Molecular pathogenesis of bone metastases in breast cancer: Proven and emerging therapeutic targets

Assessing the causal relationship between plasma proteins and osteoporosis: novel insights into pathological mechanisms and therapeutic implications

Identifying dysregulated plasma proteins in osteoporosis (OP) progression offers insights into prevention and treatment. This study found 8 such proteins associated with OP, suggesting them as therapy targets. This discovery may cut drug development costs and improve personalized treatments.

PURPOSE

This study aims to identify potential therapeutic targets for OP using summary data-based Mendelian randomization (SMR) and colocalization analysis methods. Furthermore, we seek to explore the biological significance and pharmacological value of these drug targets.

METHODS

To identify potential therapeutic targets for OP, we conducted SMR and colocalization analysis. Plasma protein (pQTL, exposure) data were sourced from the study by Ferkingstad et al. (n = 35,559). Summary statistics for bone mineral density (BMD, outcome) were obtained from the GWAS Catalog (n = 56,284). Additionally, we utilized enrichment analysis, protein-protein interaction (PPI) network analysis, drug prediction, and molecular docking to further analyze the biological significance and pharmacological value of these drug targets.

RESULTS

In the SMR analysis, while 20 proteins showed significance, only 8 potential drug targets (GCKR, ERBB3, CFHR1, GPN1, SDF2, VTN, BET1L, and SERPING1) received support from colocalization (PP.H4 > 0.8). These proteins are closely associated with immune function in terms of biological significance. Molecular docking also demonstrated favorable binding of drugs to proteins, consistent with existing structural data, further substantiating the pharmacological value of these targets.

CONCLUSIONS

The study identified 8 potential drug targets for OP. These prospective targets are believed to have a higher chance of success in clinical trials, thus aiding in prioritizing OP drug development and reducing development costs.

A nanomedicine based on stoichiometric coordination of camptothecin and organoplatinum (II) for synergistic antitumor therapy

Precise combination therapy, involving multiple chemotherapeutics with pharmacologically synergistic antitumor effects, is a promising approach to address the challenge of monotherapy with insufficient activity towards their targets of interest. We employed Pt←pyridine coordination-driven assembly to construct a stoichiometric coordination complex of camptothecin and organoplatinum (II) (Pt-CPT). The Pt-CPT complex exhibited a remarkable synergistic effect toward several tumor cell lines, which is equal to the optimal synergistic effect of (PEt3)2Pt(OTf)2 (Pt) and CPT mixture at various ratios. An amphiphilic polymer with H2O2-responsiveness and glutathione (GSH)-depleting ability (PO) was used to encapsulate Pt-CPT complex to enable the nanomedicine (Pt-CPT@PO) with prolonged blood circulation and elevated tumor accumulation. The Pt-CPT@PO nanomedicine exhibited remarkable synergistic antitumor efficacy and antimetastatic effect on a mice orthotopic breast tumor model. This work demonstrated the potential of stoichiometric coordination-driven assembly of organic therapeutics with metal-based drugs in developing advanced nanomedicine with optimal synergistic antitumor activity. STATEMENT OF SIGNIFICANCE: : In this study, for the first time, we employed Pt←pyridine coordination-driven assembly to construct a stoichiometric coordination complex of camptothecin and organoplatinum (II) (Pt-CPT), with an optimal synergistic effect at various ratios. Then it was encapsulated into an amphiphilic polymer with H2O2-responsiveness and glutathione (GSH)-depleting ability (PO) to enable the nanomedicine (Pt-CPT@PO) with prolonged blood circulation and elevated tumor accumulation. The Pt-CPT@PO nanomedicine exhibited remarkable synergistic antitumor efficacy and antimetastatic effect on a mice orthotopic breast tumor model.

Exosomal miR-19a and IBSP cooperate to induce osteolytic bone metastasis of estrogen receptor-positive breast cancer

Bone metastasis is an incurable complication of breast cancer. In advanced stages, patients with estrogen-positive tumors experience a significantly higher incidence of bone metastasis (>87%) compared to estrogen-negative patients (<56%). To understand the mechanism of this bone-tropism of ER+ tumor, and to identify liquid biopsy biomarkers for patients with high risk of bone metastasis, the secreted extracellular vesicles and cytokines from bone-tropic breast cancer cells are examined in this study. Both exosomal miR-19a and Integrin-Binding Sialoprotein (IBSP) are found to be significantly upregulated and secreted from bone-tropic ER+ breast cancer cells, increasing their levels in the circulation of patients. IBSP is found to attract osteoclast cells and create an osteoclast-enriched environment in the bone, assisting the delivery of exosomal miR-19a to osteoclast to induce osteoclastogenesis. Our findings reveal a mechanism by which ER+ breast cancer cells create a microenvironment favorable for colonization in the bone. These two secreted factors can also serve as effective biomarkers for ER+ breast cancer to predict their risks of bone metastasis. Furthermore, our screening of a natural compound library identifies chlorogenic acid as a potent inhibitor for IBSP-receptor binding to suppress bone metastasis of ER+ tumor, suggesting its preventive use for bone recurrence in ER+ patients.

Real-life prognosis of 5041 bone-only metastatic breast cancer patients in the multicenter national observational ESME program

BACKGROUND

Bone-only (BO) metastatic breast cancer (MBC) is considered a more favorable entity than other MBC presentations. However, only few retrospective series and data from selected randomized controlled trials have been reported so far.

METHODS

Using the French national multicenter ESME (Epidemiological Strategy and Medico Economics) Data Platform, the primary objective of our study was to compare the overall survival (OS) of patients with BO versus non-BO MBC at diagnosis, with adjustment on main prognostic factors using a propensity score. Secondary objectives were to compare first-line progression-free survival (PFS1), describe treatment patterns, and estimate factors associated with OS.

RESULTS

Out of 20,095 eligible women, 5041 (22.4%) patients had BO disease [hormone-receptor positive (HR+)/human epidermal growth-factor-receptor-2 negative (HER2-), n = 4 102/13,229 (31%); HER2+, n = 644/3909 (16.5%); HR-/HER2-, n = 295/2 957 (10%)]. BO MBC patients had a better adjusted OS compared with non-BO MBC [52.1 months (95% confidence interval (CI) 50.3-54.1) versus 34.7 months (95% CI 34.0-35.6) respectively]. The 5-year OS rate of BO MBC patients was 43.4% (95% CI 41.7-45.2). They also had a better PFS1 [13.1 months (95% CI 12.6-13.8) versus 8.5 months (95% CI 8.3-8.7), respectively]. This observation could be repeated in all subtypes. BO disease was an independent prognostic factor of OS [hazard ratio 0.68 (95% CI 0.65-0.72), p < 0.0001]. Results were concordant in all analyses.

CONCLUSION

BO MBC patients have better outcomes compared with non-BO MBC, consistently, through all MBC subtypes.

Low Pre-Treatment Count of Circulating Endothelial Progenitors as a Prognostic Biomarker of the High Risk of Breast Cancer Recurrence

Neoangiogenesis is mediated by circulating bone marrow-derived endothelial progenitors (circulating EPCs). The aim of the study was the quantification of circulating EPCs from the peripheral blood mononuclear cells of invasive breast cancer (IBrC) patients by flow cytometry, before and after cancer adjuvant treatment. A total of 88 stage IA-IIB primary IBrC patients were enrolled prospectively. Circulating EPCs with the immune-phenotype CD45−CD34+CD133+CD31+ were assessed. Treatment significantly reduced the number of EPCs/µL in the general IBrC cohort. However, there was a relevant elevation in the number of circulating EPCs after nine months of adjuvant treatment in the group of patients aged ≥ 55 years, of T2 clinical type, with nodal involvement (N1) and Ki67 expression > 15%. Follow-up revealed a significantly higher incidence of disease relapse in breast cancer patients with low pre-treatment circulating EPCs levels compared with those with a high baseline circulating EPCs count. The receiver-operating characteristic curve identified a tumour diameter of 2.1 cm as the best cut-off value to discriminate between disease-relapse subjects and non-relapse disease cases. Our study strongly indicates that, next to tumour diameter and Ki67 expression, circulating bone marrow-derived EPCs may serve as useful markers for predicting therapeutic outcomes as well as a future prognosis.

Updating the role of matrix metalloproteinases in mineralized tissue and related diseases

Bone development and healing processes involve a complex cascade of biological events requiring well-orchestrated synergism with bone cells, growth factors, and other trophic signaling molecules and cellular structures. Beyond health processes, MMPs play several key roles in the installation of heart and blood vessel related diseases and cancer, ranging from accelerating metastatic cells to ectopic vascular mineralization by smooth muscle cells in complementary manner. The tissue inhibitors of MMPs (TIMPs) have an important role in controlling proteolysis. Paired with the post-transcriptional efficiency of specific miRNAs, they modulate MMP performance. If druggable, these molecules are suggested to be a platform for development of "smart" medications and further clinical trials. Thus, considering the pleiotropic effect of MMPs on mammals, the purpose of this review is to update the role of those multifaceted proteases in mineralized tissues in health, such as bone, and pathophysiological disorders, such as ectopic vascular calcification and cancer.

Rictor ablation in BMSCs inhibits bone metastasis of TM40D cells by attenuating osteolytic destruction and CAF formation

The mTOR complex 2 (mTORC2) is recognized as a promising target for breast cancer treatment. As mTORC2-specific inhibitors do not yet exist, studies into the role of mTORC2 in cancer are performed by deleting Rictor or by RNAi-mediated Rictor silencing. The purpose of this study was to explore the effects of Rictor ablation in bone mesenchymal stromal cells (BMSCs) on bone metastasis of breast cancer. First, female mice with the genotype of Prx1-Cre;Rictor^f/f (hereafter RiCKO) or Rictor^f/f (as control) were injected intratibially with cells of the breast cancer cell line (TM40D) at 4 months of age. Three weeks later, osteolytic bone destruction was detected in metastatic legs by X-ray and micro-CT. We found that Rictor ablation in BMSCs inhibited TM40D-induced osteolytic bone destruction and resulted in greater bone volume maintenance in vivo. Lower CTX-I serum level, a decreased number of TRAP+ osteoclasts and lower Cathepsin-K expression observed at the tumor-bone interface indicated that osteoclastogenesis was inhibited in RiCKO mice. Additionally, co-culture experiments confirmed that Rictor deletion in BMSCs diminished osteoclast differentiation partly via down regulation of RANKL expression. Furthermore, Rictor deficiency was found to reduce the transition of BMSCs to CAFs coupled with decreased secretion of cytokines (IL-6, RANKL, TGFβ), which resulted in lower chemotaxis and less proliferation in TM40D cells. These results suggest that Rictor ablation in BMSCs plays dual roles in breast cancer bone metastasis: (1) repression of osteolytic bone destruction; (2) inhibition of tumor growth.

Stromal cells in breast cancer as a potential therapeutic target

Breast cancer in the United States is the second most commonly diagnosed cancer in women. About 1 in 8 women will develop invasive breast cancer over the course of her lifetime and breast cancer remains the second leading cause of cancer-related death. In pursuit of novel therapeutic strategies, researchers have examined the tumor microenvironment as a potential anti-cancer target. In addition to neoplastic cells, the tumor microenvironment is composed of several critical normal cell types, including fibroblasts, vascular and lymph endothelial cells, osteoclasts, adipocytes, and immune cells. These cells have important roles in healthy tissue stasis, which frequently are altered in tumors. Indeed, tumor-associated stromal cells often contribute to tumorigenesis, tumor progression, and metastasis. Consequently, these host cells may serve as a possible target in anti-tumor and anti-metastatic therapeutic strategies. Targeting the tumor associated host cells offers the benefit that such cells do not mutate and develop resistance in response to treatment, a major cause of failure in cancer therapeutics targeting neoplastic cells. This review discusses the role of host cells in the tumor microenvironment during tumorigenesis, progression, and metastasis, and provides an overview of recent developments in targeting these cell populations to enhance cancer therapy efficacy.

The molecular signature of breast cancer metastasis to bone

Distant metastasis during the advanced stage of malignant tumor progression can cause considerable morbidity in cancer patients. Bone is known to be one of the most common sites of distant metastasis in patients with breast cancer (BC). BC metastases in bone are associated with excessive skeletal complications. These complications can be fatal and reduce quality of life of patients. It is important to understand the metastatic process of BC to bone to improve quality of life and design new therapeutic methods. At present, the molecular mechanisms leading to the BC metastasis to bone are not fully understood. Studying the molecular basis of BC metastasis to bone might improve our insight into this complex process. In addition, it can provide novel approaches for designing advanced and effective targeted therapies. The present article aimed to review the published papers on the molecular basis of the metastatic process of BC to bone, focusing on involved genes and signaling networks. Furthermore, we propose potential therapeutic targets that may be more effective for the inhibition and treatment of BC metastasis to bone.

1,25(OH)2D3 deficiency increases TM40D tumor growth in bone and accelerates tumor-induced bone destruction in a breast cancer bone metastasis model

Breast cancer is one of the most common malignancies and bone is the commonest site of distant metastases. Evidences indicate that adequate supply of vitamin D will decrease the morbidity and mortality of breast cancer. However, the main role of vitamin D deficiency in breast cancer bone metastases remains unclear. In this study, the relationship between vitamin D and breast cancer bone metastases were evaluated. Results showed that 1,25(OH)₂D₃ can not only inhibit the proliferation, migration and invasion of breast cancer cell TM40D in vitro, but also attenuate the breast cancer cell TM40D-induced bone destruction in vivo, whose underlying mechanism was at least partially through decreasing the number of the osteoclasts. To our knowledge, this is the first to use 1-alpha-hydroxylase [1α(OH)ase] knockout mice which characterized vitamin D deficiency to establish the breast cancer bone metastases model. Based on this model, we also found that vitamin D deficiency will accelerate the osteolytic lesions, and 1,25(OH)₂D₃ supplement will restrain osteolytic lesions. Therefore, these findings suggest that vitamin D has the potential capacity to be a therapeutic agent for the breast cancer bone metastases.

Biomarker Studies in Early Detection and Prognosis of Breast Cancer

Breast cancer is characterized with enormous heterogeneity, which represents the major hurdle for accurate diagnosis and curative therapy. It is generally believed that genome unstability and molecular evolvability underlie the robustness of cancer cells in hostile microenvironment and their resilience to therapeutic intervention. Conventional histopathological classification of breast cancer falls short of providing sufficient prognostic and predictive power, and thus biomarkers indicative of tumor intrinsic features at molecular levels have been actively pursued in biomedical researches. Currently, a number of molecular biomarkers are being used in standard clinical practice, including the hormone receptors for breast cancer subtyping and several genes involved in genome maintenance for prediction of breast cancer susceptibility. In addition, a number of biomarkers of single genes or multigene signatures have been approved for clinical use for breast cancer prognosis. A growing body of molecular biomarkers are being studied and tested to facilitate disease diagnosis and management, especially for breast cancer early detection, accurate prediction of metastatic behaviors, and selection of therapy. However, most of them are still at the preclinical stages. Finally, biomarkers of noninvasive protocols, such as serological molecules, have advantages in detection convenience over other biomarker types and therefore are of particular interest in translational and clinical development to improve diagnosis, prognosis, and treatment.

Essential roles of the interaction between cancer cell-derived chemokine, CCL4, and intra-bone CCR5-expressing fibroblasts in breast cancer bone metastasis

From a murine breast cancer cell line, 4T1, we established a subclone, 4T1.3, which consistently metastasizes to bone upon its injection into the mammary fat pad. 4T1.3 clone exhibited similar proliferation rate and migration capacity as the parental clone. However, the intra-bone injection of 4T1.3 clone caused larger tumors than that of the parental cells, accompanied with increases in fibroblast, but not osteoclast or osteoblast numbers. 4T1.3 clone displayed an enhanced expression of a chemokine, CCL4, but not its specific receptor, CCR5. CCL4 shRNA-transfection of 4T1.3 clone had few effects on its in vitro properties, but reduced the tumorigenicity arising from the intra-bone injection. Moreover, intra-bone injection of 4T1.3 clone caused smaller tumors in mice deficient in CCR5 or those receiving CCR5 antagonist than in wild-type mice. The reduced tumor formation was associated with attenuated accumulation of CCR5-positive fibroblasts expressing connective tissue growth factor (CTGF)/CCN2. Tumor cell-derived CCL4 could induce fibroblasts to express CTGF/CCN2, which could support 4T1.3 clone proliferation under hypoxic culture conditions. Thus, the CCL4-CCR5 axis can contribute to breast cancer metastasis to bone by mediating the interaction between cancer cells and fibroblasts in bone cavity.

High SPARC Expression Starting from Dysplasia, Associated with Breast Carcinoma, Is Predictive for Bone Metastasis without Enhancement of Plasma Levels

In order to become established in the skeleton, metastatic cells disseminating from the breast carcinoma need to acquire organ-specific traits. There are no effective predictors for who will develop bone metastasis to guide long-term predictive therapy. Our purpose was to individuate events critical for bone colonization to make a molecular classification of breast carcinoma useful for bone-metastasis outcome. In dysplasia adjacent to carcinoma and in pair-matched specimens of bone metastasis we examined SPARC expression and localization as well as Endothelin 1/ET_AR signals by immunohistochemistry, and the evaluation of plasma levels of SPARC by ELISA was also performed. In patients with breast carcinoma metastasizing to bone, SPARC and Endothelin 1/ET_AR axis were highly expressed from dysplasia until bone metastasis, but the SPARC plasma level was as low as that of normal women, in contrast to patients that never develop bone metastasis, suggesting that circulating SPARC was counter adhesive. Altogether, the early identification of SPARC/Endothelin 1/ET_AR in dysplastic lesions would be important to devise therapies preventing metastasis engraftment, since often carcinoma cells spread to distant organs at the time or even before patients present with cancer.

In vitro and in vivo model systems used in prostate cancer research

New incidence of prostate cancer is a major public health issue in the Western world, and has been rising in other areas of the globe in recent years. In an effort to understanding the molecular pathogenesis of this disease, numerous cell models have been developed, arising mostly from patient biopsies. The introduction of the genetically engineered mouse in biomedical research has allowed the development of murine models that allow for the investigation of tumorigenic and metastatic processes. Current challenges to the field include lack of an animal model that faithfully recapitulates bone metastasis of prostate cancer.

Proteomic study of different culture medium serum volume fractions on RANKL-dependent RAW264.7 cells differentiating into osteoclasts

Background

Cultivation of osteoclasts is a basic tool for investigating osteolytic bone diseases. Fetal bovine serum (FBS) is the standard supplement used for in vitro cell culture medium. Typically, the serum volume fraction used for osteoclast cultivation is 10%. In this study, we investigated the use of a low serum (1% FBS) model for culturing osteoclasts.

Results

To confirm the validity of this model for use in osteoclast research, we compared the capacity for osteoclastogenesis and bone resorption of RANKL-induced RAW 264.7 cells cultured in medium supplemented with 10% FBS and 1% FBS. Osteoclasts were successfully generated in medium supplemented with 1% FBS, and exhibited prolonged longevity and similar bone resorbing ability to those generated in medium supplemented with 10% FBS, although the osteoclasts were smaller in size. Proteomics and bioinformatics analyses were performed to assess the suitability of osteoclasts formed in low serum-containing medium for use in research focusing on osteoclast differentiation and function. Our study demonstrated that a total of 100 proteins were differentially expressed in cells cultured in medium containing 1% FBS, of which 29 proteins were upregulated, and 71 proteins were downregulated. Bioinformatics analysis showed that the electron transport chain and oxidative phosphorylation pathways were downregulated obviously; however, the osteoclast signaling pathway was unaffected. The data have been deposited to the ProteomeXchange with identifier PXD001935.

Conclusion

Our study provides clear evidence of the validity of the low serum model for use in studying RANKL-dependent osteoclasts differentiation and bone resorption with the advantage of prolonged survival time.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-015-0073-6) contains supplementary material, which is available to authorized users.