Molecular and functional characterisation of a fusion protein suited for tumour specific prodrug activation

Abstract

Currently, the treatment of non-disseminated solid tumours is performed by surgery and irradiation. Both methods can be considered to be relatively tumour selective, without significantly harming the rest of the body. If however the tumour has disseminated to various organ sites, the metastases can be treated by chemo-or hormone therapy only. Chemotherapy has considerable side effects and a minor influence on patients' survival due to the lack of specificity of action or the induction of resistance. Hormone therapy alone has a limited tumour spectrum.To overcome these obvious limitations of today's treatment modalities, we tailored a fusion gene consisting of the VH and CHI Exons of a humanised MAb and the human P-glucuronidase cDNA . The product encoded by the fusion gene might be suitable for performing an antibody directed enzyme prodrug therapy (ADEPT). The concept of ADEPT as developed by Philpott et al. (1973a,b;1974) and reemphasised by Bagshawe (1987) and Bagshawe et al. (1988) assumes that an antibody enzyme conjugate after selective localisation at the tumour target site, and its clearance from normal tissues, activates a nontoxic low molecular weight prodrug to a highly toxic drug in the tumour by enzymatic catalysis.The therapeutic success of this approach depends on several factors:(a) The stability of the prodrug in vivo. (j) The immunogenicity of the antibody enzyme conjugate. Despite the obvious complexity of the system, a first clinical trial with a F(ab')2 fragment of a murine anti CEA MAb chemically linked to carboxypeptidase G2 (CPG2) from

A monoclonal antibody-β-glucuronidase conjugate as activator of the prodrug epirubicin-glucuronide for specific treatment of cancer

“…For ultimate treatment of cancer based on antibody-enzyme prodrug targeting the group of Bosslet et al (1992) has produced a fusion protein by molecular biology techniques consisting of human GUS and the humanised Fab' of MAb BW431/26. Studies are in progress to evaluate the efficiency of this conjugate in the hydrolysis of Epi-glu in vitro as well in vivo.…”

A fully human anti-Ep-CAM scFv-beta-glucuronidase fusion protein for selective chemotherapy with a glucuronide prodrug

“…Previously, the functional characterisation of a fusion protein consisting of the humanized fragment of an anti-CEA monoclonal antibody and GUSh expressed in BHK cells has been reported (Bosslet et al, 1992). The use of a humanised antibody fragment in a fusion protein is not ideal.…”

Potentiation of antitumor immunity by antibody-directed enzyme prodrug therapy

“…Our results also suggest that nonimmunogenic immunoenzymes should be employed to alleviate the need to administer immunosuppressive drugs to patients during ADEPT if repeated treatments are given. 52 Thus, immunoenzymes constructed with human ␤-glucuronidase [53][54][55] or human carboxypeptidase A1 56 may be preferable for the clinical application of ADEPT.…”