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.

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.