Metabolism of cytostatically active 6-aminobenzo[c]phenanthridines by human and porcine hepatic microsomes and recombinant cytochrome P450 enzymes

The Novel Dual Topoisomerase Inhibitor P8-D6 Shows Anti-myeloma Activity In Vitro and In Vivo

P8-D6 is a novel dual inhibitor of human topoisomerase I (TOP1) and II (TOP2) with broad pro-apoptotic antitumor activity. NCI-60 screening revealed markedly improved cytotoxicity of P8-D6 against solid and leukemia cell lines compared with other single and dual topoisomerase inhibitors, for example, irinotecan, doxorubicin, or pyrazoloacridine. In this study, we investigated the capacity of P8-D6 to inhibit myeloma cell growth in vitro and in vivo Growth inhibition assays demonstrated significant anti-myeloma effects against different myeloma cell lines with IC₅₀ values in the low nanomolar range. Freshly isolated plasma cells of patients with multiple myeloma were killed by P8-D6 with similar doses. P8-D6 activated caspase 3/7 and induced significant apoptosis of myeloma cells. Supportive effects of bone marrow stromal cells on IL6-dependent INA-6 myeloma cells were abrogated by P8-D6 and apoptosis occurred in a time- and dose-dependent manner. Of note, healthy donor peripheral blood mononuclear cells and human umbilical vein endothelial cells were not affected at concentrations toxic for malignant plasma cells. Treatment of myeloma xenografts in immunodeficient SCID/beige mice by intravenous and, notably, also oral application of P8-D6 markedly inhibited tumor growths, and significantly prolonged survival of tumor-bearing mice.

Enantioselective Distribution, Degradation, and Metabolite Formation of Myclobutanil and Transcriptional Responses of Metabolic-Related Genes in Rats

Myclobutanil (MT), a chiral fungicide, can be metabolized enantioselectively in organisms. In this work, the associated absorption, distribution, metabolism and transcriptional responses of MT in rats were determined following a single-dose (10 mg·kg^-1 body weight) exposure to rac-, (+)- or (-)-MT. The enantiomer fractions (EFs) were less than 0.5 with time in the liver, kidney, heart, lung, and testis, suggesting preferential enrichment of (-)-MT in these tissues. Furthermore, there was conversion of (+)-form to (-)-form in the liver and kidney after 6 h exposure to enantiopure (+)-MT. Enrichment and degradation of the two enantiomers differed between rac-MT and MT-enantiomers groups, suggesting that MT bioaccumulation is enantiomer-specific. Interestingly, the degradation half-life of MT in the liver with rac-MT treatment was shorter than that with both MT-enantiomer treatments. One reason may be that the gene expression levels of cytochrome P450 1a2 ( cyp1a2) and cyp3a2 genes in livers treated with rac-MT were the highest among the three exposure groups. In addition, a positive correlation between the expression of cyp2e1 and cyp3a2 genes and rac-MT concentration was found in livers exposed to rac-MT. Simultaneously, five chiral metabolites were detected, and the enantiomers of three metabolites, RH-9090, RH-9089, and M2, were separated. The detected enantiomers of (+)-MT metabolites were in complete contrast with those of (-)-MT metabolites. According to the results, a metabolic pathway of MT in male rats was proposed, which included the following five metabolites: RH-9089, RH-9090, RH-9090 Sulfate, M1, and M2. The possible metabolic enzymes were marked in the pathway. The findings of this study provide more specific insights into the enantioselective metabolic mechanism of chiral triazole fungicides.

11-Substituted Benzo[c]phenanthridines: New Structures and Insight into Their Mode of Antiproliferative Action

The synthesis of various new structures of a library of 11-substituted 6-amino-11,12-dihydrobenzo[c]phenanthridines (BP) and 11-substituted 6-aminobenzo[c]phenanthridines (BP-D) is presented. These structures, further synthetic modifications, and the preparation of follow-up products which delivered about 40 new derivatives are described. Their potential as antiproliferative drug candidates was investigated by comparison of NCI 60 developmental therapeutics program (DTP) human tumor cell line screening data based on the results of in vitro tumor cell growth inhibition, including about 40 hitherto unpublished compound test results with up to 60 cancer cell lines. NCI-COMPARE studies helped to suggest the modes of action of the highly active antiproliferative drugs. These findings are supported by in vitro biological investigations showing either inhibition of tubulin polymerization and depolymerization or topoisomerase inhibition. Together with physicochemical parameters of the drug candidates, structure-activity relationships are critically discussed. Tubulin interaction or inhibition of topoisomerase I and IIα/β activity are two rationales that can explain the antiproliferative activity observed in the NCI 60 DTP human tumor cell line screen. However, it can also be reasonably assumed that these compounds address several targets, thus prohibiting the identification of simple structure-activity relationships. The new structures described herein are thought to act as so-called multitarget drugs, thus being of special interest in the area of multidrug resistance.