HTS Assay for Functional Modulators of ABCB6 Figure 7. Three of the four compounds identified in the primary HTS screen compete for ABCB6 mediated hemin transport. (a) verteporfin (c) tomatine hydrochloride and (e) benzethonium chloride compete for the transport of 14C-labeled hemin in the presence of ATP but not in the presence of AMP in mitochondria isolated from ABCB6-overexpressing cells. (b, d, and f) Line graph showing dose dependent competition of PLoS ONE | www.plosone.org 11 July 2012 | Volume 7 | Issue 7 | e40005