ABCB1 and cancer: Finally, despite the mixed outcomes of phase 3 clinical trials with MDR1 inhibitors, mostly due to high toxicity in combination with cytotoxic agents, co-administration of PU-H71 and new-generation MDR1 inhibitors may be feasible given the high affinity of PU-H71 for active HSP90 [31, 32] and its specific targeting of complexes comprised of HSP90 and oncogenic fusion proteins in certain cancers [47].