Disposition of the prodrug 4-(bis (2-chloroethyl) amino) benzoyl-L-glutamic acid and its active parent drug in mice

P Antoniw,Kd Bagshawe,Cj Springer,Rg Melton,Rf Sherwood,Pj Burke,Gt Rogers,F Searle

doi:10.1038/bjc.1990.407

Abstract

A novel therapy for improving selectivity in cancer chemotherapy aims to modify distribution of a cytotoxic drug by generating it selectively at tumour sites. In this approach an antibody-enzyme conjugate is allowed to localise at the tumour sites before injecting a prodrug which is converted to an active drug specifically by the targeted enzyme in the conjugate. We present here pharmacokinetic studies on the prodrug 4-(bis (2-chloroethyl) amino) benzoyl-L-glutamic acid and its activated derivative, benzoic acid mustard. The glutamic acid is cleaved from the prodrug to form the active drug by carboxypeptidase G2 (CPG2), an enzyme from Pseudomonas sp., which is not found in mammalian cells. The prodrug and its parent active drug were rapidly distributed in plasma and tissues after administration of prodrug or active drug (41 mumol kg-1 intraperitoneally) to mice bearing human choriocarcinoma xenografts. Prodrug and active drug both followed a two-compartment kinetic model. Prodrug was eliminated more rapidly (t1/2 alpha = 0.12 h, t1/2 beta = 0.70 h) than active drug (t1/2 alpha = 0.37 h, t1/2 beta = 1.61 h). Conversion of the prodrug to the activated parent drug was detected within 5 min of administration to mice which had previously received a F(ab')2-anti-human chorionic gonadotrophin antibody (W14A) conjugated to the enzyme, CPG2 (1,000 U kg-1). Tumour was the only tissue that activated all the prodrug reaching the site. It contained the highest concentration of targeted enzyme conjugate capable of catalysing the reaction of prodrug to drug. Plasma and other tissues were also capable of activating the prodrug but active drug production was limited by the amount of enzyme present. The active drug measured in plasma and tissues other than tumour was attributable to residual antibody-enzyme conjugate at non-tumour sites. Low levels of conjugate in tissues and plasma militate against the advantage of tumour localised enzyme therefore necessitating removal of non-localised enzyme.

Highlights

Of A5B7, and the conjugate localises in the colon adenocarcinoma xenograft LS174T (Sharma et al, 1990)
CPG2 is not found in mammalian cells, neither is there any known mammalian homologue
Human CC3 choriocarcinoma (Searle et al, 1981) or LS174T colon adenocarcinoma (Johnson et al, 1986) xenografts were implanted into Nu/Nu mice

Summary

Introduction

Of A5B7, and the conjugate localises in the colon adenocarcinoma xenograft LS174T (Sharma et al, 1990). Since there is no CPG2 in mammalian cells, enzyme specific catalysis will occur only by administered conjugate. This two phase system has been termed Antibody-Directed Enzyme Prodrug Therapy (ADEPT) (Bagshawe, 1987). The novel prodrug 4-(bis (2-chloroethyl) amino)benzoyl-Lglutamic acid was synthesised by Springer et al (1990). It is a mustard glutamate prodrug (Figure 1) which has been designed and shown to be activated by CPG2 to form the active drug benzoic acid mustard (Bagshawe et al, 1988; Springer et al, 1990). In the studies presented here, the plasma and tissue distribution of the prodrug, the active drug and the activated prodrug derivative generated in vivo have been determined

Methods

Results

Conclusion