Analysis of a conjugate between anti-carcinoembryonic antigen monoclonal antibody and alkaline phosphatase for specific activation of the prodrug etoposide phosphate

Hidde J. Haisma, Epie Boven, Monique van Muijen, Robert De Vries, Herbert M. Pinedo

Research output: Contribution to journalArticle

Abstract

The selective targeting of tumours by enzymes conjugated to monoclonal antibodies (mAb) may be an ideal approach to convert relatively nontoxic prodrugs into active agents at the tumour site. We used the anti-carcinoembryonic antigen mAb BW431/26 conjugated to alkaline phosphatase (AP) and phosphorylated etoposide (etoposide-P) as a prodrug to study the feasibility of this concept. Etoposide was phosphorylated with POCl3. Quantitative hydrolysis of etoposide-P to etoposide occurred within 10 min in the presence of AP. BW431/26 and AP were conjugated using a thioether bond. The AP conjugate retained 93% of its calculated activity.125I-labelled AP conjugate did not show a reduction of immunoreactivity as determined by a cell-binding assay. SW1398 colon cancer cells were used to analyse the cytotoxicity of etoposide and etoposide-P. Etoposide (IC50 22 μM) was 100 times more toxic than etoposide-P (20% growth inhibition at 200 μM). Pretreatment of the cells with BW431/26-AP prior to etoposide-P exposure resulted in a dramatic increase in cytotoxicity (IC50 70 μM). The pharmacokinetics and tumour-localizing properties of BW431/27 and the AP conjugate were assessed in nude mice bearing SW1398 tumours. BW431/26 showed excellent tumour localization (10% of the injected dose/g tissue retained from 8 h to 120 h), whereas the AP conjugate showed a reduced tumour uptake (3%-0.3% of the injected dose/g tissue at 8-120 h), a faster clearance from the circulation and a high liver uptake. Radiolabelled AP showed a similar pharmacokinetic profile to the AP conjugate. Gel filtration analysis of blood, liver, and tumour samples indicated good stability of the conjugate.

Original languageEnglish (US)
Pages (from-to)343-348
Number of pages6
JournalCancer Immunology Immunotherapy
Volume34
Issue number5
DOIs
StatePublished - Sep 1992
Externally publishedYes

Keywords

  • Alkaline phosphatase
  • Etoposide
  • Monoclonal antibody
  • Prodrug activation

ASJC Scopus subject areas

  • Oncology
  • Immunology
  • Cancer Research

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