Neoadjuvant palbociclib plus either giredestrant or anastrozole in oestrogen receptor-positive, HER2-negative, early breast cancer (coopERA Breast Cancer): an open-label, randomised, controlled, phase 2 study

BACKGROUND

The development of more potent selective oestrogen receptor antagonists and degraders (SERDs) that can be orally administered could help to address the limitations of current endocrine therapies. We report the primary and final analyses of the coopERA Breast Cancer study, designed to test whether giredestrant, a highly potent, non-steroidal, oral SERD, would show a stronger anti-proliferative effect than anastrozole after 2 weeks for oestrogen receptor-positive, HER2-negative, untreated early breast cancer.

METHODS

In this open-label, randomised, controlled, phase 2 study, postmenopausal women were eligible if they were aged 18 years or older; had clinical T stage (cT)1c to cT4a-c (≥1·5 cm within cT1c) oestrogen receptor-positive, HER2-negative, untreated early breast cancer; an Eastern Cooperative Oncology Group performance status of 0-1; and baseline Ki67 score of at least 5%. The study was conducted at 59 hospital or clinic sites in 11 countries globally. Participants were randomly assigned (1:1) to giredestrant 30 mg oral daily or anastrozole 1 mg oral daily on days 1-14 (window-of-opportunity phase) via an interactive web-based system with permuted-block randomisation with block size of four. Randomisation was stratified by cT stage, baseline Ki67 score, and progesterone receptor status. A 16-week neoadjuvant phase comprised the same regimen plus palbociclib 125 mg oral daily on days 1-21 of a 28-day cycle, for four cycles. The primary endpoint was geometric mean relative Ki67 score change from baseline to week 2 in patients with complete central Ki67 scores at baseline and week 2 (window-of-opportunity phase). Safety was assessed in all patients who received at least one dose of study drug. The study is registered with ClinicalTrials.gov (NCT04436744) and is complete.

FINDINGS

Between Sept 4, 2020, and June 22, 2021, 221 patients were enrolled and randomly assigned to the giredestrant plus palbociclib group (n=112; median age 62·0 years [IQR 57·0-68·5]) or anastrozole plus palbociclib group (n=109; median age 62·0 [57·0-67·0] years). 15 (7%) of 221 patients were Asian, three (1%) were Black or African American, 194 (88%) were White, and nine (4%) were unknown races. At data cutoff for the primary analysis (July 19, 2021), the geometric mean relative reduction of Ki67 from baseline to week 2 was -75% (95% CI -80 to -70) with giredestrant and -67% (-73 to -59) with anastrozole (p=0·043), meeting the primary endpoint. At the final analysis (data cutoff Nov 24, 2021), the most common grade 3-4 adverse events were neutropenia (29 [26%] of 112 in the giredestrant plus palbociclib group vs 29 [27%] of 109 in the anastrozole plus palbociclib group) and decreased neutrophil count (17 [15%] vs 16 [15%]). Serious adverse events occurred in five (4%) patients in the giredestrant plus palbociclib group and in two (2%) patients in the anastrozole plus palbociclib group. There were no treatment-related deaths. One patient died due to an adverse event in the giredestrant plus palbociclib group (myocardial infarction).

INTERPRETATION

Giredestrant offers encouraging anti-proliferative and anti-tumour activity and was well tolerated, both as a single agent and in combination with palbociclib. Results justify further investigation in ongoing trials.

FUNDING

F Hoffmann-La Roche.

Abstract OT2-03-02: lidERA Breast Cancer: A phase III adjuvant study of giredestrant (GDC-9545) vs physician’s choice of endocrine therapy in patients with estrogen receptor+, HER2– early breast cancer

BACKGROUND Endocrine therapies (ETs) that target estrogen receptor (ER) activity and/or estrogen synthesis are the mainstay of ER+ breast cancer (BC) treatment. Despite best management, ≤20% of patients (pts) with ER+/HER2– early BC (eBC) develop resistance (in some cases due to acquisition of tumor mutations in ESR1 that can drive estrogen-independent transcription and proliferation) and still have high recurrence rates on standard ETs. New treatment alternatives for ER+/HER2– eBC are needed to reduce risk of recurrence and improve survival, tolerability, quality of life, and adherence. Giredestrant, a highly potent, nonsteroidal oral selective ER antagonist and degrader (SERD), achieves robust ER occupancy and is active against tumors that retain ER-sensitivity or have ESR1 mutation(s). It has been demonstrated to be more potent in vitro and achieves higher ER occupancy in vivo than fulvestrant, the only currently approved SERD. Early-phase clinical studies have demonstrated that single-agent giredestrant (30 mg daily) has promising clinical and pharmacodynamic activity and is well tolerated in the ER+/HER2– eBC and metastatic BC settings. TRIAL DESIGN This is a phase III, global, randomized, open-label, multicenter study evaluating efficacy and safety of adjuvant giredestrant vs physician’s choice of adjuvant ET (PCET) in pts with medium- and high-risk stage I–III histologically confirmed ER+/HER2– eBC. Pts are randomized 1:1 to oral 30 mg daily giredestrant or PCET (tamoxifen, anastrozole, letrozole, or exemestane, given according to prescribing information). Stratification factors are risk (medium vs high, based on anatomic [tumor size, nodal status] and biologic features [grade, Ki67, gene signatures if available]); geographic region (US/Canada/Western Europe vs Asia-Pacific vs rest of the world); prior chemotherapy (no vs yes); and menopausal status (pre-/perimenopausal vs postmenopausal). Beginning on Day 1 of Cycle 1, pts will be treated with giredestrant or PCET for ≥5 years. Continuing PCET after 5 years is at discretion of the investigator and per local standard of care. ELIGIBILITY Female/male pts with medium-/high-risk stage I–III ER+/HER2– eBC; prior curative surgery; completion of (neo)adjuvant chemotherapy (if administered) and/or surgery < 12 months prior to enrollment; no prior ET (≤4 weeks of [neo]adjuvant ET is allowed). For men and pre-/perimenopausal women, a luteinizing hormone-releasing hormone agonist will be given per local prescribing information (mandatory for pts in the giredestrant arm). AIMS Primary endpoint: Invasive disease-free survival (IDFS). Secondary endpoints: Overall survival; IDFS (STEEP definition, including second non-primary BC); disease-free survival; distant recurrence-free survival; locoregional recurrence-free interval; safety; pharmacokinetics; pt-reported outcomes. In addition, this study aims to improve health equity in research and expand clinical trial access. The study will also use/develop digital healthcare solutions, which will enable better understanding of pts’ needs and their adherence to ET. STATISTICAL METHODS The primary endpoint analysis will use a stratified log-rank test at an overall 0.05 significance level (two-sided). An interim analysis and a futility analysis are planned, and an independent data monitoring committee will be in place. ACCRUAL 1018/4100 pts have been recruited globally. CONTACT INFORMATION For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Clinicaltrials.gov number NCT04961996. AB, PS and CG contributed equally. This abstract was originally presented at SABCS 2021 (OT2-11-09).

a>Disclosure(s):

Peter Schmid, MD, PhD: Astellas Pharma: Contracted Research (Ongoing); AstraZeneca: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Honoraria (Ongoing); Bayer: Consulting Fees (e.g., advisory boards) (Ongoing), Honoraria (Ongoing); Boehringer Ingelheim: Consulting Fees (e.g., advisory boards) (Ongoing), Honoraria (Ongoing); Celgene: Consulting Fees (e.g., advisory boards) (Ongoing); Eisai: Consulting Fees (e.g., advisory boards) (Ongoing); F. Hoffmann-La Roche Ltd.: Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Genentech: Contracted Research (Ongoing); Medivation Inc.: Contracted Research (Ongoing); Merck: Consulting Fees (e.g., advisory boards) (Ongoing), Honoraria (Ongoing); Novartis: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Honoraria (Ongoing); OncoGenex: Contracted Research (Ongoing); Pfizer: Consulting Fees (e.g., advisory boards) (Ongoing), Honoraria (Ongoing); Puma Biotechnology: Consulting Fees (e.g., advisory boards) (Ongoing), Honoraria (Ongoing); Roche: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Honoraria (Ongoing)

Charles E. Geyer Jr, MD, FACP: Abbvie: Contracted Research (Terminated, July 1, 2022), Writing assistance (Terminated, July 1, 2022); AstraZeneca: Contracted Research (Ongoing), Writing assistance (Ongoing); Daiichi/Sankyo: Contracted Research (Ongoing); Exact Sciences: Consulting Fees (e.g., advisory boards) (Ongoing); F. Hoffman-La Roche Ltd: Contracted Research (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche) (Ongoing); Genentech: Contracted Research (Ongoing), Writing assistance (Ongoing)

Nadia Harbeck, MD, PhD: Amgen: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); AstraZeneca: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Daiichi Sankyo: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Eli Lilly: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Exact Sciences: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); MSD: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Novartis: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Pfizer: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Pierre Fabre: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Roche: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Sandoz: Consulting Fees (e.g., advisory boards) (Ongoing); Seagen: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); WSG: Ownership Interest (stocks, stock options, patent or other intellectual property or other ownership interest excluding diversified mutual funds) (Ongoing)

Mothaffar Rimawi, MD: Daiichi Sankyo: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); F. Hoffmann-La Roche Ltd.: Contracted Research (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Genentech: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Macrogenics: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Pfizer: Contracted Research (Ongoing); Seattle Genetics: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing)

Sara Hurvitz, MD, FACP: Ambrx: Contracted Research (Ongoing); Amgen: Contracted Research (Ongoing); Arvinas: Contracted Research (Ongoing); Astra Zeneca: Contracted Research (Ongoing); Bayer: Contracted Research (Ongoing); Cytomx: Contracted Research (Ongoing); Daiichi-Sankyo: Contracted Research (Ongoing); Dignitana: Contracted Research (Ongoing); Eli Lilly: Contracted Research (Ongoing); Genentech/Roche: Contracted Research (Ongoing); Gilead: Contracted Research (Ongoing); GSK: Contracted Research (Ongoing); Ideal Implant: Ownership Interest (stocks, stock options, patent or other intellectual property or other ownership interest excluding diversified mutual funds) (Ongoing); Immunomedics: Contracted Research (Ongoing); Macrogenics: Contracted Research (Ongoing); Novartis: Contracted Research (Ongoing); OBI Pharma: Contracted Research (Ongoing); Orinove: Contracted Research (Ongoing); Pfizer: Contracted Research (Ongoing); Phoenix Molecular Designs, Ltd.: Contracted Research (Ongoing); Pieris: Contracted Research (Ongoing); PUMA: Contracted Research (Ongoing); Radius: Contracted Research (Ongoing); Sanofi: Contracted Research (Ongoing); Seattle Genetics/Seagen: Contracted Research (Ongoing); Zymeworks: Contracted Research (Ongoing)

Miguel Martín, MD, PhD: AstraZeneca: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Daiichi Sankyo: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); F. Hoffmann-La Roche: Third-party writing assistance for this abstract, furnished by Eleanor Porteous, MSc, of Health Interactions, was provided by Roche (Ongoing); Genentech/Roche: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Gilead: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Lilly/ImClone: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing), Honoraria (Ongoing); Novartis: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing), Honoraria (Ongoing); Pfizer: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing), Honoraria (Ongoing); Pierre Fabre: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing), Honoraria (Ongoing); Seagen: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing), Honoraria (Ongoing)

Sherene Loi, MBBS (Hons), PhD, FRACP, FAHMS, GAICD: Aduro Biotech, Inc.: Consulting Fees (e.g., advisory boards) (Ongoing); Akamara Therapeutics: Uncompensated scientific advisory board member (Ongoing); AstraZeneca: Consulting Fees (e.g., advisory boards) (Ongoing), Uncompensated consultant (Ongoing); BMS: Uncompensated consultant (Ongoing); Breast Cancer Research Foundation, New York: Supported by the Breast Cancer Research Foundation, New York (Ongoing); G1 Therapeutics: Consulting Fees (e.g., advisory boards) (Ongoing); GlaxoSmithKline: Consulting Fees (e.g., advisory boards) (Ongoing); Merck: Uncompensated consultant (Ongoing); National Breast Cancer Foundation of Australia Endowed Chair: Supported by the National Breast Cancer Foundation of Australia Endowed Chair (Ongoing); Novartis: Consulting Fees (e.g., advisory boards) (Ongoing), Uncompensated consultant (Ongoing); Roche-Genentech: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing), Uncompensated consultant (Ongoing); Seattle Genetics: Uncompensated consultant (Ongoing); Silverback Therapeutics: Consulting Fees (e.g., advisory boards) (Ongoing)

Shigehira Saji, MD, PhD: Astra Zeneca: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Bayer: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Boerhringer-ingelheim: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Breast International Group: Executive board member (Ongoing); Chugai: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Daiichi Sankyo: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Eisai: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Eli Lilly: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); F. Hoffmann-La Roche Ltd.: Contracted Research (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Japan Breast Cancer Research Group: Executive board member (Ongoing); Japanese Breast Cancer Society: Executive board member (Ongoing); Japanese Society of Medical Oncology: Executive board member (Ongoing); Kyowa Kirin: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); MSD: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Nihonkayaku: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Novartis: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Ono: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Pfizer: Consulting Fees (e.g., advisory boards) (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Taiho: Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); Takeda: Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing)

Kyung Hae Jung, MD, MS, PhD: AstraZeneca: Consulting Fees (e.g., advisory boards) (Ongoing); Celgene: Consulting Fees (e.g., advisory boards) (Ongoing); Daiichi-Sankyo: Consulting Fees (e.g., advisory boards) (Ongoing); Eisai: Consulting Fees (e.g., advisory boards) (Ongoing); Everest Medicine: Consulting Fees (e.g., advisory boards) (Ongoing); Merck: Consulting Fees (e.g., advisory boards) (Ongoing); MSD: Consulting Fees (e.g., advisory boards) (Ongoing); Novartis: Consulting Fees (e.g., advisory boards) (Ongoing); Pfizer: Consulting Fees (e.g., advisory boards) (Ongoing); Roche: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Takeda: Consulting Fees (e.g., advisory boards) (Ongoing)

Gustavo Werutsky, MD, PhD: AstraZeneca: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Honoraria (Ongoing); Bayer: Contracted Research (Ongoing); Beigene: Contracted Research (Ongoing); Daiichi Sankyo: Consulting Fees (e.g., advisory boards) (Ongoing); Genentech/Roche: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Fees for Non-CME Services Received Directly from Commercial Interest or their Agents (e.g., speakers’ bureaus) (Ongoing); GSK: Contracted Research (Ongoing); Lilly: Contracted Research (Ongoing), Honoraria (Ongoing); MSD: Honoraria (Ongoing); Novartis: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Honoraria (Ongoing); Pfizer: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Honoraria (Ongoing); Sanofi: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Seattle Genetics: Contracted Research (Ongoing)

Daniil L. Stroyakovsky, MD: Roche: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing)

Vanesa López-Valverde, PharmD, PhD: F. Hoffmann-La Roche Ltd.: Ownership Interest (stocks, stock options, patent or other intellectual property or other ownership interest excluding diversified mutual funds) (Ongoing), Salary (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing)

Michael Davis, PsyD: F. Hoffmann-La Roche Ltd.: Ownership Interest (stocks, stock options, patent or other intellectual property or other ownership interest excluding diversified mutual funds) (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Genentech, Inc.: Salary (Ongoing)

Tanja Badovinac Crnjevic, MD, PhD: F. Hoffmann-La Roche Ltd.: Ownership Interest (stocks, stock options, patent or other intellectual property or other ownership interest excluding diversified mutual funds) (Ongoing), Salary (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing)

Pablo D. Perez-Moreno, MD: F. Hoffmann-La Roche Ltd.: Ownership Interest (stocks, stock options, patent or other intellectual property or other ownership interest excluding diversified mutual funds) (Ongoing), Third-party writing assistance for this abstract, furnished by Sunaina Indermun, BPharm, PhD, of Health Interactions, was provided by Roche (Ongoing); Genentech, Inc.: Salary (Ongoing)

Aditya Bardia, MD, MPH: AstraZeneca: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); BioTheranostics: Consulting Fees (e.g., advisory boards) (Ongoing); Daiichi Sankyo: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Eli Lilly: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Foundation Medicine: Consulting Fees (e.g., advisory boards) (Ongoing); Genentech/Roche: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Immunomedics/Gilead: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Merck: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Novartis: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Pfizer: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Phillips: Consulting Fees (e.g., advisory boards) (Ongoing); Radius Health: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing); Sanofi: Consulting Fees (e.g., advisory boards) (Ongoing), Contracted Research (Ongoing)

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Citation Format: Peter Schmid, Charles E. Geyer Jr, Nadia Harbeck, Mothaffar Rimawi, Sara Hurvitz, Miguel Martín, Sherene Loi, Shigehira Saji, Kyung Hae Jung, Gustavo Werutsky, Daniil L. Stroyakovsky, Vanesa López-Valverde, Michael Davis, Tanja Badovinac Crnjevic, Pablo D. Perez-Moreno, Aditya Bardia. lidERA Breast Cancer: A phase III adjuvant study of giredestrant (GDC-9545) vs physician’s choice of endocrine therapy in patients with estrogen receptor+, HER2– early breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-03-02.

Neoadjuvant giredestrant (GDC-9545) plus palbociclib (P) versus anastrozole (A) plus P in postmenopausal women with estrogen receptor–positive, HER2-negative, untreated early breast cancer (ER+/HER2– eBC): Final analysis of the randomized, open-label, international phase 2 coopERA BC study

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Background: Endocrine therapy (ET) is the therapeutic mainstay for ER+ BC. Giredestrant is a highly potent, nonsteroidal, oral, selective ER antagonist and degrader (SERD) which has demonstrated robust ER occupancy, is well tolerated, and has previously shown encouraging antitumor activity as monotherapy and in combination with P in metastatic BC. coopERA BC (NCT04436744) evaluated giredestrant in eBC and met its primary endpoint, highlighting superior Ki67 suppression with single-agent giredestrant vs A at Week 2. Giredestrant was well tolerated. Here, we report the final analysis. Methods: Eligible patients (pts) with measurable ER+/HER2– untreated eBC and baseline Ki67 score ≥5% (202 planned) were randomized 1:1 to receive, on Days 1–14 of a neoadjuvant window-of-opportunity phase, 30 mg oral daily (PO QD) giredestrant or 1 mg PO QD A followed by a 16-week neoadjuvant phase of QD giredestrant or A for four 28-day cycles with 125 mg PO P on Days 1–21. Randomization was stratified by tumor size, baseline Ki67 score, and progesterone receptor status. Endpoints assessed here included Ki67 suppression from baseline to surgery, complete cell cycle arrest (CCCA; Ki67 ≤2.7%) at surgery, objective response rate (ORR), and safety. Results: At final analysis (cutoff: Nov 24, 2021), 112 and 109 pts were randomized to the giredestrant and A arms, respectively (median age: 62 years each; stage I/IIa disease: 60% vs 54%). Consistent with the primary analysis, greater suppression of Ki67 was observed at surgery with giredestrant + P (–81% [95% confidence interval (CI): –86%, –75%]) vs A + P (–74% [95% CI: –80%, –67%]). Similarly, greater CCCA was achieved at surgery with giredestrant + P (20%) vs A + P (14%). ORR was similar between the two arms (giredestrant + P: 50% [95% CI: 40%, 60%]; A + P: 49% [95% CI: 39%, 59%]). ET-related adverse events (AEs) were non-serious and occurred at similar rates between the two arms. Related Grade ≥3 AE rates were also similar at 6% each. Interruption/withdrawal of ET due to AEs was low and similar for both arms. Conclusions: In this final analysis of coopERA BC, the greater suppression of Ki67 with giredestrant vs A observed at Week 2 in the primary analysis was maintained at surgery, and safety data remained consistent with the known safety profile of giredestrant. coopERA BC is the first randomized study to show superior antiproliferative activity of an oral SERD (giredestrant) over an aromatase inhibitor (A) in ER+/HER2– eBC; studies are ongoing to further assess giredestrant’s clinical benefit. Clinical trial information: NCT04436744.

Abstract PD13-06: Neoadjuvant giredestrant (GDC-9545) + palbociclib versus anastrozole + palbociclib in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer: Primary analysis of the randomized, open-label, phase II coopERA breast cancer study

Background Endocrine therapy, the therapeutic mainstay for estrogen receptor-positive breast cancer, targets estrogen receptor activity and/or estrogen synthesis. CDK4/6 inhibitors cause cell cycle arrest and significantly decrease expression of the proliferation biomarker Ki67 when used in conjunction with aromatase inhibitors such as anastrozole. Giredestrant, a highly potent, nonsteroidal, oral, selective estrogen receptor antagonist and degrader, achieves robust estrogen receptor occupancy, is well tolerated, and has encouraging antitumor activity as a monotherapy and in combination with the CDK4/6 inhibitor palbociclib in metastatic breast cancer. coopERA Breast Cancer (NCT04436744) is a phase II study investigating 2 weeks of giredestrant versus anastrozole in a window-of-opportunity phase, followed by 4 months of giredestrant plus palbociclib versus anastrozole plus palbociclib in a neoadjuvant phase in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer. We will report the results of the primary analysis. Methods Eligible patients who had measurable cT1c (≥1.5 cm)-cT4a-c estrogen receptor-positive, HER2-negative, untreated early breast cancer and baseline Ki67 score ≥5% were randomized 1:1 to 1 mg oral, daily anastrozole or 30 mg oral, daily giredestrant on Days 1-14 (window-of-opportunity phase lasting 14 days) followed by daily dosing for four 28-day cycles in combination with 125 mg oral palbociclib on Days 1-21 (neoadjuvant phase lasting 16 weeks) before surgery. Patients were stratified according to T status, Ki67 score, and progesterone receptor status. The primary efficacy endpoint was centrally assessed geometric mean relative Ki67 score change from baseline to Week 2 during the window-of-opportunity phase, which is reflective of the ability of endocrine therapies to suppress tumor-cell proliferation, and is a surrogate marker for clinical outcomes. The secondary efficacy endpoint is complete cell cycle arrest rate (CCCA), defined as Ki67 score ≤2.7%, at Week 2. Safety was also assessed. Results Results of a previous interim analysis (including 83 of the planned 202 patients) demonstrated a greater relative reduction of Ki67 at 2 weeks with giredestrant (reduction from baseline to Week 2 geometric mean = 80%; 95% CI = -85%, -72%) compared with anastrozole (reduction from baseline to Week 2 geometric mean = 67%; 95% CI = -75%, -56%; P = 0.0222). Similarly, consistent Ki67 suppression was observed in patients with baseline Ki67 ≥20% (83% reduction with giredestrant versus 71% reduction with anastrozole) or <20% (65% versus 24% reductions). At Week 2, 25% of tumors exhibited CCCA with giredestrant versus 5.1% with anastrozole (a 20% difference; 95% CI = -37%, -3%). Safety results were consistent with the known safety profile for giredestrant. Fewer patients experienced adverse events (AEs) related to giredestrant (28%) than to anastrozole (38%), and no grade ≥3 AEs or serious adverse events were assessed as related to giredestrant. We will present the results of the primary analysis, which will include data from all enrolled patients, and will report the primary and secondary efficacy endpoints (including patients with Ki67 >20%), and updated safety. Conclusions The study will proceed to the primary analysis. We expect to see encouraging results based on the favorable interim analysis data that demonstrated the superior activity of giredestrant, an oral selective estrogen receptor antagonist and degrader, compared with anastrozole.

Citation Format: Sara A Hurvitz, Vanesa Quiroga, Yeon Hee Park, Aditya Bardia, Vanesa López-Valverde, Jutta Steinseifer, Tharu M Fernando, Gonzalo Spera, Cloris Xue, Peter A Fasching. Neoadjuvant giredestrant (GDC-9545) + palbociclib versus anastrozole + palbociclib in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer: Primary analysis of the randomized, open-label, phase II coopERA breast cancer study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD13-06.

Abstract OT2-11-09: Lidera breast cancer: A phase III adjuvant study of giredestrant (GDC-9545) vs physician’s choice of endocrine therapy (ET) in patients (pts) with estrogen receptor-positive, HER2-negative early breast cancer (ER+/HER2- EBC)

BACKGROUND ETs that target ER activity and/or estrogen synthesis are the mainstay of ER+ BC treatment. Despite best management, up to 20% of pts with ER+/HER2- eBC develop resistance (in some cases due to the acquisition of tumor mutations in ESR1 that can drive estrogen-independent transcription and proliferation) and still have high recurrence rates on standard ETs. New treatment alternatives for ER+/HER2- eBC are needed to reduce risk of recurrence and improve survival, tolerability, quality of life, and adherence. Giredestrant is a highly potent, nonsteroidal oral selective ER antagonist and degrader (SERD). It achieves robust ER occupancy and is active against tumors that retain ER-sensitivity or have ESR1 mutation(s). Giredestrant has been demonstrated to be more potent in vitro and achieves higher ER occupancy in vivo than fulvestrant, the only currently approved SERD. Early phase clinical studies have demonstrated that single-agent giredestrant (30 mg daily) has promising clinical and pharmacodynamic activity, and is well-tolerated in the ER+/HER2- eBC and metastatic BC settings. TRIAL DESIGN This is a phase III, global, randomized, open-label, multicenter study evaluating the efficacy and safety of adjuvant giredestrant vs physician’s choice of adjuvant ET in pts with medium- and high-risk stage I-III histologically confirmed ER+/HER2- eBC. Pts are randomized 1:1 to oral 30 mg daily giredestrant or physician’s choice of standard ET (tamoxifen, anastrozole, letrozole, or exemestane, given according to prescribing information). Stratification factors are risk (medium vs high, based on anatomic [tumor size, nodal status] and biologic features [grade, Ki67, gene signatures if available]); geographic region (US/Canada/Western Europe vs Asia-Pacific vs rest of the world); prior chemotherapy (no vs yes); and menopausal status (pre-/perimenopausal vs postmenopausal). Beginning on Day 1 of Cycle 1, pts will be treated with giredestrant or physician’s choice of standard ET for at least 5 years. Continuing physician’s choice of standard ET after 5 years is at discretion of the investigator and per local standard of care. ELIGIBILITY Female/male pts with medium-/high-risk stage I-III ER+/HER2- eBC; prior curative surgery; completion of (neo)adjuvant chemotherapy (if administered) and/or surgery <12 months prior to enrolment; no prior ET (up to 4 weeks of [neo]adjuvant ET is allowed). For men and pre-/perimenopausal women, a luteinizing hormone-releasing hormone agonist will be given per local prescribing information (mandatory for pts in the giredestrant arm). AIMS Primary endpoint: Invasive disease-free survival (IDFS). Secondary endpoints: Overall survival; IDFS (STEEP definition, including second non-primary BC); disease-free survival; distant recurrence-free survival; locoregional recurrence-free interval; safety; pharmacokinetics; pt-reported outcomes. In addition, this study aims to improve health equity in research and expand clinical trial access. The study will also use/develop digital healthcare solutions, which will enable better understanding of patients’ needs and their adherence to ET. STATISTICAL METHODS The primary endpoint analysis will use a stratified log-rank test at an overall 0.05 significance level (two-sided). An interim analysis and a futility analysis are planned, and an independent data monitoring committee will be in place. ACCRUAL Target enrollment is 4100 pts globally once the study is open for enrollment. CONTACT INFORMATION For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Clinicaltrials.gov number NCT04961996.

Citation Format: Aditya Bardia, Peter Schmid, Nadia Harbeck, Mothaffar F Rimawi, Sara A Hurvitz, Sherene Loi, Shigehira Saji, Kyung Hae Jung, Gustavo Werutsky, Daniil Stroyakovskii, Vanesa López-Valverde, David Tesarowski, Chenglin Ye, Michael Davis, Tanja Badovinac Crnjevic, Pablo Diego Perez-Moreno, Charles E Geyer, Jr. Lidera breast cancer: A phase III adjuvant study of giredestrant (GDC-9545) vs physician’s choice of endocrine therapy (ET) in patients (pts) with estrogen receptor-positive, HER2-negative early breast cancer (ER+/HER2- EBC) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-11-09.

Abstract PD12-06: Treatment-related amenorrhea with T-DM1 plus pertuzumab (KP) is lower than with docetaxel/carboplatin/trastuzumab/pertuzumab (TCHP) in the phase III neoadjuvant KRISTINE trial

Background: Cytotoxic chemotherapy (CT) in combination with trastuzumab and pertuzumab (HP) is standard of care for patients (pts) diagnosed with HER2-positive early breast cancer (EBC). While highly effective, the toxicity associated with CT is challenging. In KRISTINE/TRIO-021, neoadjuvant T-DM1 was combined with pertuzumab (KP) and compared to standard TCHP. Pts. received six cycles of neoadjuvant treatment followed by adjuvant therapy (KP or HP). Pts. in the KP arm were allowed to receive standard adjuvant CT. Pathologic complete response (pCR) rate was significantly lower with KP versus TCHP and more pts. had disease progression prior to surgery with KP, resulting in a meaningfully lower event-free survival rate vs. the control (85.3% vs 94.2%). However, 3-year invasive disease-free survival was numerically similar in both arms. Neoadjuvant KP demonstrated less toxicity than standard CT, although treatment discontinuation was higher post-surgery. Association of KP and TCHP with treatment-related amenorrhea (TRA) in premenopausal EBC pts. has not been ascertained. Methods: All pts. with premenopausal status at study entry (those not meeting the menopause definition based on National Comprehensive Cancer Network Guidelines v3, 2012) and with menstrual period documented within 3 months of randomization, were independently evaluated for presence or absence of TRA by two reviewers. TRA, a prespecified exploratory endpoint of KRISTINE, was defined as cessation of menstruation for >12 months in the absence of treatment with ovarian suppression or other interventions that can induce amenorrhea. Pts. were followed from the time of study entry through the 3-year follow up period after surgery. For cases with inconsistent determination between the two reviewers, a third reviewer adjudicated. TRA rates were calculated per arm, hormone-receptor (HR) status, adjuvant CT and age group. Proportions were compared by estimating the odds ratio (OR) and the 95% confidence interval. Results: Of 444 pts. enrolled, 205 were excluded based on being post-menopausal per NCCN guidelines. Of 239 pts. remaining, 56 were excluded due to insufficient data. The median age of pts. included was 40 years (range: 22-53) for TCHP and 42.5 (range: 23-52) for KP. TRA was observed in 55% (50/91) of pts. treated with TCHP compared to 30% (28/92) treated with KP (OR=2.79; 95% CI 1.52-5.12). In pts. with HR-positive EBC, TRA occurred in 62% with TCHP vs 35% for KP (OR=2.998; 95% CI 1.44-6.25). In those with HR-negative EBC, TRA was observed in 42% with TCHP vs. 21% with KP (OR=2.77; 95% CI 0.88-8.72). In the KP arm, TRA was observed in 38% (8/21) of pts. treated with standard adjuvant CT vs. 28% (20/71) of those that did not (OR 1.57; 95% CI 0.57-4.36). For women age ≤ 40, the rate of TRA was 38% with TCHP vs. 17% with KP (OR=3.00; 95% CI 1.05-8.60). For those > 40 years, TRA was observed in 74% treated with TCHP vs. 39% of those with KP (OR=4.50; 95% CI 1.88-10.73). Conclusion: The rate of TRA with standard TCHP is nearly double that observed with KP, suggesting that targeted CT with an antibody-drug conjugate regimen is associated with less gonadal toxicity. Rates of TRA are higher in women over the age of 40 for each treatment arm however KP is associated with lower rate of TRA in each age group. Association of TRA with efficacy outcomes (pCR, iDFS) will be presented.

Citation Format: Sara A Hurvitz, Rodrigo Fresco, Karen Afenjar, Daniil Stroyakovskiy, Chiun-Sheng Huang, Hans Wildiers, Kyung Hae Jung, Jean-François Boileau, Mario Campone, Miguel Martín, Vicente Valero, Joseph A. Sparano, W. Fraser Symmans, Peter A. Fasching, Alastair M. Thompson, Nadia Harbeck, Vanesa López-Valverde, Chunyan Song, Thomas Boulet, Eleonora Restuccia, Dennis J. Slamon. Treatment-related amenorrhea with T-DM1 plus pertuzumab (KP) is lower than with docetaxel/carboplatin/trastuzumab/pertuzumab (TCHP) in the phase III neoadjuvant KRISTINE trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD12-06.

Abstract OT-09-06: Phase II neoadjuvant study of GDC-9545 + palbociclib (palbo) vs anastrozole (A) + palbo in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer (ER+/HER2- eBC)

Background

Endocrine therapies (ETs) are the mainstay of ER+ BC management; however, many patients (pts) have disease relapse or develop therapeutic resistance. CDK4/6 and aromatase inhibitors decrease Ki67 expression significantly and are potent in arresting the cell cycle in the neoadjuvant eBC setting. Ki67 is a proliferation biomarker with prognostic value in ER+ BC. Efficacy of ETs relies on induction of cell cycle arrest, and during neoadjuvant treatment, Ki67 scores reflect the ability of ETs to suppress proliferation. Selective ER degraders have also shown efficacy against these tumors. The highly potent, non-steroidal, oral selective ER degrader GDC-9545 has therefore been developed as a monotherapy or in combination with CDK4/6 inhibitors for ER+ BC. Preliminary phase Ib data in postmenopausal women with metastatic BC have shown that oral 100 mg once daily (PO QD) GDC-9545 is well tolerated as a monotherapy and with palbo, with encouraging antitumor activity (clinical benefit rates: 55% without palbo/81% with palbo; clinical benefit observed in pts with prior fulvestrant treatment and in pts with detectable ESR1 mutations at enrollment) (Lim et al. ASCO 2020; abstract 1023).

We present a phase II, randomized, open-label, two-arm, neoadjuvant study of GDC-9545 vs A in a window of opportunity (WoO) phase, followed by GDC-9545 + palbo vs A + palbo in a neoadjuvant phase, for postmenopausal women with ER+/HER2- untreated eBC (NCT04436744).

Trial design

Pts are randomized 1:1 to GDC-9545 or A. The WoO phase will last 14 days; and the neoadjuvant phase, 16 weeks (4 x 28-day cycles) before surgery. GDC-9545 will be given at 30 mg PO QD; A, at 1 mg PO QD. 30 mg GDC-9545 was selected as it is well tolerated with promising anti-tumor activity (Jhaveri et al. SABCS 2019; abstract PD7-05), and no improvement in efficacy is expected at doses > 30 mg. During the neoadjuvant phase, pts will receive 4 x 28-day cycles of GDC-9545 + palbo (125 mg PO QD on days 1-21 of each cycle) or A + palbo.

Eligibility

Female pts ≥ 18 years with ECOG performance status 0-1, histologically confirmed invasive breast carcinoma, measurable disease (modified RECIST v1.1), primary tumor ≥ 1.5 cm in its longest diameter (tumor size category at presentation: cT1c [≥ 1.5 cm]-cT4a-c), and Ki67 score ≥ 5% stained nuclei.

Aims

The primary efficacy endpoint is mean relative Ki67 score change from baseline to week 2 during the WoO phase. Secondary efficacy endpoints are objective response rate and complete cell cycle arrest (CCCA) rate (proportion of patients with centrally assessed Ki67 scores ≤ 2.7% stained nuclei upon treatment at week 2) in the neoadjuvant phase. Exploratory efficacy endpoints are changes in Ki67 scores from baseline to surgery and from week 2 to surgery, CCCA rate (upon treatment at surgery or post-treatment biopsy), and pathologic complete response rate in the neoadjuvant phase. Safety and tolerability, pharmacokinetics, and biomarkers will also be assessed.

Statistical methods

Randomization is stratified by T status (cT1c-cT2 vs cT3-cT4 a-c), Ki67 score (< 20% vs ≥ 20%), and progesterone receptor status (positive vs negative). Ki67 scores will be centrally assessed and measured in percentage scores. Mean relative change at week 2 will be summarized in original percentage scales for each arm, and corresponding 95% confidence intervals will be calculated by normal approximation. Change in mean score between arms will be compared via z-test. Patients with missing central scores at baseline and/or week 2 will be excluded.

Accrual

Target enrollment is 215 patients at ~90 sites globally once the study is open for enrollment.

Contact information

For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only).

Citation Format: Sara A Hurvitz, Peter A Fasching, Yeon Hee Park, Vanesa Quiroga, Tanja Badovinac Crnjevic, Rodrigo Fresco, Vanesa López-Valverde, Jutta Steinseifer, Chenglin Ye, Aditya Bardia. Phase II neoadjuvant study of GDC-9545 + palbociclib (palbo) vs anastrozole (A) + palbo in postmenopausal women with estrogen receptor-positive, HER2-negative, untreated early breast cancer (ER+/HER2- eBC) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-09-06.

Glibenclamide Reveals Role for Endothelin in Hypoxia-Induced Vasoconstriction in Rat Intrapulmonary Arteries

The present study investigated whether activation of vasodilatory mechanisms masks the involvement of endothelin in hypoxic pulmonary vasoconstriction. Rat intrapulmonary arteries were mounted in microvascular myographs. In arteries with endothelium and contracted with phenylephrine, hypoxia, evoked by exchanging 5% CO2 in air for CO2 in N2, caused a transient contraction followed by a sustained contraction. Hypoxia evoked relaxation in preparations without endothelium. An inhibitor of ATP-sensitive K+ channels (KATP), glibenclamide (10 microM), blunted hypoxic relaxation in arteries without endothelium and enhanced the sustained hypoxic vasoconstriction in arteries with endothelium. Hypoxic contraction was more pronounced in endothelin compared with phenylephrine-contracted preparations in the absence, but not in the presence of glibenclamide. Antagonism of the endothelin ETA and ETB receptors with SB217242 or the combination of BQ123 and BQ788 inhibited endothelin and hypoxic contraction, but the latter only in the presence of glibenclamide. An inhibitor of nitric oxide (NO) synthase, N-nitro-L-arginine (100 microM), evoked contractions, which were left unaltered by SB217242 in hypoxic conditions. In conclusion, hypoxic contraction is mediated in part by an unknown endothelium-derived contractile factor and incubation with glibenclamide shows endothelin enhances hypoxic contraction in part through inhibition of KATP channels. Moreover, inhibition of NO formation in pulmonary arteries does not change endothelin receptor activation in severe hypoxia.