MON-311 GH Action Upregulates ABC Transporters And EMT Markers In A Syngeneic Melanoma Mouse Model

Compared to many other forms of malignancies, melanoma expresses growth hormone receptors (GHRs) to a uniquely higher degree than other human cancers. Attenuating these receptors in cultured human melanoma cells resulted in decreased proliferation, and suppressed expression of ATP-binding cassette (ABC) transporters and epithelial-mesenchymal transition (EMT) markers. We hypothesize that GH promotes both the growth of mouse melanoma in vivo and the expression of ABC transporters and EMT markers. Thus, we propose that the use of a GH antagonist (GHA) could be effective at reversing these changes. To test these hypotheses, a syngeneic mouse B16-F10 melanoma model, cell proliferation assays, Western blotting, ELISAs, and real-time RT-qPCR were used. First, the high expression levels of GHR in B16-F10 cells were verified. Then, by knocking down GHR expression via small interfering RNA, the increased cell growth stimulated by GH administration was effectively reversed, independent of (insulin-like growth factor-1) IGF-1. To distinguish the effects of GH and IGF-1 on melanoma in vivo, bovine GH overexpressing transgenic mice (bGH) and GHR-knock out mice (GHR-/-) were used. Both mouse lines have significantly elevated GH, while bGH mice also exhibit high levels of IGF-1 whereas extremely low levels found in GHR-/- mice. Mouse melanoma cells were subcutaneously injected into bGH mice, GHR-/- mice, and their corresponding wild type (WT) littermate controls. Our data revealed that the ABC transporters and EMT markers in both bGH and GHR-/- mouse melanomas were significantly higher compared to their WT controls, implying that some of these effects were attributable directly to GH as opposed to IGF-1. Data analyzed from the Cancer Genome Atlas repository also suggests that human melanomas with higher GHR levels have significantly elevated expression levels of EMT markers, validating this syngeneic mouse melanoma model. On the other hand, transgenic mice that express a GHA and that have decreased GH action as well as circulating IGF-1 showed significantly decreased melanoma sizes, suggesting that targeting GHR, resulting in a compromised GH/IGF-1 axis, could delay the progression of melanoma. In summary, these results reveal the role of GH action in the upregulation of ABC transporters and EMT markers in vivo, both relevant with regards to tumor progression and poor clinical prognoses. Importantly, GH antagonism may inhibit the progression of melanoma in vivo. Studies are ongoing to determine whether GHA treatment is beneficial in the treatment of mouse melanoma in mice, and if so, blocking GH action may be considered as an anti-melanoma therapy in humans.