Silencing the GUCA2A-GUCY2C tumor suppressor axis in CIN, serrated, and MSI colorectal neoplasia

Abstract

Colorectal cancers (CRCs) initiate through distinct mutations, including in APC pathway components leading to tubular adenomas (TAs); in BRAF, with epigenetic silencing of CDX2, leading to serrated adenomas (SAs); and in the DNA mismatch repair machinery driving microsatellite instability (MSI). Transformation through the APC pathway involves loss of the hormone GUCA2A that silences the tumor-suppressing receptor GUCY2C. Indeed, oral hormone replacement is an emerging strategy to reactivate GUCY2C and prevent CRC initiation and progression. Moreover, retained expression by tumors arising from TAs has established GUCY2C as a diagnostic and therapeutic target to prevent and treat metastatic CRC. Here, we defined the potential role of the GUCA2A-GUCY2C axis and its suitability as a target in tumors arising through the SA and MSI pathways. GUCA2A hormone expression was eliminated in TAs, SAs, and MSI tumors compared to their corresponding normal adjacent tissues. In contrast to the hormone, the tumor-suppressing receptor GUCY2C was retained in TA and MSI tumors. Surprisingly, GUCY2C expression was nearly eliminated in SAs, reflecting loss of the transcription factor CDX2. Changes in the GUCA2A-GUCY2C axis in human SAs and MSI tumors were precisely recapitulated in genetic mouse models. These data reveal the possibility of

Silencing the intestinal GUCY2C tumor suppressor axis requires APC loss of heterozygosity

“…Thus, in FAP patients, normal colon epithelia (APC heterozygosity) exhibited robust guanylin expression while adenomas and an invasive carcinoma (biallelic APC loss) were devoid of guanylin expression, confirming previous reports. 33 It is noteworthy that the sample size of FAP patients remains a limitation of this study, and it will be important to confirm these observations in future studies with larger cohorts.…”

“…34 These observations underscore the established pathophysiological association of hormone loss with colorectal tumorigenesis across species. 29,[31][32][33][34] They suggest a role for hormone repression silencing GUCY2C in mechanisms contributing to tumor progression, for example through hyperproliferation, desmoplasia, chromosomal instability, and DNA hyper-mutation, [17][18][19][20][21]33 reflecting dependence of this repression on LOH and APC biallelic loss. 34 Beyond progression, eliminating GUCY2C expression in the Apc min/+ mouse model of genetic transformation increased the incidence and burden of tumors in the colorectum.…”

“…33,34,38 Small differences (~1.75-fold) in GUCY2C mRNA at some stages likely reflect a contribution of tumors arising from the serrated adenoma pathway, in which receptor expression is substantially reduced. 33,38 In close agreement with human samples, uroguanylin and guanylin mRNA and protein were reduced in small intestine and colon, respectively, in mice with Representative PCR genotyping for Guca2b wildtype (3Kb), homozygous knockout (1.5Kb), and heterozygous knockout mice (3Kb and 1.5Kb). (d) Representative PCR genotyping for Guca2a wildtype (3Kb), homozygous knockout (1.3Kb), and heterozygous knockout mice (3Kb and 1.3Kb).…”

“…29,31,32 Moreover, loss of these paracrine hormones occurs universally at the earliest stages of tumorigenesis in mice and humans coincident with APC LOH. 29,[31][32][33][34] In contrast, GUCY2C expression appears to be preserved in most primary and metastatic colorectal tumors. [33][34][35][36][37] In the context of these observations, we explored the hypothesis that paracrine hormone loss, which in turn silences GUCY2C, is an obligatory step contributing to the genetic vulnerability underlying LOH which establishes the premalignant field.…”

A Novel GUCY2C-CD3 T-Cell Engaging Bispecific Construct (PF-07062119) for the Treatment of Gastrointestinal Cancers

“…Given the high potency of CD3 bispecifics, it is important to demonstrate tumor selective activity with an antigen that has minimal or restricted expression in normal tissues. Guanylyl Cyclase C (GUCY2C) is expressed across gastrointestinal malignancies including more than 90% of colorectal cancer across all stages and more than 50% of gastric or gastroesophageal junction cancer (11)(12)(13). GUCY2C is normally involved in maintaining intestinal homeostasis (14) and is activated by the peptide hormones guanylin and uroguanylin (15,16), as well as by the Escherichia coli heat stable (ST) enterotoxin, which causes familial diarrhea (17,18).…”