Three-dimensional coculture provides an improved in vitro model for papillary renal cell carcinoma.

Papillary renal cell carcinoma (pRCC) represents the second most common kidney cancer and can be distinguished from other types based on its unique histological architecture and specific pattern of genomic alterations. Sporadic type 1 pRCC is almost universally driven by focal or chromosomal amplification of the receptor tyrosine kinase MET, although the specific mode of its activation is unclear. Although the MET receptors found in human tumor specimens appear highly active, those found on the surface of in vitro-cultured tumor cells are only weakly activated in the absence of exogenous hepatocyte growth factor ligand. Furthermore, pRCC cells cultured in standard two-dimensional conditions with serum fail to respond functionally to MET knockdown or the selective MET inhibitor capmatinib despite clear evidence of kinase inhibition at the molecular level. To better model pRCC in vitro, we developed a three-dimensional coculture system in which renal tumor cells are layered on top of primary fibroblasts in a fashion that mimics the papillary architecture of human tumors. In this three-dimensional spheroid model, the tumor cells survive and proliferate in the absence of serum due to trophic support of hepatocyte growth factor-producing fibroblasts. Unlike tumor cells grown in monoculture, the proliferation of cocultured tumor cells is sensitive to capmatinib and parallels inhibition of MET kinase activity. These findings demonstrate the importance of stromal fibroblasts in pRCC and indicate that accurate in vitro representation of this disease requires the presence of both tumor and fibroblast cells in a structured coculture model.