Abstract 5492
Background
Resistance to endocrine therapy in estrogen receptor positive (ER+) breast cancer drives mortality and despite new targeted therapies, resistance is the obstacle to progression-free survival. Fulvestrant (FUL), a selective estrogen receptor degrader (SERD) was approved in 2017 for fırst-line therapy of metaststic disease in postmenopausal women; however, acquired FUL-resistance in both fırst-line setting and in combination therapy with CDK4/6 inhibitor, palbociclib, has been observed clinically. The poor pharmacokinetics of FUL may contribute to acquired resistance.
Methods
Using structure-based design, we optimized: 1) novel SERDs bearing a basic side chain (B-SERDs) as an orally bioavailable and brain penetrant alternative to FUL; 2) novel pyridinone-based bromodomains and extra-terminal motif (BET) inhibitors to be used in combination with B-SERDs or FUL. Biochemical assays and growth inhibition of breast cancer cell lines, resistant to tamoxifen, and/or FUL, both in 2D and 3D cultures were used to optimize and select development candidates. Drug metabolism and pharmacokinetics(DMPK) demonstrated oral bioavailability and dose selection for validation in mouse xenograft models of endocrine resistant breast cancer.
Results
B-SERDs showed equivalence to FUL in cell culture models, with respect to ERα degradation and antiproliferative activity; and in contrast to FUL, were demonstrated to have good oral and brain bioavailability. A development candidate with improved DMPK characteristics was effective in endocrine-resistant ER+ xenograft models. Novel BET inhibitors, optimized for potency in binding to BRD4-BD1 and selectivity over the larger family of bromodomain containing proteins, inhibited growth of tamoxifen and FUL-resistant breast cancer cells.Optimized compounds showed superior in vitro activity to eight BET inhibitors in clinical trials. The optimized BET inhibitor was validated alone and in combination with B-SERD in endocrine-resistant xenograft models.
Conclusions
The combination of B-SERD with BET inhibitor provides a multi-targeted suppression of ER signaling that may extend progression-free survival and cdircumvent acquired resistance in metastatic ER+ breast cancer.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Gregory R J Thatcher.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.
Resources from the same session
592 - Effects of novel targeted anticancer drugs on cytotoxicity, apoptosis, angiogenesis, EMT, drug resistance and autophagic mechanism
Presenter: Seyma Aydinlik
Session: Poster Display session 1
Resources:
Abstract
3235 - Delineating the mechanisms of alpha 1-3 fucosyltransferase FUT11 in ovarian cancer
Presenter: Qi Chen
Session: Poster Display session 1
Resources:
Abstract
3577 - The tyrosine kinase inhibitor Dasatinib blocks tumor growth, invasion and recurrence potential by interrupting the communication between cancer cells and their surrounding microenvironment in triple negative breast cancer
Presenter: Miriam Nuncia-Cantarero
Session: Poster Display session 1
Resources:
Abstract
4808 - NORE1A induces a feedback termination of TNF signaling by antagonizing TNFR1 through ITCH-mediated destruction complex
Presenter: Jieun Ahn
Session: Poster Display session 1
Resources:
Abstract
1294 - Hsp90 inhibitors enhance the antitumoral effect of osimertinib and overcome osimertinib resistance in non-small-cell cell lung cancer cell models
Presenter: Jordi Codony-Servat
Session: Poster Display session 1
Resources:
Abstract
1559 - Expression of IL-17RA promotes cancer stem-like properties of colorectal cancer cells by Stat3 activation
Presenter: Chih-Yung Yang
Session: Poster Display session 1
Resources:
Abstract
1615 - Adaption of Pancreatic Cancer Cells to AKT1 Inhibition Induces the Acquisition of Cancer Stem-Cell Like Phenotype Through Upregulation of Mitochondrial Functions
Presenter: Hugo Arasanz
Session: Poster Display session 1
Resources:
Abstract
4793 - Bub3 is phosphorylated by the Ataxia-Telangiectasia Mutated Kinase in mitosis and required for activation of the mitotic spindle checkpoint in Breast Cancer
Presenter: Mingming Xiao
Session: Poster Display session 1
Resources:
Abstract
1448 - The regulation of INK4 locus by long non-coding RNAs
Presenter: Yojiro Kotake
Session: Poster Display session 1
Resources:
Abstract
1858 - Vascular Endothelial Growth Factor in Colorectal Cancer Pathology, Survival and Treatment
Presenter: Liz Baker
Session: Poster Display session 1
Resources:
Abstract