Safety of an amino-acetonitrile derivative (AAD), monepantel, in ewes and their offspring following repeated oral administration

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.

Potential drug development candidates for human soil-transmitted helminthiases

Background

Few drugs are available for soil-transmitted helminthiasis (STH); the benzimidazoles albendazole and mebendazole are the only drugs being used for preventive chemotherapy as they can be given in one single dose with no weight adjustment. While generally safe and effective in reducing intensity of infection, they are contra-indicated in first-trimester pregnancy and have suboptimal efficacy against Trichuris trichiura. In addition, drug resistance is a threat. It is therefore important to find alternatives.

Methodology

We searched the literature and the animal health marketed products and pipeline for potential drug development candidates. Recently registered veterinary products offer advantages in that they have undergone extensive and rigorous animal testing, thus reducing the risk, cost and time to approval for human trials. For selected compounds, we retrieved and summarised publicly available information (through US Freedom of Information (FoI) statements, European Public Assessment Reports (EPAR) and published literature). Concomitantly, we developed a target product profile (TPP) against which the products were compared.

Principal Findings

The paper summarizes the general findings including various classes of compounds, and more specific information on two veterinary anthelmintics (monepantel, emodepside) and nitazoxanide, an antiprotozoal drug, compiled from the EMA EPAR and FDA registration files.

Conclusions/Significance

Few of the compounds already approved for use in human or animal medicine qualify for development track decision. Fast-tracking to approval for human studies may be possible for veterinary compounds like emodepside and monepantel, but additional information remains to be acquired before an informed decision can be made.

There are few drugs - none ideal - for the treatment and control of gastrointestinal helminths (soil-transmitted nematodes) which, as chronic infections jeopardize children's growth, learning and ultimately individual, community and country development. Drugs for helminths are not attractive in human medicine, but are lucrative in animal health. Traditionally, investment in veterinary medicines has benefited humans for these diseases. With modern regulations an approved veterinary medicine can be tested in humans with little adaptation, reducing time and cost of development. We searched for products that could easily be transitioned into humans, having the necessary characteristics for use in communities exposed to these infections. A limited number of candidates met the main criteria for selection. We provide here a detailed analysis of two veterinary products, emodepside and monepantel, and nitazoxanide, which is approved for human use. In addition we include a less detailed analysis of all products examined, and the criteria on which the analysis was based. It is clear that the pipeline of easily obtainable human anthelminthics remains extremely limited, and further efforts are needed to find replacements for the inadequate number of products available today.

The drugs we have and the drugs we need against major helminth infections

Parasitic worms (helminths) have accompanied humans for thousands of years and, still today, they are pervasive where poverty persists, including large parts of Southeast Asia and the Western Pacific Region. The global strategy for the control of helminth infections is morbidity control and elimination as a public health problem. Regular administration of anthelminthic drugs to at-risk populations (e.g. school-aged children) serves as the backbone of interventions in areas where helminth infections are highly endemic. In this review, we focus on soil-transmitted helminthiasis (ascariasis, hookworm disease, strongyloidiasis and trichuriasis) and food-borne trematodiasis (clonorchiasis, fascioliasis, intestinal fluke infections, opisthorchiasis and paragonimiasis) and discuss the few drugs that are currently available for their treatment and control. Emphasis is placed on efficacy with new light shed on multiple dosing and combination therapy. We summarise recent advances made with anthelminthic drugs that might become the future armentarium for the control of major helminthiasis (e.g. artemisinins, cyclooctadepsipeptides, mefloquine, monepantel, nitazoxandide, synthetic peroxides and tribendimidine). Issuing from our review are current research gaps and the need for concerted efforts to discover, develop and deploy the next generation of anthelminthic drugs.