A novel anthelminthic drug suppresses the growth of medulloblastoma tumors by inhibiting PKA/Gli1 signaling axis

Abstract

Pediatric brain tumor is one of the most malignant solid tumors in children and have profound impact on the morbidity and mortality in these patients. Statistically, brain tumors are one of the leading cause of cancer-related deaths in patients from 0-19 years of age. Medulloblastoma (MB) is one of the most common pediatric brain tumors occurring in children. Sonic hedgehog (Shh) activated subgroup of MB is considered to be highly aggressive and metastatic in nature. Shh-MB is characterized by mutations in PTCH1, SMO and SuFu along with amplified activation of Gli1, a major transcription factor of this signaling pathway. In the current study, we have evaluated the anti-cancer effects of an anthelminthic drug ‘moxidectin’. Several MB cell lines such as Daoy, UW426, UW228, ONS76, and PFSK1 were treated with moxidectin in a concentration and time dependent manner. Our results demonstrated that moxidectin treatment resulted in significantly reduced proliferation of MB cells. The IC50 of moxidectin in all the MB cell lines ranged 10-17μM after 24, 48 and 72 hours of treatment. Moreover, moxidectin was able to induce 3-4 fold increase of apoptosis in all the MB cell lines as evaluated by AnnexinV-FITC/PI assay, and increased cleavage of caspase 3 and PARP. Western blotting analysis demonstrated that moxidectin treatment significantly reduced non-canonical activation of Gli1 and its downstream effector molecules such as Pax-6, Oct-4, Sox-2 and Nanog. To our knowledge, this study for the first time focuses on GABAA receptor agonist mediated PKA inhibition and ultimately suppression of non-canonical Gli1 activation. Efficacy of moxidectin was evaluated in an in vivo tumor model by subcutaneously and intracranically implanting human Daoy MB cells. Our results demonstrated that 2.5 mg/kg moxidectin by oral administration everyday suppressed the growth of Daoy tumors by 50-55% in both subcutaneous and intracranial tumor models. Conclusively, our results indicate that moxidectin effectively reduces the growth of MB tumors by inhibiting PKA/Gli1 signaling. Most importantly, moxidectin is FDA approved drug and is already in clinical use for the treatment of river blindness in humans with an established safety record, therefore any positive findings from our studies will prompt further clinical investigation into repositioning moxidectin for the treatment of MB patients.