“Camptothecin (CPT) and 4'-demethylepipodophyllotoxin ethylidene-beta-D-glucoside (VP16) at concentrations of 0-10 nM and 0-400 nM, respectively, have weak synergistic effects with retinoic acid (RA) on the induction of differentiation and growth inhibition of HL-60 cells.”