Inhibition of the activin receptor signaling pathway: A novel intervention against osteosarcoma.

Osteosarcoma is a cancer of pathological bone remodeling with high mortality and severe comorbidity. New therapies are urgently needed. Activin A, a member of the transforming growth factor ß (TGFß) superfamily, has been suggested to stimulate proliferation and invasion of osteosarcoma cells in vitro, thus representing a potential therapeutic target. In this study, inhibition of the activin receptor signaling pathway was explored as a therapy for osteosarcoma. In a murine intratibial osteosarcoma xenograft model, two types of inhibitors were tested: (a) a soluble activin type IIA decoy receptor (ActRIIA-mFc), or (b) a modified variant of follistatin (FSTΔHBS -hFc), either alone or in combination with a bisphosphonate. Both inhibitors reduced primary tumor development by nearly 50% compared to vehicle treatment. When ActRIIA-mFc was combined with bisphosphonate, the effect on tumor size became even more pronounced (78% reduction vs. vehicle). Moreover, FSTΔHBS -hFc increased body weight in the face of tumor progression (14% increase vs. vehicle), and ActRIIA-mFc reduced the number of lung metastases when combined with bisphosphonate. The present study demonstrates a novel approach to treating osteosarcoma and encourages further investigation of inhibition of the activin receptor signaling pathway as an intervention against the disease.

Evaluation of intraarterial and intravenous cisplatin chemotherapy in the treatment of metastatic osteosarcoma using an orthotopic xenograft mouse model.

BACKGROUND: Osteosarcoma is the most common primary malignancy of bone. Its treatment relies on the administration of neoadjuvant and adjuvant chemotherapy combined with surgery. Alternative to common intravenous (i.v.) administration of chemotherapeutic drugs, clinical studies also evaluated the benefit of intraarterial (i.a.) administrations. However, conflicting results were obtained when both routes of administration of cisplatin (CDDP), a gold standard drug in osteosarcoma treatment, were compared. In order to overcome clinical confounding factors, we evaluated both routes of drug administration in a mouse model of experimental osteosarcoma. METHODS: We directly compared i.v. versus i.a. drug infusions of cisplatin (CDDP), in an orthotopic xenograft mouse model of metastatic osteosarcoma. We performed tumor monitoring using caliper and micro computed tomography and measured tumor perfusion using laser speckle contrast imaging. Histopathological changes were evaluated using hematoxylin and eosin staining as well as immunohistochemistry (cleaved PARP-1, CD31, HIF-1α). RESULTS: First, an effective concentration of 4 mg/kg i.a. CDDP was determined that significantly reduced primary tumor volume. We used this concentration of i.a. CDDP and compared it to infusions of i.v. CDDP. Systemic (i.v.) CDDP only showed minor suppression of tumor growth whereas local (i.a.) CDDP strongly inhibited tumor growth and destruction of cortical bone in the tumor-bearing hind limb. Inhibition of tumor growth was linked to a reduced blood perfusion and resulted in increased amounts of tumor necrosis after i.a. CDDP. After treatment with i.a. CDDP, remaining viable tumor tissue responded by increasing expression of HIF-1α. Side effects due to administration of CDDP were minor, showing no differences in kidney damage between i.v. and i.a. CDDP. However, increased epidermal apoptosis in the foot was an indirect marker for locally increased concentrations of CDDP. CONCLUSIONS: Our findings demonstrate the great potential of local administration of cytotoxic chemotherapeutics, such as CDDP. Consequently, we provide a preclinical basis for a renewed interest in the clinical use of i.a. chemotherapy in osteosarcoma therapy.

Altered CXCL12 expression reveals a dual role of CXCR4 in osteosarcoma primary tumor growth and metastasis.

PURPOSE: Better understanding of the molecular mechanisms of metastasis-the major cause of death in osteosarcoma (OS)-is a key for the development of more effective metastasis-suppressive therapy. Here, we investigated the biological relevance of the CXCL12/CXCR4 axis in OS. METHODS: We interfered with CXCL12/CXCR4 signaling in CXCR4-expressing human 143-B OS cells through stable expression of CXCL12, of its competitive antagonist P2G, or of CXCL12-KDEL, designed to retain CXCR4 within the cell. Intratibial OS xenograft mouse model metastasizing to the lung was used to assess tumorigenic and metastatic potential of the manipulated cell lines. RESULTS: Constitutive expression of native CXCL12 promoted lung metastasis without affecting tumor growth. Stable expression of P2G or CXCL12-KDEL significantly accelerated tumor growth but diminished lung metastasis. Tumors grown from P2G- or CXCL12-KDEL-expressing cells contained higher levels of CXCR4-encoding mRNA going along with a higher percentage of CXCR4-expressing tumor cells. Lung metastases of all groups were predominantly enriched with CXCR4-expressing tumor cells. CONCLUSION: Higher abundance of CXCR4 possibly contributed to increased local retention of tumor cells by bone marrow-derived CXCL12, reflected in the increased primary tumor growth and decreased number of lung metastases in P2G and CXCL12-KDEL groups. Higher percentage of CXCR4-expressing lung metastatic cells compared to the corresponding primary tumors point to important functions of the CXCL12/CXCR4 axis in late steps of metastasis. In conclusion, based on the here reported results, local treatment of lung metastases with novel CXCR4-targeting therapeutics might be considered and favored over anti-CXCR4 systemic therapy.