Osteosarcoma (OSA) is an aggressive neoplasm, characterized with high level of heterogeneity, high metastatic potential and poor prognosis in both humans and dogs. In this study, I used drug screening studies including existing therapeutic agents and novel compounds to identify more effective approaches to treat human and canine osteosarcoma.One of the challenges in the field of OSA is to identify optimal tools for study. A limited number of human and canine OSA cell lines are available. In this study, I established and characterized a new cell line, BZ, derived from a German shepherd dog with OSA and studied key oncogenic pathways in BZ. Our findings revealed activation of STAT3 and ERK pathways in BZ, as well as in a number of other cell lines, indicating that these two pathways are critical for cell survival and proliferation in OSA and the potential of using STAT3 and ERK inhibitors.Furthermore, I screened ten tyrosine kinase inhibitors (TKIs) on two dog and one human OSA cell lines. Among the selected TKIs, sorafenib showed promising results in effectively inhibited cell growth and migration in vitro studies. In addition, the effects of combing sorafenib with current chemotherapeutics (cisplatin, carboplatin, and doxorubicin) for OSA were investigated. Data from the combination index pointed to synergistic effects of sorafenib combined with doxorubicin and resulted in profound cell arrest at G2/M phase. In contrast, combination of sorafenib with cisplatin or carboplatin in both human and canine OSA cell lines proved to be antagonistic.In addition to sorafenib, two other novel drugs with different mechanism of action were identified from the drug screening: the proteasome inhibitor bortezomib and the bromodomain inhibitor JQ1. Both drugs showed IC50 concentrations in achievable plasma ranges in all 3 human and 4 dog cell lines studied. In addition to inhibition on cell growth both drugs inhibited migration, and invasion properties of the cell lines. The co-incubation of bortezomib and JQ1 induced synergistic on both hOSA and cOSA cell lines, suggesting the use of this combination for future studies.These studies also further revealed the heterogeneity among different cell lines. The cell lines differed in their sensitivity for each drug, as well as key tumorigenic pathways that were activated. While only some showed activation of AKT, more cell lines showed ERK and STAT3 activation. This heterogeneity was present in both human and canine cell lines. While there is heterogeneity in OSA in both species, there share similar variations, and studying a wide range of cell lines and canine patients should lead to translatable findings to the human OSA patients. Our studies point out to the need and the possibility of molecular characterization of the cell lines and of the patient populations. The drugs and drug combinations identified in our studies should form the basis for trial designs that are informed by the molecular characteristic of each tumor in patients enrolled. The proteasome inhibitor bortezomib has a significant adverse effect profile, and JQ1 is still under development. However, clinical trials of sorafenib and sorafenib combined with doxorubicin in canine OSA are warranted and should yield findings translatable to the human.
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