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Onapristone · ZK-299, ZK-98299

Small molecule · Antagonist of progesterone receptor (PGR) · developed by Context Therapeutics

Phase 1/2 Most advanced trial (none active)

CNTX Developer

3 Registered trials

What is Onapristone?

Onapristone is an orally bioavailable progesterone receptor antagonist. It binds to PR and inhibits PR activation and PR-responsive gene expression, potentially blocking PR-mediated proliferation in cancer cells. It is studied in ovarian, endometrial, and breast cancers.

Summary written with AI from the sources listed at the end of this page.

At a glance

Also known as: ZK-299, ZK-98299
Drug type: Small molecule
Targets: progesterone receptor (PGR)
Mechanism: Antagonist of progesterone receptor (PGR)
Pathways: PR-responsive gene expression
Therapy area: Oncology
Developer: Context Therapeutics Inc. (CNTX)
FDA status: Investigational, not approved in the US. Most advanced trial: Phase 1/2
UNII: H6H7G23O3N

🧪 Clinical trials

Trial	Phase	Condition	Status	Sponsor
NCT05618613	Phase 1/2	Breast Cancer	Terminated	CNTX
NCT04719273	Phase 2	Refractory Endometrial Adenocarcinoma	Completed	CNTX
NCT03909152	Phase 2	Granulosa Cell Ovarian Cancer	Completed	CNTX

Trials of the companies BioRadar tracks, from ClinicalTrials.gov, most advanced phase first.

Conditions studied

Breast CancerEndometrioid Endometrial CancerGranulosa Cell Ovarian CancerLow Grade Serous Ovarian/ Primary Peritoneal CancerRefractory Endometrial AdenocarcinomaRefractory Endometrial CarcinomaRefractory Endometrial Clear Cell AdenocarcinomaRefractory Endometrial Endometrioid AdenocarcinomaRefractory Endometrial Mixed Cell AdenocarcinomaRefractory Endometrial Serous AdenocarcinomaRefractory Endometrial Undifferentiated Carcinoma

Other drugs acting on PGR

Ethinyl Estradiol/Levonorgestrel FDA approved Mifepristone FDA approved Segesterone Acetate and Ethinyl Estradiol FDA approved

More from Context Therapeutics

CT-202 Phase 1 CT-95 Phase 1 CTIM-76 Phase 1

Sources

Updated Oct 3, 2026. Something wrong or missing? Report it on the CNTX page.

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Data: FDA (Drugs@FDA, Purple Book, DailyMed), NIH (NCI Thesaurus, GSRS, RxNorm), ClinicalTrials.gov • Informational purposes only, not medical or investment advice. • All drugs A–Z