TY - JOUR
T1 - ERpS294 is a biomarker of ligand or mutational ERα activation and a breast cancer target for CDK2 inhibition
AU - Scott, Gary K.
AU - Chu, David
AU - Kaur, Ravneet
AU - Malato, Julia
AU - Rothschild, Daniel E.
AU - Frazier, Katya
AU - Eppenberger-Castori, Serenella
AU - Hann, Byron
AU - Park, Ben Ho
AU - Benz, Christopher C.
PY - 2017/1/1
Y1 - 2017/1/1
N2 - ERα phosphorylation at hinge site S294 (pS294) was recently shown to be essential for ER-dependent gene transcription and mediated by an unknown cyclindependent kinase (CDK). This study was undertaken to identify the exact CDK pathway mediating pS294 formation, and to determine if this phosphorylation event occurs with, and can be targeted to treat, the ligand-independent growth of breast cancers expressing endocrine-refractory ESR1 mutations. Using a newly developed anti-pS294 monoclonal antibody, a combination of CDK specific siRNA knockdown studies and a broad panel of CDK selective inhibitors against ligand (E2)-stimulated MCF7 cells, we first identified CDK2 as the primary mediator of pS294 formation and showed that CDK2-selective inhibitors like Dinaciclib,s but not CDK4/6 inhibitors like Palbociclib, can selectively prevent pS294 formation and repress ER-dependent gene expression. We then expressed the ER-activating mutations ERmut(Y537S) and ERmut(D538G) in MCF7 cells, and demonstrated their ability to induce ligandindependent and tamoxifen-resistant growth, associated with constitutive and CDK2- dependent pS294 expression. Following robust growth of E2-independent and TAMresistant MCF7mutER(Y537S) tumors in vivo, nude mice were also treated with either Dinaciclib or Palbociclib at doses and injection schedules unable to retard tumor growth as single agents; the TAM plus Palbociclib combination arrested further tumor growth without affecting pS294 formation, while the TAM plus Dinaciclib combination produced tumor regression associated with loss of pS294 expression. These findings, and our proposed mechanistic model, provide new rationale for the clinical evaluation of CDK2 inhibitors given in combination with endocrine agents as a new treatment strategy against ESR1 mutation expressing breast cancers.
AB - ERα phosphorylation at hinge site S294 (pS294) was recently shown to be essential for ER-dependent gene transcription and mediated by an unknown cyclindependent kinase (CDK). This study was undertaken to identify the exact CDK pathway mediating pS294 formation, and to determine if this phosphorylation event occurs with, and can be targeted to treat, the ligand-independent growth of breast cancers expressing endocrine-refractory ESR1 mutations. Using a newly developed anti-pS294 monoclonal antibody, a combination of CDK specific siRNA knockdown studies and a broad panel of CDK selective inhibitors against ligand (E2)-stimulated MCF7 cells, we first identified CDK2 as the primary mediator of pS294 formation and showed that CDK2-selective inhibitors like Dinaciclib,s but not CDK4/6 inhibitors like Palbociclib, can selectively prevent pS294 formation and repress ER-dependent gene expression. We then expressed the ER-activating mutations ERmut(Y537S) and ERmut(D538G) in MCF7 cells, and demonstrated their ability to induce ligandindependent and tamoxifen-resistant growth, associated with constitutive and CDK2- dependent pS294 expression. Following robust growth of E2-independent and TAMresistant MCF7mutER(Y537S) tumors in vivo, nude mice were also treated with either Dinaciclib or Palbociclib at doses and injection schedules unable to retard tumor growth as single agents; the TAM plus Palbociclib combination arrested further tumor growth without affecting pS294 formation, while the TAM plus Dinaciclib combination produced tumor regression associated with loss of pS294 expression. These findings, and our proposed mechanistic model, provide new rationale for the clinical evaluation of CDK2 inhibitors given in combination with endocrine agents as a new treatment strategy against ESR1 mutation expressing breast cancers.
KW - Cyclin-dependent kinase-2 inhibitors
KW - ERα phosphorylation
KW - ESR1 mutations
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UR - http://www.scopus.com/inward/citedby.url?scp=85031049378&partnerID=8YFLogxK
U2 - 10.18632/oncotarget.12735
DO - 10.18632/oncotarget.12735
M3 - Article
C2 - 29137354
AN - SCOPUS:85031049378
SN - 1949-2553
VL - 8
SP - 83432
EP - 83445
JO - Oncotarget
JF - Oncotarget
IS - 48
ER -