Synthesis, antitumor activity, and mechanism of action of benzo[b]chromeno[6,5-g][1,8]naphthyridin-7-one analogs of acronycine

A series of 6-methoxy-3,3,14-trimethyl-3,14-dihydro-7H-benzo[b]chromeno[6,5-g][1,8]naphthyridin-7-one (4), 13-aza derivatives of benzo[b]acronycine, the isomeric 5-methoxy-2,2,13-trimethyl-2,13-dihydro-6H-benzo[b]chromeno[7,6-g][1,8]naphthyridin-6-one (5), and related cis-diols mono- and diesters were designed and synthesized. Their in vitro and in vivo biological activities were evaluated. As previously observed in the acronycine series, esters were the most potent derivatives exhibiting submicromolar activities; among them monoesters are particularly active. Racemic diacetate 21 showed a strong activity against KB-3-1 cell lines and was selected for in vivo evaluation and proved to be active, inhibiting tumor growth by more than 80%. After separation of the two enantiomers, compounds 21a and 21b were also evaluated against C38 colon adenocarcinoma; their activities were found to be significantly different.

S49076 is a novel kinase inhibitor of MET, AXL, and FGFR with strong preclinical activity alone and in association with bevacizumab

Aberrant activity of the receptor tyrosine kinases MET, AXL, and FGFR1/2/3 has been associated with tumor progression in a wide variety of human malignancies, notably in instances of primary or acquired resistance to existing or emerging anticancer therapies. This study describes the preclinical characterization of S49076, a novel, potent inhibitor of MET, AXL/MER, and FGFR1/2/3. S49076 potently blocked cellular phosphorylation of MET, AXL, and FGFRs and inhibited downstream signaling in vitro and in vivo. In cell models, S49076 inhibited the proliferation of MET- and FGFR2-dependent gastric cancer cells, blocked MET-driven migration of lung carcinoma cells, and inhibited colony formation of hepatocarcinoma cells expressing FGFR1/2 and AXL. In tumor xenograft models, a good pharmacokinetic/pharmacodynamic relationship for MET and FGFR2 inhibition following oral administration of S49076 was established and correlated well with impact on tumor growth. MET, AXL, and the FGFRs have all been implicated in resistance to VEGF/VEGFR inhibitors such as bevacizumab. Accordingly, combination of S49076 with bevacizumab in colon carcinoma xenograft models led to near total inhibition of tumor growth. Moreover, S49076 alone caused tumor growth arrest in bevacizumab-resistant tumors. On the basis of these preclinical studies showing a favorable and novel pharmacologic profile of S49076, a phase I study is currently underway in patients with advanced solid tumors. Mol Cancer Ther; 12(9); 1749-62. ©2013 AACR.

Specific oncogenic activity of the Src-family tyrosine kinase c-Yes in colon carcinoma cells

c-Yes, a member of the Src tyrosine kinase family, is found highly activated in colon carcinoma but its importance relative to c-Src has remained unclear. Here we show that, in HT29 colon carcinoma cells, silencing of c-Yes, but not of c-Src, selectively leads to an increase of cell clustering associated with a localisation of β-catenin at cell membranes and a reduction of expression of β-catenin target genes. c-Yes silencing induced an increase in apoptosis, inhibition of growth in soft-agar and in mouse xenografts, inhibition of cell migration and loss of the capacity to generate liver metastases in mice. Re-introduction of c-Yes, but not c -Src, restores transforming properties of c-Yes depleted cells. Moreover, we found that c-Yes kinase activity is required for its role in β-catenin localisation and growth in soft agar, whereas kinase activity is dispensable for its role in cell migration. We conclude that c-Yes regulates specific oncogenic signalling pathways important for colon cancer progression that is not shared with c-Src.

Synthesis, checkpoint kinase 1 inhibitory properties and in vitro antiproliferative activities of new pyrrolocarbazoles

In the course of structure-activity relationship studies on granulatimide analogues, new pyrrolo[3,4-c]carbazoles have been synthesized in which the imidazole heterocycle was replaced by a five-membered ring lactam system or a dimethylcyclopentanedione. Moreover, the synthesis of an original structure in which a sugar moiety is attached to the indole nitrogen and to a six-membered D ring via an oxygen is reported. The inhibitory activities of the newly synthesized compounds toward checkpoint kinase 1 and their in vitro antiproliferative activities toward three tumor cell lines: murine leukemia L1210, and human colon carcinoma HT29 and HCT116 are described.

Synthesis, in vitro antiproliferative activities, and Chk1 inhibitory properties of pyrrolo[3,4-a]carbazole-1,3-diones, pyrrolo[3,4-c]carbazole-1,3-diones, and 2-aminopyridazino[3,4-a]pyrrolo[3,4-c]carbazole-1,3,4,7-tetraone

The synthesis of substituted pyrrolo[3,4-a]carbazole-1,3-diones, pyrrolo[3,4-c]carbazole-1,3-diones, and 2-aminopyridazino[3,4-a]pyrrolo[3,4-c]carbazole-1,3,4,7-tetraone is reported. Their inhibitory properties toward Checkpoint 1 kinase (Chk1) have been evaluated and their in vitro antiproliferative activities toward three tumor cell lines: murine leukemia L1210, human colon carcinoma HT29 and HCT116 have been determined. From the biological results, it appears that, in contrast with the upper E heterocycle, the lower D heterocycle is not absolutely required for Chk1 inhibition. The ATP binding pocket of Chk1 seems to be adaptable to substitution of the nitrogen of the imide E heterocycle with a hydroxymethyl group, allowing the fundamental hydrogen bond with the Glu(85) residue of the enzyme.

Cytotoxic turrianes of Kermadecia elliptica from the New Caledonian rainforest

In the course of an automated screening for small molecules presenting cytotoxic activity, eight new cyclophanes named kermadecins A-H (1-8), have been isolated from the bark of a New Caledonian plant, Kermadecia elliptica, Proteaceae. A LC/APCI-MS study performed on kermadecins A, B and C, provided a reliable method for the detection of other analogues existing in small quantities in the extract. This led to the isolation of five other members of this chemical series. The structures were elucidated by extensive mono- and bi-dimensional spectroscopy and mass spectrometry. The cytotoxic activity of four of them was evaluated on various cell lines.

Synthesis and biological activities of isogranulatimide analogues

The synthesis of new isogranulatimide analogues, their inhibitory activities toward the Checkpoint 1 kinase (Chk1), and their in vitro cytotoxicities toward four tumor cell lines (one murine L1210 leukemia, and three human cell lines: DU145 prostate carcinoma, A549 non-small cell lung carcinoma, and HT29 colon carcinoma) are described. The affinity for DNA of some representative compounds and their ability to induce DNA cleavage mediated by topoisomerase I have been examined. In some of the newly synthesized compounds, the imidazole heterocycle of isogranulatimide is replaced by a pyrrole and/or the indole unit is replaced by a 7-azaindole. Compounds in which a sugar part is attached to the 7-azaindole moiety have also been prepared. Some of the newly synthesized compounds are more potent Chk1 inhibitors than granulatimide. The selectivity of two potent Chk1 inhibitors 24 and 26 has been evaluated using various kinases. The strongest inhibitory properties are found toward Chk1.

Sesquiterpenoids and cytotoxic lignans from the bark of Libocedrus chevalieri

Investigation of an EtOAc extract of the bark of Libocedrus chevalieri led to the isolation of a new cytotoxic lignan, 5-methoxy-4-epipodophyllotoxin (1), and three known podophyllotoxin analogues, 5-methoxypodophyllotoxin, 5-methoxypodophyllotoxin-4-O-beta-D-glucoside, and podophyllotoxin-4-O-beta-D-glucoside. Six sesquiterpenoids and a diterpenoid were also obtained. Of these, compounds 2-4 are new sesquiterpenoids, named libocedrines A-C, and 3beta-hydroxyilicic alcohol was isolated for the first time from a higher plant. Structures of the new compounds were determined on the basis of spectroscopic methods. Cytotoxicity of the isolated compounds against KB and L1210 cells and their effects on tubulin assembly were evaluated.

Novel Stable Camptothecin Derivatives Replacing the E-Ring Lactone by a Ketone Function Are Potent Inhibitors of Topoisomerase I and Promising Antitumor Drugs

The E-ring lactone is the Achilles' heel of camptothecin derivatives: although it is considered necessary for the inhibition of the enzyme topoisomerase I (topo1), the opening of the lactone into a carboxylate abolishes the generation of topo1-mediated DNA breaks. S38809 is a novel camptothecin analog with a stable 5-membered E-ring ketone; therefore, it lacks the lactone function. DNA relaxation and cleavage assays revealed that S38809 functions as a typical topo1 poison by stimulating DNA cleavage at T downward arrow G sites. The activity was strongly dependent on the stereochemistry of the C-7 carbon atom that bears the hydroxy group. S38809 proved to be a potent cytotoxic agent, with a mean IC50 of 5.4 nM versus 11.6 nM for topotecan and 3.3 nM for SN38 (the active metabolite of irinotecan) on a panel of 31 human tumor cell lines. The cytotoxicity of S38809 and its ability to stabilize cleavable complexes was considerably reduced in camptothecin-resistant cells that express a mutated topo1, confirming that topo1 is its primary target. Cell death induced by topo1 poisoning requires the conversion of DNA single-strand breaks into double-strand breaks that can be detected by the formation of phosphorylated histone H2AX. In HCT116 cells, topotecan, SN38, and S38809 induced histone H2AX phosphorylation in S phase of the cell cycle, with S38809 being as potent as SN38 and 5-fold more potent than topotecan. In vivo, S38809 showed a marked antitumor activity against HCT116 xenografts. These findings open a new route for improving the pharmacological properties of camptothecin derivatives.

Synthesis and cytotoxic activity of dimeric analogs of acronycine in the benzo[b]pyrano[3,2-h]acridin-7-one series

Coupling of 6-hydroxy-3,3-14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one (6) with alpha,omega-diiodoalkanes of varying length under alkaline conditions gave dimers 7-10. Halogenated ethers 11-14, cyclization products 15-17, and compounds 18-22 were also isolated in small yield from the reaction mixtures. Compounds 7-10 were more potent than acronycine and benzo[b]acronycine in inhibiting L1210 cell proliferation. The length of the alkyl ether linkage between the two benzopyranoacridone units had a dramatic influence on the cytotoxic activity. Compound 9 (n=5) was the most active, with an IC(50) value against L1210 cells within the same range of magnitude as diacetate 5, currently under clinical development.

Bis-imide granulatimide analogues as potent Checkpoint 1 kinase inhibitors

Granulatimide and isogranulatimide, natural products isolated from an ascidian, were found to be abrogators of the cell cycle G2-M phase checkpoint by inhibition of Checkpoint 1 kinase (Chk1). In the course of structure-activity relationship studies on granulatimide analogues, we have synthesized a series of bis-imides, in which the imidazole moiety was replaced by an imide heterocycle. Various modifications have been introduced on one or both imide heterocycles, on the benzene ring, and on the indole nitrogen. Moreover, aza bis-imide analogues were synthesized in which the indole moiety was replaced by a 7-azaindole. Compared to those of granulatimide and isogranulatimide, the Chk1 inhibitory activities of some of the bis-imide carbazoles were stronger. In particular, 1,3,4,6-tetrahydro-10-hydroxy-7H-dipyrrolo[3,4-a:3,4-c]carbazole-1,3,4,6-tetraone 11 exhibited an IC(50) value on purified full length Chk1 of 2 nM, which makes it a more potent Chk1 inhibitor than granulatimide and isogranulatimide. To get an insight into the selectivity of this new family of compounds, the inhibitory activities of 1,3,4,6-tetrahydro-7H-dipyrrolo[3,4-a:3,4-c]carbazole-1,3,4,6-tetraone A have been evaluated on a panel of 15 kinases, the strongest inhibitory potency was found for Chk1. The inhibitory activities of compounds A, 5 and 11 toward Src tyrosine kinase and the cytotoxicity of various tumor cell lines were also evaluated.

Synthesis, in vitro antiproliferative activities, and Chk1 inhibitory properties of indolylpyrazolones and indolylpyridazinedione

The synthesis of 5-indolylpyrazol-3-one, 4-indolylpyrazol-3-one and 4-indolyl-pyridazin-3,6-dione is reported. Their Chk1 inhibitory properties have been evaluated and their in vitro antiproliferative activities toward three tumor cell lines: murine leukemia L1210, human colon carcinoma HT29 and HCT116 have been determined. 4-Indolyl-pyridazin-3,6-dione is inactive against Chk1 and exhibits weak cytotoxicities toward the tumor cell lines tested. The IC(50) values toward Chk1 of the two indolylpyrazolones are identical and are in the micromolar range, but the cytotoxicities of 4-indolylpyrazol-3-one are significantly stronger than those of 5-indolylpyrazol-3-one. Since 4-indolylpyrazol-3-one and 5-indolylpyrazol-3-one can present several conformers and tautomeric forms, molecular modelling in the ATP binding site of Chk1 has been carried out to investigate which form could induce the best stabilization in the active site of the enzyme. To get an insight into the kinase selectivity of these compounds, their inhibitory activities toward Src kinase were evaluated.

Synthesis and biological activities of 7-aza rebeccamycin analogues bearing the sugar moiety on the nitrogen of the pyridine ring

The synthesis of a new family of 7-aza-rebeccamycin analogues in which the sugar moiety is attached to the nitrogen of the pyridine ring is described. The capacity of the newly synthesized compounds to bind to DNA and to inhibit topoisomerase I has been evaluated. Their cytotoxicities toward four tumor cell lines, one murine leukemia L1210 and three human tumor cell lines, one prostate carcinoma DU145, one colon carcinoma HT29, and one non-small cell lung carcinoma A549, have been determined. Their abilities to inhibit the checkpoint kinase Chk1 have been evaluated.

Generation of Replication-Dependent Double-Strand Breaks by the Novel N2-G-Alkylator S23906-1

S23906-1, a new DNA alkylating agent that reacts with the exocyclic 2-NH2 group of guanine residues yielding monofunctional adducts, is currently under clinical evaluation in phase I trials. To investigate the mechanism of action of S23906-1, we compared parental KB-3-1 cells and KB/S23-500 cells that are 15-fold resistant to S23906-1. Cell death induced by 1 micromol/L S23906-1 in KB-3-1 cells was associated with their irreversible arrest in the G2-M phases of the cell cycle followed by apoptosis, whereas a proportion of the resistant KB/S23-500 cells were able to exit from the G2 arrest and divide, leading to a significantly lower rate of apoptosis. The attenuated apoptotic response was associated with decreased Chk2 protein phosphorylation, indicating that the DNA damage signaling pathways are more potently activated in the sensitive cells. However, similar rates of adduct formation and repair were measured in both cell lines. Exposure to S23906-1 induced a higher formation of DNA breaks, measured by the comet assay, in sensitive cells. In agreement, a histone H2AX phosphorylation assay revealed that S23906-1 induced double-strand breaks (DSB) in a dose- and time-dependent manner and that these were more persistent in the parental cells. These DSBs were found mainly in S-phase cells and inhibited by aphidicolin, suggesting that they are DNA replication-mediated DSBs. These results suggest that secondary DNA lesions play an important role in the cytotoxicity of this compound and make histone H2AX phosphorylation an attractive marker for monitoring the efficacy of S23906-1.

Analysis of cyclin B1 and CDK activity during apoptosis induced by camptothecin treatment

We have studied the role of cyclins and cyclin-dependent kinase (CDK) activity in apoptosis induced by camptothecin (CPT). In this model, 22% of the cells stain for annexin-V at 24 h and then proceed to be 93% positive by 72 h. This time window permits the analysis of cyclins in cells that are committed to apoptosis but not yet dead. We provide evidence that cyclin protein levels and then associated kinase levels increase after CPT treatment. Strikingly, cyclin B1 and cyclin E1 proteins are present at the same time in CPT treated HT29 cells. Although cyclin B1 and E1 CDK complexes are activated in CPT treated cells, only the cyclin B1 complex is required for apoptosis since reduction of cyclin B1 by RNAi or roscovitine treatment reduces the number of annexin-V-stained cells. We have detected poorly organized chromosomes and phosphorylated histone H3 epitopes at the time of maximum cyclin B1/CDK kinase activity in CPT-treated cells, which suggests that these cells enter a mitotic catastrophe. Understanding which CDKs are required for apoptosis may allow us to better adapt CDK inhibitors for use as anti-cancer compounds.

Synthesis and biological evaluation of new dipyrrolo[3,4-a:3,4-c]carbazole-1,3,4,6-tetraones, substituted with various saturated and unsaturated side chains via palladium catalyzed cross-coupling reactions

The syntheses of a series of dipyrrolo[3,4-a:3,4-c]carbazole-1,3,4,6-tetraones, substituted in 10-position with saturated and unsaturated side chains, via palladium catalyzed cross-coupling reactions, are described. These compounds can be considered as granulatimide bis-imide analogues. Their inhibitory activity toward Chk1 kinase and their antiproliferative activities in vitro in four tumor cell lines are reported.

Synthesis, Antitumor Activity, and Mechanism of Action of Benzo[a]pyrano[3,2-h]acridin-7-one Analogues of Acronycine

Twenty-two derivatives belonging to the cis-1,2-diacyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[a]pyrano[3,2-h]acridin-7-one series were synthesized in nine steps starting from 3,5-dimethoxyacetanilide (5) and 2-methoxy-1-naphthalenecarboxylic acid (7). Most of them exhibited submicromolar cytotoxicity when tested against murine leukemia (L1210) and human epidermoid carcinoma (KB-3-1) cell lines. The cytotoxic activity correlated strongly with the ability of the compounds to form covalent adducts with purified DNA. Among the most active compounds, 25, with IC50 values of 0.7 and 0.15 microM against L1210 and KB-3-1, respectively, was selected for evaluation in vivo against Colon 38 adenocarcinoma implanted in mice. This compound was active at 3 mg/kg i.v. (day 12 and 24) with 3/7 tumor free mice by day 80.

Synthesis and biological activity of 6H-isoindolo[2,1-a]indol-6-ones, analogues of batracylin, and related compounds

Closely related to batracylin, 6H-isoindolo[2,1-a]indol-6-ones including 2-nitro- 13a, 2-amino- 14, and 2-diethylaminopropionamide derivative 16 as well as D-ring substituted 13b, 13c or A-ring substituted 13d and 20 analogues, were synthesised and evaluated against L1210 leukaemia. Subsequent treatment of 13b and 13c with N,N-diethylethylenediamine at 180 degrees C, led to compounds 17a and 17b arising from an unexpected opening of the pyrrolidinone ring and amidification of the keto group. Under the same conditions, the dichloro derivative 13d led to the monoalkyl compound 20 which was the most cytotoxic of the series.

Novel benzopyridothiadiazepines as potential active antitumor agents

The synthesis of novel thiadiazepine derivatives, that could be considered as constraint analogues of E-7010, are reported. These molecules were evaluated for their antiproliferative activity toward the murine L1210 leukemia cell line. Flow cytometric studies performed on L1210 cells with the most cytotoxic compounds showed an accumulation of the cells in the G2/M phases of the cell cycle with a significant percentage of tetraploid cells (8N DNA content). Submicromolar cytotoxicities were observed with compounds 2b, 4b, 4e, 4g, and 4i. Two of them, compounds 2b and 4b, were found to be potent inhibitors of tubulin polymerization with IC50 of respectively 3.8 and 2.4 microM compared to 2.4 microM for desoxypodophyllotoxin. A 4-methoxyphenylethyl substitution on the pyridinyl nitrogen of the benzopyridothiadiazepine was found to be essential for the antiproliferative activity. The in vitro activities of compounds 2b and 4b make benzopyridothiadiazepine dioxides a promising new class of tubulin binders which warrant further in vivo evaluation.

Synthesis and biological evaluation of N-(7-indazolyl)benzenesulfonamide derivatives as potent cell cycle inhibitors

We herein describe a new synthesis of N-(7-indazolyl)benzenesulfonamide derivatives. These compounds were evaluated for their antiproliferative activities toward L1210 murine leukemia cells. One of them, 4-methoxy-N-(3-chloro-7-indazolyl)benzenesulfonamide, was identified as the most potent with an IC(50) of 0.44 microM.

Synthesis and cytotoxicities of 7-aza rebeccamycin analogues bearing various substituents on the sugar moiety, on the imide nitrogen and on the carbazole framework

The synthesis of a family of rebeccamycin analogues in which one indole unit has been replaced by a 7-azaindole moiety is described. Substitutions have been carried out on the imide nitrogen, on the carbazole framework and on the sugar part. Compounds with a lactam upper heterocycle have also been prepared. The cytotoxicities of the newly synthesized compounds toward four tumor cell lines, one murine leukemia (L1210) and three human tumor cell lines (prostate carcinoma DU145, colon carcinoma HT29, and non-small cell lung carcinoma A549) have been evaluated and compared to those of rebeccamycin and parent non-aza and aza compounds.

Cytotoxic and antitumoral properties in a series of new, ring D modified, olivacine analogues

The present study describes the synthesis and pharmacological profiles of new olivacine related compounds, possessing a modified D ring. The impact of this modification has been evaluated with respect to the cytotoxic and in vivo antitumoral effects of these molecules and in comparison with parent S 16020-2 previously prepared and investigated in our laboratory. The D ring size and number of nitrogen atoms as well as the position of the aminoalkyl substituent have a profound impact on the cytotoxic and antitumoral profiles. Thus out of the prepared pyrazinocarbazole compounds, 2 is devoid of any substantial cytotoxic and antitumoral activities while the pyrimidocarbazole 3 has a similar profile compared to 1 (S 16020-2). L1210 and P388 in vivo antitumoral effects are lost for both imidazocarbazoles 4 and 5, but the former conserves an in vivo antitumoral effect on B16 melanoma, this effect being the largest in the series. Structural similarities and differences amongst the studied compounds could be evidenced by calculation of global properties such as molecular electrostatic potentials (MEP maps) and partition coefficients (logP), thus adding information on the impact of chemical changes on these two parameters known to influence biological behavior.

Synthesis and biological study of a new series of 4'-demethylepipodophyllotoxin derivatives

Etoposide (VP-16) is a potent human DNA topoisomerase II poison, derived from 4'-demethylepipodophyllotoxin, widely used in cancer chemotherapy. Continuous efforts have driven to synthesize new related compounds, presenting decreased toxic side effects, metabolic inactivation, drug resistance, and increased water solubility. Identified structure-activity relationships have pointed out the importance of the 4beta-substitution and of the configuration of the D ring. Here we report the synthesis of two novel series of derivatives of 4'-demethylepipodophyllotoxin. The first bears a carbamate chain in the 4 position (13a-f), whereas, in the second series, in addition to this chain, the lactone ring has been modified by shifting the carbonyl from position 13 to position 11 (27a-f). Moreover, an analogue of TOP-53 having this lactone modification has also been prepared (32). From this study, structure-activity relationships were established. Compounds 13a and 27a displayed potent cytotoxic activity against the L1210 cell line (10 to 20-fold higher than VP-16) and proved to be strong topoisomerase II poisons more potent than VP-16. From preliminary in vivo investigation of both compounds against P388 leukemia and orthotopically grafted human A549 lung carcinoma, it appeared that 13a and 27a constitute promising leads for a new class of antitumor agents.

Synthesis and anticancer activity of new pyrrolocarbazoles and pyrrolo-β-carbolines

'Bended' 1, 3 or 'linear' 2 pyrrolidino-fused (aza)carbazoles were prepared and screened towards a few cancer-related targets. Whereas 'bended' derivatives 1 and 3 proved to be weakly toxic, several members of the 'linear' family strongly interact with DNA, especially derivative 28a.

Synthesis and Biological Evaluation of Novel Naphthocarbazoles as Potential Anticancer Agents

We report the efficient synthesis involving palladium-catalyzed reactions and biological evaluation of new naphthocarbazoles designed as potential anticancer agents. The use of 5- and 6-benzyloxyindoles generated three substitution sites which were successively exploited to introduce several hydrophilic side chains. The cytotoxicity of the newly designed compounds was evaluated on three cell lines. Several compounds showed a marked cytotoxicity with IC(50) values in the sub-micromolar range. This is the case for the 3-hydroxy-naphthopyrrolocarbazoledione 37, bearing a dimethylaminoethyl side chain, which is extremely cytotoxic to L1210 and DU145 cells (IC(50): 36 nM, 108 nM) and induces an accumulation of L1210 cells in the G2+M phases of the cell cycle. Some of the most cytotoxic compounds were tested for inhibition of CDK-5, GSK-3 and topoisomerase I, and their interaction with DNA was also evaluated. Interaction with DNA was detected, suggesting that nucleic acids represent a privileged target for these molecules.

Design, Synthesis, and Cytotoxic Activity of Michael Acceptors and Enol Esters in the Benzo[b]acronycine Series

A series of 2-acyl-6-methoxy-3,3,14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones (4-6) was prepared by treatment of 6-methoxy-3,3,14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one (3) with an excess of an appropriate acyl chloride in the presence of aluminum chloride. Treatment of (+/-)-cis-1-hydroxy-2-acyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones (9, 10) or (+/-)-cis-1,2-diacyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones (2, 11) with hydrochloric acid gave the corresponding 2-acyloxy-6-methoxy-3,3,14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones, exemplified by acetate 7 and butyrate 8. None of the Michael acceptors 4-6 showed significant antiproliferative activity. Enol esters 7 and 8 were markedly cytotoxic toward L1210 leukemia cells, with IC50 values within the same range of magnitude as (+/-)-cis-1,2-diacetoxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one (S23906-1), currently under phase I clinical trials. In contrast with S23906-1, enol esters 7 and 8 were not reactive toward purified DNA.

Novel carbamate derivatives of 4-β-amino-4′-O-demethyl-4-desoxypodophyllotoxin as inhibitors of topoisomerase II: synthesis and biological evaluation

A novel series of carbamate derivatives of 4-beta-amino-4'-O-demethyl-4-desoxypodophyllotoxin were synthesized. Their effect on human DNA topoisomerase II and antiproliferative activity was evaluated. Compounds 4a-c, 4g, 4j and 4k are topoisomerase II poisons that induce double-stranded breaks in DNA and exhibit increased cytotoxicity compared to etoposide.

Novel antitumor indenoindole derivatives targeting DNA and topoisomerase II

We have identified a novel series of indenoindole derivatives endowed with potent cytotoxic activities toward cancer cells. Five compounds containing a 8-[2-(dialkylamino)ethoxy]-2,3-dimethoxy-5H-10H-indeno[1,2-b]indol-10-one-O-propynyl-oxime core substituted with a phenyl, furanyl, or a methyl substituent on the propynyl side chain have been synthesized and their mechanism of action was investigated using a panel of complementary biophysical and biochemical techniques. The compounds were shown to intercalate into DNA with a preference for AT-rich sequences. They have no effect on topoisomerase I but they strongly stimulate DNA cleavage by topoisomerase II. Their capacity to stabilize topoisomerase II-DNA covalent complexes is comparable to that of the reference drug etoposide. The nature and orientation of the substituent on the propynyl chain modulate the DNA binding and topoisomerase II inhibitory properties of the compounds and, apparently, there is a correlation between the cytotoxic potential and the molecular action at the DNA-topoisomerase II level. The growth of human K562 leukemia cells is strongly reduced in the presence of the indenoindoles (IC(50) in the 50nM range) which maintain a high cytotoxic activity toward the adriamycin-resistant K562adr cells line in vitro. The low resistance indexes measured with the indenoindoles (RRI = 10-30) compared to adriamycin (RRI = 1000) suggest that our new compounds are weakly or not sensitive to drug efflux mediated by glycoprotein-P and/or multidrug resistance (MDR) protein pumps. Finally, we also show that these indenoindoles arrest K562 cells in the G2/M phase of the cell cycle and promote apoptosis, as indicated by the appearance of internucleosomal DNA cleavage. One compound in the series was tested for in vivo antitumor activity against the colon 38 model and at 25mg/kg it showed 100% complete tumor regression in the treated mice, without significant body weight loss. Altogether, the results reported here establish that our indenoindole derivatives represent a novel interesting series of DNA-targeted cytotoxic agents.

Synthesis and cytotoxic activity of benzo[c][1,7] and [1,8]phenanthrolines analogues of nitidine and fagaronine

Fagaronine and nitidine are natural benzo[c] phenanthridinium alkaloids, which display antileukemic activity. Both act as topoisomerase I and topoisomerase II inhibitors. The objective of the present study was to prepare noncharged isosters of these compounds, with replacement of the aromatic A ring by a pyridine ring, present in other topoisomerase I inhibitors. Various 7,8- and 8,9-dimethoxy and metylenedioxy benzo[c][1,7] and [1,8]phenanthrolines were readily synthesized by benzyne-mediated cyclization of the corresponding substituted N-(2-halobenzyl)-5-quinolinamines or 5-isoquinolinamines. In both series, compounds bearing oxygenated substituents at positions 8 and 9 exhibited cytotoxic properties towards L1210 murine leukemia cells, which may result from their capacities to intercalate into DNA. Topoisomerase I inhibition was observed for all active compounds.

Synthesis and biological activity of sulfonamide derivatives of epipodophyllotoxin

A series of novel 4beta-substituted sulfonamide derivatives of 4'-O-demethyl-4-desoxypodophyllotoxin has been synthesized. Their effects on human DNA topoisomerase II and, in some cases, on tubulin polymerization were evaluated. Compounds 8a, 8c, 8f, 8g, 8n, 8q, 8r, and 8s and the synthetic precursor 4 are potent topoisomerase II poisons that induce double-stranded breaks in DNA, with either improved or similar activity compared to etoposide. Only the amino precursor, compound 5, was slightly active in tubulin polymerization inhibition assays. We observed that the derivatives bearing an aromatic ring on the 4beta-sulfonamide substituent were either less cytotoxic or equivalent to the parent drug, while the sulfonamides containing an aliphatic side chain and the amino-sulfonamide derivatives, except 8d and 8g, exhibited increased cytoxicity compared to etoposide. In vivo, against the P388 leukemia and the A-549 orthotopic model of lung carcinoma, the most promising compounds were the morpholino- and the piperazino-containing sulfonamides derivatives 8r and 8s.

Design, synthesis, and evaluation of novel thienopyrrolizinones as antitubulin agents

Herein, we describe the structure-activity relationship study of a new 3-aryl-8H-thieno[2,3-b]pyrrolizin-8-one series of antitubulin agents. The pharmacological results from the National Cancer Institute in vitro human disease oriented tumor cell line screening allowed us to identify compound 1d (NSC 676693) as a very efficient antitumoral drug in all cancer cell lines tested. This prompted us to define the structural requirements essential for this antiproliferative activity. Among all analogues synthesized in this study, compound 1o was the most promising, being 10-fold more potent than compound 1d. Its activity over a panel of nine tumoral cell lines was in the nanomolar range for all of the histological types tested, and surprisingly, the resistant KB-A1 cell line was also sensitive to this compound. Moreover, a flow cytometric study showed that L1210 cells treated by the most potent compounds were arrested in the G(2)/M phases of the cell cycle with a significant percentage of cells having reinitiated a cycle of DNA synthesis without cell division. This interesting pharmacological profile, resulting from inhibition of tubulin polymerization, encouraged us to perform preliminary in vivo studies that led to a new prodrug chemical approach.

Analogues of antifungal tjipanazoles from rebeccamycin

Analogues of antifungal tjipanazoles were obtained by semi-synthesis from rebeccamycin, an antitumor antibiotic isolated from cultures of Saccharothrix aerocolonigenes. The antiproliferative activities of the new compounds were evaluated in vitro against nine tumor cell lines. The effect on the cell cycle of murine leukemia L1210 cells was examined and the antimicrobial activities against two Gram positive bacteria, a Gram negative bacterium and a yeast were determined. The inhibitory properties toward four kinases and toward topoisomerase I were evaluated. The most cytotoxic compound in the series was a dinitro derivative characterized as a potent topoisomerase I inhibitor.

Synthesis and antiproliferative activity of basic ethers of 1,2-dihydropyrrolo[1,2-a]indole, 6H-isoindolo[2,1-a]indole, and 6H-benz[5,6]isoindolo[2,1-a]indole

Monobasic ethers of 1,2-dihydropyrrolo[1,2-a]indole, 6H-isoindolo[2,1-a]indole, and 6H-benz[5,6]isoindolo[2,1-a]indole and bis-basic ethers of 6H-isoindolo[2,1-a]indole were prepared using an intramolecular Wittig cyclization as a key step. All these compounds were firstly evaluated for their cytotoxicity effects against L1210 cell line. Only the tetracyclic bis-basic ether 14d displayed submicromolar cytotoxic effect. Moreover, despite the fact that the presence of these two amino side chains in 14c, 14d, and 14f led to strong DNA binding effect, they are not topoisomerase II inhibitors. Among the monobasic ethers 14a, 14b, 22, and 29, which do not bind to DNA, the pentacyclic analog 29 exhibited micromolar cytotoxic activity against L1210 and HT-29 cell lines and induced a weak topoisomerase II inhibition.

Design of Novel Antitumor DNA Alkylating Agents: The Benzacronycine Series

Acronycine, a natural alkaloid originally extracted from the bark of the Australian ash scrub Acronychia baueri, has shown a significant antitumor activity in animal models. Acronycine has been tested against human cancers in the early 1980s, but the clinical trials showed modest therapeutic effects and its development was rapidly discontinued. In order to optimize the antineoplastic effect, different benzoacronycine derivatives were synthesized. Among those, the di-acetate compound S23906-1 was recently identified as a promising anticancer drug candidate and a novel alkylating agent specifically reacting with the exocylic 2-NH2 group of guanines in DNA. The study of DNA bonding capacity of acronycine derivatives leads to the identification of the structural requirements for DNA alkylation. In nearly all cases, the potent alkylating agents, such as S23906-1, were found to be much more cytotoxic than the unreactive analogs such as acronycine itself or diol derivatives. Alkylation of DNA by the monoacetate derivative S28687-1, which is a highly reactive hydrolysis metabolite of S23906-1, occurs with a marked preference for the N2 position of guanine. Other bionucleophiles can react with S23906-1. The benzacronycine derivatives, which efficiently alkylate DNA, also covalently bind to the tripeptide glutathione (GSH) but not to the oxidized product glutathione disulfide. Here we review the reactivity of S23906-1 and some derivatives toward DNA and GSH. The structure-activity relationships in the benzacronycine series validate the reaction mechanism implicating DNA as the main molecular target. S23906-1 stands as the most promising lead of a medicinal chemistry program aimed at discovering novel antitumor drugs based on the acronycine skeleton.

Synthesis of Mono- and Bisdihydrodipyridopyrazines and Assessment of Their DNA Binding and Cytotoxic Properties

Aminoalkyl-substituted monomeric and dimeric dihydrodipyridopyrazines have been synthesized and evaluated as antitumor agents. Potent cytotoxic compounds were identified in both series. Biochemical and biophysical studies indicated that all these compounds strongly stabilized the duplex structure of DNA and some of them elicited a selectivity for GC-rich sequences. Sequence recognition by of the dimeric dihydrodipyridopyrazines is reminiscent of that of certain antitumor bisnaphthalimides. Compared to monomers, corresponding dimeric derivatives showed higher affinity for DNA. This property was attributed to a bisintercalative binding to DNA. This assumption was indirectly probed by electric linear dichroism and DNA relaxation experiments. DNA provides a bioreceptor for these dihydrodipyridopyrazine derivatives, but no poisoning of human topoisomerases I or II was detected. Most of the compounds efficiently inhibited the growth of L1210 murine leukemia cells and perturbed the cell cycle progression (with a G2/M block in most cases). A weak but noticeable in vivo antitumor activity was observed with one of the dimeric compounds. This studies identifies monomeric and dimeric dihydrodipyridopyrazines as a new class of DNA-targeted antitumor agents.

Synthesis and Cytotoxic and Antitumor Activity of 1,2-Dihydroxy-1,2-dihydrobenzo[b]acronycine Diacid Hemiesters and Carbamates

A series of cis-1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine diacid hemiesters and dicarbamates were prepared by acylation of cis-1,2-dihydroxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one. The cytotoxicity of the dicarbamates depended on the steric hindrance of the esterifying groups at positions 1 and 2. Diacid hemiesters displayed significant in vitro cytotoxic activities and induced cell cycle perturbations similar to those obtained with cis-1,2-diacetoxy-1,2-dihydrobenzo[b]acronycine (S23906-1) currently under preclinical development. cis-1-Acetoxy-2-hemiglutaryloxy-1,2-dihydrobenzo[b]acronycine was the most promizing compound of the series, inducing complete inhibition of tumor growth when tested against C38 colon adenocarcinoma implanted in mice.

A transesterification reaction is implicated in the covalent binding of benzo[b]acronycine anticancer agents with DNA and glutathion

The benzo[b]acronycine derivative S23906-1 has been recently identified as a promising antitumor agent, showing remarkable in vivo activities against a panel of solid tumors. The anticancer activity is attributed to the capacity of the drug to alkylate DNA, selectively at the exocyclic 2-amino group of guanine residues. Hydrolysis of the C-1 and C-2 acetate groups of S23906-1 provides the diol compound S28907-1 which is inactive whereas the intermediate C-2 monoacetate derivative S28687-1 is both highly reactive toward DNA and cytotoxic. The reactivity of this later compound S28687-1 toward two bionucleophiles, DNA and the tripeptide glutathion, has been investigated by mass spectrometry to identify the nature of the (type II) covalent adducts characterized by the loss of the acetate group at position 2. On the basis of NMR and molecular modeling analyses, the reaction mechanism is explained by a transesterification process where the acetate leaving group is transferred from position C-2 to C-1. Altogether, the study validates the reaction scheme of benzo[b]acronycine derivative with its target.

Synthesis of 6-dialkylaminoalkylamino pyrano[2,3-c]acridones and benzo[b]pyrano[3,2-h]acridones: soluble acronycine analogues with increased cytotoxic activity

The novel 6-dialkylaminoalkylamino-3,3,12-trimethyl-3,12-dihydro-7H-pyrano[2,3-c]acridine-7-ones 5-11 and their benzo [b]pyrano[2,3-h]acridine-7-one counterparts 12-18 were prepared by treatment of acronycine (1) or benzo[b]acronycine (4) with an excess of the appropriate dialkylaminoalkylamine. In both series, the introduction of a dialkylaminoalkylamino side chain at position 6 resulted in a significant increase of the cytotoxic activity against L1210 cells when compared with the parent compounds bearing a methoxy group, accompanied with an increased potency to arrest cells in the G2 + M phases of the cell cycle.

Synthesis and pharmacological evaluation of novel non-lactone analogues of camptothecin

Ten novel camptothecin (CPT) derivatives devoid of the lactone function in the E-ring were synthesized and evaluated as anticancer agents. Several of these CPT analogues bearing a five-membered E-ring are potent inhibitors of the DNA relaxation and cleavage reactions catalyzed by topoisomerase I and exhibit promising cytotoxic activities with IC(50) values in the nM range. This is the first successful design of lactone-free CPT, providing thus a new avenue to the development of topoisomerase I targeted antitumor agents.

Structure-activity relationships and mechanism of action of antitumor benzo[b]pyrano[3,2-h]acridin-7-one acronycine analogues

The cytotoxic and antitumor activities of cis-1,2-diacyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one derivatives 3, 6-9 were strongly correlated with their ability to give covalent adducts with purified, as well as genomic, DNA. Such adducts involve reaction between the exocyclic N-2 amino group of guanines exposed in the minor groove of double helical DNA and the leaving ester group at the benzylic position 1 of the drug. A transesterification process of the ester group from position 2 to position 1 in aqueous medium accounted for the intense activity of the cis-1-hydroxy-2-acyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one derivatives 10-13. Compounds without acyloxy or hydroxy group at position 1, such as 15, 17, 18, and 22, were inert with respect to DNA and almost devoid of significant cytotoxic activity. Condensation of 5-amino-2,2-dimethyl-2H-chromene (26) with 3-bromo-2-naphthoic acid (27), followed by cyclization, gave access to 6-demethoxy analogues. Diacetate 32 and cyclic carbonate 33, both belonging to the latter series, were less reactive toward DNA and less cytotoxic than their 6-methoxy counterparts 3 and 34. DNA alkylation appears thus to play an important role in the antitumor properties of benzo[b]pyrano[3,2-h]acridin-7-one derivatives.