Rebecca Cook
Faculty Member
Last active: 4/15/2019

Intrinsic apoptotic pathway activation increases response to anti-estrogens in luminal breast cancers.

Williams MM, Lee L, Werfel T, Joly MMM, Hicks DJ, Rahman B, Elion D, McKernan C, Sanchez V, Estrada MV, Massarweh S, Elledge R, Duvall C, Cook RS
Cell Death Dis. 2018 9 (2): 21

PMID: 29343814 · PMCID: PMC5833697 · DOI:10.1038/s41419-017-0072-x

Estrogen receptor-α positive (ERα+) breast cancer accounts for approximately 70-80% of the nearly 25,0000 new cases of breast cancer diagnosed in the US each year. Endocrine-targeted therapies (those that block ERα activity) serve as the first line of treatment in most cases. Despite the proven benefit of endocrine therapies, however, ERα+ breast tumors can develop resistance to endocrine therapy, causing disease progression or relapse, particularly in the metastatic setting. Anti-apoptotic Bcl-2 family proteins enhance breast tumor cell survival, often promoting resistance to targeted therapies, including endocrine therapies. Herein, we investigated whether blockade of anti-apoptotic Bcl-2 family proteins could sensitize luminal breast cancers to anti-estrogen treatment. We used long-term estrogen deprivation (LTED) of human ERα+ breast cancer cell lines, an established model of sustained treatment with and acquired resistance to aromatase inhibitors (AIs), in combination with Bcl-2/Bcl-xL inhibition (ABT-263), finding that ABT-263 induced only limited tumor cell killing in LTED-selected cells in culture and in vivo. Interestingly, expression and activity of the Bcl-2-related factor Mcl-1 was increased in LTED cells. Genetic Mcl-1 ablation induced apoptosis in LTED-selected cells, and potently increased their sensitivity to ABT-263. Increased expression and activity of Mcl-1 was similarly seen in clinical breast tumor specimens treated with AI + the selective estrogen receptor downregulator fulvestrant. Delivery of Mcl-1 siRNA loaded into polymeric nanoparticles (MCL1 si-NPs) decreased Mcl-1 expression in LTED-selected and fulvestrant-treated cells, increasing tumor cell death and blocking tumor cell growth. These findings suggest that Mcl-1 upregulation in response to anti-estrogen treatment enhances tumor cell survival, decreasing response to therapeutic treatments. Therefore, strategies blocking Mcl-1 expression or activity used in combination with endocrine therapies would enhance tumor cell death.

MeSH Terms (18)

Aniline Compounds Animals Apoptosis bcl-X Protein Breast Neoplasms Cell Line, Tumor Down-Regulation Estrogen Antagonists Female Fulvestrant Gene Targeting Humans Mice Myeloid Cell Leukemia Sequence 1 Protein Receptors, Estrogen Signal Transduction Sulfonamides Up-Regulation

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