Growth Hormone Receptor Knockdown Sensitizes Human Melanoma Cells to Chemotherapy by Attenuating Expression of ABC Drug Efflux Pumps

Abstract

Melanoma remains one of the most therapy-resistant forms of human cancer despite recent introductions of highly efficacious targeted therapies. The intrinsic therapy resistance of human melanoma is largely due to abundant expression of a repertoire of xenobiotic efflux pumps of the ATP-binding cassette (ABC) transporter family. Here, we report that GH action is a key mediator of chemotherapeutic resistance in human melanoma cells. We investigated multiple ABC efflux pumps (ABCB1, ABCB5, ABCB8, ABCC1, ABCC2, ABCG1, and ABCG2) reportedly associated with melanoma drug resistance in different human melanoma cells and tested the efficacy of five different anti-cancer compounds (cisplatin, doxorubicin, oridonin, paclitaxel, vemurafenib) with decreased GH action. We found that GH treatment of human melanoma cells upregulates expression of multiple ABC transporters and increases the EC50 of melanoma drug vemurafenib. Also, vemurafenib-resistant melanoma cells had upregulated levels of GH receptor (GHR) expression as well as ABC efflux pumps. GHR knockdown (KD) using siRNA in human melanoma cells treated with sub-EC50 doses of anti-tumor compounds resulted in significantly increased drug retention, decreased cell proliferation and increased drug efficacy, compared to mock-transfected controls. Our set of findings identify an unknown mechanism of GH regulation in mediating melanoma drug resistance and validates GHR as a unique therapeutic target for sensitizing highly therapy-resistant human melanoma cells to lower doses of anti-cancer drugs.

Excess growth hormone suppresses DNA damage repair in epithelial cells

“…In addition, protective effects of GH in DNA damaged cells may be also associated with clearing of chemotherapeutic drug. Although we show that GH does not affect MDR1 expression in hNCC, GH treatment of human melanoma cells induced expression of ATP-binding xenobiotic efflux pumps associated with melanoma drug resistance (86).…”

The effects of growth hormone on therapy resistance in cancer

“…Further, protection of endocrine-resistant breast cancer from ruxolitinib, a JAK2-inhibitor, was reported to coincide with GHR expression [147] . The first clue that GH acts via direct upregulation of ABC-transporter expression in conferring this chemoresistance in tumors came from our study in human melanoma [2,132,148] . We observed that doxorubicin, cisplatin, paclitaxel, oridonin, and vemurafenib, in four different human melanoma cell lines, in presence of GH differentially upregulated ABCB1, ABCB5, ABCB8, ABCC1, ABCC2, ABCG1, and ABCG2 multi-drug efflux pump expressions.…”

“…We observed that doxorubicin, cisplatin, paclitaxel, oridonin, and vemurafenib, in four different human melanoma cell lines, in presence of GH differentially upregulated ABCB1, ABCB5, ABCB8, ABCC1, ABCC2, ABCG1, and ABCG2 multi-drug efflux pump expressions. In fact prolonged GH treatment alone rendered the melanoma cells resistant to chemotherapy, reflected by a two to five fold elevation in the vemurafenib EC50 value [148] . GHRKD reversed these effects, increased drug retention, thereby sensitizing the melanoma tumors to low doses of chemotherapy [148] .…”

“…In fact prolonged GH treatment alone rendered the melanoma cells resistant to chemotherapy, reflected by a two to five fold elevation in the vemurafenib EC50 value [148] . GHRKD reversed these effects, increased drug retention, thereby sensitizing the melanoma tumors to low doses of chemotherapy [148] . Analysis of murine tumor xenografts in immunocompetent C57BL6/J mouse models of GH excess, e.g., the bovine (b) GH transgenic mouse (bGH), found significantly upregulated ABC-transporters compared to wildtype littermates and verified our in vitro observations (unpublished results).…”

Growth hormone in the tumor microenvironment

“…GH may also impact chemotherapy resistance via its effects on multi-drug efflux pumps, which transport xenobiotics out of the cytoplasm (80). For example, GH expression in four different human melanoma cell lines upregulated expression of multiple ABC-family multi-drug efflux pumps, rendering cells resistant to chemotherapy (84).…”