The G Protein Estrogen Receptor (GPER) is involved in the resistance to the CDK4/6 inhibitor palbociclib in breast cancer.

The cyclin D1-cyclin dependent kinases (CDK)4/6 inhibitor palbociclib in combination with endocrine therapy shows remarkable efficacy in the management of estrogen receptor (ER)-positive and HER2-negative advanced breast cancer (BC). Nevertheless, resistance to palbociclib frequently arises, highlighting the need to identify new targets toward more comprehensive therapeutic strategies in BC patients. BC cell lines resistant to palbociclib were generated and used as a model system. Gene silencing techniques and overexpression experiments, real-time PCR, immunoblotting and chromatin immunoprecipitation studies as well as cell viability, colony and 3D spheroid formation assays served to evaluate the involvement of the G protein-coupled estrogen receptor (GPER) in the resistance to palbociclib in BC cells. Molecular docking simulations were also performed to investigate the potential interaction of palbociclib with GPER. Furthermore, BC cells co-cultured with cancer-associated fibroblasts (CAFs) isolated from mammary carcinoma, were used to investigate whether GPER signaling may contribute to functional cell interactions within the tumor microenvironment toward palbociclib resistance. Finally, by bioinformatics analyses and k-means clustering on clinical and expression data of large cohorts of BC patients, the clinical significance of novel mediators of palbociclib resistance was explored. Dissecting the molecular events that characterize ER-positive BC cells resistant to palbociclib, the down-regulation of ERα along with the up-regulation of GPER were found. To evaluate the molecular events involved in the up-regulation of GPER, we determined that the epidermal growth factor receptor (EGFR) interacts with the promoter region of GPER and stimulates its expression toward BC cells resistance to palbociclib treatment. Adding further cues to these data, we ascertained that palbociclib does induce pro-inflammatory transcriptional events via GPER signaling in CAFs. Of note, by performing co-culture assays we demonstrated that GPER contributes to the reduced sensitivity to palbociclib also facilitating the functional interaction between BC cells and main components of the tumor microenvironment named CAFs. Overall, our results provide novel insights on the molecular events through which GPER may contribute to palbociclib resistance in BC cells. Additional investigations are warranted in order to assess whether targeting the GPER-mediated interactions between BC cells and CAFs may be useful in more comprehensive therapeutic approaches of BC resistant to palbociclib.

Talia M ，Cirillo F ，Scordamaglia D ，Di Dio M ，Zicarelli A ，De Rosis S ，Miglietta AM ，Capalbo C ，De Francesco EM ，Belfiore A ，Grande F ，Rizzuti B ，Occhiuzzi MA ，Fortino G ，Guzzo A ，Greco G ，Maggiolini M ，Lappano R ... -  《JOURNAL OF EXPERIMENTAL & CLINICAL CANCER RESEARCH》

Resistance to cyclin-dependent kinase (CDK) 4/6 inhibitors confers cross-resistance to other CDK inhibitors but not to chemotherapeutic agents in breast cancer cells.

Ogata R ，Kishino E ，Saitoh W ，Koike Y ，Kurebayashi J ... -  《-》

AHR and GPER mediate the stimulatory effects induced by 3-methylcholanthrene in breast cancer cells and cancer-associated fibroblasts (CAFs).

Cirillo F ，Lappano R ，Bruno L ，Rizzuti B ，Grande F ，Guzzi R ，Briguori S ，Miglietta AM ，Nakajima M ，Di Martino MT ，Maggiolini M ... -  《JOURNAL OF EXPERIMENTAL & CLINICAL CANCER RESEARCH》

Dual Targeting of CDK4/6 and BCL2 Pathways Augments Tumor Response in Estrogen Receptor-Positive Breast Cancer.

Although cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors significantly extend tumor response in patients with metastatic estrogen receptor-positive (ER+) breast cancer, relapse is almost inevitable. This may, in part, reflect the failure of CDK4/6 inhibitors to induce apoptotic cell death. We therefore evaluated combination therapy with ABT-199 (venetoclax), a potent and selective BCL2 inhibitor. BCL2 family member expression was assessed following treatment with endocrine therapy and the CDK4/6 inhibitor palbociclib. Functional assays were used to determine the impact of adding ABT-199 to fulvestrant and palbociclib in ER+ breast cancer cell lines, patient-derived organoid (PDO), and patient-derived xenograft (PDX) models. A syngeneic ER+ mouse mammary tumor model was used to study the effect of combination therapy on the immune system. Triple therapy was well tolerated and produced a superior and more durable tumor response compared with single or doublet therapy. This was associated with marked apoptosis, including of senescent cells, indicative of senolysis. Unexpectedly, ABT-199 resulted in Rb dephosphorylation and reduced G1-S cyclins, most notably at high doses, thereby intensifying the fulvestrant/palbociclib-induced cell-cycle arrest. Interestingly, a CRISPR/Cas9 screen suggested that ABT-199 could mitigate loss of Rb (and potentially other mechanisms of acquired resistance) to palbociclib. ABT-199 did not abrogate the favorable immunomodulatory effects of palbociclib in a syngeneic ER+ mammary tumor model and extended tumor response when combined with anti-PD1 therapy. This study illustrates the potential for targeting BCL2 in combination with CDK4/6 inhibitors and supports investigation of combination therapy in ER+ breast cancer.

Whittle JR ，Vaillant F ，Surgenor E ，Policheni AN ，Giner G ，Capaldo BD ，Chen HR ，Liu HK ，Dekkers JF ，Sachs N ，Clevers H ，Fellowes A ，Green T ，Xu H ，Fox SB ，Herold MJ ，Smyth GK ，Gray DHD ，Visvader JE ，Lindeman GJ ... -  《-》

FGFR1 Overexpression Induces Cancer Cell Stemness and Enhanced Akt/Erk-ER Signaling to Promote Palbociclib Resistance in Luminal A Breast Cancer Cells.

Cheng Q ，Ma Z ，Shi Y ，Parris AB ，Kong L ，Yang X ... -  《Cells》