the effect of a newly developed osmium(vi ) nitrido complex , 1 , on breast 
 cancer stem cells ( cscs ) 
 is reported . the complex displays selective toxicity for hmler breast 
 cancer cells enriched with cd44-positive , csc - like cells over the 
 same cells having reduced csc character . 
 remarkably , 1 also reduces the proportion of cscs within a heterogeneous breast 
 cancer cell population and irreversibly inhibits the formation of 
 free - floating mammospheres to an extent similar to that of salinomycin , 
 a natural product that targets cscs . 
 detailed mechanistic studies 
 reveal that in breast cancer cells 1 induces dna damage 
 and endoplasmic reticulum stress , the latter being responsible for 
 the csc selectivity . 
 the anti - csc properties of 1 provide 
 a strong impetus for the development of new metal - based compounds 
 to target cscs and to treat chemotherapy - resistant and relapsed tumors .