NK4, an Antagonist of Hepatocyte Growth Factor (HGF), Inhibits Growth of Multiple Myeloma Cells In Vitro and In Vivo: A Mouse Model for Molecular Targeting of Angiogenic Growth Factor.

Background and rationale: Recent study showed that bone marrow angiogenesis and angiogenic growth factors including hepatocyte growth factor (HGF) are associated with pathogenesis and disease activity of multiple myeloma. In our experience, plasma concentration of HGF significantly elevated in 30 % of patients with clinically active myeloma and declined along with response to therapy. Thus, HGF signaling is considered to play a role in progression of myeloma and is a potential therapeutic target. The aim of this study is to establish a novel therapy targeting HGF and the receptor, c-MET, using NK4 molecule which is an HGF-antagonist consisting of N-terminal kringle domain of HGF.

Results: 1) Among eleven myeloma cell lines established from Japanese patients, two lines, KMS11 and 34, secreted HGF while c-MET is expressed in all eleven cells. 2) 10nM of NK4 protein significantly inhibited growth of the two HGF-producing cells in vitro. NK4 protein showed additive anti-myeloma effect to dexamethasone (Dex) in Dex-sensitive KMS11 cells, and is also effective for growth suppression of Dex-resistant KMS 34 cells. 3) NK4 significantly reduced phosphorylation of ERK1/2 while no significant effect on STAT3 activation. 4) Adenoviral vector carrying NK4 cDNA (Ad-NK4) was injected in femoral muscle of lcr/scid mice. Pharmacokinetic study showed that NK4 proteins were detected in plasma, liver, lung and kidney up to three weeks and attained a maximum level at day 10–14. 5) Ad-NK4 injection to tumor-bearing lcr-SCID mice significantly inhibited growth of subcutaneous tumor derived from KMS11 and 34 cells compared with empty vector injection (n=10, p<. 05). Co-injection of Ad-NK4 and Dex revealed synergistic or additive anti-tumor effect in mice bearing KMS11 tumor. Anti-myeloma effect of Ad-NK4 is also confirmed by histopathological examination.

Conclusion: Above results directly showed that HGF/c-MET signal plays an important role in progression of myeloma cells producing HGF. Molecular targeting of HGF by NK4 is considered as a novel approach for the treatment of myeloma via independent mechanism of glucocorticoid therapy.