Morpholino-driven transcriptional blockade of Dkk-1 in experimental osteosarcoma inhibits bone damage and tumor expansion by multiple mechanisms

Osteosarcoma (OS) is the most common primary bone malignancy. Chemotherapy plays an essential role in OS treatment, potentially doubling 5-year event-free survival if tumor necrosis can be stimulated, but long-term treatment results in detriment to health and quality of life. The canonical Wnt inhibitor Dickkopf-1 (Dkk-1) enhances OS survival in part through upregulation of aldehyde-dehydrogenase-1A1 (ALDH1A1) which neutralizes reactive oxygen species from nutritional stress and chemotherapeutic challenge. Dkk-1 also inhibits bone repair, exacerbating formation of osteolytic lesions caused by tumor infiltration. Therefore, targeting the expression of Dkk-1 in OS could reduce tumor burden and increase susceptibility to chemotherapeutics while restoring bone repair. Herein, we report that inhibiting Dkk-1 transcription by means of a vivo morpholino (DkkMo) reduced the expansion of experimental OS tumors, preserved bone volume and architecture, and stimulated tumor necrosis. This was observed in the presence or absence of doxorubicin (DRB), and as a single agent, inhibition of tumor expansion by DkkMo was equivalent to that achieved by DRB. DkkMo stimulated apoptotic and necrotic mechanisms in tumors and appeared to deplete the tumor stroma. These results indicate that administration of DkkMo with or without chemotherapeutics can substantially improve OS outcome with respect to tumor expansion and osteolytic corruption of bone.