Targeted suppression of DNA polymerase θ enhances calcium flux and triggers intrinsic apoptosis in gastric cancer

Gastric cancer (GC), ranking among the most prevalent malignant tumors globally, is characterized by extensive genomic, transcriptomic, and epigenomic heterogeneity. DNA polymerase θ (POLQ) is a key regulator of microhomology-mediated end joining (MMEJ) that is highly expressed in cancer and has the potential to become a molecular target for the development of anticancer drugs. Although previous studies have shown that POLQ knockdown promotes apoptosis in tumor cells, the underlying mechanisms by which POLQ regulates apoptotic pathways remains elusive. The impact of POLQ expression on prognostic outcomes was assessed through tissue microarray staining of GC specimens and comprehensive database analysis. A POLQ knockout (KO) cell line was generated using CRISPR-Cas9 technology, and RNA sequencing was performed to elucidate the signaling pathways affected by POLQ depletion. Alterations in intracellular calcium levels were monitored via flow cytometry and confocal microscopy. Furthermore, a subcutaneous xenograft tumor model was established in mice to evaluate the inhibitory effects of POLQ-targeting inhibitor on tumor progression. POLQ expression correlates with poor clinical prognosis in GC patients. CRISPR-Cas9-mediated knockout of POLQ significantly inhibited GC cell viability and induced apoptosis. Transcriptomic profiling revealed that POLQ-KO elevates calcium ion (Ca²⁺) concentrations in the cytoplasm and endoplasmic reticulum (ER). This elevation enhances mitochondrial calcium (Ca²⁺m) uptake, promoting mitochondrial stress, and cytochrome c (Cyt C) release, and initiating the intrinsic apoptosis. Additionally, treatment with the POLQ inhibitor novobiocin sodium (NVB S) effectively suppressed tumor growth in vivo. Our study demonstrates that targeted POLQ inhibition triggers ER calcium release and Ca²⁺m uptake, which induces intrinsic apoptosis in GC cells. While the POLQ inhibitor NVB S has shown compelling preclinical efficacy, its clinical translation will require further validation with more selective inhibitors and comprehensive safety assessments.