A Clinically Relevant SCID-hu in Vivo Model of Human Multiple Myeloma.

Human multiple myeloma (MM) xenografts in immunodeficient mice have limitations as a model for the human disease since they lack the human bone marrow (huBM) microenvironment. In contrast, murine models harboring a huBM microenvironment with implantation of patient MM cells in the huBM recapitulate the in vivo pathophysiology of MM and have significant advantages over conventional murine models for pre-clinical evaluation of investigational drugs. However, there are significant limitations in using patient MM cells in such models since i) not all patient MM samples engraft in the huBM; ii) only a fraction of engrafted specimens produce measurable paraprotein and/or osteolytic lesions; and iii) a limited number of MM cells can be harvested from an individual patient, thus limiting the number of mice that can be injected with cells from the same patient. To overcome these limitations, we have developed a novel murine model of MM by engrafting INA-6, a cytokine-dependent human MM cell line into SCID mice previously implanted with a human fetal bone chip (SCID-hu mice). INA-6 cells require either exogenous IL-6 or interaction with the bone marrow stromal cells (BMSCs) to proliferate in vitro. In this model, we monitored the in vivo growth of INA-6 cells stably transfected with a green fluorescent protein (GFP) expression vector (INA-6^GFP+). Serum soluble human IL-6 receptor (shuIL-6R) and fluorescence imaging of host animals were sensitive indicators of tumor burden with time dependent increase. Fluorescence imaging was able to detect the myeloma cell growth earlier than measurement of sIL-6R levels. INA-6 MM cells grew in SCID-hu mice, but not in SCID mice injected subcutaneously or intravenously without the human fetal bone. We have further confirmed the feasibility of this model in monitoring the response to therapeutic agents such as dexamethasone by detecting reduction in the intensity of the fluorescent lesions as well as shuIL-6R in SCID-hu mice following anti-MM treatment. This highly reproducible model therefore allows for evaluation of investigational drugs targeting MM cells in the huBM milieu.