[CANCER RESEARCH 64, 356–362, January 1, 2004] Molecular Determinants of the Cytotoxicity of Platinum Compounds: The Contribution of in Silico Research Antoine Vekris,1 Delphine Meynard,2 Marie-Christine Haaz,1 Martine Bayssas,3 Jacques Bonnet,2 and Jacques Robert2 1DiGEM S. A., Bordeaux, France; 2Laboratory of Pharmacology of Anticancer Agents, CNRS FRE 2618 Institut Bergonie´and Universite´Victor Segalen Bordeaux 2, Bordeaux, France; and 3Debiopharm S. A., Lausanne, Switzerland ABSTRACT compounds presenting no cross-resistance with the original com- pound. Several hundreds of cisplatin analogs have been synthesized Gene expression profiling of tumors allows the establishment of rela- and screened in various systems, but only very few of them have tionships between gene expression profiles and sensitivity to anticancer shown a clinical interest deserving their introduction in the anticancer drugs. In an attempt to study the molecular determinants of the activity of platinum compounds, we explored the publicly available databases of the armamentarium (4). National Cancer Institute (NCI; http://dtp.nci.nih.gov), which allow access Carboplatin (see structure in Fig. 1), the first analog to be approved to the gene expression profiles of the 60 cell lines for which drug cytotox- for cancer chemotherapy, is now widely used in ovarian and testicular icity patterns already existed. Using this database, we have conducted an cancer as well as in the other indications of cisplatin. In contrast, the in silico research to identify the genes the expression of which was posi- toxicity profile of carboplatin is quite different from that of cisplatin, tively or negatively correlated to the sensitivity to four platinum com- with myelosuppression as the major dose-limiting toxicity. In view of pounds (cisplatin, carboplatin, oxaliplatin and tetraplatin). Important the similarity of their indications and the difference in toxicity targets, similarities were noticed between cisplatin and carboplatin on one hand, the combination of these two platinum compounds has been proposed and tetraplatin and oxaliplatin on the other hand. In the restricted panel as a means of minimizing the toxic symptoms while preserving the of 1416 genes and molecular markers, we identified 204 markers, among which 120 corresponded to identified genes, that significantly correlated antitumor efficiency (5). (P < 0.001) with the cytotoxicity of at least one platinum compound. For Another analog, oxaliplatin (see Fig. 1), is characterized by a example, the functionality of the p53-activated pathway appeared posi- completely different spectrum of activity: its main indication has been tively correlated with the cytotoxicity of all platinum compounds. More found in colorectal cancer, a malignancy that is quite refractory to the specific are the positive correlations between RAS gene mutations and classical platinum compounds. In contrast, no indication of this analog MYC expression and the cellular sensitivity to oxaliplatin. Among the has been found in germ cell tumors or squamous cell carcinomas. parameters already known as related to the sensitivity to platinum com- Oxaliplatin is now included in the classical protocols of treatment of pounds, we identified, in the complete set of 9400 genes, numerous signif- advanced colorectal carcinoma in combination with fluorouracil (6). icant relationships, such as the negative correlations between ERB-B2 and No other platinum compound is currently available in the clinical BCL-XL expressions and the cytotoxicity of the platinum compounds. Public databases mining, therefore, appears to be a valuable tool for the setting, although several have been tested in Phase I and II trials. identification of determinants of anticancer drug activity in tumors. Among them, tetraplatin (ormaplatin, NSC363812; Fig. 1) presents original features but its anticancer spectrum and toxicity pattern have not yet been fully identified (7). INTRODUCTION These four platinum compounds have been extensively studied The discovery and development of platinum compounds has been against in vitro and in vivo models, with a special emphasis on the one of the greatest achievements of cancer chemotherapy in the past 60-cell-line panel of the National Cancer Institute (NCI; Ref. 8). Rixe three decades. Cisplatin was accidentally discovered by Rosenberg in et al. (9) have established the comparative in vitro cytotoxicity pro- 1968 as an antibiotic and very rapidly as a very powerful antiprolif- files of these agents, and have shown a strong similarity between erative agent against tumor cells. It was rapidly introduced in clinical cisplatin and carboplatin on one hand and between oxaliplatin and use, principally for the treatment of germ cell tumors of testis and tetraplatin on the other hand. Using the program COMPARE to assess ovary (1). The spectrum of activity of cisplatin includes, in addition to similarities between cytotoxicity profiles, Rixe et al. found that the germ cell tumors, all types of squamous cell carcinomas but only Pearson correlation coefficients were 0.807 between cisplatin and some adenocarcinomas such as gastric cancer. The clinical use of carboplatin and 0.756 between oxaliplatin and tetraplatin but only cisplatin has been considerably hampered by its renal toxicity, which 0.30–0.34 between cisplatin and either oxaliplatin or tetraplatin, and may lead to definitive renal failure and which requires special proce- Ͻ0.1 between carboplatin and either oxaliplatin or tetraplatin (9). dures of administration (2). Neurological toxicity is also a problem, This clear-cut distinction between the two groups of platinum because long-term cisplatin administration may lead to disabling compounds can be interpreted as due to the existence of different peripheral neuropathy. mechanisms of action of the compounds, or at least of mechanisms of A considerable effort has been made by the pharmaceutical industry resistance. This prompted us to explore the molecular determinants of for the discovery of cisplatin analogs. The main goal of this research the activity of these compounds by establishing relationships between was the identification of compounds devoid of the limiting toxicity of gene expression profiles and sensitivity to platinum compounds of cisplatin (3). Also, the emergence of cisplatin-resistant relapsing tu- tumor models. The first step of this exploration can be the mining of mors after initial sensitivity has stimulated the research of active available data in public databases, especially the NCI database. The NCI has recently explored the expression of a panel of 9400 genes in Received 7/24/03; revised 10/3/03; accepted 10/7/03. the 60 cell lines that had been used for 10 years for establishing drug Grant support: Supported by the Ligue Nationale contre le Cancer, comite´de cytotoxicity patterns (10). Using this database, we have conducted an Charente Maritime. The costs of publication of this article were defrayed in part by the payment of page in silico analysis to identify, in the 60 cell lines of the panel and charges. This article must therefore be hereby marked advertisement in accordance with among the 1416 genes or markers that had given the strongest vari- 18 U.S.C. Section 1734 solely to indicate this fact. Requests for reprints: Jacques Robert, Institut Bergonie´, 229 cours de l’Argonne, ation pattern, the genes the expression of which was positively or 33076 Bordeaux-cedex, France. negatively correlated to the sensitivity to each of the platinum com- 356 Downloaded from cancerres.aacrjournals.org on September 23, 2021. © 2004 American Association for Cancer Research. MOLECULAR DETERMINANTS OF PLATINUM COMPOUNDS ACTIVITY mining the database of the Gene Ontology Consortium,6 which gathers in a convenient manner all of the information available concerning molecular and cellular functions of the genes products. In a second part of this work, we have explored the literature dealing with the identification of individual genes involved in cell sensitivity or resistance to platinum compounds. This identification originates mainly from studies on cisplatin- or oxaliplatin-resistant cell lines. Using this approach, we identified 18 genes or protein markers; the expression of these individual markers was searched in the whole NCI database, covering not only the original subset of 1376 genes and 40 individual molecular targets but also the complete set of 9400 genes and 255 molecular targets. The coefficients of correlation between the cytotoxicity of the four platinum compounds toward the 60 cell lines and the level of expression of these 18 markers were then calculated as for the exploratory step of 1416 markers. Coefficients of correlation should be used with caution in such studies: a highly significant correlation is in no way indicative of a causal relationship; in addition, a coefficient of correlation can be highly significant without Fig. 1. Structural formulas of the four platinum compounds of the study. showing a gene to be a strong determinant of drug activity. With 58 degrees of freedom, a coefficient of correlation is significant at the P Ͻ 0.001 level from 0.394 and above; this also means that only 16% (0.3942) of the variation is pounds of interest, cisplatin, carboplatin, oxaliplatin and tetraplatin. explained by the correlation. In contrast, a coefficient of correlation of 0.85 We present here the result of this research, which can be considered indicates that 72% of the variation observed can be explained by the correla-