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Palbociclib interferes with origin firing in a pRb independent manner

ABSTRACT: Over the last decade, CDK4/6 inhibitors (palbociclib, ribociclib and abemaciclib) have emerged as promising anticancer drugs. Numerous studies have demonstrated that CDK4/6 inhibitors efficiently block the pRb-E2F pathway and induce cell cycle arrest in pRb-proficient cells. Based on these studies, the inhibitors have been approved by the FDA for treatment of advanced hormonal receptor (HR) positive breast cancers in combination with hormonal therapy. However, some evidence has recently shown unexpected effects of the inhibitors, promoting needs to understand more about the mechanism of inhibitors beyond pRb. Our study demonstrates here for the first time how palbociclib impairs the origin firing in the DNA replication process in pRb-deficient cell lines. Strikingly, despite the absence of pRb, cells treated with palbociclib synthesize less DNA without any induced cell cycle arrest. Furthermore, palbociclib treatment disturbs the temporal program of DNA replication and reduces the density of replication forks. Cells treated with palbociclib show a defect in the loading of proteins of the Pre-initiation complex (Pre-IC) on chromatin, indicating a reduced initiation of DNA replication. Our findings highlight hidden effects of palbociclib on the dynamics of DNA replication and on its cytotoxic consequences on cell viability in the absence of pRb. This study provides a potential therapeutic application of palbociclib to target genomic instability towards pRb deficient patient

ORGANISM(S): Homo sapiens

PROVIDER: GSE180530 | GEO | 2023/07/01

REPOSITORIES: GEO

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Proteomic profiling of Palbociclib arrested cells ± APC/C inactivation.

Project description:Cellular proliferation is highly regulated to ensure proper tissue homeostasis and to prevent diseases such as cancer. In actively proliferating cells, entry into S phase of the cell cycle and initiation of DNA replication is promoted by inactivation of the E3 ubiquitin ligase APC/C (anaphase promoting complex/cyclosome), though the critical S phase-promoting substrates have not been fully elucidated. The APC/C is also active in cells that have exited the cell cycle and entered an arrested state, but whether APC/C activity is essential to maintain arrest is unclear. We found that APC/C inactivation is sufficient to bypass cellular arrest induced by the CDK4/6 inhibitor Palbociclib. To identify potential APC/C substrates responsible for driving the escape from cell cycle arrest, we arrested cells using Palbociclib and then induced EMI1, inactivating the APC/C. Samples were collected at 0, 8, 16 and 20h after arrest and analyzed using proteomics. We found that inactivation of the APC/C promotes cell cycle re-entry by inducing RB phosphorylation and E2F-dependent gene transcription. Stabilization of both cyclin A and cyclin B contributes to arrest bypass, but only cyclin A accumulation is absolutely required. Direct expression of APC/C-resistant cyclin A, but not cyclin B, in arrested cells induces S phase entry analogous to APC/C inactivation. Cells bypassing arrest initiate DNA replication with severely reduced origin licensing, at least in part due to premature geminin accumulation. As a result, cells exhibit reduced rates of DNA synthesis, which leads to the accumulation of replication stress and long-term proliferation defects. Our findings suggest that CDK4/6 inhibition in cancers with reduced APC/C activity may be ineffective at promoting cytostatic cell cycle arrest but may nonetheless lead to elevated levels of replication stress that ultimately leads to a more durable cell cycle withdrawal.

2024-07-18 | PXD046783 | Pride

O-GlcNAcylation promotes Palbociclib resistance in breast cancer by regulating MITF nuclear translocation

Project description:Cyclin-dependent kinases 4 and 6 (CDK4/6) are essential drivers of the cell cycle and are also critical for the initiation and progression of diverse malignancies. Pharmacological inhibitors targeting CDK4/6 have demonstrated significant activity against various tumor types such as breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i) (such as palbociclib) remains an immense obstacle in clinical and the underlying mechanisms have not been fully understood. Using quantitative high-throughput combinational screen (qHTCS) and genomic sequencing, we report that the Microphthalmia-associated transcription factor (MITF), was significantly elevated in palbociclib-resistance cells. Inhibition of MITF can enhance the therapeutic efficacy of Palbociclib and surmount Palbociclib resistance both in vitro and in vivo. Then we found that MITF is interacting with OGT in Palbociclib-resistance cells, and we also identified that Ser49 is the main O-GlcNAc site of MITF. O-GlcNAc of MITF is critical to mediated Palbociclib-resistance in cells.

2024-05-30 | PXD042763 | Pride

O-GlcNAcylation promotes Palbociclib resistance in breast cancer by regulating MITF nuclear translocation

Project description:Cyclin-dependent kinases 4 and 6 (CDK4/6) are essential drivers of the cell cycle and are also critical for the initiation and progression of diverse malignancies. Pharmacological inhibitors targeting CDK4/6 have demonstrated significant activity against various tumor types such as breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i) (such as palbociclib) remains an immense obstacle in clinical and the underlying mechanisms have not been fully understood. Using quantitative high-throughput combinational screen (qHTCS) and genomic sequencing, we report that the Microphthalmia-associated transcription factor (MITF), was significantly elevated in palbociclib-resistance cells. Inhibition of MITF can enhance the therapeutic efficacy of Palbociclib and surmount Palbociclib resistance both in vitro and in vivo. Mechanistically, we found that O-GlcNAc transferase (OGT) modifies MITF with O-GlcNAcylation at Serine 49 (Ser49) within its nuclear localization signal (NLS), thereby promoting MITF binding to importin α/ β and facilitating its nuclear transportation, which is crucial in regulating senescence.

2024-05-30 | PXD042838 | Pride

RNA sequencing of luminal breast cancer patient-derived xenografts (PDX) library to capture tumor heterogeneity and explore the mechanisms of resistance to CDK4/6 inhibitors

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.

2024-11-18 | E-MTAB-14085 | biostudies-arrayexpress

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Project description:CDK4/6 inhibitors arrest the cell cycle in G1-phase. They are licenced to treat breast cancer and are also undergoing clinical trials against a range of other tumour types. To facilitate these efforts, it is important to understand why a temporary cell cycle arrest in G1 causes long-lasting effects on tumour growth. Here we demonstrate that a prolonged G1-arrest following CDK4/6 inhibition downregulates replisome components and impairs origin licencing. This causes a failure in DNA replication after release from that arrest, resulting in a p53-dependent withdrawal from the cell cycle. If p53 is absent, then cells bypass the G2-checkpoint and undergo a catastrophic mitosis resulting in excessive DNA damage. These data therefore link CDK4/6 inhibition to genotoxic stress; a phenotype that is shared by most other broad-spectrum anti-cancer drugs. This provides a rationale to predict responsive tumour types and effective combination therapies, as demonstrated by the fact that chemotherapeutics that cause replication stress also induce sensitivity to CDK4/6 inhibition.

2021-12-20 | PXD023435 | Pride

Treatment of Retinoblastoma 1-Intact Hepatocellular Carcinoma With Cyclin-Dependent Kinase 4/6 Inhibitor Combination Therapy

Project description:Background and aims: Synthetic cyclin-dependent kinase (CDK) 4/6 inhibitors exert antitumor effects by forcing RB1 in unphosphorylated status, causing not only cell cycle arrest but also cellular senescence, apoptosis, and increased immunogenicity. These agents currently have an indication in advanced breast cancers and are in clinical trials for many other solid tumors. HCC is one of promising targets of CDK4/6 inhibitors. RB family dysfunction is often associated with the initiation of HCC; however, this is revivable, as RB family members are not frequently mutated or deleted in this malignancy. Approach and results: Loss of all Rb family members in transformation related protein 53 (Trp53)-/- mouse liver resulted in liver tumor reminiscent of human HCC, and re-expression of RB1 sensitized these tumors to a CDK4/6 inhibitor, palbociclib. Introduction of an unphosphorylatable form of RB1 (RB7LP) into multiple liver tumor cell lines induced effects similar to palbociclib. By screening for compounds that enhance the efficacy of RB7LP, we identified an I kappa B kinase (IKK)β inhibitor Bay 11-7082. Consistently, RB7LP expression and treatment with palbociclib enhanced IKKα/β phosphorylation and NF-κB activation. Combination therapy using palbociclib with Bay 11-7082 was significantly more effective in hepatoblastoma and HCC treatment than single administration. Moreover, blockade of IKK-NF-κB or AKT pathway enhanced effects of palbociclib on RB1-intact KRAS Kirsten rat sarcoma viral oncogene homolog mutated lung and colon cancers. Conclusions: In conclusion, CDK4/6 inhibitors have a potential to treat a wide variety of RB1-intact cancers including HCC when combined with an appropriate kinase inhibitor.

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O-GlcNAcylation promotes Palbociclib resistance in breast cancer by regulating MITF nuclear translocation [ChIP-seq]

Project description:Cyclin-dependent kinases 4 and 6 (CDK4/6) are essential drivers of the cell cycle and are also critical for the initiation and progression of diverse malignancies. Pharmacological inhibitors targeting CDK4/6 have demonstrated significant activity against various tumor types such as breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i) (such as palbociclib) remains an immense obstacle in clinical and the underlying mechanisms have not been fully understood. Using quantitative high-throughput combinational screen (qHTCS) and genomic sequencing, we report that the Microphthalmia-associated transcription factor (MITF), was significantly elevated in palbociclib-resistance cells. Inhibition of MITF can enhance the therapeutic efficacy of Palbociclib and surmount Palbociclib resistance both in vitro and in vivo. Mechanistically, we found that O-GlcNAc transferase (OGT) modifies MITF with O-GlcNAcylation at Serine 49 (Ser49) within its nuclear localization signal (NLS), thereby promoting MITF binding to importin α/ β and facilitating its nuclear transportation, which is crucial in regulating senescence. Significantly, clinical studies also confirm that MITF was elevated in palbociclib-resistance patients. Collectively, these results reveal a previously unrecognized mechanism by which MITF-mediated palbociclib resistance, and provide valuable insights for the development of innovative therapeutic strategies in future clinical contexts.

2023-10-10 | GSE234515 | GEO

O-GlcNAcylation promotes Palbociclib resistance in breast cancer by regulating MITF nuclear translocation [RNA-seq]

Project description:Cyclin-dependent kinases 4 and 6 (CDK4/6) are essential drivers of the cell cycle and are also critical for the initiation and progression of diverse malignancies. Pharmacological inhibitors targeting CDK4/6 have demonstrated significant activity against various tumor types such as breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i) (such as palbociclib) remains an immense obstacle in clinical and the underlying mechanisms have not been fully understood. Using quantitative high-throughput combinational screen (qHTCS) and genomic sequencing, we report that the Microphthalmia-associated transcription factor (MITF), was significantly elevated in palbociclib-resistance cells. Inhibition of MITF can enhance the therapeutic efficacy of Palbociclib and surmount Palbociclib resistance both in vitro and in vivo. Mechanistically, we found that O-GlcNAc transferase (OGT) modifies MITF with O-GlcNAcylation at Serine 49 (Ser49) within its nuclear localization signal (NLS), thereby promoting MITF binding to importin α/ β and facilitating its nuclear transportation, which is crucial in regulating senescence. Significantly, clinical studies also confirm that MITF was elevated in palbociclib-resistance patients. Collectively, these results reveal a previously unrecognized mechanism by which MITF-mediated palbociclib resistance, and provide valuable insights for the development of innovative therapeutic strategies in future clinical contexts.

2023-10-10 | GSE234514 | GEO

Genome wide transcriptome analysis of palbociclib or GSK3326595 treated A375 cells [Palbociclib_GSK_RNASeq]

Project description:RNA-seq was performed to compare the transcriptional programmes of A375 cells treated with Palbociclib or GSK3326595 compared to untreated cells Cyclin dependent kinase 4/6 (CDK4/6) inhibitors are an established treatment in estrogen receptor positive breast cancer and are currently in clinical development in melanoma; a tumour that exhibits high rates of CDK4 activation. We analyzed melanoma cells with acquired resistance to the CDK4/6 inhibitor palbociclib, and demonstrated that palbociclib-mediated inhibition of PRMT5 is essential for sensitivity to CDK4/6 inhibitors. Mechanistically, by inhibiting PRMT5 activity, palbociclib alters MDM4 pre-mRNA splicing leading to decreased MDM4 protein expression and subsequent p53 activation. In turn, p53 increases p21 leading to inhibition of CDK2, the main kinase substituting for CDK4/6 and a key driver of resistance to palbociclib. Loss of the ability of palbociclib to regulate the PRMT5-MDM4 axis leads to resistance. Importantly, combining palbociclib with the PRMT5 inhibitor GSK3326595 enhances the efficacy of palbociclib in treatment naïve and resistant models and also delays the emergence of resistance. Our studies have uncovered a novel mechanism of action of CDK4/6 inhibitors in regulating the MDM4 oncogene and the tumor suppressor, p53. Furthermore, we have established that palbociclib inhibition of the PRMT5-MDM4 axis is essential for robust melanoma cell sensitivity and provide pre-clinical evidence that co-inhibition of CDK4/6 and PRMT5 is an effective and well tolerated therapeutic strategy. Overall our data provides a strong rationale for further investigation of novel combinations of CDK4/6 and PRMT5 inhibitors in not only melanoma but other tumour types including breast, pancreatic and esophageal carcinoma.

2019-08-23 | GSE133568 | GEO

Gene expression alterations associated with acquired-resistance to the CDK4/6 inhibitor palbociclib [Palbociclib resistance_RNASeq]

Project description:RNA-seq was performed to compare the transcriptional programmes of palbociclib-resistant A375 and CHL1 cells compared to their parental counterparts Cyclin dependent kinase 4/6 (CDK4/6) inhibitors are an established treatment in estrogen receptor positive breast cancer and are currently in clinical development in melanoma; a tumour that exhibits high rates of CDK4 activation. We analyzed melanoma cells with acquired resistance to the CDK4/6 inhibitor palbociclib, and demonstrated that palbociclib-mediated inhibition of PRMT5 is essential for sensitivity to CDK4/6 inhibitors. Mechanistically, by inhibiting PRMT5 activity, palbociclib alters MDM4 pre-mRNA splicing leading to decreased MDM4 protein expression and subsequent p53 activation. In turn, p53 increases p21 leading to inhibition of CDK2, the main kinase substituting for CDK4/6 and a key driver of resistance to palbociclib. Loss of the ability of palbociclib to regulate the PRMT5-MDM4 axis leads to resistance. Importantly, combining palbociclib with the PRMT5 inhibitor GSK3326595 enhances the efficacy of palbociclib in treatment naïve and resistant models and also delays the emergence of resistance. Our studies have uncovered a novel mechanism of action of CDK4/6 inhibitors in regulating the MDM4 oncogene and the tumor suppressor, p53. Furthermore, we have established that palbociclib inhibition of the PRMT5-MDM4 axis is essential for robust melanoma cell sensitivity and provide pre-clinical evidence that co-inhibition of CDK4/6 and PRMT5 is an effective and well tolerated therapeutic strategy. Overall our data provides a strong rationale for further investigation of novel combinations of CDK4/6 and PRMT5 inhibitors in not only melanoma but other tumour types including breast, pancreatic and esophageal carcinoma.

2019-08-23 | GSE133567 | GEO

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