Reversal of multidrug resistance by phenothiazines and structurally related compounds

Modulators of cellular cholesterol homeostasis as antiproliferative and model membranes perturbing agents

Cholesterol is an important component of mammalian cell membranes affecting their fluidity and permeability. Together with sphingomyelin, cholesterol forms microdomains, called lipid rafts. They play important role in signal transduction forming platforms for interaction of signal proteins. Altered levels of cholesterol are known to be strongly associated with the development of various pathologies (e.g., cancer, atherosclerosis and cardiovascular diseases). In the present work, the group of compounds that share the property of affecting cellular homeostasis of cholesterol was studied. It contained antipsychotic and antidepressant drugs, as well as the inhibitors of cholesterol biosynthesis, simvastatin, betulin, and its derivatives. All compounds were demonstrated to be cytotoxic to colon cancer cells but not to non-cancerous cells. Moreover, the most active compounds decreased the level of free cellular cholesterol. The interaction of drugs with raft-mimicking model membranes was visualized. All compounds reduced the size of lipid domains, however, only some affected their number and shape. Membrane interactions of betulin and its novel derivatives were characterized in detail. Molecular modeling indicated that high dipole moment and significant lipophilicity were characteristic for the most potent antiproliferative agents. The importance of membrane interactions of cholesterol homeostasis-affecting compounds, especially betulin derivatives, for their anticancer potency was suggested.

Antipsychotic phenothiazine drugs bind to KRAS in vitro

We used NMR to show that the antipsychotic phenothiazine drugs promazine and promethazine bind to GDP-KRAS. Promazine also binds to oncogenic GDP-KRAS(G12D), and to wild type GppNHp-KRAS. A panel of additional phenothiazines bind to GDP-KRAS but with lower affinity than promazine or promethazine. Binding is most dependent on substitutions at C-2 of the tricyclic phenothiazine ring. Promazine was used to generate an NMR-driven HADDOCK model of the drug/GDP-KRAS complex. The structural model shows the tricyclic phenothiazine ring of promazine associates with the hydrophobic pocket p1 that is bordered by the central β sheet and Switch II in KRAS. Binding appears to stabilize helix 2 in a conformation that is similar to that seen in KRAS bound to other small molecules. Association of phenothiazines with KRAS may affect normal KRAS signaling that could contribute to multiple biological activities of these antipsychotic drugs. Moreover, the phenothiazine ring represents a new core scaffold on which to design modulators of KRAS activity.

Blocking of efflux transporters in rats improves translational validation of brain radioligands

Background

Positron emission tomography (PET) is a molecular imaging technique that can be used to investigate the in vivo pharmacology of drugs. Initial preclinical evaluation of PET tracers is often conducted in rodents due to the accessibility of disease models as well as economic considerations. Compared to larger species, rodents display a higher expression and/or activity of efflux transporters such as the P-glycoprotein (P-gp). Low brain uptake could, therefore, be species-specific and uptake in rodents not be predictive for that in humans. We hypothesized that a better prediction from rodent data could be achieved when a tracer is evaluated under P-gp inhibition. Consequently, we compared the performance of eight neuroreceptor tracers in rats with and without P-gp inhibition including a specific binding blockade. This data set was then used to predict the binding of these eight tracers in pigs.

Methods

PET tracers targeting serotonin 5-HT_2A receptors ([¹⁸F]MH.MZ, [¹⁸F]Altanserin, [¹¹C]Cimbi-36, [¹¹C]Pimavanserin), serotonin 5-HT₇ receptors ([¹¹C]Cimbi-701, [¹¹C]Cimbi-717 and [¹¹C]BA-10) and dopamine D_2/3 receptors ([¹⁸F]Fallypride) were used in the study. The brain uptake and target-specific binding of these PET radiotracers were evaluated in rats with and without inhibition of P-gp. Rat data were subsequently compared to the results obtained in pigs.

Results

Without P-gp inhibition, the amount of target-specific binding in the rat brain was sufficient to justify further translation for three out of eight evaluated tracers. With P-gp inhibition, results for five out of eight tracers justified further translation. The performance in pigs could correctly be predicted for six out of eight tracers when rat data obtained under P-gp inhibition were used, compared to four out of eight tracers without P-gp inhibition.

Conclusions

P-gp strongly affects the uptake of PET tracers in rodents, but false prediction outcomes can be reduced by evaluating a tracer under P-gp inhibition.

Antipsychotic use is inversely associated with gastric cancer risk: A nationwide population-based nested case-control study

Objective

The association between antipsychotic use and gastric cancer risk remains unclear. Therefore, this study aimed to determine the association between antipsychotic exposure and the incidence of gastric cancer.

Methods

Using a nested case‐control design, a total of 34 470 gastric cancer patients and 163 430 nongastric cancer controls were identified from Taiwan's National Health Insurance Research Database between 1 January 1997 and 31 December 2013. We analyzed the data using a conditional logistic regression model to adjust for possible confounding variables.

Results

Antipsychotic use was independently inversely associated with gastric cancer risk after controlling for potential confounding factors including income, urbanization, medications, physical and medical illness, aspirin use, nonsteroidal anti‐inflammatory drug use and triple therapy. In addition, dose‐dependent trends against gastric cancer risk were also shown with individual antipsychotic compounds including thioridazine, haloperidol, sulpiride, clozapine, olanzapine, quetiapine, amisulpride, and risperidone. A sensitivity analysis showed that second‐generation antipsychotics had significant dose‐dependent effects in reducing the risk of gastric cancer risk in patients with and without peptic ulcer disease.

Conclusions

Antipsychotic use was inversely associated with gastric cancer risk, and dose‐dependent effects against gastric cancer were also seen with several individual antipsychotic compounds.

Multiclass Classifier for P-Glycoprotein Substrates, Inhibitors, and Non-Active Compounds

P-glycoprotein (P-gp) is a transmembrane protein that actively transports a wide variety of chemically diverse compounds out of the cell. It is highly associated with the ADMET (absorption, distribution, metabolism, excretion and toxicity) properties of drugs/drug candidates and contributes to decreasing toxicity by eliminating compounds from cells, thereby preventing intracellular accumulation. Therefore, in the drug discovery and toxicological assessment process it is advisable to pay attention to whether a compound under development could be transported by P-gp or not. In this study, an in silico multiclass classification model capable of predicting the probability of a compound to interact with P-gp was developed using a counter-propagation artificial neural network (CP ANN) based on a set of 2D molecular descriptors, as well as an extensive dataset of 2512 compounds (1178 P-gp inhibitors, 477 P-gp substrates and 857 P-gp non-active compounds). The model provided a good classification performance, producing non error rate (NER) values of 0.93 for the training set and 0.85 for the test set, while the average precision (AvPr) was 0.93 for the training set and 0.87 for the test set. An external validation set of 385 compounds was used to challenge the model’s performance. On the external validation set the NER and AvPr values were 0.70 for both indices. We believe that this in silico classifier could be effectively used as a reliable virtual screening tool for identifying potential P-gp ligands.

Increased lipid peroxidation, apoptosis and selective cytotoxicity in colon cancer cell line LoVo and its doxorubicin-resistant subline LoVo/Dx in the presence of newly synthesized phenothiazine derivatives

Cancer cells often develop the resistance to pro-apoptotic signaling that makes them invulnerable to conventional treatment. Therapeutic strategies that make cancer cells enter the path of apoptosis are desirable due to the avoidance of inflammatory reaction that usually accompanies necrosis. In the present study phenothiazines (fluphenazine and four recently synthesized derivatives) were investigated in order to identify compounds with a potent anticancer activity. Since phenothiazines are known as multidrug resistance modulators the sensitive human colorectal adenocarcinoma cell line (LoVo) and its doxorubicin-resistant, ABCB1 overexpressing, subline (LoVo/Dx) have been employed as a model system. In studied cancer cells cytotoxic effect of the phenothiazine derivatives was accompanied by apoptosis and autophagy induction as well as by the increase of cellular lipid peroxidation and intracellular reactive oxygen species generation. Molecular modelling revealed that reactivity of phenothazines (manifested by their low energy gap) but not lipophilicity was positively correlated with their anticancer potency, pro-oxidant properties and apoptosis induction ability. Additionally, some of the studied compounds turned out to be more potent cytotoxic and pro-apoptotic agents in doxorubicin-resistant (LoVo/Dx) cells than in sensitive ones (LoVo). The hypothesis was assumed that studied phenothiazine derivatives induced apoptotic cell death by increasing the production of reactive oxygen species.

Methylene blue activates the PMCA activity and cross-interacts with amyloid β-peptide, blocking Aβ-mediated PMCA inhibition

The phenothiazine methylene blue (MB) is attracting increasing attention because it seems to have beneficial effects in the pathogenesis of Alzheimer's disease (AD). Among other factors, the presence of neuritic plaques of amyloid-β peptide (Aβ) aggregates, neurofibrilar tangles of tau and perturbation of cytosolic Ca²⁺ are important players of the disease. It has been proposed that MB decreases the formation of neuritic plaques due to Aβ aggregation. However, the molecular mechanism underlying this effect is far from clear. In this work, we show that MB stimulates the Ca²⁺-ATPase activity of the plasma membrane Ca²⁺-ATPase (PMCA) in human tissues from AD-affected brain and age-matched controls and also from pig brain and cell cultures. In addition, MB prevents and even blocks the inhibitory effect of Aβ on PMCA activity. Functional analysis with mutants and fluorescence experiments strongly suggest that MB binds to PMCA, at the C-terminal tail, in a site located close to the last transmembrane helix and also that MB binds to the peptide. Besides, Aβ increases PMCA affinity for MB. These results point out a novel molecular basis of MB action on Aβ and PMCA as mediator of its beneficial effect on AD.

Antipsychotic dopamine receptor antagonists, cancer, and cancer stem cells

Cancer is one of the deadliest diseases in the world. Despite extensive studies, treating metastatic cancers remains challenging. Years of research have linked a rare set of cells known as cancer stem cells (CSCs) to drug resistance, leading to the suggestion that eradication of CSCs might be an effective therapeutic strategy. However, few drug candidates are active against CSCs. New drug discovery is often a lengthy process. Drug screening has been advantageous in identifying drug candidates. Current understanding of cancer biology has revealed various clues to target cancer from different points of view. Many studies have found dopamine receptors (DRs) in various cancers. Therefore, DR antagonists have attracted a lot of attention in cancer research. Recently, a group of antipsychotic DR antagonists has been demonstrated to possess remarkable abilities to restrain and sensitize CSCs to existing chemotherapeutics by a process called differentiation approach. In this review, we will describe current aspects of CSC-targeting therapeutics, antipsychotic DR antagonists, and their extraordinary abilities to fight cancer.

Large-scale classification of P-glycoprotein inhibitors using SMILES-based descriptors

P-glycoprotein (Pgp) inhibition has been considered as an effective strategy towards combating multidrug-resistant cancers. Owing to the substrate promiscuity of Pgp, the classification of its interacting ligands is not an easy task and is an ongoing issue of debate. Chemical structures can be represented by the simplified molecular input line entry system (SMILES) in the form of linear string of symbols. In this study, the SMILES notations of 2254 Pgp inhibitors including 1341 active, and 913 inactive compounds were used for the construction of a SMILE-based classification model using CORrelation And Logic (CORAL) software. The model provided an acceptable predictive performance as observed from statistical parameters consisting of accuracy, sensitivity and specificity that afforded values greater than 70% and MCC value greater than 0.6 for training, calibration and validation sets. In addition, the CORAL method highlighted chemical features that may contribute to increased and decreased Pgp inhibitory activities. This study highlights the potential of CORAL software for rapid screening of prospective compounds from a large chemical space and provides information that could aid in the design and development of potential Pgp inhibitors.

Effect of trifluoperazine on Tc-99m sestamibi uptake in patients with advanced nonsmall cell lung cancer

OBJECTIVE

The aim of this study was to investigate whether there is an effect of trifluoperazine on Tc-99m  methoxyisobutylisonitrile (MIBI) uptake in patients with advanced nonsmall cell lung cancer (NCLC).

MATERIALS AND METHODS

A total of 23 patients with biopsy-proven advanced NCLC who had no previous history of chemo-radiotherapy, underwent baseline dual phase planar, single photon emission computed tomography and whole body Tc-99m MIBI scintigraphy performed at 20 and 120 min. After oral administration of trifluoperazine (5 mg, 2 times a day, for 5 days), dual phase Tc-99m MIBI scintigraphy was repeated. For each patient, and for both studies, regions of interest were drawn over the tumor area (T) and over the normal lung area (L) on the contralateral side in transverse slices where tumor was visualized clearly. Then, early and delayed T/L ratios and washout rate (WR) were calculated.

RESULTS

Tc-99m MIBI was accumulated in the cancer tissue in all of the patients. Delayed ratio after the oral administration of trifluoperazine (DR2) was significantly higher (P = 0.039) than delayed ratio before trifluoperazine (DR1). We found no significant differences of early ratio before trifluoperazine (ER1) and early ratio after trifluoperazine (ER2), and washout rate before (WR1) and washout rate after trifluoperazine (WR2).

CONCLUSION

In patients with advanced NCLC, trifluoperazine treatment in addition to chemotherapy might be useful. However, our results need to be confirmed in larger series of patients.

Supra-amphiphilic aggregates formed by p-sulfonatocalix[4]arenes and the antipsychotic drug chlorpromazine

We report here a supramolecular strategy to directly assemble the small molecular antipsychotic drug chlorpromazine (CPZ) into nanostructures, induced by p-sulfonatocalix[4]arene (SC4A) and p-sulfonatocalix[4]arene tetraheptyl ether (SC4AH), with high drug loading efficiencies of 61% and 46%, respectively. The binary host-guest assembly process was monitored using optical transmittance measurements, and the size and morphology of these two kinds of supra-amphiphilic assemblies were identified using a combination of light scattering and high-resolution transmission electron microscopy, which showed solid spherical micelles. This strategy presents new opportunities for the development of high loading drug-containing carriers with easy processability for drug delivery.

In silico structure-based screening of versatile P-glycoprotein inhibitors using polynomial empirical scoring functions

P-glycoprotein (P-gp) is an ATP (adenosine triphosphate)-binding cassette transporter that causes multidrug resistance of various chemotherapeutic substances by active efflux from mammalian cells. P-gp plays a pivotal role in limiting drug absorption and distribution in different organs, including the intestines and brain. Thus, the prediction of P-gp–drug interactions is of vital importance in assessing drug pharmacokinetic and pharmacodynamic properties. To find the strongest P-gp blockers, we performed an in silico structure-based screening of P-gp inhibitor library (1,300 molecules) by the gradient optimization method, using polynomial empirical scoring (POLSCORE) functions. We report a strong correlation (r²=0.80, F=16.27, n=6, P<0.0157) of inhibition constants (Ki_exp or pKi_exp; experimental Ki or negative decimal logarithm of Ki_exp) converted from experimental IC₅₀ (half maximal inhibitory concentration) values with POLSCORE-predicted constants (Ki_POLSCORE or pKi_POLSCORE), using a linear regression fitting technique. The hydrophobic interactions between P-gp and selected drug substances were detected as the main forces responsible for the inhibition effect. The results showed that this scoring technique might be useful in the virtual screening and filtering of databases of drug-like compounds at the early stage of drug development processes.

Chemical structure of phenothiazines and their biological activity

Phenothiazines belong to the oldest, synthetic antipsychotic drugs, which do not have their precursor in the world of natural compounds. Apart from their fundamental neuroleptic action connected with the dopaminergic receptors blockade, phenothiazine derivatives also exert diverse biological activities, which account for their cancer chemopreventive-effect, as: calmodulin- and protein kinase C inhibitory-actions, anti-proliferative effect, inhibition of P-glycoprotein transport function and reversion of multidrug resistance. According to literature data on relations between chemical structure of phenothiazines and their biological effects, the main directions for further chemical modifications have been established. They are provided and discussed in this review paper.

New high-throughput screening assay to reveal similarities and differences in inhibitory sensitivities of multidrug ATP-binding cassette transporters

Cdr1p is the major ATP-binding cassette multidrug transporter conferring resistance to azoles and other antifungals in Candida albicans. In this study, the identification of new Cdr1p inhibitors by use of a newly developed high-throughput fluorescence-based assay is reported. The assay also allowed monitoring of the activity and inhibition of the related transporters Pdr5p and Snq2p of Saccharomyces cerevisiae, which made it possible to compare its performance with those of previously established procedures. A high sensitivity, resulting from a wide dynamic range, was achieved upon high-level expression of the Cdr1p, Pdr5p, and Snq2p transporters in an S. cerevisiae strain in which the endogenous interfering activities were further reduced by genetic manipulation. An analysis of a set of therapeutically used and newly synthesized phenothiazine derivatives revealed different pharmacological profiles for Cdr1p, Pdr5p, and Snq2p. All transporters showed similar sensitivities to M961 inhibition. In contrast, Cdr1p was less sensitive to inhibition by fluphenazine, whereas phenothiazine selectively inhibited Snq2p. The inhibition potencies measured by the new assay reflected the ability of the compounds to potentiate the antifungal effect of ketoconazole (KTC), which was detoxified by the overproduced transporters. They also correlated with the 50% inhibitory concentration for inhibition of Pdr5p-mediated transport of rhodamine 6G in isolated plasma membranes. The most active derivative, M961, potentiated the activity of KTC against an azole-resistant CDR1-overexpressing C. albicans isolate.

Synthesis and biochemical characterization of new phenothiazines and related drugs as MDR reversal agents

Chemotherapy is one of the most important methods in the treatment of cancer. However, development of drug resistance during chemotherapy is the leading cause of treatment failure and decreased survival in cancer patients. Multidrug resistance (MDR) is one of the extensively studied forms of drug resistance for more than 30 years. The members of ATP-binding cassette protein family are responsible for multidrug resistance with P-glycoprotein as most representative transporter. To overcome multidrug resistance, pharmacological modulation of the transporters by efflux pump inhibitors seem to be the first choice, but preclinical studies did not lead to clinical applications. Therefore, a systematical research for pharmacophor structures is a promising strategy to increase the efficacy of those drugs still influencing multidrug resistance. In this study a range of phenothiazine derivatives was synthesizied with systematical variation of three molecule domains. The biochemical determination of multidrug resistance reversal activity was achieved with the crystalviolet assay on LLC-PK1/MDR1 cells. The results will be discussed considering of hypotheses in the literature directed to new structure-acitivity relationships to overcome drug resistance in the future.

Enaminones: Exploring Additional Therapeutic Activities

Enaminones, enamines of beta-dicarbonyl compounds, have been known for many years. Their early use has been relegated to serving as synthetic intermediates in organic synthesis and of late, in pharmaceutical development. Recently, the therapeutic potential of these entities has been realized. This review provides the background and current research in this area with emphasis of these agents as potential anticonvulsants, their proposed mechanisms of action, and as potential modulators of multidrug resistance (MDR).

Interaction of phenothiazine compounds with zwitterionic lysophosphatidylcholine micelles: Small angle X-ray scattering, electronic absorption spectroscopy, and theoretical calculations

In this work, small-angle X-ray scattering (SAXS) studies on the interaction of the phenothiazine cationic compounds trifluoperazine (TFP, 2-10 mM) and chlorpromazine (CPZ, 2-10 mM) with micelles of the zwitterionic surfactant L-alpha-lysophosphatidylcholine (LPC, 30 mM), at pHs 4.0 and 7.0, are reported. The SAXS results demonstrate that, upon addition of both phenothiazines, the LPC micelle of prolate ellipsoidal shape changes into a cylindrically shaped micelle, increasing its axial ratio from 1.6 +/- 0.1 (in the absence of drug) to 2.5 +/- 0.1 (for 5 and 10 mM of phenothiazine). Such an effect is accompanied by a shrinking of the paraffinic shortest semiaxis from 22.5 +/- 0.3 to 20.0 +/- 0.5 A. Besides, a significant increase in polar shell electron density from 0.39(1) to 0.45(1) e/A3 is observed, consistent with cylinder-like aggregate geometry. Moreover, an increase of the phenothiazine concentration induces the appearance of a repulsive interference function over the SAXS curve of zwitterionic micelles, which is typical of interaction between surface-charged micelles. Such a finding provides evidence that the positively charged phenothiazine molecule must be accommodated near the hydrophobic/hydrophilic inner micellar interface in such a way that a net surface charge is altered with respect to the original overall neutral zwitterionic micelle. Such phenothiazine location is favored by both electrostatic and hydrophobic contributions, giving rise to binding constant values, obtained from electronic absorption results, that are quite larger compared to their binding to another zwitterionic surfactant, 3-(N-hexadecyl-N,N-dimethylammonio)propanesulfonate (HPS) (Caetano, W., et al. J. Colloid Int. Sci. 2003, 260, 414-422). Comparisons are made by means of theoretical calculations of the surfactant headgroup dipole moments for monomers of LPC and HPS. The theoretical results show that the dipole moment in LPC is almost perpendicular to the methylene chain, while a significant contribution along the methylene chain occurs for HPS. Besides, evidence is presented for extensive delocalization of the charges in the headgroups, which could be also relevant for the binding of the drugs.

A Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA) of Anthranilamide Derivatives That Are Multidrug Resistance Modulators

In a continuing effort to develop potent and selective modulators of P-glycoprotein (P-gp) activity overcoming the chemoresistance acquired by tumor cells during cancer chemotherapy, we developed 3D quantitative structure-activity relationship (3D QSAR) models using CoMFA and CoMSIA analyses. This study correlates the P-glycoprotein inhibitory activities of 49 structurally related anthranilamide derivatives to several physicochemical parameters representing steric, electrostatic, acceptor, donor, and hydrophobic fields. Both CoMFA and CoMSIA models using three different alignment conformations gave good internal predictions, and their cross-validated r2 values are between 0.503 and 0.644. These most comprehensive CoMFA and CoMSIA models are useful in understanding the structure-activity relationships of anthranilamide derivatives as well as aid in the design of novel derivatives with enhanced modulation of P-gp activity.

Interaction of pyridostigmine bromide and N,N-diethyl-m-toluamide alone and in combination with P-glycoprotein expressed in Escherichia coli leaky mutant

P-glycoprotein (P-gp), the most extensively studied ATP-binding transporter, functions as a biological barrier by extruding toxic substances and xenobiotics out of the cell. This study was carried out to determine the effect of N,N-diethyl-m-toluamide (DEET) and pyridostigmine bromide (PB), alone and in combination, on P-gp expression using Escherichia coli leaky mutant transformed with Mdr1 gene (pT5-7/mdr1), which codes for P-gp or lactose permease (pT5-7/lacY) as negative control. Also, daunomycin (a known P-gp sustrate) was used as a positive control and reserpine (a known P-gp inhibitor) served as a negative control. An in vitro cell-resistant assay was used to monitor the potential of test compounds to interact with P-gp. Following exposure of the cells to pyridostigmine bromide or daunomycin, P-gp conferred significant resistance against both compounds, while reserpine and DEET significantly inhibited the glycoprotein. Cells were grown in the presence of noncytotoxic concentrations of daunomycin, pyridostigmine bromide, reserpine, or DEET, and membrane fractions were examined by Western immunoblotting for expression of P-gp. Daunomycin induced P-gp expression quantitatively more than pyridostigmine bromide, while reserpine and DEET significantly inhibited P-gp expression in cells harboring mdr1. Photoaffinity labeling experiment performed with the P-gp ligand [125I]iodoarylazidoprazosin demonstrated that compounds that induced or inhibited P-gp transport activity also bound to P-gp. DEET was also found to be a potent inhibitor of P-gp-mediated ATPase activity, whereas pyridostigmine bromide increased P-gp ATPase activity. Cells expressing P-gp or lac permease were exposed to pyridostigmine bromide and DEET, alone and in combination. Noncytotoxic concentrations of DEET significantly inhibited P-gp-mediated resistance against pyridostigmine bromide, resulting in a reduction of the number of effective drug interactions with biological targets. An explanation of these results might be that DEET is a third-generation inhibitor of P-gp; it has high potency and specificity for P-gp, it inhibits hydrolysis of ATP, it exerts no appreciable impact on cytochrome P-450 3A4, and it prevents transport of xenobiotics, such as pyridostigmine bromide, out of the cell. This conclusion explains, at least in part, the increased toxicity and bioavailability of pyridostigmine bromide following combined administration with DEET. This study improves our understanding of the basis of chemical interactions with DEET by defining the ability of drugs to interact with P-gp either as inhibitors or substrates, which may in turn lead to altered efficacy or toxicity.

Tesmilifene may enhance breast cancer chemotherapy by killing a clone of aggressive, multi-drug resistant cells through its action on the p-glycoprotein pump

Tesmilifene is a novel potentiator of chemotherapy which, when added to doxorubicin, achieved an unexpected and very large survival advantage over doxorubicin alone in a randomized trial in advanced breast cancer. This trial was unusual in that the early endpoints (response rate and median progression-free survival) were equivalent in the two arms, despite the ultimate survival difference. These aspects, coupled with the absence of a coherent molecular mechanism of action, and a pending confirmatory trial, have led oncologists to hold judgement on this drug. This paper reacts to this in three ways: firstly, a forensic subgroup analysis is presented with an explanation as to why it strongly supports the veracity of the survival difference; secondly a novel cellular explanation is provided for the decoupling of the early and late (survival) endpoints; finally, a molecular mechanism of action is proposed, for the first time, which reconciles the peculiarities of the trial with the laboratory data and background literature. This hypothesis explains how tesmilifene could meld two of the apparent strengths of the cancer cell (drug resistance pumps, and hypoxia-adapted energetics) into a potent weapon of self-destruction. Tesmilifene is proposed to allow chemotherapy (e.g. anthracycline or taxane) to additionally kill a small but critical population (clone) of aggressive, multi-drug resistant cells, the benefits of which cannot be appreciated until a period of time (about 6-8 months) has elapsed. These cells, present in women with more rapidly relapsing disease, very likely carry an energy-dependent extrusion pump which is paradoxically activated by tesmilifene plus the chemotherapy. The result is that, despite the chemotherapy's remaining extracellular, the cell dies from reactive oxygen species leaking from the electron chain transport in the abnormal mitochondria which characterize cancer. These mitochondria are activated in response to the ATP cost of this pump activation, in these predominantly glycolytic cells.

Methylene blue is more toxic to erythroleukemic cells than to normal peripheral blood mononuclear cells: a possible use in chemotherapy

Methylene blue (MB) is a phenothiazine with radio and photosensitizing properties and anti-tumoral activity. Our group has shown that MB was capable of inhibiting the in vitro growth of erythroleukemic cells with multidrug resistance (MDR). However, there are no studies comparing the cytotoxicity of this molecule for normal and tumoral cells. In this work, the cytotoxicity of MB was measured by MTT method in erythroleukemic and melanoma lineages, comparing it with that of normal cells:lymphocytes and melanocytes. MB was more cytotoxic for tumoral cells; however, there was no difference between erytroleukemic cells with or without MDR phenotype. Lymphocytes and erythroleukemic cells were much more sensitive to the effects of MB than melanoma cells and melanocytes. The proliferation of phytohemagglutinin-activated lymphocytes was inhibited when 3H-thymidine incorporation to DNA was measured. We tried to analyze whether the cells were dying, via apoptosis or necrosis, using Anexin-V and propidium iodide. Despite higher levels of Anexin-V, it was not possible to distinguish necrosis from apoptosis, as the fluorescence of MB is in the same channel as propidium iodide. The production of hydrogen peroxide was measured by cytometry using dihydrorhodamine 123 (DHR). Despite the erythroleukemic cells and lymphocytes being capable of producing free radicals, there was no relation between the production and the sensitivity of various cells to MB. Our results suggest that MB should be used as a chemotherapeutic agent, because of its preferential cytotoxic effects over tumor cells, considering the fact that MDR cells are also sensitive, and due to its radio and photosensitizing activities.

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.

3D QSAR investigation of the blood-brain barrier penetration of chemical compounds

In the present study, we investigated structure-permeability relationships for the blood-brain barrier (BBB) of 16 imipramine and phenothiazine derivatives. The compounds belong to structurally related chemical classes of catamphiphiles, representatives of which have previously been investigated for membrane activity and ability to overcome multidrug resistance (MDR) in tumour cells. These studies show that phenothiazines and structurally related drugs (imipramines, thioxanthenes, acridines) interact with membrane phospholipids, and additionally inhibit the MDR transport P-glycoprotein. This study aimed to identify common 3D structural characteristics of these compounds related to their mechanism of transport across the BBB. For this purpose Genetic Algorithm Similarity Programme (GASP), Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Index Analysis (CoMSIA) were applied. The results demonstrate the importance of the spatial distribution of molecular hydrophobicity for the BBB penetration of the investigated compounds. It suggests that the compounds should follow a specific profile of two hydrophobic and one hydrophilic centres in a particular space configuration, for optimal BBB penetration.

Substituted Pyridazino[3,4-b][1,5]benzoxazepin-5(6H)ones as Multidrug-Resistance Modulating Agents

Pyridazino[3,4-b][1,5]benzoxazepin-5(6H)ones substituted with propylene-linked basic side chains were synthesized and investigated for the ability to reverse multidrug resistance (MDR) at vincristine-pretreated HeLa-MDR1 cells. The substances were found to be effective chemosensitizers with activity comparable to that of the known MDR modulator verapamil. The observed antiproliferative effects were not caused by direct drug cytotoxicity.

Presence of anionic phospholipids rules the membrane localization of phenothiazine type multidrug resistance modulator

Substances able to modulate multidrug resistance (MDR), including antipsychotic phenothiazine derivatives, are mainly cationic amphiphiles. The molecular mechanism of their action can involve interactions with transporter proteins as well as with membrane lipids. The interactions between anionic phospholipids and MDR modulators can be crucial for their action. In present work we study interactions of 2-trifluoromethyl-10-(4-[methanesulfonylamid]buthyl)-phenothiazine (FPhMS) with neutral (PC) and anionic lipids (PG and PS). Using microcalorimetry, steady-state and time-resolved fluorescence spectroscopy we show that FPhMS interacts with all lipids studied and drug location in membrane depends on lipid type. The electrostatic attraction between drug and lipid headgroups presumably keeps phenothiazine derivative molecules closer to surface of negatively charged membranes with respect to neutral ones. FPhMS effects on bilayer properties are not proportional to phosphatidylserine content in lipid mixtures. Behavior of equimolar PC:PS mixtures is similar to pure PS bilayers, while 2:1 or 1:2 (mole:mole) PC:PS mixtures resemble pure PC ones.

Quinolizidinyl derivatives of iminodibenzyl and phenothiazine as multidrug resistance modulators in ovarian cancer cells

The development of multidrug-resistance (MDR) in neoplastic cells is often responsible for the therapy failure and poor outcome of a number of human cancers. MDR may be associated with the expression of the multidrug transporter glycoprotein p170, encoded by the MDR1 gene, which acts as an ATP-dependent efflux pump by reducing the intracellular accumulation of some cytotoxic agents. A variety of iminodibenzyl and phenothiazine derivatives, characterized by the presence of a bicyclic, strongly basic, and highly lipophilic quinolizidine nucleus, were synthesized to investigate their ability to modulate the MDR phenotype. A set of 10 of them (named 1-10), bearing quinolizidine moiety linked through different connecting chains, were tested as chemoresistance-reversing agents on doxorubicin-resistant ovarian cancer cells (A2780-DX3). A 51-fold resistance to doxorubicin was reported in the A2780-DX3 compared to the parental sensitive A2780 WT with mean IC(50) values of 0.02 and 1.02 muM, respectively. Moreover, overexpression of the glycoprotein p170 in the resistant cell line was detected by Western blot analysis. By cytotoxicity assays and time-course experiments, different treatment schedules with resistance modulators (including clomipramine as reference drug) and doxorubicin were taken into account. The 16 h exposure of cells to 1 muM of modulator before doxorubicin demonstrated to be superior in sensitizing the resistant cell line. In particular, compounds 8, 7, 10, and 4 increasingly potentiated doxorubicin cytotoxicity, up to 5.6-fold in A2780-DX3 cells. The present results suggest promising indications for further development of these compounds as chemosensitizing drugs.

QSAR studies on P-glycoprotein-regulated multidrug resistance and on its reversal by phenothiazines

Multidrug resistance is brought about largely by membrane transport proteins such as P-glycoprotein (P-gp). We have developed a quantitative structure-activity relationship (QSAR) for P-gp-associated ATPase activity for a diverse set of 22 drugs, and found that such activity is related to substrate molecular size and polarity. We have also developed a QSAR for drug efflux from the blood-brain barrier of another diverse set of 22 drugs, and found that such efflux is a function of drug size and polarisability. Thirdly, we have carried out a QSAR analysis of the ability of 157 phenothiazines and related drugs to reverse multidrug resistance. We were unable to obtain a good QSAR for the whole data-set, but when we divided the data-set into sub-sets of closely related structures, a series of good correlations was obtained, most of which incorporated descriptors that model molecular size and polarity/polarisability. In no instance did we find any evidence that hydrogen bonding or hydrophobicity play a part in multidrug resistance or its reversal, despite that fact that several other workers have reported that these effects appear to be important here.

QSAR and 3D-QSAR of phenothiazine type multidrug resistance modulators in P388/ADR cells

A series of 25 phenothiazines and structurally related compounds was investigated by QSAR (quantitative structure activity relationship) and 3D-QSAR methods with respect to their MDR (multidrug resistance) reversing activity in P388/ADR- murine leukemia cell line resistant to ADR (adriamycin). The objective was to outline structural properties important for the investigated activity. Different measures for MDR reversal were used and compared. Two 3D-QSAR approaches were applied-CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis). Both, neutral and protonated forms of the compounds were investigated. Molecular models with good predictive power were derived using a hydrophobic field alone and a combination of steric, hydrophobic, and hydrogen bond acceptor fields of the compounds. In the combined models highest contribution of the hydrogen bond acceptor field was noticed. Thus, the dominant role of the hydrophobic and hydrogen bond acceptor fields for MDR reversing activity of the investigated compounds was demonstrated. The structural regions responsible for the differences in anti-MDR activity were analyzed in respect to their hydrophobic, hydrogen bond acceptor and steric nature. The results may direct design of new phenothiazines and related compounds as MDR modulators.

A light in multidrug resistance: photodynamic treatment of multidrug-resistant tumors

The major drawback of cancer chemotherapy is the development of multidrug-resistant (MDR) tumor cells, which are cross-resistant to a broad range of structurally and functionally unrelated agents, making it difficult to treat these tumors. In the last decade, a number of authors have studied the effects of photodynamic therapy (PDT), a combination of visible light with photosensitizing agents, on MDR cells. The results, although still inconclusive, have raised the possibility of treating MDR tumors by PDT. This review examines the growing literature concerning the responses of MDR cells to PDT, while stressing the need for the development of new photosensitizers that possess the necessary characteristics for the photodynamic treatment of this class of tumor.

New phenothiazine-type multidrug resistance modifiers: anti-MDR activity versus membrane perturbing potency

The phenothiazine multidrug resistance (MDR) modulators are chemically diversified but share the common feature to be hydrophobic cationic molecules. Molecular mechanisms of their action may involve interactions with either P-glycoprotein or membrane lipid matrix. In the present work we study the anti-MDR and biophysical membrane effects of new phenothiazine derivatives differing in the type of group substituting phenothiazine ring at position 2 (H-, Cl-, CF(3)-) and in the side chain group (NHCO(2)CH(3) or NHSO(2)CH(3)). Within each phenothiazine subset we found that anti-MDR activity (determined by P-glycoprotein inhibition assessed by flow cytometry) correlates with the theoretically calculated hydrophobicity value (logP) and experimental parameters (determined by calorimetry and fluorescence spectroscopy) of lipid bilayers. It is concluded that the biological and biophysical activity of phenothiazine derivatives depends more on the type of ring substitution than on the nature of the side chain group.

pH-dependent effects of chlorpromazine on liposomes and erythrocyte membranes

Chlorpromazine (CPZ) is an amphipathic antipsychotic drug that binds to erythrocytes reaching in this way the central nervous system. CPZ is a basic molecule with pK=8.6. This paper reports on CPZ-induced lysis of red blood cells and liposomes. Haemolysis was tested under hypotonic conditions, in the pH range 5.0-10.0. Cell sensitivity towards CPZ increased with increasing pH. Increasing pH caused also a decrease in the critical micellar concentrations of CPZ. These results are interpreted in terms of a competition between repulsive electrostatic forces and attractive hydrophobic forces, that would act both in pure CPZ and in mixed CPZ-phospholipid micelles. In order to eliminate possible pH effects mediated by red blood cell proteins, experiments were carried out in which CPZ induced release of a fluorescent dye from liposomes (large unilamellar vesicles). The latter observations confirmed that membrane sensitivity towards CPZ was increased at higher pH.

Trifluoperazine effects on anionic and zwitterionic micelles: a study by small angle X-ray scattering

In this work small angle X-ray scattering (SAXS) studies on the interaction of the phenothiazine trifluoperazine (TFP, 2-10 mM), a cationic drug, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) and the anionic surfactant sodium dodecyl sulfate (SDS, 40 mM) at pH 4.0, 7.0, and 9.0 are reported. The data were analyzed through the modeling of the micellar form factor and interference function, as well as by means of the distance distribution function p(r). For anionic micelles (SDS), the results evidence a micellar shape transformation from prolate ellipsoid to cylinder accompanied by micellar growth and surface charge screening as the molar ratio TFP:SDS increases in the complex for all values of pH. Small ellipsoids with axial ratio nu=1.5+/-0.1 (long dimension of 60 A) grow and reassemble into cylinder-like aggregates upon 5 mM drug incorporation (1 TFP:8 SDS monomers) with a decrease of the micelle surface charge. At 10 mM TFP:40 mM SDS cylindrical micelles are totally screened with an axial ratio nu approximately 4 (long dimension approximately 140 A at pH 7.0 and 9.0). However, at pH 4.0, where the drug is partially diprotonated, 10 mM TFP incorporation gives rise to a huge increase in micellar size, resulting in micelles at least 400 A long, without altering the intramicellar core. For zwitterionic micelles (HPS), the results have shown that the aggregates also resemble small prolate ellipsoids with averaged axial ratio approximately nu=1.6+/-0.1. Under TFP addition, both the paraffinic radius and the micellar size show a slight decrease, giving evidence that the micellar hydrophobic core may be affected by phenothiazine incorporation rather than that observed for the SDS/TFP comicelle. Therefore, our results demonstrate that the axial ratio and shape evolution of the surfactant:TFP complex are both dependent on surfactant surface-charge and drug:surfactant molar ratio. The results are compared with those recently obtained for another phenothiazine drug, chlorpromazine (CPZ), in SDS and HPS micelles (Caetano, Gelamo, Tabak, and Itri, J. Colloid Interface Science 248 (2002) 149).

Neither lipophilicity nor membrane-perturbing potency of phenothiazine maleates correlate with the ability to inhibit P-glycoprotein transport activity

Although phenothiazines are known as multidrug resistance modifiers, the molecular mechanism of their activity remains unclear. Since phenothiazine molecules are amphiphilic, the interactions with membrane lipids may be related, at least partially, to their biological effects. Using the set of phenothiazine maleates differing in the type of phenothiazine ring substitution at position 2 and/or in the length of the alkyl bridge-connecting ring system and side chain group, we investigated if their ability to modulate the multidrug resistance of cancer cells correlated with model membrane perturbing potency. The influence exerted on lipid bilayers was determined by liposome/buffer partition coefficient measurements (using the absorption spectra second-derivative method), fluorescence spectroscopy and calorimetry. Biological effects were assessed by a flow cytometric functional test based on differential accumulation of fluorescent probe DiOC(2)(3) by parental and drug-resistant cells. We found that all phenothiazine maleates were incorporated into lipid bilayers and altered their biophysical properties. With only few exceptions, the extent of membrane perturbation induced by phenothiazine maleates correlated with their lipophilicity. Within the group of studied derivatives, the compounds substituted with CF(3)- at position 2 of phenothiazine ring were the most active membrane perturbants. No clear relation was found between effects exerted by phenothiazine maleates on model membranes and their ability to modulate P-glycoprotein transport activity.

Emerging safety issues regarding long-term usage of H(1)receptor antagonists

The second generation histamine H(1)-receptor antagonists are important therapeutic tools in the treatment of atopic disease and may also have a place as an adjunct therapy for those patients whose allergic asthma coexists with allergic rhinitis. They are amongst the most widely prescribed and safest drugs in the world. However, as second generation H(1)-receptor antagonists are used to treat non-life threatening conditions, the risk of adverse effects is of vital importance. For many, the potential for sedation by some of the newer antihistamines still remains an issue, while there have recently been widespread concerns regarding the potential for cardiotoxicity and the impact of drug-drug interactions associated with some second generation H(1)-receptor antagonists. Consequently, progress with this class of drugs should involve not only increased efficacy but also improvements in their safety and specificity. Moreover, there is a trend towards using second generation H(1)-receptor antagonists as long-term therapy rather than confining their use to treating the short-term manifestations of allergic disease. To this end, a number of novel, potent and safe antihistamines have been developed which are either metabolites of active drugs or enantiomers. This review will examine some of the safety issues associated with established and newer second generation drugs particularly in relation to their long-term usage in adults and children.

The alterations of lipid bilayer fluidity induced by newly synthesized phenothiazine derivative

Using fluorescence spectroscopy, calorimetry and ESR the interactions of the phenothiazine derivative 2-trifluoromethyl-10-(4-[methylsulfonylamid]buthyl)-phenothiazine (FPhMS) with lipids were studied. Calorimetry showed biphasic effect of FPhMS on main phase transition of DPPC. At molar ratios up to 0.06 drug induced decrease of transition temperature and enthalpy, while at higher concentrations it caused subsequent increase of these parameters. For all concentrations studied we observed gradual broadening of transition peaks. Fluorescence polarization revealed that in FPhMS/lipid mixtures, order in bilayers is decreased in the gel state and increased in the liquid crystalline state. ESR experiment showed that at molar ratio of 0.06, FPhMS reduces the mobility of spin probes located in both polar and hydrophobic regions. Comparing observed effects with those reported for cholesterol/lipid mixtures, we conclude that at higher concentrations FPhMS presumably induces a new mode of bilayer packing. This structure is less co-operative than an unperturbed bilayer, but locally the mobility of lipid molecules is decreased.

Three-dimensional quantitative structure-activity relationships of inhibitors of P-glycoprotein

P-glycoprotein (P-gp) is an efflux transporter involved in limiting the oral bioavailability and tissue penetration of a variety of structurally divergent molecules. A better understanding of the structural requirements of modulators of P-gp function will aid in the design of therapeutic agents. Toward this goal, three-dimensional quantitative structure-activity relationship (3D-QSAR) models were generated using in vitro data associated with inhibition of P-gp function. Several approaches were undertaken with multiple iterations, yielding Catalyst 3D-QSAR models being able to qualitatively rank-order and predict IC(50) values for P-gp inhibitors excluded from the model in question. The success of these validations suggests that a P-gp pharmacophore for 27 inhibitors of digoxin transport in Caco-2 cells consisted of four hydrophobes and one hydrogen bond acceptor. A second pharmacophore generated with 21 inhibitors of vinblastine binding to plasma membrane vesicles derived from CEM/VLB(100) cells contained three ring aromatic features and one hydrophobic feature. A third pharmacophore generated with 17 inhibitors of vinblastine accumulation in P-gp expressing LLC-PK1 cells contained four hydrophobes and one hydrogen bond acceptor. A final pharmacophore was generated for inhibition of calcein accumulation in P-gp expressing LLC-PK1 cells and found to contain two hydrophobes, a ring aromatic feature, and a hydrogen bond donor. The similarity of features for the pharmacophores of P-gp inhibitors of digoxin transport and vinblastine binding suggest some commonality in their binding sites. Utilization of such models may prove to be of value for prediction of molecules that may modulate one or more P-gp binding sites.

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.