Novel multidrug resistance reversal agents

Pyrrolizine/indolizine-bearing (un)substituted isoindole moiety: design, synthesis, antiproliferative and MDR reversal activities, and in silico studies

Two new series of pyrrolizine/indolizine derivative-bearing (un)substituted isoindole moiety were designed and synthesized. The anticancer potential of the new compounds was evaluated against hepatocellular carcinoma (HepG-2), colorectal carcinoma, colon cancer (HCT-116), and breast cancer (MCF-7) cell lines. Compounds 6d and 6o were the most potent derivatives with IC50 values ranging from 6.02 to 13.87 μM against HePG-2, HCT-116, and MCF-7 cell lines. Moreover, methyl analog of the fluoro-substituted indolizine derivative 6m revealed significant antiproliferative activity against HePG-2, HCT-116, and MCF-7 cancer cell lines with IC50 values of 11.97, 28.37, and 19.87 μM, respectively. The most active anticancer analogs, 6d, 6m, and 6o, were inspected for their putative mechanism of action by estimating their epidermal growth factor receptor (EGFR) and cyclin-dependent kinase (CDK 2) inhibitory activities. Thus, compound 6o displayed the most inhibitory activity against EGFR and CDK 2 with IC50 values of 62 and 118 nM, respectively. Additionally, the quantitative real-time PCR analysis for the P-glycoprotein effect of compounds 6d, 6m, and 6o was performed, in which compound 6o illustrated significant down-regulation of P-gp against the HepG-2 cell line by 0.2732 fold. Mechanistic studies for the most active compounds involving the reversal doxorubicin (DOX) effect of compounds 6d, 6m, and 6o were performed, which illustrated cytotoxic activity with IC50 22.27, 3.88, and 8.79 μM, respectively. Moreover, the apoptotic activity of the most active derivative 6o on HCT-116 cancer cells showed accumulation in the G1 and S phases of the cell cycle.

A palladium catalyzed asymmetric desymmetrization approach to enantioenriched 1,3-disubstituted isoindolines

Herein, we report the first palladium/MPAA catalyzed enantioselective C-H activation/[4 + 1] annulation of diarylmethyltriflamide and olefins to construct chiral cis-1,3-disubstituted isoindoline derivatives. The use of a readily accessible mono-N-protected amino acid as a chiral ligand improves the efficiency and enantioselectivity of the catalytic transformation. The developed method provides access to both enantiomers of a product using either d or l-phenylalanine derivative as a chiral ligand facilitating the synthesis of both optically active 1,3-disubstituted isoindoline derivatives.

Fluorinated Imines in Tandem and Cycloaddition Reactions

The chemistry of fluorinated compounds has experienced extraordinary growth in recent decades due to the many and varied properties which many of the compounds that contain fluorinated groups possess. Among all of them, fluorinated chiral imines, in particular the Ellman's imines, are of great importance since they are some of the most interesting building blocks for the synthesis of a large number of enantioenriched carbocycles and heterocycles with extraordinary biological and synthetic properties. This personal account covers the most significant results obtained in our research group in the last two decades concerning asymmetric tandem reactions, paying special attention to the intramolecular aza-Michael reaction (IMAMR), diversity oriented synthesis (DOS), asymmetric tandem reactions involving a p-tolylsulfinyl group as chiral inducer and cycloaddition processes, in particular, the Pauson-Khand reaction, [2+2+2]-cycloadditions and metathesis reactions, starting mainly from enyne compounds and through the use of fluorinated chiral N-sulfinyl imines and their derivatives as starting materials.

DBU-Catalyzed Aerobic CDC Reaction of Thiophenols

A convenient method was developed for the preparation of thiolated compounds via a DBU-catalyzed aerobic cross-dehydrogenative coupling (CDC) reaction. The established protocol is environmentally friendly and operationally simple. Substrates like (hetero)aryl acetates, (hetero)aryl ketones, and indoles could be transformed into the corresponding thiolated products in moderate to high yields and further applied in the preparation of bioactive compounds in a prefunctionalization-free manner.

Discovery of New 4-Indolyl Quinazoline Derivatives as Highly Potent and Orally Bioavailable P-Glycoprotein Inhibitors

The major drawbacks of P-glycoprotein (P-gp) inhibitors at the clinical stage make the development of new P-gp inhibitors challenging and desirable. In this study, we reported our structure-activity relationship studies of 4-indolyl quinazoline, which led to the discovery of a highly effective and orally active P-gp inhibitor, YS-370. YS-370 effectively reversed multidrug resistance (MDR) to paclitaxel and colchicine in SW620/AD300 and HEK293T-ABCB1 cells. YS-370 bound directly to P-gp, did not alter expression or subcellular localization of P-gp in SW620/AD300 cells, but increased the intracellular accumulation of paclitaxel. Furthermore, YS-370 stimulated the P-gp ATPase activity and had moderate inhibition against CYP3A4. Significantly, oral administration of YS-370 in combination with paclitaxel achieved much stronger antitumor activity in a xenograft model bearing SW620/Ad300 cells than either drug alone. Taken together, our data demonstrate that YS-370 is a promising P-gp inhibitor capable of overcoming MDR and represents a unique scaffold for the development of new P-gp inhibitors.

Stereoselective synthesis of (Z)-1,3-bis(α,β-unsaturated carbonyl)-isoindolines from aldehydes and phenacyl azides under metal free conditions

Here in the present manuscript, we report our observation of an unprecedented stereoselective synthesis of 2H-isoindolin-1,3-ylidenes from 2-(formylphenyl)acrylates and phenacylazide in the presence of piperidine. Unlike in our previous findings, in which we accessed 3-keto-isoquinolines from the same starting materials under slightly modified reaction conditions, this unexpected one-pot tandem reaction allows an efficient and simple method to access a variety of highly functionalized ethyl (Z)-2-((Z)-3-(2-oxo-2-arylethylidene)-2,3-dihydro-1H-benzo[e]isoindol-1-ylidene)-acetates in very good to excellent yields (up to 91%). The present methodology is compatible with a wide variety of functional groups.

Tandem Insertion/[3,3]-Sigmatropic Rearrangement Involving the Formation of Silyl Ketene Acetals by Insertion of Rhodium Carbenes into S-Si Bonds

Allyl 2-diazo-2-phenylacetates are shown to react with trimethylsilyl thioethers in the presence of rhodium(II) catalysts to generate α-allyl-α-thio silyl esters. The transformation involves a tandem process involving formal rhodium-catalyzed insertion of the carbene group into the S-Si bond to generate a silyl ketene acetal, followed by a spontaneous Ireland-Claisen rearrangement. The silyl ester products were isolated as the corresponding carboxylic acids after aqueous workup. Intramolecular cyclopropanation of the allyl fragment generally competes with addition of the heteroatom to the carbene center. The reaction occurs under mild conditions and in high yield, allowing for rapid entry into rearrangement tetrasubstituted products. Propargyl esters were shown to generate the corresponding α-allenyl products.

An Efficient Approach to Phosphorylated Isoindoline Fused with Triazoles via Zn-Catalyzed Cascade Cyclization of 2-Propynol Benzyl Azides and Diarylphosphine Oxides

An efficient approach for the synthesis of phosphorylated isoindoline fused with triazoles via Zn(OTf)₂-catalyzed cascade cyclization of easily prepared ortho-propynol benzyl azides and diarylphosphine oxides is developed. The transformation occurred smoothly in moderate to excellent yields and tolerated various propargylic alcohol substrates.

A concise synthesis of peramine, a metabolite of endophytic fungi

The total synthesis of peramine, a natural product isolated from an endophytic fungi, has been achieved in four steps and 34% overall yield from known compounds. The key step was the one-pot construction of the pyrrolopyrazinone ring from pyrrole amide and propargyl bromide. The preparation of peramine-d4 as an internal standard for quantitative analysis by MS is also described.

Isoindoline Derivatives of α-Amino Acids as Cyclooxygenase 1 and 2 Inhibitors

IC50 values were obtained for two series of isoindolines derived from α-amino acids over cyclooxygenase 1 and 2 (COX-1 and COX-2). In order to explain the biological activity observed, a structure-activity relationship (SAR) model was achieved for the tested compounds and 19 reference compounds with known selective inhibitory activity, through the correlation of the binding energies calculated from rigid docking of the best conformations into the catalytic sites of COX-1 and COX-2, as well as their molecular descriptors: Log P, molecular weight (MW), volume (V), and solvation energy (Esol) versus their experimental IC50 values by MLR and LS-SVM methods. The model probed whether the COX-1 and COX-2 inhibitory activities of the isoindolines correlate with steric, hydrophobic, and thermodynamic parameters. The correlation values with MLR for COX-1 and COX-2 (r(2)  = 0.4193 and r(2)  = 0.5929) were optimized with LS-SVM until r(2)  = 0.6818 for COX-1 and r(2)  = 0.8985 for COX-2, resulting in a good predictive ability for COX-1 and -2 inhibition with this model. In conclusion, the data suggests that the physicochemical descriptors evaluated have an impact on the inhibitory activity and selectivity of isoindolines over COX-1 and COX-2.

Efficient access to enantiopure 1,3-disubstituted isoindolines from selective catalytic fragmentation of an original desymmetrized rigid overbred template

Enantiopure 1,3-disubstituted isoindolines are synthesized from selective C–C bond fragmentation of a rigid overbred template, obtained through an asymmetric desymmetrization reaction.

4,5-Di-substituted benzyl-imidazol-2-substituted amines as the structure template for the design and synthesis of reversal agents against P-gp-mediated multidrug resistance breast cancer cells

Over-expression of P-glycoprotein (P-gp), a primary multidrug transporter which is located in plasma membranes, plays a major role in the multidrug resistance (MDR) of cytotoxic chemotherapy. Naamidines are a class of marine imidazole alkaloids isolated from Leucetta and Clathrina sponges, possessing a Y-shaped scaffold. Based on the results previously obtained from the third-generation MDR modulator ONT-093 and other modulators developed in our group, we designed and synthesized a series of novel 4,5-di-substituted benzyl-1-methyl-1H-imidazol-2-substituted amines using the Naamidine scaffold as the structure template. Subsequently, their reversing activity for Taxol resistance has been evaluated in P-gp-mediated multidrug resistance breast cancer cell line MDA435/LCC6MDR. Compounds 12c with a Y-shaped scaffold, and compound 17c which is 'X-shaped' scaffold and possesses a 4-diethylamino group at aryl ring B, turned out to be the most potent P-gp modulators. It appears that compounds 12c and 17c at 1 μM concentration can sensitize LCC6MDR cells toward Taxol by 26.4 and 24.5 folds, with an EC50 212.5 and 210.5 nM, respectively. These two compounds are about 5-6 folds more potent than verapamil (RF = 4.5). Moreover, compounds 12c and 17c did not exhibit obvious cytotoxicity in either cancer cell lines or normal mouse fibroblast cell lines. This study has demonstrated that the synthetic Naamidine analogues can be potentially employed as effective, safe modulators for the P-gp-mediated drug resistance cancer cells.

A new approach for fused isoindolines via hexadehydro-Diels–Alder reaction (HDDA) by Fe(0) catalysis

A simple method has been developed for the synthesis of fused isoindolines via a cascade HDDA approach catalyzed by Fe₂(CO)₉.

Bioassay-guided isolation of an alkaloid with antiangiogenic and antitumor activities from the extract of Fissistigma cavaleriei root

Fissistigma cavaleriei (Levl) Rehd (Annonaceae) is used as a folklore medicine for treatment of inflammation, arthritis, and tuberculosis by Miao people in China. In the present study, the antiangiogenic activity of F. cavaleriei was investigated. The chorioallantoic membrane of the fertilized hen's egg (CAM assay) was used to determine antiangiogenic activity of the plant extract. Compound (1), a compound with antiangiogenic activity, was isolated by bioassay-guided fractionation from F. cavaleriei for the first time. The structure of compound (1) was elucidated on the basis of spectroscopic methods. Colorimetric COX (ovine) inhibitor screening assay was used to determine its inhibitory effect on COX-1 and COX-2. MTT and Sulforhodamine B assays were used to investigate its cytotoxic effects on tumor cell lines. As a result, compound (1) showed a selectively inhibiting effect on COX-2 and could inhibit the growth of tumor cells in vitro. The antitumor activity of compound (1) was further confirmed by the observation that compound (1) administration significantly inhibited the growth of S-180 cells in mice. Moreover, compound (1) was able to enhance the antitumor activity of doxorubicin in the mice bearing with S-180 cells while combined with doxorubicin. In conclusion, compound (1) is a multi-target molecule and further experimental investigations are needed to determine whether it can be used as a lead molecule for tumor treatment.

Iodination of verapamil for a stronger induction of death, through GSH efflux, of cancer cells overexpressing MRP1

The multidrug resistance protein 1 (MRP1), involved in multidrug resistance (MDR) of cancer cells, was found to be modulated by verapamil, through stimulation of GSH transport, leading to apoptosis of MRP1-overexpressing cells. In this study, various iodinated derivatives of verapamil were synthesized, including iodination on the B ring, known to be involved in verapamil cardiotoxicity, and assayed for the stimulation of GSH efflux by MRP1. The iodination, for nearly all compounds, led to a higher stimulation of GSH efflux. However, determination of concomitant cytotoxicity is also important for selecting the best compound, which was found to be 10-fold more potent than verapamil. This will then allow us to design original anti-cancer compounds which could specifically kill the resistant cancer cells.

Molecular modeling study of isoindolines as L-type Ca(2+) channel blockers by docking calculations

Two series of isoindolines 1(a-g) and 2(a-g) were found by docking calculations to be possible L-type Ca(2+) channel (LCC) blockers. The theoretical 3-D model of the outer vestibule and the selective filter of the LCC was provided by Professor Lipkind; this model consists of transmembrane segments S5 and S6 and P-loops contributed by each of four repeats (I, II, III, and IV) of Ca(v) 1.2. Therefore, two well-known LCC blockers, nifedipine 3 and (R)-ethosuccinimide 4 were also evaluated, and their binding sites on the LCC were identified and compared with those obtained for 1(a-g) and 2(a-g). Analysis of the results shows that the target compounds tested probably could be LCC blockers, since they interact with or near the glutamic acid residues Glu393, Glu736, Glu1145 and Glu1446 (the EEEE locus), which belong to the LCC selectivity region. The G values for all of the Ca(2+) channel ligands are between-10.78 and -3.67 (kcal mol(-1)), showing that LCC-1b, -1e and -1f complexes are more stable than the other compounds tested. Therefore, theoretically calculated dissociation constants K(d) (microM) were obtained for all compounds. Comparing these values reveals that compounds 1b (0.0244 microM), 1e (0.0176 microM) and 1f (0.0125 microM) exhibit more affinity for the LCC than the other compounds. This screening shows that the two series of isoindolines probably could act as LCC blockers.

Substituted tetrahydroisoquinoline compound B3 inhibited P-glycoprotein-mediated multidrug resistance in-vitro and in-vivo

P-glycoprotein (P-gp) mediated multidrug resistance (MDR) is one of the main obstacles in tumour chemotherapy. A promising approach to reverse MDR is the combined use of nontoxic and potent P-gp inhibitor with conventional anticancer drugs. We have examined the potential of a newly synthesized tetrahydroisoquinoline derivative B3 as a MDR-reversing agent. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to examine the effect of B3 on the cytotoxicity in K562/A02 and MCF-7/ADM cells caused by doxorubicin (adriamycin). Accumulation and efflux of P-gp substrate rhodamine123 in K562/A02 and primary cultured rat brain microvessel endothelial cells (RBMECs) were measured to evaluate the inhibitory effect of B3 on P-gp. The K562/A02 xenograft model in nude mice was established to examine MDR-reversing efficacy of B3 in-vivo. The results indicated that co-administration of B3 resulted in an increase on chemosensitivity of K562/A02 and MCF-7/ADM cells to doxorubicin in a dose-dependent manner. Rhodamine123 accumulation in K562/A02 cells and RBMECs were significantly enhanced after the incubation with various concentrations of B3. Furthermore, B3 inhibited the efflux of rhodamine123 from RBMECs. Co-administration of B3 with doxorubicin significantly decreased weight and volume of tumour in nude mice. In conclusion, B3 is a novel and potent MDR reversal agent with the potential to be an adjunctive agent for tumour chemotherapy.

N-Methyl-1-oxoisoindoline-2-carboxamide monohydrate

The title compound, C₁₀H₁₀N₂O₂·H₂O, is dimerized by inversion-related inter­molecular N—H⋯O hydrogen bonding. There is an intra­molecular N—H⋯O bond, resulting in a six-membered ring. Each dimer inter­acts with other dimers through hydrogen bonding with water mol­ecules. The water mol­ecules are linked to each other in a stair-like chain, thus generating two-dimensional polymeric strips. The dimers are also linked to each other through inter­molecular C—H⋯O hydrogen bonding. There are π–π inter­actions between the aromatic and heterocyclic five-membered rings [centroid–centroid distance 3.8360 (12) Å]. C—H⋯π inter­actions also exist between CH₂ groups and aromatic rings.

1-Oxoisoindoline-2-carboxamide

The title mol­ecule, C₉H₈N₂O₂, is essentially planar. The crystal structure is stabilized by hydrogen bonding. An intra­molecular N—H⋯O hydrogen bond results in a six-membered ring. Each mol­ecule inter­acts with two others through N—H⋯O and C—H⋯O hydrogen bonding, resulting in the formation of nine-membered rings. These hydrogen bonds generate a two-dimensional polymeric network. There are also π–π inter­actions between the aromatic and heterocyclic rings [centroid–centroid distance 3.638 (2) Å].

In vitro activity of novel dual action MDR anthranilamide modulators with inhibitory activity at CYP-450

Synthesis and in vitro cytotoxicity assays of new anthranilamide MDR modulators have been performed to assess their inhibition potency of the P-glycoprotein (P-gp) transporter. The aromatic spacer group between nitrogen atoms (N1 and N2) in the known inhibitor XR9576 was replaced with a flexible alkyl chain of 2 to 6 carbon atoms in length. 6,7-Dimethoxy-1,2,3,4-tetrahydroisoquinoline and their open-chain N-methylhomoveratrylamine counterparts were shown to be potent P-gp inhibitors. The maximal inhibition was obtained when using an ethyl or propyl spacer. Several compounds were more potent than verapamil and intrinsically less cytotoxic than XR9576. In addition, in vitro metabolism studies of 23a with a subset of human CYP-450 isoforms revealed that, unlike XR9576, 23a inhibited CYP3A4, an enzyme that colocalizes with P-gp in the intestine and contributes to tumor cell chemoresistance by enhancing the biodisposition of anticancer drugs such as paclitaxel toward metabolism. In this context, 22a might be a suitable candidate for further drug development.

A Naive Bayes Classifier for Prediction of Multidrug Resistance Reversal Activity on the Basis of Atom Typing

Multidrug resistance (MDR), the ability of cancer cells to become simultaneously resistant to different drugs, remains an unsolved challenge in cancer chemotherapy. The use of MDR reversal (MDRR) agents is a promising approach to overcome this problem. For the design and development of such agents, it would be desirable to have a reliable model to estimate the MDRR activity of compounds. Presented here is a naive Bayes classifier to categorize MDRR agents into active and inactive classes, which uses a universal, generic molecular-descriptor system.(1) The naive Bayes classifier was built from a 424 compound training set, selected from 609 druglike compounds in the publicly available "Klopman set". The model correctly predicted MDRR activities for 82.2% of 185 compounds in a testing set. The cumulative probabilities were proven useful for prioritizing the compounds for testing. The impact of attribute dependences on the performance of the classifier was examined. As an unsupervised learner with no tuning parameters, a naive Bayes classifier is capable of providing an objective comparison of the effectiveness of different molecular descriptors. The relative performance of the classifiers constructed from either an atom-type-based molecular descriptor or the long-range functional-class fingerprint descriptors FCFP_6 or FCFP_2 was compared. Employing an atom typing descriptor with the naive Bayes classification, it enables the interpretability of the resulting model, which offers extra information for the rational design of MDRR agents.

In vivo antitumor activity of a novel sulfonamide, HMN-214, against human tumor xenografts in mice and the spectrum of cytotoxicity of its active metabolite, HMN-176

The cytotoxic effects of HMN-176 ((E)-4-[[2-N-[4-methoxybenzenesulfonyl] amino] stilbazole] 1-oxide; a newly synthesized compound, were evaluated and compared with those of the clinically used antitumor agents cis-platinum, adriamycin, etoposide, taxol, and vincristine in 22 human tumor cell lines isolated from various organs. HMN-176 exhibited potent cytotoxicity with IC(50) values in the nM range, and the variance of its cytotoxic efficacy was remarkably small. Drug-resistant cell lines also showed low cross-resistance to HMN-176 corresponding to overall resistance indices of less than 14.3. HMN-214 was synthesized as an oral prodrug because of the poor oral absorption of HMN-176 itself. Pharmacokinetic studies showed that HMN-214 was an acceptable oral prodrug of HMN-176. In the in vivo analysis of the schedule-dependency of HMN-214, the repeated administration for over 5 days elicited potent antitumor activity, as expected from the exposure-dependency of the cytotoxicity of HMN-176 and from the cytometric studies. The antitumor activity of HMN-214 against human tumor xenografts was equal or superior to that of clinically available agents, including cis-platinum, adriamycin, vincristine, and UFT without severe toxicity such as neurotoxicity. Because of its good activity in preclinical trials, HMN-214 has entered Phase I clinical trials in the USA.

The medicinal chemistry of multidrug resistance (MDR) reversing drugs

Multidrug resistance (MDR) is a kind of resistance of cancer cells to multiple classes of chemotherapic drugs that can be structurally and mechanistically unrelated. Classical MDR regards altered membrane transport that results in lower cell concentrations of cytotoxic drug and is related to the over expression of a variety of proteins that act as ATP-dependent extrusion pumps. P-glycoprotein (Pgp) and multidrug resistance protein (MRP1) are the most important and widely studied members of the family that belongs to the ABC superfamily of transporters. It is apparent that, besides their role in cancer cell resistance, these proteins have multiple physiological functions as well, since they are expressed also in many important non-tumoural tissues and are largely present in prokaryotic organisms. A number of drugs have been identified which are able to reverse the effects of Pgp, MRPI and sister proteins, on multidrug resistance. The first MDR modulators discovered and studied in clinical trials were endowed with definite pharmacological actions so that the doses required to overcome MDR were associated with unacceptably high side effects. As a consequence, much attention has been focused on developing more potent and selective modulators with proper potency, selectivity and pharmacokinetics that can be used at lower doses. Several novel MDR reversing agents (also known as chemosensitisers) are currently undergoing clinical evaluation for the treatment of resistant tumours. This review is concerned with the medicinal chemistry of MDR reversers, with particular attention to the drugs that are presently in development.

Progress in understanding the structure-activity relationships of P-glycoprotein

Efflux out of cells by P-glycoprotein (P-gp) represents a serious liability for pharmaceuticals, particularly for anti-cancer drugs. Consequently, identification of compounds as potential substrates is important for understanding their bioavailability. Also, the development of agents which reverse this multi-drug resistance phenotype has received considerable attention. Assays for determining these activities are reviewed. Recent literature and studies into the structure-activity relationships (SAR) of the resulting data are discussed. Multiple binding sites and other complicating factors have prevented the development of a truly general, conclusive SAR either for substrate or inhibitory activities. Consequently, many models have tended to address only very general properties, such as lipophilicity and size. However, progress has been made in the last few years toward more specific SAR suggesting well-defined structural features responsible for both activities. The future of understanding the details of P-gp SAR lies in more specific assays that target specific binding sites and mechanisms of action.

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.

Quantitative analysis of the relative transcript levels of ABC transporter Atr genes in Aspergillus nidulans by real-time reverse transcription-PCR assay

The development of assays for quantitative analysis of the relative transcript levels of ABC transporter genes by real-time reverse transcription-PCR (RT-PCR) might provide important information about multidrug resistance in filamentous fungi. Here, we evaluate the potential of real-time RT-PCR to quantify the relative transcript levels of ABC transporter Atr genes from Aspergillus nidulans. The AtrA to AtrD genes showed different and higher levels in the presence of structurally unrelated drugs, such as camptothecin, imazalil, itraconazole, hygromycin, and 4-nitroquinoline oxide. We also verified the relative transcript levels of the Atr genes in the A. nidulans imazalil-resistant mutants. These genes displayed a very complex pattern in different ima genetic backgrounds. The imaB mutant has higher basal transcript levels of AtrB and -D than those of the wild-type strain. The levels of these two genes are comparable when the imaB mutant is grown in the presence and absence of imazalil. The imaC, -D, and -H mutants have higher basal levels of AtrA than that of the wild type. The same behavior is observed for the relative transcript levels of AtrB in the imaG mutant background.

Palladium-catalyzed intramolecular alpha-arylation of alpha-amino acid esters

The Pd-catalyzed intramolecular alpha-arylation of alpha-amino acid esters is described. Starting from readily available amino acids, the synthesis of a variety of isoindolines and tetrahydroisoquinoline carboxylic acid esters has been accomplished. Additionally, fused tricyclic systems can be efficiently prepared from cyclic amino acid esters. Reaction conditions have been found that allow the use of tert-butyl ester and N-(benzyloxycarbonyl) protecting groups.

DNA topoisomerases as targets for anticancer drugs

DNA topoisomerases are essential enzymes that regulate the conformational changes in DNA topology by catalysing the concerted breakage and rejoining of DNA strands during normal cellular growth. Over the past few years there has been considerable pharmacological interest in these enzymes because inhibitors of DNA topoisomerases represent a major class of anticancer drugs. This review highlights topoisomerase-targeting drugs that have shown promising anticancer activities. The mechanisms by which those drugs interfere with the catalytic cycles of type I and type II DNA topoisomerases and the factors involved in the development of resistance to these drugs are discussed.

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.