This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Rigaudy, P. Articles by Roques, B. P. Search for Related Content PubMed PubMed Citation Articles by Rigaudy, P. Articles by Roques, B. P.

Attempts to Target Antitumor Drugs toward Opioid Receptor-rich Mouse Tumor Cells with Enkephalin-Ellipticinium Conjugates¹

Département de Chimie Organique, U 266 INSERM, UA 498 CNRS, UER des Sciences Pharmaceutiques et Biologiques, 4 avenue de l'Observatoire, 75006 Paris [P. R., C. G-J., B. P. R.], and Unité de Physicochimie Macromoléculaire, Institut Gustave Roussy, Rue Camille Desmoulins, 94800 Villejuif [J-Y. C., A. J-S.], France

Human colorectal and pulmonary carcinomas have been shown to contain high levels of opioid peptides and their corresponding membranebound receptors. Therefore possible targeted drugs, consisting of modified enkephalins linked to cytotoxic drugs, were designed. Such conjugates were expected to be specifically internalized within opioid receptor-bearing cells. As a model to this approach, we have synthesized enkephalin-ellipticinium conjugates in which the D-Ala²-D-Leu⁵-enkephalin (DADLE) was coupled to the 2-nitrogen of either ellipticine or 9-hydroxyellipticine, two drugs acting through different mechanisms of cytotoxicity. These conjugates, DADLE-ellipticinium (NME) and DA-DLE-9-hydroxyellipticinium (NMHE), respectively, were previously shown to retain in vitro both opioid receptors and DNA affinities close to those of the parent compounds. In this paper, we first show that each individual moiety in the complexes remains capable of recognizing its cellular targets. Thus, pretreatment of NG108-15 cells containing -opioid receptors by the DADLE-ellipticinium conjugates induced a loss of opioid receptor (down-regulation), while the smaller peptide conjugates, tyrosinyl-D-alanylglycine-ellipticinium, prepared as control, do not. On the other hand, peptide-NMHE conjugates were able to induce DNA topoisomerase II-associated DNA strand breaks suggesting that they have a mode of action similar to that of their parent molecule, NMHE. We then examined whether or not these molecules could exert a specific toxicity on opioid receptor-bearing cells. However, when tested on NG108-15 tumor cells and L-fibroblasts as control, the enkephalin-ellipticinium conjugates (DADLE-NME and DADLE-NMHE) proved to be similarly more cytotoxic on both cell lines than their ellipticinium (NME and NMHE) precursors. In order to understand this apparent lack of specificity we examined the cellular accumulation and distribution of DADLE-NME by fluorescence techniques. These experiments revealed that an important intracellular overconcentration caused by a nonspecific process is probably masking the specific targeted effect of the conjugates. Hence, the project of linking DADLE to highly cytotoxic molecules which cannot cross the plasma membrane without site-directed targeting is discussed.

¹ This work was supported by funds from the Fondation pour la Recherche Médicale, the Association pour la Recherche sur le Cancer, the Ligue Nationale Française contre le Cancer, and the Institut National de la Santé et de la Recherche Médicale (Programme National de Recherche sur le SIDA-1987, Attribution 4644).

² To whom requests for reprints should be addressed.

Received 11/23/87. Revised 5/25/88. Revised 12/ 9/88. Accepted 1/ 3/89.