Cell surface display of a lysosomal enzyme for extracellular gene-directedenzyme prodrug therapy

Prodrug conversion is a promising approach to cytotoxic gene therapy if an efficient transfer of the generated drug to adjacent cells can be achieved. To maximize the efficacy of this strategy we sought to develop a system th at is based on a human enzyme, acts extracellularly yet in close vicinity o f the transduced cell and can be used with multiple prodrugs. Results obtai ned with a secreted version of human beta-glucuronidase suggested that this enzyme could be a suitable candidate, although a more stringent retention of the enzyme at the site of the producer cell. such as its attachment to t he cell surface, would be desirable. Here, we show that the fusion of the t ransmembrane domain of the human PDGF receptor to a C-terminally truncated form of human Beta-glucuronidase results in its surface accumulation at hig h steady-state levels. Using a doxorubicin prodrug, we demonstrate that thi s GDEPT system produces a strong bystander effect and has potent antitumor activity in vivo.