DNA Repair Deficient Chinese Hamster Ovary Cells Exhibiting Differential Sensitivity to Charged Particle Radiation under Aerobic and Hypoxic Conditions

Abstract

It has been well established that hypoxia significantly increases both cellular and tumor resistance to ionizing radiation. Hypoxia associated radiation resistance has been known for some time but there has been limited success in sensitizing cells to radiation under hypoxic conditions. These studies show that, when irradiated with low linear energy transfer (LET) gamma-rays, poly (ADP-ribose), polymerase (PARP), Fanconi Anemia (FANC), and mutant Chinese Hamster Ovary (CHO) cells respond similarly to the non-homologous end joining (NHEJ) and the homologous recombination (HR) repair mutant CHO cells. Comparable results were observed in cells exposed to 13 keV/μm carbon ions. However, when irradiated with higher LET spread out Bragg peak (SOBP) carbon ions, we observed a decrease in the oxygen enhancement ratio (OER) in all the DNA of repair mutant cell lines. Interestingly, PARP mutant cells were observed as having the largest decrease in OER. Finally, these studies show a significant increase in the relative biological effectiveness (RBE) of high LET SOBP carbon and iron ions in HR and PARP mutants. There was also an increase in the RBE of NHEJ mutants when irradiated to SOBP carbon and iron ions. However, this increase was lower than in other mutant cell lines. These findings indicate that high LET radiation produces unique types of DNA damage under hypoxic conditions and PARP and HR repair pathways play a role in repairing this damage.

Combination Therapy With Charged Particles and Molecular Targeting: A Promising Avenue to Overcome Radioresistance

“…In addition, carbon ions have been found to induce an LET dependent increase in cleaved PARP (95). Furthermore, PARP deficient cells were found to have the largest decrease in OER after carbon irradiation (100). From the current data it can be summarized that particle irradiation has a more pronounced effect on PARP expression and cleavage compared to photon irradiation.…”

Oxidative stress and genotoxicity of co-exposure to chlorpyrifos and aflatoxin B1 in HepG2 cells

“…Micronucleus formation was then counted under a microscope at 20× magnification (Nikon Inc, Tokyo, Japan). To avoid personal bias, the counting of micronuclei (MNs) was blinded and analyzed under 300 binucleated cells (BNCs) in triplicates, and the results were expressed as the number of MNs in BNCs, as previously described (Cartwright et al, 2018).…”

Modeling the Effect of Hypoxia and DNA Repair Inhibition on Cell Survival After Photon Irradiation

“…Further, they argue, that in NHEJ deficient cell lines, the lethality of isolated lesions increases depending on the cell cycle status of the cells. While we adapt and fully agree with the notion of a fixed lethality of complex damages independent of the repair capabilities of a cell, we had no information on the cell cycle distributions underlying the data taken from Cartwright et al [30] and found different radiosensitizing factors ( RSF ) for the two DNA-PK response-deficient mutants analyzed. Therefore we decided to introduce the RSF as a free parameter in UNIVERSE, fitted to each mutant cell line.…”

“…Survival data of the CHO cell line and two of its DNA-PK response-deficient mutants (V3 cell line is DNA-PKcs-deficient and xrs-5 cell line is Ku80-deficient) under normoxia and hypoxia were gathered from Cartwright et al (Figure 2) [30]. The cell line-specific parameters KiDSB and KcDSB were found by fitting our model to the normoxic survival data of the wild-type cells.…”

“…The RSF values found for the two CHO mutants V3 and xrs5 indicate that the probability of an isolated lesion to become a lethal lesion increases through DNA-PK response deficiency in these cell lines by a factor of about 10 and 15, respectively. Even though both RSF factors are related to the functional DNA-PK repair activity, the difference in the RSF of both cell lines might be retraced to the fact, that both are deficient of different enzymes taking part in the DNA-PK response: While xrs-5 cells are deficient of the Ku80 DNA-PK subunit [30,31], V3 cells lack the catalytic subunit for DNA-PK [30,32]. It is, however, unclear if and how the RSF is coupled to the activity of both proteins.…”