Replacement of an NH 3 by an Iminoether in Transplatin Makes an Antitumor Drug from an Inactive Compound MARC LENG, † DANIEL LOCKER, MARIE-JOS ` EPHE GIRAUD-PANIS, ANNIE SCHWARTZ, FRANCESCO P. INTINI, GIOVANNI NATILE, CLAUDIO PISANO, ANGELINA BOCCARELLI, DOMENICO GIORDANO, and MAURO COLUCCIA Centre de Biophysique Mole ´ culaire, Centre National de la Recherche Scientifique, Orle ´ ans, France (M.L., D.L., M.G.P., A.S.); Department of Pharmaceutical Chemistry, Bari, Italy (F.P.I., G.N.); Department of Oncology, Sigma-tau, Pomezia, Italy (C.P.); and Department of Biomedical Sciences and Human Oncology, Bari, Italy (A.B., D.G., M.C.) Received June 26, 2000; accepted September 6, 2000 This paper is available online at http://www.molpharm.org ABSTRACT To investigate the modifications of antitumor activity and DNA bind- ing mode of transplatin after replacement of one nonleaving group NH 3 by an iminoether group, trans-[PtCl 2 { Z-HN=C(OMe)Me}(NH 3 )] and trans-[PtCl 2 { E-HN=C(OMe)Me}(NH 3 )] complexes (differing in the Z or E configuration of iminoether, and abbreviated mixed Z and mixed E, respectively), have been synthesized. In a panel of hu- man tumor cell lines, both mixed Z and mixed E show a cytotoxic potency higher than that of transplatin, the mean IC 50 values being 103, 37, and 215 M, respectively. In vivo mixed Z is more active and less toxic than mixed E in murine P388 leukemia and retains its efficacy against SK-OV-3 human cancer cell xenograft in nude mice. In the reaction with naked DNA, mixed Z forms monofunc- tional adducts that do not evolve into intrastrand cross-links but close slowly into interstrand cross-links between complementary guanine and cytosine residues. The monofunctional mixed Z ad- ducts are removed by thiourea and glutathione. The interstrand cross-links behave as hinge joints, increasing the flexibility of DNA double helix. The mixed Z, transplatin, and cisplatin interstrand cross-links, as well as mixed Z monofunctional adducts are not specifically recognized by HMG1 protein, which was confirmed to be able to specifically recognize cisplatin d(GpG) intrastrand cross-links. These data demonstrate that the DNA interaction properties of the antitumor-active mixed Z are very similar to those of transplatin, thus suggesting that clinical inactivity of transplatin could not depend upon its peculiar DNA binding mode. Cisplatin, cis-diamminedichloroplatinum(II), is one of the most largely used drugs in cancer chemotherapy. It displays significant activity against several types of cancers with an exceptional efficacy against testicular cancers. Despite this success, all the patients treated with cisplatin suffer from severe side effects, and quite often tumors become resistant to cisplatin (O’Dwyer et al.,1999). In order to overcome these drawbacks and to get more efficient drugs, many platinu- m(II) complexes have been synthesized. Most of them have the cis geometry because transplatin, trans-diamminedichlo- roplatinum(II), the stereoisomer of cisplatin, is clinically in- efficient. A mechanistic explanation of transplatin inactivity has been based on the type of DNA adducts formed by this isomer, as well as on its chemical reactivity that could render the complex susceptible to deactivation before its delivery to the tumor site (Jamieson and Lippard, 1999, and references therein). However, several recent exceptions to the empiric rule that the presence of two leaving groups in cis position of platinum complexes is a necessary condition for their anti- tumor activity, have been reported. trans-Platinum(II) com- plexes with planar ligands (Farrell, 1996, and references therein), with iminoether (Coluccia et al., 1993; Natile and Coluccia, 1999) or asymmetric aliphatic amine ligands (Montero et al., 1999), and trans-ammine(amine)platinu- m(IV) complexes (Kelland et al., 1995), gave promising re- sults in in vitro and in vivo assays. Several trans-[PtCl 2 (iminoether) 2 ] complexes differing by the nature of the iminoether groups have been studied, and an overview of their main properties has been recently re- ported (Natile and Coluccia, 1999). Briefly, they show in vivo antitumor activity toward both lymphoproliferative and solid metastasizing murine tumors. Their cytotoxicity toward sev- eral human tumor cell lines is comparable to that of cisplatin. This work was supported in part by grants from Ligue Contre le Cancer Loiret, Agence Nationale pour la Recherche sur le Sida, Association pour la Recherche sur le Cancer, and European Union Cost D8/0007/97 and BMH4- CT97-2485 contracts. † Marc Leng worked to the last of his days on this paper, giving the most important contribution to its realization. Unfortunately, Marc died of cancer in May 2000, but neither our long collaboration nor our friendship are inter- rupted, because we will always remember the joy of staying together. ABBREVIATIONS: cisplatin and transplatin, cis- and trans-diamminedichloroplatinum(II); mixed E and mixed Z, trans-dichloro(ammine)(E- iminoether)platinum(II) and trans-dichloro(ammine)(Z-iminoether)platinum(II); ICL, interstrand cross-link; bp, base pairs; r i , input molar ratio of drug over nucleotide residues; dsDNA, double-stranded DNA; HMG1, high mobility group 1; %T/C, mean survival time (%) of treated animals versus controls; %TWI, percentage of tumor weight inhibition of treated mice versus controls; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. 0026-895X/00/061525-11$3.00/0 MOLECULAR PHARMACOLOGY Vol. 58, No. 6 Copyright © 2000 The American Society for Pharmacology and Experimental Therapeutics 380/866277 Mol Pharmacol 58:1525–1535, 2000 Printed in U.S.A. 1525 at ASPET Journals on September 8, 2017 molpharm.aspetjournals.org Downloaded from