17-DMAG and the related compounds 17-AAG/Tanespimycin and geldanamycin had varying efficacy in early clinical trials, due to toxicity, choice of target cancer type, and perhaps because these compounds are substrates for the P-glycoprotein efflux pump and have sub-optimal pharmacokinetics in humans (reviewed in [8]). Here, ABCB1 is linked to cancer.