Novel Tumor Organoid-Based Mouse Model to Study Image Guided Radiation Therapy of Rectal Cancer After Noninvasive and Precise Endoscopic Implantation.

PURPOSE: Preoperative (neoadjuvant) radiation therapy (RT) is an essential part of multimodal rectal cancer therapy. Recently, total neoadjuvant therapy (TNT), which combines simultaneous radiochemotherapy with additional courses of chemotherapy, has emerged as an effective approach. TNT achieves a pathologic complete remission in approximately 30% of resected patients, opening avenues for treatment strategies that avoid radical organ resection. Furthermore, recent studies have demonstrated that anti-programmed cell death protein 1 immunotherapy can induce clinical complete responses in patients with specific genetic alterations. There is significant potential to enhance outcomes through intensifying, personalizing, and de-escalating treatment approaches. However, the heterogeneous response rates to RT or TNT and strategies to sensitize patients without specific genetic changes to immunotherapy remain poorly understood. METHODS AND MATERIALS: We developed a novel orthotopic mouse model of rectal cancer based on precisely defined endoscopic injections of tumor organoids that reflect tumor heterogeneity. Subsequently, we employed endoscopic- and computed tomography-guided RT and validated rectal tumor growth and response rates to therapy using small-animal magnetic resonance imaging and endoscopic follow-up. RESULTS: Rectal tumor formation was successfully induced in all mice after 2 organoid injections. Clinically relevant RT regimens with 5 × 5 Gy significantly delayed clinical signs of tumor progression and significantly improved survival. Consistent with human disease, rectal tumor progression correlated with the development of liver and lung metastases. Notably, long-term survivors after RT showed no evidence of tumor recurrence, as demonstrated by in vivo radiologic tumor staging and histopathologic examination. CONCLUSIONS: Our novel mouse model combines orthotopic tumor growth via noninvasive and precise rectal organoid injection and small-animal RT. This model holds significant promise for investigating the effect of tumor cell-intrinsic aspects, genetic alterations of the host, and exogenous factors (eg, nutrition or microbiota) on RT outcomes. Furthermore, it allows for the exploration of combination therapies involving chemotherapy, immunotherapy, or novel targeted therapies.

SMAD4 Loss Induces c-MYC-Mediated NLE1 Upregulation to Support Protein Biosynthesis, Colorectal Cancer Growth, and Metastasis.

Growth and metastasis of colorectal cancer is closely connected to the biosynthetic capacity of tumor cells, and colorectal cancer stem cells that reside at the top of the intratumoral hierarchy are especially dependent on this feature. By performing disease modeling on patient-derived tumor organoids, we found that elevated expression of the ribosome biogenesis factor NLE1 occurs upon SMAD4 loss in TGFß1-exposed colorectal cancer organoids. TGFß signaling-mediated downregulation of NLE1 was prevented by ectopic expression of c-MYC, which occupied an E-box-containing region within the NLE1 promoter. Elevated levels of NLE1 were found in colorectal cancer cohorts compared with normal tissues and in colorectal cancer subtypes characterized by Wnt/MYC and intestinal stem cell gene expression. In colorectal cancer cells and organoids, NLE1 was limiting for de novo protein biosynthesis. Upon NLE1 ablation, colorectal cancer cell lines activated p38/MAPK signaling, accumulated p62- and LC3-positive structures indicative of impaired autophagy, and displayed more reactive oxygen species. Phenotypically, knockout of NLE1 inhibit.ed proliferation, migration and invasion, clonogenicity, and anchorage-independent growth. NLE1 loss also increased the fraction of apoptotic tumor cells, and deletion of TP53 further sensitized NLE1-deficient colorectal cancer cells to apoptosis. In an endoscopy-guided orthotopic mouse transplantation model, ablation of NLE1 impaired tumor growth in the colon and reduced primary tumor-derived liver metastasis. In patients with colorectal cancer, NLE1 mRNA levels predicted overall and relapse-free survival. Taken together, these data reveal a critical role of NLE1 in colorectal cancer growth and progression and suggest that NLE1 represents a potential therapeutic target in colorectal cancer patients. SIGNIFICANCE: NLE1 limits de novo protein biosynthesis and the tumorigenic potential of advanced colorectal cancer cells, suggesting NLE1 could be targeted to improve the treatment of metastatic colorectal cancer.