title: Protection by methylproamine of irradiated human keratinocytes correlates with reduction of DNA damage.
abstract: OBJECTIVE
  The therapeutic ratio for ionising radiation treatment of tumour is a trade-off between normal tissue side-effects and tumour control. Application of a radioprotector to normal tissue can reduce side-effects. Here we study the effects of a new radioprotector on the cellular response to radiation. Methylproamine is a DNA-binding radioprotector which, on the basis of published pulse radiolysis studies, acts by repair of transient radiation-induced oxidative species on DNA. To substantiate this hypothesis, we studied protection by methylproamine at both clonogenic survival and radiation-induced DNA damage, assessed by γH2AX (histone 2AX phosphorylation at serine 139) focus formation endpoints.
  
  
  METHODS
  The human keratinocyte cell line FEP1811 was used to study clonogenic survival and yield of γH2AX foci following irradiation (¹³⁷Cs γ-rays) of cells exposed to various concentrations of methylproamine. Uptake of methylproamine into cell nuclei was measured in parallel.
  
  
  RESULTS
  The extent of radioprotection at the clonogenic survival endpoint increased with methylproamine concentration up to a maximum dose modification factor (DMF) of 2.0 at 10 μM. At least 0.1 fmole/nucleus of methylproamine is required to achieve a substantial level of radioprotection (DMF of 1.3) with maximum protection (DMF of 2.0) achieved at 0.23 fmole/nucleus. The γH2AX focus yield per cell nucleus 45 min after irradiation decreased with drug concentration with a DMF of 2.5 at 10 μM.
  
  
  CONCLUSIONS
  These results are consistent with the hypothesis that radioprotection by methylproamine is mediated by attenuation of the extent of initial DNA damage.
authors.affiliation: Trescowthick Research Laboratories, Peter MacCallum Cancer Centre, St Andrew's Place, East Melbourne, Victoria 3002, Australia. pavel.lobachevsky@petermac.org
authors.forename: Pavel N
authors.initials: PN
authors.lastname: Lobachevsky
authors.forename: Raja S
authors.initials: RS
authors.lastname: Vasireddy
authors.forename: Sam
authors.initials: S
authors.lastname: Broadhurst
authors.forename: Carl N
authors.initials: CN
authors.lastname: Sprung
authors.forename: Tom C
authors.initials: TC
authors.lastname: Karagiannis
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Smith
authors.forename: Ian R
authors.initials: IR
authors.lastname: Radford
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McKay
authors.forename: Roger F
authors.initials: RF
authors.lastname: Martin
mesh_terms: D001562:Benzimidazoles / Q000494:pharmacology*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D005720:Gamma Rays; D006657:Histones / Q000378:metabolism; D006801:Humans; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects* / Q000528:radiation effects; D008024:Ligands; D015233:Models, Statistical; D010766:Phosphorylation; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D011837:Radiation-Protective Agents / Q000494:pharmacology
chemical_list: D001562:Benzimidazoles; C468783:H2AX protein, human; D006657:Histones; D008024:Ligands; D011837:Radiation-Protective Agents; C483319:methylproamine