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:The combination of endocrine therapy (ET) with CDK4/6 inhibitors (CDK4/6i) was the most recent life-changing hallmark in metastatic Luminal breast cancer (BC). However, intrinsic and acquired resistance affect long-term efficacy. Here, we studied the role of receptor activator of nuclear factor-kB (RANK) pathway in CDK4/6i resistance. We found that RANK overexpression in Luminal BC associates with intrinsic resistance to CDK4/6i, both in vitro and in mouse xenografts. Transcriptomic analysis of mouse tumors highlighted decreased proliferation rate and chronic interferon (IFN)-response as resistance drivers.
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:The PI3K-AKT-mTOR pathway is commonly dysregulated in cancer. Rapalogs exhibit modest clinical benefit likely due to their lack of effects on 4E-BP1. We hypothesized that bi-steric mTORC1-selective inhibitors would have greater potential for clinical benefit than rapalogs in tumors with mTORC1 dysfunction. We assessed this hypothesis in tumor models with high mTORC1 activity both in vitro and in vivo. Bi-steric inhibitors had strong growth inhibition, eliminated phosphorylated 4EBP1, and induced more apoptosis than rapamycin or MLN0128. Multi-omic analysis showed extensive effects of the bi-steric inhibitors in comparison to rapamycin. De novo purine synthesis was markedly and selectively inhibited by bi-sterics through reduction in JUN and its downstream target PRPS1 and appeared to be the cause of apoptosis. Hence, bi-steric mTORC1-selective inhibitors are a novel therapeutic strategy to treat tumors driven by mTORC1 hyperactivation.
Project description:CDK4/6 inhibitors are highly effective against ER+/HER2- breast cancer (BC); however, intrinsic and acquired resistance is common. Elucidating the molecular features of sensitivity and resistance to CDK4/6 inhibitors may lead to the identification of predictive biomarkers and novel therapeutic targets, paving the way toward improving patient outcomes. Parental BC cells and their endocrine-resistant derivatives (EndoR) were used in this study. Derivatives with acquired resistance to palbociclib (PalboR) were generated from parental and estrogen deprivation-resistant MCF7 and T47D cells. Transcriptomic and proteomic analyses were performed in palbociclib-sensitive and PalboR lines. We found that parental and EndoR BC lines showed varying degrees of sensitivity to palbociclib. Transcriptomic analysis of these cell lines identified an association between high Interferon (IFN) signaling and reduced sensitivity to CDK4/6 inhibitors, thus an ‘IFN-Related Palbociclib-Resistance Signature’ (IRPS) was derived. In two neoadjuvant trials of a CDK4/6 inhibitor plus endocrine therapy, IRPS and other IFN-related signatures were highly enriched in patients with tumors exhibiting intrinsic resistance to CDK4/6 inhibition. PalboR derivatives displayed a dramatic activation of IFN/STAT1-signaling compared to their short-term treated or untreated counterparts. In primary ER+/HER2- tumors, the IRPS score was significantly higher in lumB than lumA subtype and correlated with increased gene expression of immune checkpoints, endocrine resistance, and poor prognosis. Our study demonstrates that aberrant IFN-signaling is associated with intrinsic resistance to CDK4/6 inhibitors. Experimentally, acquired resistance to palbociclib is associated with activation of the IFN-pathway, which warrants additional studies to clarify its involvement in resistance to CDK4/6 inhibitors.
Project description:The clinical benefit of current mTOR inhibitors is limited, perhaps reflecting their intrinsic pharmacological profiles. Rapamycin analogs selectively inhibit mTORC1, but fail to suppress phosphorylation of the mTORC1 substrate 4EBP1, a translational repressor that is a key driver of oncogenic mTORC1 signaling. mTOR kinase active-site inhibitors fully suppress mTORC1 and phosphorylation of its substrates, but are active against mTORC2 and additional kinases, potentially contributing to tolerability limitations. The prototype bi-steric inhibitor RapaLink-1 exploits the selective mTORC1 interactions of rapamycin and the broad mTOR kinase inhibitory effects of an active-site inhibitor, through covalent linkage of the two pharmacophores to achieve complete mTORC1/2 inhibition. We demonstrate that the anti-proliferative activity of RapaLink-1 is dependent upon mTORC1 and suppression of 4EBP1 phosphorylation. Using a rational design strategy, we tuned the affinities of the rapamycin core and ATP-mimetic moieties to create novel bi-steric inhibitors with enhanced mTORC1 selectivity and potency against 4EBP1 phosphorylation. mTORC1-selective bi-steric compounds produced durable inhibition of 4EBP1 phosphorylation in vitro and in vivo, and drove tumor regressions at well-tolerated doses in xenograft models of breast cancer.
Project description:BET inhibitors are promising therapeutic agents for the treatment of triple-negative breast cancer (TNBC), but the rapid emergence of resistance necessitates investigation of combination therapies and their effects on tumor evolution. Here, we show that palbociclib, a CDK4/6 inhibitor, and paclitaxel, a microtubule inhibitor, synergize with the BET inhibitor JQ1 in TNBC lines. High-complexity DNA barcoding and mathematical modeling indicate a high rate of de novo acquired resistance to these drugs relative to pre-existing resistance. We demonstrate that the combination of JQ1 and palbociclib induces cell division errors, which can increase the chance of developing aneuploidy. Characterizing acquired resistance to combination treatment at single cell level shows heterogeneous mechanisms including activation of G1-S and senescence pathways. Our results establish a rationale for further investigation of combined BET and CDK4/6 inhibition in TNBC and suggest novel mechanisms of action for these drugs, and new vulnerabilities in cells after emergence of resistance.
Project description:BET inhibitors are promising therapeutic agents for the treatment of triple-negative breast cancer (TNBC), but the rapid emergence of resistance necessitates investigation of combination therapies and their effects on tumor evolution. Here, we show that palbociclib, a CDK4/6 inhibitor, and paclitaxel, a microtubule inhibitor, synergize with the BET inhibitor JQ1 in TNBC lines. High-complexity DNA barcoding and mathematical modeling indicate a high rate of de novo acquired resistance to these drugs relative to pre-existing resistance. We demonstrate that the combination of JQ1 and palbociclib induces cell division errors, which can increase the chance of developing aneuploidy. Characterizing acquired resistance to combination treatment at single cell level shows heterogeneous mechanisms including activation of G1-S and senescence pathways. Our results establish a rationale for further investigation of combined BET and CDK4/6 inhibition in TNBC and suggest novel mechanisms of action for these drugs, and new vulnerabilities in cells after emergence of resistance.