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Targeting the mevalonate pathway to overcome acquired anti-HER2 treatment resistance in breast cancer [RNA-seq]

ABSTRACT: Despite effective strategies, therapy resistance in HER2+ breast cancer remains a challenge. While the Mevalonate pathway (MVA) is suggested to promote cell growth and survival, including in HER2+ models, its potential role in resistance to HER2-targeted therapy is unknown. Using HER2+ breast cancer parental (P) cell models (AU565, SKBR3, and UACC812), we have established anti-HER2-resistant derivatives made resistant to lapatinib (LR) or lapatinib plus trastuzumab (LTR). We performed RNA-seq on these resistant models and the P cells treated with lapatinib or lapatinib plus trastuzumaba for 24 h. We found that the average expression of the key genes in the MVA pathway, as a surrogate for pathway activity, was dramatically reduced in P cells with short-term treatment. In contrast, expression was restored or further upregulated relative to P cells in all three resistant (LR/LTR) models. Specific blockade of this pathway with lipophilic but not hydrophilic statins and with the n-bisphosphonate zoledronic acid led to apoptosis and substantial growth inhibition of resistant cells. Inhibition was rescued by mevalonate or the intermediate metabolites farnesyl pyrophosphate (FPP) or geranylgeranyl pyrophosphate (GGPP), but not by cholesterol. Activated YAP/TAZ and mTORC1 signaling and their downstream target gene product Survivin were inhibited by MVA blockade especially in the LR/LTR models. Overexpression of constitutively active YAP rescued Survivin and phosphorylated S6 levels despite blockade of the MVA. The MVA may provide alternative signaling leading to cell survival and resistance when HER2 is blocked by activating YAP/TAZ-mTORC1-Survivin signaling suggesting novel therapeutic targets. MVA inhibitors including lipophilic statins and N-bisphosphonates may circumvent resistance to anti-HER2 therapy and warrant further clinical investigation.

ORGANISM(S): Homo sapiens

PROVIDER: GSE132055 | GEO | 2020/04/04

REPOSITORIES: GEO

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Project description:HER2 targeting with trastuzumab has changed the prognosis of breast cancer patients carrying amplification and/or overexpression of this oncogene. Despite this progress, however, resistance to trastuzumab occurs in the vast majority of patients. Newer anti-HER2 therapies, like the dual tyrosine-kinase inhibitor (TKI) lapatinib, show antitumor activity in a limited proportion of patients, indicating that HER2 can be still exploited as a target after trastuzumab failure. However, due to the high proportion of patients that fail to respond to these alternative strategies, it is reasonable to assume that cells escaping HER2 targeting may rely on alternative pathways not involving HER2 to sustain their growth. Their knowledge is relevant for exploiting new therapies. To investigate this hypothesis we generated a human HER2 overexpressing breast cancer cell line resistant to trastuzumab and lapatinib (T100) and we have characterized it genetically and molecularly. In T100 cells, the previously proposed mechanisms of resistance to HER2 inhibitors did not explain cell escape. Notably, silencing HER2 by shRNA did not affect the growth of T100 cells, suggesting loss of reliance upon HER2. Among the alternative pathways that we explored, altered levels of the antiapoptoptic proteins Mcl-1 and Survivin were observed. This suggested the possibility of targeting resistant cells with the multitarget inhibitor sorafenib. Moreover, sorafenib, nearly inactive in parental cells, strongly inhibited the in vitro growth of T100 cells. In conclusion, we provide a new model where the activation of HER2 independent mechanisms sustains the growth of tumor cells, significantly increasing the sensitivity to sorafenib. Keywords: HER2, breast cancer, resistance, trastuzumab, lapatinib, sorafenib Total RNA was isolated using TRIZOL reagent (Life Technologies, Gathersburg, MD) and quantified by Bioanalyzer 2100 (Agilent Technologies); following the isolation procedure, mRNA was amplified starting from 1μg using MessageAmp II aRNA Amplification kit (Ambion Inc. Austin TX, USA). Ammino-allyl modified nucleotides were incorporated in in vitro transcription step according to the manufacturer’s protocol. Labeling was performed using NHS (N-hydroxysuccinimidyl) ester Cy3 or Cy5 dies (GE Healthcare Europe GMBH, Upsala - Sweden) able to react with the modified RNA. At least 5 μg of mRNA, for each sample, were labeled and purified with columns respectively. The Dye-Swap replication procedure was applied, in order to increase the accuracy of results. Samples were hybridized on 44K glass arrays (Agilent Technologies). Arrays were scanned and the images obtained were analyzed by the Feature Extraction software Agilent (version 9.5) and the text files were then processed using the Bioconductor package Limma (Linear models for microarray analysis).

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Targeting the mevalonate pathway to overcome acquired anti-HER2 treatment resistance in breast cancer [RNA-seq]

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