Influence of the Dickkopf-related protein 1-(co)receptor axis on early bone colonization in a subcutaneous human prostate cancer xenograft model

Background The Wnt signaling pathway drives tumor cell invasion, metastasis, and bone formation, making it a key mediator of prostate cancer (PCa) skeletal metastasis. Dickkopf-related protein 1 (DKK1) inhibits canonical Wnt signaling by binding to the Wnt co-receptor LRP5/6; the DKK1-binding receptors Kremen1/2 cooperate in this inhibition. We investigated whether targeting this axis affects early bone colonization in a subcutaneous PCa xenograft model, an approach that reflects spontaneous metastatic dissemination but is limited by low metastatic frequency and the requirement for immunodeficient hosts. Methods Luc2/RGB-labelled PC-3 cells were implanted subcutaneously into male immunodeficient mice. DKK1 was neutralized with the humanized anti-DKK1 monoclonal antibody hDKN-01 during primary tumor growth (pre-OP) or following primary tumor surgical resection (post-OP). Further experiments used host mice with heterozygous Lrp5 gain-of-function mutation ( Lrp5 +/G170V ) or knockout of Kremen1 ( Krm1 −/− ), Kremen2 ( Krm2 −/− ), or both. Bone metastatic burden was quantified using anti-luciferase immunohistochemistry on serial hindlimb sections. Serum DKK1 ELISA and bone histomorphometry confirmed treatment efficacy and genotype phenotypes. Results hDKN-01 reduced serum DKK1 and increased trabecular bone volume, confirming biological activity, but did not affect tumor growth or bone metastatic burden in either treatment window. Lrp5 +/G170V and Krm1 / Krm2 double-KO mice showed expected bone phenotypes without altered bone colonization (detected in 13–33% of mice). Notably, Krm2 −/− mice showed only single disseminated tumor cells in bone, with no outgrowing colonies (0% of mice). Conclusions Neither systemic neutralization of DKK1 nor Lrp5 mutation nor Krm1 or Krm1 / Krm2 knockout had any effect on bone colonization of subcutaneous PC-3 xenografts in immunodeficient mice. In contrast, Krm2 knockout prevented the formation of colonizing bone metastases, apparently depending on the presence of Krm1 .