Oncogenic Transcription Factor Research Articles

MYC Inhibition Potentiates CD8+ T Cells Against Multiple Myeloma and Overcomes Immunomodulatory Drug Resistance

Abstract Purpose: Immunomodulatory drugs (IMiDs), such as lenalidomide and pomalidomide, are a cornerstone of multiple myeloma (MM) therapies, yet the disease inevitably becomes refractory. IMiDs exert cytotoxicity by inducing cereblon-dependent proteasomal degradation of IKZF1 and IKZF3, resulting in downregulation of the oncogenic transcription factors IRF4 and MYC. To date, clinical IMiD resistance independent of cereblon or IKZF1/3 has not been well explored. Here, we investigated the roles of IRF4 and MYC in this context. Experimental Design: Using bone marrow aspirates from patients with IMiD-naïve or refractory MM, we examined IKZF1/3 protein levels and IRF4/MYC gene expression following ex vivo pomalidomide treatment via flow cytometry and qPCR. We also assessed ex vivo sensitivity to the MYC inhibitor MYCi975 using flow cytometry. Results: We discovered that although pomalidomide frequently led to IKZF1/3 degradation in MM cells, it did not affect MYC gene expression in most IMiD-refractory samples. We subsequently demonstrated that MYCi975 exerted strong anti-MM effects in both IMiD-naïve and -refractory samples. Unexpectedly, we identified a cluster of differentiation 8+ (CD8+ T) cells from patients with MM as crucial effectors of MYCi975-induced cytotoxicity in primary MM samples, and we discovered that MYCi975 enhanced the cytotoxic functions of memory CD8+ T cells. We lastly observed synergy between MYCi975 and pomalidomide in IMiD-refractory samples, suggesting that restoring MYC downregulation can re-sensitize refractory MM to IMiDs. Conclusions: Our study supports the concept that MYC represents an Achilles’ heel in MM across disease states and that MYCi975 may be a promising therapeutic for patients with MM, particularly in combination with IMiDs.

Nucleotide depletion promotes cell fate transitions by inducing DNA replication stress.

Control of cellular identity requires coordination of developmental programs with environmental factors such as nutrient availability, suggesting that perturbing metabolism can alter cell state. Here, we find that nucleotide depletion and DNA replication stress drive differentiation in human and murine normal and transformed hematopoietic systems, including patient-derived acute myeloid leukemia (AML) xenografts. These cell state transitions begin during S phase and are independent of ATR/ATM checkpoint signaling, double-stranded DNA break formation, and changes in cell cycle length. In systems where differentiation is blocked by oncogenic transcription factor expression, replication stress activates primed regulatory loci and induces lineage-appropriate maturation genes despite the persistence of progenitor programs. Altering the baseline cell state by manipulating transcription factor expression causes replication stress to induce genes specific for alternative lineages. The ability of replication stress to selectively activate primed maturation programs across different contexts suggests a general mechanism by which changes in metabolism can promote lineage-appropriate cell state transitions.

Molecular Pathways of Genistein Activity in Breast Cancer Cells.

The most common malignancy in women is breast cancer. During the development of cancer, oncogenic transcription factors facilitate the overproduction of inflammatory cytokines and cell adhesion molecules. Antiapoptotic proteins are markedly upregulated in cancer cells, which promotes tumor development, metastasis, and cell survival. Promising findings have been found in studies on the cell cycle-mediated apoptosis pathway for medication development and treatment. Dietary phytoconstituents have been studied in great detail for their potential to prevent cancer by triggering the body's defense mechanisms. The underlying mechanisms of action may be clarified by considering the role of polyphenols in important cancer signaling pathways. Phenolic acids, flavonoids, tannins, coumarins, lignans, lignins, naphthoquinones, anthraquinones, xanthones, and stilbenes are examples of natural chemicals that are being studied for potential anticancer drugs. These substances are also vital for signaling pathways. This review focuses on innovations in the study of polyphenol genistein's effects on breast cancer cells and presents integrated chemical biology methods to harness mechanisms of action for important therapeutic advances.

Oncogene EVI1 drives acute myeloid leukemia via a targetable interaction with CTBP2.

Acute myeloid leukemia (AML) driven by the activation of EVI1 due to chromosome 3q26/MECOM rearrangements is incurable. Because transcription factors such as EVI1 are notoriously hard to target, insight into the mechanism by which EVI1 drives myeloid transformation could provide alternative avenues for therapy. Applying protein folding predictions combined with proteomics technologies, we demonstrate that interaction of EVI1 with CTBP1 and CTBP2 via a single PLDLS motif is indispensable for leukemic transformation. A 4× PLDLS repeat construct outcompetes binding of EVI1 to CTBP1 and CTBP2 and inhibits proliferation of 3q26/MECOM rearranged AML in vitro and in xenotransplant models. This proof-of-concept study opens the possibility to target one of the most incurable forms of AML with specific EVI1-CTBP inhibitors. This has important implications for other tumor types with aberrant expression of EVI1 and for cancers transformed by different CTBP-dependent oncogenic transcription factors.

Biochemical characterization, stability, and kinetics of three substrates of the recombinant TMPRSS2 serine protease domain

Transmembrane serine protease 2 (TMPRSS2) is a membrane-bound protease belonging to the type II transmembrane serine protease (TTSP) family. It is a multidomain protein, including a serine protease domain responsible for its self-activation. The protein has been implicated as an oncogenic transcription factor and for its ability to cleave (prime) the SARS-CoV-2 spike protein. In order to characterize the TMPRSS2 biochemical properties, we expressed the serine protease domain (rTMPRSS2_SP) in Komagataella phaffii using the pPICZαA vector and purified it using immobilized metal affinity (Ni Sepharose™ excel) and size exclusion (Superdex 75) chromatography. We explored operational fluorescence resonance energy transfer FRET peptides as substrates. We chose the peptide Abz-QARK-(Dnp)-NH2 (Abz = ortho-aminobenzoic acid, the fluorescence donor, and Dnp = 2,4-dinitrophenyl, the quencher group) as a substrate to find the optimal conditions for maximum enzymatic activity. We found that metallic ions such as Ca2+ and Na+ increased enzymatic activity, but ionic surfactants and reducing agents decreased catalytic capacity. Finally, we determined the rTMPRSS2_SP stability for long-term storage. Altogether, our results represent the first comprehensive characterization of TMPRSS2’s biochemical properties, providing valuable insights into its serine protease domain.

SNHG15-mediated feedback loop interplays with HNRNPA1/SLC7A11/GPX4 pathway to promote gastric cancer progression.

Dysregulation of long noncoding RNA (lncRNA) expression plays a pivotal role in the initiation and progression of gastric cancer (GC). However, the regulation of lncRNA SNHG15 in GC has not been well studied. Mechanisms for ferroptosis by SNHG15 have not been revealed. Here, we aimed to explore SNHG15-mediated biological functions and underlying molecular mechanisms in GC. The novel SNHG15 was identified by analyzing RNA-sequencing (RNA-seq) data of GC tissues from our cohort and TCGA dataset, and further validated by qRT-PCR in GC cells and tissues. Gain- and loss-of-function assays were performed to examine the role of SNHG15 on GC both invitro and invivo. SNHG15 was highly expressed in GC. The enhanced SNHG15 was positively correlated with malignant stage and poor prognosis in GC patients. Gain- and loss-of-function studies showed that SNHG15 was required to affect GC cell growth, migration and invasion both invitro and invivo. Mechanistically, the oncogenic transcription factors E2F1 and MYC could bind to the SNHG15 promoter and enhance its expression. Meanwhile, SNHG15 increased E2F1 and MYC mRNA expression by sponging miR-24-3p. Notably, SNHG15 could also enhance the stability of SLC7A11 in the cytoplasm by competitively binding HNRNPA1. In addition, SNHG15 inhibited ferroptosis through an HNRNPA1-dependent regulation of SLC7A11/GPX4 axis. Our results support a novel model in which E2F1- and MYC-activated SNHG15 regulates ferroptosis via an HNRNPA1-dependent modulation of the SLC7A11/GPX4 axis, which serves as the critical effectors in GC progression, and provides a new therapeutic direction in the treatment of GC.

NB compounds are potent and efficacious FOXM1 inhibitors in high-grade serous ovarian cancer cells

BackgroundGenetic studies implicate the oncogenic transcription factor Forkhead Box M1 (FOXM1) as a potential therapeutic target in high-grade serous ovarian cancer (HGSOC). We evaluated the activity of different FOXM1 inhibitors in HGSOC cell models.ResultsWe treated HGSOC and fallopian tube epithelial (FTE) cells with a panel of previously reported FOXM1 inhibitors. Based on drug potency, efficacy, and selectivity, determined through cell viability assays, we focused on two compounds, NB-73 and NB-115 (NB compounds), for further investigation. NB compounds potently and selectively inhibited FOXM1 with lesser effects on other FOX family members. NB compounds decreased FOXM1 expression via targeting the FOXM1 protein by promoting its proteasome-mediated degradation, and effectively suppressed FOXM1 gene targets at both the protein and mRNA level. At the cellular level, NB compounds promoted apoptotic cell death. Importantly, while inhibition of apoptosis using a pan-caspase inhibitor rescued HGSOC cells from NB compound-induced cell death, it did not rescue FOXM1 protein degradation, supporting that FOXM1 protein loss from NB compound treatment is specific and not a general consequence of cytotoxicity. Drug washout studies indicated that FOXM1 reduction was retained for at least 72 h post-treatment, suggesting that NB compounds exhibit long-lasting effects in HGSOC cells. NB compounds effectively suppressed both two-dimensional and three-dimensional HGSOC cell colony formation at sub-micromolar concentrations. Finally, NB compounds exhibited synergistic activity with carboplatin in HGSOC cells.ConclusionsNB compounds are potent, selective, and efficacious inhibitors of FOXM1 in HGSOC cells and are worthy of further investigation as HGSOC therapeutics.

Hold the MYCrophone: MYC Invades Enhancers to Control Cancer Type Gene Programs.

MYC is an oncogenic transcription factor that binds gene promoters to facilitate oncogenic gene expression. When overexpressed, as is the case in most human cancers, MYC also invades active enhancers-cis-regulatory elements that are critical for regulating gene expression. In previous studies, the regulatory significance of MYC enhancer invasion in cancer cells has been debated. In their study published in Nature Genetics, Jakobsen and colleagues establish a new role for MYC at enhancer regions: regulating cancer type-specific gene programs. Their work reveals a mechanism where MYC cooperates with other oncogenic transcription factors to recruit epigenetic regulators to enhancers, resulting in an epigenetic "switch" that promotes enhancer activation through BRD4 and RNA polymerase II. This activity was highly cancer type-specific, highlighting gene expression programs that predicted clinical outcome in a subtype-specific manner in breast cancer patients.

Disrupting prostate cancer research: Challenge accepted; report from the 2023 Coffey-Holden Prostate Cancer Academy Meeting.

The 2023 Coffey-Holden Prostate Cancer Academy (CHPCA) Meeting, themed "Disrupting Prostate Cancer Research: Challenge Accepted," was convened at the University of California, Los Angeles, Luskin Conference Center, in Los Angeles, CA, from June 22 to 25, 2023. The 2023 marked the 10th Annual CHPCA Meeting, a discussion-oriented scientific think-tank conference convened annually by the Prostate Cancer Foundation, which centers on innovative and emerging research topics deemed pivotal for advancing critical unmet needs in prostate cancer research and clinical care. The 2023 CHPCA Meeting was attended by 81 academic investigators and included 40 talks across 8 sessions. The central topic areas covered at the meeting included: targeting transcription factor neo-enhancesomes in cancer, AR as a pro-differentiation and oncogenic transcription factor, why few are cured with androgen deprivation therapy and how to change dogma to cure metastatic prostate cancer without castration, reducing prostate cancer morbidity and mortality with genetics, opportunities for radiation to enhance therapeutic benefit in oligometastatic prostate cancer, novel immunotherapeutic approaches, and the new era of artificial intelligence-driven precision medicine. This article provides an overview of the scientific presentations delivered at the 2023 CHPCA Meeting, such that this knowledge can help in facilitating the advancement of prostate cancer research worldwide.

The MYCN 5′ UTR as a therapeutic target in neuroblastoma

Tumor MYCN amplification is seen in high-risk neuroblastoma, yet direct targeting of this oncogenic transcription factor has been challenging. Here, we take advantage of the dependence of MYCN-amplified neuroblastoma cells on increased protein synthesis to inhibit the activity of eukaryotic translation initiation factor 4A1 (eIF4A1) using an amidino-rocaglate, CMLD012824. Consistent with the role of this RNA helicase in resolving structural barriers in 5' untranslated regions (UTRs), CMLD012824 increased eIF4A1 affinity for polypurine-rich 5' UTRs, including that of the MYCN and associated transcripts with critical roles in cell proliferation. CMLD012824-mediated clamping of eIF4A1 spanned the full lengths of mRNAs, while translational inhibition was mediated through 5' UTR binding in a cap-dependent and -independent manner. Finally, CMLD012824 led to growth inhibition in MYCN-amplified neuroblastoma models without generalized toxicity. Our studies highlight the key role of eIF4A1 in MYCN-amplified neuroblastoma and demonstrate the therapeutic potential of disrupting its function.

FOXA1 regulates ribosomal RNA transcription in prostate cancer.

Ribosome biogenesis is excessively activated in tumor cells, yet it is little known whether oncogenic transcription factors (TFs) are involved in the ribosomal RNA (rRNA) transactivation. Nucleolar proteomics data and large-scale immunofluorescence were re-analyzed to jointly identify the proteins localized at nucleolus. RNA-Seq data of five prostate cancer (PCa) cohorts were combined and integrated with multi-dimensional data to define the upregulated nucleolar TFs in PCa tissues. Then, ChIP-Seq data of PCa cell lines and two PCa clinical cohorts were re-analyzed to reveal the TF binding patterns at ribosomal DNA (rDNA) repeats. The TF binding at rDNA was validated by ChIP-qPCR. The effect of the TF on rRNA transcription was determined by rDNA luciferase reporter, nascent RNA synthesis, and global protein translation assays. In this study, we reveal the role of oncogenic TF FOXA1 in regulating rRNA transcription within nucleolar organization regions. By analyzing human TFs in prostate cancer clinical datasets and nucleolar proteomics data, we identified that FOXA1 is partially localized in the nucleolus and correlated with global protein translation. Our extensive FOXA1 ChIP-Seq analysis provides robust evidence of FOXA1 binding across rDNA repeats in prostate cancer cell lines, primary tumors, and castration-resistant variants. Notably, FOXA1 occupancy at rDNA repeats correlates with histone modifications associated with active transcription, namely H3K27ac and H3K4me3. Reducing FOXA1 expression results in decreased transactivation at rDNA, subsequently diminishing global protein synthesis. Our results suggest FOXA1 regulates aberrant ribosome biogenesis downstream of oncogenic signaling in prostate cancer.

Cell Context is the third axis of synergy for the combination of ATR inhibition and cisplatin in Ewing sarcoma.

The importance of cellular context to the synergy of DNA Damage Response (DDR) targeted agents is important for tumors with mutations in DDR pathways, but less well-established for tumors driven by oncogenic transcription factors. In this study, we exploit the widespread transcriptional dysregulation of the EWS-FLI1 transcription factor to identify an effective DDR targeted combination therapy for Ewing Sarcoma (ES). We used matrix drug screening to evaluate synergy between a DNA-PK inhibitor (M9831) or an ATR inhibitor (berzosertib) and chemotherapy. The combination of berzosertib and cisplatin was selected for broad synergy, mechanistically evaluated for ES selectivity, and optimized for in vivo schedule. Berzosertib combined with cisplatin demonstrates profound synergy in multiple ES cell lines at clinically achievable concentrations. The synergy is due to loss of expression of the ATR downstream target CHEK1, loss of cell cycle checkpoints, and mitotic catastrophe. Consistent with the goals of the project, EWS-FLI1 drives the expression of CHEK1 and five other ATR pathway members. The loss of CHEK1 expression is not due to transcriptional repression and instead caused by degradation coupled with suppression of protein translation. The profound synergy is realized in vivo with a novel optimized schedule of this combination in subsets of ES models leading to durable complete responses in 50% of animals bearing two different ES xenografts. These data exploit EWS-FLI1 driven alterations in cell context to broaden the therapeutic window of berzosertib and cisplatin to establish a promising combination therapy and a novel in vivo schedule.

Abstract LB037: E3 pairing and structural mechanisms underlying anti-tumor activity of clinical STAT3 degrader KT-333

Abstract To elucidate the underlying mechanisms of STAT3 degradation and the suitability of VHL as an E3 ligase partner for targeting STAT3 in cancer using our clinical degrader, KT-333. Signal transducer and activator of transcription 3 (STAT3) is an undrugged oncogenic transcription factor and its role as cancer driver and tumor microenvironment modulator has been validated in a multitude of studies. Based on it’s potential as a target for cancer therapeutics and limitations of prior approaches, we developed KT-333, a first-in-class, potent, highly selective, heterobifunctional STAT3 degrader currently in Phase 1 clinical trials. Here, based on STAT3 degradation by multiple E3s based degraders, structure of STAT3-KT333-VHL and a lysine site-resolved target ubiquitination model, we provide evidence for VHL as the ideal partner E3 for targeting STAT3 in cancer. We successfully identified potent and selective STAT3 degraders using either CRBN or VHL as the E3 ligase, but ultimately preferred VHL based degraders for their increased potency, and consistent STAT3 degradation across multiple cancer lines. KT-333, our VHL based clinical STAT3 degrader, induces a strong ternary complex between STAT3 and VHL. We present a high resolution cryo-electron microscopy based ternary complex structure of STAT3-KT333-VHL which provides mechanistic insights further validating VHL as the E3 of choice for deep, selective and fast STAT3 degradation. Specifically, KT-333 enables favorable protein-protein interactions between STAT3 and VHL, burying a large protein interface in the ternary complex to the extent typically observed only in native protein complexes. Additionally, the residues forming the STAT3-VHL interface are not conserved in other STAT family members corroborating with degradation selectivity observed with KT-333. Next, we leveraged this structure and generated a ubiquitination super-complex model by deploying a combination of biochemical and proteomics techniques and reveal that KT-333-induced ubiquitination occurs by precise targeting of specific lysine resides on STAT3. Furthermore, to decode the mechanism for KT-333 activity against SUDHL1 cell line both in vitro and in a mouse xenograft model, we measured temporal changes at protein level by discovery proteomics. Reduced expression of canonical STAT3 targets and down-regulation of cytokine-mediated signaling and cell cycle signature genes indicated that cell cycle arrest and subsequent apoptosis are the main drivers of efficacy in vitro and in vivo. In summary, we show that our clinical STAT3 degrader, KT-333, is designed and optimally paired with VHL resulting in a very stable ternary complex exhibiting properties of native protein complexes. Our data provides precise structural and molecular mechanisms behind potent, selective, consistent, and fast degradation of STAT3, and downstream mechanism of action observed in vitro and in vivo. Citation Format: Kirti Sharma, Xue Fei, Yatao Shi, Christopher Browne, Dirk Walther, Caroline Daigle, Anand Ramanathan, Richard Miller, Karen Yuan, Kiran Mahasenan, Sean Zhu, Xin Huang, Bin Yang. E3 pairing and structural mechanisms underlying anti-tumor activity of clinical STAT3 degrader KT-333 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB037.

EP300/CREBBP acetyltransferase inhibition limits steroid receptor and FOXA1 signaling in prostate cancer cells

The androgen receptor (AR) is a primary target for treating prostate cancer (PCa), forming the bedrock of its clinical management. Despite their efficacy, resistance often hampers AR-targeted therapies, necessitating new strategies against therapy-resistant PCa. These resistances involve various mechanisms, including AR splice variant overexpression and altered activities of transcription factors like the glucocorticoid receptor (GR) and FOXA1. These factors rely on common coregulators, such as EP300/CREBBP, suggesting a rationale for coregulator-targeted therapies. Our study explores EP300/CREBBP acetyltransferase inhibition’s impact on steroid receptor and FOXA1 signaling in PCa cells using genome-wide techniques. Results reveal that EP300/CREBBP inhibition significantly disrupts the AR-regulated transcriptome and receptor chromatin binding by reducing the AR-gene expression. Similarly, GR’s regulated transcriptome and receptor binding were hindered, not linked to reduced GR expression but to diminished FOXA1 chromatin binding, restricting GR signaling. Overall, our findings highlight how EP300/CREBBP inhibition distinctively curtails oncogenic transcription factors’ signaling, suggesting the potential of coregulatory-targeted therapies in PCa.

Transcription Factors in Prostate Cancer: Insights for Disease Development and Diagnostic and Therapeutic Approaches.

Transcription factors (TFs) are proteins essential for the regulation of gene expression, and they regulate the genes involved in different cellular processes, such as proliferation, differentiation, survival, and apoptosis. Although their expression is essential in normal physiological conditions, abnormal regulation of TFs plays critical role in several diseases, including cancer. In prostate cancer, the most common malignancy in men, TFs are known to play crucial roles in the initiation, progression, and resistance to therapy of the disease. Understanding the interplay between these TFs and their downstream targets provides insights into the molecular basis of prostate cancer pathogenesis. In this review, we discuss the involvement of key TFs, including the E26 Transformation-Specific (ETS) Family (ERG and SPDEF), NF-κB, Activating Protein-1 (AP-1), MYC, and androgen receptor (AR), in prostate cancer while focusing on the molecular mechanisms involved in prostate cancer development. We also discuss emerging diagnostic strategies, early detection, and risk stratification using TFs. Furthermore, we explore the development of therapeutic interventions targeting TF pathways, including the use of small molecule inhibitors, gene therapies, and immunotherapies, aimed at disrupting oncogenic TF signaling and improving patient outcomes. Understanding the complex regulation of TFs in prostate cancer provides valuable insights into disease biology, which ultimately may lead to advancing precision approaches for patients.

Development of an orally bioavailable mSWI/SNF ATPase degrader and acquired mechanisms of resistance in prostate cancer

Mammalian switch/sucrose nonfermentable (mSWI/SNF) ATPase degraders have been shown to be effective in enhancer-driven cancers by functioning to impede oncogenic transcription factor chromatin accessibility. Here, we developed AU-24118, an orally bioavailable proteolysis-targeting chimera (PROTAC) degrader of mSWI/SNF ATPases (SMARCA2 and SMARCA4) and PBRM1. AU-24118 demonstrated tumor regression in a model of castration-resistant prostate cancer (CRPC) which was further enhanced with combination enzalutamide treatment, a standard of care androgen receptor (AR) antagonist used in CRPC patients. Importantly, AU-24118 exhibited favorable pharmacokinetic profiles in preclinical analyses in mice and rats, and further toxicity testing in mice showed a favorable safety profile. As acquired resistance is common with targeted cancer therapeutics, experiments were designed to explore potential mechanisms of resistance that may arise with long-term mSWI/SNF ATPase PROTAC treatment. Prostate cancer cell lines exposed to long-term treatment with high doses of a mSWI/SNF ATPase degrader developed SMARCA4 bromodomain mutations and ABCB1 (ATP binding cassette subfamily B member 1) overexpression as acquired mechanisms of resistance. Intriguingly, while SMARCA4 mutations provided specific resistance to mSWI/SNF degraders, ABCB1 overexpression provided broader resistance to other potent PROTAC degraders targeting bromodomain-containing protein 4 and AR. The ABCB1 inhibitor, zosuquidar, reversed resistance to all three PROTAC degraders tested. Combined, these findings position mSWI/SNF degraders for clinical translation for patients with enhancer-driven cancers and define strategies to overcome resistance mechanisms that may arise.

Oncogenic STAT Transcription Factors as Targets for Cancer Therapy: Innovative Strategies and Clinical Translation.

Despite advances in our understanding of molecular aspects of oncogenesis, cancer remains a leading cause of death. The malignant behavior of a cancer cell is driven by the inappropriate activation of transcription factors. In particular, signal transducers and activators of transcription (STATs), which regulate many critical cellular processes such as proliferation, apoptosis, and differentiation, are frequently activated inappropriately in a wide spectrum of human cancers. Multiple signaling pathways converge on the STATs, highlighting their importance in the development and progression of oncogenic diseases. STAT3 and STAT5 are two members of the STAT protein family that are the most frequently activated in cancers and can drive cancer pathogenesis directly. The development of inhibitors targeting STAT3 and STAT5 has been the subject of intense investigations in the last decade, although effective treatment options remain limited. In this review, we investigate the specific roles of STAT3 and STAT5 in normal physiology and cancer biology, discuss the opportunities and challenges in pharmacologically targeting STAT proteins and their upstream activators, and offer insights into novel therapeutic strategies to identify STAT inhibitors as cancer therapeutics.

FXR Agonism with Bile Acid Mimetic Reduces Pre-Clinical Triple-Negative Breast Cancer Burden.

Bariatric surgery is associated with improved outcomes for several cancers, including breast cancer (BC), although the mechanisms mediating this protection are unknown. We hypothesized that elevated bile acid pools detected after bariatric surgery may be factors that contribute to improved BC outcomes. Patients with greater expression of the bile acid receptor FXR displayed improved survival in specific aggressive BC subtypes. FXR is a nuclear hormone receptor activated by primary bile acids. Therefore, we posited that activating FXR using an established FDA-approved agonist would induce anticancer effects. Using in vivo and in vitro approaches, we determined the anti-tumor potential of bile acid receptor agonism. Indeed, FXR agonism by the bile acid mimetic known commercially as Ocaliva ("OCA"), or Obeticholic acid (INT-747), significantly reduced BC progression and overall tumor burden in a pre-clinical model. The transcriptomic analysis of tumors in mice subjected to OCA treatment revealed differential gene expression patterns compared to vehicle controls. Notably, there was a significant down-regulation of the oncogenic transcription factor MAX (MYC-associated factor X), which interacts with the oncogene MYC. Gene set enrichment analysis (GSEA) further demonstrated a statistically significant downregulation of the Hallmark MYC-related gene set (MYC Target V1) following OCA treatment. In human and murine BC analyses in vitro, agonism of FXR significantly and dose-dependently inhibited proliferation, migration, and viability. In contrast, the synthetic agonism of another common bile acid receptor, the G protein-coupled bile acid receptor TGR5 (GPBAR1) which is mainly activated by secondary bile acids, failed to significantly alter cancer cell dynamics. In conclusion, agonism of FXR by primary bile acid memetic OCA yields potent anti-tumor effects potentially through inhibition of proliferation and migration and reduced cell viability. These findings suggest that FXR is a tumor suppressor gene with a high potential for use in personalized therapeutic strategies for individuals with BC.

Abstract 495: Targeting undruggable transcription factor HOXB13 in metastatic prostate cancer by CRISPR/Cas13d-based nanoparticle therapy

Abstract Background: The oncogenic transcription factor HOXB13, which is highly expressed in castration-resistant prostate cancer (CRPC), has been shown to promote CRPC growth and metastasis. However, HOXB13 is considered untargetable by traditional small-molecule-based drug design. Gene therapy is critical alternative strategy with potential to directly target such traditionally undruggable genes. Methods: Selective cell in organ targeting (SCORT) nanoparticles for precise delivery of nanoparticles to metastatic cancer cells in an organ were constructed and characterized by the NanoAssemblr Spark, Zetasizer Nano ZS, and transmission electron microscopy (TEM); Cas13d mRNA with pseudouridine modification was synthesized using in vitro transcription; Hemi-spleen injection of CRPC cells was performed to build CRPC liver metastatic models; RNA-seq was employed to evaluate off-target effects of Cas13d targeting. Results: By incorporating a prostate cancer-specific E3 aptamer to functionalized lipid-like nanoparticles (FTT5 LNP-E3), we have successfully constructed SCORT nanoparticles that enable preferential delivery of mRNAs to metastatic CRPC cells in the liver, as opposed to various normal cells in the surrounding liver tissue. We demonstrated that Cas13d-pre-gHOXB13 mediates highly effective and specific HOXB13 mRNA knockdown in CRPC cells. Significantly, systemic treatment of SCORT nanoparticles carrying Cas13d-pre-gHOXB13 mRNA decreased HOXB13 expression in the metastatic tumors, inhibited metastasis, and prolonged survival of mice bearing androgen receptor (AR)-positive (AR+) or negative (AR-) tumors. Notably, long term (6 and a half weeks) administration of SCORT nanoparticle-Cas13d-pre-gHOXB13 did not significant alter body weight, hepatic and renal function, chemokines and cytokines, and other factors, effectively highlighting its safety. Conclusions: This study is the first to demonstrate that undruggable oncogenic transcription factors can be targeted using nanoparticle-delivered gene therapy based on CRISPR/Cas13 RNA-targeting. The SCORT-CRISPR/Cas13d system is a highly flexible technology that would impact the larger field of translational science by allowing the design of Cas13d-based, cancer cell-specific delivered nanoparticles targeting other previously-undruggable oncogenic transcription factors in metastatic prostate cancer and other solid tumors. Citation Format: Zhifen Cui, Furong Huang, Kun Fang, Jingyue Yan, Yufan Zhou, Jeffrey Everitt, Yue Zhao, William Hankey, Zhong Chen, Hongyan Wang, Victor X. Jin, Yizhou Dong, Qianben Wang. Targeting undruggable transcription factor HOXB13 in metastatic prostate cancer by CRISPR/Cas13d-based nanoparticle therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 495.

Abstract 3033: Oncogenic ETS transcription factors avoid repression by EZH2 and FOXO1 in prostate cancer and Ewing sarcoma

Abstract ETS transcription factors play roles throughout development, aiding in hematopoiesis, blood vessel formation and cell fate. The ETS family is composed of 28 members, all of which share an ETS DNA-binding domain. Chromosomal rearrangements that lead to the overexpression of specific ETS promote oncogenic transformation and tumor development. More than half of prostate tumors are driven by aberrant expression of an ETS protein. Our lab has demonstrated that oncogenic ETS form essential interactions with a ubiquitous RNA-binding protein, EWS, to promote prostate tumorigenesis. A similar mechanism exists in Ewing sarcoma (ES). ES tumors are driven by the expression EWS/ETS fusion proteins. This project focuses on the similarities and differences between oncogenic ETS in prostate cancer and EWS/ETS fusions in Ewing sarcoma. We compared biological functions of the most common oncogenic ETS in prostate cancer, ERG, and the most common fusion in ES, EWS/FLI1. Both ERG and EWS/FLI1 promoted migration and clonogenic survival in normal prostate epithelial cell lines, RWPE1 and PNT2. These data suggest that the EWS-ERG complex and EWS/FLI1 fusion protein can function similarly in prostate cells. Knockdown of endogenous EWS/FLI1 in the ES cell line, A673, reduced anchorage-independent colony formation in soft agar. Rescue with exogenous EWS/FLI1 or EWS/ERG restored colony formation relative to control. Wildtype ERG was unable to rescue colony formation in A673. This suggests that ERG and EWS/FLI1 function differently in A673 cells. Pulldown assays from A673 lysates reveal that ERG interacts with EZH2 and FOXO1. Our lab has established that ERG acts as a transcriptional repressor through the formation of an ERG-EZH2-PRC2 complex. Others demonstrate that FOXO1 represses ERG activity by reducing its recruitment to the target sites. Both the N-terminal truncation of ERG and phosphorylation of ERG at S96 disrupted these interactions and rescued anchorage independent growth in A673 ES cells. These data suggest that EWS/ETS fusions avoid transcriptional repression in Ewing tumors due to loss of the N-terminus of the ETS protein. Citation Format: Nicholas F. Downing, Kaitlyn M. Mills, Peter C. Hollenhorst. Oncogenic ETS transcription factors avoid repression by EZH2 and FOXO1 in prostate cancer and Ewing sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3033.