To finally examine the impact of lactate-sustained P4HA1-DDR1 axis in the metastatic behavior of PCa cells in vivo, we stably silenced PCa cells for P4HA1 or DDR1 (Appendix Fig. S4A), then establishing tumor xenografts in SCID mice by subcutaneously (s.c.) co-injecting scrambled (Scr) or P4HA1- or DDR1-silenced cells with HPFs, CAFs or alone, and then exposing the xenografted mice to a daily i.p. treatment with lactate or vehicle. Here, P4HA1 is linked to neoplasm.