Novel diamidino-substituted derivatives of phenyl benzothiazolyl and dibenzothiazolyl furans and thiophenes: synthesis, antiproliferative and DNA binding properties

A series of new diamidino-, diisopropylamidino-, and diimidazolinyl-substituted derivatives of phenyl benzothiazolyl and dibenzothiazolyl furans and thiophenes were successfully prepared and evaluated for their antiproliferative activity on tumor cell lines in vitro, DNA binding propensity, and sequence selectivity as well as cellular distribution. A strong antiproliferative effect of the tested compounds was observed on all tested cell lines in a concentration-dependent response pattern. In general, imidazolinyl-substituted derivatives and/or the thiophene core were in correlation with increased antiproliferative activity. Two compounds (2b and 3b) were chosen for biological studies due to their differential antiproliferative properties. The DNA binding properties of this new series of compounds were assessed and evidenced their efficient minor groove binding properties with preferential interaction at AT-rich sites. Both compounds also present nuclear subcellular localization, suggesting that their cellular mode of action implies localization in the DNA compartment and direct inhibition of DNA replication and induction of apoptosis.

Rebeccamycin derivatives as dual DNA-damaging agents and potent checkpoint kinase 1 inhibitors

Rebeccamycin is an indolocarbazole class inhibitor of topoisomerase I. In the course of structure-activity relationship studies on rebeccamycin derivatives, we have synthesized analogs with the sugar moiety attached to either one or both indole nitrogens. Some analogs, especially those with substitutions at the 6' position of the carbohydrate moiety, exhibit potent inhibitory activity toward checkpoint kinase 1 (Chk1), a kinase that has a major role in the G(2)/M checkpoint in response to DNA damage. Some of these compounds retained a genotoxic activity either through intercalation into the DNA and/or by topoisomerase I-mediated DNA cleavage. We explored the structure-activity relationship between these compounds and their multiple targets. These rebeccamycin derivatives represent a novel class of potential antitumor agents that have a dual effect and might selectively induce the death of cancer cells.

Direct inhibition of the DNA-binding activity of POU transcription factors Pit-1 and Brn-3 by selective binding of a phenyl-furan-benzimidazole dication

The development of small molecules to control gene expression could be the spearhead of future-targeted therapeutic approaches in multiple pathologies. Among heterocyclic dications developed with this aim, a phenyl-furan-benzimidazole dication DB293 binds AT-rich sites as a monomer and 5'-ATGA sequence as a stacked dimer, both in the minor groove. Here, we used a protein/DNA array approach to evaluate the ability of DB293 to specifically inhibit transcription factors DNA-binding in a single-step, competitive mode. DB293 inhibits two POU-domain transcription factors Pit-1 and Brn-3 but not IRF-1, despite the presence of an ATGA and AT-rich sites within all three consensus sequences. EMSA, DNase I footprinting and surface-plasmon-resonance experiments determined the precise binding site, affinity and stoichiometry of DB293 interaction to the consensus targets. Binding of DB293 occurred as a cooperative dimer on the ATGA part of Brn-3 site but as two monomers on AT-rich sites of IRF-1 sequence. For Pit-1 site, ATGA or AT-rich mutated sequences identified the contribution of both sites for DB293 recognition. In conclusion, DB293 is a strong inhibitor of two POU-domain transcription factors through a cooperative binding to ATGA. These findings are the first to show that heterocyclic dications can inhibit major groove transcription factors and they open the door to the control of transcription factors activity by those compounds.

Design, synthesis and biological evaluation of new oligopyrrole carboxamides linked with tricyclic DNA-intercalators as potential DNA ligands or topoisomerase inhibitors

In the context of the design and synthesis of minor groove binding and intercalating DNA ligands some new oligopyrrole carboxamides were synthesized. These hybrid molecules (combilexins) possess a variable and conformatively flexible spacer at the N-terminal end. As intercalating tricyclic systems acridone, acridine, anthraquinones and in a special case iminostilbene terminate the N-terminal end of the pyrrole chain. The cytotoxicity was examined by the NCI antitumor screening, furthermore, biophysical as well as biochemical studies were performed in order to get some information about the DNA binding properties and topoisomerase inhibition effect of this new series of molecules.

Amino- and glycoconjugates of pyrido[4,3,2-kl]acridine. Synthesis, antitumor activity, and DNA binding

A series of amino- and glycoconjugates of pyrido[4,3,2-kl]acridine and pyrido[4,3,2-kl]acridin-4-one have been prepared. The most active molecules, the amino conjugates 7 and 11, display a cytostatic activity against HT-29 cancer cells at micromolar concentration. This activity correlates well with a strong DNA binding. The molecules, amino or glycoconjugates, bind DNA by intercalation, the amino or glyco substituent being located in one groove. None of the molecules inhibits topoisomerase activity.

Synthesis and Biological Evaluation of 4-Arylcoumarin Analogues of Combretastatins

A series of A-ring polymethoxylated neoflavonoids was prepared by ligand coupling reactions involving either Suzuki or Stille reactions. Cytotoxicity studies indicated a potent activity against a CEM leukemia cell line for the compounds presenting a substitution pattern related to that of combretastatin A-4. The two compounds having a 3'-OH and a 4'-OCH(3) substituents on the 4-phenyl B-ring have no effect on human topoisomerases I and II but potently inhibit, in vitro, microtubule assembly. At the cell level, the active compounds were characterized as proapoptotic agents, but they can also trigger cell death via a nonapoptotic pathway.

Chromophore-modified bisnaphthalimides: DNA recognition, topoisomerase inhibition, and cytotoxic properties of two mono- and bisfuronaphthalimides

Bisnaphthalimides represent a promising group of DNA-targeted anticancer agents. In this series, the lead compounds elinafide and bisnafide have reached clinical trials, and the search for more potent analogues remains a priority. In the course of a medicinal chemistry program aimed at discovering novel antitumor drugs based on the naphthalimide skeleton, different dimeric molecules containing two tetracyclic neutral DNA intercalating chromophores were synthesized. The naphthalimide unit has been fused to a benzene ring (azonafide derivatives), an imidazole, a pyrazine, or, as reported here, a furan ring which increases the planar surface of the chromophore and enhances its stacking properties. We report a detailed investigation of the DNA binding capacity of the dimeric molecule MCI3335 composed of two furonaphthalimide units connected by a 12 A long amino alkyl linker [(CH(2))(2)-NH-(CH(2))(3)-NH-(CH(2))(2)] identical to that of elinafide. Qualitative and quantitative binding studies, in particular using surface plasmon resonance, establish that the dimer binds considerably more tightly to DNA (up to 1000 times) than the corresponding monomer and exhibits a higher sequence selectivity for GC-rich sequences. DNase I footprinting experiments attest that the dimer, and to a lesser extent the monomer, preferentially intercalate at GC sites. The strong binding interaction between the drugs and DNA perturbs the relaxation of supercoiled DNA by topoisomerases, but the test compounds do not promote DNA cleavage by topoisomerase I or II. Despite the lack of poisoning effect toward topoisomerase II, MCI3335 displays a very high cytotoxicity toward CEM human leukemia cells, with an IC(50) in the low nanomolar range, approximately 4 times inferior to that of the reference drug elinafide. Confocal microscopy observations indicate that the monomer shows a stronger tendency to accumulate in the cell nuclei than the dimer. The extremely high cytotoxic potential of MCI3335 is attributed to its enhanced capacity to bind to DNA and to inhibit DNA synthesis, as evidenced by flow cytometry experiments using the BrdU assay. The results provide novel mechanistic information that furthers the understanding of the structure-activity relationships in the bisnaphthalimide series and identify MCI3335 as a novel lead compound for further preclinical investigations.

Induction of apoptosis in HL-60 leukemia and B16 melanoma cells by the acronycine derivative S23906-1

The benzoacronycine derivative S23906-1 is a highly potent antitumor agent with a broad spectrum of activity against different human solid tumor xenografts. The marked cytotoxic potential of this drug may be the result of its interaction with DNA but the precise mechanism of action remains unclear at present. We have investigated the induction of apoptosis in human promyelocytic leukemia HL-60 and murine melanoma B16 cells treated with S23906-1. With both cell lines, the drug induces cell cycle perturbations (G2/M arrest) and triggers apoptosis as revealed by the externalization of Annexin V-targeted PS residues at the periphery of the cells. But the biochemical pathways leading to apoptosis are different for the two cancer cell lines. In HL-60 cells, the drug induces significant variations of the Delta Psi(mt), measured by flow cytometry using the fluorochromes JC-1 and cm-X-ros. Activation of caspase-3 and chromatin condensation in HL-60 cells exposed to submicromolar concentrations of S23906-1 for 24hr were also clearly seen by flow cytometry and confocal microscopy experiments. In contrast, the extent of apoptosis induced by S23906-1 was found to be much more limited in B16 cells. No significant variations of Delta Psi(mt) and no cleavage of the fluorescent caspase-3 substrate GDEVDGI (PhiPhiLux-G(1)D(2) probe) could be detected by cytometry in B16 cells exposed to S23906-1. In addition, we characterized the mitochondrial production of reactive oxygen species (ROS) using the probe dihydroethidine (HE) and the variations of the mitochondrial mass using the cardiolipin-interacting probe nonyl acridine orange (NAO). S23906-1 stimulates the production of ROS in both cell lines but the number of mitochondria seems to increase only in drug-treated B16 cells. Collectively these findings identify S23906-1 as a potent inducer of cell apoptosis in the leukemia cells and to a lower extent in the melanoma cells. The results help to understand the downstream cytotoxic actions of this new anticancer agent which is currently undergoing preclinical development.

Apoptosis induced by the homocamptothecin anticancer drug BN80915 in HL-60 cells

The homocamptothecin (hCPT) derivative BN80915 containing a seven-membered lactone ring represents one of the most potent topoisomerase I inhibitors described. This anticancer agent, currently undergoing phase I clinical trials, has been shown to produce a greater number of DNA strand breaks than conventional camptothecins with a six-membered lactone ring. To shed light on the mechanism of action of hCPT at the cellular level, we compared the effects of BN80915 and the classic camptothecin SN-38, the active metabolite of irinotecan, on HL-60 human promyelocytic cancer cells. A variety of biochemical events, at both the mitochondrial and the nuclear levels, were characterized to determine how and to what extent the hCPT derivative can induce apoptotic cell death. The use of cytometry, Western blot analysis, confocal microscopy, and different colorimetric assays enabled us to demonstrate that BN80915 is a potent inducer of apoptosis in HL-60 cells. This induction of apoptosis is associated with cell cycle changes, a marked decrease of intracellular pH, activation of caspase-3 and -8, DNA fragmentation, and externalization of phosphatidylserine lipids but no significant changes of the mitochondrial membrane potential or the expression of Bcl-2. The interconnections between these different events are discussed. Collectively, the results indicate that the superior activity expressed at the topoisomerase I level leads to a more pronounced induction of apoptosis by BN80915 compared with SN-38. The study identifies and delineates signaling factors involved in BN80915-induced apoptosis in HL-60 cells.

Genomic organization and refined mapping of the human nuclear corepressor 2 (NCOR2)/ silencing mediator of retinoid and thyroid hormone receptor (SMRT) gene on chromosome 12q24.3

The human nuclear co-repressor 2 (N-CoR2) gene (NCOR2, previously called silencing mediator for retinoid and thyroid hormone receptor SMRT) is recruited to nuclear and non-nuclear receptors in a large repressing complex containing also N-CoR1, mSin3 and HDACs. This large complex represses transcription in absence of ligand. Herein we report the high- resolution and refined mapping of NCOR2 at the boundary of sub-bands 12q24.23 and 12q24.31, and its intron/exon structure. The gene contains 45 exons. This information should allow further study of potential NCOR2 genomic alteration in some subsets of malignancies.

Nonrandom 4p13 rearrangements of the RhoH/TTF gene, encoding a GTP-binding protein, in non-Hodgkin's lymphoma and multiple myeloma

We recently isolated the RhoH/TTF gene by its fusion to the LAZ3/BCL6 gene, in a non-Hodgkin's lymphoma (NHL) cell line, which bore a t(3;4)(q27;p11-13) translocation. This gene encodes a novel Rho GTP-binding protein and is specifically expressed in hematopoietic tissues. We made its precise mapping at band 4p13, and described its partial genomic structure. Using fluorescence in situ hybridization and molecular analyses, we report here on the rearrangement of the RhoH/TTF gene, at band 4p13, in four cases of NHL with t(3;4)(q27;p13) translocation and its fusion to the LAZ3/BCL6 gene at band 3q27, in three of these cases. RT-PCR analysis of two cases allowed the detection of variable fusion transcripts emerging from the rearranged alleles, and in one case, a deregulated expression of both RhoH/TTF and LAZ3/BCL6 genes, by promoter substitution, was observed. We also show here another rearrangement of the RhoH/TTF gene in a patient with multiple myeloma and t(4;14)(p13;q32) translocation, with breakage within the IGH gene. It is the first report which describes the recurrent chromosomal alteration of a GTP-binding protein encoding gene, in patients with hematopoietic malignancies.

Nonrandom fusion of L-plastin(LCP1) and LAZ3(BCL6) genes by t(3;13)(q27;q14) chromosome translocation in two cases of B-cell non-Hodgkin lymphoma

The LAZ3(BCL6) gene on chromosome band 3q27 is nonrandomly disrupted in B-cell non-Hodgkin lymphoma (B-NHL) by chromosomal translocations clustered within a 3.3-kb MTC (major translocation cluster) located between the two first noncoding exons. These translocations generally result in the expression of a chimeric mRNA transcript between the LAZ3 gene and sequences derived from the partner chromosome. Using RACE RT-PCR, we previously demonstrated fusion of LAZ3 with the RhoH/TTF gene, a hemopoietic cell-specific small GTPase involved in cytoskeleton organization, and with the BOB1/OBF1 gene, a B-cell-specific coactivator of octamer-binding transcription factors, following translocations t(3;4)(q27;p13) and t(3;11)(q27;q23), respectively. Here we report the identification of the L-Plastin(LCP1) gene as a novel LAZ3 partner in chimeric transcripts resulting from a t(3;13)(q27;q14) translocation, in two cases of B-cell lymphoma. As a consequence of the translocation, the 5' regulatory region of each gene was exchanged, creating both LCP1-LAZ3 and reciprocal LAZ3-LCP1 fusion transcripts in one case, and only a LCP1-LAZ3 fusion transcript in the other. The 13q14 chromosome region is frequently disrupted in various proliferative disorders, and the LCP1 gene defines a new breakpoint site in this region. This gene encodes an actin-binding protein and is the second LAZ3 partner gene, with the RhoH/TTF gene, involved in actin cytoskeleton organization. Genes Chromosomes Cancer 26:97-105, 1999.

The B cell transcriptional coactivator BOB1/OBF1 gene fuses to the LAZ3/BCL6 gene by t(3;11)(q27;q23.1) chromosomal translocation in a B cell leukemia line (Karpas 231)

The LAZ3/BCL6 gene on chromosone 3q27 is recurrently disrupted in B cell non-Hodgkin's lymphomas by translocations involving immunoglobulin genes or other chromosone regions. We have cloned the breakpoint region and chromosone derivatives of the t(3;11)(q27;q23.1) translocation, present in a B cell leukemia cell line (Karpas 231), which define a novel 11q23.1 breakpoint site. As a consequence of the translocation, LAZ3 regulatory regions upstream of non-coding exon 2 are replaced by those of BOB1/OBF1, a recently described B cell-specific coactivator of octamer-binding transcription factors. A detailed structural study of the BOB1/OBF1 genomic DNA and of a nearly full-length cDNA revealed particular features in the 3' untranslated region, such as an Alu motif and a polymorphic tetranucleotide microsatellite. Two mutations leading to two potential amino acid changes in the C-terminal region, were also detected in one allele of a lymphoma B cell line, Raji. Due to its cell-specific expression and role as a coactivating transcription factor, chromosomal translocation and/or point mutation of BOB1/OBF1 may contribute to B cell tumorigenesis.

Fusion of the LAZ3/BCL6 and BOB1/OBF1 genes by t(3; 11) (q27; q23) chromosomal translocation

The LAZ3/BCL6 gene on chromosome 3q27 is recurrently disrupted in B-cell non Hodgkin's lymphomas by translocations involving immunoglobulin genes or other chromosome regions. We have studied the t(3; 11) (q27; q23) translocation, present in a B-cell leukemia cell line (Karpas 231). As a consequence of this translocation, a LAZ3 chimeric transcript was created by fusion, 5' to the LAZ3 exon 2, with a transcribed sequence identical to BOB1/OBF1, a B cell-specific coactivator of octamer-binding transcription factors, recently described. Nucleotidic sequence of a nearly full-length cDNA of the BOB1/OBF1 gene revealed particular features in the 3' untranslated region of the gene, including pyrimidine-rich sequence repeats, an Alu motif, and a polymorphic [CCTT] tetranucleotide microsatellite. Two A to G transition mutations were also detected in the coding region of one allele of a lymphoma B-cell line, Raji, leading to 2 amino-acid changes in the C-terminal region. Due to its cell-specificity and role as a coactivating transcription factor, chromosomal translocation and/or perhaps point mutation of BOB1/OBF1 may contribute to B cell tumorigenesis.

TTF, a gene encoding a novel small G protein, fuses to the lymphoma-associated LAZ3 gene by t(3;4) chromosomal translocation

We have previously shown that the LAZ3/BCL6 gene encoding a potential transcription factor, is disrupted in B-diffuse large cell non-Hodgkin's lymphomas (NHL) with 3q27 chromosomal abnormalities involving the immunoglobulin (IG) genes. However, LAZ3 rearrangement also occurs in NHL bearing 3q27 translocations without involvement of the IG genes: for example the VAl cell line exhibits t(3;4)(q27;p11). In the present work we have used a RT-PCR method to detect and to sequence the LAZ3 mRNA products from the VAL cell line. We report that the consequence of the t(3;4) is the expression of a chimeric transcript of LAZ3 with a new gene encoding a small G-like protein, termed TTF (Translocation Three Four). Nucleotide sequence analysis of a 1.4 kb cDNA predicts that the TTF gene encodes a protein of 191 amino-acids similar to members of the RAS superfamily including HRAS (27% identical), RAB1A (30% identical) and RHO proteins: the human RAC1, RHOB and CDC42Hs proteins (respectively 43, 44 and 45% identical) and the yeast RHO2 protein (44% identical). Unlike most other small G proteins which are expressed ubiquitously, TTF was transcribed only in hemopoietic cells as a 2.2 kb transcript. TTF may define a new subgroup of RHO-like proteins.

Molecular cloning of a t(11;14)(q13;q32) translocation breakpoint centromeric to the BCL1-MTC

In B-cell malignancies, the t(11;14)(q13;q32) at the 11q13 BCL1 locus is characterized by a scattering of breakpoint sites along a 100 kb genomic region, between the BCL1 major translocation cluster (MTC) and the PRAD1 (also termed cyclin D1 or CCND1) gene. Recently, the 11q13 breakpoint region was extended on both sides, centromeric to the MTC and telomeric to PRAD1. We report here the molecular cloning of a new t(11;14) breakpoint site, 20 kb centromeric to the MTC, from a patient with prolymphocytic leukemia. We subcloned a non-repetitive DNA fragment near the breakpoint and mapped this new 11q13 probe (pHO11c) relative to already identified breakpoint sites, using long- and short-range physical mapping within the BCL1 locus. Rearrangements in the BCL1 locus are associated with deregulation of the PRAD1 gene, which is often overexpressed, particularly in mantle-cell malignancies. The detectable but weak PRAD1 expression in the case we present suggests that this breakpoint centromeric to the MTC still lies inside the BCL1 locus boundaries. We think that attention should be focused on this region centromeric to the BCL1-MTC, where the investigation of previously unidentified translocations may increase understanding of the PRAD1 gene deregulation in t(11;14) associated pathologies.