Trimethoxybenzanilide-Based P-Glycoprotein Modulators: An Interesting Case of Lipophilicity Tuning by Intramolecular Hydrogen Bonding

A Critical Appraisal of the Protective Activity of Polyphenolic Antioxidants against Iatrogenic Effects of Anticancer Chemotherapeutics

Polyphenolic compounds, encompassing flavonoids (e.g., quercetin, rutin, and cyanidin) and non-flavonoids (e.g., gallic acid, resveratrol, and curcumin), show several health-related beneficial effects, which include antioxidant, anti-inflammatory, hepatoprotective, antiviral, and anticarcinogenic properties, as well as the prevention of coronary heart diseases. Polyphenols have also been investigated for their counteraction against the adverse effects of common anticancer chemotherapeutics. This review evaluates the outcomes of clinical studies (and related preclinical data) over the last ten years, with a focus on the use of polyphenols in chemotherapy as auxiliary agents acting against oxidative stress toxicity induced by antitumor drugs. While further clinical studies are needed to establish adequate doses and optimal delivery systems, the improvement in polyphenols' metabolic stability and bioavailability, through the implementation of nanotechnologies that are currently being investigated, could improve therapeutic applications of their pharmaceutical or nutraceutical preparations in tumor chemotherapy.

4-(3-Phenyl-4-(3,4,5-trimethoxybenzoyl)-1H-pyrrol-1-yl)benzenesulfonamide, a Novel Carbonic Anhydrase and Wnt/β-Catenin Signaling Pathway Dual-Targeting Inhibitor with Potent Activity against Multidrug Resistant Cancer Cells

We synthesized new pyrrole and indole derivatives as human carbonic anhydrase (hCA) inhibitors with the potential to inhibit the Wnt/β-catenin signaling pathway. The presence of both N1-(4-sulfonamidophenyl) and 3-(3,4,5-trimethoxyphenyl) substituents was essential for strong hCA inhibitors. The most potent hCA XII inhibitor 15 (Ki = 6.8 nM) suppressed the Wnt/β-catenin signaling pathway and its target genes MYC, Fgf20, and Sall4 and exhibited the typical markers of apoptosis, cleaved poly(ADP-ribose)polymerase, and cleaved caspase-3. Compound 15 showed strong inhibition of viability in a panel of cancer cells, including colorectal cancer and triple-negative breast cancer cells, was effective against the NCI/ADR-RES DOX-resistant cell line, and restored the sensitivity to doxorubicin (DOX) in HT29/DX and MDCK/P-gp cells. Compound 15 is a novel dual-targeting compound with activity against hCA and Wnt/β-catenin. It thus has a broad targeting spectrum and is an anticancer agent with specific potential in P-glycoprotein overexpressing cell lines.

Discovery of 2,5-disubstituted furan derivatives featuring a benzamide motif for overcoming P-glycoprotein mediated multidrug resistance in MCF-7/ADR cell

P-glycoprotein (P-gp) is one of the drug efflux transporters that triggers multidrug resistance (MDR) in cells. Herein, by utilizing the strategies of active skeleton splicing and structural optimization on the lead compound 5 m, a total of 50 novel 2,5-disubstituted furan derivatives were designed, synthesized, and screened for P-gp inhibitory activity. The structure-activity relationship analysis enabled the identification of an important pharmacophore N-phenylbenzamide, which resulted in the discovery of a promising drug lead compound Ⅲ-8. Ⅲ-8 possesses broad-spectrum reversal activity and low toxicity in MCF-7/ADR cells. Western blot and Rh123 accumulation assay demonstrated that Ⅲ-8 displayed the reversal activity by inhibiting P-gp efflux. Molecular docking analysis indicated a potent affinity of Ⅲ-8 to P-gp by forming H-bond interactions with residues Asn 721 and Met 986. Ⅲ-8 was determined to be a highly effective and safe P-gp inhibitor in an MCF-7/ADR xenograft mouse model.

Triterpenoids with modified A-ring as modulators of P-gp-dependent drug-resistance in cancer cells

Semi-synthetic A-cycle modified triterpenic derivatives with A-cycle condensed with a heterocyclic fragment (compound 1) and fragmented A-ring (compound 2) were tested for cytotoxicity against several tumor cell cultures and doxorubicin (Dox)-resistant cell lines. The equal cytotoxicity of the tested compounds to the parental tumor cell lines (HBL-100, K562) and their resistant subclones (HBL-100/Dox, K562/i-S9) was revealed. The overexpression of ABCB1 (MDR1) gene and P-glycoprotein (P-gp) was confirmed for both resistant subclones of tumor cells. Compounds 1 and 2 were shown to inhibit the ABC-transporter gene expression (MDR1, MRP, MVP, and BCRP) and the transport of well-known P-gp substrate Rhodamine 123 from resistant cells. The docking of triterpenoids 1 and 2 into the drug binding site of P-gp revealed a similarity between the conformation of the tested triterpenoids and that of classical inhibitor verapamil, thus assuming these compounds to be more likely the inhibitors than the substrates of P-gp. Any tested triterpenic derivatives, when combined at non-toxic concentrations with doxorubicin, improved cytotoxic effect of the therapeutic drug against resistant subclones of tumor cells.

Novel Antiproliferative Biphenyl Nicotinamide: NMR Metabolomic Study of its Effect on the MCF-7 Cell in Comparison with Cisplatin and Vinblastine

A 1H-NMR-based metabolomic study was performed on MCF-7 cell lines treated with a novel nicotinamide derivative (DT-8) in comparison with two drugs characterized by a well-established mechanism of action, namely the DNA-metalating drug cisplatin (cis-diamminedichloridoplatinum(II), CDDP) and the antimitotic drug vinblastine (vinblastine, VIN). The effects of the three compounds, each one at the concentration corresponding to the IC50 value, were investigated, with respect to the controls (K), by the 1H-NMR of cells lysates and multivariate analysis (MVA) of the spectroscopic data. Relevant differences were found in the metabolic profiles of the different treatments with respect to the controls. A large overlap of the metabolic profiles in DT-8 vs. K and VIN vs. K suggests a similar biological response and mechanism of action, significantly diverse with respect to CDDP. On the other hand, DT8 seems to act by disorganizing the mitotic spindle and ultimately blocking the cell division, through a mechanism implying methionine depletion and/or S-adenosylmethionine (SAM) limitation.

Medicinal chemistry strategies to discover P-glycoprotein inhibitors: An update

The presence of multidrug resistance (MDR) in malignant tumors is one of the primary causes of treatment failure in cancer chemotherapy. The overexpression of the ATP binding cassette (ABC) transporter, P-glycoprotein (P-gp), which significantly increases the efflux of certain anticancer drugs from tumor cells, produces MDR. Therefore, inhibition of P-gp may represent a viable therapeutic strategy to overcome cancer MDR. Over the past 4 decades, many compounds with P-gp inhibitory efficacy (referred to as first- and second-generation P-gp inhibitors) have been identified or synthesized. However, these compounds were not successful in clinical trials due to a lack of efficacy and/or untoward toxicity. Subsequently, third- and fourth-generation P-gp inhibitors were developed but dedicated clinical trials did not indicate a significant therapeutic effect. In recent years, an extraordinary array of highly potent, selective, and low-toxicity P-gp inhibitors have been reported. Herein, we provide a comprehensive review of the synthetic and natural products that have specific inhibitory activity on P-gp drug efflux as well as promising chemosensitizing efficacy in MDR cancer cells. The present review focuses primarily on the structural features, design strategies, and structure-activity relationships (SAR) of these compounds.

Prediction of P-glycoprotein inhibitors with machine learning classification models and 3D-RISM-KH theory based solvation energy descriptors

Development of novel in silico methods for questing novel PgP inhibitors is crucial for the reversal of multi-drug resistance in cancer therapy. Here, we report machine learning based binary classification schemes to identify the PgP inhibitors from non-inhibitors using molecular solvation theory with excellent accuracy and precision. The excess chemical potential and partial molar volume in various solvents are calculated for PgP± (PgP inhibitors and non-inhibitors) compounds with the statistical-mechanical based three-dimensional reference interaction site model with the Kovalenko-Hirata closure approximation (3D-RISM-KH molecular theory of solvation). The statistical importance analysis of descriptors identified the 3D-RISM-KH based descriptors as top molecular descriptors for classification. Among the constructed classification models, the support vector machine predicted the test set of Pgp± compounds with highest accuracy and precision of ~ 97% for test set. The validation of models confirms the robustness of state-of-the-art molecular solvation theory based descriptors in identification of the Pgp± compounds.

3-benzazecine-based cyclic allene derivatives as highly potent P-glycoprotein inhibitors overcoming doxorubicin multidrug resistance

Aim: Enamino 3-benzazecine compounds, incorporating the C6-C8 allene system, were synthesized and evaluated in vitro as inhibitors of P-glycoprotein (P-gp) and/or multidrug resistance-associated protein 1 (MRP1), two efflux pumps mainly connected with multidrug resistance (MDR) in cancer cells. Results & methodology: Most of the synthesized compounds were selective P-gp inhibitors in Calcein-AM uptake assay. Structure–activity relationships (SARs) pointed out that CO2Me derivatives are more potent than acetyl derivatives, and 10,11-dimethoxy compounds are five to tenfold more potent inhibitors than the respective unsubstituted compounds, and that the P-gp inhibition potency is mainly related to volume parameters. Conclusion: Nanomolar P-gp inhibitors, such as 23 (IC50 = 4.2 nM), restored the antiproliferative activity of doxorubicin in multidrug-resistant cells. The observed activities showed that 3-benzazecine-based compounds may be promising MDR reversers.

Intramolecular hydrogen bonding: An opportunity for improved design in medicinal chemistry

Recent literature shows that intramolecular hydrogen bond (IMHB) formation can positively impact upon the triad of permeability, solubility, and potency of drugs and candidates. IMHB modulation can be applied to compounds in any chemical space as a means for discovering drug candidates with both acceptable potency and absorption, distribution, metabolism, and excretion-Tox profiles. Integrating IMHB formation in design of drugs is, therefore, an exciting and timely challenge for modern medicinal chemistry. In this review, we first provide some background about IMHBs from the medicinal chemist's point of view and highlight some IMHB-associated misconceptions. Second, we propose a classification of IMHBs for drug discovery purposes, review the most common in silico tactics to include IMHBs in lead optimization and list some experimental physicochemical descriptors, which quantify the propensity of compounds to form IMHBs. By focusing on the compounds size and the number of IMHBs that can potentially be formed, we also outline the major difficulties encountered when designing compounds based on the inclusion of IMHBs. Finally, we discuss recent case studies illustrating the application of IMHB to optimize cell permeability and physicochemical properties of small molecules, cyclic peptides and macrocycles.

Synthesis and biological evaluation of N-biphenyl-nicotinic based moiety compounds: A new class of antimitotic agents for the treatment of Hodgkin Lymphoma

We previously demonstrated that some N-biphenylanilides caused cell-cycle arrest at G2/M transition in breast cancer cells. Among them we choose three derivatives, namely PTA34, PTA73 and RS35 for experimentation in solid tumor cell lines, classical Hodgkin Lymphoma (cHL) cell lines and bona fide normal cell lines. Almost all tumor cells were sensitive to compounds in the nanomolar range whereas, they were not cytotoxic to normal ones. Interestingly the compounds caused a strong G2/M phase arrest in cHL cell lines, thus, here we investigated whether they affected the integrity of microtubules in such cells. We found that they induced a long prometaphase arrest, followed by induction of apoptosis which involved mitochondria. PTA73 and RS35 induced the mitotic arrest through the fragmentation of microtubules which prevented the kinethocore-mitotic spindle interaction and the exit from mitosis. PTA34 is instead a tubulin-targeting agent because it inhibited the tubulin polymerization as vinblastine. As such, PTA34 maintained the Cyclin B1-CDK1 regulatory complex activated during the G2/M arrest while inducing the inactivation of Bcl-2 through phosphorylation in Ser70, the degradation of Mcl-1 and a strong activation of BIML and BIMS proapoptotic isoforms. In addition PTA34 exerted an antiangiogenic effect by suppressing microvascular formation.

Crown ethers reverse P-glycoprotein-mediated multidrug resistance in cancer cells

Multidrug resistance (MDR) is a widespread phenomenon exhibited by many cancers and represents a fundamental obstacle for successful cancer treatments. Tumour cells commonly achieve MDR phenotype through overexpression and/or increased activity of ABC transporters. P-glycoprotein transporter (P-gp, ABCB1) is a major cause of MDR and therefore represents a valuable target for MDR reversal. Several naturally occurring potassium ionophores (e.g. salinomycin) were shown to inhibit P-gp effectively. We have previously shown antitumour activity of a number of 18-crown-6 ether compounds that transport potassium ions across membranes. Here we present data on P-gp inhibitory activity of 16 adamantane-substituted monoaza- and diaza-18-crown-6 ether compounds, and their effect on MDR reversal in model cell lines. We show that crown ether activity depends on their lipophilicity as well as on the linker to adamantane moiety. The most active crown ethers were shown to be more effective in sensitising MDR cells to paclitaxel and adriamycin than verapamil, a well-known P-gp inhibitor. Altogether our data demonstrate a novel use of crown ethers for inhibition of P-gp and reversal of MDR phenotype.

A New Class of 1-Aryl-5,6-dihydropyrrolo[2,1-a]isoquinoline Derivatives as Reversers of P-Glycoprotein-Mediated Multidrug Resistance in Tumor Cells

A number of aza-heterocyclic compounds, which share the 5,6-dihydropyrrolo[2,1-a]isoquinoline (DHPIQ) scaffold with members of the lamellarin alkaloid family, were synthesized and evaluated for their ability to reverse in vitro multidrug resistance in cancer cells through inhibition of P-glycoprotein (P-gp) and/or multidrug-resistance-associated protein 1. Most of the investigated DHPIQ compounds proved to be selective P-gp modulators, and the most potent modulator, 8,9-diethoxy-1-(3,4-diethoxyphenyl)-3-(furan-2-yl)-5,6-dihydropyrrolo[2,1-a]isoquinoline-2-carbaldehyde, attained sub-micromolar inhibitory potency (IC₅₀ : 0.19 μm). Schiff bases prepared by the condensation of some 1-aryl-DHPIQ aldehydes with p-aminophenol also proved to be of some interest, and one of them, 4-((1-(4-fluorophenyl)-5,6-dihydro-8,9-dimethoxypyrrolo[2,1-a]isoquinolin-2-yl)methyleneamino)phenol, had an IC₅₀ value of 1.01 μm. In drug combination assays in multidrug-resistant cells, some DHPIQ compounds, at nontoxic concentrations, significantly increased the cytotoxicity of doxorubicin in a concentration-dependent manner. Studies of structure-activity relationships and investigation of the chemical stability of Schiff bases provided physicochemical information useful for molecular optimization of lamellarin-like cytotoxic drugs active toward chemoresistant tumors as well as nontoxic reversers of P-gp-mediated multidrug resistance in tumor cells.

Targeting P-glycoprotein: Investigation of piperine analogs for overcoming drug resistance in cancer

P-glycoprotein (P-gp) is a drug transporter that effluxes chemotherapeutic drugs and is implicated in the development of resistance of cancer cells to chemotherapeutic drugs. To date, no drug has been approved to inhibit P-gp and restore chemotherapy efficacy. Moreover, majority of the reported inhibitors have high molecular weight and complex structures, making it difficult to understand the basic structural requirement for P-gp inhibition. In this study, two structurally simple, low molecular weight piperine analogs Pip1 and Pip2 were designed and found to better interact with P-gp than piperine in silico. A one step, acid-amine coupling reaction between piperic acid and 6,7-dimethoxytetrahydroisoquinoline or 2-(3,4-dimethoxyphenyl)ethylamine afforded Pip1 and Pip2, respectively. In vitro testing in drug resistant P-gp overexpressing KB (cervical) and SW480 (colon) cancer cells showed that both analogs, when co-administered with vincristine, colchicine or paclitaxel were able to reverse the resistance. Moreover, accumulation of P-gp substrate (rhodamine 123) in the resistant cells, a result of alteration of the P-gp efflux, was also observed. These investigations suggest that the natural product analog - Pip1 ((2E,4E)-5-(benzo[d][1,3]dioxol-5-yl)-1-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1 H)-yl)penta-2,4-dien-1-one) - is superior to piperine and could inhibit P-gp function. Further studies are required to explore the full potential of Pip1 in treating drug resistant cancer.

Mannich base approach to 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone: A water-soluble prodrug for a multitarget inhibition of cholinesterases, beta-amyloid fibrillization and oligomer-induced cytotoxicity

Targeting protein aggregation for the therapy of neurodegenerative diseases remains elusive for medicinal chemists, despite a number of small molecules known to interfere in amyloidogenesis, particularly of amyloid beta (Aβ) protein. Starting from previous findings in the antiaggregating activity of a class of indolin-2-ones inhibiting Aβ fibrillization, 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone 1 was identified as a multitarget inhibitor of Aβ aggregation and cholinesterases with IC₅₀s in the low μM range. With the aim of increasing aqueous solubility, a Mannich-base functionalization led to the synthesis of N-methylpiperazine derivative 2. At acidic pH, an outstanding solubility increase of 2 over the parent compound 1 was proved through a turbidimetric method. HPLC analysis revealed an improved stability of the Mannich base 2 at pH2 along with a rapid release of 1 in human serum as well as an outstanding hydrolytic stability of the parent hydrazone. Coincubation of Aβ_1-42 with 2 resulted in the accumulation of low MW oligomers, as detected with PICUP assay. Cell assays on SH-SY5Y cells revealed that 2 exerts strong cytoprotective effects in both cell viability and radical quenching assays, mainly related to its active metabolite 1. These findings show that 2 drives the formation of non-toxic, off-pathway Aβ oligomers unable to trigger the amyloid cascade and toxicity.

Investigating Structural Requirements for the Antiproliferative Activity of Biphenyl Nicotinamides

A number of trimethoxybenzoic acid anilides, previously studied as permeability glycoprotein (P-gp) modulators, were screened with the aim of identifying new anticancer agents. One of these compounds, which showed antiproliferative activity against resistant MCF-7 cell line, was selected as the hit structure. Replacement of the trimethoxybenzoyl moiety with a nicotinoyl group, in order to overcome solubility issues, led to a new series of N-biphenyl nicotinoyl anilides, among which a nitro derivative, N-(3',5'-difluoro-3-nitro-[1,1'-biphenyl]-4-yl)nicotinamide (3), displayed antiproliferative activity against MCF-7 and MDA-MB-231 cells in the nanomolar range. The search for a bioisostere of the nitro group led to nitrile analogue N-(3-cyano-4'-fluoro-[1,1'-biphenyl]-4-yl)nicotinamide (36), which shows a strong increase in activity against MCF-7 and MDA-MB-231 cells. Compound 36 induced a dose-dependent accumulation of G₂ - and M-phase MCF-7 cell populations, and a decrease in S-phase cells. Relative to vinblastine, a well-known potent antimitotic agent, compound 36 also induced G₁ -phase arrest at low doses (20-40 nm), but did not inhibit in vitro tubulin polymerization.

Computational modelling of efflux pumps and their inhibitors

Antimicrobial resistance is based on the multifarious strategies that bacteria adopt to face antibiotic therapies, making it a key public health concern of our era. Among these strategies, efflux pumps (EPs) contribute significantly to increase the levels and profiles of resistance by expelling a broad range of unrelated compounds - buying time for the organisms to develop specific resistance. In Gram-negative bacteria, many of these chromosomally encoded transporters form multicomponent 'pumps' that span both inner and outer membranes and are driven energetically by a primary or secondary transporter component.One of the strategies to reinvigorate the efficacy of antimicrobials is by joint administration with EP inhibitors (EPI), which either block the substrate binding and/or hinder any of the transport-dependent steps of the pump. In this review, we provide an overview of multidrug-resistance EPs, their inhibition strategies and the relevant findings from the various computational simulation studies reported to date with respect to deciphering the mechanism of action of inhibitors with the purpose of improving their rational design.