignancies. A series of hurdles has arisen with respect to CAR-T cell-based immunotherapy, which needs to be overcome to target solid tumors. The major challenge for CAR-T cell therapy in solid tumors is the selection of the appropriate specific antigen to demarcate the tumor from normal tissue. In this review, we discuss the application of CAR-T cells to gastrointestinal and hepatic carcinomas in preclinical and clinical research. Furthermore, we analyze the usefulness of several specific markers in the study of gastrointestinal tumors and hepatic carcinoma.

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.

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.

Selective antigen-specific CD4(+) T-cell, but not CD8(+) T- or B-cell, tolerance corrupts cancer immunotherapy

Self-tolerance, presumably through lineage-unbiased elimination of self-antigen-specific lymphocytes (CD4(+) T, CD8(+) T, and B cells), creates a formidable barrier to cancer immunotherapy. In contrast to this prevailing paradigm, we demonstrate that for some antigens, self-tolerance reflects selective elimination of antigen-specific CD4(+) T cells, but preservation of CD8(+) T- and B-cell populations. In mice, antigen-specific CD4(+) T-cell tolerance restricted CD8(+) T- and B-cell responses targeting the endogenous self-antigen guanylyl cyclase c (GUCY2C) in colorectal cancer. Although selective CD4(+) T-cell tolerance blocked GUCY2C-specific antitumor immunity and memory responses, it offered a unique solution to the inefficacy of GUCY2C vaccines through recruitment of self-antigen-independent CD4(+) T-cell help. Incorporating CD4(+) T-cell epitopes from foreign antigens into vaccines against GUCY2C reconstituted CD4(+) T-cell help, revealing the latent functional capacity of GUCY2C-specific CD8(+) T- and B-cell pools, producing durable antitumor immunity without autoimmunity. Incorporating CD4(+) T-cell epitopes from foreign antigens into vaccines targeting self-antigens in melanoma (Trp2) and breast cancer (Her2) produced similar results, suggesting selective CD4(+) T-cell tolerance underlies ineffective vaccination against many cancer antigens. Thus, identification of self-antigens characterized by selective CD4(+) T-cell tolerance and abrogation of such tolerance through self-antigen-independent T-cell help is essential for future immunotherapeutics.

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.

Immunotherapeutic strategies to target prognostic and predictive markers of cancer

Throughout the last century medical advances in cancer treatment in the fields of surgery, radiation therapy and chemotherapy have greatly impacted patients' survival rates. Nevertheless, cancer remains a significant cause of mortality, with an estimated 7.6 million deaths worldwide in 2008, reflecting the inability of existing therapies to effectively cure disease. The emergence of vaccines and their successes in preventing the spread of infectious diseases has demonstrated the unique specificity and therapeutic potential of the immune system. This potential has driven the development of novel cancer immunotherapeutics. This review focuses on the current status of the use of immunologic effectors to target known biomarkers in cancer.

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.

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.

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.

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.

Gene Expression of Mesenchyme Forkhead 1 (FOXC2) Significantly Correlates With the Degree of Lymph Node Metastasis in Colorectal Cancer

In stage III colorectal cancer, patients with N1 stage tumors show poorer outcome than patients with N2 stage tumors. Our objective was to identify genes that are predictive for the presence of lymph node metastasis, and to characterize the aggressiveness of lymph node metastases. Gene expression profiles of colorectal cancer were determined by microarray in training (n  =  116) and test (n  =  25) sets of patients. We identified 40 discriminating probes in patients with and without lymph node metastases. Using these probes, we could predict the presence of lymph node metastasis with an accuracy of 87.1% (training set) and 76.0% (test set). Among discriminating probes, FOXC2 expression was significantly correlated with the degree of lymph node metastasis. FOXC2 was expressed significantly and disparately in patients with N1 and N2 stage tumors as analyzed by real-time reverse transcriptase–polymerase chain reaction. FOXC2 appears to be involved in determining the aggressiveness of lymph node metastasis in colorectal cancer.

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.

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.

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.

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.

Association of GUCY2C expression in lymph nodes with time to recurrence and disease-free survival in pN0 colorectal cancer

CONTEXT

The established relationship between lymph node metastasis and prognosis in colorectal cancer suggests that recurrence in 25% of patients with lymph nodes free of tumor cells by histopathology (pN0) reflects the presence of occult metastases. Guanylyl cyclase 2C (GUCY2C) is a marker expressed by colorectal tumors that could reveal occult metastases in lymph nodes and better estimate recurrence risk.

OBJECTIVE

To examine the association of occult lymph node metastases detected by quantifying GUCY2C messenger RNA, using the reverse transcriptase-polymerase chain reaction, with recurrence and survival in patients with colorectal cancer.

DESIGN, SETTING, AND PARTICIPANTS

Prospective study of 257 patients with pN0 colorectal cancer enrolled between March 2002 and June 2007 at 9 US and Canadian centers (7 academic medical centers and 2 community hospitals) provided 2570 fresh lymph nodes measuring 5 mm or larger for histopathology and GUCY2C messenger RNA analysis. Patients were followed up for a median of 24 months (range, 2-63 months) for disease recurrence or death.

MAIN OUTCOME MEASURES

Time to recurrence (primary outcome) and disease-free survival (secondary outcome) relative to expression of GUCY2C in lymph nodes.

RESULTS

Thirty-two patients (12.5%) had lymph nodes negative for GUCY2C (pN0 [mol-]), and all but 2 remained free of disease during follow-up (recurrence rate, 6.3%; 95% confidence interval [CI], 0.8%-20.8%). Conversely, 225 patients (87.5%) had lymph nodes positive for GUCY2C (pN0 [mol+]), and 47 developed recurrent disease (20.9%; 95% CI, 15.8%-26.8%) (P = .006). Multivariate analyses revealed that GUCY2C in lymph nodes was an independent marker of prognosis. Patients who were pN0 (mol+) exhibited earlier time to recurrence (adjusted hazard ratio, 4.66; 95% CI, 1.11-19.57; P = .04) and reduced disease-free survival (adjusted hazard ratio, 3.27; 95% CI, 1.15-9.29; P = .03).

CONCLUSION

Expression of GUCY2C in histologically negative lymph nodes appears to be independently associated with time to recurrence and disease-free survival in patients with pN0 colorectal cancer.

Previstage GCC test for staging patients with colorectal cancer

The presence of tumor cells in regional lymph nodes is the most important prognostic and predictive marker in staging patients with colorectal cancer. Cancer cells in lymph nodes are associated with a poorer prognosis and an increased risk of recurrent disease. Additionally, nodal metastases identify patients who derive maximum benefit from adjuvant therapy. However, traditional paradigms for staging patients with colorectal cancer underestimate the extent of metastases and patients whose lymph nodes are ostensibly free of tumor cells by histopathology (pN0) have a 25-30% risk of developing recurrent disease, reflected by the presence of occult nodal metastases. These observations underscore the unmet clinical need for molecular approaches to accurately detect metastatic disease and identify patients at risk for disease relapse that could benefit from adjuvant chemotherapy. Detection of disease-specific mRNA targets as prognostic and predictive markers employing quantitative reverse transcription (qRT)-PCR is an emerging technology that has become a benchmark for individualization of patient management. However, to date, applications of qRT-PCR to detecting occult nodal metastases in colorectal cancer have been equivocal, reflecting markers with suboptimal sensitivity and specificity; limitations of utilizing qualitative, rather than quantitative, RT-PCR; and underpowered study designs based on inadequate patient populations. In that context, guanylyl cyclase C (GCC) is the most sensitive and specific biomarker for metastatic colorectal cancer in extra-intestinal tissues. GCC qRT-PCR detects occult metastases in lymph nodes, providing the most powerful independent prognostic information for predicting disease recurrence in pN0 patients in prospective multicenter clinical trials. This technology forms the basis for the Previstagetrade mark GCC Colorectal Cancer Staging Test encompassing a proprietary multiplex qRT-PCR assay compatible with formalin-fixed, paraffin-embedded lymph nodes for detecting occult metastases. Previstage GCC is a new diagnostic tool that may improve the accuracy of staging, prognosis of clinical outcomes and prediction of therapeutic responses to adjuvant therapy, representing a key advance in the management of patients with colorectal cancer.

Guanylyl cyclase C-induced immunotherapeutic responses opposing tumor metastases without autoimmunity

BACKGROUND

One of the greatest impediments to cancer immunotherapy is the paucity of antigens that are tumor specific, sufficiently immunogenic, and shared among patients. Mucosa-restricted antigens that are expressed by tumor cells represent a novel class of vaccine targets that are characterized by immunologic privilege, which limits systemic tolerance to those antigens, and immunologic partitioning, which shields mucosae from systemic autoimmune responses. Here we defined the immunogenicity and antitumor efficacy of guanylyl cyclase C (GCC), a protein that is normally restricted to intestinal mucosa and universally expressed by metastatic colorectal cancer.

METHODS

BALB/c mice (n = 197) were immunized with recombinant GCC-expressing viral vectors before (prophylactic) or after (therapeutic) a lethal challenge of GCC-expressing mouse colon cancer cells, and antitumor efficacy was monitored by quantifying metastasis and survival. Induction of autoimmunity was monitored by histopathology. Induction of GCC-specific B-cell and CD4(+) and CD8(+) T-cell responses were determined by enzyme-linked immunosorbent assay and ELISpot, respectively. Tolerance to GCC was quantified by comparing responses in GCC-deficient (n = 45) and wild-type (n = 69) C57BL/6 mice. Statistical tests were two-sided.

RESULTS

Immunization with GCC-expressing viral vectors reduced the formation of metastases to liver (control vs GCC: mean = 30.4 vs 3.55 nodules, difference = 26.9 nodules, 95% confidence interval [CI] = 8.47 to 45.3 nodules; P = .008) and lung (control vs GCC: mean = 263 vs 55.7 nodules, difference = 207, 95% CI = 163 to 251; P < .001) and extended the median survival of mice with established lung metastases following therapeutic immunization (control vs GCC: 29 vs 38 days, P = .024), without autoimmunity. Antitumor efficacy reflected asymmetrical tolerance that was characterized by CD8(+) T-cell, but not CD4(+) T-cell or antibody, responses.

CONCLUSIONS

Immunologic partitioning together with immunologic privilege highlight the potential of mucosa-restricted antigens, particularly GCC, as therapeutic targets for metastatic cancer.

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

PURPOSE

Guanylyl cyclase C (GCC), a receptor for bacterial diarrheagenic enterotoxins, may be a prognostic and predictive marker to detect occult micrometastases in patients undergoing staging for colorectal cancer. However, quantification of GCC expression in tissues by the quantitative reverse transcription-PCR (qRT-PCR) has not undergone analytic and clinicopathologic validation.

EXPERIMENTAL DESIGN

A technique to quantify GCC mRNA in tissues employing RT-PCR was developed and validated employing external calibration standards of RNA complementary to GCC.

RESULTS

GCC qRT-PCR exhibited reaction efficiencies >92%, coefficients of variations <5%, linearity >6 orders of magnitude, and a limit of quantification of >25 copies of GCC cRNA. This assay confirmed that GCC mRNA was overexpressed by colorectal tumors from 41 patients, which correlated with increased GCC protein quantified by immunohistochemistry. Analyses obtained with 164 lymph nodes from patients free of cancer and 15 nodes harboring metastases established a threshold for metastatic disease of approximately 200 GCC mRNA copies/mug total RNA, with a sensitivity of 93% and specificity of 97%. GCC mRNA above that threshold was detected in 76 of 367 (approximately 21%) nodes free of disease by histopathology from 6 of 23 (26%) patients, suggesting the presence of occult micrometastases.

CONCLUSIONS

Quantifying GCC mRNA in tissues by RT-PCR employing external calibration standards is analytically robust and reproducible, with high clinicopathologic sensitivity and specificity. This validated assay is being applied to approximately 10,000 lymph nodes in a prospective trial to define the sensitivity of GCC qRT-PCR for staging patients with colorectal cancer.

Mucosally restricted antigens as novel immunological targets for antitumor therapy

Colorectal cancer is the third most common malignancy and the second most common cause of cancer-related mortality worldwide. While surgery remains the mainstay of therapy, approximately 50% of persons who undergo resection develop parenchymal metastatic disease. Unfortunately, current therapeutic regimens offer little improvement in survival. Using immunotherapy to fill this therapeutic gap has enjoyed limited success, reflecting a paucity of tumor-associated antigens. In that context, there is a significant unrealized opportunity to exploit structural and functional immune system compartmentalization to generate a therapeutic immune response against metastatic colorectal tumors employing biomarkers whose expression is normally confined to intestinal epithelial cells and their derivative malignancies. This novel class of biomarkers, here termed cancer mucosa antigens, may fill the unmet therapeutic need for colorectal cancer-associated immune targets. As a concrete example, guanylyl cyclase C is an intestinal mucosa-specific biomarker ideally suited to test this hypothesis and serve as the first cancer mucosa antigen for colorectal cancer immunotherapy. Here, we discuss colorectal cancer immunity, immune compartmentalization and preliminary results targeting guanylyl cyclase C in mouse models of colorectal cancer, as well as the potential paradigm shift to employing cancer mucosa antigens in immunotherapy of colorectal cancer.

Guanylin peptides and colorectal cancer (CRC)

Agonists of guanylyl-C receptor, such as guanylin/uroguanylin, are correlated not only with the intestinal cell epithelial physiology but also with the colorectal cancer tumorigenesis. Activation of the second intracellular messenger cyclic guanosine monophosphate by guanylyl cyclase-C receptor results in a complex intracellular signalling cascade involving the phosphodiesterase, the ion channels and the protein kinase. After an analytical review of relevant new knowledge, new diagnostic and therapeutic approaches for colorectal cancer are discussed.

Applications of nanoparticles to diagnostics and therapeutics in colorectal cancer

Nanotechnology has considerable promise for the detection, staging and treatment of cancer. Here, we outline one such promising application: the use of nanostructures with surface-bound ligands for the targeted delivery and ablation of colorectal cancer (CRC), the third most common malignancy and the second most common cause of cancer-related mortality in the US. Normal colonic epithelial cells as well as primary CRC and metastatic tumors all express a unique surface-bound guanylyl cyclase C (GCC), which binds the diarrheagenic bacterial heat-stable peptide enterotoxin ST. This makes GCC a potential target for metastatic tumor ablation using ST-bound nanoparticles in combination with thermal ablation with near-infrared or radiofrequency energy absorption. Furthermore, the incorporation of iron or iron oxide into such structures would provide advantages for magnetic resonance imaging (MRI). Although the scenarios outlined in this article are hypothetical, they might stimulate ideas about how other cancers could be attacked using nanotechnology.