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
3305 - A phase I dose-escalation and expansion trial of intratumorally administered CV8102, alone and in combination with anti-PD-1 in patients with advanced solid tumors
Presenter: Jürgen Krauss
Session: Poster Display session 1
Resources:
Abstract
5353 - Phase 1/2 Study of 9-ING-41, a small molecule selective Glycogen Synthase Kinase-3 Beta (GSK-3β) Inhibitor, as a Single Agent and Combined with Chemotherapy, in Patients with Refractory Hematological Malignancies or Solid Tumors
Presenter: Benedito Carneiro
Session: Poster Display session 1
Resources:
Abstract
3946 - Trial in progress: a Phase I, open-label study of GSK1795091 administered in combination with immunotherapies in participants with advanced solid tumors (NCT03447314).
Presenter: Aaron Hansen
Session: Poster Display session 1
Resources:
Abstract
3449 - Radiographic Phenotyping to Identify Intracranial Disseminated Recurrence in Brain metastases Treated With Radiosurgery Using Contrast-enhanced MR Imaging
Presenter: CheYu Hsu
Session: Poster Display session 1
Resources:
Abstract
4553 - Association between TP53 mutations and efficacy of Osimertinib for brain metastasis from EGFR-mutant lung cancer
Presenter: Lijuan Chen
Session: Poster Display session 1
Resources:
Abstract
4942 - Response assessment of melanoma brain metastases treated by stereotactic radiotherapy or immunotherapy or both: a comparison of RECIST 1.1, RANO and iRANO criteria
Presenter: Emilie Le Rhun
Session: Poster Display session 1
Resources:
Abstract
3529 - Management of multiple brain metastases by Staged SRS focusing on utmost risk lesions
Presenter: shaoqun Li
Session: Poster Display session 1
Resources:
Abstract
5315 - Whole brain radiotherapy plus simultaneous in-field boost versus whole brain radiotherapy plus fractionated stereotactic radiotherapy for multiple brain metastases of non-small cell lung cancer
Presenter: Lu Li
Session: Poster Display session 1
Resources:
Abstract
1116 - 3D based texture analysis serving as potential diagnostic factor in discriminating primary central nervous system lymphoma from metastatic brain tumors: A preliminary study
Presenter: Wen Guo
Session: Poster Display session 1
Resources:
Abstract
5344 - Global trends in population-based survival for 303,169 adults diagnosed with glioblastoma in 44 countries during 2000-2014 (CONCORD-3)
Presenter: Fabio Girardi
Session: Poster Display session 1
Resources:
Abstract