Additive effects of a prolactin receptor antagonist, G129R, and herceptin on inhibition of HER2-overexpressing breast cancer cells

Abstract

Breast cancers overexpressing human epidermal growth factor receptor 2 (HER2) have been reported to have higher proliferative and metastatic activity in the presence of autocrine prolactin (PRL), indicating potential cooperation between HER2 and the PRL receptor (PRLR) during breast cancer progression. PRL can induce the tyrosine phosphorylation of HER2 which stimulates mitogen-activated protein kinase (MAPK) activity. To determine if this transactivation of HER2 by PRL contributes to anti-HER2 therapy resistance we examined the potential of combining Herceptin with a PRLR antagonist, G129R, which inhibits PRL-induced signaling, as a novel therapeutic strategy. Two PRL-expressing human breast cancer cell lines (T-47D and BT-474) that overexpress PRLR and HER2 to different degrees were chosen for this study. The phosphorylation status of HER2 and activation of MAPK, signal transducers and activators of transcription (STAT), as well as phosphatidylinositol-3 kinase (PI3K) signaling cascades were examined in response to Herceptin, G129R or a combination of the two in either the absence or presence of exogenous PRL. As a single agent, Herceptin was more effective than G129R at inhibiting AKT phosphorylation; whereas, G129R was superior at blocking STAT3 and STAT5 activation. G129R was also able to directly inhibit the HER2 phosphorylation. The combination of Herceptin and G129R had an additive inhibitory effect on HER2 and MAPK phosphorylation, confirming that the MAPK signaling is a converging pathway shared by both HER2 and the PRLR. Combination of Herceptin and G129R also additively inhibited cell proliferation in vitro and in vivo as measured by inhibition of the growth of T-47D and BT-474 xenografts in athymic nude mice. We conclude that an anti-HER2 and anti-PRLR regimen may offer a new approach to treat HER2-overexpressing breast cancers.

Improving the pharmacokinetics/pharmacodynamics of prolactin, GH, and their antagonists by fusion to a synthetic albumin-binding peptide

“…Carcinogen-treated and syngeneic murine models of mammary carcinoma , Beck et al 2003, Tomblyn et al 2005, xenografts of established breast cancer cell lines in athymic nude mice , and clonogenic survival assays of breast cancer cell lines and clinical tumors (Howell et al 2008) predict that hPRL-G129R will have clinical utility. In vitro studies also suggest that hPRL-G129R will enhance the effectiveness of conventional breast cancer chemotherapies (Chen et al 1999, Howell et al 2008, Scotti et al 2008.…”

Combination therapy using three novel prolactin receptor antagonist-based fusion proteins effectively inhibits tumor recurrence and metastasis in HER2/neu transgenic mice

“…The use of dasatinib, a small molecule inhibitor of src has proven beneficial to HER2-positive breast cancer when used in combination with trastuzumab (33). Furthermore, use of trastuzumab in combination with the PRLR antagonist, G129R, has also been shown to have an additive inhibitory effect on HER2 and MAPK phosphorylation, and the proliferation of T-47D and BT-474 breast cancer cells both in vitro and in vivo (4). Finally, attacking multiple hallmarks of cancer simultaneously using various cancer therapeutics is under investigation.…”

“…Studies have shown that PRL is expressed in the epithelium of human breast cancers and that PRL receptor (PRLR) levels are higher in a majority of benign and malignant mammary tumors than the surrounding normal tissue (1,2). In addition, PRL and PRLR appear to have a role in both hormone responsive and hormone-independent breast cancers (3)(4)(5). For example, PRL has been shown to interact synergistically with estrogen and progesterone to promote cancerous growth; the receptors for these ligands are often co-expressed in primary breast cancers (3).…”

“…For example, PRL has been shown to interact synergistically with estrogen and progesterone to promote cancerous growth; the receptors for these ligands are often co-expressed in primary breast cancers (3). Furthermore, PRL is able to transactivate HER2 through the activation of PRLR (4,5). In accordance, anti-proliferative effects of tamoxifen (6) or trastuzumab (7) were enhanced when they were combined with a PRLR antagonist, G129R.…”

Autocrine prolactin: an emerging market for homegrown (prolactin) despite the imports

“…Inhibition of the prolactin receptor using G129R (prolactin receptor antagonist) inhibits ErbB2 phosphorylation, suggesting an opportunity for combination therapy. Consistent with this possibility, combination of Herceptin (anti-HER2 therapeutic antibody) and G129R has an additive effect in inhibiting both MAPK activation and growth of BT474 breast cancer cells in cell culture and in xenograft mouse models (Scotti et al 2008). Further studies are needed to explore this novel therapeutic strategy for patients with HER-positive breast cancers that also express autocrine prolactin.…”