Influence of inoculation sites and tumor cell culture techniques on the phenotype of a mixed cartilage- and bone-producing mouse mammary tumor.

We have previously reported the characterization of an intraperitoneally (IP) transplantable bone-forming MXT tumor. However, the question was unresolved as whether the bone-forming cells originated from either the host animal or from the neoplasm itself. The present work attempts to answer this question by studying the influences of inoculation sites (subcutaneously, SC; intraperitoneally, IP; in the brain, IB; intracranially, ICR) on both the cartilage- and bone-forming tumor phenotypes. Furthermore the influence of cell culture procedures (two- and three- dimensional cultures) on these phenotypes was investigated. SC administered MXT cancer cells never produce bone-forming tumors, suggesting the existence in the dermis of substance(s) inhibitory to the formation of cartilage or bone. On the contrary, our data clearly demonstrate that bone-forming tumors can be obtained by either IP route, in a way which mimics endochondral ossification, or in the brain (IB), a region usually devoid of connective tissue. This observation substantiates the hypothesis according to which the tumor itself is able to produce osseous tissue. Another main finding is the increasing occurrence of skeletal tissues produced by cells proceeding from three-dimensional culture. Finally, ICR and IB tumors exerted a bone-lytic action against the host skull suggesting that tumor cells either produce osteolytic substances (prostaglandins, enzymes) and/or that they contain various cell types exhibiting different properties toward osteogenesis. This model offers new perspectives for studying the mechanisms of both normal and pathologic osteogenesis.