By definition, cells in a side population have distinguishing biological characteristics (for example, they may exhibit stem cell-like characteristics), but the exact nature of this distinction depends on the markers used in identifying the side population.
SP cells can rapidly efflux lipophilic fluorescent dyes to produce a characteristic profile based on fluorescence-activated flow cytometric analysis.
These new data indicate that the ability of malignant SP cells to expel anticancer drugs may directly improve their survival and sustain their clonogenicity during exposure to cytostatic drugs, allowing disease recurrence when therapy is withdrawn.
Identification of a tumor progenitor population with intrinsic mechanisms for cytostatic drug resistance might also provide clues for improved therapeutic intervention.
[4] The molecules involved in effluxing Hoechst 33342 are members of the ATP-binding cassette family, such as MDR1 (P-glycoprotein) and ABCG2.