C-met Receptor as a Potential Target for the Treatment of Patients with Multiple Myeloma.

Despite progress in the treatment of Multiple Myeloma (MM), it is still an incurable disease with average survival of 3–4 years. Because MM is often resistant to conventional therapies, new treatment strategies are necessary. The presence of elevated HGF (Hepatocytic Grow Factor) expression has been well documented in multiple myeloma. The c-met oncogene has been shown to be present in MM cell lines at the mRNA and protein level. Some data suggested that this axis could be responsible for proliferation and inhibition of apoptosis in MM cells. In this study we have analyzed c-met expression in 15 patients with (MM) before and after treatment. Seven of these pts responded well and eight pts responded poorly to the employed therapy. All 15 pts were c-met positive before therapy. Bone marrow cellularity of patients who responded well was 76% before (range: 10% – 100%) and 46% after treatment (range: 40% – 60%). In this group plasmocyte infiltration of bone marrow consisted of 59% before (range: 10% – 80%) and 9% after chemotherapy (range: 0% – 20%). Five of them had undetectable c-met positive cells among bone marrow cells after treatment. In the group of poor responders cellularity of bone marrow was 40% (range: 20% – 70%) before treatment and 46% (range: 20% – 70%) after therapy. Plasmocytes consisted of 20% (range: 10% – 50%) of bone marrow cells before and 44% (range: 10% – 90%) after treatment. All patients in this group had cells positive for c-met receptor after therapeutic regiment. This results suggested that c-met-HGF axis might be a good target for alternative therapy in MM. We looked for potential therapeutics that interferes with this axis and we found that geldanamycin (GA) has been shown to decrease expression of c-met at the protein level in several different cell types. Using inhibitors that belongs to geldanamycin family (GA, 17AAG and 17DMAG) we treated MM cell lines and primary sample. We found that these molecules strongly inhibited expression of c-met in both MM cell lines and patients sample as assessed by western blot analysis. We also tested the influence of these inhibitors on proliferation of MM cells. We found that 100nM dose of GA and 17DMAG inhibited growth of MM cell lines by 80% and 100nM dose of 17AAG inhibited growth of these cells by 20%. Primary cells were more resistant to treatment but we still obtained 30% inhibition with GA and 17DMAG. 17AAG was ineffective and proliferation decreased by less than 10%. Grow inhibition was probably not only due to c-met-HGF axis blockade because these molecules also inhibit other proteins (AKT, RAF). In our experiments we have shown that the level of c-met expression correlates with response to therapy. Patients who respond well had substantially decreased number of c-met positive plasmocytes after chemotherapy in comparison to poor responders. We have also showed that drugs that block c-met-HGF axis could be used in treatment of MM. These drugs could potentially inhibit cells proliferation, increase apoptosis and disrupt MM cells interaction with bone marrow environment. Based on these data we postulate that the c-met receptor is a potential target for MM therapy especially in patients who do not respond to the first line of treatment.