Targeted therapies, chemotherapy, and immunotherapy are used to treat patients with mismatch repair–deficient (dMMR)/microsatellite instability-high (MSI-H) colorectal cancer. The clinical effectiveness of targeted therapy and chemotherapy is limited by resistance and drug toxicities, and about half of patients receiving immunotherapy have disease that is refractory to immune checkpoint inhibitors. Loss of Werner syndrome ATP-dependent helicase (WRN) is a synthetic lethality in dMMR/MSI-H cells. To inform the development of WRN as a therapeutic target, we performed WRN knockout or knockdown in 60 heterogeneous dMMR colorectal cancer preclinical models, demonstrating that WRN dependency is an almost universal feature and a robust marker for patient selection. Furthermore, models of resistance to clinically relevant targeted therapy, chemotherapy, and immunotherapy retain WRN dependency. These data show the potential of therapeutically targeting WRN in patients with dMMR/MSI-H colorectal cancer and support WRN as a therapeutic option for patients with dMMR/MSI-H cancers refractory to current treatment strategies. Significance: We found that a large, diverse set of dMMR/MSI-H colorectal cancer preclinical models, including models of treatment-refractory disease, are WRN-dependent. Our results support WRN as a promising synthetic-lethal target in dMMR/MSI-H colorectal cancer tumors as a monotherapy or in combination with targeted agents, chemotherapy, or immunotherapy. This article is highlighted in the In This Issue feature, p. 1861

Drug resistance is a principal limitation to the long-term efficacy of cancer therapies. Cancer genome sequencing can retrospectively delineate the genetic basis of drug resistance, but this requires large numbers of post-treatment samples to nominate causal variants. Here we prospectively identify genetic mechanisms of resistance to ten oncology drugs from CRISPR base editing mutagenesis screens in four cancer cell lines using a guide RNA library predicted to install 32,476 variants in 11 cancer genes. We identify four functional classes of protein variants modulating drug sensitivity and use single-cell transcriptomics to reveal how these variants operate through distinct mechanisms, including eliciting a drug-addicted cell state. We identify variants that can be targeted with alternative inhibitors to overcome resistance and functionally validate an epidermal growth factor receptor (EGFR) variant that sensitizes lung cancer cells to EGFR inhibitors. Our variant-to-function map has implications for patient stratification, therapy combinations and drug scheduling in cancer treatment.

Organoid models allow for the study of key pathophysiological processes such as cancer biology in vitro. They offer insights into all aspects covering tumor development, progression and response to the treatment of tissue obtained from individual patients. Tumor organoids are therefore not only a better tumor model than classical monolayer cell cultures but can be used as personalized avatars for translational studies. In this review, we discuss recent developments in using organoid models for cancer research and what kinds of advanced models, testing procedures and readouts can be considered.

While microsatellite-instable (MSI) colorectal cancers (CRC), reflecting mismatch repair deficiency, often respond to immune checkpoint inhibitors, microsatellite-stable (MSS) tumors remain largely resistant. This disparity is typically attributed to differences in neoantigen load. However, whether antigen-independent mechanisms contribute to immune evasion in MSS-CRC remains unclear. To address this, we engineered a model in which MSI- and MSS-CRC cells express identical levels of a defined antigen recognized by TCR-engineered T cells. Despite equivalent antigen presentation, MSS tumors exhibited impaired T-cell activation, reduced cytotoxicity, and resistance to killing. We linked this immune evasion to the MSS tumor secretome, which suppressed immune responses even in immunogenic MSI cells by impairing immune synapse formation. Surfaceome profiling by mass spectrometry identified glycosylation-dependent alterations that impair immune recognition. Our findings demonstrate that MSS-CRC evades immune attack via intrinsic secretome-driven mechanisms, independent of antigenicity. Targeting glycosylation-linked suppressive pathways may restore T-cell responsiveness and improve immunotherapy efficacy in MSS-CRC.

The Cell Model Network-UK group author list