Abstract 1686
Background
Novel therapeutic strategies are needed for the treatment of triple negative breast cancer (TNBC). Inhibition of bromo and extraterminal domains (BET) has shown an anti-proliferative effect in TNBC as well as a synergistic interaction with polo-like kinase (PLK) inhibitors. As for many other therapeutic interventions, resistance to BET inhibitors is expected to occur at a given treatment point.
Methods
We generated two resistant models to the BET inhibitor JQ1, MDA-MB 231R and HS578TR. Western-blot, flow cytometry analysis, genomic and pharmacologic inhibition were executed to evaluate the anti-proliferative activity and biochemical effect. Nude mice were used to explore the in vivo pharmacological efficacy.
Results
We report the generation of two resistant models to the BET inhibitor JQ1. In both models, resistant cells were particularly sensitive to PLK1 inhibition, and reduced cell proliferation in 2D and 3D cell cultures. Although PLK1 levels were similar in sensitive and resistant cell lines, pharmacological inhibition of BRD4 using JQ1 reduced PLK1 to a less extent in the resistant model, effect not observed with BRD4 gene downregulation. PLK1 inhibitor volasertib induced G2/M arrest in both cell lines, and this effect was more evident in resistant cells, in addition to an increase in pH3 and pCDK1. Combination of volasertib and JQ1 induced apoptosis that was partially caspase dependent. A slight activation of Erk1/2 and pS6 was observed in the resistant model, but the inhibition of these kinases did not have a different effect on proliferation compared with the sensitive one. Finally, JQ1-resistant cells xenografted in mice displayed resistance to JQ1 that was reversed after administration of the PLK1 inhibitor volasertib.
Conclusions
PLK1 inhibition reverts resistance to BET inhibitors in our in vivo and in vitro models. These findings open avenues for further drug combinations in the clinical setting.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Universidad de Castilla-La Mancha.
Funding
Instituto de Salud Carlos III; ACEPAIN; CRIS CANCER; Diputación Albacete; UCLM.
Disclosure
All authors have declared no conflicts of interest.
Resources from the same session
4874 - Complete Responses in Patients With 2nd-Line or Greater Metastatic Triple-Negative Breast Cancer (TNBC) Following First-in-Human Immunotherapy Combining NK and T Cell Activation with Off-the-Shelf High-Affinity CD16 NK Cell Line (haNK)
Presenter: Chaitali Nangia
Session: Poster Display session 2
Resources:
Abstract
4362 - Reproducibility and concordance of 4 clinically developed programmed death-ligand 1 (PD-L1) immunohistochemistry (IHC) assays in triple-negative breast cancer (TNBC)
Presenter: Aurelia Noske
Session: Poster Display session 2
Resources:
Abstract
4528 - Systemic Therapy in 2nd-Line Metastatic Triple Negative Breast Cancer (mTNBC): A Systematic Literature Review (SLR) and Meta-Analysis (MA) of Efficacy
Presenter: Peter Kaufman
Session: Poster Display session 2
Resources:
Abstract
4112 - Cisplatin given at three divided doses for three consecutive days in metastatic breast cancer: an alternative schedule for one full dose with comparable efficacy but less CINV and hypomagnesaemia
Presenter: Yang Chen
Session: Poster Display session 2
Resources:
Abstract
5699 - Patterns and predictors of first-line (1L) taxane use in US patients with metastatic triple-negative breast cancer (mTNBC)
Presenter: Joyce O’Shaughnessy
Session: Poster Display session 2
Resources:
Abstract
1931 - Maintenance Chemotherapy is effective in Patients with Metastatic Triple Negative Breast Cancer After First-line Platinum-based Chemotherapy
Presenter: Jian Zhang
Session: Poster Display session 2
Resources:
Abstract
4696 - Using the Patient-Reported Outcomes Measurement Information System (PROMIS) to investigate symptom burden enrichment in Stage IV patients at an academic center
Presenter: Madeline Matthys
Session: Poster Display session 2
Resources:
Abstract
4582 - Measures of functional status in adults aged ≥70 years with advanced breast cancer (ABC) receiving palbociclib (PAL) combination therapy in POLARIS
Presenter: Meghan Karuturi
Session: Poster Display session 2
Resources:
Abstract
3565 - Real-World 1-Year Survival Analysis of Patients with Metastatic Breast Cancer with Liver or Lung Metastasis Treated with Eribulin, Gemcitabine or Capecitabine
Presenter: Shayma Kazmi
Session: Poster Display session 2
Resources:
Abstract
3608 - Prognostic impact of Body Mass Index (BMI) on overall survival in patients with metastatic breast cancer
Presenter: Khalil SALEH
Session: Poster Display session 2
Resources:
Abstract