Substituted dibenzo[c,h]cinnolines: topoisomerase I-targeting anticancer agents

Several substituted dibenzo[c,h]cinnolines were synthesized and evaluated for their potential to target topoisomerase I and for their relative cytotoxic activity. Select benzo[i]phenanthridines are capable of stabilizing the cleavable complex formed with topoisomerase I and DNA. This study was initiated to examine whether dibenzo[c,h]cinnolines, which are in essence aza analogues of benzo[i]phenanthridines, possess similar pharmacological properties. 2,3-Dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine is one of the more potent benzo[i]phenanthridine derivatives in regard to topoisomerase I-targeting activity and cytotoxicity. The structure-activity relationship observed with these substituted dibenzo[c,h]cinnolines parallels that observed for benzo[i]phenanthridine derivatives. Compared to similarly substituted benzo[i]phenanthridines, the dibenzo[c,h]cinnoline analogues exhibit more potent topoisomerase I-targeting activity and cytotoxicity. The relative IC(50) values obtained in assessing the cytotoxicity of 2,3-dimethoxy-8,9-methylenedioxydibenzo[c,h]cinnoline and 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine in the human lymphoblastma cell line, RPMI8402, are 70 and 400 nM, respectively. In tumor cell lines selected for resistance to camptothecin and known to express mutant topoisomerase I, benzo[i]phenanthridine derivatives were not cross-resistant. In contrast, similarly substituted dibenzo[c,h]cinnolines with significant topoisomerase I-targeting activity did exhibit cross-resistance in these camptothecin-resistant cell lines. The cytotoxicity of these dibenzo[c,h]cinnolines was not diminished in cells overexpressing the efflux transporter, MDR1. These data indicate that substituted dibenzo[c,h]cinnolines can exhibit potent topoisomerase I-targeting activity and are capable of overcoming the multi-drug resistance associated with this efflux transporter.     

2,3-Dimethoxybenzo[i]phenanthridines: topoisomerase I-targeting anticancer agents

Appropriately substituted benzo[i]phenanthridines structurally related to nitidine, a benzo[c]phenanthridine alkaloid with antitumor activity, are active as topoisomerase I-targeting agents. Studies on benzo[i]phenanthridines have indicated analogues that possess a 2,3-methylenedioxy moiety and at least one and preferably two methoxyl groups at the 8- and 9-positions, such as 8,9-dimethoxy-2,3-methylenedioxybenzo[i]phenanthridine, 2, are active as topoisomerase I-targeting agents. Tetramethoxylated benzo[i]phenanthridines, wherein the 2,3-methylenedioxy moiety is replaced with methoxyl groups at the 2- and 3-position, are inactive as a topoisomerase I-targeting agent. These results initially suggested that the 2,3-methylenedioxy moiety was critical to the retention of potent activity. Further studies revealed that 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine, 7a, is more potent than 2 as a topoisomerase I-targeting agent. The observation that 2,3-dimethoxylated benzo[i]phenanthridines can actually exhibit enhanced activity prompted the present study in which several 8-substituted 2,3-dimethoxybenzo[i]phenanthridines were prepared and their pharmacological activities evaluated. The influence of NH(2), CN, CH(2)OH, OBn, OCH(3), OH, and NHCOCH(3 )substituents at the 8-position on the relative activity of these 2,3-dimethoxybenzo[i]phenanthridines was examined. Relative to these derivatives, 7a was the most potent topoisomerase I-targeting agent, possessing similar cytotoxicity to that of nitidine in the human lymphoblast tumor cell line, RPMI8402.     

11-Substituted 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine derivatives as novel topoisomerase I-targeting agents

Several 11-substituted benzo[i]phenanthridine derivatives were synthesized, and their TOP1-targeting activity and cytotoxicity were assessed. Comparative data indicate that TOP1-targeting was often the primary molecular target associated with their cytotoxicity. Several 11-aminoalkyl derivatives, 11-aminocarboxy derivatives as well as the 11-[(2-dimethylamino)ethyl]carboxamide of 2,3-dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine were synthesized and did exhibit considerable cytotoxicity with IC(50) values ranging from 20 to 120 nM in the human lymphoblast tumor cell line RPMI8402.     

Substituted benzo[i]phenanthridines as mammalian topoisomerase-targeting agents

Several benzo[c]phenanthridine and protoberberine alkaloids, such as nitidine and berberrubine, are known to induce DNA cleavage in the presence of either topoisomerase I or II. Structure-activity studies performed on various analogues related to benzo[c]phenanthridine and protoberberine alkaloids have provided insights into structural features that influence this topoisomerase-targeting activity. Modifications within the A-ring of benzo[c]phenanthridine and protoberberine alkaloids can significantly alter their ability to enhance the cleavable complex formation that occurs between DNA and topoisomerases. Select benzo[i]phenanthridines were synthesized as potential bioisosteres of nitidine and its analogues. In the present study, 2,3-methylenedioxy-8,9-dimethoxybenzo[i]phenanthridine, 2,3-methylenedioxy-8,9-dimethoxy-5-methylbenzo[i]phenanthridine, 2,3,8,9-tetramethoxybenzo[i]phenanthridine and 5-methyl-2,3,8,9-tetramethoxybenzo[i]phenanthridine were synthesized. These benzo[i]phenanthridine derivatives were evaluated for their ability to enhance cleavable complex formation in the presence of topoisomerases and DNA as well as for their cytotoxicity against the human lymphoblastoma cell line, RPMI8402. 2,3-Methylenedioxy-8,9-dimethoxybenzo[i]phenanthridine (4a) and its 5-methyl derivative (4b) are active as topoisomerase I-targeting agents. In contrast to nitidine, the presence of the 5-methyl substituent in the case of 4b is not associated with enhanced activity. Consistent with previous structure-activity studies on nitidine and protoberberine alkaloids, 2,3,8,9-teramethoxybenzo[i]phenanthridine, 5a, and its 5-methyl derivative, 5b, are inactive as topoisomerase I-targeting agents. These studies were extended to an evaluation of the relative pharmacological activities of 2,8,9-trimethoxybenzo[i]phenanthridine, 3,8,9-trimethoxybenzo[i]phenanthridine, and 2,3-methylenedioxy-8,9-methylenedioxybenzo[i]phenanthridine.     

Dimethoxybenzo[i]phenanthridine-12-carboxylic acid derivatives and 6H-dibenzo[c,h][2,6]naphthyridin-5-ones with potent topoisomerase I-targeting activity and cytotoxicity

The exceptional TOP1-targeting activity and antitumor activity of ARC-111, 1, prompted studies on similarly substituted benzo[i]phenanthridine-12-carboxylic ester and amide derivatives. These studies were extended to include 6-substituted 8,9-dimethoxy-2,3-methylenedioxy-dibenzo[c,h][2,6]naphthyridin-5-ones, which represent reversed lactam analogues of 1. Several of these analogues retained the potent TOP1-targeting activity and cytotoxicity observed for ARC-111.     

8,9-methylenedioxybenzo[i]phenanthridines: topoisomerase I-targeting activity and cytotoxicity

Substituted benzo[i]phenanthridines that have incorporated within their structure an 8,9-methylenedioxy group can exhibit topoisomerase I-targeting activity. Structure-activity studies were performed to examine the influence of saturation at the 11,12-positions of several substituted 8,9-methylenedioxybenzo[i]phenanthridines. The activities of these dihydro analogues were compared to those of their unsaturated analogues. In addition, the influence of varying substituents at the 2- and 3-positions within the A-ring of these 8,9-methylenedioxybenzo[i]phenanthridines on their relative potency as topoisomerase I-targeting agents and cell proliferation as determined using the MTT assay was investigated. 2,3-Dimethoxy-8,9-methylenedioxybenzo[i]phenanthridine and its 11,12-dihydro derivative were among the more potent analogues evaluated with regard to topoisomerase I-targeting activity and cytotoxicity.     

11H-Isoquino[4,3-c]cinnolin-12-ones; novel anticancer agents with potent topoisomerase I-targeting activity and cytotoxicity

Recent studies have identified 2,3-dimethoxy-8,9-methylenedioxy-11-[(2-dimethylamino)ethyl]-11H-isoquino[4,3-c]cinnolin-12-one (1a) as a novel topoisomerase I-targeting agent with potent cytotoxic activity. The effect of varied substituents at the 11-position of 2,3-dimethoxy-8,9-methylenedioxy-11H-isoquino[4,3-c]cinnolin-12-ones on topoisomerase I-targeting activity and cytotoxicity was evaluated. Potent TOP1-targeting activity was observed when the 11-position was substituted with either a 2-(N,N-dimethylamino)ethyl, a 2-(N,N-diethylamino)ethyl, a n-butyl, or a 2-(pyrrolidin-1-yl)ethyl group. The addition of a beta-methyl group to 1a provided an analogue with dramatically reduced TOP1-targeting activity and cytotoxicity. Analogues of 1a wherein the 2-(N,N-dimethylamino)ethyl group was replaced with a (2-tetrahydrofuranyl)methyl, a 2-(piperidin-1-yl)ethyl, or a 2-(4-methylpiperazin-1-yl)ethyl substituent exhibited decreased activity as TOP1-targeting agents. Replacement of the dimethoxy groups of 1a with hydrogen atoms resulted in an analogue with significantly decreased TOP1-targeting activity and cytotoxicity. Removal of both the vicinal dimethoxyl groups and the methylenedioxy moiety resulted in a complete loss of TOP1-targeting activity. The presence of a 9-nitro substituent in place of the 8,9-methylenedioxy group of 1a resulted in a decrease in relative TOP1-targeting activity and cytotoxicity. Compounds 1a and the 11-n-butyl analogue 1d were evaluated for antitumor activity in the human tumor xenograft model using athymic nude mice. The non-estrogen responsive breast tumor cell line MDA-MB-435 was used in these assays. At dose levels that approached its maximum tolerated dose, 1a proved to be effective in inhibiting tumor growth in vivo when administered orally or by ip injection.     

6-Substituted 6H-dibenzo[c,h][2,6]naphthyridin-5-ones: reversed lactam analogues of ARC-111 with potent topoisomerase I-targeting activity and cytotoxicity

6-Substituted 8,9-dimethoxy-2,3-methylenedioxy-6H-dibenzo[c,h][2,6]naphthyridin-5-ones were synthesized and evaluated for topoisomerase I-targeting activity and cytotoxicity. Several of these reversed lactam analogues of ARC-111 exhibited exceptional cytotoxicity with IC50 values ranging from 0.5 to 3.0 nM. In contrast to topotecan, no resistance was observed with several of these reversed lactam analogues in tumor cell lines that overexpressed the efflux transporters MDR1 or BCRP.     

Synthesis and bioactivity of 4,10-dimethyl-pyridino[2,3-h]quinolin-2(1H)-one-9-carboxylic acid and its esters

4,10-Dimethyl-pyridino[2,3-h]quinolin-2(1H)-one-9-carboxylic acid (1) was synthesized by a new approach via the key intermediate 7-[1-aza-2-(dimethylamino)vinyl]-4-methylquinolin-2(1H)-one (4). Compound 1 and its esters were evaluated in cytotoxicity and anti-HIV assays. The 9-carboxyl (1s)-endo-(-)-borneol ester (9) showed marginal cytotoxic activity in CAK1-1, HOS, KB, and HCT-8 cells.     

The synthesis and biochemical evaluation of new A1 selective adenosine receptor agonists containing 6-hydrazinopurine moieties

The synthesis and SAR of a series of novel derivatives of N-aminoadenosine is described, along with their in vitro effects in biochemical assays. The rat brain A₁ adenosine receptor binding of these compounds is very dependent upon the purine 2-substituent. The novel agonist, 2-chloro-N-[4-(phenylthio)-1-piperidinyl]adenosine, exhibits a L_i value for A₁ receptor binding of <1 nM.     

Structure-activity relationships of adenosines with heterocyclic N6-substituents

Two series of N⁶-substituted adenosines with monocyclic and bicyclic N⁶ substituents containing a heteroatom were synthesized in good yields. These derivatives were assessed for their affinity ([³H]CPX), potency, and intrinsic activity (cAMP accumulation) at the A₁ adenosine receptor in DDT₁ MF-2 cells. In the monocyclic series, the N⁶-tetrahydrofuran-3-yl and thiolan-3-yl adenosines (1 and 26, respectively) were found to possess similar activities, whereas the corresponding selenium analogue 27 was found to be more potent. A series of nitrogen containing analogues showed varying properties, N⁶-((3R)-1-benzyloxycarbonylpyrrolidin-3-yl)adenosine (30) was the most potent at the A₁AR; IC₅₀ = 3.2 nM. In the bicyclic series, the effect of a 7-azabicyclo[2.2.1]heptan-2-yl substituent in the N⁶-position was explored. N⁶-(7-Azabicyclo[2.2.1]heptan-2-yl)adenosine (38) proved to be a reasonably potent A₁ agonist (K_i = 51 nM, IC₅₀ = 35 nM) while further substitution on the 7″-nitrogen with tert-butoxycarbonyl (31, IC₅₀ = 2.5 nM) and 2-bromobenzyloxycarbonyl (34, IC₅₀ = 9.0 nM) gave highly potent A₁AR agonists.     

Chemistry of cyclodicarbaphosphatriazene: Synthesis and structural studies of pentaerythritoxy-bridged and lariat ether type spirocyclic derivatives

Reactions of dilithiated diols [HO(CH₂CH₂O)_n+1H, n = 1, 2 and 3] with 3,5-bis(N,N-dimethylamino)-1,1-dichlorodicarbaphosphazene (1) in THF have been carried out to afford the first examples of lariat ether type cyclocarbaphosphazene derivatives (C₄H₈O₃PN)(Me₂NCN)₂ (2), (C₆H₁₂O₄PN)(Me₂NCN)₂ (3) and (C₈H₁₆O₅PN)(Me₂NCN)₂ (4). Reaction of the tetrasodium salt of pentaerythritol with 1 and bis(morpholino)dichlorodicarbaphosphazene (1a) yielded the first examples of pentaerythritoxy-bridged cyclodicarbaphosphatriazenes [(Me₂NCN)₂PN(OCH₂)₂]₂C (5) and [(OC₄H₈NCN)₂PN(OCH₂)₂]₂C (6). The spectral and structural properties of these compounds are determined and compared with spirocyclic 1,3-propanedioxy derivative of 1 (7) and analogous compounds of cyclophosphazenes. The crystal structures of the compounds 4, 5 and 7 are reported. In addition, complexation studies of compounds 3 and 4 with Na^I, K^I, Ag^I and Cu^II ions were carried out by conductance measurements. The studies indicate mostly 1:1 complex formation between the metal ions and lariat ether type cyclocarbaphosphazene derivatives.     

Novel 5-azaindolocarbazoles as cytotoxic agents and Chk1 inhibitors

We describe here an efficient synthesis of new 5-azaindolocarbazoles designed for cytotoxic and Chk1 inhibiting properties. The synthesis of ‘symmetrical’ and ‘dissymmetrical’ structures is discussed. Concerning the dissymmetrical 5-azaindolocarbazoles derivatives, with both an indole moiety and a 5-azaindole moiety, the synthesis was achieved using two very efficient key steps. The first one is a Stille reaction with a 3-trimethylstannyl-5-azaindole derivative and the second one a photochemical step leading to the proposed polycyclic structure. Various pharmacomodulations were performed to investigate the structure–activity relationships (SAR). Several substituents such as OBn, OH, and methylenedioxy groups were successfully introduced on the indole moiety of the 5-azaindolocarbazole. Compounds with or without substituents on the nitrogen atom of the maleimide were prepared, as well as derivatives with glucopyranosyl substituent on the nitrogen atom of the indole moiety. The cytotoxicity of these new compounds was evaluated on two cell lines (L1210, HT29). Several compounds showed cytotoxicity in the sub-micromolar range. Among the most cytototoxic was the 1,3-dioxolo[4,5-b]-6-(2-dimethylaminoethyl)-1H-pyrido[3′,4′:4,5]pyrrolo[3,2-i]pyrrolo[3,4-g]carbazole-5,7(6H,12H)-dione (35, IC₅₀ = 195 nM on L1210). The compounds were also investigated for their Chk1 inhibiting activity. Compounds without any substitution on the maleimide moiety were the most potent. This is the case of compounds 45–47 with IC₅₀ of, respectively, 72, 27, and 14 nM toward Chk1. Compound 46, which exhibits moderate cytotoxicity, appears to be a good candidate for development in a multi-drug anticancer therapy.     

Ring-substituted 11-oxo-11H-indeno[1,2-b]quinoline-6-carboxamides with similar patterns of cytotoxicity to the dual topo I/II inhibitor DACA

A series of ring-substituted analogues of the topoisomerase inhibitor 11-oxo-11H-indeno[1,2-b]quinoline-6-carboxamides was prepared and evaluated. The compounds were prepared by Pfitzinger reaction of the appropriate isatin-7-carboxylic acids and 1-indanones, followed by selective thermal decarboxylation of the resulting tetracyclic diacids, subsequent oxidation of the methylene group with alkaline permanganate under carefully controlled conditions, and 1,1'-carbonyldiimidazole-induced amidation. The compounds were evaluated in a panel of cell lines in culture. The largest increases in cytotoxicity (five to tenfold) were shown by 4-substituted analogues, with the 4-Cl derivative having an IC₅₀ of 8 nM against the Lewis lung carcinoma.     

Biocatalytic oxidation of S-alkylcysteine derivatives by chloroperoxidase and Beauveria species

Treatment of N-methoxycarbonyl C-carboxylate ester derivatives of S-methyl- -cysteine by chloroperoxidase (CPO)/hydrogen peroxide resulted in oxidation at sulfur to produce the (R_S) sulfoxide in moderate to high diastereomeric excess (DE). The (S_S) natural product sulfoxide chondrine was obtained via biotransformation of the N-t.boc derivative of -4-S-morpholine-2-carboxylic acid using Beauveria bassiana or Beauveria caledonica.     

Fluorescent ligands for the histamine H2 receptor: synthesis and preliminary characterization

3-[3-(Piperidinomethyl)phenoxy]alkyl, N-cyano-N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidine and 2-(5-methyl-4-imidazolyl)methyl thioethyl derivatives containing fluorescent functionalities were synthesized and the histamine H₂ receptor affinity was evaluated using the H₂ antagonist [¹²⁵I]-aminopotentidine. The compounds exhibited weak to potent H₂ receptor affinity with pK_i values ranging from <4 to 8.85. The highest H₂ receptor affinity was observed for N-cyano-N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidines substituted with methylanthranilate (13), cyanoindolizine (6) and cyanoisoindole (11) moieties via an ethyl or propyl linker.     

Design, synthesis, and antitumor evaluation of novel acenaphtho[1,2-b]pyrrole-carboxylic acid esters with amino chain substitution

8-Oxo-8H-acenaphtho[1,2-b]pyrrole-9-carboxylic acid esters and derivatives were prepared and evaluated for cytotoxicity against A549 and P388 cell lines. Based on a novel chromophore precursor 8-oxo-8H-acenaphtho[1,2-b]pyrrol-9-carbonitrile 1, the very insoluble 1 was converted to more soluble esters 5 and a series of 3-amino derivatives from 5 were obtained by mild S(N)Ar(H) reaction between 5 and various amines. The biological evaluation indicated that methyl esters 5a are the most cytotoxic with IC(50) values of 0.45 and 0.80 microM (against A549 and P388, respectively) among the parent esters 5a-5f, but 3-amino derivatives 4b and 4c of 5f with bromine showed the highest activity (with IC(50) values of 0.019-0.60 microM) among the 3-amino derivatives.     

Stereognostic coordination chemistry 4 the design and synthesis of a selective uranyl ion complexant

A new approach to ligand design for the sequestration of metal-oxo cations has been called stereognostic coordination chemistry, in that the ligand incorporates a traditional Lewis base coordination to the metal center and a hydrogen bond donor to interact with the oxo group. This paper reports the synthesis of ligands that are more rigid and sterically predisposed to bind the targeted UO₂²⁺ cation. These are the tripod ligands tris-N,N′,N′′-[2-(2-carboxy-phenoxy)ethyl]-1,4,7-triazacyclononane bis-hydrochloride (ETAC · 2HCl) and tris-N,N′,N′′-[2-(2-carboxy-4-decyl-phenoxy)ethyl]-1,4,7-triazacyclononane tris-hydrochloride (DETAC · 3HCl), which chelate uranyl with a tris-carboxylate coordination sphere and provide a hydrogen bond donor through a protonated amine on the triazacyclononane macrocycle to interact with one uranyl oxo atom. Structural models predict that upon uranyl binding the hydrogen bond donor must point directly towards the oxo atom, enforcing a stereognostic interaction. Both ETAC and DETAC chelate the uranyl ion; DETAC is a powerful extractant and will quantitatively extract uranyl into an organic phase at pH 1.9 and above. The extraction coefficient is estimated to be 10¹⁴ in neutral aqueous conditions. Vibrational spectra of ¹⁸O labeled UO₂²⁺ have been used to probe the stereognostic coordination to uranyl utilizing hydrogen bonding.     

5H-Dibenzo[c,h]1,6-naphthyridin-6-ones: novel topoisomerase I-targeting anticancer agents with potent cytotoxic activity

5H-Dibenzo[c,h]1,6-naphthyridine-6-ones can exhibit potent antitumor activity. The effect of varied substituents at the 5-position of 5H-8,9-dimethoxy-2,3-methylenedioxydibenzo[c,h]1,6-naphthyridine on relative cytotoxicity and topoisomerase I-targeting activity was evaluated. Potent TOP-1-targeting activity is observed when the 5-position is substituted with either a 2-(N,N-dimethylamino)ethyl group, as in 3a, or a 2-(pyrrolidin-1-yl)ethyl substituent, 3c. In contrast, the addition of a beta-methyl group or a beta-hydroxymethyl group to compound 3a, as in 3b and 3j, results in a loss of significant TOP1-targeting activity. While the presence of a 3-(N,N-dimethylamino)propyl substituent at the 5-position or a methyl(2-tetrahydrofuranyl) group allows for retention of TOP1-targeting activity, the 2-(4-methyl-1-piperazinyl)ethyl analogue, 3d, did not exhibit significant activity. Replacement of the N,N-dimethylamino group of 3a with either C(2)H(5) or OH, as in 3f and 3h, respectively, also had a negative impact on both cytotoxicity and TOP1-targeting activity. Treatment of 3a with LAH gave the 5,6-dihydrodibenzo[c,h]naphthyridine, 4a. This dihydro derivative has approximately 2/3 the potency of 3a as a TOP1-targeting agent. Compounds 3a, 3b, 3h, 3i, and 4a were evaluated for antitumor activity in the human tumor xenograft model using athymic nude mice. The non-estrogen responsive breast tumor cell line, MDA-MB-435, was used in these assays. Compound 3a proved to be effective in regressing tumor growth in vivo when administered either by ip injection or orally 3x week at a dose of 2.0mg/kg. Compound 4a when administered orally 5x weekly at a dose of 40 mg/kg also suppressed tumor growth.