Study of the efficacy of new drugs in a mouse model of multiple myeloma

Multiple myeloma (MM) is a clonal plasma cell disorder accounting for approximately 10% of all haematological malignancies. MM development dramatically depends on plasma cell interactions with bone marrow (BM) microenvironment, which supports plasma cell growth, survival and drug resistance through cell-cell adhesion and release of a large number of growth factors, including interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF). Some crucial pathogenetic events in MM, such as neoangiogenesis and osteolysis, are ignited inside BM by MM cells themselves. Although standard chemotherapy is usually effective in lowering the disease burden, complete remission is achievable only in a minority of patients, and clinical responses are rarely persistent. Recent studies showed that a significantly higher number of patients may achieve clinical major responses when treated with therapeutic schedules based on the use of anti-angiogenic or biological agents, such as thalidomide, lenalidomide and bortezomib, especially when employed in combination with dexamethasone. However, MM still remains an incurable disease. Therefore, the identification of new key targets is crucial for the development of innovative therapeutic strategies, which should have not only direct effects on MM cells, but also interfering effects on MM-supporting BM microenvironment. To this aim, the use of mouse models that may closely resemble human MM development are mostly useful to foresee the clinical effects in patients. Some kinds of murine MM, such as 5TMM, originate from spontaneously developed MM in elderly mice of C57BL/KalwRij strain. The characteristics of these models, including the localization of the MM cells in the BM, the presence of serum M-component, the induction of osteolytic bone disease and neo-angiogenesis in the BM, are similar to human MM. In this study, we examined the effects of several new drugs in different murine and human myeloma cell lines and we tested these molecules in vivo in the murine 5T33MM model. T8 induced a reduction in cell activity only for high concentrations of molecule, with IC50 value of 4315 nM after 48 hours of incubation; for this reason it was not used for further studies. As expected, N80 did not show any cytotoxic activity on treated cells as compared to controls. However, when tested in vivo for a preventive and curative treatment, N80 showed immediate toxicity and reduction of the tumor burden. There were not differences in IgG2b levels in serum of mice treated with N80 using the therapeutical schedule as compared to controls, while the preventive schedule induced a statistically significant reduction in IgG2b levels. L9, N0 and N2 were able to inhibit the activity of MM cells in vitro. They appeared the most potent compounds, with nanomolar IC50 values, capable of reducing cell viability, in correlation with cell apoptosis in vitro. These molecules reduced the M-component and VEGF serum levels in vivo and eventually the tumor burden, although they did not modify significantly, with the treatment schedules employed, the overall survival in 5T33vtMM model.