Pre‐clinical evaluation of proteasome inhibitors for canine and human osteosarcoma

Abstract

Osteosarcoma, a common malignancy in large dog breeds, typically metastasises from long bones to lungs and is usually fatal within 1 to 2 years of diagnosis. Better therapies are needed for canine patients and their human counterparts, a third of whom die within 5 years of diagnosis. We compared the in vitro sensitivity of canine osteosarcoma cells derived from 4 tumours to the currently used chemotherapy drugs doxorubicin and carboplatin, and 4 new anti-cancer drugs. Agents targeting histone deacetylases or PARP were ineffective. Two of the 4 cell lines were somewhat sensitive to the BH3-mimetic navitoclax. The proteasome inhibitor bortezomib potently induced caspase-dependent apoptosis, at concentrations substantially lower than levels detected in the bones and lungs of treated rodents. Co-treatment with bortezomib and either doxorubicin or carboplatin was more toxic to canine osteosarcoma cells than each agent alone. Newer proteasome inhibitors carfilzomib, ixazomib, oprozomib and delanzomib manifested similar activities to bortezomib. Human osteosarcoma cells were as sensitive to bortezomib as the canine cells, but slightly less sensitive to the newer drugs. Human osteoblasts were less sensitive to proteasome inhibition than osteosarcoma cells, but physiologically relevant concentrations were toxic. Such toxicity, if replicated in vivo, may impair bone growth and strength in adolescent human osteosarcoma patients, but may be tolerated by canine patients, which are usually diagnosed later in life. Proteasome inhibitors such as bortezomib may be useful for treating canine osteosarcoma, and ultimately may improve outcomes for human patients if their osteoblasts survive exposure in vivo, or if osteoblast toxicity can be managed.

Targeting Molecular Mechanisms Underlying Treatment Efficacy and Resistance in Osteosarcoma: A Review of Current and Future Strategies

“…Direct targeting of Bcl-2 family members is independent of p53 status since p53 lies upstream of the Bcl-2 pathway [348], which is especially relevant in osteosarcoma as most osteosarcoma tumours have p53 abnormalities [82]. Navitoclax is a Bcl-xL inhibitor that has been demonstrated to inhibit cell proliferation in two canine osteosarcoma cell lines [349]. Navitoclax has had promising response rates in clinical trials in chronic lymphocytic leukaemia (CLL), a cancer type highly dependent upon Bcl-2 pathways for survival, but with high levels of toxicity: severe thrombocytopenia in one-third of patients.…”

The Proteasome Inhibitor Ixazomib Inhibits the Formation and Growth of Pulmonary and Abdominal Osteosarcoma Metastases in Mice

“…We previously reported the in vitro sensitivity of canine and human osteosarcoma cells to a panel of proteasome inhibitors including bortezomib and ixazomib [9]. In this study we compared the efficacy of bortezomib to ixazomib in vivo, using human osteosarcoma cell lines that are tumorigenic and metastasize to the lungs of athymic mice [39][40][41].…”

“…When the proteasome inhibitors were combined with doxorubicin or carboplatin, the treatments were barely additive. This may be a consequence of doxorubicin's cytotoxicity being dependent on cell division [52] while proteasome inhibitors halt the cell cycle [9,10]. Established and minimally passaged primary osteosarcoma cell lines are more sensitive to proteasome inhibitors than current treatments for osteosarcoma.…”

“…Bortezomib induces cell death through proteotoxic stress and altering the equilibrium of pro/anti-apoptotic proteins by inhibiting the degradation of ubiquitinated proteins by the 20S proteasome [8]. Multiple studies have documented the sensitivity of osteosarcoma cells to bortezomib in vitro and in vivo [9][10][11]. Despite promising preclinical data, a phase 1 clinical trial investigating the efficacy of bortezomib in pediatric patients with solid tumors (including two osteosarcoma patients) [12] and a phase II clinical trial investigating the efficacy of bortezomib for treatment of metastatic sarcomas (including a single osteosarcoma participant) [13] concluded that the drug had minimal activity in these contexts as a single agent.…”

“…In pre-clinical models, ixazomib reduced the growth of solid tumors and enhanced survival compared to bortezomib [15]. Osteosarcoma cells were found to be sensitive to ixazomib in vitro [9,31], but no studies have investigated the anti-osteosarcoma efficacy of ixazomib in vivo.…”