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

Abstract

Sunmary 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 tsmol kg-' intraperitoneally) to mice bearing human choriocarcinoma xenografts. Prodrug and active drug both followed a two-compartment kinetic model. Prodrug was eliminated more rapidly (t,/2 = 0.12 h, t,/2P = 0.70 h) than active drug (t,/2a = 0.37 h, t,12P = 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-'). 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.

Novel Prodrugs of Alkylating Agents Derived from 2-Fluoro- and 3-Fluorobenzoic Acids for Antibody-Directed Enzyme Prodrug Therapy

“…3 Hz, H-3), 6.40 (dd, 1 H, Jh-5,h-6 = 8. 6 Hz, H-5), 7.42 (dd, 1 H, JH-6,f = 8. 7 Hz, H-6), 7.69 (dd, 1 H, Jh-n h-c = 6.8 Hz, Jh-n,f = 13.9 Hz, NH); 19F NMR ó -112.…”

In silico design, synthesis, and biological evaluation of radioiodinated quinazolinone derivatives for alkaline phosphatase–mediated cancer diagnosis and therapy

“…The major advantages provided by antibody-directed, enzyme -prodrug therapy are (a) low normal tissue toxicity (prodrug is mildly toxic), (b) specific conversion of prodrug in tumors, (c) high prodrug-to-drug turnover, and (d) a bystander effect. However, at a minimum, antibodydirected, enzyme -prodrug therapy has two major limitations: (a) to be therapeutically effective, the cytotoxic agent must be internalized by each cell within the tumor mass (21 -23) and (b) the toxic agents formed have relatively long biological half-lives (24) and have been shown to escape from within the tumor mass, thereby decreasing tumor therapeutic efficacy and increasing nonspecific normal tissue toxicity (21). The alternative concept of genedirected, enzyme -prodrug therapy (25 -27) uses a variety of vector systems, including liposomes, replicating and nonreplicating viruses, and anaerobic bacteria, to deliver to and express in tumor cells the gene coding for an exogenous enzyme.…”

Prostate-specific antigen: a diagnostic marker and a tool for targeted delivery of drugs to prostate tumours

“…The drugs generated in this manner would be expected to diffuse into tumour cells and cause their growth inhibition or death [42]. Unfortunately, plasma and other normal tissues are often capable of activating the prodrugs, due partly to the presence elsewhere of the converting enzyme and partly to the binding of antibodyenzyme conjugate at non-tumour sites, most likely through Fc receptors [43]. In addition, the targeted enzymes are generally of microbial origin [106,107], thus, potentially producing antibody responses in humans.…”