Plant Flavonoids Emerge as Multi-Target Weapon Against Drug-Resistant Tuberculosis

Tuberculosis remains one of the most stubborn infectious diseases on the planet, and the therapeutic arsenal against it is showing its age. A new review published in Molecular Biology Reports by Ankita Bansal, Diksha Sharma, Sonia Yadav, Virender Kumar and Vishal Sharma takes stock of an unlikely family of candidates for the next generation of anti-TB drugs: flavonoids, the polyphenolic compounds that plants have been producing for millions of years as chemical defenses. The review, which appeared online on 10 October 2026, weaves together molecular pharmacology, microbiology and medicinal chemistry to argue that these abundant plant molecules deserve a far more prominent place in the tuberculosis drug development pipeline than they currently occupy.

The urgency behind the search is easy to appreciate. Mycobacterium tuberculosis, the bacterium responsible for tuberculosis, continues to exact a devastating toll, particularly in low- and middle-income countries where the burden of disease is concentrated. Standard treatment regimens demand months of multidrug therapy, and their effectiveness is being steadily eroded by the rise of multidrug-resistant and rifampicin-resistant strains. On top of the resistance problem sit the familiar liabilities of existing anti-TB drugs: significant toxicity, high treatment costs and poor outcomes in difficult cases. The authors frame flavonoids as a response to precisely this convergence of problems, pointing to their potent anti-mycobacterial activity alongside host-directed therapeutic properties, meaning they can act on the bacterium directly while simultaneously modulating the infected patient’s own immune machinery.

What makes flavonoids especially interesting from a pharmacological standpoint is the breadth of their mechanisms. The review catalogues an impressive list of targets. Flavonoids can reduce oxidative stress within infected tissues, disrupt the integrity of the waxy mycobacterial cell wall that shields the pathogen from hostile environments, and inhibit the bacterial efflux pumps that expel antibiotics before they can accumulate to lethal concentrations. They interfere with DNA replication and nucleic acid synthesis, and they perturb the energy metabolism that the bacillus depends on for survival inside host cells. They also modulate the MAPK/ERK signaling pathway, a central communication route in mammalian cells that shapes the inflammatory response to infection. This multi-targeted action profile carries a strategic advantage that single-target drugs lack: when a compound attacks several vulnerabilities at once, the probability that the bacterium can evolve resistance to all of them simultaneously drops sharply.

Some of the most concrete mechanistic evidence comes from studies of individual flavonoids against specific bacterial enzymes. Quercetin and apigenin have been shown to target D-alanine:D-alanine ligase, an enzyme essential for building the peptidoglycan layer of the bacterial cell wall. Screening efforts have identified flavonoids as inhibitors of glutamate racemase, another enzyme critical to cell wall biosynthesis in M. tuberculosis. Quercetin 3-O-glucoside, recovered from a wild plant found in the Egyptian Sahara, has demonstrated inhibition of glutamine synthetase, an enzyme the bacterium needs to build its characteristic cell wall and sustain virulence. Synthetic quercetin has been reported to inhibit mycobacterial growth, possibly through interaction with DNA gyrase, while the flavonol galangin has been characterized as an inhibitor of DnaB helicase, a molecular motor that unwinds DNA during replication. Flavonoid inhibitors have also been shown to target Rv0636, a putative dehydratase enzyme involved in the fatty acid synthase II system that manufactures the mycolic acids defining the mycobacterial envelope.

The review also highlights compounds that act on the host side of the host-pathogen standoff. Luteolin has emerged as a candidate for host-directed immunotherapy, with studies suggesting it could serve as an adjunct to isoniazid treatment. Phloretin has been reported to exert anti-tuberculosis activity while suppressing lung inflammation, and it inhibits inflammatory signaling through MAPK, Akt and NF-kappaB pathways in human lung epithelial cells. The flavonoid apigenin dampens lipopolysaccharide-induced inflammatory responses in macrophages through multiple mechanisms. A flavonoid mixture has been shown to inhibit the survival and infectivity of M. tuberculosis in experimental settings. Perhaps most strikingly, epigallocatechin gallate, the celebrated green tea polyphenol, was delivered directly to the lungs in a targeted formulation, where it controlled mycobacterial growth by enhancing autophagy, the cellular recycling process that infected immune cells use to digest intracellular bacteria, while suppressing bacterial burden.

Efflux pump inhibition deserves particular attention because it addresses one of the central drivers of drug resistance. Mycobacteria deploy membrane transporters that pump antibiotics out of the cell, and elevated efflux activity is a recognized mechanism by which resistance develops and intensifies. Flavonoids have been identified as novel efflux pump inhibitors active against both environmental and pathogenic intracellular mycobacterial species, and carvotacetones from Sphaeranthus africanus have shown both antimicrobial and efflux pump inhibitory activity against mycobacteria. In principle, pairing a flavonoid efflux inhibitor with an existing antibiotic could restore the drug’s potency against strains that would otherwise survive, effectively using plant chemistry as a force multiplier for conventional therapy. Reviews of plant-derived polyphenols against efflux-mediated antibiotic resistance suggest this strategy has momentum across the antimicrobial field more broadly.

The translation of these laboratory findings into medicines, however, faces a formidable obstacle course, and the review is candid about it. Flavonoids suffer from low oral bioavailability, limited metabolic stability, poor water solubility and, in some cases, toxicity concerns, all of which constrain how much active compound actually reaches the site of infection in a patient. A molecule that performs brilliantly in a test tube is of little clinical value if it is destroyed by first-pass metabolism or never dissolves in the gut. These pharmacokinetic weaknesses are not unique to flavonoids, but they are acute, and they explain why a class of compounds with such compelling biology has yet to produce a registered anti-TB drug.

This is where structure-activity relationship studies, the systematic mapping of how molecular architecture determines biological effect, become the review’s most technically valuable contribution. The authors distill a set of design rules from the accumulated data. Biological activity is strongly influenced by the pattern of hydroxylation, the degree of molecular planarity and the overall lipophilicity of the molecule. The C2=C3 double bond connecting the C-ring to the B-ring, a defining feature of flavones and flavonols, enhances target binding. Catechol moieties, the adjacent hydroxyl pairs on the B-ring, contribute to activity, as do strategically placed lipophilic substitutions that improve cellular permeability through the lipid-rich mycobacterial envelope. Conversely, excessive methylation or glycosylation of the scaffold tends to decrease activity, a finding with direct implications for how derivative libraries should be designed. These principles have already guided work on chalcones, the open-chain relatives of flavonoids, where QSAR-driven design has yielded potent antitubercular derivatives, and on prenylated and C-dimethylated flavones where added lipophilicity appears to pay dividends.

The path forward, as the review sketches it, combines rational structural optimization with modern delivery technology. Nanosuspension and nanoparticle formulations have been shown to enhance the oral bioavailability of quercetin and baicalin, and targeted pulmonary delivery of epigallocatechin gallate has already demonstrated proof of concept for getting flavonoids to the anatomical site where tuberculosis takes hold. Patent activity around anti-tubercular flavonoid compositions suggests that the translational community is paying attention. The authors position flavonoids as promising, inexpensive and less toxic candidates for novel anti-TB treatments, while emphasizing that further research is essential to optimize bioavailability and establish clinical applicability. In an era when the tuberculosis pipeline desperately needs new chemistry and resistance keeps outpacing old drugs, the humble plant polyphenols, refined by structure-guided design and smart formulation, may yet earn a place in the clinic.

Subject of Research: Anti-tubercular mechanisms and structure-activity relationships of plant flavonoids

Article Title: Flavonoids in treatment of tuberculosis: from molecular mechanisms to structure activity relationships

Article References: Bansal, A., Sharma, D., Yadav, S., Kumar, V., & Sharma, V. (2026). Flavonoids in treatment of tuberculosis: from molecular mechanisms to structure activity relationships. Molecular Biology Reports, 53(1), Article 1694. https://doi.org/10.1007/s11033-026-12869-6

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12869-6

Keywords: tuberculosis, flavonoids, drug resistance, structure-activity relationship, mycobacterial cell wall, efflux pumps, oxidative stress, MAPK signaling, host-directed therapy, natural products, pharmacokinetics, quercetin