8,11-dihydroxy-6-[(aminoalkyl)amino]-7H-benzo[e]perimidin-7-ones with activity in multidrug-resistant cell lines: synthesis and antitumor evaluation

Heterocyclic Iminoquinones and Quinones from the National Cancer Institute (NCI, USA) COMPARE Analysis

This review uses the National Cancer Institute (NCI) COMPARE program to establish an extensive list of heterocyclic iminoquinones and quinones with similarities in differential growth inhibition patterns across the 60-cell line panel of the NCI Developmental Therapeutics Program (DTP). Many natural products and synthetic analogues are revealed as potential NAD(P)H:quinone oxidoreductase 1 (NQO1) substrates, through correlations to dipyridoimidazo[5,4-f]benzimidazoleiminoquinone (DPIQ), and as potential thioredoxin reductase (TrxR) inhibitors, through correlations to benzo[1,2,4]triazin-7-ones and pleurotin. The strong correlation to NQO1 infers the enzyme has a major influence on the amount of the active compound with benzo[e]perimidines, phenoxazinones, benz[f]pyrido[1,2-a]indole-6,11-quinones, seriniquinones, kalasinamide, indolequinones, and furano[2,3-b]naphthoquinones, hypothesised as prodrugs. Compounds with very strong correlations to known TrxR inhibitors had inverse correlations to the expression of both reductase enzymes, NQO1 and TrxR, including naphtho[2,3-b][1,4]oxazepane-6,11-diones, benzo[a]carbazole-1,4-diones, pyranonaphthoquinones (including kalafungin, nanaomycin A, and analogues of griseusin A), and discorhabdin C. Quinoline-5,8-dione scaffolds based on streptonigrin and lavendamycin can correlate to either reductase. Inhibitors of TrxR are not necessarily (imino)quinones, e.g., parthenolides, while oxidising moieties are essential for correlations to NQO1, as with the mitosenes. Herein, an overview of synthetic methods and biological activity of each family of heterocyclic imino(quinone) is provided.

Spectral and Kinetic Properties of Radical Cations Derived from Oxoisoaporphines: Relevance to Electron-Transfer Processes Involving Phytoalexins

The thermally induced intermolecular electron transfer reaction in acetonitrile between the tetracyanoethylene (TCNE), a π-electron acceptor with a large electron affinity, and six oxoisoaporphines (2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one, 5-methoxy-2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one, 1-azabenzo[de]anthracen-7-one, 5-methoxy-1-azabenzo[de]anthracen-7-one, 7H-benzo[e]perimidin-7-one, and 2-methyl-7h-benzo[e]perimidin-7-one) is reported. Spectral and kinetic characteristics are presented for radical cations derived from these six oxoisoaporphines either generated by a thermal reaction or generated radiolytically in argon-saturated 1,2-dichloroethane, oxygen-saturated acetone, and acetonitrile. The radical cations of oxoisoaporphines are insensitive to oxygen and are mostly characterized by absorption maxima of their most intense bands located at λ_max = 400-410 nm, except of the radical cations derived from 2,3-dihydrooxoisoaporphines. For the latter compounds, the absorption maxima of the most intense absorption bands are located at λ_max = 290-295 nm. Their locations are independent of the presence of functional groups and the solvents used. They are formed in bimolecular processes with pseudo-first-order rate constants ranging from 2.1 × 10⁵ to 1.5 × 10⁶ s^-1 (in solutions containing 10^-4 M of the substrate), depending on the derivative and the solvent used. They are stable either when formed via the electron-transfer reaction with TCNE or when generated in isolation in pulse radiolysis of Ar-saturated 1,2-dichloroethane. In acetone and acetonitrile they decay predominantly by first-order kinetics with the first-order rate constants ranging from 2.3 × 10⁴ to 5.1 × 10⁴ s^-1. Formation of dimeric radical cations for all of the oxoisoaporphines studied was observed in acetonitrile solutions, and for azaoxoisoaporphines also in acetone solutions. The experimental spectra show a reasonably good agreement with the ZINDO/S semiempirical quantum mechanical calculations of radical cation absorptions.

Synthesis of 2-phenylazonaphtho[1,8-ef][1,4]diazepines and 9-(3-arylhydrazono)pyrrolo[1,2-a]perimidines as antitumor agents

Two series of naphtho[1,8-ef][1,4]diazepines and pyrrolo[1,2-a]perimidines were prepared starting from 1,8-diaminonaphthalene and hydrazonoyl chlorides. The structures of the products were determined on the basis of their spectral data and elemental analyses. The mechanism of formation of such products was also discussed. The prepared compounds were screened for their antitumor activity against three cell lines, namely, MCF-7, TK-10 and UACC-62, and some derivatives showed promising activity.

Anthraquinone antitumour agents, doxorubicin, pirarubicin and benzoperimidine BP1, trigger caspase-3/caspase-8-dependent apoptosis of leukaemia sensitive HL60 and resistant HL60/VINC and HL60/DOX cells

We examined the effect of selected anthraquinone antitumour agents - doxorubicin (DOX), pirarubicin (PIRA) and benzoperimidine BP1 - on inducing apoptosis of the sensitive leukaemia HL60 cell line and its multidrug resistance sublines overexpressing P-glycoprotein (HL60/VINC) and multidrug resistance-associated protein 1 (HL60/DOX). All agents used at IC50 and IC90 were able to influence the cell cycle of sensitive HL60 and resistant cells and induce apoptosis. Interestingly, it was seen that HL60/VINC cells were more susceptible to undergo caspase-3/caspase-8-dependent apoptosis induced by the studied anthraquinone compounds compared with HL60 and HL60/DOX cells. However, the examined agents did not change the expression of Fas receptors on the surface of HL60-sensitive and-resistant cells.

Natural and synthetic acridines/acridones as antitumor agents: their biological activities and methods of synthesis

Acridine derivatives constitute a class of compounds that are being intensively studied as potential anticancer drugs. Acridines are well-known for their high cytotoxic activity; however, their clinical application is limited or even excluded because of side effects. Numerous synthetic methods are focused on the preparation of target acridine skeletons or modifications of naturally occurring compounds, such as acridone alkaloids, that exhibit promising anticancer activities. They have been examined in vitro and in vivo to test their importance for cancer treatment and to establish the mechanism of action at both the molecular and cellular level, which is necessary for the optimization of their properties so that they are suitable in chemotherapy. In this article, we review natural and synthetic acridine/acridone analogs, their application as anticancer drugs and methods for their preparation.

QSAR analysis and molecular modeling of ABCG2-specific inhibitors

In addition to its critical role is controlling drug availability and protecting sensitive organs and stem cells through cellular detoxification, breast cancer resistance protein (BCRP/ABCG2) plays an important role in cancer cell resistance to chemotherapy, together with P-glycoprotein/ABCB1. A main approach to abolish multidrug resistance is to find out specific inhibitors of the drug-efflux activity, able to chemosensitize cancer cell proliferation. Many efforts have been primarily focused on ABCB1, discovered thirty years ago, whereas very few studies have concerned ABCG2, identified much more recently. This review describes the main types of inhibitors presently known for ABCG2, and how quantitative structure-activity relationship analysis among series of compounds may lead to build up molecular models and pharmacophores allowing to design lead inhibitors as future candidates for clinical trials. A special attention is drawn on flavonoids which constitute a structurally-diverse class of compounds, well suited to identify potent ABCG2-specific inhibitors.

A New Entry to Polycyclic Indole Derivatives via Intramolecular Imino Diels−Alder Reaction: Observation of Unexpected Reaction

A new, efficient, and highly diastereoselective synthesis of polycyclic indole derivatives through intramolecular imino Diels-Alder reaction of aminoanthraquinone with N-prenylated indole-2-carboxaldehydes in the presence of 20 mol % of triphenylphosphonium perchlorate (TPPP) is reported with extremely high cis selectivity in good yield.

In vitro antileukaemic activity of extracts from berry plant leaves against sensitive and multidrug resistant HL60 cells

The aim of the present study was to determine in vitro antileukaemic activity of extracts obtained from selected berry plant leaves (Fragaria x ananassa Duch. cv Elsanta, raspberry Rubus ideus L. cv Polana and blueberry Vaccinium corymbosum L. cv Bluecrop) against promyelocytic HL60 cell line and its multidrug resistant sublines exhibiting two different MDR phenotypes: HL60/VINC (overexpressing P-glycoprotein) and HL60/DOX (overexpressing MRP1 protein). It was found that the blueberry extract was the most efficient against sensitive HL60 cell line (about 2-fold more active than strawberry and raspberry extracts) but presented much lower activity towards resistant cells. In contrast, strawberry and raspberry extracts exhibited the high cytotoxic activity against sensitive leukaemia HL60 cell line as well as its MDR sublines. The values of resistance factor (RF) found for these extracts were very low lying in the range 0.32/2.0.

Synthesis of 7-oxo-7H-naphtho[1,2,3-de]quinoline derivatives as potential anticancer agents active on multidrug resistant cell lines

Following our earlier finding that tetracyclic anthraquinone analogs with a fused pyridone ring exhibit cytotoxic activity toward multidrug resistant tumor cells, a series of new potential antitumor agents, 7-oxo-7H-naphtho[1,2,3-de]quinoline derivatives (3, 6-8, 10-12, 14, 15, and 18), bearing one or two basic side chains and various substituents at the pyridone ring, have been synthesized. The compounds have been obtained from 1-amino-4-chloroanthraquinone or 1-aminoanthraquinone by cyclization with diethyl malonate and the subsequent reactions of the key intermediates 2, 4, and 17. The compounds exhibited cytotoxic activity toward sensitive human leukemia cell line HL-60 and against its resistant sublines HL-60/VINC (MDR1 type) and HL-60/DX (MRP1 type).

Synthesis of analogues of anthraquinones linked to tuftsin or retro-tuftsin residues as potential topoisomerase inhibitors

A novel group of [(4-, 5- or 8)-hydroxy-9,10-anthraquinone-1-yl]-(tuftsin or retro-tuftsin) acids and methyl esters has been synthesized as potential anticancer compounds. The corresponding protected tuftsin or retro-tuftsin derivatives were also synthesized. We hope that combining compounds of different mechanisms of action will improve their clinical properties, and that our new analogues will be much more effective against multidrug-resistant tumour cell lines.

2,7-Dihydro-3H-pyridazino[5,4,3-kl]acridin-3-one derivatives, novel type of cytotoxic agents active on multidrug-resistant cell lines. Synthesis and biological evaluation

We have earlier postulated that the presence of a pyridazone ring fused with an anthracenedione moiety resulted in the analog's ability to overcome multidrug resistance of tumor cells [J. Med. Chem.1999, 42, 3494]. High cytotoxic activity of obtained anthrapyridazones [Bioorg. Med. Chem.2003, 11, 561] toward the resistant cell lines, prompted us to synthesize the similarly modified acridine compounds. A series of pyridazinoacridin-3-one derivatives (2b-h) were prepared from the reaction of 9-oxo-9,10-dihydroacridine-1-carboxylate with POCl(3), followed by addition of the appropriate (alkylamino)alkylhydrazines. In vitro cytotoxic activity toward sensitive and resistant leukemia cell lines: L1210, K562, K562/DX, HL-60, HL-60/VINC, and HL-60/DX, with various type of multidrug resistance (MDR and MRP) was determined. The compounds studied exhibited in comparison to the reference cytostatics (DX, MIT) desirable very low resistance indexes (RI). Variations have been observed depending upon the substituent and the type of drug exporting pump. The cytotoxic activities of examined compounds, as well as of model anthrapyridazone derivative PDZ, were lower than those of reference drugs (DX, MIT) due to their diminished affinity to DNA.

The role of structural factors in the kinetics of cellular uptake of pyrazoloacridines and pyrazolopyrimidoacridines: implications for overcoming multidrug resistance towards leukaemia K562/DOX cells

The appearance of multidrug resistance (MDR) of tumour cells to a wide array of antitumour drugs, structurally diverse and having different mechanisms of action, constitutes the major obstacle to the successful treatment of cancer. Our approach to search for non-cross resistant antitumour agents is based on the rational design of derivatives, which have a high kinetics of passive cellular uptake rendering their active efflux by MDR exporting pumps inefficient. Recently, two families of acridine cytotoxic agents were obtained, pyrazoloacridines (PACs) and pyrazolopyrimidoacridines (PPACs). The aim of this study was to examine molecular basis of the reported differences in retaining cytotoxic activity of these derivatives at cellular level against resistant erythroleukaemia K562/DOX (overexpressing P-glycoprotein) cell line. The study was performed using a spectrofluorometric method, which allows continuous monitoring of the uptake and efflux of fluorescent molecules by living cells. It was demonstrated that the presence of two additional rings, pyrazole and pyrimidine, fused to the acridine chromophore structure (PPAC) favoured more rapid cellular diffusion than the presence of only one additional pyrazole ring (PAC). The presence of hydrophobic substituent OCH3 markedly favoured the cellular uptake of pyrazoloacridines and pyrazolopyrimidoacridines while compounds having hydrophilic substituent OH exhibited very low kinetics of cellular uptake. In contrast, it was found that neither structure of the ring system nor the hydrophobic/hydrophilic character of examined substituents determined the rate of active efflux of these compounds by P-glycoprotein. Our data showed that a nearly linear relation exists between the resistance factor (RF) and lnV+ reflecting the impact of the cellular uptake rate (V+) on the ability of these compounds to overcome MDR.

The activity of latent benzoperimidine esters to inhibit P-glycoprotein and multidrug resistance-associated protein 1 dependent efflux of pirarubicin from several lines of multidrug resistant tumor cells

Multidrug resistance of tumor cells is associated with the presence of membrane proteins responsible for the cytostatics export. Recently, we have synthesized a new family of benzoperimidines causing the futile cycle of MDR pumps. In this study, biological data for benzoperimidine esters are presented for selected cell lines: sensitive (HL-60, GLC4, K562), P-gp resistant (HL-60/VINC, K562/DX), MRP1 resistant (HL-60/DX) and MRP1/LRP resistant (GLC4/DX). Their ability to inhibit the efflux of anthracycline antitumor drug, pirarubicin and to restore its accumulation in MDR cells was studied using a spectrofluorometric method which allows to follow the uptake and efflux of fluorescent molecules by living cells. Benzoperimidine esters had high effectiveness in inhibiting pirarubicin efflux and in restoring its accumulation in resistant cells. In contrast, examined esters were less active in vitro in restoration of pirarubicin cytotoxicity towards resistant cells because an enzymatic cleavage of esters occurs in presence of serum esterases.

Synthesis and biological evaluation of 2,7-Dihydro-3H-dibenzo[de,h]cinnoline-3,7-dione derivatives, a novel group of anticancer agents active on a multidrug resistant cell line

A series of anthrapyridazone derivatives with one or two basic side chains at various positions in the tetracyclic chromophore have been synthesized. The key intermediates in the synthesis are 2,7-dihydro-3H-dibenzo[de,h]cinnoline-3,7-diones 1, 12 and 15 monosubstituted at position 2 (4d, 16a-e), or 6 (2a-f) or disubstituted at positions 2 and 6 (4a-c) or 2 and 8 (17a-e) with appropriate alkylaminoalkylamines. All analogues showed in vitro cytotoxic activity against murine leukemia (L1210) and human leukemia (K562) cell lines. The compounds were also active against human leukemia multidrug resistant (K562/DX) cell line with resistance index (RI) in the range 1-3 depending on the compound's structure. Two of the most active in vitro compounds 4a and 11 were tested in vivo against murine P388 leukemia and displayed antileukemic activity comparable with that of Mitoxantrone. DNA-binding assays were performed and DNA affinity data were correlated with the structures of the compounds. The cytoplasmatic membrane affinity values (log k'(IAM)) have also been determined and the correlation with the resistance indexes discussed. The anthrapyridazones constitute a novel group of antitumor compounds that can overcome multidrug resistance.

Effect of modification of 6-[(aminoalkyl)amino]-7H-benzo[e]-perimidin-7-ones on their cytotoxic activity toward sensitive and multidrug resistant tumor cell lines. Synthesis and biological evaluation

Benzoperimidines, a novel group of antitumor anthracenedione analogues, are of interest due to their ability to overcome multidrug resistance of tumor cells (Stefańska, B., Dzieduszycka, M., Bontemps-Gracz, M. M., Borowski, E., Martelli, S., Supino, R., Pratesi, G., De Cesare, MA., Zunino, F., Kuśnierczyk, H., Radzikowski, Cz. J. Med. Chem. 1999, 42, 3494). Although the structural factor essential for exhibiting this desirable property is the presence in the molecule of a fused heterocyclic ring, the cytotoxicity against resistant cells is highly influenced by the nature and location of the substituents. A series of novel synthetic derivatives, comprising monohydroxylated benzoperimidines and 2-aminobenzoperimidines, allowed the establishment of an in vitro structure-activity relationship for a panel of leukemia sensitive, as well as P-gp dependent multidrug resistance (MDR) and multidrug resistance associated protein dependent resistance (MRP) resistant cell lines. The membrane affinity for the compounds has also been determined.

Anthrapyridones, a novel group of antitumour non-cross resistant anthraquinone analogues. Synthesis and molecular basis of the cytotoxic activity towards K562/DOX cells

1. Multidrug resistance (MDR) to antitumour agents, structurally dissimilar and having different intracellular targets, is the major problem in cancer therapy. MDR phenomenon is associated with the presence of membrane proteins which belong to the ATP-binding cassette family transporters responsible for the active drug efflux leading to the decreased intracellular accumulation. 2. The search of new compounds able to overcome MDR is of prime importance. 3. Recently we have synthesized a new family of anthrapyridone compounds. The series contained derivatives modified with appropriate hydrophobic or hydrophylic substituents at the side chain. 4. The interaction of these derivatives with erythroleukemia K562 sensitive and K562/DOX resistant (overexpressing P-glycoprotein) cell lines has been examined. The study was performed using a spectrofluorometric method which allows to continuously follow the uptake and efflux of fluorescent molecules by living cells. 5. It was demonstrated that the increase in the lipophilicity of anthrapyridones favoured the very fast cellular uptake exceeding the rate of P-gp dependent efflux out of the cell. For these derivatives, very high accumulation (the same for sensitive and resistant cells) was observed and the in vitro biological data confirmed that these compounds exhibited comparable cytotoxic activity towards sensitive and P-gp resistant cell line. In contrast, anthrapyridones modified with hydrophylic substituents exhibited relatively low kinetics of cellular uptake. 6. For these derivatives decreased accumulation in resistant cells was observed and the in vitro biological data demonstrated that they were much less active against P-gp resistant cells in comparison to sensitive cells. 7. We also studied, using confocal microscopy, the intracellular distribution of anthrapyridones in NIH-3T3 cells. Our data showed that these compounds were strongly accumulated in the nucleus and lysosomes.

Photosensitizer accumulation in spontaneous multidrug resistant cells: a comparative study with Rhodamine 123, Rose Bengal acetate and Photofrine

The influence both of overexpression of multidrug transporter proteins and of phenotype changes occurring in cells developing spontaneous resistance on the accumulation of photosensitizer molecules was studied on two tumor-derived cell lines (B16, A2780) expressing the MDR-1 phenotype. Rhodamine 123, Rose Bengal acetate (a fluorogenic substrate that is restored to the native active molecule by specific enzyme activity inside cells) and Photofrin were considered. The two resistant variants accumulate Rhodamine 123 to a lesser extent than the respective wild types. Treatment with verapamil markedly enhances Rhodamine 123 accumulation in resistant cells, blocking the drug's extrusion. The amount of Rose Bengal is larger in resistant cells than in wild type cells. Verapamil does not affect drug accumulation, although it significantly impairs the efflux process. The results are explained by the enhancement of both membrane traffic and esterase activity resulting in intracellular Rose Bengal production that counterbalances the increased ability in the outward transport of resistant cells. Photofrin is accumulated to a lower degree in resistant than in wild type cells. Verapamil does not alter the drug accumulation, although the release process is somewhat affected. Different intracellular turnovers of Photofrin take place in the cell variants, and the release of the monomeric fluorescent fractions is greater in resistant than in wild type cells.

Transport of new non-cross-resistant antitumor compounds of the benzoperimidine family in multidrug resistant cells

Multidrug resistance (MDR) phenotype in mammalian cells is often correlated with overexpression of P-glycoprotein or multidrug resistance-associated protein (MRP1). Both proteins are energy-dependent drug efflux pumps that efficiently reduce the intracellular accumulation and hence the cytotoxicity of many natural cytotoxins. The influx and efflux of drugs across the cell membrane are in large part responsible for their intracellular concentrations, and in the search for new compounds able to overcome MDR, it is of prime importance to determine the molecular parameters whose modification would lead to an increase in the kinetics of uptake and/or to a decrease in the pump-mediated efflux. Here, we studied three members of a new family of benzoperimidine antitumor compounds which exhibit comparable cytotoxicity towards resistant cells expressing P-glycoprotein, or MRP1, and sensitive cells. We used spectrofluorometric methods to determine the kinetics of the uptake and release of these three drugs in different cell lines: the erythroleukemia cell line K562 and the resistant K562/Adr expressing P-glycoprotein, the small-cell lung cancer cell line GLC4 and resistant GLC4/Adr expressing MRP1. We also studied, using confocal microscopy, the intracellular distribution of these drugs in NIH/3T3 cells. Our data show that (i) the kinetics for the uptake of these drugs is very rapid, higher than 2 x 10(-17) mole cell(-1) s(-1), (ii) the drugs are strongly accumulated in the nucleus and lysosomes, (iii) the three drugs are recognized and pumped out by both transporters, as shown by the inhibition of P-glycoprotein- and MRP1-mediated efflux of pirarubicin by benzoperimidine, with inhibitory constants of 1.5 and 2.1 microM for P-glycoprotein and MRP1, respectively, suggesting that benzoperimidine is transported by the two transporters with K(m) approximately 2 microM. In conclusion, the fast uptake kinetics of the benzoperimidines counterbalance their efflux by P-glycoprotein and MRP1.