Emergence of mTOR mutation as an acquired resistance mechanism to AKT inhibition, and subsequent response to mTORC1/2 inhibition.
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ABSTRACT:
SUBMITTER: Coleman N
PROVIDER: S-EPMC8636467 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Acquired resistance (AQR) to drug treatment occurs frequently in cancer patients and remains an impediment to successful therapy. The aim of this study was to gain insight into how AQR arises following the application of PI3K/mTOR inhibitors. H1975 lung cancer cells with EGFR T790M mutations that confer resistance to EGFR inhibitors underwent prolonged treatment with the PI3K/mTOR inhibitor, BEZ235. Monoclonal cells with stable and increased resistance to BEZ235 were obtained after 8 months treatment. These AQR clones showed class-specific resistance to PI3K/mTOR inhibitors, reduced G1 cell cycle arrest and impedance of migration following PI3K/mTOR inhibition, reduced PTEN expression and increased Akt and S6RP phosphorylation. Transcriptome analysis revealed the AQR clones had increased expression of the metabolite transporters SLC16A9 and SLC16A7, suggestive of altered cell metabolism. Subsequent experiments revealed that AQR clones possess features consistent with elevated glycolysis, including increased levels of glucose, lactate, glutamine, glucose dependence, GLUT1 expression, and rates of post-glucose extracellular acidification, and decreased levels of reactive oxygen species and rates of oxygen consumption. Combination treatment of BEZ235 with the glycolysis inhibitor 3-bromopyruvate was synergistic in AQR clones, but only additive in parental cells. DNA sequencing revealed the presence of a mitochondrial DNA (mtDNA) MT-C01 variant in AQR but not parental cells. Depletion of mitochondrial DNA in parental cells induced resistance to BEZ235 and other PI3K/mTOR inhibitors, and was accompanied by increased glycolysis. The results of this study provide the first evidence that a metabolic switch associated with mtDNA mutation can be an underlying mechanism for AQR.
| S-EPMC5746370 | biostudies-literature
Project description:BRAF inhibitors (BRAFi) and the combination therapy of BRAF and MEK inhibitors (MEKi) were recently approved for therapy of metastatic melanomas harbouring the oncogenic BRAFV600 mutation. Although these therapies have shown pronounced therapeutic efficacy, the limited durability of the response indicates an acquired drug resistance that still remains mechanistically poorly understood at the molecular level. We conducted transcriptome gene profiling in BRAFi-treated melanoma cells and identified that Mer tyrosine kinase (MerTK) is specifically upregulated. MerTK overexpression was demonstrated not only in melanomas resistant to BRAFi monotherapy (5 out of 10 samples from melanoma patients) but also in melanoma resistant to BRAFi+MEKi (1 out of 3), although MEKi alone does not affect MerTK. Mechanistically, BRAFi-induced activation of Zeb2 stimulates MerTK in BRAFV600 melanoma through mTORC1-triggered activation of autophagy. Co-targeting MerTK and BRAFV600 significantly reduced tumour burden in xenografted mice, which was pheno-copied by co-inhibition of autophagy and mutant BRAFV600.
| S-EPMC5642473 | biostudies-literature
Project description:The mammalian target of rapamycin (mTOR) protein kinase is a master growth promoter that nucleates two complexes, mTORC1 and mTORC2. Despite the diverse processes controlled by mTOR, few substrates are known. We defined the mTOR-regulated phosphoproteome by quantitative mass spectrometry and characterized the primary sequence motif specificity of mTOR using positional scanning peptide libraries. We found that the phosphorylation response to insulin is largely mTOR dependent and that mTOR exhibits a unique preference for proline, hydrophobic, and aromatic residues at the +1 position. The adaptor protein Grb10 was identified as an mTORC1 substrate that mediates the inhibition of phosphoinositide 3-kinase typical of cells lacking tuberous sclerosis complex 2 (TSC2), a tumor suppressor and negative regulator of mTORC1. Our work clarifies how mTORC1 inhibits growth factor signaling and opens new areas of investigation in mTOR biology.
| S-EPMC3177140 | biostudies-literature
Project description:BACKGROUND:The PI3K pathway is hyperactivated in many cancers, including 70 % of breast cancers. Pan- and isoform-specific inhibitors of the PI3K pathway are currently being evaluated in clinical trials. However, the clinical responses to PI3K inhibitors when used as single agents are not as efficient as expected. METHODS:In order to anticipate potential molecular mechanisms of resistance to the p110? isoform-selective inhibitor BYL719, we developed resistant breast cancer cell lines, assessed the concomitant changes in cellular signaling pathways using unbiased phosphotyrosine proteomics and characterized the mechanism of resistance using pharmacological inhibitors. RESULTS:We found an increase in IGF1R, IRS1/IRS2 and p85 phosphorylation in the resistant lines. Co-immunoprecipitation experiments identified an IGF1R/IRS/p85/p110? complex that causes the activation of AKT/mTOR/S6K and stifles the effects of BYL719. Pharmacological inhibition of members of this complex reduced mTOR/S6K activation and restored sensitivity to BYL719. CONCLUSION:Our study demonstrates that the IGF1R/p110?/AKT/mTOR axis confers resistance to BYL719 in PIK3CA mutant breast cancers. This provides a rationale for the combined targeting of p110? with IGF1R or p110? in patients with breast tumors harboring PIK3CA mutations.
| S-EPMC4820873 | biostudies-literature
Project description:PIK3CA, which encodes the p110α subunit of PI3K, is frequently mutated and oncogenic in breast cancer. PI3Kα inhibitors are in clinical development and despite promising early clinical activity, intrinsic resistance is frequent among patients. We have previously reported that residual downstream mTORC1 activity upon treatment with PI3Kα inhibitors drives resistance to these agents. However, the mechanism underlying this phenotype is not fully understood. Here we show that in cancer cells resistant to PI3Kα inhibition, PDK1 blockade restores sensitivity to these therapies. SGK1, which is activated by PDK1, contributes to the maintenance of residual mTORC1 activity through direct phosphorylation and inhibition of TSC2. Targeting either PDK1 or SGK1 prevents mTORC1 activation, restoring the antitumoral effects of PI3Kα inhibition in resistant cells.
| S-EPMC4982440 | biostudies-literature
Project description:Mammalian target of rapamycin (mTOR) regulates cellular processes important for progression of human cancer. RAD001 (everolimus), an mTORC1 (mTOR/raptor) inhibitor, has broad antitumor activity in preclinical models and cancer patients. Although most tumor lines are RAD001 sensitive, some are not. Selective mTORC1 inhibition can elicit increased AKT S473 phosphorylation, involving insulin receptor substrate 1, which is suggested to potentially attenuate effects on tumor cell proliferation and viability. Rictor may also play a role because rictor kinase complexes (including mTOR/rictor) regulate AKT S473 phosphorylation. The role of raptor and rictor in the in vitro response of human cancer cells to RAD001 was investigated. Using a large panel of cell lines representing different tumor histotypes, the basal phosphorylation of AKT S473 and some AKT substrates was found to correlate with the antiproliferative response to RAD001. In contrast, increased AKT S473 phosphorylation induced by RAD001 did not correlate. Similar increases in AKT phosphorylation occurred following raptor depletion using siRNA. Strikingly, rictor down-regulation attenuated AKT S473 phosphorylation induced by mTORC1 inhibition. Further analyses showed no relationship between modulation of AKT phosphorylation on S473 and T308 and AKT substrate phosphorylation patterns. Using a dual pan-class I phosphatidylinositol 3-kinase/mTOR catalytic inhibitor (NVP-BEZ235), currently in phase I trials, concomitant targeting of these kinases inhibited AKT S473 phosphorylation, eliciting more profound cellular responses than mTORC1 inhibition alone. However, reduced cell viability could not be predicted from biochemical or cellular responses to mTORC1 inhibitors. These data could have implications for the clinical application of phosphatidylinositol 3-kinase/mTOR inhibitors.
| S-EPMC3440776 | biostudies-literature
Project description:INTRODUCTION:Upregulation of PI3K/Akt/mTOR signalling in endocrine-resistant breast cancer (BC) has identified mTOR as an attractive target alongside anti-hormones to control resistance. RAD001 (everolimus/Afinitor®), an allosteric mTOR inhibitor, is proving valuable in this setting; however, some patients are inherently refractory or relapse during treatment requiring alternative strategies. Here we evaluate the potential for novel dual mTORC1/2 mTOR kinase inhibitors, exemplified by AZD8055, by comparison with RAD001 in ER?+?endocrine resistant BC cells. METHODS:In vitro models of tamoxifen (TamR) or oestrogen deprivation resistance (MCF7-X) were treated with RAD001 or AZD8055 alone or combined with anti-hormone fulvestrant. Endpoints included growth, cell proliferation (Ki67), viability and migration, with PI3K/AKT/mTOR signalling impact monitored by Western blotting. Potential ER cross-talk was investigated by immunocytochemistry and RT-PCR. RESULTS:RAD001 was a poor growth inhibitor of MCF7-derived TamR and MCF7-X cells (IC50 ?1 ?M), rapidly inhibiting mTORC1 but not mTORC2/AKT signalling. In contrast AZD8055, which rapidly inhibited both mTORC1 and mTORC2/AKT activity, was a highly effective (P?<0.001) growth inhibitor of TamR (IC50 18?nM) and MCF7-X (IC50 24 nM), and of a further T47D-derived tamoxifen resistant model T47D-tamR (IC50 19 nM). AZD8055 significantly (P?<0.05) inhibited resistant cell proliferation, increased cell death and reduced migration. Furthermore, dual treatment of TamR or MCF7-X cells with AZD8055 plus fulvestrant provided superior control of resistant growth versus either agent alone (P?<0.05). Co-treating with AZD8055 alongside tamoxifen (P?<0.01) or oestrogen deprivation (P?<0.05) also effectively inhibited endocrine responsive MCF-7 cells. Although AZD8055 inhibited oestrogen receptor (ER) ser167 phosphorylation in TamR and MCF7-X, it had no effect on ER ser118 activity or expression of several ER-regulated genes, suggesting the mTOR kinase inhibitor impact was largely ER-independent. The capacity of AZD8055 for ER-independent activity was further evidenced by growth inhibition (IC5018 and 20 nM) of two acquired fulvestrant resistant models lacking ER. CONCLUSIONS:This is the first report demonstrating dual mTORC1/2 mTOR kinase inhibitors have potential to control acquired endocrine resistant BC, even under conditions where everolimus fails. Such inhibitors may prove of particular benefit when used alongside anti-hormonal treatment as second-line therapy in endocrine resistant disease, and also potentially alongside anti-hormones during the earlier endocrine responsive phase to hinder development of resistance.
| S-EPMC3978713 | biostudies-literature
Project description:Amplified and/or mutated MET can act as both a primary oncogenic driver and as a promoter of tyrosine kinase inhibitor (TKI) resistance in non-small cell lung cancer (NSCLC). However, the landscape of MET-specific targeting agents remains underdeveloped, and understanding of mechanisms of resistance to MET TKIs is limited. Here, we present a case of a patient with lung adenocarcinoma harboring both a mutation in EGFR and an amplification of MET, who after progression on erlotinib responded dramatically to combined MET and EGFR inhibition with savolitinib and osimertinib. When resistance developed to this combination, a new MET kinase domain mutation, D1228V, was detected. Our in vitro findings demonstrate that METD1228V induces resistance to type I MET TKIs through impaired drug binding, while sensitivity to type II MET TKIs is maintained. Based on these findings, the patient was treated with erlotinib combined with cabozantinib, a type II MET inhibitor, and exhibited a response.SignificanceWith several structurally distinct MET inhibitors undergoing development for treatment of NSCLC, it is critical to identify mechanism-based therapies for drug resistance. We demonstrate that an acquired METD1228V mutation mediates resistance to type I, but not type II, MET inhibitors, having therapeutic implications for the clinical use of sequential MET inhibitors. Cancer Discov; 6(12); 1334-41. ©2016 AACR.See related commentary by Trusolino, p. 1306This article is highlighted in the In This Issue feature, p. 1293.
| S-EPMC5140694 | biostudies-literature
Project description:Clinical resistance to chemotherapy is a frequent event in cancer treatment and is closely linked to poor outcome. High-grade serous (HGS) ovarian cancer is characterized by p53 mutation and high levels of genomic instability. Treatment includes platinum-based chemotherapy and initial response rates are high; however, resistance is frequently acquired, at which point treatment options are largely palliative. Recent data indicate that platinum-resistant clones exist within the sensitive primary tumor at presentation, implying resistant cell selection after treatment with platinum chemotherapy. The AKT pathway is central to cell survival and has been implicated in platinum resistance. Here, we show that platinum exposure induces an AKT-dependent, prosurvival, DNA damage response in clinically platinum-resistant but not platinum-sensitive cells. AKT relocates to the nucleus of resistant cells where it is phosphorylated specifically on S473 by DNA-dependent protein kinase (DNA-PK), and this activation inhibits cisplatin-mediated apoptosis. Inhibition of DNA-PK or AKT, but not mTORC2, restores platinum sensitivity in a panel of clinically resistant HGS ovarian cancer cell lines: we also demonstrate these effects in other tumor types. Resensitization is associated with prevention of AKT-mediated BAD phosphorylation. Strikingly, in patient-matched sensitive cells, we do not see enhanced apoptosis on combining cisplatin with AKT or DNA-PK inhibition. Insulin-mediated activation of AKT is unaffected by DNA-PK inhibitor treatment, suggesting that this effect is restricted to DNA damage-mediated activation of AKT and that, clinically, DNA-PK inhibition might prevent platinum-induced AKT activation without interfering with normal glucose homeostasis, an unwanted toxicity of direct AKT inhibitors.
| S-EPMC3223610 | biostudies-literature
Project description:Epithelial ovarian cancer is characterized by universal TP53 mutations, which result in G1/S checkpoint deficiencies. Therefore, it is hypothesized that the abrogation of the G2/M checkpoint with Wee1 inhibitor might preferentially sensitize TP53-defective ovarian cancer cells. Given the extremely high molecular diversity in ovarian cancer, one approach to improving the clinical efficacy is to identify drug combinations that either broaden the applicable spectrum or circumvent resistance. Here, through a high-throughput unbiased proteomic profiling (RPPA), we found the complementary activated mTOR pathway contributes greatly to Wee1 inhibitor resistance. A combination of Wee1 and mTOR inhibits synergistically inhibiting tumor growth in ovarian cancer cell lines and patient-derived xenograft that closely mimic the heterogeneity of patient tumors. Mechanistically, dual Wee1/mTOR inhibition induced massive DNA replication stress, leading to fork stalling and DNA damage. Moreover, we found that the addition of nucleotide metabolic substrate dNTPs alleviated replication stress, restored the cell cycle and reduced apoptosis to some extent, supporting dNTPs depletion is necessary for the synergy between Wee1 and mTOR inhibits. These results suggest that our study opening up a wider therapeutic window of Wee1 inhibitor for the treatment in epithelial ovarian cancers.
| S-EPMC7136919 | biostudies-literature