Available information on preclinical toxicology studies with PEGylated drugs did not show any PEG-related toxicities for PEGASYS® and Mircera®. In toxicity studies with Cimzia® in cynomolgus monkeys and rats conducted

with high doses of the PEGylated protein, the only PEG-related finding was vacuolation mainly in macrophages and after chronic dosing. This vacuolation did not result in functional SCH727965 nmr changes in the animals. No PEG-related effects have been reported in clinical studies with Cimzia®. Vacuolation of macrophages and some other cell types at high PEG doses was also reported for some PEGylated proteins including PEGylated haemoglobin [13, 17, 18, 22, 23]. No changes in other tissues have been reported. The larger PEG molecules do not penetrate into tissue to the extent as PEG molecules smaller than 20 kDa [37, 38]. Therefore, it can be assumed that large PEG molecules linked to a large protein, such as FVIII, will remain in circulation until FVIII is removed through the protein-related

removal mechanisms thought to be mainly in the liver. Thus, the penetration of large PEG or PEGylated rFVIII into tissues, such as brain, can be assumed to be negligible. This is supported by the toxicology studies with the PEGylated proteins and/or with PEG alone where no indication of vacuolation of neuronal cells or microglia (derived from the same lineage as macrophages) has been observed in any of the studies. ABT-263 clinical trial The 60 kDa PEG moiety in BAY 94–9027 did not show any toxicity when assessed in acute and repeat administration toxicity studies, up to the highest dose tested of 210 mg kg−1 in the acute and 11 mg kg−1 in the 4 weeks toxicity study. The large safety margins medchemexpress of the clinical dose of PEG for Cimzia®, PEGASYS® and the expected clinical dose of BAY 94–9027 to the observed vacuolation

in cells of the RES system in rats and monkeys seen only with Cimzia® (Fig. 3) suggests that long-term administration of 60 kDa PEGylated rFVIII could be a safe option. Several key points can be extracted from the experiments with 60 kDa PEG and the review of the literature on safety of high molecular weight PEG. The toxicity of a PEGylated protein is usually the same or lower than the un-PEGylated protein and the toxicity seen is related to the action of the protein moiety, not the PEG [12, 13]. The removal of the PEGylated protein from circulation is driven by mechanisms specific to the protein [12, 13], and PEGylated proteins can have reduced immunogenicity when compared to their un-PEGylated protein [4, 5, 13]. Polyethylene glycol molecules, given at low doses as in most therapeutic proteins, can be removed by the kidney and liver with low organ accumulation [33, 38].