An in vivo model of human multidrug-resistant multiple myeloma in SCID mice.

We have established a reproducible in vivo model of human multiple myeloma in the severe combined immunodeficient (SCID) mouse using both the RPMI 8226 human myeloma cell line and the P-glycoprotein-expressing multidrug-resistant 8226/C1N subline. SCID mice 5 to 8 weeks of age were injected intraperitoneally with either 8226 drug-sensitive or P-glycoprotein-expressing multidrug-resistant myeloma cells (8226/C1N). Tumors were detected within 5 days after injection by the presence of human lambda light chain excretion in the mouse urine. Growth of the tumor was observed primarily in the abdominal cavity with spread to the abdominal organs. The anti-neoplastic agent doxorubicin was effective in treating the drug-sensitive 8226 human-SCID xenografts but had no effect on the multi-drug-resistant 8226/C1N human-SCID xenografts. In the 8226-sensitive xenografts, treatment with doxorubicin resulted in a sharp decline in the concentration of human lambda light chain being excreted in the mouse urine. This correlated with an increased survival of the drug-treated animals. This mouse model offers an in vivo means of evaluating efficacy and toxicity of new therapeutic approaches, including development of chemosensitizers directed against P-glycoprotein in multidrug-resistant myelomas.