Abstract 1735
Background
Breast cancer is the malignant neoplasm with the highest incidence and mortality in women worldwide. Approximately 70% of breast tumors express hormone receptors (HR+). Although antiestrogen tamoxifen has been successful for HR+ breast cancer treatment, a significant amount of these tumors eventually develop resistance. In these cases, the addition of CDK4/6 inhibitor palbociclib has shown clinical effectiveness. However, there is still a need to elucidate the mechanisms underlying resistance to these treatments in order to design better combination therapies for each case and improve patient outcomes. The aim of this work was to study these mechanisms using cell variants generated to mimic what occurs in the clinic.
Methods
We developed three cell lines with acquired resistance to tamoxifen (T47D-TR), palbociclib (T47D-PR) and tamoxifen+palbociclib (T47D-TPR), by exposing T47D wild type cells to progressively increasing concentrations of the drugs over a period of about 12 months.
Results
Western blot analysis showed decreased levels of HR, higher activation levels of PI3K/Akt/mTOR pathway, along with greater levels of cell cycle associated proteins in all resistant cell lines. The resistant tumors generated as xenografts in immunosuppressed mice showed more invasive characteristics than those generated from the T47D-wt cell line, despite the lower growth rates showed by all resistant lines. Finally, we analyzed the response to palbociclib and to PI3K/Akt/mTOR inhibitors in the resistant cell lines. We found that all resistant lines were sensitive to BKM-120 (PI3K inhibitor) and to rapamycin (mTOR inhibitor), and the combination with palbociclib showed an additive inhibitory effect in both cases. However, the sensitivity of the resistant cells was greater to rapamycin than to BKM-120.
Conclusions
Taken together, our results support the use of mTOR inhibitors, rather than PI3K inhibitors, in combination with CDK4/6 inhibitors in the treatment of both tamoxifen and palbociclib resistant tumors.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
FONCYT-INC-CONICET.
Funding
FONCYT-INC-CONICET.
Disclosure
All authors have declared no conflicts of interest.
Resources from the same session
3690 - PD-L1 expression in resected undifferentiated pleomorphic sarcoma and its clinical implications
Presenter: Kyoungmin Lee
Session: Poster Display session 1
Resources:
Abstract
2013 - PD-L1 expression as a potential therapeutic target and prognostic biomarker in well-differentiated and dedifferentiated liposarcoma.
Presenter: Heejung Chae
Session: Poster Display session 1
Resources:
Abstract
5021 - Soft tissue sarcomas express a distinct mRNA immune profile
Presenter: Viktor Grünwald
Session: Poster Display session 1
Resources:
Abstract
3029 - The molecular landscape of fusion genes in endometrial stromal sarcomas include three nosological entities with different natural history
Presenter: Mehdi Brahmi
Session: Poster Display session 1
Resources:
Abstract
3914 - Clinical validation of a novel assay for the detection of diagnostic alterations in sarcomas
Presenter: Lauren Mc Connell
Session: Poster Display session 1
Resources:
Abstract
1912 - A prospective correlative trial of personalized patient-derived xenograft (PDX) as avatars for drug therapy in patients with metastatic or recurrent soft tissue sarcomas (STS).
Presenter: Kanan Alshammari
Session: Poster Display session 1
Resources:
Abstract
5097 - Fusion of immortalized myoblasts induces genomic instability that drives tumor development and progression.
Presenter: Candice Merle
Session: Poster Display session 1
Resources:
Abstract
1383 - let-7a suppress Ewing sarcoma CSCs' malignant phenotype through forms a positive feedback regulation loop with lin28 via STAT3
Presenter: Xu Jiang
Session: Poster Display session 1
Resources:
Abstract
3386 - Myoepithelial Tumors of Soft Tissues and Extraskeletal Myxoid Chondrosarcomas feature a distinct transcriptional pattern
Presenter: Dominga Racanelli
Session: Poster Display session 1
Resources:
Abstract
1844 - In Vivo Efficacy and Enhanced Tumor Accumulation of Liposomal Vinorelbine (TLC178) in Human Sarcoma Xenograft Mice Model
Presenter: Wan-ni Yu
Session: Poster Display session 1
Resources:
Abstract