Abstract 1265: PRKDC regulates CDK2 expression and pancreatic neuroendocrine cancer sensitivity to chemotherapy.

Abstract 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. Citation Format: Subin Kim, Mahnaz Norouzi, Courtney M. Townsend, B. Mark Evers, Piotr Rychahou. PRKDC regulates CDK2 expression and pancreatic neuroendocrine cancer sensitivity to chemotherapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1265.