Synthesis and Antibacterial Evaluation of Novel Small-Molecule Antibacterials of a Reduced Acridine Structure in S. aureus Strains Including MRSA.

BACKGROUND: The increasing antibacterial drug resistance remains a threat to global health with increasing mortality and morbidity. There is an urgent need to find novel antibacterials and develop alternative strategies to combat the increasing antibacterial drug resistance.

Evaluation of Novel Benzo-annelated 1,4-dihydropyridines as MDR Modulators in Cancer Cells.

BACKGROUND: Multidrug resistance (MDR) is the main problem in anticancer therapy today. Causative transmembrane efflux pumps in cancer cells have been reconsidered as promising anticancer target structures to restore anticancer drug sensitivity by various strategies, including MDR modulators. MDR modulators interfere with the efflux pumps and improve the cellular efficiency of chemotherapeutics. So far, only a few candidates have gone through clinical trials with disappointing results because of low specificity and toxic properties. AIM: This study aimed to find Novel MDR modulators to effectively combat multidrug resistance in cancer cells. OBJECTIVE: We synthesized various novel benzo-annelated 1,4-dihydropyridines to evaluate them as MDR modulators towards ABCB1 in cancer cells. METHODS: Synthesized compounds were purified by column chromatography. The MDR modulation of ABCB1 was determined in cellular efflux assays using the flow cytometry technique and cellular fluorescent measurements by the use of each fluorescent substrate. RESULTS: Compounds were yielded in a two-step reaction with structurally varied components. Further, substituent- dependent effects on the determined MDR inhibiting properties towards ABCB1 were discussed. Cellular studies prove that there is no toxicity or restoration of cancer cell sensitivity towards the used anticancer drug. CONCLUSION: Novel MDR modulators could be identified with favorable methoxy and ester group functions. Their use in both ABCB1 non-expressing and overexpressing cells proves a selective toxicity-increasing effect of the applied anticancer agent in the ABCB1 overexpressing cells, whereas the toxicity effect of the anticancer drug was almost unchanged in the non-expressing cells. These results qualify our novel compounds as perspective anticancer drugs compared to MDR modulators with nonselective toxicity properties.

Synthesis and Evaluation of Novel Substituted N-Aryl 1,4-Dihydropyridines as Antituberculostatic Agents.

BACKGROUND: Tuberculosis has been the main cause of mortality of infectious diseases worldwide, with strongly limited therapeutic options. With increasing resistance and missing suitable drugs in those cases, there is a strong need for novel antituberculostatic drugs. We developed novel N-aryl 1,4-dihydropyridines with various substitution patterns to evaluate them as antituberculostatic agents. METHODS: 1,4-Dihydropyridine derivatives were synthesized and purified by column chromatography or recrystallization. The mycobacterial growth inhibition was determined in a fluorescent mycobacterial growth assay. RESULTS: The compounds were prepared in a simple one-pot reaction under acidic conditions with structurally varied components. The substituent effects on the determined mycobacterial growth inhibitory properties are discussed. CONCLUSION: Lipophilic diester substituted derivatives show promising activities that were additionally affected by the aromatic substituent functions. Thus, we identified compounds with activities almost reaching that of the used antimycobacterial drug as control.

Novel Effective Fluorinated Benzothiophene-Indole Hybrid Antibacterials against S. aureus and MRSA Strains.

Increasing antibacterial drug resistance threatens global health, unfortunately, however, efforts to find novel antibacterial agents have been scaled back by the pharmaceutical industry due to concerns about a poor return on investment. Nevertheless, there is an urgent need to find novel antibacterial compounds to combat antibacterial drug resistance. The synthesis of novel drugs from natural sources is mostly cost-intensive due to those drugs' complicated structures. Therefore, it is necessary to find novel antibacterials by simple synthesis to become more attractive for industrial production. We succeeded in the discovery of four antibacterial compound (sub)classes accessible in a simple one-pot reaction based on fluorinated benzothiophene-indole hybrids. They have been evaluated against various S. aureus and MRSA strains. Structure- and substituent-dependent activities have been found within the (sub)classes and promising lead compounds have been identified. In addition, bacterial pyruvate kinase was found to be the molecular target of the active compounds. In conclusion, simple one-pot synthesis of benzothiophene-indoles represents a promising strategy for the search of novel antimicrobial compounds.

Novel effective small-molecule inhibitors of protein kinases related to tau pathology in Alzheimer's disease.

Background: Alzheimer's disease (AD) drugs in therapy are limited to acetylcholine esterase inhibitors and memantine. Newly developed drugs against a single target structure have an insufficient effect on symptomatic AD patients. Results: Novel aromatically anellated pyridofuranes have been evaluated for inhibition of AD-relevant protein kinases cdk1, cdk2, gsk-3b and Fyn. Best activities have been found for naphthopyridofuranes with a hydroxyl function as part of the 5-substituent and a hydrogen or halogen substituent in the 8-position. Best results in nanomolar ranges were found for benzopyridofuranes with a 6-hydroxy and a 3-alkoxy substitution or an exclusive 6-alkoxy substituent. Conclusion: First lead compounds were identified inhibiting two to three kinases in nanomolar ranges to be qualified as an innovative approach for AD multitargeting.

Correction: Döring et al. Discovery of Novel Symmetrical 1,4-Dihydropyridines as Inhibitors of Multidrug-Resistant Protein (MRP4) Efflux Pump for Anticancer Therapy. Molecules 2021, 26, 18.

The authors would like to correct an error made through no fault of their own in the title paper [...].

Discovery of a novel class of small-molecule antibacterial agents against Staphylococcus aureus.

Background: With constantly increasing resistance against the known antibiotics, the search for novel antibacterial compounds is a challenge. The number of synthetic antibacterial agents is limited. Materials & methods: We discovered novel small-molecule antibacterial agents that are accessible via a simple two-step procedure. The evaluation against Staphylococcus aureus showed antibacterial effects depending on the substituent positioning at the residues of the molecular scaffold. Additionally, we investigated the potential of the compounds to increase the antibacterial activity of tetracycline. Results: The most effective antibacterial compounds possessed a 3-methoxy function at an aromatic residue. In combination with tetracycline, we found a strong effect for a few compounds in boosting the antibacterial activity, so the first promising lead compounds with dual activities could be identified.

Novel Symmetrical Cage Compounds as Inhibitors of the Symmetrical MRP4-Efflux Pump for Anticancer Therapy.

Within the last decades cancer treatment improved by the availability of more specifically acting drugs that address molecular target structures in cancer cells. However, those target-sensitive drugs suffer from ongoing resistances resulting from mutations and moreover they are affected by the cancer phenomenon of multidrug resistance. A multidrug resistant cancer can hardly be treated with the common drugs, so that there have been long efforts to develop drugs to combat that resistance. Transmembrane efflux pumps are the main cause of the multidrug resistance in cancer. Early inhibitors disappointed in cancer treatment without a proof of expression of a respective efflux pump. Recent studies in efflux pump expressing cancer show convincing effects of those inhibitors. Based on the molecular symmetry of the efflux pump multidrug resistant protein (MRP) 4 we synthesized symmetric inhibitors with varied substitution patterns. They were evaluated in a MRP4-overexpressing cancer cell line model to prove structure-dependent effects on the inhibition of the efflux pump activity in an uptake assay of a fluorescent MRP4 substrate. The most active compound was tested to resentisize the MRP4-overexpressing cell line towards a clinically relevant anticancer drug as proof-of-principle to encourage for further preclinical studies.

Novel Small-Molecule Hybrid-Antibacterial Agents against S. aureus and MRSA Strains.

Ongoing resistance developments against antibiotics that also affect last-resort antibiotics require novel antibacterial compounds. Strategies to discover such novel structures have been dimerization or hybridization of known antibacterial agents. We found novel antibacterial agents by dimerization of indols and hybridization with carbazoles. They were obtained in a simple one-pot reaction as bisindole tetrahydrocarbazoles. Further oxidation led to bisindole carbazoles with varied substitutions of both the indole and the carbazole scaffold. Both the tetrahydrocarbazoles and the carbazoles have been evaluated in various S. aureus strains, including MRSA strains. Those 5-cyano substituted derivatives showed best activities as determined by MIC values. The tetrahydrocarbazoles partly exceed the activity of the carbazole compounds and thus the activity of the used standard antibiotics. Thus, promising lead compounds could be identified for further studies.

Discovery of Novel Symmetrical 1,4-Dihydropyridines as Inhibitors of Multidrug-Resistant Protein (MRP4) Efflux Pump for Anticancer Therapy.

Despite the development of targeted therapies in cancer, the problem of multidrug resistance (MDR) is still unsolved. Most patients with metastatic cancer die from MDR. Transmembrane efflux pumps as the main cause of MDR have been addressed by developed inhibitors, but early inhibitors of the most prominent and longest known efflux pump P-glycoprotein (P-gp) were disappointing. Those inhibitors have been used without knowledge about the expression of P-gp by the treated tumor. Therefore the use of inhibitors of transmembrane efflux pumps in clinical settings is reconsidered as a promising strategy in the case of the respective efflux pump expression. We discovered novel symmetric inhibitors of the symmetric efflux pump MRP4 encoded by the ABCC4 gene. MRP4 is involved in many kinds of cancer with resistance to anticancer drugs. All compounds showed better activities than the best known MRP4 inhibitor MK571 in an MRP4-overexpressing cell line assay, and the activities could be related to the various substitution patterns of aromatic residues within the symmetric molecular framework. One of the best compounds was demonstrated to overcome the MRP4-mediated resistance in the cell line model to restore the anticancer drug sensitivity as a proof of concept.

Novel Nonsymmetrical 1,4-Dihydropyridines as Inhibitors of Nonsymmetrical MRP-Efflux Pumps for Anticancer Therapy.

Cancer is a strong global burden with increasing numbers of diseases and ongoing anticancer drug resistance. The number of structurally novel anticancer drugs is strongly limited. They cause high costs for the social health systems. Most critical so-called multidrug resistances (MDR) are caused by transmembrane efflux pumps that transport drugs with various structures out of the cancer cells. Multidrug resistance proteins (MRPs) type 1 and 2 are found overexpressed in various kinds of cancer. There is a strong need for inhibitors of those efflux pumps. We developed novel nonsymmetrical 1,4-dihydropyridines as novel inhibitors of cancer relevant MRP types 1 and 2. The structure-dependent activities of the differently substituted derivatives were evaluated in cellular assays of respective cancer cells and are discussed. Promising candidates were identified. One candidate was demonstrated to resensitize a cisplatin resistant cancer cell line and thus to overcome the anticancer drug resistance.

Novel effective antibacterial small-molecules against Staphylococcus and Enterococcus strains.

Background: Resistance developments against established antibiotics are an emerging problem for antibacterial therapies. Novel antibiotics are urgently needed. Materials & methods: We developed novel small-molecule antibacterials which are easily accessible in a simple one-pot synthesis. The central cyclopentaindole core is substituted with two indole residues. Various indole and cyclopentane substituents have been introduced. Additionally, first indole substituted propene compounds as ring-open variants of the cyclopentaindoles have been yielded and evaluated as antibacterials against Staphylococcus aureus and Enterococcus strains. Results: Most effective compounds have been those with a bromo cyclopentane and a chloro indole substitution. First lead compounds were identified with promising activities similar to that observed in vitro for last resort antibiotics, so that the novel compounds enriche the pool of perspective small-molecule antibacterial drug candidates.

Novel Small-molecule Antibacterials against Gram-positive Pathogens of Staphylococcus and Enterococcus Species.

Defeat of the antibiotic resistance of pathogenic bacteria is one great challenge today and for the future. In the last century many classes of effective antibacterials have been developed, so that upcoming resistances could be met with novel drugs of various compound classes. Meanwhile, there is a certain lack of research of the pharmaceutical companies, and thus there are missing developments of novel antibiotics. Gram-positive bacteria are the most important cause of clinical infections. The number of novel antibacterials in clinical trials is strongly restricted. There is an urgent need to find novel antibacterials. We used synthetic chemistry to build completely novel hybrid molecules of substituted indoles and benzothiophene. In a simple one-pot reaction, two novel types of thienocarbazoles were yielded. Both indole substituted compound classes have been evaluated as completely novel antibacterials against the Staphylococcus and Enterococcus species. The evaluated partly promising activities depend on the indole substituent type. First lead compounds have been evaluated within in vivo studies. They confirmed the in vitro results for the new classes of small-molecule antibacterials.

Dually Acting Nonclassical 1,4-Dihydropyridines Promote the Anti-Tuberculosis (Tb) Activities of Clofazimine.

The number of effective antituberculotic drugs is strongly limited to four first-line drugs in standard therapy. In case of resistances second-line antibiotics are used with a poor efficacy and tolerability. Therefore, novel antituberculotic drugs are urgently needed. We synthesized novel nonclassical 1,4-dihydropyridines and evaluated their antituberculotic properties depending on substituent effects. Preferred substituents could be identified. As related classical 1,4-dihydropyridines are known as inhibitors of the transmembrane efflux pump ABCB1 in cancer cells, we wondered whether a use of our compounds may be of favour to enhance the antituberculotic drug efficacy of the second-line antituberculotic drug clofazimine, which is a known substrate of ABCB1 by a suggested inhibition of a corresponding efflux pump in Mycobacterium tuberculosis (Mtb). For this, we determined the ABCB1 inhibiting properties of our compounds in a mouse T-lymphoma cell line model and then evaluated the drug-enhancing properties of selected compounds in a co-application with clofazimine in our Mtb strain. We identified novel enhancers of clofazimine toxicity which could prevent clofazimine resistance development mediated by an efflux pump activity.

Antibacterial Evaluation of Novel Substituted Cycloheptaindoles in Staphylococcus and Enterococcus Strains.

BACKGROUND: Due to emerging resistances against antibiotics there is a strong need to find novel antibacterial agents with a novel structure to prevent early resistance developments. OBJECTIVE: Bisindole compounds with antibacterial activities which formally result from the reaction of an aldehyde with indole motivated to investigate the reaction of a dialdehyde and indole to give novel structures with potential antibacterial activities. METHODS: Compounds were yielded by chemical synthesis and purified using column chromatography. The antibacterial activity was determined as minimal inhibitory growth activity in cultures of Gram-positive strains of Staphylococcus aureus and Enterococcus species. RESULTS: Cyclohepta[2,3-b]indoles have been yielded in a one-step reaction procedure with indole substitutions at the cycloheptane central core matching a solution for achieving fused novel cycloalkane indoles with functionalized residues of promising biological activity. So far fused cycloalkane indoles have not been available in a one-step procedure and moreover, core functionalizations have been additional challenges. Various indole substitutions have been done to provide a first set of compounds. CONCLUSION: Substituent-dependent effects have been suggested to influence the antibacterial activity and first compounds were identified with specific Staphylococcus activities and Enterococcus species effects towards Enterococcus faecalis as critical pathogens in the hospital with upcoming resistances against standard antibiotics.

Antistaphylococcal evaluation of indole-naphthalene hybrid analogs.

Resistance developments against established antibiotics are an emerging problem for antibacterial therapies. Infections with Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) have become more difficult to treat with standard antibiotics that often fail, especially against MRSA. In consequence, novel antibiotics are urgently needed. Antibiotics from natural sources own complicated structures that cause difficulties for a chemical synthetic production. We developed novel small-molecule antibacterials that are easily accessible in a simple one-pot synthesis. The central indolonaphthalene core is substituted with indole residues at various positions. Both the varied indole substitutions and their positions at the molecular scaffold influence the determined antibacterial activity against the evaluated Staphylococcus strains. Best activities have been found for 5-chloro, -cyano, and -hydroxyl indole substitutions. Therefore, first promising lead compounds could be identified that are nontoxic in human HEK and SH-SY5Y cells and exceed the activity of used standard antibiotics, especially against MRSA.

Novel Protein Kinase Inhibitors Related to Tau Pathology Modulate Tau Protein-Self Interaction Using a Luciferase Complementation Assay.

The current number of drugs available for the treatment of Alzheimer's disease (AD) is strongly limited and their benefit for therapy is given only in the early state of the disease. An effective therapy should affect those processes which mainly contribute to the neuronal decay. There have been many approaches for a reduction of toxic Aß peptides which mostly failed to halt cognitive deterioration in patients. The formation of neurofibrillary tangles (NFT) and its precursor tau oligomers have been suggested as main cause of neuronal degeneration because of a direct correlation of their density to the degree of dementia. Reducing of tau aggregation may be a viable approach for the treatment of AD. NFT consist of hyperphosphorylated tau protein and tau hyperphosphorylation reduces microtubule binding. Several protein kinases are discussed to be involved in tau hyperphosphorylation. We developed novel inhibitors of three protein kinases (gsk-3ß, cdk5, and cdk1) and discussed their activity in relation to tau phosphorylation and on tau⁻tau interaction as a nucleation stage of a tau aggregation in cells. Strongest effects were observed for those inhibitors with effects on all the three kinases with emphasis on gsk-3ß in nanomolar ranges.

Discovery of Novel Enhancers of Isoniazid Toxicity in Mycobacterium tuberculosis.

The number of effective first-line antibiotics for the treatment of Mycobacterium tuberculosis infection is strongly limited to a few drugs. Due to emerging resistance against those drugs, second- and third-line antibiotics have been established in therapy with certain problems and also increasing mycobacterial resistance. An alternative to such novel drugs or combined therapeutic regimes which may reduce resistance development is finding enhancers of mycobacterial drug effectiveness, especially enhancers that counteract causative resistance mechanisms. Such enhancers may reduce the extracellular drug efflux mediated by bacterial efflux pumps and thus enhance the intracellular drug toxicity. We developed novel 1,4-dihydropyridines (DHPs) as potential efflux pump inhibitors with some determined P-gp affinities. The influence on the antituberculotic drug toxicity has been investigated for three prominent antituberculotic drugs. Exclusive and selective toxicity enhancing effects have been detected for isoniazid (INH) which could be related to certain substituent effects of the 1,4-DHPs. So, structure-dependent activities have been found. Thus, promising enhancers could be identified and a suggested efflux pump inhibition is discussed.

Discovery of novel dual inhibitors of receptor tyrosine kinases EGFR and PDGFR-ß related to anticancer drug resistance.

With ongoing resistance problems against the marketed EGFR inhibitors having a quinazoline core scaffold there is a need for the development of novel inhibitors having a modified scaffold and, thus, expected lower EGFR resistance problems. An additional problem concerning EGFR inhibitor resistance is an observed heterodimerization of EGFR with PDGFR-ß that neutralises the sole inhibitor activity towards EGFR. We developed novel pyrimido[4,5-b]indoles with varied substitution patterns at the 4-anilino residue to evaluate their EGFR and PDGFR-ß inhibiting properties. We identified dual inhibitors of both EGFR and PDGFR-ß in the nanomolar range which have been initially screened in cancer cell lines to prove a benefit of both EGFR and PDGFR-ß inhibition.