Repurposing the orphan drug nitisinone to control the transmission of African trypanosomiasis

Mode of toxicity of the β-triketone leptospermone to Aedes aegypti mosquitoes

Leptospermone, a natural β-triketone and major constituent of manuka oil (Leptospermum scoparium), is an established inhibitor of plant HPPD and was identified to induce rapid knockdown and induce high toxicity to Aedes aegypti adults via topical and tarsal contact exposure with LD50 values of 150 ng/mg of mosquito and 357 ng/cm2, respectively. Although toxic to mosquitoes, leptospermone was non-toxic to ticks, the honey bee, or the fruit fly indicating a high degree of insect specificity. Importantly, leptospermone was equally toxic to non-blood fed and blood-fed mosquitoes suggesting the mode of action is not via HPPD inhibition. Molecular modeling suggested high structural similarities between leptospermone and mammalian sulfonamide carbonic anhydrase (CA) inhibitors. In vitro potency assays with mosquito midgut homogenate or purified CA verify leptospermone inhibits Ae. aegypti CA, but not mammalian CAs. CAs are metalloenzymes that regulate the pH of tissues and ubiquitously expressed throughout insect tissues but are abundantly expressed in the mosquito midgut and, thus, we tested leptospermone to alter pH regulation in the mosquito midgut. Indeed, leptospermone significantly reduced the pH of Ae. aegypti midguts when compared to control mosquitoes which further supports the notion that leptospermone mode of action in insects is via inhibition of CA. These data verify leptospermone is an effective mosquitocide that induces rapid knockdown and toxicity to Ae. aegypti at doses that approach natural pyrethrins against pyrethroid-resistant mosquito strains. Further, the data indicate leptospermone mode of action is CA inhibition, which is a novel mosquitocide target and is different when compared to the mode of action in plants.

Deployment and transcriptional evaluation of nitisinone, an FDA-approved drug, to control bed bugs

BACKGROUND

Bed bugs are blood-feeders that rapidly proliferate into large indoor infestations. Their bites can cause allergies, secondary infections and psychological stress, among other problems. Although several tactics for their management have been used, bed bugs continue to spread worldwide wherever humans reside. This is mainly due to human-mediated transport and their high resistance to several classes of insecticides. New treatment options with novel modes of action are required for their control. In this study, we evaluated the use of nitisinone (NTBC), an FDA-approved drug, for bed bug control in an insecticide-susceptible (HH) and an insecticide-resistant (CIN) population.

RESULTS

Although NTBC was lethal to both populations when administered orally or applied topically in very low doses, we observed a slight but significant resistance in the CIN population. Transcriptomic analysis in both populations indicated that NTBC treatment elicited a broad suppression of genes associated with RNA post-transcriptional modifications, translation, endomembrane system, protein post-translational modifications and protein folding. The CIN population exhibited higher adenosine triphosphate (ATP) production and xenobiotic detoxification. Feeding studies on a mouse model suggest that NTBC could be used as a control method of bed bugs by host treatment.

CONCLUSION

The results indicate that NTBC can be used as a new active ingredient for bed bug control by topical or oral treatment and shed light on the molecular mechanisms of suppressed tyrosine metabolism following NTBC treatment. © 2025 Society of Chemical Industry.

Anopheles mosquito survival and pharmacokinetic modeling show the mosquitocidal activity of nitisinone

One approach to interrupting the transmission of insect-borne diseases that is successfully used in veterinary medicine is exploiting the ability of antiparasitic drugs to make vertebrate blood toxic for blood-feeding insects. Recent studies have identified 4-hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme of the tyrosine detoxification pathway, as essential for hematophagous arthropods to digest their blood meals. Such blood-feeding insects include anopheline mosquitoes, which transmit malaria-causing Plasmodium parasites. A US Food and Drug Administration-approved HPPD enzyme inhibitor called nitisinone is a drug used to treat rare human-inherited disorders of the tyrosine pathway. Here, we demonstrate that feeding human blood containing nitisinone to insectary-reared female Anopheles gambiae mosquitoes was mosquitocidal to both young and old mosquitoes as well as insecticide-resistant Anopheles strains. Pharmacokinetic-pharmacodynamic (PK/PD) modeling of nitisinone's dose-response relationship (when administered at the highest recommended doses for adults and children) demonstrated improved efficacy against mosquitoes compared with the gold standard endectocidal drug, ivermectin. Furthermore, blood samples from individuals with alkaptonuria (a rare genetic metabolic disorder in the tyrosine degradation pathway), who were taking a daily low dose of 2 milligrams of nitisinone, were shown to be lethal to mosquitoes. Thus, inhibiting the Anopheles HPPD enzyme with nitisinone warrants further investigation as a complementary intervention for vector control and the prevention of malaria transmission.

Exploration of innovative drug repurposing strategies for combating human protozoan diseases: Advances, challenges, and opportunities

Protozoan infections (e.g., malaria, trypanosomiasis, and toxoplasmosis) pose a considerable global burden on public health and socioeconomic problems, leading to high rates of morbidity and mortality. Due to the limited arsenal of effective drugs for these diseases, which are associated with devastating side effects and escalating drug resistance, there is an urgent need for innovative antiprotozoal drugs. The emergence of drug repurposing offers a low-cost approach to discovering new therapies for protozoan diseases. In this review, we summarize recent advances in drug repurposing for various human protozoan diseases and explore cost-effective strategies to identify viable new treatments. We highlight the cross-applicability of repurposed drugs across diverse diseases and harness common chemical motifs to provide new insights into drug design, facilitating the discovery of new antiprotozoal drugs. Challenges and opportunities in the field are discussed, delineating novel directions for ongoing and future research.

Deployment and transcriptional evaluation of nitisinone, an FDA-approved drug, to control bed bugs

Bed bugs are blood-feeders that rapidly proliferate into large indoor infestations. Their bites can cause allergies, secondary infections and psychological stress, among other problems. Although several tactics for their management have been used, bed bugs continue to spread worldwide wherever humans reside. This is mainly due to human-mediated transport and their high resistance to several classes of insecticides. New treatment options with novel modes of action are required for their control. In this study, we evaluated the use of nitisinone (NTBC), an FDA-approved drug, for bed bug control in an insecticide-susceptible (HH) and an insecticide-resistant (CIN) population. Although NTBC was lethal to both populations when administered orally or applied topically in very low doses, we observed a slight but significant resistance in the CIN population. Transcriptomic analysis in both populations indicated that NTBC treatment elicited a broad suppression of genes associated with RNA post-transcriptional modifications, translation, endomembrane system, protein post-translational modifications and protein folding. The CIN population exhibited higher ATP production and xenobiotic detoxification. Feeding studies on a mouse model highlight that NTBC could be used as a control method of bed bugs by host treatment. The results demonstrate that NTBC can be used as a new active ingredient for bed bug control by topical or oral treatment and shed light on the molecular mechanisms of suppressed tyrosine metabolism following NTBC treatment.

eIF3 subunit M regulates blood meal digestion in Rhodnius prolixus affecting ecdysis, reproduction, and survival

In triatomines, blood-feeding triggers many physiological processes including post embryonic development and reproduction. Different feeding habits, such as hematophagy, can shape gene functions to meet the challenges of each type of diet. The gut of blood-sucking insects faces particular challenges after feeding due to the quantity and the quality of the food ingested. A comparison of transcriptomic and proteomic data indicates that post transcriptional regulation of gene expression is crucial in the triatomine gut. It was proposed that eukaryotic translation initiation factor 3 subunit m (eIF3m) and eIF3e define 2 different eIF3 complexes with a distinct affinity for the different mRNAs, thus selecting the set of mRNAs to be translated and constituting a post transcriptional mode of regulation of gene expression. Because the eIF3m is mainly expressed in the gut, we evaluated its relevance in Rhodnius prolixus physiology through RNA interference-mediated gene silencing. The knockdown of eIF3m reduced the digestion rate, affecting the processes triggered by a blood meal. Its silencing inhibited molting and caused premature death in nymphs while impaired ovary development, oviposition and increased resistance to starvation in adult females. The survival of males after feeding (resistance to starvation) was not affected by eIF3m knockdown. The information regarding the eIF3m function in insects is scarce and the phenotypes observed in R. prolixus upon eIF3m silencing are different and more severe than those previously described in Drosophila melanogaster, indicating a pleiotropic role of this gene in triatomines.

Defining the toxicological profile of 4-hydroxyphenylpyruvate dioxygenase-directed herbicides to Aedes aegypti and Amblyomma americanum

Inhibitors targeting the 4-hydroxyphenyl pyruvate dioxygenase (HPPD) enzyme are well established herbicides and HPPD is also a primary enzyme within the tyrosine metabolism pathway in hematophagous arthropods, which is an essential metaboilic pathway post-blood feeding to prevent tyrosine-mediated toxicity. The objective of this study was to characterize the toxicity of triketone, pyrazole, pyrazolone, isoxazole, and triazole herbicides that inhibit HPPD to blood-fed mosquitoes and ticks. Topical exposure of nitisinone to blood-fed Aedes aegypti yielded high toxicity with an LD50 of 3.81 ng/insect (95% CI: 3.09 to 4.67 ng; Hillslope: 0.97, r2: 0.99), yet was non-toxic to non-blood fed (NBF) mosquitoes. The rank order of toxicity was nitisinone > tembotrione > pyrazoxyfen > tebuconazole > mesotrione against blood-fed Ae. Aegypti, but nitisinone was approximately 30-fold more toxic than other chemicals tested. We also assessed the toxicity of HPPD-inhibiting herbicides to the lone star tick, Amblyomma americanum and similarly, nitisinone was toxic to Am. americanum with a lethal time to kill 50% of subjects (LT50) of 23 h at 10 μM. Knockdown of the gene encoding the HPPD enzyme was performed through RNA-interference led to significant mortality after blood feeding in both, Ae. aegypti and Am. americanum. Lastly, a fluorescence assay was developed to determine relative quantities of L-tyrosine in Ae. aegypti and Am. americanum treated with HPPD inhibitors. L-tyrosine levels correlated with toxicity with nitisinone exposure leading to increased tyrosine concentrations post-blood feeding. Taken together, these data support previous work suggesting HPPD-inhibitors represent a novel mode of toxicity to mosquitoes and ticks and may represent base scaffolds for development of novel insecticides specific for hematophagous arthropods.

Unlocking the potential of snake venom-based molecules against the malaria, Chagas disease, and leishmaniasis triad

Malaria, leishmaniasis and Chagas disease are vector-borne protozoal infections with a disproportionately high impact on the most fragile societies in the world, and despite malaria-focused research gained momentum in the past two decades, both trypanosomiases and leishmaniases remain neglected tropical diseases. Affordable effective drugs remain the mainstay of tackling this burden, but toxicicty, inneficiency against later stage disease, and drug resistance issues are serious shortcomings. One strategy to overcome these hurdles is to get new therapeutics or inspiration in nature. Indeed, snake venoms have been recognized as valuable sources of biomacromolecules, like peptides and proteins, with antiprotozoal activity. This review highlights major snake venom components active against at least one of the three aforementioned diseases, which include phospholipases A2, metalloproteases, L-amino acid oxidases, lectins, and oligopeptides. The relevance of this repertoire of biomacromolecules and the bottlenecks in their clinical translation are discussed considering approaches that should increase the success rate in this arduous task. Overall, this review underlines how venom-derived biomacromolecules could lead to pioneering antiprotozoal treatments and how the drug landscape for neglected diseases may be revolutionized by a closer look at venoms. Further investigations on poorly studied venoms is needed and could add new therapeutics to the pipeline.

Role of the tyrosine aminotransferase AccTATN gene in the response to pesticide and heavy metal stress in Apis cerana cerana

Tyrosine aminotransferase (TATN) is the first enzyme involved in the metabolic degradation of tyrosine, and it plays an important role in tyrosine detoxification and helps the body resist oxidative damage. However, the function of TATN in Apis cerana cerana (A. c. cerana) remains unclear. To explore the role of TATN in the response to pesticide and heavy metal stress in A. c. cerana, AccTATN was isolated and identified. AccTATN was highly expressed in the integument and the adult stage. Exposure to multiple pesticides and heavy metal stress upregulated AccTATN expression. RNA interference experiments showed that silencing AccTATN reduced the resistance of A. c. cerana to glyphosate and avermectins stress. The expression of antioxidant-related genes and the activity of antioxidant enzymes were reduced after AccTATN was silenced, leading to the accumulation of oxidative damage. Overexpression of the recombinant AccTATN protein in a prokaryotic system also confirmed its role in heavy metal stress and improved antioxidant capacity. Our study showed that AccTATN may promote resistance to pesticide and heavy metal stress by regulating the antioxidant capacity of A. c. cerana. This study provides a valuable theoretical basis for A. c. cerana conservation.

Molecular targets of insecticides and herbicides - Are there useful overlaps?

New insecticide modes of action are needed for insecticide resistance management strategies. The number of molecular targets of commercial herbicides and insecticides are fewer than 35 for both. Few commercial insecticide targets are found in plants, but ten targets of commercial herbicides are found in insects. For several of these commonly held targets, some compounds kill both plants and insects. For example, herbicidal inhibitors of p-hydroxyphenylpyruvate dioxygenase are effective insecticides on blood-fed insects. The glutamine synthetase-inhibiting herbicide glufosinate is insecticidal by the same mechanism of action, inhibition of glutamine synthetase. These and other examples of shared activities of commercial herbicides with insecticides through the same target site are discussed. Compounds with novel herbicide targets shared by insects that are not commercialized as pesticides (such as statins) are also discussed. Compounds that are both herbicidal and insecticidal can be used for insect pests not associated with crops or with crops made resistant to the compounds.

Survey on the Recent Advances in 4-Hydroxyphenylpyruvate Dioxygenase (HPPD) Inhibition by Diketone and Triketone Derivatives and Congeneric Compounds: Structural Analysis of HPPD/Inhibitor Complexes and Structure-Activity Relationship Considerations

The serendipitous discovery of the HPPD inhibitors from allelopathic plants opened the way for searching new and effective herbicidal agents by application of classical hit-to-lead optimization approaches. A plethora of active and selective compounds were discovered that belong to three major classes of cyclohexane-based triketones, pyrazole-based diketones, and diketonitriles. In addition, to enhance inhibitory constant and herbicidal activity, many efforts were also made to gain broader weed control, crop safety, and eventual agricultural applicability. Moreover, HPPD inhibitors emerged as therapeutic agents for inherited and metabolic human diseases as well as vector-selective insecticides in the control of hematophagous arthropods. Given the large set of experimental data available, structure-activity relationship analysis could be used to derive suggestions for next generation optimized compounds.

On the use of inhibitors of 4-hydroxyphenylpyruvate dioxygenase as a vector-selective insecticide in the control of mosquitoes

BACKGROUND

Blood-sucking insects incorporate many times their body weight of blood in a single meal. Because proteins are the major component of vertebrate blood, its digestion in the gut generates extremely high concentrations of free amino acids. Previous reports showed that the tyrosine degradation pathway plays an essential role in adapting these animals to blood feeding. Inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD), the rate-limiting step of tyrosine degradation, results in the death of insects after a blood meal. Therefore, it has been suggested that compounds that block the catabolism of tyrosine could act selectively on blood-feeding insects. Here, we evaluated the toxicity against mosquitoes of three HPPD inhibitors currently used as herbicides and in human health.

RESULTS

Of the compounds tested, nitisinone (NTBC) proved to be more potent than mesotrione (MES) and isoxaflutole (IFT) in Aedes aegypti. NTBC was lethal to Ae. aegypti in artificial feeding assays [median lethal dose (LD₅₀ ): 4.53 μm] and in topical application (LD₅₀ : 0.012 nmol/mosquito). NTBC was also lethal to Ae. aegypti populations that were resistant to neurotoxic insecticides, and to other mosquito species (Anopheles and Culex).

CONCLUSION

HPPD inhibitors, particularly NTBC, represent promising new drugs for mosquito control. Because they affect only blood-feeding organisms, they represent a safer and more environmentally friendly alternative to conventional neurotoxic insecticides. © 2021 Society of Chemical Industry.

Critical Insight into Plausible Acquired Tocopherol Pathway in Neglected Human Trypanosomatids

Despite global therapeutic advancements, tropical parasitic infections like trypanosomiasis and leishmaniasis continue to be a major health concern in developing countries. These two tropical infectious diseases lead to enormous economic loss, significant disability, and morbidity, accounting for over one million deaths per year worldwide. The causative parasites, which shuttle between an insect vector and a mammalian host, thrive either in the bloodstream or in the intramacrophage environments. Essentially, the parasites live in an environment of oxidative stress and therefore require metabolic pathways to counterbalance the host immune response and survive the adverse conditions. Apart from the trypanothione pathway elucidated in the parasites, there exists a tocopherol pathway that functions to scavenge the reactive chemical species. This pathway, unique to photosynthetic organisms, is essential for the parasite's survival, though the enzymes involved remain largely uncharacterized. Consequently, an understanding of the origin of the pathway and where and how the interconnected tocopherol pathway functions may result in the identification of promising and potential therapeutic interventions to combat these deadly diseases. Recent works underline the presence of the tocopherol pathway in trypanosomatids and hypothesize that trypanosomatids may be tocopherol prototrophs. This review focuses on the biosynthesis of tocopherols in Trypanosoma and Leishmania in light of the current evidence.

Emergence of the invasive malaria vector Anopheles stephensi in Khartoum State, Central Sudan

The emergence of the Asian invasive malaria vector, Anopheles stephensi, has been identified in Khartoum, the capital city of Sudan. This is the first report that confirms the geographical expansion of this urban mosquito into Central Sudan. We urgently recommend the launch of a national entomological survey to determine the distribution of this invasive disease vector and to generate essential information about its bionomics and susceptibility to available malaria control measures.

Early Post-Prandial Regulation of Protein Expression in the Midgut of Chagas Disease Vector Rhodnius prolixus Highlights New Potential Targets for Vector Control Strategy

Chagas disease is a vector-borne parasitic disease caused by the flagellated protozoan Trypanosoma cruzi and transmitted to humans by a large group of bloodsucking triatomine bugs. Triatomine insects, such as Rhodnius prolixus, ingest a huge amount of blood in a single meal. Their midgut represents an important interface for triatomine–trypanosome interactions. Furthermore, the development of parasites and their vectorial transmission are closely linked to the blood feeding and digestion; thus, an understanding of their physiology is essential for the development of new strategies to control triatomines. In this study, we used label-free quantitative proteomics to identify and analyze the early effect of blood feeding on protein expression in the midgut of Rhodnius prolixus. We both identified and quantified 124 proteins in the anterior midgut (AM) and 40 in the posterior midgut (PM), which vary significantly 6 h after feeding. The detailed analysis of these proteins revealed their predominant involvement in the primary function of hematophagy, including proteases, proteases inhibitors, amino acids metabolism, primary metabolites processing, and protein folding. Interestingly, our proteomics data show a potential role of the AM in protein digestion. Moreover, proteins related to detoxification processes and innate immunity, which are largely accepted to be triggered by blood ingestion, were mildly modulated. Surprisingly, one third of blood-regulated proteins in the AM have unknown function. This work contributes to the improvement of knowledge on the digestive physiology of triatomines in the early hours post-feeding. It provides key information for selecting new putative targets for the development of triatomine control tools and their potential role in the vector competence, which could be applied to other vector species.