FGFR Signaling Research Articles

Enhancer landscape of lung neuroendocrine tumors reveals regulatory and developmental signatures with potential theranostic implications

Well-differentiated low-grade lung neuroendocrine tumors (lung carcinoids or LNETs) are histopathologically classified as typical and atypical LNETs, but each subtype is still heterogeneous at both the molecular level and its clinical manifestation. Here, we report genome-wide profiles of primary LNETs' cis-regulatory elements by H3K27ac ChIP-seq with matching RNA-seq profiles. Analysis of these regulatory landscapes revealed three regulatory subtypes, independent of the typical/atypical classification. We identified unique differentiation signals that delineate each subtype. The "proneuronal" subtype emerges under the influence of ASCL1, SOX4, and TCF4 transcription factors, embodying a pronounced proneuronal signature. The "luminal-like" subtype is characterized by gain of acetylation at markers of luminal cells and GATA2 activation and loss of LRP5 and OTP. The "HNF+" subtype is characterized by a robust enhancer landscape driven by HNF1A, HNF4A, and FOXA3, with notable acetylation and expression of FGF signaling genes, especially FGFR3 and FGFR4, pivotal components of the FGF pathway. Our findings not only deepen the understanding of LNETs' regulatory and developmental diversity but also spotlight the HNF+ subtype's reliance on FGFR signaling. We demonstrate that targeting this pathway with FGF inhibitors curtails tumor growth both in vitro and in xenograft models, unveiling a potential vulnerability and paving the way for targeted therapies. Overall, our work provides an important resource for studying LNETs to reveal regulatory networks, differentiation signals, and therapeutically relevant dependencies.

Integrative Modeling of Signaling Network Dynamics Identifies Cell Type-Selective Therapeutic Strategies for FGFR4-Driven Cancers.

Oncogenic FGFR4 signaling represents a potential therapeutic target in various cancer types, including triple-negative breast cancer and hepatocellular carcinoma. However, resistance to FGFR4 single-agent therapy remains a major challenge, emphasizing the need for effective combinatorial treatments. Our study sought to develop a comprehensive computational model of FGFR4 signaling and to provide network-level insights into resistance mechanisms driven by signaling dynamics. An integrated approach, combining computational network modeling with experimental validation, uncovered potent AKT reactivation following FGFR4 targeting in triple-negative breast cancer cells. Analyzing the effects of cotargeting specific network nodes by systematically simulating the model predicted synergy of cotargeting FGFR4 and AKT or specific ErbB kinases, which was subsequently confirmed through experimental validation; however, cotargeting FGFR4 and PI3K was not synergistic. Protein expression data from hundreds of cancer cell lines was incorporated to adapt the model to diverse cellular contexts. This revealed that although AKT rebound was common, it was not a general phenomenon. For example, ERK reactivation occurred in certain cell types, including an FGFR4-driven hepatocellular carcinoma cell line, in which there is a synergistic effect of cotargeting FGFR4 and MEK but not AKT. In summary, this study offers key insights into drug-induced network remodeling and the role of protein expression heterogeneity in targeted therapy responses. These findings underscore the utility of computational network modeling for designing cell type-selective combination therapies and enhancing precision cancer treatment. Significance: Computational predictive modeling of signaling networks can decipher mechanisms of cancer cell resistance to targeted therapies and enable identification of more effective cancer type-specific combination treatment strategies.

Flavonoid chrysin activates both TrkB and FGFR1 receptors while upregulates their endogenous ligands such as brain derived neurotrophic factor to promote human neurogenesis.

Neurogenesis is the process of generating new neurons from neural stem cells (NSCs) and plays a crucial role in neurological diseases. The process involves a series of steps, including NSC proliferation, migration and differentiation, which are regulated by multiple pathways such as neurotrophic Trk and fibroblast growth factor receptors (FGFR) signalling. Despite the discovery of numerous compounds capable of modulating individual stages of neurogenesis, it remains challenging to identify an agent that can regulate multiple cellular processes of neurogenesis. Here, through screening of bioactive compounds in dietary functional foods, we identified a flavonoid chrysin that not only enhanced the human NSCs proliferation but also facilitated neuronal differentiation and neurite outgrowth. Further mechanistic study revealed the effect of chrysin was attenuated by inhibition of neurotrophic tropomyosin receptor kinase-B (TrkB) receptor. Consistently, chrysin activated TrkB and downstream ERK1/2 and AKT. Intriguingly, we found that the effect of chrysin was also reduced by FGFR1 blockade. Moreover, extended treatment of chrysin enhanced levels of brain-derived neurotrophic factor, as well as FGF1 and FGF8. Finally, chrysin was found to promote neurogenesis in human cerebral organoids by increasing the organoid expansion and folding, which was also mediated by TrkB and FGFR1 signalling. To conclude, our study indicates that activating both TrkB and FGFR1 signalling could be a promising avenue for therapeutic interventions in neurological diseases, and chrysin appears to be a potential candidate for the development of such treatments.

Fibroblast Growth Factor 2 (FGF2) Activates Vascular Endothelial Growth Factor (VEGF) Signaling in Gastrointestinal Stromal Tumors (GIST): An Autocrine Mechanism Contributing to Imatinib Mesylate (IM) Resistance.

We showed previously that the autocrine activation of the FGFR-mediated pathway in GIST lacking secondary KIT mutations was a result of the inhibition of KIT signaling. We show here that the FGF2/FGFR pathway regulates VEGF-A/VEGFR signaling in IM-resistant GIST cells. Indeed, recombinant FGF2 increased the production of VEGF-A by IM-naive and resistant GIST cells. VEGF-A production was also increased in KIT-inhibited GIST, whereas the neutralization of FGF2 by anti-FGF2 mAb attenuated VEGFR signaling. Of note, BGJ 398, pan FGFR inhibitor, effectively and time-dependently inhibited VEGFR signaling in IM-resistant GIST T-1R cells, thereby revealing the regulatory role of the FGFR pathway in VEGFR signaling for this particular GIST cell line. This also resulted in significant synergy between BGJ 398 and VEGFR inhibitors (i.e., sunitinib and regorafenib) by enhancing their pro-apoptotic and anti-proliferative activities. The high potency of the combined use of VEGFR and FGFR inhibitors in IM-resistant GISTs was revealed by the impressive synergy scores observed for regorafenib or sunitinib and BGJ 398. Moreover, FGFR1/2 and VEGFR1/2 were co-localized in IM-resistant GIST T-1R cells, and the direct interaction between the aforementioned RTKs was confirmed by co-immunoprecipitation. In contrast, IM-resistant GIST 430 cells expressed lower basal levels of FGF2 and VEGF-A. Despite the increased expression VEGFR1 and FGFR1/2 in GIST 430 cells, these RTKs were not co-localized and co-immunoprecipitated. Moreover, no synergy between FGFR and VEGFR inhibitors was observed for the IM-resistant GIST 430 cell line. Collectively, the dual targeting of FGFR and VEGFR pathways in IM-resistant GISTs is not limited to the synergistic anti-angiogenic treatment effects. The dual inhibition of FGFR and VEGFR pathways in IM-resistant GISTs potentiates the proapoptotic and anti-proliferative activities of the corresponding RTKi. Mechanistically, the FGF2-induced activation of the FGFR pathway turns on VEGFR signaling via the overproduction of VEGF-A, induces the interaction between FGFR1/2 and VEGFR1, and thereby renders cancer cells highly sensitive to the dual inhibition of the aforementioned RTKs. Thus, our data uncovers the novel mechanism of the cross-talk between the aforementioned RTKs in IM-resistant GISTs lacking secondary KIT mutations and suggests that the dual blockade of FGFR and VEGFR signaling might be an effective treatment strategy for patients with GIST-acquired IM resistance via KIT-independent mechanisms.

Distinct phenotypic consequences of cholangiocarcinoma-associated FGFR2 alterations depend on biliary epithelial maturity.

Epithelial cancers disrupt tissue architecture and are often driven by mutations in genes that normally play important roles in epithelial morphogenesis. The intrahepatic biliary system is an epithelial tubular network that forms within the developing liver via the de novo initiation and expansion of apical lumens. Intrahepatic biliary tumors are often driven by different types of mutations in the FGFR2 receptor tyrosine kinase which plays important roles in epithelial morphogenesis in other developmental settings. Using a physiologic and quantitative 3D model we have found that FGFR signaling is important for biliary morphogenesis and that oncogenic FGFR2 mutants disrupt biliary architecture. Importantly, we found that both the trafficking and signaling of normal FGFR2 and the phenotypic consequences of FGFR2 mutants are influenced by the epithelial state of the cell. Unexpectedly, we found that different tumor-driving FGFR2 mutants disrupt biliary morphogenesis in completely different and clinically relevant ways, informing our understanding of morphogenesis and tumorigenesis and highlighting the importance of convergent studies of both.

Specific 3-O-sulfated heparan sulfate domains regulate salivary gland basement membrane metabolism and epithelial differentiation

Heparan sulfate (HS) regulation of FGFR function, which is essential for salivary gland (SG) development, is determined by the immense structural diversity of sulfated HS domains. 3-O-sulfotransferases generate highly 3-O-sulfated HS domains (3-O-HS), and Hs3st3a1 and Hs3st3b1 are enriched in myoepithelial cells (MECs) that produce basement membrane (BM) and are a growth factor signaling hub. Hs3st3a1;Hs3st3b1 double-knockout (DKO) mice generated to investigate 3-O-HS regulation of MEC function and growth factor signaling show loss of specific highly 3-O-HS and increased FGF/FGFR complex binding to HS. During development, this increases FGFR-, BM- and MEC-related gene expression, while in adult, it reduces MECs, increases BM and disrupts acinar polarity, resulting in salivary hypofunction. Defined 3-O-HS added to FGFR pulldown assays and primary organ cultures modulates FGFR signaling to regulate MEC BM synthesis, which is critical for secretory unit homeostasis and acinar function. Understanding how sulfated HS regulates development will inform the use of HS mimetics in organ regeneration.

FGF Signaling Regulates Development of the Anterior Fontanelle.

The calvarial bones of the infant skull are connected by transient fibrous joints known as sutures and fontanelles, which are essential for reshaping during birth and postnatal growth. Genetic disorders such as Apert, Pfeiffer, Crouzon, and Bent bone dysplasia linked to FGFR2 variants often exhibit multi-suture craniosynostosis and a persistently open anterior fontanelle (AF). This study leverages mouse genetics and single-cell transcriptomics to determine how Fgfr2 regulates closure of the AF closure and its transformation into the frontal suture during postnatal development. We find that cells of the AF, marked by the tendon/ligament factor SCX, are spatially restricted to ecto- or endocranial domains and undergo regionally selective differentiation into ligament, bone, and cartilage. Differentiation of SCX+ AF cells is dependent on FGFR2 signaling in cells of the osteogenic fronts which, when fueled by FGF18 from the ectocranial mesenchyme, express the secreted WNT inhibitor WIF1 to regulate WNT signaling in neighboring AF cells. Upon loss of Fgfr2 , Wif1 expression is lost, and cells of the AF retain a connective tissue-like fate failing to form the posterior frontal suture. This study provides new insights into regional differences in suture development by identifying an FGF-WNT signaling circuit within the AF that links frontal bone advancement with suture joint formation.

ATRT-12. EXPLORING FGFR INHIBITION AND COMBINATION THERAPIES FOR ATYPICAL TERATOID/RHABDOID TUMORS

Abstract BACKGROUND Atypical teratoid/rhabdoid tumors (ATRTs) are aggressive pediatric brain neoplasms characterized by an inactivation of the SWI/SNF chromatin remodeling complex members SMARCB1 or SMARCA4. Based on epigenetic profiling ATRTs can be divided into four different molecular subgroups. Despite improvements in treatment strategies, the prognosis for ATRT patients remains dismal. The FGF/FGFR signaling pathway plays a crucial role in many physiological processes, including embryonic development, tissue repair, angiogenesis. Dysregulation of the signaling axis is driving tumorigenesis. Targeted therapeutic approaches, particularly FGFR inhibitors, have demonstrated potential in enhancing treatment outcomes for various tumors, including pediatric brain tumors. METHODS We used bulk and single-cell RNA sequencing (scRNA-seq) data to examine the expression patterns of FGF family members in ATRTs. Subsequently, we conducted in vitro analysis on a panel of FGFR inhibitors and combination treatments. RESULTS Transcriptomic analysis of more than 130 ATRT tissues samples, revealed a widespread expression of FGFR1 and FGFR2 across all ATRT subtypes. Notably, FGFR1 displayed distinctly elevated expression in ATRT-SHH, surpassing levels seen in other ATRT subtypes and brain tumor types. Utilizing scRNA-seq data of murine ATRT models, we elucidated an autocrine FGFR signaling loop. To assess the therapeutic feasibility of targeting FGFR, we evaluated a panel of FGFR inhibitors, currently in clinical development, across 10 in house established patient-derived cell models (6 ATRT-MYC, 3 ATRT-SHH, 1 ATRT-TYR), revealing sensitivity in a nanomolar to a low-micromolar range. We further explored combination therapies, demonstrating that Erdafitinib, the most effective inhibitor when combined with Abemaciclib and radiation, exhibited enhanced synergistic effects in 2D as well as in 3D tumoroid models. Investigations towards testing these combinations in an organoid co-culture system, along with in vivo models are ongoing. CONCLUSIONS This study emphasizes the prospect of combining FGFR inhibition with radiation and CDK4/6 inhibition as a therapeutic target for ATRTs.

Evaluation of antitumor potential of an anti-glypican-1 monoclonal antibody in preclinical lung cancer models reveals a distinct mechanism of action.

The main objective of this study was to investigate the antitumor effect of a mouse anti-human glypican-1 (GPC1) monoclonal antibody (mAb) on non-small cell lung carcinoma (NSCLC) and associated molecular mechanisms. The anti-proliferative and anti-migratory activities of anti-GPC1 mAb were examined in A549 and H460 NSCLC cells and LL97A lung fibroblasts. The inhibitory effect of anti-GPC1 mAb on tumor growth was evaluated in an orthotopic lung tumor model. The in vitro study showed that anti-GPC1 mAb profoundly inhibited the anchorage-independent growth of A549 and H460 NSCLC cells and exhibited relatively high cytotoxic activities towards LL97A lung fibroblasts, A549/LL97A and H460/LL97A coculture spheroids. Moreover, anti-GPC1 mAb significantly decreased the expression of phospho-Src (p-Src; Tyr416), p-Akt (Ser473) and β-catenin in the co-cultured LL97A lung fibroblasts, and the expression of phospho-mitogen-activated protein kinase kinase (p-MEK; Ser217/221) and phospho-90 kDa ribosomal s6 kinase (p-p90RSK; Ser380) in co-cultured A549 cells. When anti-GPC1 mAb was administered to tumor-bearing mice, the inhibitory effect of anti-GPC1 mAb on the orthotopic lung tumor growth was not statistically significant. Nonetheless, results of Western blot analysis showed significant decrease in the phosphorylation of fibroblast growth factor receptor 1 (FGFR1) at Tyr766, Src at Tyr416, extracellular signal-regulated kinase (ERK) at Thr202/Tyr204, 90 kDa ribosomal S6 kinase (RSK) at Ser380, glycogen synthase kinases 3α (GSK3α) at Ser21 and GSK3β at Ser9 in tumor tissues. These data implicate that anti-GPC1 mAb treatment impairs the interaction between tumor cells and tumor associated fibroblasts by attenuating the paracrine FGFR signal transduction. The relatively potent cytotoxicity of anti-GPC1 mAb in lung fibroblasts and its potential inhibitory effect on the paracrine FGFR signal transduction warrant further studies on the combined use of this mAb with targeted therapeutics to improve therapeutic outcomes in lung cancer.

Diverse Fgfr1 signaling pathways and endocytic trafficking regulate mesoderm development.

The fibroblast growth factor (FGF) pathway is a conserved signaling pathway required for embryonic development. Activated FGF receptor 1 (FGFR1) drives multiple intracellular signaling cascade pathways, including ERK/MAPK and PI3K/AKT, collectively termed canonical signaling. However, unlike Fgfr1-null embryos, embryos containing hypomorphic mutations in Fgfr1 lacking the ability to activate canonical downstream signals are still able to develop to birth but exhibit severe defects in all mesodermal-derived tissues. The introduction of an additional signaling mutation further reduces the activity of Fgfr1, leading to earlier lethality, reduced somitogenesis, and more severe changes in transcriptional outputs. Genes involved in migration, ECM interaction, and phosphoinositol signaling were significantly downregulated, proteomic analysis identified changes in interactions with endocytic pathway components, and cells expressing mutant receptors show changes in endocytic trafficking. Together, we identified processes regulating early mesoderm development by mechanisms involving both canonical and noncanonical Fgfr1 pathways, including direct interaction with cell adhesion components and endocytic regulation.

Turning sublimed sulfur and bFGF into a nanocomposite to accelerate wound healing via co-activate FGFR and Hippo signaling pathway

Clinical treatment of diabetic refractory ulcers is impeded by chronic inflammation and cell dysfunction associated with wound healing. The significant clinical application of bFGF in wound healing is limited by its instability in vivo. Sulfur has been applied for the treatment of skin diseases in the clinic for antibiosis. We previously found that sulfur incorporation improves the ability of selenium nanoparticles to accelerate wound healing, yet the toxicity of selenium still poses a risk for its clinical application. To obtain materials with high pro-regeneration activity and low toxicity, we explored the mechanism by which selenium-sulfur nanoparticles aid in wound healing via RNA-Seq and designed a nanoparticle called Nano-S@bFGF, which was constructed from sulfur and bFGF. As expected, Nano-S@bFGF not only regenerated zebrafish tail fins and promoted skin wound healing but also promoted skin repair in diabetic mice with a profitable safety profile. Mechanistically, Nano-S@bFGF successfully coactivated the FGFR and Hippo signalling pathways to regulate wound healing. Briefly, the Nano-S@bFGF reported here provides an efficient and feasible method for the synthesis of bioactive nanosulfur and bFGF. In the long term, our results reinvigorated efforts to discover more peculiar unique biofunctions of sulfur and bFGF in a great variety of human diseases.

SLC7A5 correlated with malignancies and immunotherapy response in bladder cancer

BackgroundMetabolic reprogramming contributes to bladder cancer development. This study aimed to understand the role of SLC7A5 in bladder cancer.MethodsWe systematically analyzed the correlation between SLC7A5 and bladder cancer through various approaches, including bioinformatics, western blotting, cell cycle analysis, cell proliferation assays, and invasion experiments. We also investigated the immunological features within the tumor microenvironment (TME), encompassing cancer immune cycles, immune modulators, immune checkpoints, tumor-infiltrating immune cells (TIIC), T cell inflammation scores, and treatment responses. Additionally, for a comprehensive assessment of the expression patterns and immunological roles of SLC7A5, pan-cancer analysis was performed using cancer genomics datasets.ResultsSLC7A5 was associated with adverse prognosis in bladder cancer patients, activating the Wnt pathway and promoting bladder cancer cell cycle progression, proliferation, migration, and invasion. Based on the evidence that SLC7A5 positively correlated with immunomodulators, TIIC, the cancer immune cycle, immune checkpoint and T cell inflammation scores, we also found that SLC7A5 was associated with the inflammatory tumor immune microenvironment. EGFR-targeted therapy, cancer immunotherapy, and radiation therapy were effective for patients with high SLC7A5 expression in bladder cancer. Low SLC7A5 patients were, however, sensitive to targeted therapies and anti-angiogenic therapy, such as blocking β-catenin network, PPAR-γ and FGFR3 signaling. Anti-SLC7A5 combined with cancer immunotherapy may have greater effectiveness than either therapy alone. Furthermore, we observed specific overexpression of SLC7A5 in TME of various cancers.ConclusionSLC7A5 can predict therapeutic response to immunotherapy, radiotherapy and chemotherapy in bladder cancer patients. Targeting SLC7A5 in combination with immunotherapy may be a potentially appropriate treatment option.

Interruption of KLF5 acetylation promotes PTEN-deficient prostate cancer progression by reprogramming cancer-associated fibroblasts.

Inactivation of phosphatase and tensin homolog (PTEN) is prevalent in human prostate cancer and causes high-grade adenocarcinoma with a long latency. Cancer-associated fibroblasts (CAFs) play a pivotal role in tumor progression, but it remains elusive whether and how PTEN-deficient prostate cancers reprogram CAFs to overcome the barriers for tumor progression. Here, we report that PTEN deficiency induced Krüppel-like factor 5 (KLF5) acetylation and that interruption of KLF5 acetylation orchestrated intricate interactions between cancer cells and CAFs that enhance FGF receptor 1 (FGFR1) signaling and promote tumor growth. Deacetylated KLF5 promoted tumor cells to secrete TNF-α, which stimulated inflammatory CAFs to release FGF9. CX3CR1 inhibition blocked FGFR1 activation triggered by FGF9 and sensitized PTEN-deficient prostate cancer to the AKT inhibitor capivasertib. This study reveals the role of KLF5 acetylation in reprogramming CAFs and provides a rationale for combined therapies using inhibitors of AKT and CX3CR1.

FGFR2-triggered autophagy and activation of Nrf-2 reduce breast cancer cell response to anti-ER drugs

BackgroundGenetic abnormalities in the FGFR signalling occur in 40% of breast cancer (BCa) patients resistant to anti-ER therapy, which emphasizes the potential of FGFR-targeting strategies. Recent findings indicate that not only mutated FGFR is a driver of tumour progression but co-mutational landscapes and other markers should be also investigated. Autophagy has been recognized as one of the major mechanisms underlying the role of tumour microenvironment in promotion of cancer cell survival, and resistance to anti-ER drugs. The selective autophagy receptor p62/SQSTM1 promotes Nrf-2 activation by Keap1/Nrf-2 complex dissociation. Herein, we have analysed whether the negative effect of FGFR2 on BCa cell response to anti-ER treatment involves the autophagy process and/or p62/Keap1/Nrf-2 axis.MethodsThe activity of autophagy in ER-positive MCF7 and T47D BCa cell lines was determined by analysis of expression level of autophagy markers (p62 and LC3B) and monitoring of autophagosomes’ maturation. Western blot, qPCR and proximity ligation assay were used to determine the Keap1/Nrf-2 interaction and Nrf-2 activation. Analysis of 3D cell growth in Matrigel® was used to assess BCa cell response to applied treatments. In silico gene expression analysis was performed to determine FGFR2/Nrf-2 prognostic value.ResultsWe have found that FGFR2 signalling induced autophagy in AMPKα/ULK1-dependent manner. FGFR2 activity promoted dissociation of Keap1/Nrf-2 complex and activation of Nrf-2. Both, FGFR2-dependent autophagy and activation of Nrf-2 were found to counteract the effect of anti-ER drugs on BCa cell growth. Moreover, in silico analysis showed that high expression of NFE2L2 (gene encoding Nrf-2) combined with high FGFR2 expression was associated with poor relapse-free survival (RFS) of ER+ BCa patients.ConclusionsThis study revealed the unknown role of FGFR2 signalling in activation of autophagy and regulation of the p62/Keap1/Nrf-2 interdependence, which has a negative impact on the response of ER+ BCa cells to anti-ER therapies. The data from in silico analyses suggest that expression of Nrf-2 could act as a marker indicating potential benefits of implementation of anti-FGFR therapy in patients with ER+ BCa, in particular, when used in combination with anti-ER drugs.Graphical

Abstract PO5-24-05: The Metabolic and Epigenetic Contributions of Fibroblast Growth Factor Receptor-Mediated Breast Cancer Progression

Abstract Despite recent improvements in treatment options, breast cancer remains the second leading cause of cancer-related deaths among women, with metastasis of the primary tumor accounting for most of these deaths. Signaling by fibroblast growth factor receptors (FGFRs) is active in 85% of breast cancers and results in enhanced proliferation, migration, invasion, and therapeutic resistance of tumor cells. A common feature of breast cancer is altered cholesterol metabolism including an increase in cholesterol stored intracellularly as cholesteryl esters (CEs). In breast cancer cells, high levels of CEs are associated with aggressive disease and CEs are essential for growth and migration of cancer cells. Furthermore, there is mounting evidence that modifications to metabolic pathways impact epigenetic processes including DNA methylation and histone post-translational modifications. These epigenetic changes support tumor progression and metastasis through oncogene activation and silencing of tumor suppressors. While there have been numerous studies focused on the role of metabolic and epigenetic changes in breast cancer, none have attempted to connect these altered pathways to upstream growth factor receptor pathways, such as the FGFR pathway, in cancer cells. We hypothesize that FGFR signaling promotes changes to cholesterol metabolism and epigenetic regulation which lead to breast cancer progression. To study the proposed roles of FGFR signaling, we utilized murine mammary cells of differing metastatic abilities with inducible, oncogenic FGFR1 signaling. We also included the FGFR-dependent murine mammary tumor lines 4T1 and 4T07 which demonstrate differing metastatic capabilities. Through gene expression studies, we found an FGFR-mediated increase in cholesterol metabolic processes including cholesterol storage, uptake, and synthesis. Along with this, we found an FGFR-mediated increase in CE content in our models. Interestingly, these changes were exclusive to our highly metastatic models. Additionally, we have identified FGFR-mediated changes in the expression of histone modifying enzymes in our cell lines. Many of the enzymes modified by FGFR have been previously reported to play a role in breast cancer metastasis. To further elucidate the role of enhanced cholesterol storage in breast cancer progression, we treated cells with pharmacological inhibitors of cholesterol storage. Using in vitro assays, we demonstrate that cell survival, migration, and invasion all decrease when cholesterol storage is inhibited. Again, we observe that our highly metastatic cell line models are more sensitive to this inhibition. Taken together, these data suggest a role for FGFR signaling in promoting breast cancer progression and metastasis. With further studies, this connection may inform the development of novel therapeutic strategies to combat therapeutic resistance in breast cancer. Citation Format: Jennifer Tuokkola, Lyndsay Reese, Kaylee Schwertfeger. The Metabolic and Epigenetic Contributions of Fibroblast Growth Factor Receptor-Mediated Breast Cancer Progression [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-24-05.

Abstract P24: Elucidating the Mechanism of Action of Lenvatinib in Estrogen Receptor-Positive (ER+) Breast Cancer

Abstract Background: ER+ breast cancer is the most common subtype of breast cancer. Although most patients respond initially to endocrine therapy (ET), endocrine resistance inevitably develops, leading to disease progression. Lenvatinib, a multi-kinase inhibitor, demonstrated clinical benefit in the treatment of patients with advanced ER+ breast cancer who have progressed on ET in a phase Ib/II clinical trial from our group. Our study aims to elucidate the molecular mechanism of action of lenvatinib in ER+ breast cancer. Methods: A cell viability assay was performed to assess the sensitivity of four ER+ cell lines to lenvatinib. Western blot was used to elucidate its effect on downstream pathway signalling, and cell cycle arrest investigated through flow cytometry. A series of functional assays, including BrdU, colony formation and wound-healing assays assessed proliferative, clonogenic and migratory activity respectively. The effect of lenvatinib on epithelial-mesenchymal transition (EMT) was analysed using RT-qPCR, and compared with siRNA knockdown (KD) of Fgfr1 and Fgfr2. Results: ER+ cell lines demonstrated sensitivity to lenvatinib in the micromolar range. Western blot showed downregulation of FGFR1, FGFR2, pERK and pAKT expression post-treatment. Lenvatinib was found to induce a G1 phase arrest, suppressed cell proliferation in a dose-dependent manner, and diminished both the clonogenic ability and migratory activity of ER+ cells. Lenvatinib treatment reduced expression of Fgfr1, Fgfr2 and the mesenchymal markers N-cad and Fibronectin, while increasing the expression of the epithelial markers E-cad and Claudin-1, indicating potential inhibition of EMT. A similar change in EMT marker expression was observed in Fgfr1 KD but not Fgfr2 KD cells. Conclusion: Lenvatinib demonstrated potent anti-cancer activity and induction of G1 phase arrest, leading to decreased cell proliferation, reduction of clonogenic ability and cell migration. EMT inhibition was also observed, possibly through the FGFR1 signalling pathway. Citation Format: Natasha Gandasasmita, Gauri Vaidya, Arpita Datta, Charlie Marvalim, Joline Si Jing Lim, Soo Chin Lee. Elucidating the Mechanism of Action of Lenvatinib in Estrogen Receptor-Positive (ER+) Breast Cancer [abstract]. In: Proceedings of Frontiers in Cancer Science; 2023 Nov 6-8; Singapore. Philadelphia (PA): AACR; Cancer Res 2024;84(8_Suppl):Abstract nr P24.

Abstract LB319: Klf5 acetylation remodels tumor microenvironment to constrain PTEN-deficient prostate tumor growth

Abstract Prostate cancer is the most common cancer and the second leading cause of cancer-related death in men in the United States. PTEN deficiency is prevalent in patients with prostate cancer. As a tumor suppressor, PTEN is mutated in approximately 20% of primary prostate cancers, and up to 50% of metastatic castration resistant prostate cancer. PTEN inactivation results in high-grade adenocarcinoma with a long latency. The limited tumor progression induced by PTEN deficiency suggests that additional molecular events are activated to constrain tumor progression, and second hits are required. Understanding these secondary genetic hits will provide the rationale for combined therapies in prostate cancer treatment. In this study, we employed a unique genetically knockin mouse model and found that PTEN deficiency induces a KLF5 K369 acetylation-dependent barrier that attenuates FGFR1 signaling and constrains prostate tumor growth. More importantly, we discovered novel microenvironmental crosstalk between prostate cancer cells and cancer associated fibroblasts (CAFs). As suggested by RNA-seq and bioinformatic analyses and further validated by molecular and cellular experiments, we found that interruption of KLF5 acetylation in cancer cells stimulates CAFs to release FGF9 via TNF-α, and FGF9 activating FGFR1 signaling in cancer cells. In addition to this paracrine crosstalk, deacetylated KLF5 induces CX3CR1 and facilitates FGFR1 activation. Our findings provide a proof of concept for posttranslational modifications as essential molecular events induced by PTEN inactivation to stall prostate cancer progression and demonstrate KLF5 acetylation as a key component in a negative feedback loop by which FGFR1 was suppressed by AKT activation. This study reveals a paracrine reciprocal communication between cancer cells and fibroblasts and provides a clinical rationale for combined therapies using FGFR1 inhibitors (or CX3CR1 inhibitors) and p-AKT inhibitors in PTEN-deficient prostate cancer. Citation Format: Baotong Zhang, Mingcheng Liu, Fengyi Mai, Siyuan Xia, Jin-Tang Dong. Klf5 acetylation remodels tumor microenvironment to constrain PTEN-deficient prostate tumor growth [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 LB319.

Abstract 6547: Dysregulated FGFR3 signaling alters immune landscape in bladder cancer and presents therapeutic possibilities

Abstract Bladder cancer is an increasingly prevalent global disease that continues to cause morbidity and mortality despite recent advances in treatment. Immune checkpoint inhibitors (ICI) and FGFR-targeted therapeutics have had limited success in bladder cancer when used as monotherapy. Emerging data suggests that the combination of these two therapies could lead to improved clinical outcomes. The optimal strategy for combining these agents remains uncertain. Mathematical models, and more specifically agent-based models (ABMs), have shown recent successes in uncovering the multiscale dynamics that shape the trajectory of cancer. They have enabled the optimization of treatment methods and identification of novel therapeutic strategies. To assess the combined effects of anti-PD-1 antibodies and anti-FGFR3 small molecule inhibitors (SMI) on tumor growth and the immune response, we built an ABM that captures key facets of tumor heterogeneity and CD8+ T cell compartments, their spatial interactions, and their response to therapeutic pressures. With our model, we quantify how tumor antigenicity and FGFR3 activating mutations impact disease trajectory and response to anti-PD-1 antibodies and anti-FGFR3 SMI. We find that even a small population of weakly antigenic tumor cells bearing an FGFR3 mutation can render the tumor resistant to combination therapy. However, highly antigenic tumors can overcome therapeutic resistance mediated by FGFR3 mutation. The optimal therapy depends on the strength of the FGFR3 signaling pathway. Under certain conditions, ICI alone is optimal; in others, ICI followed by anti-FGFR3 therapy is best. These results point to the need to quantify FGFR3 signaling and the fitness advantage conferred on bladder cancer cells harboring this mutation. Employing this ABM modeling approach may enable rationally designed treatment plans to improve clinical outcomes. Citation Format: Daniel R. Bergman, Erica Trujillo, Lie Li, Alexander T. Pearson, Randy Sweis, Trachette L. Jackson. Dysregulated FGFR3 signaling alters immune landscape in bladder cancer and presents therapeutic possibilities [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 6547.

Abstract 6836: Single-cell RNA sequencing of FUS::DDIT3 myxoid/round cell liposarcoma delineates mechanisms of oncogenic progression and immune escape

Abstract Myxoid/Round Cell Liposarcoma (MRCL) is an understudied soft tissue sarcoma that typically affects young adults and accounts for 30% of all liposarcomas. MRCL is characterized by oncogenic DDIT3 fusions, with FUS::DDIT3 being present in over 90% of cases. However, the cellular origins and oncogenic mechanisms of MRCL remain incompletely defined. Here we report oncogene transcription, and tumor-immune interactions in a cohort of 5 patient tumors with matched normal tissue for which we sequenced the transcriptomes of approximately 45,000 single cells using 10X Genomics, and full-length transcripts in approximately 20,000 single cells via Oxford Nanopore in 2 of these patients. Our results reveal two distinct cancer cell populations: Early Cancer Cells (ECC) and Advanced Cancer Cells (ACC). These cells appear to derive from adipose stem progenitor cells (ASPC) and fall along an ASPC→ECC→ACC pseudo-time axis. Along this axis, a distinct pattern emerges where oncogenes tend to be upregulated and tumor suppressor genes (TSG) tend to be downregulated and these appear to be mutually exclusive. Comparing ECC to ASPC we see increased expression of HIPPO and PI3K pathway oncogenes, FGFR2 and IGF1R RTKs, and downregulation of the TSG CDKN2A and CDKN1A. ACC show upregulation of hedgehog, ErbB, WNT, HIPPO, PI3K, and MAPK signaling pathways compared to ECC. Full-length transcript sequencing at the single-cell level shows a consistent expression of the FUS::DDIT3 fusion transcript in both ECC and ACC populations, confirming that these populations are cancer cells. Furthermore, MRCL displays several immune escape mechanisms, including poor immune infiltration and a marked decline of HLA Class I expression along the pseudo-time axis from ECC to ACC, suggesting a complex interplay between oncogenic signaling and immune evasion. These results suggest that MRCL likely originates from ASPC and expression of FUS:DDIT3 oncoprotein induces early HIPPO, PI3K, FGFR2, and insulin signaling pathway expression in ECC with further hedgehog, ErbB, MAPK, and WNT pathway activation in ACC. This progressive activation in oncogenic signaling is associated with immune evasion. This is the first single-cell RNA seq analysis to detect the presence of the FUS::DDIT3 fusion in ECC and ACC significantly advancing our understanding of the mechanisms of MRCL oncogenesis, immune escape, and identifies potential novel therapeutic targets. Citation Format: Rodrigo Gularte-Mérida, Evan Seffar, George Li, Young-Mi Kim, Narasimhan P. Agaram, Nicholas Socci, Francisco Sanchez-Vega, Nikolaus Schultz, Samuel Singer. Single-cell RNA sequencing of FUS::DDIT3 myxoid/round cell liposarcoma delineates mechanisms of oncogenic progression and immune escape [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 6836.

Abstract 3308: A selective FGFR1/2 degrader overcomes endocrine resistance in ER+/FGFR1-amplified andFGFR1/2-mutant breast cancer

Abstract FGFR1 amplification and FGFR1/2 activating mutations are associated with resistance to antiestrogens in the estrogen receptor-positive (ER+) breast cancer. In this study, we investigated selective degradation of FGFR1/2 using the proteolysis-targeted chimera (PROTAC) DGY-09-192 as a novel therapeutic strategy to overcome resistance to antiestrogens in ER+ breast cancers harboring FGFR1-amplification or FGFR1/2 activating mutations. Treatment of ER+/FGFR1-amplified CAMA1 and MDA-MB-134 breast cancer cells with DGY-09-192 degraded FGFR1 and suppressed phosphorylation of FGFR1 and its downstream targets FRS2, AKT, and ERK1/2. DGY-09-192-mediated FGFR1 degradation were rescued by a proteasome inhibitor, MG132, suggesting that the antitumor activity of DGY-09-192 depends on proteasome-mediated degradation. Growth of CAMA1 and MDA-MB-134 cells were modestly inhibited by single-agent DGY-09-192 or the ER degrader fulvestrant, but the combination completely arrested cell proliferation. Treatment of female NSG mice bearing established ER+/FGFR1-amplified patient-derived xenografts (PDXs) with single-agent DGY-09-192 (40 mg/kg/day, i.p.) or fulvestrant (5 mg/week, s.c.) delayed tumor growth, respectively. However, treatment with DGY-09-192 + fulvestrant induced tumor regression in all mice (n=7), suggesting that a FGFR1 degrader plus an antiestrogen can serve as an effective therapeutic combination for ER+/FGFR1-amplified breast cancer. Next, we examined whether ER+ breast cancer cells harboring FGFR1/2 hotspot mutations are sensitive to DGY-09-192. Ectopic expression of FGFR1N546K, the most common FGFR1 mutation in breast cancer, activated FGFR1 signaling and induced resistance to fulvestrant compared to MCF7 cells transduced with wild-type FGFR1. EFM-19 cells harboring FGFR2K659E exhibited resistance to fulvestrant in vitro. Treatment of both cell lines with DGY-09-192 degraded the mutant FGFR1N546K and FGFR2K659E, respectively, blocked phosphorylation of the FGFR downstream targets, and markedly inhibited cell proliferation. These results suggest that PROTAC-mediated degradation of FGFR1/2 effectively blocks the growth of ER+, FGFR1/2-mutant breast cancers resistant to antiestrogens. Conclusions: DGY-09-192 induced FGFR1/2 degradation and blocks FGFR downstream signaling in ER+/FGFR1-amplified and FGFR1/2-mutant breast cancer cells. The combination of DGY-09-192 and fulvestrant exhibited superior antitumor effects relative to each monotherapy alone in vitro and/or in vivo. Therefore, PROTAC-mediated FGFR1/2 degradation represents a promising therapeutic strategy for ER+ breast cancers harboring FGFR1-amplification or FGFR1/2 activating mutations. Citation Format: Yasuaki Uemoto, Chang-Ching Lin, Bingnan Wang, Dan Ye, Emmanuel Bikorimana, Alberto Servetto, Luigi Formisano, Fabiana Napolitano, Rosario Chica Parrado, Saurabh Mendiratta, Chuo Chen, Ariella B. Hanker, Carlos L. Arteaga. A selective FGFR1/2 degrader overcomes endocrine resistance in ER+/FGFR1-amplified andFGFR1/2-mutant breast cancer [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 3308.