Outcomes for patients diagnosed with osteosarcoma (OS) hinge primarily on the development pulmonary metastasis. Looking to identify novel opportunities for therapeutic intervention, we have sought mechanisms that facilitate colonization of lung tissues by osteosarcoma cells. We have shown that metastatic colonization of lung by OS cells requires production of the signaling factors IL6 and CXCL8, which is elicited upon the interaction of OS cells with lung epithelium. Lung-derived signals that trigger this behavior and the effector mechanisms by which IL6 and CXCL8 facilitate metastasis remain unknown.
Here, we hypothesized that the interaction of OS cells lung epithelium triggers production of cytokines that establish paracrine signal amplification loops. We postulated that OS cell-derived IL6 and CXCL8 stimulate lung-resident cells to produce secondary signaling molecules that, in turn, stimulate OS cells. If our paracrine loop hypothesis is correct, we expect these lung-derived factors elicit further production of IL6 and CXCL8, resulting in feed-forward paracrine signaling.
To identify specific factors responsible for this effect, we used RNA-seq to filter soluble ligands produced by lung epithelial cells capable of activating cognate receptors produced by OS cells. Epithelial cell production of a subset of these candidate ligands increased following exposure to supernatants from OS cells. Ten candidate epithelial-to-tumor ligand-receptor interactions were identified by our in vitro analysis.
Interpreting these results in the context of prior known biology, IL1 stands ouit as the prime candidate for a lung-to-tumor signal eliciting production of IL6 and CXCL8 in disseminated OS cells. We show that stimulation of OS cells with IL1 drastically increases production of both IL6 and CXCL8. Additionally, we show inhibition of IL1 alone eliminates this response in multiple co-culture models. We also verified production of IL-1α/β by lung epithelium and are currently working to confirm these findings in vitro, utilizing a mouse model of OS metastasis.