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MGMT inhibition restores ER? functional sensitivity to antiestrogen therapy.

ABSTRACT: Antiestrogen therapy resistance remains a huge stumbling block in the treatment of breast cancer. We have found significant elevation of O(6) methylguanine DNA methyl transferase (MGMT) expression in a small sample of consecutive patients who have failed tamoxifen treatment. Here, we show that tamoxifen resistance is accompanied by upregulation of MGMT. Further we show that administration of the MGMT inhibitor, O(6)-benzylguanine (BG), at nontoxic doses, leads to restoration of a favorable estrogen receptor alpha (ER?) phosphorylation phenotype (high p-ER? Ser167/low p-ER? Ser118), which has been reported to correlate with sensitivity to endocrine therapy and improved survival. We also show BG to be a dual inhibitor of MGMT and ER?. In tamoxifen-resistant breast cancer cells, BG alone or in combination with antiestrogen (tamoxifen [TAM]/ICI 182,780 [fulvestrant, Faslodex]) therapy enhances p53 upregulated modulator of apoptosis (PUMA) expression, cytochrome C release and poly (ADP-ribose) polymerase (PARP) cleavage, all indicative of apoptosis. In addition, BG increases the expression of p21(cip1/waf1). We also show that BG, alone or in combination therapy, curtails the growth of tamoxifen-resistant breast cancer in vitro and in vivo. In tamoxifen-resistant MCF7 breast cancer xenografts, BG alone or in combination treatment causes significant delay in tumor growth. Immunohistochemistry confirms that BG increases p21(cip1/waf1) and p-ER? Ser167 expression and inhibits MGMT, ER?, p-ER? Ser118 and ki-67 expression. Collectively, our results suggest that MGMT inhibition leads to growth inhibition of tamoxifen-resistant breast cancer in vitro and in vivo and resensitizes tamoxifen-resistant breast cancer cells to antiestrogen therapy. These findings suggest that MGMT inhibition may provide a novel therapeutic strategy for overcoming antiestrogen resistance.

SUBMITTER: Bobustuc GC

PROVIDER: S-EPMC3459485 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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MGMT inhibition restores ERα functional sensitivity to antiestrogen therapy.

Bobustuc George C GC Smith Joshua S JS Maddipatla Sreeram S Jeudy Sheila S Limaye Arati A Isley Beth B Caparas Maria-Lourdes M ML Constantino Susan M SM Shah Nikita N Baker Cheryl H CH Srivenugopal Kalkunte S KS Baidas Said S Konduri Santhi D SD

Molecular medicine (Cambridge, Mass.) 20120907

Antiestrogen therapy resistance remains a huge stumbling block in the treatment of breast cancer. We have found significant elevation of O(6) methylguanine DNA methyl transferase (MGMT) expression in a small sample of consecutive patients who have failed tamoxifen treatment. Here, we show that tamoxifen resistance is accompanied by upregulation of MGMT. Further we show that administration of the MGMT inhibitor, O(6)-benzylguanine (BG), at nontoxic doses, leads to restoration of a favorable estro ...[more]

PMID: 22549111

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Project description:Introduction: Obesity and overweight affect more than one third of the world population, and are significant risk factors for type II diabetes, cardiovascular disease and cancer. Common obesity is usually accompanied by hyperleptinemia and leptin resistance. Purpose: Here, we investigate the molecular pathways underlying the effects of HDAC6 inhibition in reversing diet-induced obesity and interrogate potential pathways that link HDAC6 with leptin receptor signaling by conducting whole transcriptome analysis in white adipose tissues of the diet-induced obese mice that were treated with tubastatin A (an HDAC6-specific inhibitor) and in fat-specific HDAC6 knockout mice. Methods: Male 4-5 week-old C57B/6J wild type mice were fed with high fat diet for 16-20 weeks to generate diet-induced obese (DIO) mice. Around 28 weeks of age, mice were treated with daily ip injections of either tubastatin A-HCl (TubA, 25 mg/kg) or vehicle for four days. We probed the whole transcriptome in epididymal white adipose tissue (eWAT), and inguinal white adipose tissue (iWAT) following vehicle or TubA administration (eWAT.Veh, eWAT.TubA, iWAT.Veh, iWAT.TubA groups). In a separate cohort, DIO HDAC6 global knockout mice were treated with vehicle (Veh group) or TubA (TubA group). eWAT was excised for RNA extraction. In the third cohort, adipose tissue specific HDAC6 knockout mice were generated crossing adiponectin-Cre mice with HDAC6-floxed mice. These fat specific HDAC6 KO mice (AdKO) and their adiponectin-Cre controls (AdCre) were treated with vehicle for five weeks. eWAT was excised for RNA extraction.Total RNA samples from each tissue were extracted using Trizol. RNA Sequencing for the wild-type iWAT and eWAT samples from vehicle or TubA-treated mice was performed by the University of Michigan Sequencing Core, using the Illumina Hi-Seq 4000 platform. RNA sequencing for the other samples were conducted by Novogene, NovaSeq 6000 PE150, HiSeq SE50 platform. The following bioinformatics analysis have been conducted by Novogene: 1. Data Quality Control: filtering reads containing adapter or with low quality. 2. Statistics Analysis of Data Production and Quality. 3. Mapping Reads to Reference Genome. 4. Gene Expression Quantification. 5. Correlation analysis (For biological replicates only). 6. Differential Expression Analysis (two or more groups of samples). 7. GO Enrichment Analysis of Differentially Expressed Genes (DEGs) (two or more groups of samples). 8. KEGG Pathway Enrichment Analysis of Differentially Expressed Genes (DEGs) (two or more groups of samples). 9. GSEA Enrichment Analysis of Expressed Genes (two or more groups of samples). 10. Protein Protein Interaction Analysis. 11. Reactome Pathway Enrichment Analysis of Differentially Expressed Genes (DEGs) (two or more groups of samples and only for mouse samples). 12. Oncogene Functional Annotation analysis of Differentially Expressed Genes (DEGs) (two or more groups of samples and only for mouse sample). Results: Inhibitors of the cytosolic enzyme histone deacetylase 6 (HDAC6) act as potent anti-obesity agents, and leptin sensitizers. HDAC6 inhibitor TubA suppresses food intake and reduce obesity, in an HDAC6-dependent manner, resulting in up to fifty percent decrease in fat mass in DIO mice accompanied by significantly reduced hepatic steatosis and improved systemic glucose homeostasis. Conclusions: Mechanistically, peripheral -but not central- inhibition of HDAC6 confers central leptin sensitivity, and the anti-obesity effect of TubA is significantly attenuated in animals defective in the central leptin-melanocortin circuitry, including the db/db and MCR4 KO mice.

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MGMT inhibition restores ER? functional sensitivity to antiestrogen therapy.

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MGMT inhibition restores ERα functional sensitivity to antiestrogen therapy.

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