Therapeutic enzymes for the treatment of leukemia: Molecular engineering of L-asparaginases to improve activity and stability

5^th World Congress on Cancer Therapy

September 28-30, 2015 Atlanta, USA

Manfred Konrad

Max Planck Institute for Biophysical Chemistry, Germany

Posters-Accepted Abstracts: J Cancer Sci Ther

Abstract :

This lecture will highlight the development of novel strategies for the amelioration of the enzyme L-asparaginase (L-ASNase) which is a protein drug of high value in antileukemic therapy. L-ASNases catalyze the deamidation of the free amino acid L-asparagine (L-Asn) to L-aspartate (L-Asp) and ammonia. Bacterial L-ASNases are FDA-approved therapeutic enzymes for use in the treatment of various blood cancers to deplete serum L-Asn levels. Their efficacy as protein drugs is based on the fact that several hematological malignancies, in particular Acute Lymphoblastic Leukemia (ALL), depend for growth on the extracellular supply of L-Asn. To avoid the immune response and other side reactions inherent to the bacterial enzymes, it would be beneficial to substitute them with human L-ASNases. One human isoform, hASNase-3, belongs to the N-terminal nucleophile (Ntn) hydrolase superfamily where the protein is synthesized as a single polypeptide chain that is devoid of activity. Autoproteolytic cleavage of this protein generates two tightly associated subunits that constitute the catalytically active enzyme. The free amino acid glycine was found to selectivelyaccelerate intramolecular processing of hASNase-3 both in vitro and in human cells. We evolved the enzyme in vitro aiming to select for variants of enhanced activity. Since increased expression of hASNase-3 was observed in several tumors, the dependence of hASNase-3 activation on glycine may be related to the altered metabolic profile of cancer cells.To increase the serum half-life of the enzyme, we packaged L-ASNases into microcapsules, thus enhancing stability and potentially preventing exposure of the enzyme to the immune system. We applied the Layer-by- Layer (LbL) strategy of biocompatible microcapsule formation, using calcium carbonate particles as core templates for protein adsorption, which were coated with poly-L-arginine and dextran sulfate polymers. Our work suggests that microcarriers in combination with enzyme engineering will set the basis for novel ways to treat blood cancers.

Biography :

Email: mkonrad@mpibpc.mpg.de