Selective DNA-PKcs inhibition extends the therapeutic index of localized radiotherapy and chemotherapy
Catherine E. Willoughby, … , Anderson J. Ryan, Stephen R. Wedge
Catherine E. Willoughby, … , Anderson J. Ryan, Stephen R. Wedge
Published October 3, 2019
Citation Information: J Clin Invest. 2020;130(1):258-271. https://doi.org/10.1172/JCI127483.
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Research Article Oncology

Selective DNA-PKcs inhibition extends the therapeutic index of localized radiotherapy and chemotherapy

Abstract

Potentiating radiotherapy and chemotherapy by inhibiting DNA damage repair is proposed as a therapeutic strategy to improve outcomes for patients with solid tumors. However, this approach risks enhancing normal tissue toxicity as much as tumor toxicity, thereby limiting its translational impact. Using NU5455, a newly identified highly selective oral inhibitor of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity, we found that it was indeed possible to preferentially augment the effect of targeted radiotherapy on human orthotopic lung tumors without influencing acute DNA damage or a late radiation-induced toxicity (fibrosis) to normal mouse lung. Furthermore, while NU5455 administration increased both the efficacy and the toxicity of a parenterally administered topoisomerase inhibitor, it enhanced the activity of doxorubicin released locally in liver tumor xenografts without inducing any adverse effect. This strategy is particularly relevant to hepatocellular cancer, which is treated clinically with localized drug-eluting beads and for which DNA-PKcs activity is reported to confer resistance to treatment. We conclude that transient pharmacological inhibition of DNA-PKcs activity is effective and tolerable when combined with localized DNA-damaging therapies and thus has promising clinical potential.

Authors

Catherine E. Willoughby, Yanyan Jiang, Huw D. Thomas, Elaine Willmore, Suzanne Kyle, Anita Wittner, Nicole Phillips, Yan Zhao, Susan J. Tudhope, Lisa Prendergast, Gesa Junge, Luiza Madia Lourenco, M. Raymond V. Finlay, Paul Turner, Joanne M. Munck, Roger J. Griffin, Tommy Rennison, James Pickles, Celine Cano, David R. Newell, Helen L. Reeves, Anderson J. Ryan, Stephen R. Wedge

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Figure 2

NU5455 is an effective radiosensitizer in vitro.

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NU5455 is an effective radiosensitizer in vitro. (A) Clonogenic survival...
(A) Clonogenic survival of MCF7 cells pretreated with NU5455, the ATM inhibitor KU55933, the PARP inhibitor rucaparib, or the ATR inhibitor VE-821 for 1 hour before IR (2 Gy). Clonogenic assays involved continued incubation with compounds prior to reseeding of cells into drug-free media 24 hours after irradiation. SER, sensitization enhancement ratio. (B and C) MCF7 (B) and MCF10A (C) clonogenic survival under confluent or exponentially growing conditions. Cells were treated with vehicle or NU5455 (1 μM) for 1 hour before irradiation and reseeding 24 hours after irradiation. SER80 indicates the SER between radiation doses with and without NU5455 that induced an 80% inhibition of clonogenic cell survival (LD80). (D) Clonogenic survival of MCF7 cells pretreated with NU5455 (1 μM) for 1 hour before irradiation, and for a further 1, 2, 4, 6, or 24 hours after irradiation before incubation in drug-free media prior to reseeding at 24 hours. (E) Integrated total nuclear fluorescence of γH2AX foci in MCF7 cells pretreated with NU5455 (1 μM) for 1 hour and fixed 0–24 hours after irradiation (2.5 Gy). At least 50 cells were analyzed per treatment group. (F) LD80 values from clonogenic survival assays of cell lines treated with vehicle or NU5455 (1 μM) for 1 hour before, and 24 hours after, irradiation. Fold potentiation is shown above each cell line. All graphs (A–F) represent the mean ± SEM from at least 3 independent experiments, with the exception of graph E, which is a single representative of 2 independent experiments (see also Supplemental Figure 6). Statistical significance was assessed using unpaired t tests, with the exception of graph E, for which Mann-Whitney U tests were used. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001.