Hirata, N. et al. Cell Rep. 6, 1165–1174 (2014).

Probes for detecting human pluripotent stem cells (hPSCs) are needed for basic research and therapeutic applications. Hirata et al. performed a screen of a fluorescent small-molecule library and identified a rhodamine derivative, KP-1, that shows promise as a label for hPSCs in some contexts. Labeling with KP-1 appears to be due to the fact that hSPCs inhibit the expression of ABC drug transporters ABCB1 and ABCG2, which export KP-1 from other cells. Labeling with KP-1 is not entirely specific: the probe shows only weak labeling of hematopoietic stem cells, hPSC-derived cardiomyocytes and several other human cell types, but it strongly labels neural stem cells, astrocytes and some cancer cell lines. The researchers also determined that KP-1 probably cannot be used to identify fully reprogrammed cells during the induction of pluripotency.