Biology subjects

Vietor, K.

Publications and source records attributed to Vietor, K..

4 recordsLinked to original sources

bioRxiv2026

Folate metabolism in tumor-associated macrophages drives immunosuppressive function to promote tumor growth

Tumor-associated macrophages (TAMs) promote tumor growth, inhibit effector lymphocytes, and induce resistance to immune checkpoint inhibitors (ICI). Therapies designed to deplete TAMs have had little success in the clinic, and strategies aimed to repolarize immunosuppressive TAMs to pro-inflammatory states have struggled with systemic toxicity. We have identified that the combination of low folate in the tumor microenvironment and TAM dependency on the high affinity folate receptor beta (FR{beta}) for folate uptake results in a unique metabolic dependency of TAMs necessary for their immunosuppressive function. FR{beta} (encoded by Folr2) is uniquely expressed on myeloid cells and upregulated on TAMs. FR{beta}+ TAMs exhibit an immunosuppressive phenotype in melanoma and are associated with worse clinical outcomes and resistance to ICI in melanoma patients. We generated a novel Folr2-/- mouse model to study why TAMs express a unique folate receptor and showed that tumor growth was slowed in the absence of Folr2 in a T-cell dependent manner. We observed a dramatic repolarization of Folr2-/- TAMs in vivo to pro-inflammatory states, resulting in increased cytotoxic T cell and NK cell infiltration into tumors. Importantly, we show that folate is low in the tumor microenvironment by performing metabolomics on melanoma tumors and adjacent normal tissue from warm autopsy patient specimens, and that we could increase tumor growth in Folr2-/- mice by increasing serum folate to supraphysiologic concentrations with a high folate diet. Integrated metabolomics and transcriptomic analysis demonstrated that Folr2-/- macrophages have impaired folate uptake and 1C metabolism-based reduction of oxidized glutathione in low folate conditions, resulting in increased mitochondrial reactive oxygen species (ROS) in Folr2-/- cells. Excess ROS results in leakage of mitochondrial DNA into the cytoplasm, activating cGAS-STING signaling and promoting pro-inflammatory macrophage polarization through TBK1 and NF-kB. Together, our data demonstrate that TAM expression of FR{beta} promotes their immunosuppressive functions by maintaining folate uptake in the low folate tumor microenvironment, suggesting that FR{beta} is a novel metabolic checkpoint on TAMs.

immunology↗

bioRxiv2026

Harnessing Inflammatory Monocytes to Overcome Resistance to Anti-PD-1 Immunotherapy

BackgroundResistance to immune checkpoint inhibitors represents a major therapeutic challenge, as less than 50% of patients with melanoma achieve long-term response to immune checkpoint inhibitor therapy. One mechanism of acquired resistance involves somatic mutations, such as loss of beta-2 microglobulin (B2m), that enable tumor cells to evade T cell-mediated killing. MethodsThis study used single-cell RNA-seq, flow cytometry, and ex vivo functional assays to characterize tumor-infiltrating immune cells in antigen presentation-deficient tumors. Tumor-bearing mice were treated with anti-PD-1 or CD40 agonist antibodies and cell depletion or cytokine blocking antibodies to define mechanisms of action. Analysis of published human RNA-seq datasets was performed to dissect the contributions of inflammatory monocytes to patient outcomes. ResultsWe found an increase in immunosuppressive macrophages in B2m-null tumors. We hypothesized that repolarizing myeloid cells may restore control of tumor growth. Treatment with CD40 agonist antibody, which promotes differentiation of monocytes and macrophages towards a proinflammatory phenotype, reduced tumor growth and improved survival in B2m-null melanoma and colorectal cancer models. Unexpectedly, both CD8+ T cells and NK cells, but not CD4+ T cells, were required for the efficacy of CD40 agonist, even though CD8+ T cells cannot directly recognize antigen presentation-deficient tumor cells. Instead, these lymphocytes control tumor growth via secretion of IFN{gamma}, as depletion of IFN{gamma} inhibited the therapeutic effect of CD40 agonist. IFN{gamma} receptor (Ifngr1) expression was required on host cells, not tumor cells, for CD40 agonist-mediated tumor control. Single-cell analysis identified a distinct population of inflammatory monocytes that were enriched for an IFN{gamma} response signature in CD40 agonist-treated tumors, suggesting that these cells may be important for tumor control. Analysis of human bulk and single-cell RNA-seq datasets demonstrated that an inflammatory monocyte signature derived from our data was associated with improved patient outcomes and response to immune checkpoint inhibitors. ConclusionsThese data demonstrate that CD8+ T cells contribute to tumor control even in the absence of direct antigen presentation by tumor cells. More broadly, our work suggests that strategies to activate the effector functions of inflammatory monocytes may limit tumor growth and overcome acquired resistance to immune checkpoint inhibitors.

immunology↗

bioRxiv2022

Localization of the pioneer factor GAF to subnuclear foci is driven by DNA binding and required to silence satellite repeat expression

Abstract/SummaryThe eukaryotic genome is organized to enable the precise regulation of gene expression required for development. This organization is established during early development when the embryo transitions from a fertilized germ cell to the totipotent zygote. To understand the factors and processes that drive genomic organization, we focused on the pioneer factor GAGA factor (GAF) that is required for early embryonic development in Drosophila. GAF transcriptionally activates the zygotic genome and is localized to subnuclear foci. We show that this non-uniform distribution is driven by binding to the highly abundant GA-satellite repeats. At GA-repeats, GAF is necessary to form heterochromatin and silence transcription. Thus, GAF is required to establish both active and silent regions. We propose that foci formation enables GAF to have opposing transcriptional roles within a single nucleus. Our data support a model in which modulation of the subnuclear concentration of transcription factors acts to organize the nucleus into functionally distinct domains that are essential for the robust regulation of gene expression.

developmental biology↗

bioRxiv2022

A synthetic lethal screen for Snail-induced enzalutamide resistance identifies JAK/STAT signaling as a therapeutic vulnerability in prostate cancer

Despite substantial improvements in the treatment landscape of prostate cancer, the evolution of hormone therapy-resistant and metastatic prostate cancer remains a major cause of cancer-related death globally. The mainstay of treatment for advanced prostate cancer is targeting of androgen receptor signaling, including androgen deprivation therapy plus second-generation androgen receptor blockade (e.g., enzalutamide, apalutamide, darolutamide), and/or androgen synthesis inhibition (abiraterone). While these agents have significantly prolonged the lives of patients with advanced prostate cancer, the evolution of resistance to these treatments in nearly universal. This therapy resistance is mediated by diverse mechanisms, including both androgen receptor-dependent mechanisms, such as androgen receptor mutations, amplifications, alternatively spliced isoforms, and structural rearrangements, as well as non-androgen receptor-mediated mechanisms, such as lineage plasticity toward neuroendocrine-like or epithelial-mesenchymal transition (EMT)-like lineages. Our prior work identified the EMT transcriptional regulator Snail as critical to hormonal therapy resistance and commonly detected in human metastatic prostate cancer. In the current study, we sought to interrogate the actionable landscape of EMT-mediated hormone therapy-resistant prostate cancer to identify synthetic lethality and collateral sensitivity approaches to treating this aggressive disease state. Using a combination of high-throughput drug screens and multi-parameter phenotyping by confluence imaging, ATP production, and phenotypic plasticity reporters of EMT, we identified candidate synthetic lethalities to Snail-mediated EMT in prostate cancer. These analyses identified multiple actionable targets, such as XPO1, PI3K/mTOR, aurora kinases, c-MET, polo-like kinases, and JAK/STAT as synthetic lethalities in Snail+ prostate cancer. We validated these targets in a subsequent validation screen in an LNCaP-derived model of resistance to sequential androgen deprivation and enzalutamide. This follow-up screen provided validation of inhibitors of JAK/STAT and PI3K/mTOR as therapeutic vulnerabilities for Snail+ and enzalutamide-resistant prostate cancer.

cancer biology↗