PRKDC regulates CDK2 expression and pancreatic neuroendocrine cancer sensitivity to chemotherapy

Background: Pancreatic neuroendocrine tumors (pNETs) frequently present with extensive inoperable metastases that develop resistance to DNA-damaging chemotherapy. This study evaluated DNA‑PK inhibition as a strategy to enhance doxorubicin efficacy against metastatic tumors and examined the DNA-PK-CDK2 axis, with PRKDC identified as a regulator of CDK2 expression. Methods: DNA double-strand breaks were induced using the topoisomerase II inhibitor doxorubicin. DNA-PK activity was inhibited with peposertib or via siRNA-mediated DNA-PK knockdown in BON and QGP-1 neuroendocrine cell lines. Transcriptomic data from DNA-PK knockdown cell lines were analyzed to identify gene expression relationships. Dose-dependent effects of doxorubicin on CDK2 levels were evaluated by western blot and confocal microscopy. The effect of DNA-PK inhibition and knockdown on doxorubicin-induced CDK2 expression was assessed by western blot. Therapeutic efficacy of combined low-dose doxorubicin (2 mg/kg, i.p.) and peposertib (100 mg/kg, oral gavage) was evaluated in a BON metastatic lung colonization mouse model using bioluminescence imaging to quantify metastatic burden. Results: In BON and QGP‑1 cells, doxorubicin consistently induced CDK2 upregulation, and both Western blotting and confocal microscopy showed a dose‑dependent increase in CDK2 protein levels, implicating a chemotherapy‑activated program of adaptive resistance. Transcriptomic analyses revealed a positive correlation between PRKDC (encoding the DNA-PK catalytic subunit) and CDK2 expression. Importantly, PRKDC knockdown or pharmacologic DNA‑PK inhibition prevented this CDK2 induction, establishing a PRKDC‑dependent mechanism of CDK2‑mediated chemoresistance and identifying DNA‑PK as a therapeutic target to block the adaptive response. Consistent with these in vitro findings, two cycles of low‑dose doxorubicin combined with peposertib markedly suppressed pulmonary metastatic growth and limited extrathoracic dissemination in a BON lung metastasis model. Conclusions: These findings support a role for DNA-PK in mediating CDK2 upregulation in response to chemotherapy and highlight the clinical relevance of low PRKDC and CDK2 expression with improved survival in NET patients. Collectively, these findings identify a PRKDC-CDK2 survival axis as a driver of chemoresistance and demonstrate that sustained, low‑intensity DNA damage, when coupled with selective DNA‑PK inhibition, disrupts this adaptive program, substantially reduces metastatic burden, and delivers more durable responses in pNETs. AI use disclosure: Portions of this abstract were revised with the assistance of generative AI and were fully reviewed and verified by the authors.