A preliminary assessment of oral monepantel's tolerability and pharmacokinetics in individuals with treatment-refractory solid tumors.

PURPOSE: Monepantel is an approved veterinary anthelmintic with a strong safety profile. Preclinical evidence suggests novel mTOR pathway-associated anticancer activity. An open-label Phase I trial assessed tolerability, pharmacokinetics, pharmacodynamics and PET-CT imaging following oral Zolvix® monepantel administration to adults with treatment refractory, progressing and unresectable solid tumors. METHODS: Subjects were scheduled to daily home-based monepantel administration for 28 days in a 3 + 3 dose escalation study (5.0, 25.0 and 62.5 mg/kg bw). RESULTS: Of 41 reported drug-related AEs, 68% were Grade 1 and 24% were Grade 2; 35 AEs related to gastrointestinal effects including very poor palatability. DLT and MTD could not be determined due to early termination. Myelosuppression was not observed at the lowest level tested. Three of four Cohort 1 subjects had reduced mTOR pathway marker p-RPS6KB1 levels in PBMCs and achieved RECISTv1.1 SD by CT; one had progressive bony metastases by FDG-PET. One subject recorded PD on day 28, correlating with no detectable plasma monepantel from day 7. Monepantel sulfone dominated monepantel in pharmacokinetics. Both Cohort 2 subjects withdrew early due to AEs and the trial was terminated. CONCLUSIONS: Short-term 5 mg/kg bw monepantel administration provides a combined steady-state trough plasma monepantel and monepantel sulfone concentration of 0.5 µM. Gastrointestinal AEs including very poor palatability are concerning and suggested to be resolved by future drug product reformulation. RECISTv1.1, p-RPS6KB1 and plasma tumor marker outcomes provide preliminary evidence of anticancer activity.

The uptake, effects and biotransformation of monepantel in meadow plants used as a livestock feed.

Drugs are potentially dangerous environmental contaminants, as they are designed to have biological effects at low concentrations. Monepantel (MOP), an amino-acetonitrile derivative, is frequently used veterinary anthelmintics, but information about MOP environmental circulation and impact is almost non-existent. We studied the phytotoxicity, uptake and biotransformation of MOP in two fodder plants, Plantago lanceolata and Medicago sativa. The seeds and whole plant regenerants were cultivated with MOP. The plant roots and the leaves were collected after 1, 2, 3, 4, 5 and 6 weeks of cultivation. The lengths of roots and proline concentrations in the roots and leaves were measured to evaluate MOP phytotoxicity. The UHPLC-MS/MS technique with a Q-TOF mass analyser was used for the identification and semi-quantification of MOP and its metabolites. Our results showed no phytotoxicity of MOP. However, both plants were able to uptake, transport and metabolize MOP. Comparing both plants, the uptake of MOP was much more extensive in Medicago sativa (almost 10-times) than in Plantago lanceolate. Moreover, 9 various metabolites of MOP were detected in Medicago sativa, while only 7 MOP metabolites were found in Plantago lanceolata. Based on metabolites structures, scheme of the metabolic pathways of MOP in both plants was proposed. MOP and its main metabolite (MOP sulfone), both anthelmintically active, were present not only in roots but also in leaves that can be consumed by animals. This indicates the potential for undesirable circulation of MOP in the environment, which could lead to many pharmacological and toxicological consequences.

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 .

Host pharmacokinetics and drug accumulation of anthelmintics within target helminth parasites of ruminants.

Anthelmintic drugs require effective concentrations to be attained at the site of parasite location for a certain period to assure their efficacy. The processes of absorption, distribution, metabolism and excretion (pharmacokinetic phase) directly influence drug concentrations attained at the site of action and the resultant pharmacological effect. The aim of the current review article was to provide an overview of the relationship between the pharmacokinetic features of different anthelmintic drugs, their availability in host tissues, accumulation within target helminths and resulting therapeutic efficacy. It focuses on the anthelmintics used in cattle and sheep for which published information on the overall topic is available; benzimidazoles, macrocyclic lactones and monepantel. Physicochemical properties, such as water solubility and dissolution rate, determine the ability of anthelmintic compounds to accumulate in the target parasites and consequently final clinical efficacy. The transcuticular absorption process is the main route of penetration for different drugs in nematodes and cestodes. However, oral ingestion is a main route of drug entry into adult liver flukes. Among other factors, the route of administration may substantially affect the pharmacokinetic behaviour of anthelmintic molecules and modify their efficacy. Oral administration improves drug efficacy against nematodes located in the gastroinestinal tract especially if parasites have a reduced susceptibility. Partitioning of the drug between gastrointestinal contents, mucosal tissue and the target parasite is important to enhance the drug exposure of the nematodes located in the lumen of the abomasum and/or small intestine. On the other hand, large inter-animal variability in drug exposure and subsequent high variability in efficacy is observed after topical administration of anthelmintic compounds. As it has been extensively demonstrated under experimental and field conditions, understanding pharmacokinetic behaviour and identification of different factors affecting drug activity is important for achieving optimal parasite control and avoiding selection for drug resistance. The search for novel alternatives to deliver enhanced drug concentrations within target helminth parasites may contribute to avoiding misuse, and prolong the lifespan of existing and novel anthelmintic compounds in the veterinary pharmaceutical market.

Hepatic biotransformation pathways and ruminal metabolic stability of the novel anthelmintic monepantel in sheep and cattle.

Monepantel (MNP) is a new amino-acetonitrile derivative anthelmintic drug used for the treatment of gastrointestinal (GI) nematodes in sheep. The present work investigated the main enzymatic pathways involved in the hepatic biotransformation of MNP in sheep and cattle. The metabolic stability in ruminal fluid of both the parent drug and its main metabolite (monepantel sulphone, MNPSO2 ) was characterized as well. Additionally, the relative distribution of both anthelmintic molecules between the fluid and particulate phases of the ruminal content was studied. Liver microsomal fractions from six (6) rams and five (5) steers were incubated with a 40 µm of MNP. Heat pretreatment (50 °C for 2 min) of liver microsomes was performed for inactivation of the flavin-monooxygenase (FMO) system. Additionally, MNP was incubated in the presence of 4, 40, and 80 µm of methimazole (MTZ), a FMO inhibitor, or equimolar concentrations of piperonyl butoxide (PBx), a well-known general cytochrome P450 (CYP) inhibitor. In both ruminant species, MNPSO2 was the main metabolite detected after MNP incubation with liver microsomes. The conversion rate of MNP into MNPSO2 was fivefold higher (P < 0.05) in sheep (0.15 ± 0.08 nmol/min·mg) compared to cattle. In sheep, the relative involvement of both FMO and CYP systems (FMO/CYP) was 36/64. Virtually, only the CYP system appeared to be involved in the production of MNPSO2 in cattle liver. Methimazole significantly reduced (41 to 79%) the rate of MNPSO2 production in sheep liver microsomes whereas it did not inhibit MNP oxidation in cattle liver microsomes. On the other hand, PBx inhibited the production of MNPSO2 in liver microsomes of both sheep (58 to 98%, in a dose-dependent manner) and cattle (almost 100%, independently of the PBx concentration added). The incubation of MNP and MNPSO2 with ruminal contents of both species showed a high chemical stability without evident metabolism and/or degradation as well as an extensive degree of adsorption (83% to 90%) to the solid phase of the ruminal content. Overall, these results are a further contribution to the understanding of the metabolic fate of this anthelmintic drug in ruminants.

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.

Basic and clinical pharmacology contribution to extend anthelmintic molecules lifespan.

The correct use of pharmacology-based information is critical to design successful strategies for the future of parasite control in livestock animals. Integrated pharmaco-parasitological research approaches have greatly contributed to optimize drug activity. In an attempt to manage drug resistance in helminths of ruminants, combinations of two or more anthelmintics are being used or promoted, based on the fact that individual worms may have a lower degree of resistance to a multiple component formulation, when each chemical has a different mode of action compared to that observed when a single compound is used. However, as emphasized in the current review, the occurrence of potential pharmacokinetic and/or pharmacodynamic interactions between drug components highlights the need for deeper and integrated research to identify the advantages or disadvantages associated with the use of combined drug preparations. This review article provides integrated pharmacokinetic/pharmacodynamic and clinical pharmacology information pertinent to preserve the traditional and modern active ingredients as practical tools for parasite control. Novel pharmacological data on derquantel and monepantel, as representatives of modern anthelmintics for use in livestock, is summarized here. The article also summarizes the pharmaco-parasitological knowledge considered critical to secure and/or extend the lifespan of the recently available novel molecules.

Accumulation of monepantel and its sulphone derivative in tissues of nematode location in sheep: pharmacokinetic support to its excellent nematodicidal activity.

The amino-acetonitrile derivatives (AADs) are a new class of anthelmintic molecules active against a wide range of sheep gastrointestinal (GI) nematodes including those that are resistant to other anthelmintic families. The plasma disposition of monepantel (MNP) has been previously characterized in sheep. However, information on drug concentration profiles attained at tissues of parasite location is necessary to fully understand the pharmacological action of this novel compound. The current work aimed to study the relationship between the concentrations of MNP parent drug and its main metabolite monepantel sulphone (MNPSO2), measured in the bloodstream and in different GI tissues of parasite location in sheep. Twenty two (22) uninfected healthy Romney Marsh lambs received MNP (Zolvix, Novartis Animal Health) orally administered at 2.5 mg/kg. Blood samples were collected from six animals between 0 and 14 days post-treatment to characterize the drug/metabolite plasma disposition kinetics. Additionally, 16 lambs were sacrificed at 8, 24, 48 and 96 h post-administration to assess the drug concentrations in the GI fluid contents and tissues. MNP and MNPSO2 concentrations were determined by HPLC. MNP parent compound was rapidly oxidized into MNPSO2. MNP systemic availability was significantly lower than that observed for MNPSO2. The peak plasma concentrations were 15.1 (MNP) and 61.4 ng/ml (MNPSO2). The MNPSO2 to MNP plasma concentration profile ratio (values expressed in AUC) reached a value of 12. Markedly higher concentrations of MNP and MNPSO2 were measured in both abomasal and duodenal fluid contents, and mucosal tissues compared to those recovered from the bloodstream. A great MNP availability was measured in the abomasal content with concentration values ranging between 2000 and 4000 ng/g during the first 48 h post-treatment. Interestingly, the metabolite MNPSO2 was also recovered in abomasal content but its concentrations were significantly lower compared to MNP. The parent drug and its sulphone metabolite were detected in the different segments of the sheep intestine. MNPSO2 concentrations in the different intestine sections sampled were significantly higher compared to those measured in the abomasum. Although MNP is metabolized to MNPSO2 in the liver, the large concentrations of both anthelmintically active molecules recovered during the first 48 h post-treatment from the abomasum and small intestine may greatly contribute to the well-established pharmacological activity of MNP against GI nematodes.

Discovery and development of veterinary antiparasitic drugs: past, present and future.

Despite investment in programs to manage the development of resistance to existing agents, this continues to drive the need for discovery of novel antiparasitic agents for veterinary medicine. Historically, antiparasitic drug discovery was driven by empirical screening, but technological advances have lead to an increased focus on mechanism-based approaches to drug discovery and this is projected to increase as our capabilities advance to improve both the throughput of assays and the quality of data generated. Investment in the development of combination products with novel agents is increasing and, despite regulatory hurdles in some regions, efforts to globally harmonize regulations will aid in delivering safe, efficacious drugs to help in resistance management and integrated parasite control programs.

Effect of route of administration on the efficacy and pharmacokinetics of an experimental formulation of the amino-acetonitrile derivative monepantel in sheep.

The effect of the route of administration (oral, intraruminal and intra-abomasal) on the efficacy and pharmacokinetics of the new anthelmintic monepantel in sheep was investigated. The target nematodes were fourth-stage Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis and Cooperia curticei. A clear difference in efficacy was identified between the routes of administration, although the difference did not consistently reach statistical significance; oral treatment was most effective, followed by intraruminal and then intra-abomasal administration. The same pattern was observed in the pharmacokinetic analysis, with lambs treated orally having more favourable exposure to monepantel and its sulfone metabolite (albeit in all but one instance not significantly different) than the lambs treated by the other routes of administration, which were very similar for most parameters.

The effect of sheep breed, age, and gender on the pharmacokinetics and efficacy of monepantel, an amino-acetonitrile derivative.

This analysis investigated the influence of breed and gender on the pharmacokinetics of monepantel, and influence of breed, age, and gender on its efficacy against gastrointestinal nematodes of sheep. In a comparison of pharmacokinetic profiles from two studies, Merino lambs had significantly greater maximum concentrations of monepantel and monepantel sulfone, and faster times to reach these concentrations than Dorset cross lambs. Males had a statistically greater area under the curve (0-504 h) than females for monepantel sulfone. The biological relevance of these relatively small differences is unclear because efficacy was not evaluated in these studies. For efficacy, a breed effect existed for some nematodes when sheep were treated at a sub-optimum dose (1.25 mg/kg). There were no gender effects between sheep infected with adult parasites and treated at 1.25 mg/kg but there were differences between females and males treated at this dose when infected with fourth-stage larvae of Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis, and Cooperia curticei. There were no breed or gender differences for sheep treated at the recommended dose (2.5 mg/kg). There was a potential trend for declining efficacy with increasing animal age for fourth-stage Trichostrongylus axei. This analysis demonstrated that, similarly to what is observed with other anthelmintics, the pharmacokinetics and efficacy of monepantel can vary with factors like breed, age, and gender. Identifying these covariates is important for understanding inter-individual variability in drug response. While further investigation is warranted, correctly treating sheep at the recommended dose of 2.5 mg/kg appears to mitigate any associated risk.

Pharmacokinetics of monepantel and its sulfone metabolite, monepantel sulfone, after intravenous and oral administration in sheep.

The pharmacokinetic properties of the developmental Amino-Acetonitrile Derivative (AAD), monepantel and its sulfone metabolite, monepantel sulfone were investigated in sheep following intravenous (i.v.) and oral administrations. The sulfone metabolite was rapidly formed and predominated over monepantel 4 h after dosing, irrespective of the route of administration. The steady-state volume of distribution, total body clearance and mean residence time of monepantel were 7.4 L/kg, 1.49 L/(kg x h) and 4.9 h, respectively and 31.2 L/kg, 0.28 L/(kg x h) and 111 h, respectively for monepantel sulfone. The overall bioavailability of monepantel was 31%, but it was demonstrated that approximately the same amount of monepantel sulfone was produced whether monepantel was given intravenously or orally (AUC((0-infinity)) oral/AUC((0-infinity)) i.v. of 94% for monepantel sulfone), making oral administration a very efficient route of administration for monepantel in terms of the amount of sulfone metabolite generated. Because monepantel sulfone is the main chemical entity present in sheep blood after monepantel administration and because it is also an active metabolite, its pharmacokinetic properties are of primary importance for the interpretation of future residue and efficacy studies. Overall, these pharmacokinetic data aid in the evaluation of monepantel as an oral anthelmintic in sheep.

A new class of anthelmintics effective against drug-resistant nematodes.

Anthelmintic resistance in human and animal pathogenic helminths has been spreading in prevalence and severity to a point where multidrug resistance against the three major classes of anthelmintics--the benzimidazoles, imidazothiazoles and macrocyclic lactones--has become a global phenomenon in gastrointestinal nematodes of farm animals. Hence, there is an urgent need for an anthelmintic with a new mode of action. Here we report the discovery of the amino-acetonitrile derivatives (AADs) as a new chemical class of synthetic anthelmintics and describe the development of drug candidates that are efficacious against various species of livestock-pathogenic nematodes. These drug candidates seem to have a novel mode of action involving a unique, nematode-specific clade of acetylcholine receptor subunits. The AADs are well tolerated and of low toxicity to mammals, and overcome existing resistances to the currently available anthelmintics.

Production of DNA single-strand breaks in unstimulated splenocytes by dimethylnitrosamine.

In an attempt to elucidate the mechanism whereby primary hepatocytes, but not liver S9 homogenates, generate immunosupprssive metabolites of dimethylnitrosamine (DMN), the production of DNA single-strand breaks (SSB) in unstimulated splenocytes was investigated with alkaline-elution analysis. Both hepatocytes and S9 homogenates induced SSB in cultured splenocytes by DMN - minimum detectable doses with the two metabolic activation systems (MAS) were 1 microM and 5 mM, respectively. DNA elution profiles were linear in splenocytes co-cultured with DMN and hepatocytes and convex in splenocytes incubated with DMN and S9 homogenates. Aminoacetonitrile (AAN; 10 mM), a DMN demethylase inhibitor, reversed SSB in splenocytes when incubated with either MAS. Addition of exogenous calf-thymus DNA to the hepatocyte co-culture medium did not affect the production of SSB. Rocking the hepatocyte-splenocyte cultures changed the elution profile from linear to convex. All of these treatments have been previously shown to block the immunosuppression by DMN in the hepatocyte co-culture system. These results indicate that the immunosuppression by DMN is not related to DNA damage, as measured by the production of SSB, and suggest that the metabolism of DMN to intermediates capable of producing genotoxicity and immunotoxicity may be qualitatively and/or quantitatively different.