Concurrent use of two dual-combination drenches containing monepantel/abamectin and oxfendazole/levamisole in sheep: effect on marker residues 21 and 28 days after administration

AIMS

To determine the concentration, in comparison with the maximum residue limit (MRL), of anthelmintic marker residues in the target tissues (liver and fat) of sheep treated concurrently with two oral drenches, one containing monepantel and abamectin and the other oxfendazole and levamisole.

METHODS

On day 0 of the study, 12 sheep (six male and six female; 8-9-months old) were dosed according to individual body weight determined the day prior. Zolvix Plus (dual-active oral drench containing 25 g/L monepantel and 2 g/L abamectin) was administered to all animals prior to administration of Scanda (dual-active oral drench containing 80 g/L levamisole hydrochloride and 45.3 g/L oxfendazole). Six sheep (three male and three female) were slaughtered 21 and 28 days after treatment and renal fat and liver samples were collected.Using validated methods, analyses for monepantel sulfone, abamectin, levamisole and oxfendazole (expressed as total fenbendazole sulfone following conversion of the combined concentrations of oxfendazole, fenbendazole and fenbendazole sulfone) were performed on liver samples while renal fat specimens were analysed for monepantel sulfone and abamectin residues only. Detected concentrations were compared to the established MRL in sheep for each analyte determined by the Ministry for Primary Industries.

RESULTS

All residues detected in samples of liver and fat collected 21 and 28 days after treatment were below the MRL for each analyte. All liver samples collected on day 21 had detectable monepantel sulfone (mean 232 (min 110, max 388) μg/kg) and oxfendazole (mean 98.7 (min 51.3, max 165) μg/kg) residues below the MRL (5,000 and 500 μg/kg, respectively). Monepantel sulfone (mean 644 (min 242, max 1,119) μg/kg; MRL 7,000 μg/kg) residues were detected in 6/6 renal fat samples. Levamisole residues were detected in 3/6 livers (mean 40.0 (min 14.3, max 78.3) μg/kg; MRL 100 μg/kg), and abamectin residues in 1/6 livers (0.795 μg/kg; MRL 25 μg/kg) and 2/6 fat samples, (mean 0.987 (min 0.514, max 1.46) μg/kg; MRL 50 μg/kg) 21 days after treatment.

CONCLUSION AND CLINICAL RELEVANCE

These results suggest that concurrent administration of Zolvix Plus and Scanda to sheep is unlikely to result in an extended residue profile for any of the active ingredients, with all analytes measured being under the approved New Zealand MRL 21 days after treatment. This work was not completed in line with guidance for establishing official residue profiles, nor is it sufficient to propose a new withholding period.

Induction of endoplasmic reticulum stress is associated with the anti-tumor activity of monepantel across cancer types

BACKGROUND

Monepantel is an anti-helminthic drug that also has anti-cancer properties. Despite several studies over the years, the molecular target of monepantel in mammalian cells is still unknown, and its mechanism-of-action is not fully understood, though effects on cell cycle, mTOR signalling and autophagy have been implicated.

METHODS

Viability assays were performed on >20 solid cancer cell cells, and apoptosis assays were performed on a subset of these, including 3D cultures. Genetic deletion of BAX/BAK and ATG were used to establish roles of apoptosis and autophagy in killing activity. RNA-sequencing was performed on four cell lines after monepantel treatment, and differentially regulated genes were confirmed by Western blotting.

RESULTS

We showed that monepantel has anti-proliferative activity on a broad range of cancer cell lines. In some, this was associated with induction of apoptosis which was confirmed using a BAX/BAK-deficient cell line. However, proliferation is still inhibited in these cells following monepantel treatment, indicating cell-cycle disruption as the major anti-cancer effect. Previous studies have also indicated autophagic cell death occurs following monepantel treatment. We showed autophagy induction in multiple cell lines; however, deletion of a key autophagy regulator ATG7 had minimal impact on monepantel's anti-proliferative activity, suggesting autophagy is associated with, but not required for its anti-tumour effects. Transcriptomic analysis of four cell lines treated with monepantel revealed downregulation of many genes involved in the cell cycle, and upregulation of genes linked to ATF4-mediated ER stress responses, especially those involved in amino-acid metabolism and protein synthesis.

CONCLUSIONS

As these outcomes are all associated with mTOR signalling, cell cycle and autophagy, we now provide a likely triggering mechanism for the anti-cancer activity of monepantel.

The Caenorhabditis elegans DEG-3/DES-2 Channel Is a Betaine-Gated Receptor Insensitive to Monepantel

Natural plant compounds, such as betaine, are described to have nematocidal properties. Betaine also acts as a neurotransmitter in the free-living model nematode Caenorhabditis elegans, where it is required for normal motility. Worm motility is mediated by nicotinic acetylcholine receptors (nAChRs), including subunits from the nematode-specific DEG-3 group. Not all types of nAChRs in this group are associated with motility, and one of these is the DEG-3/DES-2 channel from C. elegans, which is involved in nociception and possibly chemotaxis. Interestingly, the activity of DEG-3/DES-2 channel from the parasitic nematode of ruminants, Haemonchus contortus, is modulated by monepantel and its sulfone metabolite, which belong to the amino-acetonitrile derivative anthelmintic drug class. Here, our aim was to advance the pharmacological knowledge of the DEG-3/DES-2 channel from C. elegans by functionally expressing the DEG-3/DES-2 channel in Xenopus laevis oocytes and using two-electrode voltage-clamp electrophysiology. We found that the DEG-3/DES-2 channel was more sensitive to betaine than ACh and choline, but insensitive to monepantel and monepantel sulfone when used as direct agonists and as allosteric modulators in co-application with betaine. These findings provide important insight into the pharmacology of DEG-3/DES-2 from C. elegans and highlight the pharmacological differences between non-parasitic and parasitic nematode species.

Monepantel antitumor activity is mediated through inhibition of major cell cycle and tumor growth signaling pathways

In women, epithelial ovarian cancer is the leading cause of gynaecological malignancy-related deaths. Development of resistance to standard platinum and taxane based chemotherapy and recurrence of the disease necessitate development of novel drugs to halt disease progression. An established concept is to target molecular and signaling pathways that substantially contribute to development of drug resistance and disease progression. We have previously shown that, monepantel (MPL) a novel small molecule acetonitrile derivative is highly effective in suppressing growth, proliferation and colony formation of ovarian cancer cells. These effects are achieved through inhibition of the mTOR/p70S6K pathway in cancer cells. The present study was conducted to find in vivo corroboration and explore the effect of MPL om other growth stimulating putative signaling pathways. Here, female nude mice with subcutaneous OVCAR-3 xenografts were treated with 25 and 50 mg/kg doses of MPL administered (IP) three times weekly for 2 weeks. At the doses employed, MPL was modestly effective at suppressing tumor growth, but highly effective in inhibiting, mTOR, P70S6K and 4EBP1. There were also modest reductions in tumor cyclin D1 and retinoblastoma protein expression. Furthermore, it was found that MPL treatment causes down-regulation of IGF-1R, and c-MYC thus unveiling new dimensions to the growing antitumor actions of this potential anticancer drug. MPL treatment led to reduced tumor volume and weights without causing any detectable side effects. Coupled with the recent human safety data published on this molecule, expanded future trials are highly anticipated.

Pharmacokinetic assessment of the monepantel plus oxfendazole combined administration in dairy cows

Monepantel (MNP) is a novel anthelmintic compound launched into the veterinary pharmaceutical market. MNP is not licenced for use in dairy animals due to the prolonged elimination of its metabolite monepantel sulphone (MNPSO₂ ) into milk. The goal of this study was to evaluate the presence of potential in vivo drug-drug interactions affecting the pattern of milk excretion after the coadministration of the anthelmintics MNP and oxfendazole (OFZ) to lactating dairy cows. The concentrations of both parent drugs and their metabolites were measured in plasma and milk samples by HPLC. MNPSO₂ was the main metabolite recovered from plasma and milk after oral administration of MNP. A high distribution of MNPSO₂ into milk was observed. The milk-to-plasma ratio (M/P ratio) for this metabolite was equal to 6.75. Conversely, the M/P ratio of OFZ was 1.26. Plasma concentration profiles of MNP and MNPSO₂ were not modified in the presence of OFZ. The pattern of MNPSO₂ excretion into milk was also unchanged in animals receiving MNP plus OFZ. The percentage of the total administered dose recovered from milk was 0.09 ± 0.04% (MNP) and 2.79 ± 1.54% (MNPSO₂ ) after the administration of MNP alone and 0.06 ± 0.04% (MNP) and 2.34 ± 1.38% (MNPSO₂ ) after the combined treatment. The presence of MNP did not alter the plasma and milk disposition kinetics of OFZ. The concentrations of the metabolite fenbendazole sulphone tended to be slightly higher in the coadministered group. Although from a pharmacodynamic point of view the coadministration of MNP and OFZ may be a useful tool, the presence of OFZ did not modify the in vivo pharmacokinetic behaviour of MNP and therefore did not result in reduced milk concentrations of MNPSO₂ .

Comparison of biotransformation and efficacy of aminoacetonitrile anthelmintics in vitro

The present in vitro study was designed to test and compare anthelmintic activity, hepatotoxicity, and biotransformation of four selected aminoacetonitrile derivatives (AADs): monepantel (MOP, anthelmintic approved for the treatment), AAD-970, AAD-1154, and AAD-1336. Micro-agar larval development test, MTT test of cytotoxicity, and biotransformation study coupled with Ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) technique were used for this purpose. Larvae of two Haemonchus contortus strains (drug susceptible and multi-drug resistant) and primary cultures of rat and ovine hepatocytes served as model systems. All AADs (including MOP) exhibited significant larvicidal effect in H. contortus susceptible as well as multi-resistant strains, much higher than those of reference anthelmintics thiabendazole and flubendazole. AAD-1154 provides the best results for most tested parameters among all AADs in this study. The cytotoxicity test showed that all AADs can be considered as nontoxic for hepatocytes. In the biotransformation study, Phase I and Phase II metabolites of AADs were identified and schemes of possible metabolic pathways in ovine hepatocytes were proposed. Biotransformation of MOP was much more extensive than biotransformation of other AADs. Based on obtained results, AAD-1154 and AAD-1336 can be considered as promising candidates for further in vivo testing.

elegans: What about parasitic nematodes?

In 2008, Novartis Animal Health developed a new class of anthelmintics, the amino-acetonitrile derivatives (AAD) of which monepantel is the most prominent compound. Monepantel was designed for the treatment of sheep against the parasitic nematode Haemonchus contortus. Because monepantel acts through a different mechanism, it is effective against nematodes that have acquired resistance to long-standing anthelmintics. In order to benefit from a maximum lifespan and efficacy of this new compound, the mode of action of monepantel needs to be understood. Studies on the model nematode Caenorhabditis elegans led to the identification of at least one target of monepantel: the monovalent cation channel ACR-23. Here we comment on the effects of monepantel on C. elegans and on the development of resistant parasitic nematode strains.