Removal of carcinoma cells from contaminated bone marrow using the lipophilic cation rhodamine 123

Autologous bone marrow transplants for solid tumor treatment are severely limited by the potential presence of residual cancer cells in the reinfused bone marrow and can lead to future tumor recurrence. This article presents a novel method of removing carcinoma cells from bone marrow with contaminating cancer cells. This method is based on our previous studies demonstrating that carcinoma cells have a higher uptake of lipophilic cations such as rhodamine 123 than their normal epithelial counterparts. When the relative differences in rhodamine 123 uptake are quantified, carcinoma cell lines demonstrated a 7.4-21 times greater uptake of rhodamine 123 than normal mouse bone marrow cells. More important, when normal bone marrow cells and carcinoma cell lines are mixed to simulate carcinoma-contaminated bone marrow, individual cell populations continue to exhibit characteristic and identifiable relative differences (10-20 times) in rhodamine 123 uptake. Differential sorting of bone marrow/carcinoma cell mixtures with respect to rhodamine 123 fluorescence intensity resulted in the removal of 95-99% of the "contaminating carcinoma cells." The recovered bone marrow cells were fully viable as ascertained by their ability to form splenic colonies. In our preliminary experiments, sorted bone marrow cells transplanted into lethally irradiated C57BL6 mice allowed the mice to survive for more than 8 months. In light of these promising results, we propose that lipophilic cations may play a role in the purification of autologous bone marrow used in transplants for patients with advanced solid tumors.