Antibody-directed enzyme prodrug therapy: pharmacokinetics and plasma levels of prodrug and drug in a phase I clinical trial

Abstract

Antibody-directed enzyme prodrug therapy (ADEPT) was administered to ten patients in a phase I clinical trial. The aim was to measure plasma levels of the prodrug 4-[(2-chloroethyl)(2-mesyloxyethyl) amino] benzoyl-L-glutamic acid (CMDA) and the bifunctional alkylating drug (CJS11) released from it by the action of tumour-localised carboxypeptidase G2 (CPG2) enzyme. New techniques were developed to extract the prodrug and drug from plasma by solid-phase absorption and elution and to measure CPG2 activity in plasma and tissue. All extracts were analysed by high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). CPG2 activity was found in metastatic tumour biopsies but not in normal tissue, indicating that localisation had been successful. The clearing agent SB43-gal, given at 46.5 mg/m2, achieved the aim of clearing non-tumour-localised enzyme in the circulation, indicating that conversion of prodrug to drug could take place only at the site of localised conjugate. Plasma prodrug did not always remain above its required threshold of 3 microM for the "therapeutic window" of 120 min after dosing, but the presence of residual prodrug after the first administration of each day indicated that this could be achieved during the remaining four doses over the following 8 h. Despite considerable inter-patient prodrug plasma concentration variability, the elimination half-life of the prodrug was remarkably reproducible at 18 +/- 8 min. Rapid appearance of the drug in plasma indicated that successful conversion from the prodrug had taken place, but also undesirable leakback from the site of localisation into the bloodstream. However, drug plasma levels fell rapidly by at least 50% at between 10 and 60 min with a half-life of 36 +/- 14 min. Analysis of the plasma extracts by LC/MS indicated that this technique might be used to confirm qualitatively the presence of prodrug, drug and their metabolites.

In vivo activity in a catalytic antibody-prodrug system: Antibody catalyzed etoposide prodrug activation for selective chemotherapy

“…Administration of a foreign protein typically elicits a vigorous antibody response that limits repeated administration of the protein. Indeed, immunogenicity has been problematic in clinical studies of ADEPT (23). To suppress antibody responses against the enzyme-antibody conjugate, the immunosuppressive agent cyclosporin has been used in early clinical studies of the ADEPT approach (24).…”

Novel Gene Therapeutic Approaches to Brain Cancer

“…The species of origin for CD may produce more catalytically active forms as observed with S. cerevisiae CD compared to E. coli CD (160,161). Currently Phase I trials of adenovirally delivered CD in patients with metastatic liver disease are ongoing (162)(163)(164).…”

New approaches to antibody therapy

“…In preclinical models, this PRIT strategy yields exceptional, highly selective tumor targeting and impressive anti-tumor ecacy (Martin et al, 1997). These ®ndings have formed the basis for clinical trials Figure 2 Antibody-pretargeted therapy that have been associated with substantial toxicity and disappointing ecacy, due to several factors (Knox et al, 2000).…”

“…An inactive chemotherapy prodrug is then administered that rapidly clears from the host, but is selectively retained at tumor sites by the antibodytargeted enzyme to liberate the active chemotherapy agent at tumor sites (Bagshawe et al, 1993). Various iterations of this strategy have been tested in preclinical models and in human clinical trials (Bagshawe et al, 1991;Martin et al, 1997;Siemers et al, 1997). More recently, antibody pre-targeted radioimmunotherapy (PRIT) has been tested, primarily employing the antiEp-CAM antibody NR-LU-10, conjugated to streptavidin.…”