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DNA-PK Inhibition Shows Differential Radiosensitization in Orthotopic GBM PDX Models Based on DDR Pathway Deficits
Sonja Dragojevic1, Emily J Smith1, Michael S Regan2
1Department of Radiation Oncology, Mayo Clinic, Rochester, Minnesota.
Abstract:
Glioblastoma (GBM) remains one of the most therapy-resistant malignancies with frequent local failures despite aggressive surgery, chemotherapy, and ionizing radiation (IR). Small molecule inhibitors of DNA-dependent protein kinase (DNA-PKi) are potent radiosensitizers currently in clinical trials. Determining which patients may benefit from radiosensitization with DNA-PKi is critical to avoid unnecessary increased risk of normal tissue toxicity. In this study, we used GBM patient-derived xenografts (PDX) in orthotopic murine models to study the relationship between molecular features, pharmacokinetics, and the radiosensitizing potential of the DNA-PKi peposertib. We show that peposertib radiosensitizes established and PDX GBM lines in vitro at 300 nmol/L and above, with a significant increase in radiosensitization by maintaining post-IR exposure for >12 hours. Radiosensitization by peposertib is mediated by catalytic inhibition of DNA-PK, and knockdown of DNA-PK by short hairpin RNA (shRNA) largely abolished the radiosensitizing effect. Peposertib decreased auto-phosphorylation of DNA-PKcs after IR in a dose-dependent manner with a delay in resolution of γH2AX foci at 24 hours. The addition of peposertib to IR significantly increased survival in GBM120 orthotopic xenografts, but not in GBM10. There was no difference in plasma or average tumor concentrations of peposertib in the two cohorts. Although the mechanism underpinning this discordant effect in vitro versus in vivo is not clear, there was an association for greater sensitization in TP53 mutant lines. Transfection of a dominant-negative TP53 mutant in baseline TP53 wild-type GBM lines significantly delayed growth and decreased nonhomologous end joining efficiency (but not homologous recombination), after peposertib exposure. See related commentary by Buchsbaum, p. 840.
Insights
DNA-PK inhibitors like peposertib show promise in radiosensitizing glioblastoma (GBM) cells. However, patient benefit varies, with TP53 mutations potentially predicting response to this DNA-PK inhibitor therapy.
Area of Science:
- Oncology
- Cancer Biology
- Radiotherapy
Background:
- Glioblastoma (GBM) is a highly therapy-resistant brain tumor with poor outcomes.
- Ionizing radiation (IR) is a standard GBM treatment, but local failures are common.
- DNA-dependent protein kinase inhibitors (DNA-PKi) are being investigated as radiosensitizers to improve GBM treatment efficacy.
Purpose of the Study:
- To investigate the radiosensitizing potential of the DNA-PKi peposertib in patient-derived glioblastoma xenografts.
- To explore the relationship between molecular features, pharmacokinetics, and peposertib's radiosensitizing efficacy.
- To identify predictive biomarkers for patient selection in DNA-PKi-based radiosensitization therapy.
Main Methods:
- Utilized orthotopic murine models with patient-derived glioblastoma xenografts (PDX).
- Assessed peposertib's radiosensitizing effects in vitro and in vivo, measuring DNA-PK inhibition and DNA damage repair markers (γH2AX foci).
- Analyzed the impact of TP53 mutation status on treatment response and DNA repair pathways (nonhomologous end joining and homologous recombination).
Main Results:
- Peposertib demonstrated radiosensitizing effects on GBM cells in vitro at concentrations ≥300 nmol/L, enhanced by prolonged post-IR exposure.
- In vivo, peposertib significantly increased survival in GBM120 xenografts but not in GBM10 xenografts, despite similar drug concentrations.
- Greater radiosensitization was associated with TP53 mutant GBM lines; introducing a dominant-negative TP53 mutant delayed tumor growth and impaired nonhomologous end joining.
Conclusions:
- Peposertib effectively inhibits DNA-PK and radiosensitizes GBM cells, but in vivo efficacy is variable.
- TP53 mutation status may serve as a predictive biomarker for response to peposertib-based radiosensitization.
- Further research is needed to elucidate the mechanisms behind discordant in vitro and in vivo responses and to optimize patient selection for DNA-PKi therapy.
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