In vitro chelating, cytotoxicity, and blood compatibility of degradable poly(ethylene glycol)-based macromolecular iron chelators.

Desferrioxamine (DFO) is used to treat an excess accumulation of iron in the body and is currently the most commonly used iron chelator for the treatment of 'iron overload' disorder. However, the disadvantages of DFO surround its high toxicity and very short plasma half-life. Here, the detailed in vitro evaluation of a novel class of high molecular weight iron chelators based on DFO and polyethylene glycol methacrylate is reported. Reversible addition fragment chain transfer (RAFT) copolymerization afforded polymer conjugates (P-DFO) with well-controlled molecular weight (27-127 kDa) and substitution of DFO (5-26 units per chain) along the copolymer. Human umbilical vein endothelial cell (HUVEC) based cell viability assays showed that the cytotoxicity of P-DFO decreased more than 100-fold at identical concentrations of DFO. The hemocompatibilities of various P-DFO samples were determined by measuring prothrombin time (PT), activated partial thromboplastin time (APTT), thrombelastograph parameters (TEG), complement activation, platelet activation, and red blood cell aggregation. Furthermore, the iron binding properties and chelating efficiency of P-DFO were compared to DFO by measuring the spectral properties upon binding to iron(III), while the prevention of iron(III) mediated oxidation of hemoglobin was also determined. Degradation of the P-DFO conjugates via cleavable ester linkages between the polymer backbone and the PEG side chains was evaluated using gel permeation chromatography (GPC) and NMR. Since the chelating ability of DFO remains intact after conjugation to the copolymer backbone, these macromolecular, blood compatible and degradable conjugates are promising candidates as long circulating, non-toxic iron chelators.

Slx4 regulates DNA damage checkpoint-dependent phosphorylation of the BRCT domain protein Rtt107/Esc4.

RTT107 (ESC4, YHR154W) encodes a BRCA1 C-terminal-domain protein that is important for recovery from DNA damage during S phase. Rtt107 is a substrate of the checkpoint protein kinase Mec1, although the mechanism by which Rtt107 is targeted by Mec1 after checkpoint activation is currently unclear. Slx4, a component of the Slx1-Slx4 structure-specific nuclease, formed a complex with Rtt107. Deletion of SLX4 conferred many of the same DNA-repair defects observed in rtt107delta, including DNA damage sensitivity, prolonged DNA damage checkpoint activation, and increased spontaneous DNA damage. These phenotypes were not shared by the Slx4 binding partner Slx1, suggesting that the functions of the Slx4 and Slx1 proteins in the DNA damage response were not identical. Of particular interest, Slx4, but not Slx1, was required for phosphorylation of Rtt107 by Mec1 in vivo, indicating that Slx4 was a mediator of DNA damage-dependent phosphorylation of the checkpoint effector Rtt107. We propose that Slx4 has roles in the DNA damage response that are distinct from the function of Slx1-Slx4 in maintaining rDNA structure and that Slx4-dependent phosphorylation of Rtt107 by Mec1 is critical for replication restart after alkylation damage.