RXRA

引言 机体组织内存在干细胞以实现组织稳态和损伤修复。在成年人中，组织内每天因磨损而损失的500-700亿个细胞通过谱系限制的驻留性干细胞得到补充【1】。正常情况下，驻留性干细胞定居在组织独特的生态位中，通过复杂的微环境维持自我更新和向特定细胞的定向分化。研究发现，组织结构损伤会破坏这种干细胞的局部微环境，导致稳态失衡。在这个过程中，干细胞会发生一种名为谱系可塑性（lineage plasticity）的改变，并向组织损伤部位迁移，增殖分化为其他谱系细胞【2】。谱系可塑性是一种典型的损伤诱导应激反应，赋予干细胞命运选择的灵活性，其特征是同时表达新谱系和旧谱系细胞的经典转录因子【2】。损伤组织修复完毕后，干细胞会退出可塑性状态，重新定居于生态位中重塑稳态。这种退出过程一旦发生紊乱会导致慢性损伤状态或癌变（Science | 前列腺癌谱系可塑性依赖于JAK/STAT炎症信号通路）。然而，谱系可塑性状态如何退出目前仍然不清楚。 干细胞谱系可塑性研究多在皮肤损伤、移植和肿瘤等领域。作为一个较为理想模型，皮肤内存在两种成体干细胞，位于毛囊突起的毛囊干细胞（hair follicle stem cells，HFSCs）和表皮基底层的表皮干细胞（epidermal stem cells，EpSCs）【3, 4】。在不同损伤深度下，不同程度的HFSCs和EpSCs会迁移出生态位，进入谱系可塑性状态，修复损伤组织。皮肤干细胞谱系可塑性的典型特征是同时表达HFSCs的转录因子Sox9和EpSCs的转录因子Klf5【3】。有意思的是，离体分离的HFSCs在富血清和营养因子培养下，会模拟类似的谱系可塑性状态，表现为Sox9和Klf5的共表达，以及广泛的谱系可塑性相关染色质重塑【5】。这种现象背后的影响因素和机制仍不清楚。 近来，美国洛克菲勒大学霍华德休斯医学研究所的Elaine Fuchs研究团队在Science杂志在线发表题为Vitamin A resolves lineage plasticity to orchestrate stem cell lineage choices的研究文章。该研究以小鼠皮肤损伤为模型，发现未退出谱系可塑性的皮肤干细胞不能有效促进毛发再生和皮肤修复，并首次鉴定维生素A作为毛囊干细胞生态位的关键活性物质调节毛囊干细胞的谱系选择。 团队首先构建Klf5-EGFP-NLS的HFSCs细胞，该细胞在富血清条件下表达Klf5，血清撤掉后Klf5表达降低。通过此细胞体外模型，作者筛选3种小分子可以显著降低Klf5水平，包括ERK抑制剂（ERKi）、蛋白酶C抑制剂（PKCi）和全反式维甲酸（atRA）。鉴于ERKi在正常毛发周期中的作用，作者关注PKCi和atRA。虽然atRA在降低Klf5水平上不如PKCi，但其能显著促进Sox9表达，两者同时处理更能促进谱系可塑性状态退出并支持HFSCs身份。scRNA-seq在单细胞转录组上进一步支持上述发现。总之，这些数据表明atRA和PKCi在脱离谱系可塑性状态而维持HFSCs身份的作用。 随后，作者在HFSCs中转染视黄酸反应原件（retinoic acid response element，RARE）-RFP腺病毒，可以在视黄酸（retinoic acid，RA）存在下与视黄酸受体（retinoic acid receptor，RAR）-维甲酸X受体（retinoid X receptor，RXR）结合促进RFP表达而监测视黄酸代谢活性。atRA、视黄醇或维生素A都可以激活上述细胞的RFP表达，表明HFSCs可以代谢视黄醇为 atRA以及具有atRA受体。在体内RARE-RFP腺病毒转染后同样监测到皮肤损伤时RFP活性降低而谱系可塑性状态诱导；损伤2周后RFP活性恢复而SOX9+KLF5+细胞数量降低，表明atRA与谱系可塑性在损伤修复中的负相关。使用Sox9CreER;Rxra-fl/fl小鼠在HFSCs中敲除RXRa时，小鼠皮肤在没有损伤时HFSCs也表现出谱系可塑性表型，充分说明atRA信号抑制谱系可塑性以及维持HFSCs身份。随后，团队分离WT和RXR敲除小鼠的HFSCs并给予谱系可塑性诱导（FBS）和谱系可塑性消除（atRA+PKCi）后行ATAC-seq分析，结果的确说明atRA在染色质水平上消除谱系可塑性状态并促进HFSCs身份。 尽管atRA对于谱系可塑性状态的退出是至关重要的，但其并足以完全复制HFSCs体内特征。团队进一步研究atRA如何与已知的调控HFSCs的信号通路发挥功能。BMPs由HFSCs生态位的内突出层产生并维持HFSCs静息状态。虽然atRA允许HFSCs增殖，但低剂量atRA（10 nM）+BMPs却引发细胞周期退出并表现出静息特征，表明atRA建立必要的染色质基础并与BMPs协同促进静息并维持干性。相反，在新的生发周期中，HFSCs在BMP抑制剂和WNT激活调控下从静息态转变为激活态。激活的HFSCs产生SOX9+TCF3/4+和LEF1+TCF1+两种干细胞群体。有意思的是，R-spondins（WNT激动剂）与atRA结合也能促进HFSCs由静息向激活转换，但所需atRA最优浓度要比维持静息的atRA最优浓度高10倍，提示atRA的相对浓度决定HFSCs维持静息（低水平）或激活（高水平）状态。随后，作者使用atRA介导的表皮抑制和谱系可塑性退出特性建立培养平台研究不同信号对HFSC的分化影响。结果显示HFSCs的谱系可塑性退出状态是接受毛囊微环境多种信号协调发育分化的先决条件。 最后，作者使用Sox9CreER;Rxra-fl/fl小鼠以及皮肤Cyp26b1（atRA降解酶）转染实验均证实在皮肤损伤时，atRA代谢缺陷的HFSCs更容易进入损伤皮肤上皮；然而，此时毛发的生长却受限，表明皮肤损伤后恢复atRA活性对于谱系可塑性退出以及毛发生长是必要的。与此同时，为了进一步贴近临床，作者也在维生素A饮食缺陷的小鼠中发现皮肤损伤时更多HFSCs进入谱系可塑性，但此过程可以被皮肤atRA涂抹补充抑制。尽管皮肤损伤时atRA代谢缺陷促进HFSCs向上皮募集并向表皮转化参与修复，但矛盾的是，实际皮肤屏障的恢复却仍旧延迟，表明皮肤可塑性退出同时也是皮肤修复的基础。 综上所述，这项研究不仅指出干细胞谱系可塑性的退出是组织稳态维持的重要因素，也证实维生素A代谢作为干细胞谱系选择的关键作用，对毛发生长、损伤修复和肿瘤等有治疗意义。 模式图（Credit: Science） 参考文献 1. Yejing, Ge., Elaine, Fuchs.(2018). Stretching the limits: from homeostasis to stem cell plasticity in wound healing and cancer. Nat Rev Genet, 19(5), 0. doi:10.1038/nrg.2018.9 2. Yejing, Ge., Nicholas C, Gomez., Rene C, Adam., Maria, Nikolova., Hanseul, Yang., Akanksha, Verma., Catherine Pei-Ju, Lu., Lisa, Polak., Shaopeng, Yuan., Olivier, Elemento., Elaine, Fuchs.(2017). Stem Cell Lineage Infidelity Drives Wound Repair and Cancer. Cell, 169(4), 0. doi:10.1016/j.cell.2017.03.042 3. Cedric, Blanpain., William E, Lowry., Andrea, Geoghegan., Lisa, Polak., Elaine, Fuchs.(2004). Self-renewal, multipotency, and the existence of two cell populations within an epithelial stem cell niche. Cell, 118(5), 0. doi:10.1016/j.cell.2004.08.012 4. Kevin Andrew Uy, Gonzales., Lisa, Polak., Irina, Matos., Matthew T, Tierney., Anita, Gola., Ellen, Wong., Nicole R, Infarinato., Maria, Nikolova., Shijing, Luo., Siqi, Liu., Jesse S S, Novak., Kenneth, Lay., Hilda Amalia, Pasolli., Elaine, Fuchs.(2021). Stem cells expand potency and alter tissue fitness by accumulating diverse epigenetic memories. Science, 374(6571), 0. doi:10.1126/science.abh2444 5. V R, Iyer., M B, Eisen., D T, Ross., G, Schuler., T, Moore., J C, Lee., J M, Trent., L M, Staudt., J Jr, Hudson., M S, Boguski., D, Lashkari., D, Shalon., D, Botstein., P O, Brown.(1999). The transcriptional program in the response of human fibroblasts to serum. Science, 283(5398), 0. doi:10.1126/science.283.5398.83 https://doi.org/10.1126/science.adi7342 责编|探索君 排版|探索君 文章来源|“BioArt” End 往期精选 围观 一文读透细胞死亡(Cell Death) | 24年Cell重磅综述（长文收藏版） 热文 Cell | 是什么决定了细胞的大小？ 热文 Nature | 2024年值得关注的七项技术 热文 Nature | 自身免疫性疾病能被治愈吗？科学家们终于看到了希望 热文 CRISPR技术进化史 | 24年Cell综述

--First-in-human trial evaluating safety, tolerability, and clinical activity of FX-909 in patients with advanced solid malignancies including advanced urothelial carcinoma-- CAMBRIDGE, Mass., Jan. 26, 2024 /PRNewswire/ -- Flare Therapeutics Inc., a biotechnology company targeting transcription factors (TF) to discover precision medicines for cancer and other diseases, today announced a poster presentation outlining the Phase 1 clinical trial design of FX-909, a highly potent and selective inhibitor of PPARG, at the 2024 ASCO Genitourinary Cancers Symposium taking place from January 25-27, 2024 in San Francisco, CA. "FlareTx has built a robust body of preclinical evidence that supports investigation of FX-909 in clinical trials in patients," said Michael L. Meyers, M.D., Ph.D., Chief Medical Officer of Flare Therapeutics. "Results shown to date reveal that FX-909 eradicates tumors in urothelial cancer (UC) animal models at low oral doses. Our scientists have also leveraged high PPARG expression as a defining feature of luminal muscle-invasive UC (MIUC) to identify genetically defined populations and select the patients that may be more likely to benefit from a treatment like FX-909. In addition, we recently shared novel translational data correlating increased PPARG expression with an immunosuppressive tumor microenvironment (TME) and shorter real-world progression-free survival to anti-PD1 treatment." PPARG drives luminal cell identity and accounts for two-thirds of all advanced cases of UC. Targeting PPARG offers a novel approach to treating advanced UC that could pave the way to improved clinical outcomes in patients with a luminal subtype. Treatment of genetically defined UC xenografts with FX-909 has shown an 84% tumor growth inhibition at a dose expected to be equivalent to a 50 mg dose in humans – the starting dose in the Phase 1 clinical study. FX-909-CLINPRO-1 (NCT05929235) is a first-in-human, multicenter, open-label Phase 1 study designed to assess the safety and tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary clinical activity of FX-909 given orally to patients with advanced solid malignancies. Exploratory objectives include the evaluation of patient selection biomarkers from tissue and blood samples and association with clinical outcomes. In the US, approximately 10 sites are planned for Phase 1A and 12-15 sites for Phase 1B. "While advanced bladder cancer and MIUC remain lethal diseases, we are starting to see a real renaissance in providing new treatment options, thanks to increasing knowledge of the underlying molecular pathways involved," said Gopa Iyer, Genitourinary Oncologist & Early Drug Development Specialist, Memorial Sloane Kettering Cancer Center. "FlareTx's novel mechanism of action offers the possibility of a much needed second line option for patients who demonstrate disease progression following standard-of-care platinum chemotherapy, immune checkpoint inhibition, and/or ADC-based therapies." Details for the presentation are as follows: Poster Title: A Phase 1, First-in-Human, Dose-Escalation and Expansion Study of FX-909 in Patients with Advanced Solid Malignancies, Including Advanced Urothelial Carcinoma Abstract Number: TPS709 Presenter: Gopa Iyer MD, Memorial Sloane Kettering Cancer Center Date, Time: Session B: Urothelial Carcinoma – Friday, January 26, 2024, 11:30 AM-1:00 PM PT; 5:45 PM-6:45 PM PT Location: Moscone West Conference Center, San Francisco, California Posters, Exhibits, and Food Room About FX-909 Flare Therapeutics' lead investigational compound, FX-909, is a first-in-class, highly potent and selective small molecule that inhibits the transcription factor peroxisome proliferator-activated receptor gamma (PPARG) to treat patients with the luminal subtype of advanced urothelial carcinoma (UC) and potentially other solid tumors. Preclinical data for FX-909 has demonstrated robust anti-tumor activity, excellent PK/PD correlation, durable efficacy, and a favorable safety profile in mouse models of UC (PPARG-amp and RXRA-mut) at very low oral doses. About the FX-909 Phase 1 Study The ongoing Phase 1 study is a first-in-human, dose-escalation and -expansion study of FX-909 in patients with advanced solid malignancies, including advanced urothelial carcinoma. The study will evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics and clinical activity of FX-909. FX-909 will be given initially in a dose-escalation phase (Part A) to determine the recommended Phase 2 dose. FX-909 will be given initially orally once daily in 28-day cycles. Part B will be a monotherapy expansion phase to further evaluate the efficacy, safety, tolerability, pharmacokinetics, and pharmacodynamics of FX-909 in patients with locally advanced (unresectable) or metastatic urothelial carcinoma. Additional information on this clinical trial can be found on (NCT05929235). About Advanced Urothelial Carcinoma (UC) There are an estimated 725,549 people living with bladder cancer in the United States alone, making it the sixth most common cancer overall, and fourth most common among men (SEER – 2020). Each year, there are more than 83,000 new cases diagnosed among men and women, and about 25% of those cases are classified as muscle-invasive UC (DRG 2020). Treatment outcomes have remained poor with typical five-year survival rates of 8% in advanced metastatic disease (SEER – 2020). The transcription factor peroxisome proliferator-activated receptor gamma (PPARG) is associated with the luminal lineage subtype which represents approximately 65% of all advanced UC cases (Robertson, Cell 2017). Recurrent genetic alterations in PPARG are characteristic of this molecular subtype. About Flare Therapeutics Inc. Flare Therapeutics is a biotechnology company exclusively focused on drugging transcription factors (TFs) to fully unlock the therapeutic potential of this previously elusive target class. Flare Therapeutics' integrated discovery engine converges rich genetic, biochemical, and chemical insights to reveal druggable pockets and identify small molecule ligands capable of modulating TFs of high therapeutic potential. Our proteomic and mass spectrometry platform is powered by a proprietary library of electrophilic compounds unique to Flare Therapeutics. The team has rapidly established an emerging pipeline of programs, highlighted by FX-909, a first-in-class investigational orally bioavailable small molecule inhibitor of PPARG, a master regulator of the luminal lineage in advanced urothelial cancer that has entered the clinic. For more information, please visit and follow us on LinkedIn. SOURCE Flare Therapeutics

--Poster presentation proposes targeting PPARG for the treatment of muscle-invasive urothelial cancer (MIUC) may help overcome resistance to immunotherapy-- CAMBRIDGE, Mass., Nov. 3, 2023 /PRNewswire/ -- Flare Therapeutics Inc., a clinical-stage biotechnology company targeting transcription factors to discover precision medicines for cancer and other diseases, today revealed molecular real-world data (RWD) demonstrating that high PPARG expression in patients with MIUC is associated with an immunosuppressive tumor microenvironment (TME) and shorter real-world progression-free survival to anti-PD1 treatment. The translational data were shared at the Society for Immunotherapy of Cancer's 38th Annual Meeting (SITC) 2023 taking place November 1-5, 2023 in San Diego, California. "While immunotherapy approvals have changed the treatment landscape for MIUC, approximately 70% of patients will still succumb to refractory or acquired resistance," said Michaela Bowden, Ph.D., Chief Development Officer at Flare Therapeutics. "These results offer a unique opportunity to further investigate an immune-mediated mechanism of action for FX-909 with potential to combine with an anti-PD1 agent." In the poster presentation titled, "PPARG amplification is associated with lack of response to anti-PD1 in Muscle-Invasive Urothelial Cancer," molecular RWD, comprising 1,393 genomic and/or transcriptomic profiles from MIUC patients were utilized to evaluate baseline PPARG expression and amplification associated with anti-PD1 response in MIUC patients. Additional key takeaways are as follows: Higher PPARG expression and PPARG amplification are negatively correlated with PD-L1 expression in MIUC. Tumors with elevated PPARG levels and PPARG amplification exhibited a suppressive immune phenotype, typified by an inverse association with CD8+ T cell infiltration. PPARG amplification is significantly associated with shorter real-world Progression Free Survival to anti-PD1. FX-909, a first-in-class covalent PPARG inhibitor, entered the clinic this year and is currently being evaluated in a Phase 1 study. The data presented today suggest that FX-909 in combination with ICI agents could potentially provide a new therapeutic strategy that helps MIUC patients with high PPARG expression overcome resistance to immunotherapy. About FX-909 Flare Therapeutics' lead investigational compound, FX-909, is a first-in-class novel, highly potent and selective small molecule that inhibits the transcription factor peroxisome proliferator-activated receptor gamma (PPARG) to treat patients with the luminal subtype of advanced urothelial carcinoma (UC) and potentially other solid tumors. Preclinical data for FX-909 has demonstrated robust anti-tumor activity, excellent PK/PD correlation, durable efficacy, and a favorable safety profile in mouse models of UC (PPARG-amp and RXRA-mut) at very low oral doses. About the FX-909 Phase 1 Study The ongoing phase 1 study is a first-in-human, dose-escalation and -expansion study of FX-909 in patients with advanced solid malignancies, including advanced urothelial carcinoma. The study will evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics and clinical activity of FX-909. FX-909 will be given initially in a dose-escalation phase (Part A) to determine the recommended phase 2 dose. FX-909 will be given initially orally once daily in 28-day cycles. Part B will be a monotherapy expansion phase to further evaluate the efficacy, safety, tolerability, pharmacokinetics, and pharmacodynamics of FX-909 in patients with locally advanced (unresectable) or metastatic urothelial carcinoma. Additional information on this clinical trial can be found on (NCT05929235). About Advanced Urothelial Carcinoma (UC) In 2020, there were an estimated 725,549 people living with bladder cancer in the United States alone, making it the sixth most common cancer overall, and fourth most common among men (SEER – 2020). Each year, there are more than 83,000 new cases diagnosed among men and women, and about 25% of those cases are classified as muscle-invasive UC (DRG 2020). Advanced UC has high rates of recurrence, where treatment outcomes have remained poor with typical five-year survival rates of 8% in advanced metastatic disease (SEER – 2020). The transcription factor peroxisome proliferator-activated receptor gamma (PPARG) is associated with the luminal lineage subtype reflecting approximately 65% of all advanced UC cases (Robertson, Cell 2017). Recurrent genetic alterations in PPARG are characteristic of this molecular subtype. About Flare Therapeutics Inc. Flare Therapeutics is a biotechnology company exclusively focused on drugging transcription factors (TFs) to fully unlock the therapeutic potential of this previously elusive target class. Flare Therapeutics' integrated discovery engine converges rich genetic, biochemical, and chemical insights to reveal druggable pockets and identify small molecule ligands capable of modulating TFs of high therapeutic potential. Our proteomic and mass spectrometry platform is powered by a proprietary library of electrophilic compounds unique to Flare Therapeutics. The team has rapidly established an emerging pipeline of programs, highlighted by FX-909, a first-in-class investigational orally bioavailable small molecule inhibitor of PPARG, a master regulator of the luminal lineage in advanced Urothelial Cancer that has entered the clinic. For more information, please visit and follow us on LinkedIn. SOURCE Flare Therapeutics