Targeted apc;twist double-mutant mice: a new model of spontaneous osteosarcoma that mimics the human disease.

TWIST and adenomatosis polyposis coli (APC) are critical signaling factors in normal bone development. In previous studies examining a homogeneously treated cohort of pediatric osteosarcoma patients, we reported the frequent and concurrent loss of both TWIST and APC genes. On these bases, we created a related animal model to further explore the oncogenic cooperation between these two genes. We performed intercrosses between twist-null/+ and Apc1638N/+ mice and studied their progeny. The Apc1638N/+;twistnull/+ mice developed bone abnormalities observed by macroscopic skeletal analyses and in vivo imaging. Complementary histologic, cellular, and molecular analyses were used to characterize the identified bone tumors, including cell culture and immunofluorescence of bone differentiation markers. Spontaneous localized malignant bone tumors were frequently identified in Apc1638N/+;twist-null/+ mice by in vivo imaging evaluation and histologic analyses. These tumors possessed several features similar to those observed in human localized osteosarcomas. In particular, the murine tumors presented with fibroblastic, chondroblastic, and osteoblastic osteosarcoma histologies, as well as mixtures of these subtypes. In addition, cellular analyses and bone differentiation markers detected by immunofluorescence on tumor sections reproduced most murine and human osteosarcoma characteristics. For example, the early bone differentiation marker Runx2, interacting physically with hypophosphorylated pRb, was undetectable in these murine osteosarcomas, whereas phosphorylated retinoblastoma was abundant in the osteoblastic and chondroblastic tumor subtypes. These characteristics, similar to those observed in human osteosarcomas, indicated that our animal model may be a powerful tool to further understand the development of localized osteosarcoma.