Microsatellite instability-high colorectal cancer patient-derived xenograft models for cancer immunity research

Combination of multiple omics techniques for a personalized therapy or treatment selection

Despite targeted therapies and immunotherapies have revolutionized the treatment of cancer patients, only a limited number of patients have long-term responses. Moreover, due to differences within cancer patients in the tumor mutational burden, composition of the tumor microenvironment as well as of the peripheral immune system and microbiome, and in the development of immune escape mechanisms, there is no "one fit all" therapy. Thus, the treatment of patients must be personalized based on the specific molecular, immunologic and/or metabolic landscape of their tumor. In order to identify for each patient the best possible therapy, different approaches should be employed and combined. These include (i) the use of predictive biomarkers identified on large cohorts of patients with the same tumor type and (ii) the evaluation of the individual tumor with "omics"-based analyses as well as its ex vivo characterization for susceptibility to different therapies.

TSPYL5 inhibits the tumorigenesis of colorectal cancer cells in vivo by triggering DNA damage

Context

Testis-specific protein Y-encoded-like 5 (TSPYL5) suppresses several cancers in vivo, including colorectal cancer (CRC); however, its mechanism and role in CRC cell tumorigenesis in vivo remain unknown.

Aims

To elucidate the molecular mechanisms of colorectal cancer and find new therapeutic targets to improve CRC patient outcomes.

Settings and Design

Male mice (4 weeks old, 16-22 g) were housed in sterile cages in a temperature-controlled room (20-25°C) with a 12 h light/dark cycle and ad libitum food and water.

Methods and Materials

TSPYL5 overexpressing or non-overexpressing HCT116 cells were used to create a nude mouse tumor model. Tumor tissue was evaluated histologically after hematoxylin and eosin (H and E) staining. TUNEL staining assessed tumor cell apoptosis. Ki67 expression in excised tumor tissue was measured by immunohistochemistry. Western blotting examined double-stranded break (DBS)-associated protein expression in vivo.

Statistical Analysis Used

IBM SPSS Statistics for Windows, Version 21.0 was used for all analyses (IBM Corp., Armonk, NY, USA). At least three independent experiments yield a mean value ± standard deviation. Unpaired Student's t-tests compared groups. One-way analysis of variance and Dunnett's test were used to compare groups with a P value < 0.5.

Results

TSPYL5 overexpression inhibited CRC cell tumorigenicity and damaged tumor cells in vivo. TSPYL5 overexpression also significantly increased Bax and p-H2AX (early double-stranded break indicators) and decreased Ki67, Bcl-2, and peroxisome proliferator-activated receptor expression.

Conclusions

Collectively, TSPYL5 overexpression inhibited the tumorigenicity of CRC cells in vivo by inducing DNA damage.

Immune escape and resistance to immunotherapy in mismatch repair deficient tumors

Up to 30% of colorectal, endometrial and gastric cancers have a deficiency in mismatch repair (MMR) protein expression due to either germline or epigenetic inactivation. Patients with Lynch Syndrome who inherit an inactive MMR allele have an up to 80% risk for developing a mismatch repair deficient (MMRd) cancer. Due to an inability to repair DNA, MMRd tumors present with genomic instability in microsatellite regions (MS). Tumors with high MS instability (MSI-H) are characterized by an increased frequency of insertion/deletions (indels) that can encode novel neoantigens if they occur in coding regions. The high tumor antigen burden for MMRd cancers is accompanied by an inflamed tumor microenvironment (TME) that contributes to the clinical effectiveness of anti-PD-1 therapy in this patient population. However, between 40 and 70% of MMRd cancer patients do not respond to treatment with PD-1 blockade, suggesting that tumor-intrinsic and -extrinsic resistance mechanisms may affect the success of checkpoint blockade. Immune evasion mechanisms that occur during early tumorigenesis and persist through cancer development may provide a window into resistance pathways that limit the effectiveness of anti-PD-1 therapy. Here, we review the mechanisms of immune escape in MMRd tumors during development and checkpoint blockade treatment, including T cell dysregulation and myeloid cell-mediated immunosuppression in the TME. Finally, we discuss the development of new therapeutic approaches to tackle resistance in MMRd tumors, including cancer vaccines, therapies targeting immunosuppressive myeloid programs, and immune checkpoint combination strategies.

Patient-derived xenograft models in cancer therapy: technologies and applications

Patient-derived xenograft (PDX) models, in which tumor tissues from patients are implanted into immunocompromised or humanized mice, have shown superiority in recapitulating the characteristics of cancer, such as the spatial structure of cancer and the intratumor heterogeneity of cancer. Moreover, PDX models retain the genomic features of patients across different stages, subtypes, and diversified treatment backgrounds. Optimized PDX engraftment procedures and modern technologies such as multi-omics and deep learning have enabled a more comprehensive depiction of the PDX molecular landscape and boosted the utilization of PDX models. These irreplaceable advantages make PDX models an ideal choice in cancer treatment studies, such as preclinical trials of novel drugs, validating novel drug combinations, screening drug-sensitive patients, and exploring drug resistance mechanisms. In this review, we gave an overview of the history of PDX models and the process of PDX model establishment. Subsequently, the review presents the strengths and weaknesses of PDX models and highlights the integration of novel technologies in PDX model research. Finally, we delineated the broad application of PDX models in chemotherapy, targeted therapy, immunotherapy, and other novel therapies.

Recent advances in the development of transplanted colorectal cancer mouse models

Despite progress in prevention and treatment, colorectal cancer (CRC) remains the third most common malignancy worldwide and the second most common cause of cancer death in 2020. To evaluate various characteristics of human CRC, a variety of mouse models have been established. Transplant mouse models have distinct advantages in studying the clinical behavior and therapeutic progress of CRC. Host, xenograft, and transplantation routes are the basis of transplant mouse models. As the effects of the tumor microenvironment and the systemic environment on cancer cells are gradually revealed, 3 key elements of transplanted CRC mouse models have been revolutionized. This has led to the development of humanized mice, patient-derived xenografts, and orthotopic transplants that reflect the human systemic environment, patient's tumor of origin, and tumor growth microenvironments in immunodeficient mice, respectively. These milestone events have allowed for great progress in tumor biology and the treatment of CRC. This article reviews the evolution of these events and points out their strengths and weaknesses as innovative and useful preclinical tools to study CRC progression and metastasis and to exploit novel treatment schedules by establishing a testing platform. This review article depicts the optimal transplanted CRC mouse models and emphasizes the significance of surgical models in the study of CRC behavior and treatment response.