Mark E. Tometsko

A homologue of the TNF receptor and its ligand enhance T-cell growth and dendritic-cell function

Dendritic cells are rare haematopoietic cells that reside in a number of organs and tissues. By capturing, processing and presenting antigens to T cells, dendritic cells are essential for immune surveillance and the regulation of specific immunity. Several members of the tumour necrosis factor receptor (TNFR) superfamily are integral to the regulation of the immune response. These structurally related proteins modulate cellular functions ranging from proliferation and differentiation to inflammation and cell survival or death. The functional activity of dendritic cells is greatly increased by signalling through the TNFR family member CD40 (refs 7, 8). Here we report the characterization of RANK (for receptor activator of NF-κB), a new member of the TNFR family derived from dendritic cells, and the isolation of a RANK ligand (RANKL) by direct expression screening. RANKL augments the ability of dendritic cells to stimulate naive T-cell proliferation in a mixed lymphocyte reaction, and increases the survival of RANK+T cells generated with interleukin-4 and transforming growth factor (TGF)-β. Thus RANK and RANKL seem to be important regulators of interactions between T cells and dendritic cells.

RANK Induces Epithelial–Mesenchymal Transition and Stemness in Human Mammary Epithelial Cells and Promotes Tumorigenesis and Metastasis

Paracrine signaling through receptor activator of NF-κB (RANK) pathway mediates the expansion of mammary epithelia that occurs during pregnancy, and activation of RANK pathway promotes mammary tumorigenesis in mice. In this study we extend these previous data to human cells and show that the RANK pathway promotes the development of mammary stem cells and breast cancer. Overexpression of RANK (FL-RANK) in a panel of tumoral and normal human mammary cells induces the expression of breast cancer stem and basal/stem cell markers. High levels of RANK in untransformed MCF10A cells induce changes associated with both stemness and transformation, including mammary gland reconstitution, epithelial-mesenchymal transition (EMT), increased migration, and anchorage-independent growth. In addition, spheroids of RANK overexpressing MCF10A cells display disrupted acinar formation, impair growth arrest and polarization, and luminal filling. RANK overexpression in tumor cells with nonfunctional BRCA1 enhances invasiveness in acinar cultures and increases tumorigenesis and metastasis in immunodeficient mice. High levels of RANK were found in human primary breast adenocarcinomas that lack expression of the hormone receptors, estrogen and progesterone, and in tumors with high pathologic grade and proliferation index; high RANK/RANKL expression was significantly associated with metastatic tumors. Together, our findings show that RANK promotes tumor initiation, progression, and metastasis in human mammary epithelial cells by increasing the population of CD44(+)CD24(-) cells, inducing stemness and EMT. These results suggest that RANK expression in primary breast cancer associates with poor prognosis.

RANK expression on breast cancer cells promotes skeletal metastasis

RANK ligand (RANKL), acting through its cognate receptor RANK, is a key factor for bone remodeling and metastasis by regulating the differentiation, survival and activation of osteoclasts. RANKL is also crucial for the development of mouse mammary glands during pregnancy and has been recently linked to the etiology of breast cancer via its direct activity on RANK-expressing normal or transformed breast epithelial cells, leading to increased mitogenesis, enhanced regenerative potential of mammary stem cells, and increased invasion and migration. We demonstrate that higher RANK expression in MDA-MB-231 breast cancer cells (MDA-231-RANK cells) is sufficient to confer a significantly greater metastatic growth rate in the bone compared with MDA-MB-231 cells which do not express high levels of RANK. Blockade of osteoclastic bone resorption, achieved with treatment by either RANKL inhibition or zoledronic acid, did reduce skeletal tumor progression of MDA-231-RANK cells suggesting that the vicious cycle contributes to metastatic growth. However, RANKL inhibition reduced skeletal growth of MDA-231-RANK tumors to a significantly greater extent than zoledronic acid, indicating that skeletal growth of RANK-positive tumors is also driven by direct RANKL effects. RANKL stimulated the expression of multiple genes associated with cell invasive behavior, including several matrix metalloproteinases and other genes previously defined as part of a bone metastasis gene signature. These data indicate that RANKL provokes breast cancer bone metastases via two distinct, but potentially overlapping mechanisms: stimulation of tumor-associated osteoclastogenesis and stimulation of RANK-expressing tumor cells.

SLC46A3 Is Required to Transport Catabolites of Noncleavable Antibody Maytansine Conjugates from the Lysosome to the Cytoplasm

Antibody-drug conjugates (ADC) target cytotoxic drugs to antigen-positive cells for treating cancer. After internalization, ADCs with noncleavable linkers are catabolized to amino acid-linker-warheads within the lysosome, which then enter the cytoplasm by an unknown mechanism. We hypothesized that a lysosomal transporter was responsible for delivering noncleavable ADC catabolites into the cytoplasm. To identify candidate transporters, we performed a phenotypic shRNA screen with an anti-CD70 maytansine-based ADC. This screen revealed the lysosomal membrane protein SLC46A3, the genetic attenuation of which inhibited the potency of multiple noncleavable antibody-maytansine ADCs, including ado-trastuzumab emtansine. In contrast, the potencies of noncleavable ADCs carrying the structurally distinct monomethyl auristatin F were unaffected by SLC46A3 attenuation. Structure-activity experiments suggested that maytansine is a substrate for SLC46A3. Notably, SLC46A3 silencing led to relative increases in catabolite concentrations in the lysosome. Taken together, our results establish SLC46A3 as a direct transporter of maytansine-based catabolites from the lysosome to the cytoplasm, prompting further investigation of SLC46A3 as a predictive response marker in breast cancer specimens.

Intracellular Catabolism of an Antibody Drug Conjugate with a Noncleavable Linker.

Antibody drug conjugates are emerging as a powerful class of antitumor agents with efficacy across a range of cancers; therefore, understanding the disposition of this class of therapeutic is crucial. Reported here is a method of enriching a specific organelle (lysosome) to understand the catabolism of an anti-CD70 Ab-MCC-DM1, an antibody drug conjugate with a noncleavable linker. With such techniques a higher degree of concentration-activity relationship can be established for in vitro cell lines; this can aid in understanding the resultant catabolite concentrations necessary to exert activity.

RANKL Inhibition Blocks Osteolytic Lesions and Reduces Skeletal Tumor Burden in Models of Non–Small-Cell Lung Cancer Bone Metastases

Introduction: Bone metastasis is a serious complication in patients with lung cancer, occurring in up to 40% of patients. Tumor cell–mediated osteolysis occurs ultimately through induction of RANK ligand (RANKL) within the bone stroma although this hypothesis has not been tested extensively in the setting of non–small-cell lung cancer (NSCLC). By using two novel NSCLC bone metastasis mouse models, we examined the effects of RANKL inhibition on osteolysis and tumor progression. Methods: We treated mice bearing skeletal NSCLC tumors with osteoprotegerin-Fc (OPG-Fc) to assess whether osteoclast inhibition through RANKL inhibition would affect bone metastases at early or late stages of bone colonization. Progression of skeletal tumor was determined by radiography, longitudinal bioluminescent imaging, and histological analyses. Results: OPG-Fc reduced development and progression of radiographically evident osteolytic lesions and also significantly reduced skeletal tumor progression in both NSCLC bone metastasis models. In the H1299 human NSCLC bone metastasis model, OPG-Fc plus docetaxel in combination resulted in significantly greater inhibition of skeletal tumor growth compared with either single agent alone. The observed ability of RANKL inhibition to reduce NSCLC osteolytic bone destruction or skeletal tumor burden was associated with decreases in tumor-associated osteoclasts. Conclusions: These results demonstrate that RANKL is required for the development of tumor-induced osteolytic bone destruction caused by NSCLC cells in vivo. RANKL inhibition also reduced skeletal tumor burden, presumably through the indirect mechanism of blocking tumor-induced osteoclastogenesis and resultant production of growth factors and calcium from the bone microenvironment. RANKL inhibition also provided an additive benefit to docetaxel treatment by augmenting the reduction of tumor burden.

RANK and RANK ligand expression in primary human osteosarcoma

Receptor activator of nuclear factor kappa-B ligand (RANKL) is an essential mediator of osteoclast formation, function and survival. In patients with solid tumor metastasis to the bone, targeting the bone microenvironment by inhibition of RANKL using denosumab, a fully human monoclonal antibody (mAb) specific to RANKL, has been demonstrated to prevent tumor-induced osteolysis and subsequent skeletal complications. Recently, a prominent functional role for the RANKL pathway has emerged in the primary bone tumor giant cell tumor of bone (GCTB). Expression of both RANKL and RANK is extremely high in GCTB tumors and denosumab treatment was associated with tumor regression and reduced tumor-associated bone lysis in GCTB patients. In order to address the potential role of the RANKL pathway in another primary bone tumor, this study assessed human RANKL and RANK expression in human primary osteosarcoma (OS) using specific mAbs, validated and optimized for immunohistochemistry (IHC) or flow cytometry. Our results demonstrate RANKL expression was observed in the tumor element in 68% of human OS using IHC. However, the staining intensity was relatively low and only 37% (29/79) of samples exhibited≥10% RANKL positive tumor cells. RANK expression was not observed in OS tumor cells. In contrast, RANK expression was clearly observed in other cells within OS samples, including the myeloid osteoclast precursor compartment, osteoclasts and in giant osteoclast cells. The intensity and frequency of RANKL and RANK staining in OS samples were substantially less than that observed in GCTB samples. The observation that RANKL is expressed in OS cells themselves suggests that these tumors may mediate an osteoclastic response, and anti-RANKL therapy may potentially be protective against bone pathologies in OS. However, the absence of RANK expression in primary human OS cells suggests that any autocrine RANKL/RANK signaling in human OS tumor cells is not operative, and anti-RANKL therapy would not directly affect the tumor.

Altering Antibody–Drug Conjugate Binding to the Neonatal Fc Receptor Impacts Efficacy and Tolerability

Antibody-drug conjugates (ADC) rely on the target-binding specificity of an antibody to selectively deliver potent drugs to cancer cells. IgG antibody half-life is regulated by neonatal Fc receptor (FcRn) binding. Histidine 435 of human IgG was mutated to alanine (H435A) to explore the effect of FcRn binding on the pharmacokinetics, efficacy, and tolerability of two separate maytansine-based ADC pairs with noncleavable linkers, (c-DM1 and c-H435A-DM1) and (7v-Cys-may and 7v-H435A-Cys-may). The in vitro cell-killing potency of each pair of ADCs was similar, demonstrating that H435A showed no measurable impact on ADC bioactivity. The H435A mutant antibodies showed no detectable binding to human or mouse FcRn in vitro, whereas their counterpart wild-type IgG ADCs were found to bind to FcRn at pH = 6.0. In xenograft bearing SCID mice expressing mouse FcRn, the AUC of 7v-Cys-may was 1.6-fold higher than that of 7v-H435A-may, yet the observed efficacy was similar. More severe thrombocytopenia was observed with 7v-H435A-Cys-may as compared to 7v-Cys-may at multiple dose levels. The AUC of c-DM1 was approximately 3-fold higher than that of c-H435A-DM1 in 786-0 xenograft bearing SCID mice, which led to a 3-fold difference in efficacy by dose. Murine FcRn knockout, human FcRn transgenic line 32 SCID animals bearing 786-0 xenografts showed an amplified exposure difference between c-DM1 and c-H435A-DM1 as compared to murine FcRn expressing SCID mice, leading to a 10-fold higher dose required for efficacy despite a 6-fold higher AUC of the c-H435A-DM1. The accelerated clearance observed for the noncleavable maytansine ADCs with the H435A FcRn mutation led to reduced efficacy at equivalent doses and exacerbation of clinical pathology parameters (decreased tolerability) at equivalent doses. The results show that reduced ADC clearance mediated by FcRn modulation can improve therapeutic index.

P3-01-14: RANK and RANK Ligand (RANKL) Expression in Invasive Breast Carcinoma and Human Breast Cancer Cell Lines.

Purpose: RANK and its ligand (RANKL), key factors for bone remodeling and metastasis, are crucial for the development of mouse mammary gland during pregnancy. RANKL functions as a major paracrine effector of the mitogenic action of progesterone in mouse mammary epithelium and has a role in ovarian hormone-dependent expansion and regenerative potential of mammary stem cells (MaSC). RANKL inhibition has been shown to reduce mammary tumor formation and pulmonary metastases in mouse models. Many published expression analyses of RANK and RANKL have been performed using immunohistochemistry (IHC) without documented validation of antibody specificity. This study assessed the expression of human RANK and RANKL in human invasive breast carcinoma (IBC) and human breast cancer cell lines using specific, monoclonal antibodies validated and optimized for IHC or flow cytometry. Methods: RANK and RANKL expression was analyzed in a panel of human breast cancer cell lines representing luminal or basal breast subtypes using qPCR, flow cytometry and surface receptor quantitation. Antibodies against human RANK (N-1H8, N-2B10; Amgen) and human RANKL (M366, AMG161; Amgen) were used for flow cytometry, surface receptor quantitation or IHC staining. For human IBC, the intensity of IHC staining was scored on a semiquantitative scale (0=absent, 1=weak, 2=moderate, 3=intense). Incidence was scored as a positive IHC signal (any intensity). In vitro responses of cell lines to RANKL were also tested. Results: The specificity of the antibodies was substantiated by concordant signals observed using multiple independent analyses, including IHC, flow cytometry and Western blots of positive and negative control cells and xenograft samples. Analysis of primary human IBC using IHC demonstrated that 25/114 (22%) IBC samples expressed RANK and 18/97 IBC (19%) expressed RANKL protein within the tumor epithelium. RANK protein was observed in monocytic cells infiltrating the tumor in 87/114 (76%) and within normal mammary epithelium adjacent to tumors in 35/79 (44%) of samples. RANKL was observed in infiltrating monocytic cells within the tumor in 60/115 (52%) and within normal mammary epithelium adjacent to tumors in 15/68 (22%) of samples. Both mRNA and RANK surface protein were detected in multiple breast cancer cell lines, including basal and luminal subtypes. Functional RANK expression on cell lines was confirmed in vitro by the observation of RANKL-dependent increases in mRNAs (e.g. MMP-9, IL-6 or IL-8) or proteins in conditioned media (e.g. IL-6, IL-8), despite the relatively low surface expression of RANK observed (range = 1240–9120 sites/cell). Conclusion: RANK and RANKL expression was observed in the epithelial carcinoma element in human IBC using IHC. RANK and RANKL expression was also observed in normal mammary epithelium and monocytic cells adjacent to breast tumors. Functional RANK expression was observed in human breast cancer cell lines, including both basal and luminal subtypes. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-01-14.

Receptor activator of NF-kB (RANK) and RANK ligand protein expression in invasive ductal carcinoma.

Abstract #2057 Purpose: Bone metastases are commonly observed in patients with advanced breast cancer. Tumor cells interact with the bone microenvironment to induce osteoclastogenesis via local bone stromal expression of receptor activator of NF-kB ligand (RANKL), leading to bone destruction and release of growth factors. In addition to its critical role in tumor-induced osteolysis, RANKL has been demonstrated to enhance the invasive behavior of epithelial tumor cells that express RANK, and RANK over-expression in transgenic mice using the breast-specific MMTV promoter results in increased mammary carcinoma. This study assessed the expression of human RANK and its ligand (RANKL) in invasive ductal carcinoma (IDC).
 Methods: We studied a total of 57 IDC specimens. Antibodies against human RANK (AF683) and human RANKL (M366; Amgen) were used for immunohistochemistry (IHC) cell staining along with an isotype control. The specificity of the 2 antibodies was substantiated by IHC, flow cytometry and Western blot analysis of positive and negative control cells. In addition, for RANK, mass spectrometry/protein sequencing of immunoprecipitated proteins was performed. The intensity of IHC staining was scored on a semiquantitative scale (1=weak, 2=moderate, 3=intense) or a complex scale (sum of percentages of stained tumor cells x staining intensity (0-3)).
 Results: Using a complex score with a threshold of 10, 20/57 IDC (35%) expressed minimal level of RANK (range 0 to Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2057.