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Overcoming hypoxia-induced tumor radioresistance in non-small cell lung cancer by targeting DNA-dependent protein kinase in combination with carbon ion irradiation



Hypoxia-induced radioresistance constitutes a major obstacle for a curative treatment of cancer. The aim of this study was to investigate effects of photon and carbon ion irradiation in combination with inhibitors of DNA-Damage Response (DDR) on tumor cell radiosensitivity under hypoxic conditions.


Human non-small cell lung cancer (NSCLC) models, A549 and H1437, were irradiated with dose series of photon and carbon ions under hypoxia (1% O2) vs. normoxic conditions (21% O2). Clonogenic survival was studied after dual combinations of radiotherapy with inhibitors of DNA-dependent Protein Kinase (DNAPKi, M3814) and ATM serine/threonine kinase (ATMi).


The OER at 30% survival for photon irradiation of A549 cells was 1.4. The maximal oxygen effect measured as survival ratio was 2.34 at 8 Gy photon irradiation of A549 cells. In contrast, no significant oxygen effect was found after carbon ion irradiation. Accordingly, the relative effect of 6 Gy carbon ions was determined as 3.8 under normoxia and. 4.11 under hypoxia. ATM and DNA-PK inhibitors dose dependently sensitized tumor cells for both radiation qualities. For 100 nM DNAPKi the survival ratio at 4 Gy more than doubled from 1.59 under normoxia to 3.3 under hypoxia revealing a strong radiosensitizing effect under hypoxic conditions. In contrast, this ratio only moderately increased after photon irradiation and ATMi under hypoxia. The most effective treatment was combined carbon ion irradiation and DNA damage repair inhibition.


Carbon ions efficiently eradicate hypoxic tumor cells. Both, ATMi and DNAPKi elicit radiosensitizing effects. DNAPKi preferentially sensitizes hypoxic cells to radiotherapy.


Tumor hypoxia is a critical factor contributing to acquired radioresistance and therapy failure [1, 2]. In line, tumor hypoxia was shown to correlate with poor prognosis and inferior therapeutic outcome in non-small cell lung cancer (NSCLC) [3, 4]. The lack of oxygen leads to decreased production of reactive oxygen species and consequently to reduced DNA damage after conventional radiotherapy with high energy photons [5, 6]. In vitro studies are usually conducted at relatively high oxygen concentrations (20%) compared to the physiological range of 3–7.4% detected in normal tissues [7]. In tumor tissues, average oxygen levels are found to be even lower than 2%, hence referring to a hypoxic microenvironment [8]. There is a relationship between decreased oxygen tension and gradual decline of radiation cell killing changing with different radiation qualities [9]. However, relevant in vitro data on oxygen enhancement ratio (OER) measurements are sparse [10] but urgently needed to adjust treatment planning with more faithful oxygen concentrations and to evaluate the impact of different radiation qualities and multimodal treatments.

Induction of DNA damage is a hallmark of radiation induced cell toxicity [11]. The relevant, lethal DNA damage, complex double-strand breaks (DSB), are repaired by two major pathways, i.e., homologous recombination and non-homologous end-joining. For each of these pathways, members of the phosphotidylinositol-3-kinase (PIK) family are recruited to DSBs: Ataxia-telangiectasia mutated (ATM) and DNA-dependent protein kinase with its catalytic subunit (DNA-PKc). Inhibitors of these key players in DNA damage response (DDR) pathways were shown to enhance the efficacy of radiotherapy [12]. In contrast to sparsely ionizing photon radiation, carbon ions are densely ionizing along their traversal and are considered high linear energy transfer (LET) irradiation [13]. The application of high-LET beams has been shown to increase tumor cell killing by inducing more complex DNA damage that results in an increased radiobiological effectiveness (RBE) [14]. It has been further reported that cell killing by high-LET radiation might be less dependent on the tumor oxygen status [9, 15].

In this study, the effect of carbon ions vs. conventional photon irradiation was investigated on two NSCLC cell lines. We report on the radiosensitizing effect of two novel DDR inhibitors, DNAPKi and ATMi, with photon- and carbon ion irradiation under hypoxic conditions.


Cell lines

The US National Cancer Institute (NCI) offers a panel of 60 human tumor cell lines (NCI-60 panel, for in vitro evaluations including anti-cancer compounds [16]. From this panel, the NSCLC cell lines A549 and NCI-H1437 (H1437) cells were purchased from the American Type Culture Collection (ATCC). Cells were grown in RPMI 1640 Medium (Gibco) supplemented with 10% Fetal Bovine Serum (FBS) at 37 °C and 5% CO2 atmosphere. Experiments in hypoxic conditions were performed at 1% O2 and 5% CO2.

Experimental design

To assess clonogenic survival under hypoxic conditions, we devised a system to irradiate cells in 96-well plates while incubated in a hypoxia chamber (C-chamber; Biospherix) allowing online monitoring of CO2 and O2 concentrations (ProOx and ProCO2 model; Biospherix) during the entire experiment (Fig. 1a). 50, 100 or 200 A549 cells/well and 100, 200 or 300 H1437 cells /well were seeded up to 16 h before irradiation. Cell numbers increased with escalation of dose and drug concentration. Inhibitors were added to the cells at 50 nM, 100 nM, 200 nM, 500 nM, or 1000 nM for normoxia and at 100 nM, 200 nM, or 500 nM for hypoxia and at 100 nM for carbon ion irradiation. Both ATM and DNA-PK inhibitors were dissolved in DMSO and diluted in RPMI 1640 medium. Controls also contained <0.1% DMSO. To determine the effect of drug treatment alone on clonogenic survival (Plating efficiency, PE), dose series of both compounds at 0, 50, 100, 200, 500, and 1000 nM were analyzed without irradiation. After exposure to inhibitors, cells were incubated for 4 h in hypoxia or in normoxia, respectively. For photon radiation, a vertical beam direction was used to irradiate plates at four different doses. For horizontal carbon ion beams, an irradiation plan was developed to deliver four different doses in SOBP region of the beam.

Fig. 1
figure 1

Oxygen effect after photon and carbon ion irradiation. a Schematic of the devised hypoxia chamber and 96-well cell culture plates setup for high-throughput clonogenic survival analysis in vertical photon and horizontal carbon ion beam direction. Hypoxia was continuously monitored by sensors for O2 and CO2 concentrations. b Clonogenic survival of the NSCLC cell line A549 irradiated under normoxia (black) and hypoxia (1% O2, red) with photons (solid line) and carbon ions (dashed line). In contrast to carbon irradiation, a significant ratio of survival fractions hypoxia vs. normoxia was found at doses ≥4 Gy after photon irradiation. Consequently, the RBE of carbon ions was enhanced under hypoxic conditions. Bars represent mean ± SD of three independent experiments with n:4 technical replicates each. SOBP: Spread-Out Bragg Peak, PMMA: Poly(methyl methacrylate) for tissue/water-equivalent thickness, arrows: beam direction, *: p < 0.05, **: p < 0.01

Cells were irradiated in the hypoxia chamber with a dose series of photons (1, 2, 4, or 8 Gy) and carbon ions (approx. 1, 2, 4, or 6 Gy) and thereafter incubated under normoxic conditions. Inhibitors were left in the media for 24 h and then replaced with fresh RPMI 1640 medium and the plates were returned to the incubator for colony formation. After 4 (A549) or 7 days (H1437) plates were imaged by microscopy at 4× magnification (IncuCyte, Essen Bioscience). The images were analyzed by the IncuCyte Zoom Software (Essen Bioscience) and colony counts were confirmed by manual curation. Counts were normalized to non-irradiated samples at each corresponding baseline inhibitor concentration.

Dose planning and simulations

Photon planning was done with Raystation treatment planning system (RaySearch Laboratories) based on a CT scan of the hypoxia chamber containing 96-well plates filled with water. Irradiation was performed on a Siemens Artiste (6 MV). For carbon ion delivery, Spread-out Bragg peak (SOBP) was physically optimized with the Treatment Planning for Particles (TRiP98) system, using a 30x30x30 cm3 water phantom positioned at 100 cm source-surface distance (SSD) [17]. To reduce physical uncertainties on cell survival introduced by the heterogeneous target, a detailed geometry of the utilized 96-well plates was incorporated into a FLUKA Monte Carlo simulation of the Heidelberg Ion Beam Therapy (HIT) beam-line [18]. Dose maps were generated, with dose uniformity found to be within 2% range in the SOBP region. Carbon dose levels for planned 1, 2, 4 and 6 Gy were corrected accordingly to actual prescribed 0.95, 1.9, 3.8, and 5.64 Gy.

Software and calculations

The survival fractions derived from the clonogenic survival data were fitted according to the linear-quadratic model for photons. A linear model was applied to carbon ion data. The fits as well as OER, RBE, and SER values (Additional file 1: Table S5 and Table S6) were calculated using an in-house tool based on Minuit package available in ROOT [19]. PE values were plotted with GraphPad Prism 5. To display the oxygen effect, the relative effect of carbon ions, and the sensitization effect of inhibitors, measured data points were used to determine ratios of clonogenic survival at a corresponding dose: Ratios were calculated as survival fractions of hypoxic cells and normoxic cells; survival fractions of cells irradiated with photons and cells irradiated with carbon ions; survival fractions of mock-treated cells and cells treated with inhibitors at the same dose, respectively. Effects were compared at a preferential dose of 4 Gy being a reasonable dose for patients in fractionated therapy.


Data are presented as means and standard deviations (SD). Statistical significance was determined using unpaired t-test (two-tailed). The asterisks represent significantly different values. Data represent average values of at least three independent experiments, each performed with technical quadruplicates (n:4).


Oxygen effect and relative effect for photon vs. carbon irradiation under hypoxia

Hypoxia increased the survival fraction of A549 cells significantly (between 1.36 to 2.34-fold) at photon doses ≥4 Gy under hypoxia vs. normoxia (p < 0.05). In contrast, no significant oxygen effect was found after carbon ion irradiation (Fig. 1b, Table 1). The calculated OER at 30% survival was 1.4 for photons and 1.2 for carbon ions (Additional file 1: Table S5A). Accordingly, the survival ratios displaying the relative effect of carbon ion vs. photon irradiation at 4 Gy increased from 3.8 under normoxia to 4.11 at 1% O2 concentration (Table 2). Corresponding RBE values calculated from fits at 30% survival are 2.7 under normoxia and 3.1 under hypoxia. The survival data for H1437 cells are presented in the supplemental material.

Table 1 Ratio of survival fractions normoxia vs. hypoxia for A549 cells at indicated doses
Table 2 Relative effect of photons vs. carbon ions for A549 cells at the indicated dose

Preferential Radiosensitization of hypoxic cells to DNAPKi

Next, we investigated the inherent and radiosensitizing effect of two novel DNAPK and ATM serine-threonine kinase inhibitors. The PE was not significantly reduced after ATMi treatment. The PE was only significantly reduced by 15% after 1000 nM of DNAPKi (Fig. 2). This is in line with the reported high selectivity and on target potency of these compounds: DNAPKi (M3814) is a highly potent and selective inhibitor of DNA-PK with subnanomolar potency on its target [20, 21]. The split to closely related PIKK proteins has been measured in biochemical assays and is about 150-fold to PI3K delta and greater than 400-fold to the other family members (ATM, PI3Kalpha – delta, mTOR). The preclinical ATM inhibitor tested is a subnanomolar potent inhibitor with 50-fold selectivity over DNA-PK and greater than 1000-fold selectivity against the other PIKK family members (ATR, PI3Kalpha – delta, mTOR).

Fig. 2
figure 2

Lack of cytotoxicity of utilized ATMi and DNAPKi alone at pharmacologically relevant doses. PE of A549 cells after treatment with dose series of ATMi (light grey) or DNAPKi (dark grey), respectively, under normoxia (a) and hypoxia (b). Statistically significant reduction of PE was only found under normoxia for doses ≥1000 nM. Bars represent mean ± SD of three independent experiments with n:4 technical replicates each

After photon irradiation both compounds exhibited dose dependent radiosensitizing effects under normoxic and hypoxic conditions (Fig. 3). For 100 nM ATMi, the sensitization effect at 4 Gy photons increased from 1.4 under normoxia to 1.6 under hypoxia (Table 3). The radiosensitizing effect of DNAPKi was markedly enhanced under hypoxic conditions. For 100 nM DNAPKi the survival ratio at 4 Gy more than doubled from 1.5 under normoxia to 3.3 under hypoxia (Fig. 3, Table 3). The enhanced sensitizing effect of DNAPKi under hypoxia was found in both cell lines (Additional file 1: Fig. S3).

Fig. 3
figure 3

Dose dependent radiosensitizing effect of ATMi and DNAPKi after photon irradiation. Clonogenic survival of A549 tumor cells irradiated with photons under normoxia (a) and hypoxia (b) in combination with increasing concentrations of ATMi (upper panel) or DNAPKi (lower panel), respectively. Both DDR inhibitors exhibited potent dose dependent radiosensitizing effects. Note, the ratio of survival fractions with and without DNAPKi increased significantly under hypoxic conditions (Table 3). Bars represent mean ± SD of three independent experiments with n:4 technical replicates each. **: p < 0.01; ***: p < 0.005

Table 3 Effect of ATMi and DNAPKi for photon irradiation of A549 cells at indicated doses

Effect of DDR inhibition in combination with carbon ion irradiation

Next, we aimed to discover the potential of DDR inhibitors to further improve eradication of radioresistant hypoxic cells. Based on the PE data demonstrating no relevant cytotoxicity at 100 nM for both inhibitors (Fig. 2), but strong radiosensitizing effects after photon irradiation (Fig. 3), this concentration was selected for combinations with carbon ion irradiation. Both inhibitors exhibit potent radiosensitizing effects in combination with high-LET carbon irradiation (Fig. 4). The SER at 30% survival was 1.5 for 100 nM ATMi and carbon irradiation under normoxic conditions (Additional file 1: Table S5B). This radiosensitizing effect was not further enhanced by addition of ATMi to carbon ions under hypoxic condition. In contrast, the SER at 30% survival increased from 1.7 under normoxia to 1.9 under hypoxia after combined carbon irradiation and DNAPKi. When comparing survival ratios after treatment with DNAPKi and 4 Gy carbon ion irradiation the ratios increased from 3.4 to 5.1 normoxia vs. hypoxia (Table 4). Overall, combination of DNAPKi and carbon irradiation most efficiently eradicated hypoxic NSCLC tumor cells.

Fig. 4
figure 4

DNAPKi further augments efficient eradication of hypoxic tumor cells by carbon ion. Clonogenic survival data for A549 cells irradiated with carbon ions under normoxia (a) and hypoxia (b) in combination with 100 nM ATMi (upper panel) or DNAPKi (lower panel), respectively. Both inhibitors radiosensitized carbon ions under normoxia. In line with photon irradiation, with DNAPKi the ratio of survival fractions was further increased after carbon irradiation under hypoxic conditions. Bars represent mean ± SD of three independent experiments with n:4 technical replicates each. *: p < 0.05, **: p < 0.01

Table 4 Effect of ATMi and DNAPKi for irradiation of A549 cells with carbon ions at indicated doses


We report here efficient eradication of hypoxic NSCLC tumor cells, in particular, after combined DNAPKi and ionizing radiation. Both, ATMi and DNAPKi demonstrated a gradual dose dependent radiosensitizing effect under normoxia and hypoxic conditions. Our data further confirmed findings from previous work reporting on a minimal dependency of high-LET carbon beams on cellular oxygen concentration [22, 23]. A combination of DNAPKi and carbon ions most efficiently eradicated hypoxic tumor cells (Fig. 4b).

To investigate irradiation effects under hypoxic conditions, establishing an in vitro experimental approach closest to the in vivo situation was a prerequisite. Current systems for conducting radiation experiments under hypoxic conditions may show some limitations e.g., utilize a strict anoxic environment that may not reflect the moderate hypoxic niche of the radioresistant tumor cell populations [24, 25]. We devised a system that allows to work with standard cell culture plates and conveniently transfer them between normoxia and different online monitored hypoxic conditions such as the 1% O2 utilized in this study. Moreover, the high-throughput performance in 96-well format with cell lines that form circumscribed colonies outperforms currently existing petri dish-sized hypoxia systems [26]. With this option, we were able to combine potential radiosensitizers with irradiation in an identical setting under normoxia and hypoxia.

ATM and DNA-PKc are two central constituents of DDR and their inhibition was shown to radiosensitize NSCLC cell lines [27, 28] as well as other tumor entities [29, 30] to photon irradiation under normoxia. However, only little is known about the effect of DNA-PKc inhibition on the radiosensitivity of hypoxic cells. Lindquist and colleagues described radiosensitivity effects with photon irradiation of DNA-PK deficient mouse embryonic fibroblast cells (SCID/st) under normoxic and hypoxic conditions compared to isogenic DNA-PK wildtype cells (CB.17) and that DNA-PK inhibition in combination with photon irradiation decreases the clonogenic survival of both oxic and hypoxic cells [31]. They suggested that impairment of DNA-PK radiosensitizes independently of cellular oxygen status. In contrast, we found a marked enhancement of DNAPKi radiosensitizing effects under hypoxia, in both cell lines, but not for ATM inhibition. One plausible explanation for this phenomenon is that moderate hypoxia may alter DNA repair signaling e.g., by post-translational modifications in a HIF-dependent manner [32]. Our data suggest that the therapeutic window for DNAPKi might be broader than originally anticipated by efficient eradication of the most radioresistant cells residing in the hypoxic tumor niche. This hypothesis, once successfully confirmed by in vivo experiments, could form the basis for rationally designed clinical trials investigating the impact of DNAPKi in otherwise radioresistant hypoxic tumors.

In addition to pharmacological radiosensitization of hypoxic cells, we provide here novel rationale to combine DDR inhibitors with high-LET carbon ion irradiation. The high RBE of carbon ions is attributed to their ability to form more complex unrepairable DSB correlating with large nuclear repair foci and increased number of residual DNA damage [14, 33]. Our results with NSCLC cell lines confirm data for CHO-K1 cells [26] showing that the low dependency of high-LET irradiation on cellular oxygen would further increase the RBE under hypoxic conditions. Additionally, these findings justify the usage of carbon ions to treat patients with hypoxia-associated radioresistant tumors.

We further evaluated the significance of inhibiting DDR with carbon ions. Interestingly, the sensitizing effect of DNAPKi was more pronounced than the effect of ATM inhibition. Moreover, the DNAPKi sensitizing effect was substantially enhanced (between ~50–60%) in survival ratios after carbon irradiation under hypoxic compared to normoxic conditions. On the contrary, the ATMi sensitizing effect remained in the same range under hypoxic vs. normoxic conditions after carbon ion irradiation. It is conceivable that the formation of lethal complex DNA damages is enhanced with higher photon doses, higher LET and inhibition of DNA-PKc. However, further mechanistic studies are needed to dissect the molecular mechanisms underlying the superior radiosensitizing principle behind DNAPKi treatment under hypoxic conditions.


Dual therapy with DNAPKi and carbon ion irradiation demonstrated the highest efficacy in eradicating otherwise radioresistant hypoxic tumors. Our data suggest potent reversal of the radioresistant phenotype of hypoxic tumors by DNAPKi that warrants further preclinical and clinical evaluation.



Ataxia-telangiectasia mutated


Inhibitor of ATM


DNA damage response


Catalytic subunit of DNA-dependent Protein Kinase


Inhibitor of DNA-dependent Protein Kinase


Heidelberger Ionenstrahl-Therapiezentrum


Linear energy transfer


Non-small cell lung cancer


Oxygen enhancement ratio


Plating efficiency




Relative biological effect


Reactive oxygen species


Sensitization enhancement ratio


Spread-out Bragg peak


Source-surface distance


  1. Overgaard J. Hypoxic radiosensitization: adored and ignored. J Clin Oncol. 2007;25(26):4066–74.

    Article  PubMed  Google Scholar 

  2. Tawk B, Schwager C, Deffaa O, et al. Comparative analysis of transcriptomics based hypoxia signatures in head- and neck squamous cell carcinoma. Radiother Oncol. 2016;118(2):350–8.

    Article  CAS  PubMed  Google Scholar 

  3. Vera P, Thureau S, Chaumet-Riffaud P, et al. Phase II study of a radiotherapy total dose increase in hypoxic lesions identified by 18F-misonidazole PET/CT in patients with non–small cell lung carcinoma (RTEP5 study). J Nucl Med. 2017;58:1045–53.

    Article  PubMed  Google Scholar 

  4. Eschmann SM, Paulsen F, Reimold M, et al. Prognostic impact of hypoxia imaging with 18F-misonidazole PET in non-small cell lung cancer and head and neck cancer before radiotherapy. J Nucl Med. 2005;46:253–60.

    PubMed  Google Scholar 

  5. Quintiliani M. The oxygen effect in radiation inactivation of DNA and enzymes. Int J Radiat Biol Relat Stud Phys Chem Med. 1986;50(4):573–94.

    Article  CAS  PubMed  Google Scholar 

  6. Ward JF. DNA damage produced by ionizing radiation in mammalian cells: identities, mechanisms of formation, and reparability. Prog Nucleic Acid Res Mol Biol. 1988;35:95–125.

    Article  CAS  PubMed  Google Scholar 

  7. Gray LH, Conger AD, Ebert M, Hornsey S, OCA S. The concentration of oxygen dissolved in tissues at the time of irradiation as a factor in radiotherapy. Br J Radiol. 1953;26(312):638–48.

    Article  CAS  PubMed  Google Scholar 

  8. McKeown SR. Defining normoxia, physoxia and hypoxia in tumors - implications for treatment response. Br J Radiol. 2014;87(1035):20130676.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  9. Antonovic L, Brahme A, Furusawa Y, Toma-Dasu I. Radiobiological description of the LET dependence of the cell survival of oxic and anoxic cells irradiated by carbon ions. J Radiat Res. 2013;54(1):18–26.

    Article  CAS  PubMed  Google Scholar 

  10. Scifoni E, Tinganelli W, Kraft-Weyrather W, et al. Including oxygen enhancement ratio in ion beam treatment planning: model implementation and experimental verification. Phys Med Biol. 2013;58(11):3871.

    Article  CAS  PubMed  Google Scholar 

  11. Toulany M, Rodemann HP. Phosphatidylinositol 3-kinase/Akt signaling as a key mediator of tumor cell responsiveness to radiation. Semin Cancer Biol. 2015;35:180–90.

    Article  CAS  PubMed  Google Scholar 

  12. Darzynkiewicz Z, Traganos F, Wlodkowic D. Impaired DNA damage response--an Achilles’ heel sensitizing cancer to chemotherapy and radiotherapy. Eur J Pharmacol 2009;625(1–3):143–50.

  13. Curtis SB. Calculated LET distributions of heavy ion beams. Int J Radiat Oncol Biol Phys. 1977;3:87–91.

    Article  CAS  PubMed  Google Scholar 

  14. Dokic I, Mairani A, Niklas M, et al. Next generation multi-scale biophysical characterization of high precision cancer particle radiotherapy using clinical proton, helium-, carbon- and oxygen ion beams. Oncotarget. 2016;7(35):56676–89.

    Article  PubMed  PubMed Central  Google Scholar 

  15. Wenzl T, Wilkens JJ. Modelling of the oxygen enhancement ratio for ion beam radiation therapy. Phys Med Biol. 2011;56(11):3251–68.

    Article  PubMed  Google Scholar 

  16. Wang H, Huang S, Shou J, et al. Comparative analysis and integrative classification of NCI60 cell lines and primary tumors using gene expression profiling data. BMC Genomics. 2006;7:166.

    Article  PubMed  PubMed Central  Google Scholar 

  17. Krämer M, Jäkel O, Haberer T, Kraft G, Schardt D, Weber U. Treatment planning for heavy-ion radiotherapy: physical beam model and dose optimization. Phys Med Biol. 2000;45(11):3299–317.

    Article  PubMed  Google Scholar 

  18. Tessonnier T, Marcelos T, Mairani A, et al. Phase space generation for proton and carbon ion beams for external Users' applications at the Heidelberg ion therapy Center. Front Oncol. 2016;5:297.

    Article  PubMed  PubMed Central  Google Scholar 

  19. Brun R, Rademakers F. ROOT — an object oriented data analysis framework. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 1997;389(1–2):81–6.

    Article  CAS  Google Scholar 

  20. Damstrup L, Zimmerman A, Sirrenberg C, Zenke FT, Vassilev L. M3814, a DNA-dependent protein Kinase inhibitor (DNA-PKi), potentiates the effect of ionizing radiation (IR) in Xenotransplanted Tumors in nude mice. Int J Rad Onc. 2016;94(4):940–1.

    Article  Google Scholar 

  21. Zenke FT, Zimmermann A, Sirrenberg C et al. Abstract 1658: M3814, a novel investigational DNA-PK inhibitor: enhancing the effect of fractionated radiotherapy leading to complete regression of tumors in mice. July 2016 Proceedings: AACR 107th Annual Meeting 2016;16–20, 2016; New Orleans, LA.

  22. Bopp C, Hirayama R, Inaniwa T, et al. Adaptation of the microdosimetric kinetic model to hypoxia. Phys Med Biol. 2016;61(21):7586–99.

    Article  CAS  PubMed  Google Scholar 

  23. Tinganelli W, Durante M, Hirayama R, et al. Kill-painting of hypoxic tumours in charged particle therapy. Scientific Reports. 2015;5:17016.

  24. Wouters BG, Brown JM. Cells at intermediate oxygen levels can be more important than the ‘hypoxic fraction’ in determining tumor response to fractionated radiotherapy. Radiat Res. 1997;147(5):541.

    Article  CAS  PubMed  Google Scholar 

  25. Bussink J, Kaanders JHAM, van der Kogel AJ. Tumor hypoxia at the micro-regional level: clinical relevance and predictive value of exogenous and endogenous hypoxic cell markers. Radiother Oncol. 2003;67(1):3–15.

    Article  PubMed  Google Scholar 

  26. Tinganelli W, Ma N-Y, Von Neubeck C, et al. Influence of acute hypoxia and radiation quality on cell survival. J Radiat Res. 2013;54(suppl 1):i23–30.

    Article  PubMed  PubMed Central  Google Scholar 

  27. Toulany M, Mihatsch J, Holler M, Chaachouay H, Rodemann HP. Cisplatin-mediated radiosensitization of non-small cell lung cancer cells is stimulated by ATM inhibition. Radiother Oncol. 2014;111(2):228–36.

    Article  CAS  PubMed  Google Scholar 

  28. Sunada S, Kanai H, Lee Y, et al. Nontoxic concentration of DNA-PK inhibitor NU7441 radio-sensitizes lung tumor cells with little effect on double strand break repair. Cancer Sci. 2016;107(9):1250–5.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  29. Batey MA, Zhao Y, Kyle S, et al. Preclinical evaluation of a novel ATM inhibitor, KU59403, in vitro and in vivo in p53 functional and dysfunctional models of human cancer. Mol Cancer Ther. 2013;12(6):959–67.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  30. Ciszewski WM, Tavecchio M, Dastych J, Curtin NJ. DNA-PK inhibition by NU7441 sensitizes breast cancer cells to ionizing radiation and doxorubicin. Breast Cancer Res Treat. 2014;143(1):47–55.

    Article  CAS  PubMed  Google Scholar 

  31. Lindquist KE, Cran JD, Kordic K, et al. Selective radiosensitization of hypoxic cells using BCCA621C: a novel hypoxia activated prodrug targeting DNA-dependent protein kinase. Tumor Microenvironment and Therapy. 2013;03:46–55.

    Google Scholar 

  32. Scanlon SE, Glazer PM. Multifaceted control of DNA repair pathways by the hypoxic tumor microenvironment. DNA Repair. 2015;32:180–9.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  33. Sørensen BS, Horsman MR, Alsner J, et al. Relative biological effectiveness of carbon ions for tumor control, acute skin damage and late radiation-induced fibrosis in a mouse model. Acta Oncol. 2015;54(9):1623–30.

    Article  PubMed  Google Scholar 

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This study was conducted in the frame of German Research Foundation (DFG) “clinical research group heavy ion therapy (KFO-214)” within the project TP5 “Heavy Ions in Lung Cancer”. Both ATM and DNA-PK inhibitors were kindly provided by Merck (Darmstadt). The authors would like to thank Claudia Rittmüller, Nora Schuhmacher, and Christiane Rutenberg for their excellent technical assistance.


This work was supported by German Research Foundation (DFG-KFO214, TP5), It was also in part funded by Deutsche Krebshilfe (Max-Eder 108,876) and intramural funds from National Center for Tumor diseases (NCT3.0_2015.21/22 NCT-PRO and Biodose programs). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

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CK, OJ, TH, AZ, FZ, AB, JD, and AA were involved in the conception and design of the work. CK conducted the experiments. AZ, FZ, AB provided the kinase inhibitors and performed the biochemical characterization of the kinase inhibitors. CK, ID, AM analyzed and interpreted the data. PH, AM, and SM generated irradiation plans for photon and carbon ion irradiation, including simulations for dose corrections. SB was responsible for quality assurance of carbon ion beam. CK and AA wrote the manuscript. All authors read, critically revised and approved the final manuscript.

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Correspondence to Amir Abdollahi.

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Astrid Zimmerman, Frank Zenke and Andree Blaukat are Merck employee. Amir Abdollahi and Jürgen Debus received research funds from Merck and are involved as academic mentors in the DNA-Repair Cluster initiative with Merck-BioMedX. Other authors declare no conflict of interest.

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Additional file

Additional file 1:

S1-S4 Clonogenic survival of H1437 cells; In parallel to A549, another NSCLC cell line, H1437, was used in the same setup to compare the oxygen effect as well as sensitizing effects of inhibitors with photon vs. carbon ion irradiations. S5 Table listing OER, RBE, and SER for A549 and H1437 cells. OER, RBE, and SER were calculated from linear quadratic fits at 30% survival. (PDF 524 kb)

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Klein, C., Dokic, I., Mairani, A. et al. Overcoming hypoxia-induced tumor radioresistance in non-small cell lung cancer by targeting DNA-dependent protein kinase in combination with carbon ion irradiation. Radiat Oncol 12, 208 (2017).

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