Project description:Whole-exome sequencing was performed on DNA samples extracted from seven melanoma cell lines resistant to either vemurafenib (BRAF V600E inhibitor) or trametinib (MEK1/2 inhibitor). The aim of the experiment was to search for genetic alterations responsible for phenotypic diversity of melanoma cell lines reported at the level of cell morphology, activity of signaling pathways essential for melanoma development and progression, and resistance to targeted therapeutics.
Project description:Whole-exome sequencing was performed on DNA samples extracted from seven melanoma cell lines resistant to either vemurafenib (BRAF V600E inhibitor) or trametinib (MEK1/2 inhibitor). The aim of the experiment was to search for genetic alterations responsible for phenotypic diversity of melanoma cell lines reported at the level of cell morphology, activity of signaling pathways essential for melanoma development and progression, and resistance to targeted therapeutics.
Project description:While effective therapy is available for melanoma patients harbouring BRAF mutations, to date, the efficient therapeutic approaches for NRAS-mutant melanoma patients are limited. Therapeutic regimen involving combinatorial inhibition of MEK1/2 and CDK4/6 prove to be beneficial as targeted therapy for NRAS-mutant melanoma. Yet, only a subset of melanoma patients responded to this treatment, whereas acquired resistance eventually emerge in responders. Upon prolonged therapy with MEK1/2 and CDK4/6 inhibitors cells switch to fully drug-resistant or senescent phenotype in vitro. Consequently, there is a necessity to portray cell populations sensitive to targeted therapy, but also cell transitions associated with NRAS-mutant melanoma resistance. To define transcriptional states arising under indicated therapy and cell fate decisions governing resistance, we performed single-cell RNA sequencing at four distinguished time points during treatment. In this study, we identified a cell population highly enriched in calcium signalling, among others, associated with positive drug response. In particular, prolonged expression of ATP-gated ion channel P2RX7 was related to a senescent-like phenotype. Next, we described an immune-like melanoma state that acquired drug resistance and re-enter the cell cycle under treatment, as well as cell populations with intrinsic potential to evade drug pressure.
Project description:Approximately 50% of melanomas harbor an activating BRAFV600E mutation. Standard of care involves a combination of inhibitors targeting mutant BRAF and MEK1/2, the substrate for BRAF in the MAPK pathway. PTEN loss of function mutations occur in 40% of BRAFV600E melanomas, resulting in increased PI3K/AKT activity that enhances resistance to BRAF/MEK combination inhibitor therapy. To compare the response of PTEN null to PTEN wild type cells in an isogenic background, CRISPR was used to knock out PTEN in the A375 melanoma cell line that harbors a BRAFV600E mutation. RNA sequencing and functional kinome analysis revealed the loss of PTEN led to an induction of FOXD3 and an increase in expression of the FOXD3 target gene, ERBB3/HER3. Inhibition of BRAFand MEK1/2 in PTEN null, BRAFV600E cells dramatically induced expression of ERBB3/HER3 relative to wild type cells. A synergy screen of epigenetic modifiers and kinase inhibitors in combination with inhibitors for mutant BRAF/MEK1/2 identified the pan ERBB/HER inhibitor, neratinib, as reversing the resistance observed in PTEN null, BRAFV600E cells. The findings indicate PTEN null BRAFV600E melanoma becomes dependent on ERBB/HER signaling when treated with clinically approved BRAF and MEK inhibitors. Future studies are warranted to test neratinib reversal of resistance in patient melanomas expressing ERBB3/HER3 in combination with its dimerization partner ERBB2/HER2.
Project description:The CDK4/6 kinase is dysregulated in melanoma highlighting a potential therapeutic benefit. Indeed, such CDK4/6 inhibitors are being evaluated in trials for melanoma and additional cancers. While beneficial, resistance to therapy is a concern and the molecular mechanisms of such resistance remain undefined. Here, we demonstrate that reactivation of mTORC1 signaling through increased expression of the amino acid transporter, SLC36A1, drives resistance to CDK4/6 inhibitors. Increased expression of SLC36A1 reflects two distinct mechanisms; 1) Rb loss which drives SLC36A1 via reduced suppression of E2f; 2) FXR1 overexpression which promotes SLC36A1 translation and subsequently mTORC1. Finally, we demonstrate that a combination of a CDK4/6 inhibitor with an mTORC1 inhibitor has increased therapeutic efficacy in vivo providing an important avenue for improved therapeutic intervention in aggressive melanoma.
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.
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.
Project description:Despite overall good prognosis associated to thyroid cancer, poorly differentiated carcinomas (PDTC) and anaplastic carcinomas (ATC) represent major clinical challenges. We have shown that the presence of active T172-phosphorylated CDK4 predicts sensitivity to CDK4/6 inhibitory drugs (CDK4/6i) including palbociclib. Here, CDK4 phosphorylation was detected in all well-differentiated thyoid carcinomas (n=29), 19/20 PDTC, 16/23 ATC, and 18/21 thyroid cancer cell lines including 11 ATC-derived ones. The cell lines lacking CDK4 phosphorylation were insensitive to CDK4/6i. RNA-sequencing and immunohistochemistry revealed that tumors and cell lines without phosphorylated CDK4 presented very high p16CDKN2A levels that were associated with proliferative activity. One of the main mechanisms of resistance to CDK4/6i is RB1 defects or inactivation. RB1 mutations were present in the 3 insensitive cell lines but were not found in 5 of the 7 tumors without phosphorylated CDK4. p16/KI67 immunohistochemistry and a previously developed 11-gene signature identified the likely insensitive tumors and cell lines lacking CDK4 phosphorylation. In cell lines, palbociclib synergized with dabrafenib/trametinib, completely and irreversibly arresting proliferation. The combined drugs prevented resistance mechanisms induced by palbociclib, most notably Cyclin E1-CDK2 activation and a paradoxical stabilization of phosphorylated CDK4 complexes. Our study supports the evaluation of CDK4/6i for ATC/PDTC treatment, including in combination with MEK/BRAF inhibitors.
Project description:Background: Advanced gastrointestinal stromal tumor (GIST) is characterized by genomic perturbations of key cell cycle regulators. Oncogenic activation of CDK4/6 results in RB1 inactivation and cell cycle progression. Given that single-agent CDK4/6 inhibitor therapy failed to show clinical activity in advanced GIST, we evaluated strategies for maximizing response to therapeutic CDK4/6 inhibition. Methods: Targeted next-generation sequencing and multiplexed protein imaging were used to detect cell cycle regulator aberrations in GIST clinical samples. The impact of inhibitors of CDK2, CDK4, and CDK2/4/6 was determined through cell proliferation and protein detection assays. CDK-inhibitor resistance mechanisms were characterized in GIST cell lines after long-term exposure. Results: We identify recurrent genomic aberrations in cell cycle regulators causing co-activation of the CDK2 and CDK4/6 pathways in clinical GIST samples. Therapeutic co-targeting of CDK2 and CDK4/6 is synergistic in GIST cell lines with intact RB1, through inhibition of RB1 hyperphosphorylation and cell proliferation. Moreover, RB1 inactivation and a novel oncogenic cyclin D1 resulting from an intragenic rearrangement (CCND1::chr11.g:70025223) are mechanisms of acquired CDK inhibitor resistance in GIST. Conclusions: These studies establish the biologic rationale for CDK2 and CDK4/6 co-inhibition as therapeutic strategy in patients with advanced GIST, including metastatic GIST progressing on tyrosine kinase inhibitors.