ABCB1 and neoplasm: In our model, after pre-incubation with verapamil (a blocker of the drug-pumping-out activity of P-glycoprotein), HBL-100, FRO and B16 tumor cell lines still did not react to treatments with the Hsp90 inhibitors; thus, probably, other (non-related to MDR1/P-glycoprotein) mechanisms are involved.