DNA damaging properties of G-quadruplex ligand QN-302 are potentiated by the DNA repair inhibitor Olaparib and mitigated by the molecular helicase PhpC

BACKGROUND: QN-302 is a tetra-substituted naphthalene diimide (NDI) designed to bind G-quadruplex (G4) DNA and is in a phase 1 clinical trial for pancreatic ductal adenocarcinoma (PDAC) and other solid tumors. The mechanistic basis of its anticancer activity remains to be fully understood. RESULTS: Using in vitro fluorescence quenching and FRET-melting assays together with cell-based in situ click imaging and γH2AX immunodetection, we show that QN-302 engages cellular G4s and triggers G4-associated DNA damage in human cancer cells. In HeLa cells, short exposures increase G4 foci and double strand break (DSB) markers, whereas pre-incubation with the G4-disruptor PhpC reduces both, supporting a G4-dependent mechanism. In PDAC (MIA PaCa-2) cells, QN-302's antiproliferative activity synergizes with the PARP1 inhibitor Olaparib. Combination treatment produces supra-additive increases in γH2AX foci and yields Bliss synergy across multiple dose pairs, consistent with chemically induced synthetic lethality. CONCLUSIONS: QN-302 induces G4-mediated DNA damage that underpins potent antiproliferative effects. Inhibition of DNA repair with Olaparib augments this activity, whereas pharmacological G4 destabilization with PhpC attenuates it. These findings support a defined mechanism of action for QN-302 and provide a rationale for clinical combination strategies in PDAC and potentially other cancer.