This tool is for research exploration only. It is not a medical device and does not provide medical advice. Drug candidates, evidence scores, and AI-generated content are not clinical recommendations. Always consult your medical team before making any treatment decisions.

Back to Drug Candidates

Niraparib

Zejula

PARP inhibitor (PARP1/2)

Evidence Score

45

theoretical
Mechanism of Action

Selective, orally bioavailable PARP1/2 inhibitor with a long half-life (~36 hours) suited for once-daily maintenance dosing. The mechanistic rationale mirrors olaparib: succinate-driven KDM4B inhibition creates an HR-deficient 'BRCAness' phenotype in SDH-deficient cells (Sulkowski et al., Nat Genet 2018, PMID: 30013182; Nature 2020, PMID: 32494005), making them hypersensitive to PARP trapping. The clinical rationale for niraparib specifically — beyond the shared mechanism — is its registration in HRD-positive tumors irrespective of BRCA mutation status: the PRIMA Phase 3 trial (González-Martín et al., NEJM 2019, PMID: 31562799) showed that niraparib maintenance benefit extended to the biomarker-selected non-gBRCA HRD-positive population (HR 0.43, 95% CI 0.31–0.59) — establishing that HRD measured by genomic scar assay (rather than BRCA mutation) is a sufficient criterion for PARP inhibitor benefit. If succinate-driven HRD creates a comparable genomic scar signature in SDH-deficient tumors, niraparib's approval framework may translate directly. Once-daily dosing and no CYP3A4 interactions offer a pharmacological advantage over olaparib for combination studies. No SDH-deficient-specific clinical data yet; biomarker validation (HRD genomic scar assay, RAD51 foci) in SDH-deficient patient tumor samples is the critical missing step.

Pathway Connections
Succinate-Driven Homologous Recombination Deficiency

Succinate accumulation competitively inhibits the α-KG-dependent histone demethylases KDM4A and KDM4B (JMJD2A/B), which normally erase repressive H3K9me3 marks at sites of DNA double-strand breaks. When KDM4B is inhibited, H3K9me3 hypermethylation persists at break sites, blocking recruitment of TIP60 acetyltransferase and ATM kinase — both required for DNA end-resection and initiation of homology-directed repair (HDR/HR). The result is a 'BRCAness' phenotype: SDH-deficient tumor cells have impaired HR capacity despite wild-type BRCA1/2. Sulkowski et al. (Nat Genet 2018, PMID: 30013182) directly demonstrated HR deficiency and olaparib hypersensitivity in cells and tumors from SDH-deficient hereditary paraganglioma/PPGL patients; Sulkowski et al. (Nature 2020, PMID: 32494005) dissected the KDM4B/H3K9me3 chromatin mechanism.

Upstream event:

SDH loss → succinate accumulation → competitive inhibition of KDM4A/KDM4B (α-KG-dependent H3K9me3 demethylases) → H3K9me3 persistence at DNA double-strand break sites → impaired TIP60/ATM recruitment → defective DNA end-resection → HR deficiency

Downstream effects:

H3K9me3 hypermethylation at DNA double-strand break sitesImpaired TIP60 acetyltransferase and ATM kinase recruitmentDefective homologous recombination (BRCAness phenotype in BRCA1/2-wild-type cells)PARP inhibitor synthetic lethality (trapping unrepaired single-strand breaks in HR-deficient background)Selective sensitivity to olaparib and other PARP inhibitors in SDH-deficient versus SDH-intact cells
Molecular Targets

PARP1

Poly(ADP-ribose) polymerase 1

synthetic_lethal

DNA repair enzyme activated by ROS-induced damage. PARP inhibition in ROS-elevated cells may cause synthetic lethality.

UniProt: P09874

KDM4B

Lysine demethylase 4B (JMJD2B)

direct

Primary α-KG-dependent H3K9me3 demethylase at DNA break sites. KDM4B is the demethylase whose oncometabolite-mediated inhibition was identified as the mechanistic basis for HR deficiency in succinate-accumulating (SDH-deficient) and fumarate-accumulating (FH-deficient) tumors. Sulkowski et al. (Nature 2020, PMID: 32494005) showed that 2-HG, succinate, and fumarate all inhibit KDM4B, causing H3K9me3-masked DNA breaks that cannot recruit the HR machinery; restoration of KDM4B activity rescued HR competence. Together with KDM4A, KDM4B constitutes the α-KG-dependent chromatin checkpoint for DNA end-resection.

UniProt: O94953

Quick Facts
FDA Approved

Approved Indications

  • HRD-positive advanced ovarian cancer (maintenance after first-line platinum)
  • Advanced ovarian cancer regardless of BRCA status (maintenance after response to platinum)
  • Recurrent ovarian cancer (maintenance after platinum-based chemotherapy)
Evidence

Evidence from PubMed, OpenTargets, and ChEMBL will appear here once external data integration is enabled.

Coming in Phase 3

For research exploration only — not medical advice. Consult your doctor before acting on any information.

AI Analysis

Have Claude analyze this drug's repurposing potential for SDH-deficient diseases.