{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T09:52:09Z","timestamp":1776937929911,"version":"3.51.4"},"reference-count":30,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T00:00:00Z","timestamp":1776902400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Multidrug (MDR) resistances against various classes of antibiotics used in S. aureus and MRSA infections have emerged. With limited options for novel antibacterial compounds, there is a strong focus on finding agents against MDR phenomenon, namely causative efflux pumps. We synthesised novel benzo-annelated 1,4-dihydropyridines with various substitution patterns both at the 4- and N-alkyl substituents and, additionally, at the annelated aromatic residues. MDR efflux pump-inhibiting activity was evaluated in S. aureus strains including MRSA and was measured in a fluorescent assay system using ethidium bromide as the overall substrate of S. aureus efflux pumps. Favourable substituents for inhibiting efflux pump activity in S. aureus have been 4-methoxy and 4- and 3-chloro at the 4-phenyl position of the 1,4-dihydropyridine ring combined with an N-benzyl residue. The most favourable substituents for the activity inMRSA strains have been those 4-phenyl chloro substituents combined with additional pyrido residues attached to the benzo substituent at the 1,4-dihydropyridine core. Benzo-annelated 1,4-dihydropyridines are a novel class of inhibitors of MDR relevant efflux pumps in S. aureus strains including MRSA.<\/jats:p>","DOI":"10.3390\/ijms27093738","type":"journal-article","created":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T09:09:12Z","timestamp":1776935352000},"page":"3738","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Evaluation of Novel Benzo-Annelated 1,4-Dihydropyridines as Potential Inhibitors of Antibacterial Efflux Pumps in S. aureus and MRSA Strains"],"prefix":"10.3390","volume":"27","author":[{"given":"Peter","family":"Werner","sequence":"first","affiliation":[{"name":"Institute of Pharmacy, Martin-Luther-University Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8638-5815","authenticated-orcid":false,"given":"Nikoletta","family":"Szemer\u00e9di","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology, University of Szeged, Dom t\u00e9r 10, 6720 Szeged, Hungary"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8085-0950","authenticated-orcid":false,"given":"Gabriella","family":"Spengler","sequence":"additional","affiliation":[{"name":"Department of Medical Microbiology, University of Szeged, Dom t\u00e9r 10, 6720 Szeged, Hungary"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5261-0984","authenticated-orcid":false,"given":"Frank","family":"Erdmann","sequence":"additional","affiliation":[{"name":"Institute of Pharmacy, Martin-Luther-University Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Andreas","family":"Hilgeroth","sequence":"additional","affiliation":[{"name":"Institute of Pharmacy, Martin-Luther-University Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,4,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"368","DOI":"10.15698\/mic2024.11.839","article-title":"Efflux pumps: Gatekeepers of antibiotic resistance in Staphylococcus aureus biofilms","volume":"11","author":"Sinha","year":"2024","journal-title":"Microb. Cell"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"42","DOI":"10.1038\/nrmicro3380","article-title":"Molecular mechanisms of antibiotic resistance","volume":"13","author":"Blair","year":"2015","journal-title":"Nat. Rev. Microbiol."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Esposito, S., Blasi, F., Curtis, N., Kaplan, S., Lazzarotto, T., Meschiari, M., Mussini, C., Peghin, M., Rodrigo, C., and Vena, A. (2023). New Antibiotics for Staphylococcus aureus Infection: An Update from the World Association of Infectious Diseases and Immunological Disorders (WAidid) and the Italian Society of Anti-Infective Therapy (SITA). Antibiotics, 12.","DOI":"10.3390\/antibiotics12040742"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"367","DOI":"10.3934\/medsci.2022018","article-title":"Staphylococcus aureus antimicrobial efflux pumps and their inhibitors: Recent developments","volume":"9","author":"Lekshemi","year":"2022","journal-title":"AIMS Med. Sci."},{"key":"ref_5","first-page":"518","article-title":"Methicillin-resistant Staphylococcus aureus in Nepal","volume":"59","author":"Shrestha","year":"2021","journal-title":"J. Nepal Med. Assoc."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"71","DOI":"10.1016\/j.cmi.2018.03.045","article-title":"Methicillin resistance in Staphylococcus aureus infections among patients colonized with methicillin-susceptible Staphylococcus aureus","volume":"25","author":"Shrestha","year":"2019","journal-title":"Clin. Microbiol. Infect."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1539","DOI":"10.7754\/Clin.Lab.2020.200930","article-title":"Staphylococcus aureus, ESKAPE bacteria challenging current health care and community settings: A literature review","volume":"67","author":"Tigabu","year":"2021","journal-title":"Clin. Lab."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"001333","DOI":"10.1099\/mic.0.001333","article-title":"Role of bacterial efflux pumps in antibiotic resistance, virulence, and the strategies to discover novel efflux pump inhibitors","volume":"169","author":"Gaurav","year":"2023","journal-title":"Microbiology"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"135","DOI":"10.1038\/s41586-021-04265-w","article-title":"Emergence of methicillin resistance predates the clinical use of antibiotics","volume":"602","author":"Larsen","year":"2022","journal-title":"Nature"},{"key":"ref_10","unstructured":"WHO (2026, January 31). Antimicrobial Resistance. Available online: https:\/\/www.who.int\/news-room\/fact-sheets\/detail\/antimicrobial-resistance."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"227","DOI":"10.2147\/IDR.S134497","article-title":"Cefazolin potency against methicillin-resistant Staphylococcus aureus: A microbiologic assessment in support of a novel drug delivery system for skin and skin structure infections","volume":"10","author":"Nicolau","year":"2017","journal-title":"Infect. Drug Resist."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Gherardi, G. (2023). Staphylococcus aureus infections: Pathogenesis and antimicrobial resistance. Int. J. Mol. Sci., 24.","DOI":"10.3390\/ijms24098182"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"e18","DOI":"10.1093\/cid\/ciq146","article-title":"Clinical practice guidelines by the Infectious Diseases Society of America for the Treatment of methicillin-resistant Staphylococcus aureus infections in adults and children","volume":"52","author":"Liu","year":"2011","journal-title":"Clin. Infect. Dis."},{"key":"ref_14","unstructured":"(2026, February 02). European Medicines Agency Sivextro. Available online: https:\/\/www.ema.europa.eu\/en\/medicines\/human\/EPAR\/sivextro."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"17","DOI":"10.1111\/j.1749-6632.2011.06354.x","article-title":"The history of tetracyclines","volume":"1241","author":"Nelson","year":"2011","journal-title":"Ann. N. Y. Acad. Sci."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1059","DOI":"10.1016\/j.apjtm.2017.10.003","article-title":"Antimicrobial resistance and underlying mechanisms in Staphylococcus aureus isolates","volume":"10","author":"Yilmaz","year":"2017","journal-title":"Asian Pac. J. Trop. Med."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"382","DOI":"10.1128\/CMR.19.2.382-402.2006","article-title":"Clinically relevant chromosomally encode multidrug resistance efflux pumps in bacteria","volume":"19","author":"Piddock","year":"2006","journal-title":"Clin. Microbiol. Rev."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"430","DOI":"10.1093\/femsre\/fux007","article-title":"Antibiotic resistance in Staphylococcus aureus. Current status and future prospects","volume":"41","author":"Foster","year":"2017","journal-title":"FEMS Microbiol. Rev."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"2003","DOI":"10.1093\/jac\/dky042","article-title":"Role of bacterial efflux pumps in biofilm formation","volume":"73","author":"Alav","year":"2018","journal-title":"J. Antimicrob. Chemother."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"4321","DOI":"10.1021\/jm701623q","article-title":"From Phenothiazine to 3-Phenyl-1,4-benzothiazine Derivatives as Inhibitors of the Staphylococcus aureus NorA Multidrug Efflux Pump","volume":"51","author":"Sabatini","year":"2008","journal-title":"J. Med. Chem."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"26003","DOI":"10.1038\/s41598-025-11226-0","article-title":"Mechanistic studies on the effect of berberine on methicillin-resistant Staphylococcus aureus drug resistance through modulation of wall teichoteic acid","volume":"15","author":"Zhou","year":"2025","journal-title":"Sci. Rep."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1433","DOI":"10.1073\/pnas.030540597","article-title":"Synergy in a medicinal plant: Antimicrobial action of berberine potentiated by 5\u2019-methoxyhydnocarpin, a multidrug pump inhibitor","volume":"97","author":"Stermitz","year":"2000","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1270","DOI":"10.1093\/jac\/dkn088","article-title":"Novel structural analogues of piperine as inhibitor of the NorA efflux pump of Staphylococcus aureus","volume":"61","author":"Kumar","year":"2008","journal-title":"J. Antimicrob. Chemother."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2401","DOI":"10.1093\/jac\/dks232","article-title":"Capsaicin, a novel inhibitor of the NorA efflux pump, reduces the intracellular invasion of Staphylococcus aureus","volume":"67","author":"Kalia","year":"2012","journal-title":"J. Antimicrob. Chemother."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"337","DOI":"10.1128\/CMR.00117-14","article-title":"The challenge of efflux-mediated antibiotic resistance in Gram-negative bacteria","volume":"28","author":"Li","year":"2015","journal-title":"Clin. Microbiol. Rev."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"415","DOI":"10.1038\/sj.bjp.0705635","article-title":"3,5-Dibenzoyl-4-(3-phenoxyphenyl)-1,4-dihydro.2,3-dimethylpyridine (DP7) as a new multidrug resistance reverting agent devoid of effects on vascular smooth muscle contractility","volume":"14","author":"Saponara","year":"2004","journal-title":"Br. J. Pharmacol."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1392","DOI":"10.1007\/s12272-013-0149-8","article-title":"Reversal of multidrug resistance in cancer cells by novel asymmetrical 1,4-dihydropyridines","volume":"36","author":"Firuzi","year":"2013","journal-title":"Arch. Pharm. Res."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"415","DOI":"10.2174\/1871520610909040415","article-title":"Recent Advances in the Development of P-gp Inhibitors","volume":"9","author":"Baumert","year":"2009","journal-title":"Anti-Cancer Agents Med. Chem."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"568","DOI":"10.1021\/acs.molpharmaceut.1c00678","article-title":"Forced Solid-State Oxidation Studies of Nifedipine-PVP Amorphous Solid Dispersion","volume":"19","author":"Saraf","year":"2022","journal-title":"Mol. Pharm."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Kreutzer, D., D\u00f6ring, H., Werner, P., Ritter, C.A., and Hilgeroth, A. (2021). Novel Symmetrical Cage Compounds as Inhibitors of the Symmetrical MRP4-Efflux Pump for Anticancer Therapy. Int. J. Mol. Sci., 22.","DOI":"10.3390\/ijms22105098"}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/9\/3738\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T09:10:57Z","timestamp":1776935457000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/9\/3738"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,23]]},"references-count":30,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,5]]}},"alternative-id":["ijms27093738"],"URL":"https:\/\/doi.org\/10.3390\/ijms27093738","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,23]]}}}