PMID: 7542144May 1, 1995Paper

The effect of hetastarch on the stability of L-asparaginase during freeze-thaw cycling

PDA Journal of Pharmaceutical Science and Technology
F JameelR Bogner

Abstract

L-asparaginase, a therapeutic agent for the treatment of acute lymphoblastic leukemia, was evaluated for its susceptibility to cold denaturation. It was found that the enzyme derived from Erwinia chrysanthemi loses its activity when exposed to freeze-thaw cycling. When it was frozen at -40 degrees C and thawed, the enzyme lost 67.3% of its activity; whereas, when frozen in liquid nitrogen (-190 degrees C), it lost almost all of its activity. Rheological studies of hetastarch showed that its viscosity dramatically increases with decreasing temperature, suggesting that at sub-zero temperatures it will create a highly viscous environment around the enzyme. It is proposed that this highly viscous environment retards the rate of conformational changes leading to losses in activity. Hetastarch solutions of various concentrations and degrees of hydroxyethylation were evaluated for their protective ability against the freeze-thaw denaturation of L-asparaginase. It was found that the cryoprotective effect of hetastarch with 0.8 degree of substitution at a concentration of 0.2% was sustained over many freeze-thaw cycles while that of the lesser substituted starch was not. The cryoprotective effect of hetastarch was compared to that of ot...Continue Reading

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