Inhibition of mitochondrial translation selectively targets osteosarcoma

Highlights

• Tigecycline inhibits osteosarcoma cells with less toxicity to normal osteoblasts.

• Tigecycline inhibits mitochondrial translation and respiration in osteosarcoma.

• Osteosarcoma cells have increased mitochondrial biogenesis than normal osteoblasts.

• Inhibition of mitochondrial translation via EF-Tu depletion inhibits osteosarcoma.

Abstract

The unique dependence of cancer cells on mitochondrial metabolism has been exploited therapeutically in various cancers but not osteosarcoma. In this work, we demonstrate that inhibition of mitochondrial translation is effective and selective in targeting osteosarcoma. We firstly showed that tigecycline at pharmacological achievable concentrations inhibited growth and induced apoptosis of multiple osteosarcoma cell lines while sparing normal osteoblast cells. Similarly, tigecycline at effective doses that delayed osteosarcoma growth did not cause significant toxicity to mice. We next showed that tigecycline specifically inhibits mitochondrial translation, resulting in defective mitochondrial respiration in both osteosarcoma and normal osteoblast cells. We further confirm mitochondrial respiration as the target of tigecycline using three independent approaches. In addition, we demonstrate that compared to normal osteoblasts, osteosarcoma cells have higher mitochondrial biogenesis. We finally show that specific inhibition of mitochondrial translation via EF-Tu depletion produces the similar anti-osteosarcoma effects of tigecycline. Our work highlights the therapeutic value of targeting mitochondrial metabolism in osteosarcoma and tigecycline as a useful addition to the treatment of osteosarcoma.

Introduction

Osteosarcoma is the most frequent primary sarcoma of the skeleton and originates from primitive mesenchymal bone forming cells [1]. It is ranked among the leading causes of cancer mortality in pediatric population [2]. Although standard therapies, including surgery, preoperative and postoperative chemotherapy (cisplatin, methotrexate and doxorubicin), have improved clinical responses and outcomes significantly, advanced osteosarcoma remains a major therapeutic challenge [3]. Mutation of tumor suppressor genes (eg, p53), activation of oncogenes (eg, C-FOS, C-JUN, Cyclin D and C-MYC) and signaling pathways (eg, Notch, Wnt/β-catenin) play essential roles in osteosarcoma development and chemoresistance [1,4]. Genetic profiling shows that osteosarcoma is extensively intra- and inter-heterogenous [5]. Targeting common rather than somatically mutated genes/signaling pathways may represent an alternative therapeutic strategy for osteosarcoma.

Apart from the production of ATP and the metabolites necessary to fulfill the bioenergetic and biosynthetic demands of the cell, mitochondria also function as signaling organelles via altering their bioenergetic and biosynthetic functions to meet energy demands [6]. Substantial evidence has shown that the majority of ATP in tumor cells is produced by the mitochondria and targeting mitochondrial bioenergetics has emerged as a viable therapeutic strategy against cancer [[7], [8], [9], [10], [11]]. Compared to normal tissues, there are subsets of tumors that are more dependent on oxidative phosphorylation rather than glycolysis to meet metabolic demands and maintain survival, such as leukemia, breast cancer and hepatocellular carcinoma [8,[12], [13], [14], [15]].

Tigecycline is a FDA-approved broad-spectrum antibiotic drug with high binding affinity to bacterial ribosomes and thereby inhibition of protein synthesis [16,17]. Various recent studies have demonstrate the selective anti-cancer activity of tigecycline through inhibiting mitochondrial translation [10,15,18,19]. In this study, we asked 1) whether tigecycline is effective in targeting osteosarcoma; 2) whether tigecycline displays selective anti-osteosarcoma activity; 3) what is the underlying mechanism of tigecycline's selective activities in osteosarcoma. Based on these results, we further investigated the dependence of osteosarcoma on mitochondrial protein translation using genetic approach.