A phase I trial of antibody directed enzyme prodrug therapy (ADEPT) in patients with advanced colorectal carcinoma or other CEA producing tumours

Abstract

Antibody-directed enzyme prodrug therapy is a targeted therapy in which a prodrug is activated selectively at the tumour site by an enzyme, which has been targeted to the tumour by an antibody (antibody-enzyme conjugate). Previous clinical trials have shown evidence of tumour response, however, the activated drug had a long half-life, which resulted in dose-limiting myelosuppression. Also, the targeting system, although giving high tumour to blood ratios of antibody-enzyme conjugate (10 000 : 1) required administration of a clearing antibody in addition to the antibody-enzyme conjugate. The purpose of this current study therefore was to attempt tumour targeting of the antibody-enzyme conjugate without the clearing antibody, and to investigate a new prodrug (bis-iodo phenol mustard, ZD2767P) whose activated form is highly potent and has a short halflife. Twenty-seven patients were treated with antibody-directed enzyme prodrug therapy using A5CP antibody-enzyme conjugate and ZD2767P prodrug, in a dose-escalating phase I trial. The maximum tolerated dose of ZD2767P was reached at 15.5 mg m 72 6three administrations with a serum carboxypeptidase G2 level of 0.05 U ml 71 . Myelosuppression limited dose escalation. Other toxicities were mild. Patients' quality of life was not adversely affected during the trial as assessed by the measures used. There were no clinical or radiological responses seen in the study, but three patients had stable disease at day 56. Human anti-mouse antibody and human anti-carboxypeptidase G2 antibody were produced in response to the antibody enzyme conjugate (A5CP). The antibody-enzyme conjugate localisation data (carboxypeptidase G2 enzyme levels by HPLC on tumour and normal tissue samples, and gamma camera analysis of I-131 radiolabelled conjugate) are consistent with inadequate tumour localisation (median tumour: normal tissue ratios of antibody-enzyme conjugate of less than 1). A clearance system is therefore desirable with this antibody-enzyme conjugate or a more efficient targeting system is required. ZD2767P was shown to clear rapidly from the circulation and activated drug was not measurable in the blood. ZD2767P has potential for use in future antibody-directed enzyme prodrug therapy systems.

Modifying an immunogenic epitope on a therapeutic protein: a step towards an improved system for antibody-directed enzyme prodrug therapy (ADEPT)

“…Results from these experiments showed that only 23% of patients (three out of 13) treated with MFECPHis had detectable HACA after a single administration of MFECPHis (Figure 7), while 97% (36/37) of patients had detectable HACA when treated with A5CP in previous trials (Napier et al, 2000;Francis et al, 2002). Fisher's exact test confirmed statistical significance (Po0.0001) between the HACA response of these two patient groups.…”

“…and MFEdmCPHis (endotoxin 1.1 EU ml À1 ) and the second experiment comparing MFECPHis and A5CP (endotoxin o0.1 EU ml À1 ). A5CP was supplied by Lonza Biologics (UK) for the previous clinical trial (Francis et al, 2002) and consists of an F(ab 0 ) 2 derived from the affinity-purified monoclonal anti-CEA antibody A5B7 covalently linked to CP (Melton et al, 1993). Groups of eight Balb/c mice were injected 4 Â intraperitoneally (i.p.)…”

“…Sera were obtained between 21 and 43 days after treatment with 3000 U m À2 A5CP (Francis et al, 2002) or 5000 U m À2 MFECPHis followed by the prodrug ZD2767P for ADEPT. Both studies were approved by the local research ethics committee and informed consent was obtained from all patients.…”

“…ADEPT aims to overcome the shortcomings of systemic cancer treatment such as lack of tumour selectivity and drug resistance. Clinical ADEPT studies (Bagshawe et al, 1995;Napier et al, 2000;Francis et al, 2002) have used the bacterial enzyme carboxypeptidase G2 (CP) conjugated to A5B7, a monoclonal anticarcinoembryonic antigen (CEA) F(ab) 2 . This antibody -enzyme conjugate, termed A5CP, has demonstrated feasibility of ADEPT and evidence of therapeutic response in patients with advanced CEA-expressing adenocarcinomas.…”

“…However, the development of human anti-CP antibody (HACA) and human anti-mouse antibody (HAMA) was a serious limitation of ADEPT with A5CP. HACA were observed in 97% and HAMA in 100% after single administration of A5CP (Napier et al, 2000;Francis et al, 2002). Hence, methods of reducing immunogenicity of the antibodyenzyme molecule are required since neutralising antibodies can inactivate therapeutics (Baert et al, 2003) and are potentially detrimental to the patient.…”