Hepatocyte Growth Factor-Producing Multiple Myeloma (HGF myeloma) Is a Distinct Clinical Entity and Needs for Molecular Targeted Therapy.

Background and Objective: Disease control of refractory or relapsed multiple myeloma (MM) remains a therapeutic challenge. Classification of the patients in the molecular basis and development of targeted therapy are crucial to overcome the situation. We previously reported that 20–30% of MM cells produce hepatocyte growth factor (HGF), and its serum concentration was specifically elevated in symptomatic MM patients. The purpose of this study is to elucidate the clinical characteristics of HGF-producing MM (HGF myeloma) and to explore a novel therapy.

Patients & Methods: Serum concentrations of HGF obtained from 76 patients with MM were measured by ELIZA. Less than 0.3μg/L was considered as a normal range. Association of serum HGF levels with various clinical parameters for disease activity was examined, including age, ISS stage, type of M protein, hemoglobin level, serum creatinine, Ca, β2M, albumin, LDH, CRP, bone marrow MM cell %, chromosomal abnormality, presence of lytic bone lesion and extramedullar plasmacytoma. Phase 2 thalidomide monotherapy was also conducted in 56 patients with refractory MM. HGF-specific competitive inhibitor, NK4 protein, was used for in vitro experiments such as growth inhibition by MTT assay, induction of apoptosis by flow cytometer and activation of intracellular signaling molecules by Western blot analysis. Recombinant adenovirus containing NK4 cDNA (AdCMV.NK4) was intramuscularly injected into lcr/scid-mice bearing tumors derived from HGFproducing KMS11 and 34 cells.

Results:

1. Elevated serum HGF level was significantly associated with the presence of anemia (p=0.03) and lytic bone lesion (p=0.009). Seven out of eight patients with high CRP levels without infection and five out of nine patients with extramedullar plasmacytoma also demonstrated elevated serum HGF level.

2. Furthermore, in thalidomide monotherapy for refractory MM, increase in pre- and posttreatment serum HGF level was significant poor prognostic factors for overall survival (OS) in univariate analyses, p=0.025 and 0.01, respectively. Elevation of post-treatment HGF level was also independent poor prognostic factor for OS in multivariate analysis.

3. We next examined the possibility of molecular targeted therapy of HGF using NK4.

NK4 protein stabilized the growth of HGF-producing MM cell lines and primary bone marrow MM cells in vitro. NK4 also increased in annexin V+ apoptotic cell fraction and regulated the activation of c-Met, ERK1/2, STAT3, and AKT-1. AdCMV.NK4 significantly delayed growth of KMS 11 and 34-derived tumors in vivo. Histological examination revealed that AdCMV.NK4 induced apoptosis of the tumor cells, accompanied by a reduction in neovascularization in the tumors. AdCMV.NK4 injection prolonged survival of KMS 11 tumor-bearing mice.

Conclusion: HGF myeloma is characterized by increased disease activity such as anemia, bone lesion, high CRP level and extramedullar plasmacytoma and also by shorter survival by conventional therapy including thalidomide, and it should be recognized as a distinct clinical entity. Since NK4 showed direct anti-myeloma effect as well as anti-angiogenic activity against HGF-producing MM cells, molecular targeted therapy, for example using NK4, is to be established to improve the therapeutic outcome of HGF myloma.