A Novel Mouse Model of Multiple Myeloma Representative of Human Disease and Its Use in Preclinical Therapeutic Assessment

Abstract 2907

In order to aid the pre-clinical development of novel therapeutics for multiple myeloma, an in vivo model which recapitulates the human condition in particular tumor growth patterns and response to treatment is required. An important feature of such a model is the interaction of the myeloma cells with the bone marrow microenvironment as this is known to modulate tumor activity and protect against drug-induced apoptosis. We have developed a model with myeloma restricted to the bone marrow, which proceeds rapidly from initial inoculation to disease progression, and possesses a range of chemo-sensitive markers with which to monitor anti-tumor response.

Female NOD/SCID γc^null mice were injected inta-osseously with luciferase-tagged myeloma cell lines. Disease progression was monitored weekly by bioluminescent imaging (BLI) and measurement of paraprotein levels (ELISA). These methods were compared to histological assessment of tumor infiltration and MRI which provided a quantitative measurement of progression. On T₂-weighted images tumor was identified as a hyperintense signal enclosed within cortical bone. Tumor burden was quantified from regions of interest drawn on the periphery of the hyperintense signal.

Luciferase-tagged cells engrafted by 3 weeks at the injection site and progressed to the femurs, spine and pelvis from week 4. BLI showed a significant increase in radiance from 5.6×10⁵ to 43.0×10⁵p/s/cm²/sr between weeks 5 and 7 (p<0.05). Quantification of tumor volume by MRI showed a significant increase from 6.4mm³ to 27.6mm³ between weeks 4 and 8 (p<0.05) and μCT demonstrated lytic disease. Serum levels of Igλ increased from 860ng/ml to 4325ng/ml during this period (p<0.05), which mirrored the changes seen with BLI and MRI. Flow cytometry and histology confirmed the confinement of CD138 positive myeloma cells within the bone. These results indicate successful engraftment of human myeloma cell lines with induction of myeloma in a pattern similar to the human condition.

We have adapted this model to study primary patient material. 10 mice were implanted with samples from 3 cases of plasma cell leukemia with complex cytogenetics. 5 of these developed myeloma confined to the bone marrow, 2 with additional plasmacytoma localized at the injection site, over a period of 1–5months. We have characterized the original patient cells with gene expression, SNP based gene mapping and have characterized the nature of the engrafted cells using similar technology.

We have also shown the model is suitable for preclinical assessment of anti-myeloma agents using bortezomib and a novel aminopeptidase inhibitor, tosedostat (CHR-2797). Non-treated mice displayed a significant increase in radiance from 16.13×10⁵ to 69.00×10⁵p/s/cm²/sr (p<0.01). In comparison, in the bortezomib and tosedostat treated groups no significant increase in radiance was seen (bortezomib: 5.22×10⁵ to 1.12×10⁵ p/s/cm²/sr; tosedostat: 9.92×10⁵ to 13.78×10⁵p/s/cm²/sr). Paraprotein levels mimicked these changes in BLI. At the end of treatment Igλ levels in control, bortezomib and tosedostat treated mice were 2473.7, 132.5 and 923.0ng/ml, respectively. Igλ levels in both treatment groups were significantly different from control (p<0.001). Average tumor volumes derived from MRI were significantly different in bortezomib (14.7mm³) and tosedostat treated (23.4mm³) groups compared to non-treatment (33.0mm³). The volumes for the bortezomib treated group showed no significant difference from control mice. In addition, there was a decrease in CD138 expression by flow cytometry in bone aspirates from treatment groups compared to control which was mirrored in histological samples.

In conclusion using both myeloma cell lines and primary patient cells, we have developed a model which recapitulates human myeloma with secretion of paraprotein, disease confined to the bone marrow, lytic bone lesions and spinal compression. In addition, this model is suitable for assessing the efficacy of novel therapeutics in vivo, using a number of non-invasive tumor markers such as BLI and MRI.