Serum Concentrations of DKK-1 Correlate with the Extent of Bone Disease in Multiple Myeloma.

Objectives: Lytic bone disease is a hallmark of multiple myeloma (MM) and is caused by osteoclast activation and osteoblast inhibition. Secretion of Dickkopf (DKK)-1 by myeloma cells was reported to cause inhibition of osteoblast precursors. DKK-1 is an inhibitor of the Wnt/β-catenin signaling, which is a critical signaling pathway for the differentiation of mesenchymal stem cells into osteoblasts. So far there is no study showing a significant difference in serum DKK-1 levels in MM patients with or without lytic bone lesions.

Methods: DKK-1 serum levels were quantified in 184 previously untreated MM patients and 33 MGUS patients by ELISA, using a monoclonal anti-DKK-1 antibody. For the evaluation of bone disease, skeletal X-rays were performed.

Results: Serum DKK-1 was elevated in MM as compared to MGUS (mean 11,963 pg/mL versus 1993 pg/mL, P < 0.05). Serum DKK-1 levels significantly correlated with myeloma stage according to Durie and Salmon (mean 2223 pg/mL versus 15,209 pg/mL in stage I and II/III, respectively; P = 0.005). Importantly, myeloma patients without lytic lesions in conventional radiography had significantly lower DKK-1 levels than patients with lytic bone disease (mean 3114 pg/mL versus 17,915 pg/mL; P = 0.003). Of interest, serum DKK-1 correlated with the number of bone lesions (0 vs. 1–3 vs. >3 lesions: mean 3114 pg/mL vs. 3559 pg/mL vs. 24,068 pg/mL; P = 0.002).

Conclusion: This is the largest study of DKK-1 serum levels in multiple myeloma patients and data show for the first time a correlation between DKK-1 serum concentration and the amount of lytic bone disease, suggesting that DKK1 is an important factor for the extent of bone disease and supporting the hypothesis of DKK-1 as a therapeutic target in myeloma bone disease.