CXCR2: A Novel Mediator of Mammary Tumor Bone Metastasis.

Most breast cancer patients die due to bone metastasis. Although metastasis accounts for 5% of the breast cancer cases, it is responsible for most of the deaths. Sometimes even before the detection of a primary tumor, most of the patients have bone and lymph node metastasis. Moreover, at the time of death, breast cancer patients have the bulk of the tumor burden in their bones. Therapy options are available for the treatment of primary tumors, but there are minimal options for treating breast cancer patients who have bone metastasis. C-X-C motif chemokine receptor type 2 (CXCR2) receptor-mediated signaling has been shown to play a critical role during bone-related inflammations and its ligands C-X-C motif chemokine ligand 6 (CXCL6) and 8 (CXCL8) aid in the resorption of bone during bone metastasis. In this study, we tested the hypothesis that CXCR2 contributes to mammary tumor-induced osteolysis and bone metastasis. In the present study, we examined the role of both tumor cell-derived and host-derived CXCR2 in influencing mammary tumor cell bone metastasis. For understanding the role of tumor cell-derived CXCR2, we utilized Cl66 CXCR2 knockdown (Cl66-shCXCR2) and Cl66-Control cells (Cl66-Control) and observed a significant decrease in tumor growth and tumor-induced osteolysis in Cl66-shCXCR2 cells in comparison with the Cl66-Control cells. Next, for understanding the role of host-derived CXCR2, we utilized mice with genomic knockdown of CXCR2 (Cxcr2-/-) and injected Cl66-Luciferase (Cl66-Luc) or 4T1-Luciferase (4T1-Luc) cells. We observed decreased bone destruction and metastasis in the bone of Cxcr2-/- mice. Our data suggest the importance of both tumor cell- and host-derived CXCR2 signaling in the bone metastasis of breast cancer cells.

Anti-ACVR1 antibodies exacerbate heterotopic ossification in fibrodysplasia ossificans progressiva (FOP) by activating FOP-mutant ACVR1.

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder whose most debilitating pathology is progressive and cumulative heterotopic ossification (HO) of skeletal muscles, ligaments, tendons, and fascia. FOP is caused by mutations in the type I BMP receptor gene ACVR1, which enable ACVR1 to utilize its natural antagonist, activin A, as an agonistic ligand. The physiological relevance of this property is underscored by the fact that HO in FOP is exquisitely dependent on activation of FOP-mutant ACVR1 by activin A, an effect countered by inhibition of anti-activin A via monoclonal antibody treatment. Hence, we surmised that anti-ACVR1 antibodies that block activation of ACVR1 by ligands should also inhibit HO in FOP and provide an additional therapeutic option for this condition. Therefore, we generated anti-ACVR1 monoclonal antibodies that block ACVR1's activation by its ligands. Surprisingly, in vivo, these anti-ACVR1 antibodies stimulated HO and activated signaling of FOP-mutant ACVR1. This property was restricted to FOP-mutant ACVR1 and resulted from anti-ACVR1 antibody-mediated dimerization of ACVR1. Conversely, wild-type ACVR1 was inhibited by anti-ACVR1 antibodies. These results uncover an additional property of FOP-mutant ACVR1 and indicate that anti-ACVR1 antibodies should not be considered as therapeutics for FOP.

Role of chemokine receptor CXCR2 expression in mammary tumor growth, angiogenesis and metastasis.

BACKGROUND: Chemokines and their receptors have long been known to regulate metastasis in various cancers. Previous studies have shown that CXCR2 expression is upregulated in malignant breast cancer tissues but not in benign ductal epithelial samples. The functional role of CXCR2 in the metastatic phenotype of breast cancer still remains unclear. We hypothesize that the chemokine receptor, CXCR2, mediates tumor cell invasion and migration and promotes metastasis in breast cancer. The objective of this study is to investigate the potential role of CXCR2 in the metastatic phenotype of mouse mammary tumor cells. MATERIALS AND METHODS: We evaluated the functional role of CXCR2 in breast cancer by stably downregulating the expression of CXCR2 in metastatic mammary tumor cell lines Cl66 and 4T1, using short hairpin RNA (shRNA). The effects of CXCR2 downregulation on tumor growth, invasion and metastatic potential were analyzed in vitro and in vivo. RESULTS: We demonstrated knock down of CXCR2 in Cl66 and 4T1 cells (Cl66-shCXCR2 and 4T1-shCXCR2) cells by reverse transcriptase polymerase chain reaction (RT-PCR) at the transcriptional level and by immunohistochemistry at the protein level. We did not observe a significant difference in in vitro cell proliferation between vector control and CXCR2 knock-down Cl66 or 4T1 cells. Next, we examined the invasive potential of Cl66-shCXCR2 cells by in vitro Matrigel invasion assay. We observed a significantly lower number (52 ± 5) of Cl66-shCXCR2 cells invading through Matrigel compared to control cells (Cl66-control) (182 ± 3) (P < 0.05). We analyzed the in vivo metastatic potential of Cl66-shCXCR2 using a spontaneous metastasis model by orthotopically implanting cells into the mammary fat pad of female BALB/c mice. Animals were sacrificed 12 weeks post tumor implantation and tissue samples were analyzed for metastatic nodules. CXCR2 downregulation significantly inhibited tumor cell metastasis. All the mice (n = 10) implanted with control Cl66 cells spontaneously developed lung metastasis, whereas a significantly lower number of mice (40%) implanted with Cl66-shCXCR2 cells exhibited lung metastases. CONCLUSIONS: Together, these results suggest that CXCR2 may play a critical role in breast cancer invasion and metastasis.

Small interfering RNA-mediated CXCR1 or CXCR2 knock-down inhibits melanoma tumor growth and invasion.

CXCR1 and CXCR2 are receptors for CXCL-8 and are differentially expressed on melanoma and endothelial cells. In this study, we determined the functional role of these receptors in melanoma progression. We stably knock-down the expression of CXCR1 and/or CXCR2 in A375-SM (SM; high metastatic) human melanoma cells by short-hairpin RNA transfection. Cell proliferation, migration, invasion, ERK phosphorlyation and cytoskeletal rearrangements were carried out in vitro. In vivo growth was evaluated using murine subcutaneous xenograft model. Our data demonstrate that knock-down of CXCR1 and/or CXCR2 expression, inhibited melanoma cell proliferation, survival, migration and invasive potential in vitro. Moreover, we also observed inhibition of ERK phosphorylation and cytoskeltal rearrangement in SM-shCXCR1, SM-shCXCR2 and SM-shCXCR1/2 cells. Furthermore, when SM-shCXCR1 or SM-shCXCR2 cells implanted in nude mice, tumor growth, proliferation and microvessel density was significantly inhibited as compared to SM-control cells. In addition, we observed a significant increase in melanoma cell apoptosis in SM-shCXCR1 and SM-shCXCR2 tumors compared to SM-control tumors. Together, these data demonstrate that CXCR1 and CXCR2 expression play a critical role in human melanoma tumor progression and, functional blockade of CXCR1 and CXCR2 could be potentially used for future therapeutic intervention in malignant melanoma.

Small-molecule antagonists for CXCR2 and CXCR1 inhibit human melanoma growth by decreasing tumor cell proliferation, survival, and angiogenesis.

PURPOSE: Melanoma, the most aggressive form of skin cancer, accounts for 75% of all skin cancer-related deaths and current therapeutic strategies are not effective in advanced disease. In the current study, we have investigated the efficacy of orally active small-molecule antagonist targeting CXCR2/CXCR1. EXPERIMENTAL DESIGN: Human A375SM melanoma cells were treated with SCH-479833 or SCH-527123, and their effect on proliferation, motility, and invasion was evaluated in vitro. We examined the downstream signaling events in the cells following treatment with antagonists. For in vivo studies, A375SM cells were implanted subcutaneously into athymic nude mice followed by administration of SCH-479833, SCH-527123, or hydroxypropyl-beta-cyclodextrin (20%) orally for 21 days and their effect on tumor growth and angiogenesis was evaluated. RESULTS: Our data show that SCH-479833 or SCH-527123 inhibited the melanoma cell proliferation, chemotaxis, and invasive potential in vitro. Treatment of melanoma cells with SCH-479833 or SCH-527123 also inhibited tumor growth. Histologic and histochemical analyses showed significant (P < 0.05) decreases in tumor cell proliferation and microvessel density in tumors. Moreover, we observed a significant increase in melanoma cell apoptosis in SCH-479833- or SCH-527123-treated animals compared with controls. CONCLUSION: Together, these studies show that selectively targeting CXCR2/CXCR1 with orally active small-molecule inhibitors is a promising therapeutic approach for inhibiting melanoma growth and angiogenesis.

Tumor-stromal interactions in bone metastasis.

The metastasis of tumor cells to distant organs is the primary cause of cancer-related mortality in most cancers. The interaction of tumor cells with local stroma at the metastatic site plays a critical role in metastatic dissemination and the establishment of metastases. These tumor-stromal interactions regulate several important steps including degradation of extracellular matrix, release of sequestered growth factors, and expression of chemokines, cytokines, and receptors on tumor cells and the interacting stromal cells. Breast, prostate, and lung cancers preferentially metastasize to bone. Tumor cell interactions with the bone microenvironment initiate a series of complex cellular interactions that promotes establishment of osteoclastic and/or osteoblastic metastasis. Understanding the interactions between tumor cells and the stroma is important to identify molecular targets to develop novel therapies aimed at reducing metastasis formation. In this article, we review the important mechanisms of tumor-stromal interaction in the development of bone metastasis.

Activin A does not drive post-traumatic heterotopic ossification.

Heterotopic ossification (HO), the formation of ectopic bone in soft tissues, has been extensively studied in its two primary forms: post-traumatic HO (tHO) typically found in patients who have experienced musculoskeletal or neurogenic injury and in fibrodysplasia ossificans progressiva (FOP), where it is genetically driven. Given that in both diseases HO arises via endochondral ossification, the molecular mechanisms behind both diseases have been postulated to be manifestations of similar pathways including those activated by BMP/TGFß superfamily ligands. A significant step towards understanding the molecular mechanism by which HO arises in FOP was the discovery that FOP causing ACVR1 variants trigger HO in response to activin A, a ligand that does not activate signaling from wild type ACVR1, and that is not inherently osteogenic in wild type settings. The physiological significance of this finding was demonstrated by showing that activin A neutralizing antibodies stop HO in two different genetically accurate mouse models of FOP. In order to explore the role of activin A in tHO, we performed single cell RNA sequencing and compared the expression of activin A as well as other BMP pathway genes in tHO and FOP HO. We show that activin A is expressed in response to injury in both settings, but by different types of cells. Given that wild type ACVR1 does not transduce signal when engaged by activin A, we hypothesized that inhibition of activin A will not block tHO. Nonetheless, as activin A was expressed in tHO lesions, we tested its inhibition and compared it with inhibition of BMPs. We show here that anti-activin A does not block tHO, whereas agents such as antibodies that neutralize ACVR1 or ALK3-Fc (which blocks osteogenic BMPs) are beneficial, though not completely curative. These results demonstrate that inhibition of activin A should not be considered as a therapeutic strategy for ameliorating tHO.

Activin A forms a non-signaling complex with ACVR1 and type II Activin/BMP receptors via its finger 2 tip loop.

Activin A functions in BMP signaling in two ways: it either engages ACVR1B to activate Smad2/3 signaling or binds ACVR1 to form a non-signaling complex (NSC). Although the former property has been studied extensively, the roles of the NSC remain unexplored. The genetic disorder fibrodysplasia ossificans progressiva (FOP) provides a unique window into ACVR1/Activin A signaling because in that disease Activin can either signal through FOP-mutant ACVR1 or form NSCs with wild-type ACVR1. To explore the role of the NSC, we generated 'agonist-only' Activin A muteins that activate ACVR1B but cannot form the NSC with ACVR1. Using one of these muteins, we demonstrate that failure to form the NSC in FOP results in more severe disease pathology. These results provide the first evidence for a biological role for the NSC in vivo and pave the way for further exploration of the NSC's physiological role in corresponding knock-in mice.

Functional biology of the Steel syndrome founder allele and evidence for clan genomics derivation of COL27A1 pathogenic alleles worldwide.

Previously we reported the identification of a homozygous COL27A1 (c.2089G>C; p.Gly697Arg) missense variant and proposed it as a founder allele in Puerto Rico segregating with Steel syndrome (STLS, MIM #615155); a rare osteochondrodysplasia characterized by short stature, congenital bilateral hip dysplasia, carpal coalitions, and scoliosis. We now report segregation of this variant in five probands from the initial clinical report defining the syndrome and an additional family of Puerto Rican descent with multiple affected adult individuals. We modeled the orthologous variant in murine Col27a1 and found it recapitulates some of the major Steel syndrome associated skeletal features including reduced body length, scoliosis, and a more rounded skull shape. Characterization of the in vivo murine model shows abnormal collagen deposition in the extracellular matrix and disorganization of the proliferative zone of the growth plate. We report additional COL27A1 pathogenic variant alleles identified in unrelated consanguineous Turkish kindreds suggesting Clan Genomics and identity-by-descent homozygosity contributing to disease in this population. The hypothesis that carrier states for this autosomal recessive osteochondrodysplasia may contribute to common complex traits is further explored in a large clinical population cohort. Our findings augment our understanding of COL27A1 biology and its role in skeletal development; and expand the functional allelic architecture in this gene underlying both rare and common disease phenotypes.

Transforming growth factor-beta signaling at the tumor-bone interface promotes mammary tumor growth and osteoclast activation.

Understanding the cellular and molecular changes in the bone microenvironment is important for developing novel therapeutics to control breast cancer bone metastasis. Although the underlying mechanism(s) of bone metastasis has been the focus of intense investigation, relatively little is known about complex molecular interactions between malignant cells and bone stroma. Using a murine syngeneic model that mimics osteolytic changes associated with human breast cancer, we examined the role of tumor-bone interaction in tumor-induced osteolysis and malignant growth in the bone microenvironment. We identified transforming growth factor-beta receptor 1 (TGF-betaRI) as a commonly upregulated gene at the tumor-bone (TB) interface. Moreover, TGF-betaRI expression and activation, analyzed by nuclear localization of phospho-Smad2, was higher in tumor cells and osteoclasts at the TB interface as compared to the tumor-alone area. Furthermore, attenuation of TGF-beta activity by neutralizing antibody to TGF-beta or TGF-betaRI kinase inhibitor reduced mammary tumor-induced osteolysis, TGF-betaRI expression and its activation. In addition, we demonstrate a potential role of TGF-beta as an important modifier of receptor activator of NF-kappaB ligand (RANKL)-dependent osteoclast activation and osteolysis. Together, these studies demonstrate that inhibition of TGF-betaRI signaling at the TB interface will be a therapeutic target in the treatment of breast cancer-induced osteolysis.