Gene expression profiling of tumors allows the establishment of relationships between gene expression profiles and sensitivity to anticancer drugs. In an attempt to study the molecular determinants of the activity of platinum compounds, we explored the publicly available databases of the National Cancer Institute (NCI; http://dtp.nci.nih.gov), which allow access to the gene expression profiles of the 60 cell lines for which drug cytotoxicity patterns already existed. Using this database, we have conducted an in silico research to identify the genes the expression of which was positively or negatively correlated to the sensitivity to four platinum compounds (cisplatin, carboplatin, oxaliplatin and tetraplatin). Important similarities were noticed between cisplatin and carboplatin on one hand, and tetraplatin and oxaliplatin on the other hand. In the restricted panel of 1416 genes and molecular markers, we identified 204 markers, among which 120 corresponded to identified genes, that significantly correlated (P < 0.001) with the cytotoxicity of at least one platinum compound. For example, the functionality of the p53-activated pathway appeared positively correlated with the cytotoxicity of all platinum compounds. More specific are the positive correlations between RAS gene mutations and MYC expression and the cellular sensitivity to oxaliplatin. Among the parameters already known as related to the sensitivity to platinum compounds, we identified, in the complete set of 9400 genes, numerous significant relationships, such as the negative correlations between ERB-B2 and BCL-X L expressions and the cytotoxicity of the platinum compounds. Public databases mining, therefore, appears to be a valuable tool for the identification of determinants of anticancer drug activity in tumors.

Irinotecan (CPT-11) is a new camptothecine derivative presently in development for the treatment of several advanced malignancies. It is converted in vivo to a highly potent metabolite, SN-38, by carboxylesterases. All camptothecine derivatives undergo lactonolysis in a pH-dependent reversible manner, generating inactive carboxylate forms. We have investigated in vitro the kinetics of transformation of CPT-11 to SN-38 by human liver microsomes originating from several donors. Microsomes from seven livers were studied individually or as a pooled preparation. CPT-11, either in its lactone or its carboxylate form, was added at a range of concentrations. The SN-38 formed was measured by HPLC with fluorometric detection. In the deacylation-limited carboxylesterase reaction, the linear steady-state kinetics between 10 and 60 min were determined. At all concentrations of CPT-11, the steady-state velocity of SN-38 formation as well as the intercept concentrations of SN-38 were about 2-fold higher when the substrate was under the lactone form than under the carboxylate form. We estimated the values (+/-SD) of K'm and Vmax to be 23.3 +/- 5.3 microM and 1.43 +/- 0.15 pmol/min/mg for the lactone and 48.9 +/- 5.5 microM and 1.09 +/- 0.06 pmol/min/mg for the carboxylate form of CPT-11, respectively. We conclude that the greater rate of conversion of CPT-11 lactone may contribute to the plasma predominance of SN-38 lactone observed in vivo. The inter-individual variation of SN-38 formation was relatively high (ratio of 4 between extreme values) but no large age- or gender-related differences were seen. The effect of twelve drugs of different therapeutic classes (antibiotics, antiemetics, antineoplastics, antidiarrhoeics, analgesics), which could be administered in association with irinotecan in the clinical setting, was evaluated in this system (drug concentration: 100 microM; CPT-11 lactone concentration: 10 microM). Loperamide and ciprofloxacine where the only drugs exerting a weak inhibition of CPT-11 conversion to SN-38.

Abstract:We have investigated the glucuronidation in vitro of SN-38, the active metabolite of irinotecan, a semi-synthetic anticancer drug derived from ZO(S)camptothecin. Preparations of human hepatic microsomes (final concentration : 1 mg prot./ml), were incubated for 1 hr in 0.1 M Tris buffer, pH 7.4, containing 10 mM MgC12, in the presence of UDPglucuronic acid (4 mM), saccharolactone (4 mM), and a detergent. Microsomes from five livers were studied individually or as a pooled preparation. SN-38, either in its lactone or its carboxylate form, was added at a range of concentrations. The SN-38 P-glucuronide formed was measured by HPLC with fluorometric detection. The glucuronidation reaction appeared linear over 1 hr in these conditions and Brij 35 at 0.5 mg/mg prot. was the best activator. The apparent parameters of the reaction were independent of the molecular form of the substrate. The half-saturation constant was 17-20 pM and Vmax was 60-75 pmol/min./mg prot. The interindividual variation of SN-38 glucuronidation was relatively low (ratio of 1.8 between extreme values). In addition, the effect of twelve drugs currently associated with irinotecan in clinics was evaluated in this system (drug concentration: 100 pM; SN-38 concentration: 5 pM). These produced little if any interference with SN-38 glucuronidation. Therefore, major interferences of this transformation by comedications are unlikely to occur in viva Irinotecan (7-ethyl-l0-[4-( 1-piperidin0)-1-piperidinolcarbonyloxycamptothecin), also known as CPT-11, is a semisynthetic derivative of 20(S)camptothecin with promising activity in colorectal cancer (Rougier & Bugat 1996). Camptothecins stabilize transient "cleavable" complexes formed between DNA and the nuclear enzyme topoisomerase I, which is required for DNA processing leading to DNA damage. This action appears to be more important than inhibition of the catalytic activity of topoisomerase I per se, and camptothecins are, therefore, considered to be "poisons" of this enzyme (Pommier 1996). Irinotecan is thought to exert its anticancer activity following transformation in vivo to a highly potent metabolite, SN-38 (7-ethyl-10-hydroxycampthothecin), and can be assumed to be essentially a prodrug of SN-38 (Kawato et al. 1991).During the study of plasma pharmacokinetics of irinotecan in 19 patients treated with this drug during phase 1/11 studies, we recently identified two major circulating metabolites and identified one of these as SN-38 p-glucuronide (Rivory & Robert 1995). The total plasma concentrations of this metabolite were found to be systematically higher than those of SN-38 in all patients studied . The elimination of SN-38 p-glucuronide from plasma closely paralleled that of SN-38 itself, suggesting that the transformation of SN-38 to the glucuronide was the rate-limiting step in the elimination Author for correspondence: Jacques Robert, Institut Bergonie, 180, rue Saint-Genes, F-33076 Bordeaux Cedex, France (fax +33 556 333389).of SN-38 and could play a key role in its pharmacokinetics (Rivo...