Cellular senescence is characterized by stable cell cycle arrest and a secretory program that modulates the tissue microenvironment 1 , 2 . Physiologically, senescence serves as a tumor suppressive mechanism that prevents the expansion of premalignant cells 3 , 4 and plays a beneficial role in wound healing responses 5 , 6 . Pathologically, the aberrant accumulation of senescent cells generates an inflammatory milieu that leads to chronic tissue damage and contributes to diseases such as liver and lung fibrosis, atherosclerosis, diabetes, and osteoarthritis 1 , 7 . Accordingly, elimination of senescent cells from damaged tissues in mice ameliorates symptoms of these pathologies and even promotes longevity 1 , 2 , 8 – 10 . Here we test the therapeutic concept that chimeric antigen receptor (CAR) T cells targeting senescent cells can be effective senolytics. We identify the urokinase plasminogen activator receptor (uPAR) 11 as a cell surface protein broadly induced during senescence and demonstrate that uPAR-specific CAR T cells efficiently ablate senescent cells in vitro and in vivo . uPAR-directed CAR T cells extend the survival of mice harboring lung adenocarcinoma treated with a senescence-inducing drug combination, and restore tissue homeostasis in chemical- or diet-induced liver fibrosis. These results establish the therapeutic potential of senolytic CAR T cells for senescence-associated diseases.

Summary Activation-induced cytidine deaminase (AID) initiates both somatic hypermutation (SHM) for antibody affinity maturation and DNA breakage for antibody class switch recombination (CSR) via transcription-dependent cytidine deamination of single stranded DNA targets. While largely specific for immunoglobulin genes, AID also acts on a limited set of off-targets, generating oncogenic translocations and mutations that contribute to B cell lymphoma. How AID is recruited to off-targets has been a long-standing mystery. Based on deep GRO-Seq studies of mouse and human B lineage cells activated for CSR or SHM, we report that most robust AID off-target translocations occur within highly focal regions of target genes in which sense and antisense transcription converge. Moreover, we found that such AID-targeting “convergent” transcription arises from antisense transcription that emanates from Super-Enhancers within sense transcribed gene bodies. Our findings provide an explanation for AID off-targeting to a small subset of mostly lineage-specific genes in activated B cells.

To study genetic factors infl uencing the progression and therapeutic responses of advanced prostate cancer, we developed a fast and fl exible system that introduces genetic alterations relevant to human disease directly into the prostate glands of mice using tissue electroporation. These electroporation-based genetically engineered mouse models (EPO-GEMM) recapitulate features of traditional germline models and, by modeling genetic factors linked to latestage human disease, can produce tumors that are metastatic and castration-resistant. A subset of tumors with Trp53 alterations acquired spontaneous WNT pathway alterations, which are also associated with metastatic prostate cancer in humans. Using the EPO-GEMM approach and an orthogonal organoid-based model, we show that WNT pathway activation drives metastatic disease that is sensitive to pharmacologic WNT pathway inhibition. Thus, by leveraging EPO-GEMMs, we reveal a functional role for WNT signaling in driving prostate cancer metastasis and validate the WNT pathway as therapeutic target in metastatic prostate cancer. SIGNIFICANCE:Our understanding of the factors driving metastatic prostate cancer is limited by the paucity of models of late-stage disease. Here, we develop EPO-GEMMs of prostate cancer and use them to identify and validate the WNT pathway as an actionable driver of aggressive metastatic disease.

Metastatic gastric carcinoma is a highly lethal cancer that responds poorly to conventional and molecularly targeted therapies. Despite its clinical relevance, the mechanisms underlying the behavior and therapeutic response of this disease are poorly understood owing, in part, to a paucity of tractable models that faithfully recapitulate different subtypes of the human disease. To close this gap, we developed methods to somatically introduce different oncogenic lesions directly into the stomach epithelium and show that genotypic configurations observed in patients produce metastatic gastric cancers that recapitulate the histological, molecular, and clinical features of all non-viral molecular subtypes of the human disease. Applying this platform to both wild-type and immune-deficient mice revealed previously unappreciated links between the genotype, organotropism and immune surveillance of metastatic cells that produced distinct patterns of metastasis that were mirrored in patients. Our results establish and credential a highly portable platform for producing autochthonous cancer models with flexible genotypes and host backgrounds, which can unravel mechanisms of gastric tumorigenesis or test new therapeutic concepts aimed at improving outcomes in gastric cancer patients.

<div>Abstract<p>To study genetic factors influencing the progression and therapeutic responses of advanced prostate cancer, we developed a fast and flexible system that introduces genetic alterations relevant to human disease directly into the prostate glands of mice using tissue electroporation. These electroporation-based genetically engineered mouse models (EPO-GEMM) recapitulate features of traditional germline models and, by modeling genetic factors linked to late-stage human disease, can produce tumors that are metastatic and castration-resistant. A subset of tumors with <i>Trp53</i> alterations acquired spontaneous WNT pathway alterations, which are also associated with metastatic prostate cancer in humans. Using the EPO-GEMM approach and an orthogonal organoid-based model, we show that WNT pathway activation drives metastatic disease that is sensitive to pharmacologic WNT pathway inhibition. Thus, by leveraging EPO-GEMMs, we reveal a functional role for WNT signaling in driving prostate cancer metastasis and validate the WNT pathway as therapeutic target in metastatic prostate cancer.</p>Significance:<p>Our understanding of the factors driving metastatic prostate cancer is limited by the paucity of models of late-stage disease. Here, we develop EPO-GEMMs of prostate cancer and use them to identify and validate the WNT pathway as an actionable driver of aggressive metastatic disease.</p><p><i>This article is highlighted in the In This Issue feature, p. 890</i></p></div>

<p>Supplementary Figures and Legends</p>

The majority of human breast cancers are dependent on Estrogen Receptor Alpha (ER) and sensitive to its inhibition. In advanced, ER+ dependent breast cancers, resistance usually develops and is associated with insensitivity of the estrogen receptor to inhibition. Mutations that activate PI3K signaling occur in over 40% of ER-driven breast cancers. The PI3K pathway regulates cap-dependent protein translation by controlling mTOR complex I (mTORC1). Inhibitors of PI3K/mTOR are effective in this setting when given with anti-estrogens, but induce ER activity and expression. We now show that despite reducing global cap-dependent translation, PI3K/mTOR inhibition does not reduce ER translation or expression. Translation of ER instead depends on the translation initiation factor, EIF4A. Inhibitors of EIF4A significantly reduce the expression of WT and mutant ER, with attendant blockage of breast cancer model growth in vivo, including models driven by estrogen-independent ER fusions that are unaffected by estrogen receptor antagonists. The utility of EIF4A inhibition can be enhanced when combined with Fulvestrant, a degrader of ER. Combining inhibition of ER translation and induction of ER degradation causes synergistic deep and durable inhibition of ER expression and tumor growth. Inhibition of ER translation represents a new potent strategy for treating ER-dependent breast cancers with acquired resistance to current therapies. Citation Format: Jacob A. Boyer, Madeline A. Dorso, Corina Amor, Jason Reiter, Jianing Xu, Elisa de Stanchina, Hans-Guido Wendel, Sarat Chandarlapaty, Neal Rosen. Estrogen receptor expression and ER dependent breast tumor growth are dependent on translation initiation factor EIF4A [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 835.

<p>Supplementary Figures and Legends</p>