Nonhomologous End Joining Is More Important Than Proton Linear Energy Transfer in Dictating Cell Death

Bright, Scott J.; Flint, David B.; Chakraborty, Sharmistha; McFadden, Conor H.; Yoon, David S.; Bronk, Lawrence F.; Titt, Uwe; Mohan, Radhe; Grosshans, David R.; Sumazin, Pavel; Shaitelman, Simona F.; Asaithamby, Aroumougame; Sawakuchi, Gabriel O.

doi:10.1016/j.ijrobp.2019.08.011

Cited by 25 publications

(47 citation statements)

References 35 publications

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“…Moreover, deficiency in DNA-PKcs resulted in more pronounced damage persistence, as revealed by enhanced residual DNA damage foci in M059J cells 24 h upon irradiation with X-ray photons compared to SOBP protons. Our observations corroborate the major role of NHEJ for survival of irradiated cancer cells irrespective of the radiation quality, thereby confirming previous observations by others [46,78]. The importance of NHEJ in ensuring cell survival upon both proton and photon irradiation also corresponds to the reported involvement of NHEJ in the repair of approx.…”

Section: Discussionsupporting

confidence: 92%

“…However, calculated RBE values for 10% of clonogenic survival for EP and SOBP were approx. 1, which has already been observed by others [28,78]. These findings reveal that deficiency in NHEJ caused by the loss of DNA-PKcs already causes a dramatic radiosensitization to X-ray photon irradiation that overrides potential small differences in survival caused by the distinct biology of the DNA damage induced by X-ray photon and proton irradiation, respectively.…”

Section: Discussionsupporting

confidence: 76%

“…However, the delay was less pronounced than the delay observed in NHEJ-deficient cells after X-ray photon irradiation. This suggests that NHEJ is also involved in repair of clustered DNA lesions induced by SOBP proton irradiation and that HRR plays an additional and supportive role in processing the induced DNA DSB, as suggested by others [46,78].…”

Section: Discussionsupporting

confidence: 59%

“…We speculate that the repair of smaller DNA lesions induced by X-ray photons will mainly rely on NHEJ, so that cells with a deficiency in proper NHEJ will accumulate residual DNA damage [28,29]. In contrast, a delay in DNA repair kinetics of HRR-deficient cell lines was only observed after SOBP proton irradiation underlining the increased importance of HRR for the repair of clustered DNA damage induced by irradiation with SOBP protons [14,28,29,46,65,68,78]. However, the delay was less pronounced than the delay observed in NHEJ-deficient cells after X-ray photon irradiation.…”

Section: Discussionmentioning

confidence: 95%

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Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

Szymonowicz

Krysztofiak

Linden

et al. 2020

Cells

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Technical improvements in clinical radiotherapy for maximizing cytotoxicity to the tumor while limiting negative impact on co-irradiated healthy tissues include the increasing use of particle therapy (e.g., proton therapy) worldwide. Yet potential differences in the biology of DNA damage induction and repair between irradiation with X-ray photons and protons remain elusive. We compared the differences in DNA double strand break (DSB) repair and survival of cells compromised in non-homologous end joining (NHEJ), homologous recombination repair (HRR) or both, after irradiation with an equal dose of X-ray photons, entrance plateau (EP) protons, and mid spread-out Bragg peak (SOBP) protons. We used super-resolution microscopy to investigate potential differences in spatial distribution of DNA damage foci upon irradiation. While DNA damage foci were equally distributed throughout the nucleus after X-ray photon irradiation, we observed more clustered DNA damage foci upon proton irradiation. Furthermore, deficiency in essential NHEJ proteins delayed DNA repair kinetics and sensitized cells to both, X-ray photon and proton irradiation, whereas deficiency in HRR proteins sensitized cells only to proton irradiation. We assume that NHEJ is indispensable for processing DNA DSB independent of the irradiation source, whereas the importance of HRR rises with increasing energy of applied irradiation.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionsupporting

confidence: 76%

Section: Discussionsupporting

confidence: 59%

Section: Discussionmentioning

confidence: 95%

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Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

Szymonowicz

Krysztofiak

Linden

et al. 2020

Cells

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“…Images were analyzed using an ImageJ plugin developed in-house that automatically counts colonies containing more than 50 cells. 24 Details of the clonogenic cell survival assay are in Supplementary Note 3.…”

mentioning

confidence: 99%

Cell lines of the same anatomic site and histologic type show large variability in radiosensitivity and relative biological effectiveness to protons and carbon ions

Flint

Bright

McFadden

et al. 2020

Preprint

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Purpose: To show that radiation response across cancer cell lines of the same anatomic site and histologic type varies remarkably for protons and carbon (C) ions. Materials and Methods: We measured and obtained from the literature clonogenic survival of human cancer cell lines of the lung (n=18), brain (n=10) and pancreas (n=10) exposed to photons, protons, and C-ions to assess their variability in response. We also treated cancer cell lines with DNA repair inhibitors prior to irradiation to assess how DNA repair capacity affects their variability in response. We quantified the variability in response by calculating the relative range (range/mean) and the coefficient of variation (COV) of the dose at 10% survival fraction (D10%) and relative biological effectiveness (RBE10%). Results: The relative range of D10% for lung cancer cell lines varied from 55-92% for photons, protons, and Cions, with the relative range in RBE varying from 16-45% for protons and C-ions. For brain and pancreatic cancer cell lines, the relative range of D10% varied from 95-112%, and 39-75%, respectively, with the relative range in RBE varying from 27-33% and 25-50%, respectively. However, the COVs in D10% were approximately equal across radiation qualities, varying from 0.24±0.07-0.35±0.10, 0.35±0.09-0.69±0.62 and 0.13±0.03-0.21±0.04 for lung, brain and pancreatic cancer cell lines, respectively. Greater relative ranges in D10% were observed in the cell lines with inhibited DNA repair, varying from 108%-157% for photons, protons, and C-ions, with relative ranges in RBE varying from 29-67%. The COVs in the D10% were also greater for the cell lines treated with inhibitors of DNA repair, varying from 0.34±0.09-0.41±0.06. Conclusions: Cell lines of the same anatomic site and histologic type have a remarkable variability in response, not only to photons but also to protons and C-ions. We attributed this variability to differences in DNA repair capacity. Category: Biological Physics and Response PredictionClonogenic cell survival assay Cells were trypsinized 18-24 hours prior to irradiation and seeded into 6-well plates or T-12.5 flasks at appropriate numbers for each dose. Cell lines were allowed to form colonies for 7-14 days and then were fixed and stained with pure ethanol containing 0.5% crystal violet. Plates were allowed to air dry overnight and then scanned using a high-resolution flatbed scanner (Epson Expression 10000 XL). Images were analyzed using an ImageJ plugin developed in-house that automatically counts colonies containing more than 50 cells. 24 Details of the clonogenic cell survival assay are in Supplementary Note 3. Statistical analysesStatistical analyses were performed in MATLAB 2017 (Mathworks, Natick, MA) and Graph Pad Prism 7 (Graph Pad, San Diego, CA). Error bars represent the standard error propagated from the survival curve parameters (α and β) fits, including their covariance, to the parameter estimates. RESULTSWe found large variability in the D10% values of several lung, brain and pancreatic cancer cell lines to ph...

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Proton and photon radiosensitization effects of niraparib, a PARP‐1/‐2 inhibitor, on human head and neck cancer cells

et al. 2020

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Background Combining photon or proton radiotherapy with targeted therapy shows promise for head and neck cancer (HNSCC). The poly (adenosine diphosphate [ADP]‐ribose) polymerase‐1/2 inhibitor niraparib targets DNA damage repair (DDR). We evaluated the effects of niraparib in combination with photons or protons, and its effects on the relative biological effectiveness (RBE) of protons, in human HNSCC cell lines. Methods Radiosensitivity was assessed and RBE was calculated with clonogenic survival assays; unrepaired DNA double‐strand breaks were evaluated using immunocytochemical analysis of 53BP1 foci. Results Niraparib reduced colony formation in two of the four cell lines tested (P < .05), enhanced radiosensitivity in all four cell lines, delayed DDR (P < .05), and increased proton vs photon RBE. Conclusion Niraparib enhanced the sensitivity of four HNSCC cell lines to both photons and protons and increased the RBE of protons, possibly by inhibiting DDR. Niraparib may enhance the effectiveness of both photon and proton radiotherapy for patients with HNSCC.

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Nonhomologous End Joining Is More Important Than Proton Linear Energy Transfer in Dictating Cell Death

Cited by 25 publications

References 35 publications

Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

Proton Irradiation Increases the Necessity for Homologous Recombination Repair Along with the Indispensability of Non-Homologous End Joining

Cell lines of the same anatomic site and histologic type show large variability in radiosensitivity and relative biological effectiveness to protons and carbon ions

Proton and photon radiosensitization effects of niraparib, a PARP‐1/‐2 inhibitor, on human head and neck cancer cells

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