Synergistic Effects of Bortezomib with Low Dose Melphalan Against Human AML Cells.

The treatment of AML in the elderly population is difficult given the inherent resistant disease, the toxic effects of therapy and the presence of co-morbid conditions. We proposed preclinical studies to investigate the potential synergy of bortezomib with melphalan against AML cells, with the anticipation of developing a clinical trial. To test the killing potential of bortezomib or melphalan, limiting dilution experiments were performed with subsequent analysis using the MTT assay. Two human AML cell lines, GDM-1 and Kasumi-1, were used as targets. Tumor cells (7.5 x 10³ cells/well) were plated on 96-well tissue culture plates and incubated overnight at 37 °C with 5% CO₂. At 24 hrs, varying concentrations of melphalan (doses: 100 uM to 1 uM) or bortezomib (doses: 100 nM to 1 nM) were added to each well. After 48 hrs of culture, the MTT assay was performed. Each test was run in triplicate. When using the GDM-1 cell line, the addition of melphalan alone (1 uM) resulted in 80% viability (+/− 1.7%), while bortezomib alone (1 nM) yielded 86% viability (+/− 3.6%). An increased dose of each medication decreased the viability of the GDM-1 cells. An increased dose of Melphalan (3 uM) reduced the viability to 23% (+/− 4.2 %). The viability dropped to 62% (+/− 4.9 %) with an increased dose of Bortezomib (3 nM). After combining the medications, the inhibitory activity against the GDM-1 cells required lower doses then either drug alone. For example, melphalan (1uM) with bortezomib (1 nM) reduced the viability of GDM-1 cells to 20% (+/− 2.8%); While melphalan (3 uM) and bortezomib (3 nM) further suppressed the viability to 3.7 % (+/−2.5 %). Similar results were found using the Kasumi-1 AML cell line. These results demonstrate the potential synergy of the combination of bortezomib with melphalan against AML cells. These preclinical results are currently being tested in a clinical trial using low dose melphalan with bortuzimab in elderly AML and MDS patients.