DNA-PK inhibition shows differential radiosensitization in orthotopic GBM PDX models based on DDR pathway deficits.

in Molecular cancer therapeutics by Sonja Dragojevic, Emily J Smith, Michael S Regan, Sylwia A Stopka, Gerard Baquer, Zhiyi Xue, Wenjuan Zhang, Margaret A Connors, Jake A Kloeber, Zeng Hu, Katrina K Bakken, Lauren L Ott, Brett L Carlson, Danielle M Burgenske, Paul A Decker, Shulan Tian, Shiv K Gupta, Daniel J Laverty, Jeanette E Eckel-Passow, William F Elmquist, Nathalie Y R Agar, Zachary D Nagel, Jann N Sarkaria, Cameron M Callaghan

TLDR

  • The study investigates whether a drug called peposertib can make cancer cells more sensitive to radiation therapy. The study used mice with cancer cells that were grown in their bodies and compared how well the cancer cells responded to radiation therapy with and without peposertib. The study found that peposertib made the cancer cells more sensitive to radiation therapy, and that this was due to the drug inhibiting a protein called DNA-PK. The study also found that cancer cells with a certain genetic mutation were more sensitive to peposertib. This study could help doctors find new ways to treat cancer with radiation therapy.

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's) are potent radiosensitizers currently in clinical trials. Determining which patients may benefit from radiosensitization with DNA-PKi's is critical to avoid unnecessary increased risk of normal tissue toxicity. In this study we used GBM patient derived xenografts (PDXs) 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 300nM and above, with significant increase in radiosensitization by maintaining post-IR exposure for >12 hours. Radiosensitization by peposertib is mediated by catalytic inhibition of DNA-PK, and knock-down 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 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. While the mechanism underpinning this discordant effect in vitro vs. 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 wildtype GBM lines significantly delayed growth and decreased NHEJ efficiency (but not Homologous Recombination), after peposertib exposure.

Overview

  • The study investigates the radiosensitizing potential of peposertib in GBM patient-derived xenografts (PDXs) in orthotopic murine models. The study aims to determine the relationship between molecular features, pharmacokinetics, and the radiosensitizing potential of peposertib. The hypothesis being tested is whether peposertib radiosensitizes established and PDX GBM lines in vitro and in vivo. The methodology used for the experiment includes the use of GBM PDXs in orthotopic murine models, in vitro studies of radiosensitization, and pharmacokinetic studies. The primary objective of the study is to determine the radiosensitizing potential of peposertib in GBM and identify the molecular features that may predict radiosensitivity.

Comparative Analysis & Findings

  • The study shows that peposertib radiosensitizes established and PDX GBM lines in vitro at 300nM and above, with significant increase in radiosensitization by maintaining post-IR exposure for >12 hours. Radiosensitization by peposertib is mediated by catalytic inhibition of DNA-PK, and knock-down 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 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. While the mechanism underpinning this discordant effect in vitro vs. 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 wildtype GBM lines significantly delayed growth and decreased NHEJ efficiency (but not Homologous Recombination), after peposertib exposure.

Implications and Future Directions

  • The study's findings suggest that peposertib radiosensitizes GBM in vitro and in vivo, and that the mechanism of radiosensitization is mediated by catalytic inhibition of DNA-PK. The study also identifies TP53 mutant lines as being more sensitive to peposertib radiosensitization. Future research directions could include further investigation of the mechanism of radiosensitization in vivo, as well as the use of peposertib in combination with other therapies for GBM. Additionally, the study highlights the importance of considering molecular features when determining radiosensitivity in GBM, and the potential for personalized approaches to radiosensitization therapy.
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