Antimetastatic effect of a novel indolocarbazole (NB-506) on IMC-HM murine tumor cells metastasized to the liver

Plasma stability of two glycosyl indolocarbazole antitumor agents

In recent years, several glycosyl indolocarbazole derivatives have been developed as antitumor agents targeting the topoisomerase I-DNA complex and a few of them were evaluated in clinical trials. The lead drug in the series is compound A which bears a formylamino substituent on the N-imide F-ring. This compound has shown promising antitumor activities in vivo and was tested clinically but it has been recently replaced with a more active analogue, J-107088, bearing a (hydroxymethyl-2-hydroxy) ethylamino substituent on the N-imide F-ring. We have compared the plasma stability of two molecules in this series, compounds A and D, which only differ by the nature of the group on the imide ring. The conversion of the compounds into the anhydride species B was studied by HPLC and the resulting metabolite, formed both in human plasma ultrafiltrate and in water, was characterized by NMR and mass spectrometry. Absorption measurements provided a facile method to follow the conversion of compounds A and D into their metabolite product B. Altogether, the experimental data demonstrate that the replacement of the NHCHO substituent of compound A with a hydrophilic NHCH(CH(2)OH)(2) chain preserves the intact imide function that is known to be essential for topoisomerase I inhibition and cytotoxicity. The transformation of compound A into the anhydride metabolite B (or its diacid open form) occurs much more slowly compared to compound D. Half-life parameter t(1/2) of 67 and 245 min(-1) were calculated for compounds A and D, respectively. A molecular modeling analysis, performed to compare the conformation and electronic properties of compounds A and D, offers a rational explanation for the gain of chemical stability of the indolocarbazole derivative D. The data provide important information for the rational design of antitumor indolocarbazole derivatives.

Structure-activity relationship in O-glucuronidation of indolocarbazole analogs

The glucuronidation of 6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13-(beta-D-glucopyranosyl)5H-indolo[2,3-a]pyrrolo[3,4-c]carbazole-5,7(6H)-dione (compound 1), a potent inhibitor of DNA topoisomerase I, and its related indolocarbazole compounds was studied using human liver microsomes. Compound 1 and its structurally related compounds with the NHCHO moiety at the N-6 position were glucuronidated even if the positions of the phenolic hydroxy moiety were different in these molecules. Compounds that have the NHCH(CH(2)OH)(2) moiety at the N-6 position, however, were not glucuronidated. The three-dimensional structure of these substrates was determined by the semiempirical molecular-orbitals calculation method. Computer-modeling studies, however, revealed that the O-glucuronidation of indolocarbazole analogs depended on the molecular size of the substrates. Compounds larger than 14.5 A in diameter perpendicular to the phenolic hydroxy moiety were not glucuronidated. The chemical reactivity of the hydroxy moiety, evaluated by the atom electron density and the electrostatic potential charges, was very similar in these substrates. These results suggest that a molecular length less than 14.5 A may be required for a substrate to interact with the active site of UDP-glucuronosyltransferase (UGT). To further characterize the glucuronidation of indolocarbazole analogs, compound 1 was used as a representative compound to assess expressed human UGTs. The glucuronidation of compound 1 was catalyzed by recombinant UGT1A9 and UGT1A10 among UGT isoforms tested.

Genomic construct and mapping of the gene for CMAP (leukocystatin/cystatin F, CST7) and identification of a proximal novel gene, BSCv (C20orf3)

It is proposed that CMAP (leukocystatin/cystatin F, HGMW-approved symbol CST7) expression is correlated with the metastatic potential of malignant tumors. FISH analysis of human and murine CMAP revealed the genomic loci 20p11.21-p11.22 of the human family 2 cystatin cluster and mouse chromosome region 2G1-G3, respectively. Like murine CMAP, the human CMAP gene is constructed from four divided exons, all of which encode the functional domains of the putative translational product. Based on the computational analysis, a novel gene weakly similar to the plant strictosidine synthase, named BSCv (HGMW-approved symbol C20orf3), was identified on the opposite allele at a distance of a few kilobases from the human CMAP gene. In between human CMAP and the BSCv gene, there is a unique tandem repeat sequence. CpG-rich island characteristics and GC-box features normally observed in housekeeping genes were not seen around exon 1 of the CMAP gene, reflecting the restricted expression of CMAP in hematopoietic cells.

NB-506, an indolocarbazole topoisomerase I inhibitor, binds preferentially to triplex DNA

A novel competition dialysis method was used to study the structural selectivity of the nucleic acid binding of NB-506, a promising indolocarbazole anticancer agent. A pronounced preference for NB-506 binding to the DNA triplex poly [dA]:(poly[dT])(2) was observed among potential binding to 12 different nucleic acid structures and sequences. Structures included in the assay ranged from single-stranded DNA, through a variety of right-handed DNA duplexes, to multistranded triplex and tetraplex forms. RNA and left-handed Z DNA were also included in the assay. The preferential binding to triplex was confirmed by UV melting experiments. The novel and unexpected structural selectivity shown by NB-506 may arise from a complementary shape between its extended aromatic ring system and the planar triplex stack.

In vivo anti-tumor activity of a novel indolocarbazole compound, J-107088, on murine and human tumors transplanted into mice

J-107088 (6-N-(1-hydroxymethyl-2-hydroxy)ethylamino-12,13-dihydro-2,10-dihydroxy- 13-(beta-D-glucopyranosyl)-5H-indolo[2,3-a]-pyrrolo [3,4-c]carbazole-5,7(6H)-dione) is a derivative of NB-506, an indolocarbazole compound previously reported as an anti-tumor agent targeting topoisomerase I. The optimal administration schedule of J-107088 was found to be intermittent injections. The GID75 (75% growth inhibiting total dose) values of J-107088 against LX-1 lung cancer and PC-3 prostate cancer when given by intermittent injection (twice a week for 2 consecutive weeks) were 200 and 15 mg/m2, respectively, whereas the 10% lethal dose (LD10) values of J-107088 against LX-1- and PC-3-bearing mice were 578 and 1200 mg/m2. The ratio of LD10/GID75 indicates the therapeutic window of an anti-tumor agent. Although the ratios of doxorubicin, paclitaxel and cisplatin against PC-3 were <0.3, <0.5 and <0.2, J-107088 showed the widest therapeutic window among the anti-tumor drugs tested. J-107088 was also effective on cells that had acquired resistance related to P-glycoprotein. Furthermore, J-107088 was found to be highly effective in inhibiting proliferation of micro-metastases of tumors to the liver in mice. Therefore, J-107088 is considered to be a promising candidate as an anti-tumor drug for treatment of solid tumors in humans.

Identification and cloning of a novel isoform of mouse secretory leukocyte protease inhibitor, mSLPI-beta, overexpressed in murine leukemias and a highly liver metastatic tumor, IMC-HA1 cells

Several genes showing transcriptional alteration in a highly liver metastatic murine carcinoma cell line, IMC-HA1, were identified by mRNA differential display system. Among them, a gene identical to mSLPI was isolated as mSLPI-alpha and -beta. They were produced through an alternative splicing. Their full-length cDNA sequences were determined, and their expression in various murine tumors and normal tissues was analysed. The deduced translation product of mSLPI-alpha showed 59% identity to hSLPI. Although mSLPI-beta had the same 103-amino-acid sequence from the carboxyl terminus, the amino terminus showed hydrophilicity opposite mSLPI-alpha or hSLPI. The mSLPI-alpha was expressed ubiquitously in various tumor cell lines. Interestingly, however, mSLPI-beta expression was only observed in P388 and L1210 leukemias and IMC-HA1 cells, and in lower amounts in three normal tissues (thymus, lung and spleen), suggesting that mSLPI, and in particular the unusual splicing product, mSLPI-beta, plays a specific role in these cells, including malignant processes of tumor cells.

Mechanism of action of eukaryotic DNA topoisomerase I and drugs targeted to the enzyme

DNA topoisomerase I is essential for cellular metabolism and survival. It is also the target of a novel class of anticancer drugs active against previously refractory solid tumors, the camptothecins. The present review describes the topoisomerase I catalytic mechanisms with particular emphasis on the cleavage complex that represents the enzyme's catalytic intermediate and the site of action for camptothecins. Roles of topoisomerase I in DNA replication, transcription and recombination are also reviewed. Because of the importance of topoisomerase I as a chemotherapeutic target, we review the mechanisms of action of camptothecins and the other topoisomerase I inhibitors identified to date.

Diversity of DNA topoisomerases I and inhibitors

The present review first describes the different type I topoisomerases found in eukaryotic cells: nuclear topoisomerase I (top1), topoisomerase 3 (top3), mitochondrial topoisomerase I and viral topoisomerases I. The second part of the review provides extensive information on the topoisomerase I inhibitors identified to date. These drugs can be grouped in two categories: top1 poisons and top1 suppressors. Both inhibit enzyme catalytic activity but top1 poisons trap the top1 catalytic intermediates ('cleavage complexes') while top1 suppressors prevent or reverse top1 cleavage complexes. The molecular interactions of camptothecin with the top1 cleavage complexes are discussed as well as the mechanisms of selective killing of cancer cells.