Purging of myeloma cells using all-trans retinoic acid in a mouse model

Objective, The 5T33 murine model of multiple myeloma was used to investigat e the potential of all-trans retinoic acid (ATRA) to purge clonogenic myelo ma cells from autologous hemopoietic stem-cell harvests by differentiating immature 5T33 cells into terminal-stage plasma cells with limited repopulat ion capacity. Materials and Methods, 5T33 cells were treated with 10 muM ATRA and the eff ect on cell clonogenicity was determined by measuring the time to paraprote in detection in C57Bl/KaLwRij mice compared to control animals. Cell differ entiation and apoptosis following ATRA treatment were investigated using fl ow cytometry and caspase-3 assay. Results. Treatment with ATRA resulted in a 33% reduction in the in vitro cl oning efficiency of 5T33 cells, Reduced in vitro clonogenicity of 5T33 cell s following ATRA treatment was supported by a 16-49% increase in the time t aken for C57Bl/KaLwRij mice to develop paraprotein following injection of 5 T33 cells pretreated with ATRA for 8 days. Although ATRA was shown not to a lter the in vitro growth characteristics of 5T33 cells, significant inhibit ion of apoptosis was observed. Treatment with ATRA also resulted in an incr ease in the proportion of 5T33 cells expressing the CD54 adhesion molecule, which is known to be highly expressed on mature myeloma cells. Conclusion. The ability of ATRA to decrease the clonogenicity of 5T33 cells in vitro and increase the time to disease development in vivo suggests tha t this drug may be useful for purging autologous stem cell harvests in the clinical setting. (C) 2001 International Society for Experimental Hematolog y. Published by Elsevier Science Inc.