Table 2.
Summary of in vitro studies on biological responses to clustered DNA damage induction.
| Cell Type | Radiation Type | Biological Response | Ref. |
|---|---|---|---|
| HeLa and oropharyngeal squamous cell carcinoma (UMSCC74A and UMSCC6) cells | High-LET α-particles (121 keV/μm) or protons (12 keV/μm), versus low-LET protons (1 keV/μm) and X-rays | Τhe signaling and repair of complex DNA damage, particularly induced by high-LET IR is coordinated through the specific induction of H2Bub catalyzed by MSL2 and RNF20/40, a mechanism that contributes to decreased cell survival after irradiation. | [125,130] |
| Human peripheral blood lymphocytes | Mixed beam of alpha-particles (241Am source, 0.223 Gy/min, LET: 90.9 keV/μm) and X-rays (190 kV, 4.0 mA, 0-2 Gy) | Induced DNA damage was above the level predicted by assuming additivity. The activation levels of DDR proteins and mRNA levels of the studied genes were highest in cells exposed to mixed beams. The repair of damage occurs with a delay. |
[131] |
| Human dermal fibroblasts | High-LET IR with carbon ions (9.5 MeV/n; LET 190 keV/μm; calculated mean dose: 1.52 Gy) or calcium ions (7.7 MeV/n; LET 1800 keV/μm; calculated mean dose: 14.4 Gy), versus low-LET IR with 6-MV photons (10 Gy) | High-LET-IR induced clustered DNA damage and triggered profound changes in chromatin structure along particle trajectories. DSBs exhibited delayed repair despite cooperative activity of 53BP1, pATM, pKap-1. |
[26] |
| Normal human skin fibroblasts | 60Co γ-rays (LET=0.3 keV/μm), accelerated 11B (E = 8.1 MeV/nucleon, LET=138 keV/μm) ions | It has been found that heavy charged particles induce clustered DNA damage in the genome of cells that can lead not only to gene mutations, but also to large deletions. | [132] |
| HeLa Kyoto cells | Pulsed UV laser (micro-irradiation, IR) | Recruitment and dissociation of 70 DNA repair proteins to laser-induced complex DNA lesions. | [83] |
| Human uveal melanoma (92–1) cells | Carbon ions (LET: 80 keV/μm) and iron ions (LET: 400 keV/μm) at different doses, versus X-rays (LET: 4 keV/μm) | Heavy ions were more effective at inducing senescence than X-rays. Less-efficient repair was observed when DNA damage was induced by heavy ions compared to X-rays and most of the irreparable damage was complex of SSBs and DSBs, while DNA damage induced by X-rays was mostly repaired in 24 h. Results suggest that DNA damage induced by heavy ion is complex and difficult to repair, thus presenting as persistent DNA damage, and pushes the cell into senescence. |
[128] |
| Human dermal fibroblasts, NFFh-TERT foreskin fibroblasts | Low-LET irradiation with 6 MV photons, versus high-LET irradiation with carbon ions (9.5 MeV/n; LET = 190 keV/μm) | High-LET irradiation caused localized energy deposition within the particle tracks and generated highly clustered DNA lesions with multiple DSBs in close proximity. Ηuge DSB clusters predominantly localized in condensed heterochromatin. High-LET irradiation-induced clearly higher DSB yields than low-LET irradiation, and large fractions of these heterochromatic DSBs remained unrepaired. |
[24] |
| Human osteosarcoma cell line (U2-OS) | X-rays (250 keV, 16 mA; LET: 2 keV/μm), versus heavy ions: 238U ions (LET: 15,000 keV/μm), 207Pb ions (LET: 13,500 keV/μm), 197Au ions (LET: 13,000 keV/μm), 119Sn ions (LET: 7,880 keV/μm), 59Ni (LET: 3,430 keV/μm), 48Ti (LET: 2,180 keV/μm), 14N ions (LET: 400 keV/μm), and 12C ions (LET: 170 keV/μm) | DSB complexity plays a critical role in the decision for DSB end-resection in G1-cells. CtIP, MRE11, and EXO1 are required for the resection of complex DSBs in G. Repair of complex DSBs relies on resection independent of the cell cycle stage. |
[133] |
| Human cells (fibroblasts, HBECs) | 1 Gy of Si (LET: 44 keV/μm) or Fe (LET: 150 keV/μm) ions | Direct visualization of clustered DNA lesions at the single-cell level using 53BP1, XRCC1, and hOGG1 as surrogate markers for DSBs, SSBs, and base damage, respectively, reveals that most complex DNA damage is not repaired in human cells. Unrepaired clustered DNA lesions result in the generation of a spectrum of chromosome aberrations. Checkpoint release before the completion of clustered DNA damage repair is a major cause of chromosomal aberrations. |
[23] |
| Human Lung Adenocarcinoma (A5490) cells | 12C ions (62 MeV, LET: 290 keV/μm), versus 60Co γ-rays (1–3 Gy) | Carbon ions were three times more cytotoxic than γ-rays. The observed decrease in number of γ-H2AX foci 4 h after γ-rays irradiation indicates repair of damage and is supported by nearly 100% survival, whilst the decrease in γ-H2AX foci after carbon ion irradiation was not indicative of repair. |
[134] |
| HF12 primary male human fibroblast cells | 238Pu α-particles (range, ∼20 μm; peak energy, 3.26 MeV; LET=121.4 keV/μm) | Many α-particle-induced mutations are large deletions. Rejoining at microhomologies characterizes large deletion junctions. Intra- and interchromosomal insertions and inversions occur at the sites of some large deletions. Novel fragments found in complex rearrangements derive from other sites of radiation damage in the same cell. |
[135] |