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
2304 - Synthetic peptide of tumor–associated antigen L6 formulated with polymer-based adjuvant enhances anti-tumor effects in mice
Presenter: Shih-jen Liu
Session: Poster Display session 1
Resources:
Abstract
4419 - Improving detection level of somatic mosaicism in neurofibromatosis type 1
Presenter: Kristina Karandasheva
Session: Poster Display session 1
Resources:
Abstract
5283 - Preclinical pharmacokinetic/pharmacodynamic (PK/PD) relationship of ABN401, a highly selective Met inhibitor, in gastric and non-small-cell lung cancer models
Presenter: JooSeok Kim
Session: Poster Display session 1
Resources:
Abstract
5488 - Transcription factors of Snail family in the regulation of resistance of breast cancer cells to hypoxic conditions
Presenter: Alvina Khamidullina
Session: Poster Display session 1
Resources:
Abstract
5417 - Metastasis is impaired by endothelial-specific Dll4 loss-of-function through inhibition of epithelial-to-mesenchymal transition and reduction of cancer stem cells and circulating tumour cells
Presenter: Liliana Mendonça
Session: Poster Display session 1
Resources:
Abstract
5494 - Identification of novel and known FGFR gene fusions in Chinese non-small cell lung cancer
Presenter: Weixin Zhao
Session: Poster Display session 1
Resources:
Abstract
3412 - WNT pathway mutations (APC/CTNNB1) and immune checkpoint inhibitors (ICI) response in metastatic non-small cell lung cancer (NSCLC) patients.
Presenter: Francisco Javier Ros Montana
Session: Poster Display session 1
Resources:
Abstract
1815 - Leukocytosis as a negative prognostic factor in patients with lung cancer: Which subpopulation of leukocytes is responsible?
Presenter: Filip Kohutek
Session: Poster Display session 1
Resources:
Abstract
5022 - Identification of MET gene amplifications using next-generation sequencing in non-small cell lung cancer patients
Presenter: Sergi Clavé
Session: Poster Display session 1
Resources:
Abstract
4925 - Prognostic role of CD73 in metastatic Non Small Cell Lung Cancer according to the presence of driver alterations
Presenter: Giulia Galli
Session: Poster Display session 1
Resources:
Abstract