A Dkk-1 targeting antisense therapy for human osteosarcoma, developed with help from man’s best friend

ABSTRACT. Osteosarcoma (OS) is the most common primary bone malignancy accounting for approximately 9% of pediatric cancer deaths. Bone destruction, drug resistance, and metastasis are all hallmarks of poor prognosis in OS, but current treatment strategies continue to have limited utility in collectively targeting these drivers of mortality. Experiments utilizing mice harboring human OS (hOS) and murine OS (mOS) indicate that an antisense morpholino (termed DkkMo) that inhibits production of the tumor-derived Wnt-inhbitor-Dickkopf1 (Dkk-1) has the capacity to reduce bone destruction, induce tumor necrosis, slow tumor growth and inhibit pulmonary metastases. Confirming, these observations in a large animal that closely mimics the human disease would significantly facilitate clinical translation. OS is common in dogs and it shares similarities with hOS pathology, genetics, etiology, survival rates and standards of treatment. There is therefore a strong rationale for utilization of dogs with OS to promote clinical translation of experimental therapies. A canine version of DkkMo (cDkkMo) has been synthesized with the ultimate goal of performing veterinary clinical trials in client-owned dogs with OS at the Texas A&M Department of Small Animal Clinical Sciences. Despite clinical and genetic similarities between hOS and canine OS (cOS), the specific role of Dkk-1 in activating mortality drivers in cOS, and the effectiveness of cDkkMo in inhibiting them, should be defined empirically in vitro and in mice before planning such trials. For this purpose, the proposed work will establish whether the contribution of Dkk-1 signaling to cOS pathology is mechanistically and therapeutically equivalent to what has been observed in hOS and mOS models. These findings will ultimately address the question of whether the testing of cDkkMo in dogs represents an appropriate milestone for clinical translation of DkkMo to humans. Aim 1 will involve characterization of the effects of cDkkMo on proliferation, survival, and stress resistance by cOS cell lines and canine patient derived xenografts (cPDX-OS). The molecular mechanisms that govern the effect of Dkk-1 on bone destruction, growth, and survival of cOS cells will be compared to existing data on hOS. Aim 2 will test to what extent cDkkMo inhibits tumor growth, metastases and bone destruction in mice harboring cOS tumors derived from cell lines and cPDX-OS. Experiments will be performed with cDkkMo alone or with the chemotherapeutic cisplatin. Successful execution of this project will provide the rationale and conceptual framework for developing DkkMo further as a safe and effective therapeutic for OS in human patients via preclinical veterinary trials in dogs. While novel basic research is not a priority of this proposal, the work will ultimately contribute to the understanding of the comparative biology of OS in dogs and in humans through provision of newly characterized cOS PDX-OS specimens and cell lines for distribution to researchers.