GH1 and melanoma: Tyrosine phosphorylation of STAT5, the hallmark surrogate assay for hGHR activation, was evaluated using hGHR-rich human melanoma cells, and employing both western blots and ELISA showed that the efficacy of the MAL-dPEG-A conjugate of double cysteine–substituted GGSSG-hGH-G120K (compound G) was comparable to the unpegylated GGSSG-hGH-G120K and suppressed STAT5 phosphorylation by >90% (Fig. 2, C–E).