GHR and melanoma: One week pretreatment of melanoma cells with GH and/or GHR antagonists, followed by drug-retention assay loading DiOC2 (3) as a drug surrogate, showed a 1.5- to 2-fold increase in the amount of dye retained within the cells over a 2-h period by compounds D and G compared to the hGH-induced efflux (Fig. 4G).