Introduction

Progressive pulmonary metastases are expected for dogs diagnosed with osteosarcoma (OS) when localized treatment(s) are effective. Less than 5% of dogs that have measurable pulmonary metastasis will benefit from chemotherapy. Procaspase-3 (PC-3) is overexpressed in a variety of malignancies, including canine OS, and can be targeted with PAC-1 to enhance tumor killing effects of different chemotherapy drugs. Here, we investigate the combination of PAC-1 and doxorubicin for management of measurable OS pulmonary metastases.

Methods

PC-3 expression is evaluated in canine OS patient samples and OS cell lines by western blot and/or IHC. In vitro combination studies include cytotoxicity assays, apoptosis assessment, PARP cleavage, and biomass assessment. Metastatic murine models using luciferase-expressing cell lines are utilized for serial evaluation of single-agent and combination treatment. In an ongoing prospective clinical trial, dogs with radiographic evidence of pulmonary metastases are enrolled to assess the cytoreductive efficacy of PAC-1 and doxorubicin treatment.

Results

PC-3 is expressed by all OS cell lines and patient samples. In vitro experiments and murine models demonstrate favorable trend in combination treatment over single-agent activities. Of the current 12 dogs, response outcomes include 4 SD (>8 weeks), 1 PR, and 1 CR resulting in 50% BRR and 16.7% ORR.

Conclusion

OS cells express PC-3 and this can be targeted using PAC-1. In vitro and murine models suggest combination therapy is superior to historical single-agent treatment. The observed ORR and BRR suggests combining PAC-1 and doxorubicin treatment has potential to improve the management of measurable OS pulmonary metastases in dogs.

Funding Information

National Cancer Institute: R01 CA120439-09 PuppyUp Foundation