Radioprotection of targeted and bystander cells by methylproamine

Abstract

IntroductionRadioprotective agents are of interest for application in radiotherapy for cancer and in public health medicine in the context of accidental radiation exposure. Methylproamine is the lead compound of a class of radioprotectors which act as DNA binding anti-oxidants, enabling the repair of transient radiation-induced oxidative DNA lesions. This study tested methylproamine for the radioprotection of both directly targeted and bystander cells.MethodsT98G glioma cells were treated with 15 μM methylproamine and exposed to 137Cs γ-ray/X-ray irradiation and He2+ microbeam irradiation. Radioprotection of directly targeted cells and bystander cells was measured by clonogenic survival or γH2AX assay.ResultsRadioprotection of directly targeted T98G cells by methylproamine was observed for 137Cs γ-rays and X-rays but not for He2+ charged particle irradiation. The effect of methylproamine on the bystander cell population was tested for both X-ray irradiation and He2+ ion microbeam irradiation. The X-ray bystander experiments were carried out by medium transfer from irradiated to non-irradiated cultures and three experimental designs were tested. Radioprotection was only observed when recipient cells were pretreated with the drug prior to exposure to the conditioned medium. In microbeam bystander experiments targeted and nontargeted cells were co-cultured with continuous methylproamine treatment during irradiation and postradiation incubation; radioprotection of bystander cells was observed.Discussion and conclusionMethylproamine protected targeted cells from DNA damage caused by γ-ray or X-ray radiation but not He2+ ion radiation. Protection of bystander cells was independent of the type of radiation which the donor population received.

Targeted and Off-Target (Bystander and Abscopal) Effects of Radiation Therapy: Redox Mechanisms and Risk/Benefit Analysis

“…Early experiments highlighted the multiple roles of ROS and RNS in bystander effects. Specifically, they showed that radical scavengers (ascorbic acid, N-acetyl l -cysteine), NOS inhibitors (NG-nitro- l -arginine methyl ester [L-NAME]), NO scavenger (2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide [c-PTIO] ( 281 ), antioxidant enzymes (superoxide dismutase [SOD], catalase) ( 10 , 303 ), and DNA-binding antioxidants (methylproamine) ( 39 ) inhibit the appearance of bystander effects. For example, genomic instability due to bystander effects can be rescued by restoring mitochondrial function through overexpression of manganese-dependent superoxide dismutase (MnSOD) ( 103 ).…”

DNA damage foci: Meaning and significance

“…Obviously, the same concepts and possibilities apply to the use of foci assays as pharmacodynamic tools for characterising anti-cancer therapies [Redon et al, 2010a], combinations of therapeutics [Sak et al, 2009] or DNA damage response modifiers, whether used alone or in combination with DNA-damaging treatments [e.g. Lim et al, 2014;Srivastava et al, 2014;Burdak-Rothkamm et al, 2015b]. In cells undergoing apoptosis H2AX phosphorylation occurs in an intranuclear shell.…”

Cancer Radiotherapy: Understanding the Price of Tumor Eradication

“…A delayed DDR is well-established for the cellular RIBE (Sedelnikova et al, 2007). Interestingly, methylproamine protects bystander cells in the in vitro RIBE setting, e.g., if present with recipient cells at the time of transfer of media irradiated cells (Burdak-Rothkamm et al, 2015). By contrast, in the context of targeted radiation effects, methylproamine must be present before and during irradiation to endow radioprotection of cultured cells (Lobachevsky et al, 2011), consistent with the mechanism (DNAbinding antioxidant) of radioprotection (Martin and Anderson, 1998).…”