Drug Repurposing of β-blocker Propranolol in Osteosarcoma: Preclinical Antitumor Efficacy Alone or in Combination with Chemotherapy.

Abstract

Background: Osteosarcoma is still associated with poor response to therapy and alarmingly elevated mortality rates, especially in developing countries, highlighting the urgent need of novel therapeutic strategies. Given that β-adrenergic receptor (β-AR) signaling regulates many cellular processes involved in the initiation and progression of cancer, multiple efforts have been made to repurpose non-selective β-blocker propranolol in oncology. Considering the unsatisfied clinical needs of osteosarcoma, we evaluated the in vitro and in vivo antitumoral activity of propranolol as a monotherapy or in combination with metronomic chemotherapy, in β-AR-expressing human osteosarcoma cells. Methods: In vitro anti-osteosarcoma effects of propranolol were assessed on high-density cell growth, chemotaxis, colony-forming ability and three-dimensional spheroids. Cell cycle phase distribution and apoptosis were evaluated using flow cytometry analysis, and quantification of hypodiploid cell population and TUNEL labelling, respectively. Propranolol addition to chemotherapy was evaluated in vitro and in human osteosarcoma xenografts generated in athymic mice.Results: Propranolol significantly impaired MG-63 and U-2 OS cellular growth in a concentration range of 10-100 µM (IC50 ≈ 45µM) and was capable of blocking in vitro protumoral effects triggered by catecholamines. Cytostatic activity of propranolol was associated to reduced mitosis and G0/G1 cell cycle, but not to apoptosis induction. Moreover, β-blocker drastically reduced colony formation, spheroid progression and migration of osteosarcoma cells. Synergistic effects were observed in vitro after combining propranolol with chemotherapeutic agents methotrexate or cisplatin. In vivo, treatment with propranolol (10 mg/kg i.p.), alone and especially in addition to non-interrupted low-dose cisplatin (2 mg/kg i.p.), markedly abrogated xenograft progression, reducing tumor growth rates by 25 or 70%, respectively. After histological analysis, propranolol and cisplatin combined therapy resulted in low tumor mitotic index and increased tumor necrosis. Conclusions: Considering its robust antitumoral effects, β-AR antagonization using β-blocker propranolol seems to be an achievable and cost-effective therapeutic approach to modulate osteosarcoma aggressiveness, in addition to chemotherapy. Propranolol could be proposed as a co-adjuvant agent for the management of osteosarcoma, especially in low- and middle-income countries where access to treatment resources are limited. Further preclinical and clinical studies of propranolol repurposing in osteosarcoma are warranted.