Chronic inflammation of the colon (colitis) is a known risk factor for inflammatory-driven colorectal cancers (id-CRCs), and intestinal microbiota has been implicated in the etiology of id-CRCs. Manipulation of the microbiome is a clinically viable therapeutic approach to limiting id-CRCs. To understand the microbiome changes that occur over time in id-CRCs, we used a mouse model of id-CRCs with the treatment of azoxymethane (AOM) and dextran sodium sulfate (DSS) and measured the microbiome over time. We included cohorts where the microbiome was restored using cage bedding swapping and where the microbiome was depleted using antibiotics to compare to untreated animals. We identified consistent increases in Akkermansia in mice receiving horizontal microbiome transfer (HMT) via cage bedding swapping, while the control cohort had consistent longitudinal increases in Anaeroplasma and Alistipes. Additionally, fecal lipocalin-2 (Lcn-2), a marker of intestinal inflammation, was elevated in unrestored animals compared to restored and antibiotic-treated counterparts following HMT. These observations suggest a potential role for Akkermansia, Anaeroplasma, and Alistipes in regulating colonic inflammation in id-CRCs.

Colorectal cancer (CRC) currently ranks as the third most common cancer in the United States, and its incidence is on the rise, especially among younger individuals. Despite the remarkable success of immune checkpoint inhibitors (ICIs) in various cancers, most CRC patients fail to respond due to intrinsic resistance mechanisms. While microsatellite instability-high phenotypes serve as a reliable positive predictive biomarker for ICI treatment, the majority of CRC patients with microsatellite-stable (MSS) tumors remain ineligible for this therapeutic approach. In this study, we investigated the role of centrosomal protein 55 (CEP55) in shaping the tumor immune microenvironment in CRC. CEP55 is overexpressed in multiple cancer types and was shown to promote tumorigenesis by upregulating the PI3K/AKT pathway. Our data revealed that elevated CEP55 expression in CRC was associated with reduced T cell infiltration, contributing to immune exclusion. As CRC tumors progressed, CEP55 expression increased alongside sequential mutations in crucial driver genes (APC, KRAS, TP53, and SMAD4), indicating its involvement in tumor progression. CEP55 knockout significantly impaired tumor growth in vitro and in vivo, suggesting that CEP55 plays a crucial role in tumorigenesis. Furthermore, the CEP55 knockout increased CD8⁺ T cell infiltration and granzyme B production, indicating improved anti-tumor immunity. Additionally, we observed reduced regulatory T cell infiltration in CEP55 knockout tumors, suggesting diminished immune suppression. Most significantly, CEP55 knockout tumors demonstrated enhanced responsiveness to immune checkpoint inhibition in a clinically relevant orthotopic CRC model. Treatment with anti-PD1 significantly reduced tumor growth in CEP55 knockout tumors compared to control tumors, suggesting that inhibiting CEP55 could improve the efficacy of ICIs. Collectively, our study underscores the crucial role of CEP55 in driving immune exclusion and resistance to ICIs in CRC. Targeting CEP55 emerges as a promising therapeutic strategy to sensitize CRC to immune checkpoint inhibition, thereby improving survival outcomes for CRC patients.

Background Colorectal cancer (CRC) progression is driven by a series of sequential mutations in key driver genes; however, the factors underlying tumor progression and metastasis remain poorly understood. Mutations in TP53 and SMAD4, in particular, are associated with CRC progression. Although gut microbiome dysbiosis is implicated in CRC initiation and progression, the interactions between the microbiome and specific CRC driver mutations, especially those promoting metastasis, are not well defined. Methods In this study, we utilized triple mutant (Apc, Kras, Tp53; AKP) and quadruple mutant (Apc, Kras, Tp53, Smad4; AKPS) organoid-based orthotopic mouse models of CRC to investigate the impact of the SMAD4 mutation on microbiome composition. Results Our results reveal significant differences in metastatic potential and microbial community dynamics between the two tumor models. AKPS tumors exhibited metastasis to the lymph nodes, liver, and lungs, while AKP tumors remained confined to the colon. Longitudinal microbiome analysis showed shifts in microbial composition within each tumor model. Both AKP and AKPS models demonstrated enrichment of Faecalibaculum and a decrease in Dubosiella over time; however, additional shifts were noted with distinct taxa associated with late-stage tumors in each group. Notably, the AKPS model exhibited higher relative abundances of pro-inflammatory taxa, including Turicibacter, Romboutsia, and Akkermansia, suggesting that the SMAD4 mutation promotes a more immunosuppressive and pro-metastatic microbiome profile. Conclusions These findings emphasize the significance of SMAD4 mutation and microbiome modulation, revealing the interaction between host genetics and gut microbiota in driving colorectal cancer aggressiveness and suggesting potential microbial targets.