Novel Combination Therapy: Monensin Potentiates Erlotinib-Induced Cytotoxicity

Abstract

Receptor Tyrosine Kinase (RTK) inhibitors, such as erlotinib/tarceva, have been introduced in the past decade as a promising therapeutic option in Head and Neck Squamous Cell Carcinoma (HNSCC), however, they lack significant efficacy as single agents. As a result, RTK inhibitors require a combination based therapeutic approach with other treatment modalities. To uncover such a combination of agents, we performed a high throughput Prestwick library screen that included 1200 compounds approved by the FDA on HNSCC cell lines and found that monensin, a coccidial antibiotic, synergistically enhanced the cytotoxicity of erlotinib. RT-PCR revealed that monensin induced the expression of Activation of Transcription Factor (ATF) 3 and its downstream target C/EBP homologous protein (CHOP) which are key regulators of apoptosis. Furthermore, RNA-Seq analysis suggests that monensin augments erlotinib cytotoxicity by disturbing lipid and sterol biosynthesis. Therefore, identifying the mechanism of action exerted by monensin may open alternative avenues of cancer treatment.