Enhanced anti-cancer effect using MMP-responsive L-asparaginase fused with cell-penetrating 30Kc19 protein

As the acute lymphoblastic leukaemia (ALL) develops, expression of L-asparaginase (ASNase) protein is known to decrease. Therefore, deficiency of the ASNase protein would be regarded as one of the significant indications of the ALL. For the treatment of ALL, recombinant ASNase protein derived from bacterial origin is used which causes cytotoxicity by deprivation of Asn. However, short half-life of the protein is an obstacle for medical use. In order to overcome this limit, recombinant ASNase was fused to 30Kc19 with protein-stabilizing and cell-penetrating properties. As the 30Kc19 protein may induce steric hindrance, we further added a PLGLAG linker sequence (LK) between the ASNase and 30Kc19. The treatment of ASNase-LK-30Kc19 fusion protein demonstrated enhanced stability, cell-penetrating property, and anti-cancer activity. Intracellular delivery of both the non-cleaved and cleaved forms of the protein were observed, suggesting that ASNase acted both internally and externally, performing high anti-cancer activity by effective depletion of intracellular Asn. Additionally, ASNase-LK-30Kc19 showed high selectivity towards cancer cells. In terms of the dosage, releasable ASNase from ASNase-LK-30Kc19 reached the same half-maximal inhibitory concentration at a concentration five times lower than non-releasable ASNase-30Kc19. Altogether, the findings suggest that this fusion approach has potential applications in the treatment of ALL.