Design of Long Circulating Nontoxic Dendritic Polymers for the Removal of Iron in Vivo

Abstract

Patients requiring chronic red blood cell (RBC) transfusions for inherited or acquired anemias are at risk of developing transfusional iron overload, which may impact negatively on organ function and survival. Current iron chelators are suboptimal due to the inconvenient mode of administration and/or side effects. Herein, we report a strategy to engineer low molecular weight iron chelators with long circulation lifetime for the removal of excess iron in vivo using a multifunctional dendritic nanopolymer scaffold. Desferoxamine (DFO) was conjugated to hyperbranched polyglycerol (HPG) and the plasma half-life (t1/2) in mice is defined by the structural features of the scaffold. There was a 484 fold increase in t1/2 between the DFO (5 min) versus the HPG-DFO (44 h). In an iron overloaded mouse model, efficient iron excretion by HPG-DFO in the urine and feces was demonstrated (p = 0.0002 and 0.003, respectively) as was a reduction in liver, heart, kidney, and pancreas iron content, and plasma ferritin level (p = 0.003, 0.001, 0.001, 0.001, and 0.003, respectively) compared to DFO. Conjugates showed no apparent toxicity in several analyses including body weight, serum lactate dehydrogenase level, necropsy analysis, and by histopathological examination of organs. These findings were supported by in vitro biocompatibility analyses, including blood coagulation, platelet activation, complement activation, red blood cell aggregation, hemolysis, and cell viability. This nanopolymer-based chelating system would potentially benefit patients suffering from transfusional iron overload.

In vivo efficacy, toxicity and biodistribution of ultra-long circulating desferrioxamine based polymeric iron chelator

“…This was first described by Hallaway et al, who achieved half-life extension up to 80 minutes and reduced toxicity after conjugating DFO to hydroxyl ethyl starch and dextran [5]. Similarly, we have previously shown that hyperbranched polyglycerol (HPG) conjugates of DFO with circulation half-life of 16 h was capable of efficiently removing iron from iron overloaded mice when treated every other day, demonstrating the proof-of-concept [20].…”

“…ULC-DFO was obtained by conjugating DFO to HPG of different MW using reductive amination as previously reported [20]. In a typical reaction, 100-200 mg of HPG (25, 44 and 494 KDa) was dissolved in MilliQ water (2-4 mL).…”

“…The conjugates were characterized for their hydrodynamic size, number of DFO/polymer and the molecular weight. Radio-labeled versions of ULC-DFO conjugates were used for biodistribution studies and were obtained by using tritiated sodium cyanoborohydride for reductive amination in the conjugation of DFO to HPG, as previously described [20]. The stability of the HPG-DFO in physiological buffer solutions at 37°C was determined using gel permeation chromatography analysis and iron binding studies (see supplementary information for details).…”

“…On day 7, mice were grouped (n=3) and injected with ULC-637 conjugate (637 KDa) and DFO at 50 mg/kg DFO or DFO equivalent dose each week up to a total of four injections; 200 µL/20g via tail vein. We chose to study this particular ULC-DFO because our previous study showing its long circulation half-life in mice (44 h) [20]. We considered that extended half-life would be the most important mediating factor in optimizing dose regimen.…”

“…This was achieved using high MW biocompatible polymers [5,6,[18][19][20][21]. Different studies have shown that the properties of DFO can be tuned and enhanced to generate more suitable safety profiles, metal chelating efficacy and slower elimination.…”