BACKGROUND: Pathogenesis of multiple myeloma is partly attributed to an aberrant expression of proliferation-, pro-angiogenic and bone-metabolism modifying factors by malignant plasma-cells.

AIM. Given the long and variable time-span from first diagnosis of early-stage plasma-cell dyscrasias to overt myeloma and the low proliferation rate of malignant plasma-cells, we hypothesize these to concomitantly express a novel class of anti-proliferative factors of potential prognostic relevance. Here, bone morphogenic proteins (BMPs) represent possible candidates, as they inhibit proliferation, stimulate bone formation, and have an impact on the survival of cancer patients.

PATIENTS AND METHODS. We assessed expression of BMPs and its receptors by Affymetrix DNA-microarrays (n=434) including CD138-purified primary myeloma-cell-samples, normal bone-marrow plasma-cell-samples, polyclonal plasmoblasts-samples, human myeloma-cell-lines (HMCL), and whole bone-marrow. Presence and differential gene expression was determined by PANP-algorithm and empirical Bayes statistics. Event-free (EFS) and overall survival (OAS) were investigated for the 168 patients undergoing high-dose chemotherapy (HM-group) using Cox’s proportional hazard model. Findings were validated using the same strategy on an independent group of 345 patients from the Arkansas-group. For validation, quantitative real-time PCR and flow cytometry were performed. In vitro induction of angiogenesis was assessed using the AngioKit-assay. Effect of BMP6 on proliferation of HMCL was assessed by 3H-thymidine uptake.

RESULTS. BMP6 is the only BMP expressed by normal- (13/14 samples) and malignant plasma-cells (228/233 samples). It is significantly lower expressed in proliferating non-malignant plasmablastic cells and human myeloma cell-lines. In vitro, BMP6 significantly inhibits proliferation of myeloma-cell-lines with an IC50 ranged from 0.08–2.15μg/ml, survival of primary myeloma-cells, and in vitro tubule formation down to the level of the negative control. High BMP6-expression in malignant plasma cells delineates significantly superior overall-survival for patients undergoing high-dose chemotherapy in both independent series of patients (n=168, P=.02 and n=345, P=.03, respectively, see below).

CONCLUSION. With BMP6 we report for the first time the autocrine expression of a prognostically relevant anti-angiogenic and anti-proliferative factor and its receptors by normal and malignant plasma-cells.

Disclosures: No relevant conflicts of interest to declare.

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