Resistance to everolimus driven by epigenetic regulation of MYC in ER+ breast cancers

Abstract

Acquired resistance to PI3K/mTOR/Akt pathway inhibitors is often associated with compensatory feedback loops involving the activation of oncogenes. Here, we have generated everolimus resistance in ER+ breast cancer cells and in long-term estrogen deprived (LTED) models that mimic progression on anti-estrogens. This allowed us to uncover MYC as a driver of mTOR inhibitor resistance. We demonstrate that both everolimus resistance and acute treatment of everolimus can lead to the upregulation of MYC mRNA, protein expression and, consequently, the enrichment of MYC signatures as revealed by RNA sequencing data. Depletion of MYC resulted in resensitization to everolimus, confirming its functional importance in this setting. Furthermore, ChIP assays demonstrate that MYC upregulation in the everolimus resistant lines is mediated by increased association of the BRD4 transcription factor with the MYC gene. Finally, JQ1, a BRD4 inhibitor combined with everolimus exhibited increased tumor growth inhibition in 3D Matrigel models and an in vivo xenograft model. These data suggest that MYC plays an important role in mediating resistance to everolimus in ER+ and ER+/LTED models. Furthermore, given the regulation ofMYCby BRD4 in this setting, these data have implications for increased therapeutic potential of combining epigenetic agents with mTOR inhibitors to effectively downregulate otherwise difficult to target transcription factors such as MYC.

AZD2014, an Inhibitor of mTORC1 and mTORC2, Is Highly Effective in ER+ Breast Cancer When Administered Using Intermittent or Continuous Schedules

“…The HCC1428 long-term estrogen-deprived everolimus-resistant (LTED-eveR) line was generated and cultured in phenol red-free medium þ 10% charcoal dextran-treated FBS (Hyclone), 1% L-glutamine and antibiotics. Everolimus resistance was generated as previously described (26). To perform compound treatment assays, everolimus was removed during plating and cells were treated the following day with indicated compounds.…”

Bromodomain-Containing Protein 4 (BRD4) Inhibition Sensitizes Palomid 529-Induced Anti-Renal Cell Carcinoma Cell Activity in Vitro and in Vivo

“…First, pharmacologic inhibition of BRD4 enhanced Palomid 529-induced 786-O cell death Inhibition of BRD4 could be a fine strategy to sensitize Palomid 529 in RCC cells. Previous studies have established synergistic to additive effects between mTORC1 inhibitors and bromodomain protein inhibition in various human cancers [52][53][54]. For example, Lee et al, reported the synergistic anti-osteosarcoma activity by the BRD4 inhibitor JQ1 and rapamycin [54].…”

Exosomes and development of cancer cell resistance to metformin: pilot study

“…Известны лишь единичные работы, в которых изучалось раз-витие устойчивости рака молочной железы (РМЖ) к ингибитору mTOR эверолимусу [5] и метформину [6] и описывались изменения отдельных сигнальных каскадов в основном пролиферативного и проме-тастатического профилей при развитии резистент-ности.…”