Improvement of pharmacokinetic, immunological and stability properties of asparaginase by conjugation to linear and branched monomethoxy poly(ethylene glycol)

A comparative pre formulation study of native asparaginase and conjugated with linear monomethoxypoly(ethylene glycol) 5000 (mPEG) or branched monomethoxypoly(ethylene glycol) (mPEG2) is reported. The first polymer, mPEG, was obtained with norleucine as spacer between polymer chain and protein, while mPEG2 was obtained by linking of mPEG 5000 Mw to the α- and ϵ-lysine amino groups. The comparison regarded the enzymatic activity, stability, pharmacokinetic and immunological properties of the different enzyme forms. The enzyme modified by the branched polymer showed increased in vitro activity and proteolytic resistance, improved stability towards temperature and pH variations and enhanced half life. Furthermore, the conjugation with mPEG largely reduced recognition by polyclonal antibodies raised against native asparaginase, the effect being more marked in the mPEG2 conjugate. All these data are in favour of the use of asparaginase modified by the mPEG2 in the treatment of patients with tumour responding to this enzyme, in particular in case of intolerance to native asparaginase.