Protein arginine methyltransferase 5 (PRMT5) is an actionable therapeutic target in CDK4/6 inhibitor-resistant ER+/RB-deficient breast cancer [RNA-seq_Pemrametostat]
Ontology highlight
ABSTRACT: CDK4/6 inhibitors (CDK4/6i) have improved survival of patients with estrogen receptor-positive (ER+) breast cancer. However, patients treated with CDK4/6i eventually develop drug resistance and progress. RB1 loss-of-function alterations confer resistance to CDK4/6i, but the optimal therapy for these patients is unclear. Through a genome-wide CRISPR screen, we identified protein arginine methyltransferase 5 (PRMT5) as a molecular vulnerability in ER+/RB1-knockout (RBKO) breast cancer cells. Inhibition of PRMT5 blocked the G1-to-S transition in the cell cycle independent of RB, leading to growth arrest in RBKO cells. Proteomics analysis uncovered fused in sarcoma (FUS) as a downstream effector of PRMT5. Inhibition of PRMT5 resulted in dissociation of FUS from RNA polymerase II (Pol II), which led to Ser2 Pol II hyperphosphorylation, intron retention, and subsequent downregulation of proteins involved in DNA synthesis. Furthermore, treatment with the PRMT5 inhibitor pemrametostat and a selective ER degrader fulvestrant synergistically inhibited growth of ER+/RB-deficient cell-derived and patient-derived xenografts. These findings highlight the potential of dual ER and PRMT5 blockade as a novel therapeutic strategy to overcome resistance to CDK4/6i in ER+/RB-deficient breast cancer.
Project description:CDK4/6 inhibitors (CDK4/6i) have improved survival of patients with estrogen receptor-positive (ER+) breast cancer. However, patients treated with CDK4/6i eventually develop drug resistance and progress. RB1 loss-of-function alterations confer resistance to CDK4/6i, but the optimal therapy for these patients is unclear. Through a genome-wide CRISPR screen, we identified protein arginine methyltransferase 5 (PRMT5) as a molecular vulnerability in ER+/RB1-knockout (RBKO) breast cancer cells. Inhibition of PRMT5 blocked the G1-to-S transition in the cell cycle independent of RB, leading to growth arrest in RBKO cells. Proteomics analysis uncovered fused in sarcoma (FUS) as a downstream effector of PRMT5. Inhibition of PRMT5 resulted in dissociation of FUS from RNA polymerase II (Pol II), which led to Ser2 Pol II hyperphosphorylation, intron retention, and subsequent downregulation of proteins involved in DNA synthesis. Furthermore, treatment with the PRMT5 inhibitor pemrametostat and a selective ER degrader fulvestrant synergistically inhibited growth of ER+/RB-deficient cell-derived and patient-derived xenografts. These findings highlight the potential of dual ER and PRMT5 blockade as a novel therapeutic strategy to overcome resistance to CDK4/6i in ER+/RB-deficient breast cancer.
Project description:CDK4/6 inhibitors (CDK4/6i) have improved survival of patients with estrogen receptor-positive (ER+) breast cancer. However, patients treated with CDK4/6i eventually develop drug resistance and progress. RB1 loss-of-function alterations confer resistance to CDK4/6i, but the optimal therapy for these patients is unclear. Through a genome-wide CRISPR screen, we identified protein arginine methyltransferase 5 (PRMT5) as a molecular vulnerability in ER+/RB1-knockout (RBKO) breast cancer cells. Inhibition of PRMT5 blocked the G1-to-S transition in the cell cycle independent of RB, leading to growth arrest in RBKO cells. Proteomics analysis uncovered fused in sarcoma (FUS) as a downstream effector of PRMT5. Inhibition of PRMT5 resulted in dissociation of FUS from RNA polymerase II (Pol II), which led to Ser2 Pol II hyperphosphorylation, intron retention, and subsequent downregulation of proteins involved in DNA synthesis. Furthermore, treatment with the PRMT5 inhibitor pemrametostat and a selective ER degrader fulvestrant synergistically inhibited growth of ER+/RB-deficient cell-derived and patient-derived xenografts. These findings highlight the potential of dual ER and PRMT5 blockade as a novel therapeutic strategy to overcome resistance to CDK4/6i in ER+/RB-deficient breast cancer.
Project description:CDK4/6 inhibitors (CDK4/6i) have improved survival of patients with estrogen receptor-positive (ER+) breast cancer. However, patients treated with CDK4/6i eventually develop drug resistance and progress. RB1 loss-of-function alterations confer resistance to CDK4/6i, but the optimal therapy for these patients is unclear. Through a genome-wide CRISPR screen, we identified protein arginine methyltransferase 5 (PRMT5) as a molecular vulnerability in ER+/RB1-knockout (RBKO) breast cancer cells. Inhibition of PRMT5 blocked the G1-to-S transition in the cell cycle independent of RB, leading to growth arrest in RBKO cells. Proteomics analysis uncovered fused in sarcoma (FUS) as a downstream effector of PRMT5. Inhibition of PRMT5 resulted in dissociation of FUS from RNA polymerase II (Pol II), which led to Ser2 Pol II hyperphosphorylation, intron retention, and subsequent downregulation of proteins involved in DNA synthesis. Furthermore, treatment with the PRMT5 inhibitor pemrametostat and a selective ER degrader fulvestrant synergistically inhibited growth of ER+/RB-deficient cell-derived and patient-derived xenografts. These findings highlight the potential of dual ER and PRMT5 blockade as a novel therapeutic strategy to overcome resistance to CDK4/6i in ER+/RB-deficient breast cancer.
Project description:The retinoblastoma tumor suppressor (RB1) plays a critical role in coordinating multiple pathways that impact on tumor initiation, disease progression, and therapeutic responses. Here we interrogated the effect of CDK4/6 inhibitor in combination with mTOR inhibtor. Also, we interrogtaed the efffect of AURK and WEE1 inhibition in ER+ breast cacner models While the RB-pathway has been purported to exhibit multiple mutually exclusive events, only RB1 is mutually exclusive with multiple genetic events that deregulate CDK4/6 activity. Using an isogenic ER+ breast cancer model with targeted RB1 deletion, we identified gene expression features that link CDK4/6 activity and RB-dependency (CDK4/6-RB integrated signature). We also investigated the role of RB on apoptotic pathway. Single copy loss on chromosome 13q encompassing the RB1 locus is prevalent in many cancers, and is associated with reduced expression of multiple genes on 13q including RB1, and inversely related to the CDK4/6-RB integrated signature supporting a genetic cause/effect relationship. To probe the broader implications on tumor biology, we investigated genes that are positively and inversely correlated with the CDK4/6-RB integrated signature. This approach defined tumor-specific pathways that could represent new therapeutic vulnerabilities associated with RB-pathway activity.
Project description:The retinoblastoma tumor suppressor (RB1) plays a critical role in coordinating multiple pathways that impact on tumor initiation, disease progression, and therapeutic responses. Here we interrogated the TCGA pan-cancer data collection to probe fundamental molecular features associated with the RB-pathway across 31 tumor-types. While the RB-pathway has been purported to exhibit multiple mutually exclusive events, only RB1 is mutually exclusive with multiple genetic events that deregulate CDK4/6 activity. Using an isogenic ER+ breast cancer model with targeted RB1 deletion, we identified gene expression features that link CDK4/6 activity and RB-dependency (CDK4/6-RB integrated signature). This gene expression signature is associated with prognosis across a spectrum of tumors that exhibit average lower signature value indicative of more indolent diseases. Single copy loss on chromosome 13q encompassing the RB1 locus is prevalent in many cancers, and is associated with reduced expression of multiple genes on 13q including RB1, and inversely related to the CDK4/6-RB integrated signature supporting a genetic cause/effect relationship. To probe the broader implications on tumor biology, we investigated genes that are positively and inversely correlated with the CDK4/6-RB integrated signature. This approach defined tumor-specific pathways that could represent new therapeutic vulnerabilities associated with RB-pathway activity.
Project description:Combined CDK4/6 inhibitor (CDK4/6i) and endocrine therapy significantly improves the outcome of patients with advanced estrogen receptor-positive (ER+) breast cancer. However, resistance to this treatment and resultant disease progression remains a major clinical challenge. High expression of the receptor tyrosine kinase REarranged during Transfection (RET) has been associated with resistance to endocrine therapy in breast cancer, but the role of RET in CDK4/6i treatment response/resistance remains unexplored. To identify gene expression alterations associated with resistance to combined endocrine therapy and CDK4/6i, we performed global gene expression analysis and RNA sequencing of two ER+ breast cancer cell models resistant to this combined therapy.
Project description:Resistance to aromatase inhibitor (AI) treatment and combined CDK4/6 inhibitor (CDK4/6i) and endocrine therapy (ET) are crucial clinical challenges in treating estrogen receptor-positive (ER+) breast cancer. Understanding the resistance mechanisms and identifying reliable predictive biomarkers and novel treatment combinations to overcome resistance are urgently needed. Herein, we show that upregulation of CDK6, p-CDK2, and/or cyclin E1 is associated with adaptation and resistance to AI-monotherapy and combined CDK4/6i and ET in ER+ advanced breast cancer. Importantly, co-targeting CDK2 and CDK4/6 with ET synergistically impairs cellular growth, induces cell cycle arrest and apoptosis, and delays progression in AI-resistant and combined CDK4/6i and fulvestrant-resistant cell models and in an AI-resistant autocrine breast tumor in a postmenopausal xenograft model. Analysis of CDK6, p-CDK2, and/or cyclin E1 expression as a combined biomarker in metastatic lesions of ER+ advanced breast cancer patients treated with AI-monotherapy or combined CDK4/6i and ET revealed a correlation between high biomarker expression and shorter progression-free survival (PFS), and the biomarker combination was an independent prognostic factor in both patients cohorts. Our study supports the clinical development of therapeutic strategies co-targeting ER, CDK4/6 and CDK2 following progression on AI-monotherapy or combined CDK4/6i and ET to improve survival of patients exhibiting high tumor levels of CDK6, p-CDK2, and/or cyclin E1.
Project description:The combination of CDK4/6 inhibitors (CDK4/6i) and endocrine therapy (ET) has significantly improved outcomes for patients with hormone receptor-positive (HR+) metastatic breast cancer. However, most patients eventually develop resistance, leading to treatment discontinuation. The therapeutic benefits of maintaining CDK4/6i or transitioning to CDK2 inhibitors (CDK2i) beyond disease progression remain unclear. Here, we show that maintaining CDK4/6i and ET or combining them with CDK2i effectively suppresses the growth of drug-resistant HR+ breast cancer cells by prolonging G1-phase progression. CDK4/6i maintenance triggers a non-canonical pathway for Rb inactivation through post-translational degradation, resulting in attenuated E2F activity and slowed G1 progression. ET further augments this effect by inhibiting c-Myc-mediated E2F amplification. Although the maintenance of CDK4/6i and ET outperforms CDK2i with ET, the triple combination of CDK4/6i, CDK2i, and ET most effectively suppresses both E2F activity and tumor growth. Moreover, while overexpression of both cyclin E and A can promote resistance to the CDK4/6i and CDK2i combination, cyclin E plays a more pivotal role in developing resistance. These findings highlight the potential of sustained CDK4/6i therapy and the incorporation of CDK2i to mitigate resistance in HR+ breast cancer.
Project description:Combining CDK4/6 inhibitors (CDK4/6i) with endocrine therapy has proven clinically effective and represents now the first-line treatment for advanced Luminal Breast Cancer (LBC) patients. However, resistance to CDK4/6i almost invariably arises in these patients, emphasising the critical need to comprehend these mechanisms and develop new strategies to overcome resistance. We report on the generation and characterisation of a LBC PDX displaying acquired resistance to CDK4/6i palbociclib. Treating a sensitive luminal BC PDX with the CDK4/6i palbociclib revealed that, despite initial tumour shrinkage, some tumours might eventually regrow under drug treatment. RNA sequencing, followed by gene set enrichment analyses, unveiled that this PDX have become refractory to CDK4/6i, both at biological and molecular level.
Project description:CDK4/6 inhibitors (CDK4/6i) have significantly improved the prognosis for hormone-positive (HR+) breast cancer patients. However, the emergence of drug resistance severely limits their long-term efficacy, and CDK4/6i monotherapy remains largely ineffective against triple-negative breast cancer (TNBC). Here, we demonstrate that combining CDK4/6i with CDK7 inhibitors (CDK7i) offers a promising therapeutic strategy to overcome resistance in both HR+ breast cancer and TNBC. Kinetic analyses reveal that CDK7i primarily targets RNA polymerase II-mediated transcription, a key driver of CDK4/6i resistance by amplifying E2F activity following the degradation of the retinoblastoma protein. Consequently, the combination of CDK4/6i and CDK7i synergistically suppresses E2F activity and inhibits the growth of drug-resistant tumors. Furthermore, this combination stimulates immune response pathways and cytokine production in cancer cells, enhancing anti-tumor immunity. These findings provide critical insights into evolving CDK inhibition strategies and highlight the therapeutic application of CDK7i in breast cancer management.