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
920 - Efficacy of intravenous (IV) NEPA, a fixed NK1/5-HT3 receptor antagonist (RA) combination, for prevention of CINV following cisplatin- and anthracycline cyclophosphamide (AC)-based chemotherapy (CT)
Presenter: Lee Schwartzberg
Session: Poster Display session 1
Resources:
Abstract
5146 - Efficacy of olanzapine combination in prevention of nausea & vomiting in highly emetogenic chemotherapy
Presenter: Smitha Saldanha
Session: Poster Display session 1
Resources:
Abstract
1947 - Patient-reported outcome data during real-world use of NEPA for prevention of chemotherapy-induced nausea and vomiting in high-risk platin-receiving patients - A prospective multicenter trial
Presenter: Meinolf Karthaus
Session: Poster Display session 1
Resources:
Abstract
6163 - A study evaluating steroid induced metabolic syndrome after antiemetic dexamethasone therapy in patients received high emetic risk chemotherapy
Presenter: Hee Jun Kim
Session: Poster Display session 1
Resources:
Abstract
2154 - High incidence of nausea during initial and repeated courses if intravenous chemotherapy in patients receiving guideline consistent antiemetic prophylaxis - a prospective, observational, real world study.
Presenter: Teresa Smit
Session: Poster Display session 1
Resources:
Abstract
1637 - "Randomised controlled trial of Scalp Cooling (SC) for the prevention of Chemotherapy Induced Alopecia (CIA)”
Presenter: Jyoti Bajpai
Session: Poster Display session 1
Resources:
Abstract
5351 - Performance of the ‘4S rule’ to predict short-term outcomes in cancer outpatients with unsuspected pulmonary embolism.
Presenter: David Pesántez Coronel
Session: Poster Display session 1
Resources:
Abstract
1189 - Prevalence of venous thromboembolism based on intensive screening for patients with advanced solid tumor in prospective observational study
Presenter: Shota Omori
Session: Poster Display session 1
Resources:
Abstract
4340 - Short-term outcomes of cancer patients with pulmonary embolism according to the setting (hospital-acquired vs. outpatient) at diagnosis.
Presenter: Diego Muñoz Guglielmetti
Session: Poster Display session 1
Resources:
Abstract
4658 - Patient-reported outcomes associated with switching to rivaroxaban for the treatment of venous thromboembolism (VTE) in patients with active cancer
Presenter: Alexander Cohen
Session: Poster Display session 1
Resources:
Abstract