The Impact of Cell of Origin on Murine Osteosarcoma Cell Characteristics, Aggressiveness, and Drug Response — 69p — Nick Schefers, Leetoria Hinojosa, Dr. Jianning Tao

Purpose/Background: Osteosarcoma (OS) is the predominant form of malignant bone cancer and most commonly occurs in adolescents. Most treatment methods include excision of the bone tumor paired with chemotherapy. Unfortunately, even such invasive treatment methods cannot prevent metastasis in every case. Fortunately, it has been demonstrated that osteosarcoma found in mice can be used to accurately model human OS. It has also been made evident that loss of function mutations in the tumor suppressor gene p53 are linked with tumor generation. Previously, p53 ^f/f mice, where Exons 2-10 are flanked by loxP sites, were crossed with transgenic mice expressing Cre recombinase under the control of the Prx1 derived enhancer (Prx), Osterix (Osx) or Osteocalcin (Oc) promoters to transform mesenchymal cells, OB progenitors and mature OBs, respectively. This study aims to explore the role of cell of origin in osteosarcoma aggressiveness and chemotherapy response, providing insights into targeted therapies to improve prognosis and treatment outcomes in pediatric patients.  Design: With the goal of better understanding the effect that the stage in osteoblast development from which the OS cell originates has on OS cell characteristics, cell lines were derived from tumors harvested from the Prx-Cre p53 ^f/f, Osx-Cre p53 ^f/f, and Oc-Cre p53 ^f/f mice. These cells were then studied using multiple mammalian cell culture techniques, including colony formation, adipogenic differentiation, osteogenic differentiation, scratch migration, proliferation, and drug treatment assays. These assays were chosen because they allow for efficient assessment of cellular behaviors indicative of tumorigenic potential and invasiveness. They also allow us to directly visualize and quantify key OS cell characteristics to understand the dynamics of cancer progression and metastasis.  Results: Our results suggest the cell of origin significantly affects the characteristics of resulting OS cells. OS cells originating from the less differentiated states (PrxOS- and OsxOS-positive cells) had higher rates of proliferation, migration, and colony formation than OS cells originating from Oc-positive committed osteoblasts. Specifically, our data indicates that OS cells originating from Osx-positive osteoblast progenitors both migrate and proliferate at a rate that is about twice as fast as that of OS cells originating from Oc-positive committed osteoblasts. Cell of origin also has a significant effect of OS cell differentiation capabilities. Interestingly, we have demonstrated that of these three cell lines, the only cells with the capability to differentiate into adipose cells are the OS cells originating from Osx-positive osteoblast progenitors. Nonetheless, at the concentrations used, cell of origin does not appear to affect Doxorubicin resistance. Discussion: This study indicates that different tumor-originating cells produce OS cells with differing capabilities. This may inspire further research into differences in drug resistance and may lead to more personalized care for children who suffer from OS. The observed differences in cell behavior may be attributed to differences in epigenetic states at different stages of osteoblast development, which may affect the mechanisms by which cells respond to oncogenic stress. In addition, this study relied on a single cancer model and chemotherapeutic agent, which is a limitation; future studies should explore these phenomena in a variety of models and with other therapeutic compounds to validate these findings and expand their applicability.

Sanford Research
Dr. Jianning Tao