Bone marrow microenvironment and tumor progression

Cancer-Associated Stromal Cells Promote the Contribution of MMP2-Positive Bone Marrow-Derived Cells to Oral Squamous Cell Carcinoma Invasion

Simple Summary

Based on its invasiveness, oral squamous cell carcinoma (OSCC) shows two different subtypes: less-invasive verrucous squamous carcinoma (VSCC) or highly invasive squamous cell carcinoma (SCC). The stromal component influences OSCC progression and invasion. On the other hand, bone marrow-derived cells (BMDCs) are recruited into tumors and involved in tumor development. We hypothesized that stromal factors might also affect the relation of BMDCs and tumor invasion. We established the OSCC models transplanted with stromal cells from VSCC and SCC, and we compared the potential stromal factors of VSCC and SCC for the involvement of BMDCs in tumor invasion. Our study showed that stromal factors IL6 and IL1B might promote the contribution of MMP-2 positive BMDCs to OSCC invasion.

Abstract

Tumor stromal components contribute to tumor development and invasion. However, the role of stromal cells in the contribution of bone marrow-derived cells (BMDCs) in oral squamous cell carcinoma (OSCC) invasion is unclear. In the present study, we created two different invasive OSCC patient-derived stroma xenografts (PDSXs) and analyzed and compared the effects of stromal cells on the relation of BMDCs and tumor invasion. We isolated stromal cells from two OSCC patients: less invasive verrucous OSCC (VSCC) and highly invasive conventional OSCC (SCC) and co-xenografted with the OSCC cell line (HSC-2) on green fluorescent protein (GFP)-positive bone marrow (BM) cells transplanted mice. We traced the GFP-positive BM cells by immunohistochemistry (IHC) and detected matrix metalloproteinase 2 (MMP2) expression on BM cells by double fluorescent IHC. The results indicated that the SCC-PDSX promotes MMP2-positive BMDCs recruitment to the invasive front line of the tumor. Furthermore, microarray analysis revealed that the expressions of interleukin 6; IL-6 mRNA and interleukin 1 beta; IL1B mRNA were higher in SCC stromal cells than in VSCC stromal cells. Thus, our study first reports that IL-6 and IL1B might be the potential stromal factors promoting the contribution of MMP2-positive BMDCs to OSCC invasion.

Resident stroma-secreted chemokine CCL2 governs myeloid-derived suppressor cells in the tumor microenvironment

Accumulating evidence has shown that cancer stroma and BM-derived cells (BMDCs) in the tumor microenvironment (TME) play vital roles in tumor progression. However, the mechanism by which oral cancer stroma recruits any particular subset of BMDCs remains largely unknown. Here, we sought to identify the subset of BMDCs that is recruited by cancer stroma. We established a sequential transplantation model in BALB/c nude mice, including (a) BM transplantation of GFP-expressing cells and (b) coxenografting of patient-derived stroma (PDS; 2 cases, designated PDS1 and PDS2) with oral cancer cells (HSC-2). As controls, xenografting was performed with HSC-2 alone or in combination with normal human dermal fibroblasts (HDF). PDS1, PDS2, and HDF all promoted BMDC migration in vitro and recruitment in vivo. Multicolor immunofluorescence revealed that the PDS coxenografts recruited Arginase-1⁺CD11b⁺GR1⁺GFP⁺ cells, which are myeloid-derived suppressor cells (MDSCs), to the TME, whereas the HDF coxenograft did not. Screening using microarrays revealed that PDS1 and PDS2 expressed CCL2 mRNA (encoding C-C motif chemokine ligand 2) at higher levels than did HDF. Indeed, PDS xenografts contained significantly higher proportions of CCL2⁺ stromal cells and CCR2⁺Arginase-1⁺CD11b⁺GR1⁺ MDSCs (as receiver cells) than the HDF coxenograft. Consistently, a CCL2 synthesis inhibitor and a CCR2 antagonist significantly inhibited the PDS-driven migration of BM cells in vitro. Furthermore, i.p. injection of the CCR2 antagonist to the PDS xenograft models significantly reduced the CCR2⁺Arginase-1⁺CD11b⁺GR1⁺ MDSC infiltration to the TME. In conclusion, oral cancer stroma–secreted CCL2 is a key signal for recruiting CCR2⁺ MDSCs from BM to the TME.

Cancer-Associated Fibroblasts in the Breast Tumor Microenvironment

Years of investigation have shed light on a theory in which breast tumor epithelial cells are under the effect of the stromal microenvironment. This review aims to discuss recent findings concerning the phenotypic and functional characteristics of cancer associated fibroblasts (CAFs) and their involvement in tumor evolution, as well as their potential implications for anti-cancer therapy. In this manuscript, we reviewed that CAFs play a fundamental role in initiation, growth, invasion, and metastasis of breast cancer, and also serve as biomarkers in the clinical diagnosis, therapy, and prognosis of this disease.

Progress in Targeted Alpha-Particle-Emitting Radiopharmaceuticals as Treatments for Prostate Cancer Patients with Bone Metastases

Bone metastasis remains a major cause of death in cancer patients, and current therapies for bone metastatic disease are mainly palliative. Bone metastases arise after cancer cells have colonized the bone and co-opted the normal bone remodeling process. In addition to bone-targeted therapies (e.g., bisphosphonate and denosumab), hormone therapy, chemotherapy, external beam radiation therapy, and surgical intervention, attempts have been made to use systemic radiotherapy as a means of delivering cytocidal radiation to every bone metastatic lesion. Initially, several bone-seeking beta-minus-particle-emitting radiopharmaceuticals were incorporated into the treatment for bone metastases, but they failed to extend the overall survival in patients. However, recent clinical trials indicate that radium-223 dichloride (223RaCl2), an alpha-particle-emitting radiopharmaceutical, improves the overall survival of prostate cancer patients with bone metastases. This success has renewed interest in targeted alpha-particle therapy development for visceral and bone metastasis. This review will discuss (i) the biology of bone metastasis, especially focusing on the vicious cycle of bone metastasis, (ii) how bone remodeling has been exploited to administer systemic radiotherapies, and (iii) targeted radiotherapy development and progress in the development of targeted alpha-particle therapy for the treatment of prostate cancer bone metastasis.

Targeting of radioactive platinum-bisphosphonate anticancer drugs to bone of high metabolic activity

Platinum-based chemotherapeutics exhibit excellent antitumor properties. However, these drugs cause severe side effects including toxicity, drug resistance, and lack of tumor selectivity. Tumor-targeted drug delivery has demonstrated great potential to overcome these drawbacks. Herein, we aimed to design radioactive bisphosphonate-functionalized platinum (^195mPt-BP) complexes to confirm preferential accumulation of these Pt-based drugs in metabolically active bone. In vitro NMR studies revealed that release of Pt from Pt BP complexes increased with decreasing pH. Upon systemic administration to mice, Pt-BP exhibited a 4.5-fold higher affinity to bone compared to platinum complexes lacking the bone-seeking bisphosphonate moiety. These Pt-BP complexes formed less Pt-DNA adducts compared to bisphosphonate-free platinum complexes, indicating that in vivo release of Pt from Pt-BP complexes proceeded relatively slow. Subsequently, radioactive ^195mPt-BP complexes were synthesized using ^195mPt(NO₃)₂(en) as precursor and injected intravenously into mice. Specific accumulation of ^195mPt-BP was observed at skeletal sites with high metabolic activity using micro-SPECT/CT imaging. Furthermore, laser ablation-ICP-MS imaging of proximal tibia sections confirmed that ^195mPt BP co-localized with calcium in the trabeculae of mice tibia.

Gap Junction Intercellular Communication in the Carcinogenesis Hallmarks: Is This a Phenomenon or Epiphenomenon?

If occupational tumors are excluded, cancer causes are largely unknown. Therefore, it appeared useful to work out a theory explaining the complexity of this disease. More than fifty years ago the first demonstration that cells communicate with each other by exchanging ions or small molecules through the participation of connexins (Cxs) forming Gap Junctions (GJs) occurred. Then the involvement of GJ Intercellular Communication (GJIC) in numerous physiological cellular functions, especially in proliferation control, was proven and accounts for the growing attention elicited in the field of carcinogenesis. The aim of the present paper is to verify and discuss the role of Cxs, GJs, and GJIC in cancer hallmarks, pointing on the different involved mechanisms in the context of the multi-step theory of carcinogenesis. Functional GJIC acts both as a tumor suppressor and as a tumor enhancer in the metastatic stage. On the contrary, lost or non-functional GJs allow the uncontrolled proliferation of stem/progenitor initiated cells. Thus, GJIC plays a key role in many biological phenomena or epiphenomena related to cancer. Depending on this complexity, GJIC can be considered a tumor suppressor in controlling cell proliferation or a cancer ally, with possible preventive or therapeutic implications in both cases.

Pancreatic cancer: disease dynamics, tumor biology and the role of the microenvironment

Pancreatic cancer is known for its propensity to metastasize. Recent studies have challenged the commonly held belief that pancreatic cancer is a stepwise process, where tumor cells disseminate late in primary tumor development. Instead it has been suggested that pancreatic tumor cells may disseminate early and develop independently and in parallel to the primary tumor. Circulating tumor cells can be found in most patients with pancreatic cancer, even in those with localized stage. Also, recent phylogenetic analyses have revealed evidence for a branched evolution where metastatic lineages can develop early in tumor development. In this Review, we discuss current models of pancreatic cancer progression and the importance of the tumor microenvironment, in order to better understand the recalcitrant nature of this disease.

CXCR7 maintains osteosarcoma invasion after CXCR4 suppression in bone marrow microenvironment

The major cause of death in osteosarcoma is the invasion and metastasis. Better understanding of the molecular mechanism of osteosarcoma invasion is essential in developing effective tumor-suppressive therapies. Interaction between chemokine receptors plays a crucial role in regulating osteosarcoma invasion. Here, we investigated the relationship between CXCR7 and CXCR4 in osteosarcoma invasion induced by bone marrow microenvironment. Human bone marrow mesenchymal stem cells were co-cultured with osteosarcoma cells to mimic actual bone marrow microenvironment. Osteosarcoma cell invasion and CXCL12/CXCR4 activation were observed within this co-culture model. Interestingly, in this co-culture model, osteosarcoma cell invasion was not inhibited by suppressing CXCR4 expression with neutralizing antibody or specific inhibitor AMD3100. Downstream signaling extracellular signal-regulated kinase and signal transducer and activator of transcription 3 were not significantly affected by CXCR4 inhibition. However, suppressing CXCR4 led to CXCR7 upregulation. Constitutive expression of CXCR7 could maintain osteosarcoma cell invasion when CXCR4 was suppressed. Simultaneously, inhibiting CXCR4 and CXCR7 compromised osteosarcoma invasion in co-culture system and suppressed extracellular signal-regulated kinase and signal transducer and activator of transcription 3 signals. Moreover, bone marrow microenvironment, not CXCL12 alone, is required for CXCR7 activation after CXCR4 suppression. Taken together, suppressing CXCR4 is not enough to impede osteosarcoma invasion in bone marrow microenvironment since CXCR7 is activated to sustain invasion. Therefore, inhibiting both CXCR4 and CXCR7 could be a promising strategy in controlling osteosarcoma invasion.

Metastasis to the Jawbones: A review of 453 cases

The purpose of the present article was to review the characteristics of the jawbone metastases to analyze all variables. A relevant English Literature search in PubMed, Scopus, and Google Scholar was performed. All variables such as age, gender, primary and secondary tumor sites were analyzed. There were 453 metastatic cases. The male-to-female ratio was 1.2:1, and the mean age of the patients was 53.4 years. The lung was the most common primary site in men, and breast in women. The most common metastatic site was the mandible, and adenocarcinoma was the most frequent histological diagnosis. Metastases to the jaw bones occur in the advanced stages of a malignancy hence; a careful examination of patients with jaw bone lesions is strongly suggested. Dentists, as well as general physicians, should take into consideration the possible presence of jaw metastases in cases which present atypical symptoms, especially in patients with known malignant disease.

The Role of the Microenvironment in Prostate Cancer-Associated Bone Disease

The bone is a common site for metastasis in patients with advanced prostate carcinoma, and provides a 'fertile' milieu which stimulates tumour growth and associated bone disease. For years, the concept of treatment strategies has remained targeting the tumour itself; however, the occurrence of chemoresistance remains a challenge now more than ever. The attraction of targeting the bone microenvironment in order to disrupt tumour localisation and proliferation stems from the idea that stromal cells are superiorly stable at a genetic level, thus decreasing the risk of resistance manifestation. In this review, we will discuss recent findings with regards to the pathogenesis of prostate cancer-induced bone disease and recent therapeutic strategies in an aim to evaluate the ever increasing role of the microenvironment in disease progression.

Malignant Transformation in Glioma Steered by an Angiogenic Switch: Defining a Role for Bone Marrow-Derived Cells

Low-grade gliomas, such as pilocytic astrocytoma and subependymoma, are often characterized as benign tumors due to their relative circumscription radiologically and typically non-aggressive biologic behavior. In contrast, low-grades that are by their nature diffusely infiltrative, such as diffuse astrocytomas and oligodendrogliomas, have the potential to transform into malignant high-grade counterparts and, given sufficient time, invariably do so. These high-grade gliomas carry very poor prognoses and are largely incurable, warranting a closer look at what causes this adverse transition. A key characteristic that distinguishes low- and high-grade gliomas is neovascularization: it is absent in low-grade gliomas, but prolific in high-grade gliomas, providing the tumor with ample blood supply for exponential growth. It has been well described in the literature that bone marrow-derived cells (BMDCs) may contribute to the angiogenic switch that is responsible for malignant transformation of low-grade gliomas. In this review, we will summarize the current literature on BMDCs and their known contribution to angiogenesis-associated tumor growth in gliomas.

Targeted Proapoptotic Peptides Depleting Adipose Stromal Cells Inhibit Tumor Growth

Progression of many cancers is associated with tumor infiltration by mesenchymal stromal cells (MSC). Adipose stromal cells (ASC) are MSC that serve as adipocyte progenitors and endothelium-supporting cells in white adipose tissue (WAT). Clinical and animal model studies indicate that ASC mobilized from WAT are recruited by tumors. Direct evidence for ASC function in tumor microenvironment has been lacking due to unavailability of approaches to specifically inactivate these cells. Here, we investigate the effects of a proteolysis-resistant targeted hunter-killer peptide D-WAT composed of a cyclic domain CSWKYWFGEC homing to ASC and of a proapoptotic domain KLAKLAK2. Using mouse bone marrow transplantation models, we show that D-WAT treatment specifically depletes tumor stromal and perivascular cells without directly killing malignant cells or tumor-infiltrating leukocytes. In several mouse carcinoma models, targeted ASC cytoablation reduced tumor vascularity and cell proliferation resulting in hemorrhaging, necrosis, and suppressed tumor growth. We also validated a D-WAT derivative with a proapoptotic domain KFAKFAK2 that was found to have an improved cytoablative activity. Our results for the first time demonstrate that ASC, recruited as a component of tumor microenvironment, support cancer progression. We propose that drugs targeting ASC can be developed as a combination therapy complementing conventional cancer treatments.

Bone metastasis and the metastatic niche

The bone marrow has been long known to host a unique environment amenable to colonization by metastasizing tumor cells. Yet, the underlying molecular interactions within this specialized microenvironment which give rise to the high incidence of bone metastasis in breast and prostate cancer patients have long remained uncharacterized. With the recent description of the bone metastatic "niche," considerable focus has been placed on understanding how the bone stroma contributes to each step of metastasis. Discoveries within this field have demonstrated that when cancer cells home to the niche in which hematopoietic and mesenchymal stem/progenitor cells normally reside, a bidirectional crosstalk emerges between the tumor cells and the bone metastatic stroma. This communication modulates every step of cancer cell metastasis to the bone, including the initial homing and seeding, formation of micrometastases, outgrowth of macrometastases, and the maintenance of long-term dormancy of disseminated tumor cells in the bone. In clinical practice, targeting the bone metastatic niche is evolving into a promising avenue for the prevention of bone metastatic relapse, therapeutic resistance, and other aspects of cancer progression. Here, we review the current knowledge concerning the role of the bone metastatic niche in bone metastasis.

Obesity, proinflammatory mediators, adipose tissue progenitors, and breast cancer

PURPOSE OF REVIEW

There is emerging evidence that obesity is associated with an increase in the incidence, severity, and mortality from different types of cancer, including postmenopausal breast cancer. Here, we discuss the role of white adipose tissue (WAT) cells and of related soluble factors in the local and metastatic growth of this neoplastic disease. Moreover, we discuss the recent increase in the use of WAT-derived progenitor cells in breast cancer patients to enhance the quality of breast reconstruction and the related risks.

RECENT FINDINGS

In several murine models, WAT cells and progenitors were found to have cooperative roles in promoting local breast cancer. Moreover, they were found to contribute to adipocytes and pericytes supporting the cancer vasculature, and stimulated the metastatic progression of breast cancer. There are some clinically retrospective data showing a significant increase in the frequency of intraepithelial neoplasia in patients who received a lipofilling procedure for breast reconstruction compared with controls.

SUMMARY

Preclinical models and clinical studies are urgently needed to investigate how to inhibit the tumor-promoting activity of WAT cells and progenitors. The risks associated with the use of WAT cells for breast reconstructions should be better investigated retrospectively and prospectively.

The deregulated promoter methylation of the Polo-like kinases as a potential biomarker in hematological malignancies

Deregulation of Polo-like kinase (PLK) transcription via promoter methylation results in perturbations at the protein level, which has been associated with oncogenesis. Our objective was to further characterize the methylation profile for PLK1-4 in bone marrow aspirates displaying blood neoplasms as well as in cells grown in vitro. Clinically, we have determined that more than 70% of lymphoma and myelodysplastic syndrome (MDS)/leukemia bone marrow extracts display a hypermethylated PLK4 promoter region in comparison to the normal. Decreased PLK4 protein expression due to promoter hypermethylation was negatively correlated with JAK2 overexpression, a common occurrence in hematological malignancies. In vitro examination of the PLKs under biologically relevant condition of 5% O2 revealed that the highly conserved PLKs respond to lower oxygen tension at both the DNA and the protein level. These findings suggest that PLK promoter methylation status correlates with disease and tumorigenesis in blood neoplasms and could serve as a biomarker.

The bone marrow metastasis niche in retinoblastoma

BACKGROUND

Retinoblastoma (Rb) is a progressive cancer which mainly occurs in children, and which is caused by different genetic or epigenetic alterations that lead to inactivation of both alleles of the RB1 gene. Hereditary and non-hereditary forms of Rb do exist, and the hereditary form is associated with an increased risk of secondary malignancies. Metastasis to distant organs is a critical feature of many tumors, and may be caused by various molecular alterations at different stages. Recognition of these alterations and, thus, insight into the processes underlying the development of metastases may result in novel preventive as well as effective targeted treatment options. Rb is associated with metastases to various organs and tissues, including the bone marrow (BM).

METHODS

Here, we provide an overview of mutations and other molecular changes known to be involved in Rb development and metastasis to the BM. This overview is based on a literature search ranging from 1990 to 2015.

CONCLUSIONS

The various BM metastasis-related molecular changes identified to date may be instrumental for a better diagnosis, prognosis and classification of Rb patients, as well as for the development of novel comprehensive (targeted) therapies.

CXCR4 inhibition in tumor microenvironment facilitates anti-programmed death receptor-1 immunotherapy in sorafenib-treated hepatocellular carcinoma in mice

Sorafenib, a broad tyrosine kinase inhibitor, is the only approved systemic therapy for advanced hepatocellular carcinoma (HCC) but provides limited survival benefits. Recently, immunotherapy has emerged as a promising treatment strategy, but its role remains unclear in HCCs, which are associated with decreased cytotoxic CD8(+) T-lymphocyte infiltration in both murine and human tumors. Moreover, in mouse models after sorafenib treatment intratumoral hypoxia is increased and may fuel evasive resistance. Using orthotopic HCC models, we now show that increased hypoxia after sorafenib treatment promotes immunosuppression, characterized by increased intratumoral expression of the immune checkpoint inhibitor programmed death ligand-1 and accumulation of T-regulatory cells and M2-type macrophages. We also show that the recruitment of immunosuppressive cells is mediated in part by hypoxia-induced up-regulation of stromal cell-derived 1 alpha. Inhibition of the stromal cell-derived 1 alpha receptor (C-X-C receptor type 4 or CXCR4) using AMD3100 prevented the polarization toward an immunosuppressive microenvironment after sorafenib treatment, inhibited tumor growth, reduced lung metastasis, and improved survival. However, the combination of AMD3100 and sorafenib did not significantly change cytotoxic CD8(+) T-lymphocyte infiltration into HCC tumors and did not modify their activation status. In separate experiments, antibody blockade of the programmed death ligand-1 receptor programmed death receptor-1 (PD-1) showed antitumor effects in treatment-naive tumors in orthotopic (grafted and genetically engineered) models of HCC. However, anti-PD-1 antibody treatment had additional antitumor activity only when combined with sorafenib and AMD3100 and not when combined with sorafenib alone.

CONCLUSION

Anti-PD-1 treatment can boost antitumor immune responses in HCC models; when used in combination with sorafenib, anti-PD-1 immunotherapy shows efficacy only with concomitant targeting of the hypoxic and immunosuppressive microenvironment with agents such as CXCR4 inhibitors.

CD133+ and Nestin+ Glioma Stem-Like Cells Reside Around CD31+ Arterioles in Niches that Express SDF-1α, CXCR4, Osteopontin and Cathepsin K

Poor survival of high-grade glioma is at least partly caused by glioma stem-like cells (GSLCs) that are resistant to therapy. GSLCs reside in niches in close vicinity of endothelium. The aim of the present study was to characterize proteins that may be functional in the GSLC niche by performing immunohistochemistry on serial cryostat sections of human high-grade glioma samples. We have found nine niches in five out of five high-grade glioma samples that were all surrounding arterioles with CD31+ endothelial cells and containing cellular structures that were CD133+ and nestin+. All nine niches expressed stromal-derived factor-1α (SDF-1α), its receptor C-X-C chemokine receptor type 4 (CXCR4), osteopontin and cathepsin K. SDF-1α plays a role in homing of CXCR4+ stem cells and leukocytes, whereas osteopontin and cathepsin K promote migration of cancer cells and leukocytes. Leukocyte-related markers, such as CD68, macrophage matrix metalloprotease-9, CD177 and neutrophil elastase were often but not always detected in the niches. We suggest that SDF-1α is involved in homing of CXCR4+ GSLCs and leukocytes and that cathepsin K and osteopontin are involved in the migration of GSLCs out of the niches.

Mesenchymal stromal cell secretome up-regulates 47 kDa CXCR4 expression, and induce invasiveness in neuroblastoma cell lines

Neuroblastoma accounts for 15% of childhood cancer deaths and presents with metastatic disease of the bone and the bone marrow at diagnosis in 70% of the cases. Previous studies have shown that the Mesenchymal Stromal Cell (MSC) secretome, triggers metastases in several cancer types such as breast and prostate cancer, but the specific role of the MSC factors in neuroblastoma metastasis is unclear. To better understand the effect of MSC secretome on chemokine receptors in neuroblastoma, and its role in metastasis, we studied a panel of 20 neuroblastoma cell lines, and compared their invasive potential towards MSC-conditioned-RPMI (mRPMI) and their cytokine receptor expression profiles. Western blot analysis revealed the expression of multiple CXCR4 isoforms in neuroblastoma cells. Among the five major isoforms, the expression of the 47 kDa isoform showed significant correlation with high invasiveness. Pretreatment with mRPMI up-regulated the expression of the 47 kDa CXCR4 isoform and also increased MMP-9 secretion, expression of integrin α3 and integrin β1, and the invasive potential of the cell; while blocking CXCR4 either with AMD 3100, a CXCR4 antagonist, or with an anti-47 kDa CXCR4 neutralizing antibody decreased the secretion of MMP-9, the expression of integrin α3 and integrin β1, and the invasive potential of the cell. Pretreatment with mRPMI also protected the 47 kDa CXCR4 isoform from ubiquitination and subsequent degradation. Our data suggest a modulatory role of the MSC secretome on the expression of the 47 kDa CXCR4 isoform and invasion potential of the neuroblastoma cells to the bone marrow.

CXCL12-CXCR4 contributes to the implication of bone marrow in cancer metastasis

The CXCL12-CXCR4 axis is postulated to be a key pathway in the interaction between (cancer) stem cells and their surrounding supportive cells in the (cancer) stem cell niche. As the bone marrow constitutes a unique microenvironment for cancer cells, the CXCL12-CXCR4 axis assists the bone marrow in regulating cancer progression. This interaction can be disrupted by CXCR4 antagonists, and this concept is being used clinically to harvest hematopoietic stem/progenitor cells from the bone marrow. The functions of CXCL12-CXCR4 axis in cancer cell-tumor microenvironment interaction and angiogenesis have been recently studied. This review focuses on how CXCL12-CXCR4 helps the bone marrow in creating a tumor mircoenvironment that results in the cancer metastasis. It also discusses ongoing research regarding the clinical feasibility of CXCR4 inhibitors.

CD26-positive/CD326-negative circulating cancer cells as prognostic markers for colorectal cancer recurrence

The present study evaluated the presence and clinical relevance of a cluster of differentiation (CD)26⁺/CD326^- subset of circulating tumor cells (CTCs) in pre- and post-operative blood samples of colorectal cancer patients, who had undergone curative or palliative intervention, in order to find a novel prognostic factor for patient management and follow-up. In total, 80 colorectal cancer patients, along with 25 healthy volunteers were included. The easily transferable methodology of flow cytometry, along with multiparametric antibody staining were used to selectively evaluate CD26⁺/CD326^- CTCs in the peripheral blood samples of colorectal cancer patients. The multiparametric selection allowed any enrichment methods to be avoided thus rendering the whole procedure suitable for clinical routine. The presence of CD26⁺/CD326^- cells was higher in advanced Dukes' stages and was significantly associated with poor survival and high recurrence rates. Relapsing and non-surviving patients showed the highest number of CD26⁺/CD326^- CTCs. High pre-operative levels of CD26⁺/CD326^- CTCs correctly predicted tumor relapse in 44.4% of the cases, while 69% of post-operative CD26⁺/CD326^- CTC-positive patients experienced cancer recurrence, with a test accuracy of 88.8%. By contrast, post-operative CD26⁺/CD326^- CTC-negative patients showed an increase in the three-year progression-free survival rate of 86%, along with a reduced risk of tumor relapse of >90%. In conclusion, CD26⁺/CD326^- CTCs are an independent prognostic factor for tumor recurrence rate in multivariate analysis, suggesting that their evaluation could be an additional factor for colorectal cancer recurrence risk evaluation in patient management.

Association of obesity and circulating adipose stromal cells among breast cancer survivors

A positive association of obesity with breast cancer incidence and mortality is well established. Recent reports indicate that adipose stromal cells (ASCs) play an important role in breast cancer development and progression by producing estrogens and tumor-promoting cytokines. Furthermore, circulating ASCs have been uniquely detected in obese individuals, which is likely due to increased tissue remodeling and cell mobilization. The number of circulating ASCs is even more prominent in obese patients with colon and prostate cancers, both of which are exacerbated by obesity. To determine whether a similar association exists for breast cancer, we collected blood samples from a cohort of breast cancer survivors and enumerated circulating ASCs by flow cytometry on the basis of the previously established ASC-associated immunophenotype (CD34+/CD31-/CD45-). We found significantly higher levels of circulating ASCs (p<0.001) in breast cancer survivors with body mass index (BMI)≥30 kg/m2 than their non-obese counterparts (BMI<30). We also compared circulating ASCs before and after exercise of only the obese subjects enrolled in a 6-month individualized exercise program, but found no statistically significant difference, likely due to limited number of subjects in the study. Our findings suggest that circulating ASCs can serve as a potential biomarker for future studies of the impacts of obesity and physical activity on breast cancer recurrence and survival.

Molecular changes in bone marrow, tumor and serum after conductive ablation of murine 4T1 breast carcinoma

Thermal ablation of solid tumors using conductive interstitial thermal therapy (CITT) produces coagulative necrosis in the center of ablation. Local changes in homeostasis for surviving tumor and systemic changes in circulation and distant organs must be understood and monitored in order to prevent tumor re-growth and metastasis. The purpose of this study was to use a mouse carcinoma model to evaluate molecular changes in the bone marrow and surviving tumor after CITT treatment by quantification of transcripts associated with cancer progression and hyperthermia, serum cytokines, stress proteins and the marrow/tumor cross-talk regulator stromal-derived factor 1. Analysis of 27 genes and 22 proteins with quantitative PCR, ELISA, immunoblotting and multiplex antibody assays revealed that the gene and protein expression in tissue and serum was significantly different between ablated and control mice. The transcripts of four genes (Cxcl12, Sele, Fgf2, Lifr) were significantly higher in the bone marrow of treated mice. Tumors surviving ablation showed significantly lower levels of the Lifr and Sele transcripts. Similarly, the majority of transcripts measured in tumors decreased with treatment. Surviving tumors also contained lower levels of SDF-1α and HIF-1α proteins whereas HSP27 and HSP70 were higher. Of 16 serum chemokines, IFNγ and GM-CSF levels were lower with treatment. These results indicate that CITT ablation causes molecular changes which may slow cancer cell proliferation. However, inhibition of HSP27 may be necessary to control aggressiveness of surviving cancer stem cells. The changes in bone marrow are suggestive of possible increased recruitment of circulatory cancer cells. Therefore, the possibility of heightened bone metastasis after thermal ablation needs to be further investigated and inhibition strategies developed, if warranted.

One cell, multiple roles: contribution of mesenchymal stem cells to tumor development in tumor microenvironment

The discovery of tissue reparative and immunosuppressive abilities of mesenchymal stem cells (MSCs) has drawn more attention to tumor microenvironment and its role in providing the soil for the tumor cell growth. MSCs are recruited to tumor which is referred as the never healing wound and altered by the inflammation environment, thereby helping to construct the tumor microenvironment. The environment orchestrated by MSCs and other factors can be associated with angiogenesis, immunosuppression, inhibition of apoptosis, epithelial-mesenchymal transition (EMT), survival of cancer stem cells, which all contribute to tumor growth and progression. In this review, we will discuss how MSCs are recruited to the tumor microenvironment and what effects they have on tumor progression.

Stromal progenitor cells from endogenous adipose tissue contribute to pericytes and adipocytes that populate the tumor microenvironment

Epidemiologic studies associate cancer with obesity, but the pathophysiologic connections remain obscure. In this study, we show that obesity facilitates tumor growth in mice irrespective of concurrent diet, suggesting a direct effect of excess white adipose tissue (WAT). When transplanted into mice, adipose stromal cells (ASC) can serve as perivascular adipocyte progenitors that promote tumor growth, perhaps helping explain the obesity-cancer link. In developing this hypothesis, we showed that ASCs are expanded in obesity and that they traffic from endogenous WAT to tumors in several mouse models of cancer. Strikingly, a comparison of circulating and tumor-infiltrating cell populations in lean, and obese mice revealed that cancer induces a six-fold increase of ASC frequency in the systemic circulation. We obtained evidence that ASCs mobilized in this way can be recruited into tumors, where they can be incorporated into blood vessels as pericytes and they can differentiate into adipocytes in an obesity-dependent manner. Extending this evidence, we found that increased tumor vascularization (reflected by changes in tumor vascular morphology and a two-fold increase in vascular density) was associated with intratumoral adipocytes and elevated proliferation of neighboring malignant cells. Taken together, our results suggest that ASCs recruited from endogenous adipose tissue can be recruited by tumors to potentiate the supportive properties of the tumor microenvironment.

Behaviour of mesenchymal stem cells from bone marrow of untreated advanced breast and lung cancer patients without bone osteolytic metastasis

Tumour cells can find in bone marrow (BM) a niche rich in growth factors and cytokines that promote their self-renewal, proliferation and survival. In turn, tumour cells affect the homeostasis of the BM and bone, as well as the balance among haematopoiesis, osteogenesis, osteoclastogenesis and bone-resorption. As a result, growth and survival factors normally sequestered in the bone matrix are released, favouring tumour development. Mesenchymal stem cells (MSCs) from BM can become tumour-associated fibroblasts, have immunosuppressive function, and facilitate metastasis by epithelial-to-mesenchymal transition. Moreover, MSCs generate osteoblasts and osteocytes and regulate osteoclastogenesis. Therefore, MSCs can play an important pro-tumorigenic role in the formation of a microenvironment that promotes BM and bone metastasis. In this study we showed that BM MSCs from untreated advanced breast and lung cancer patients, without bone metastasis, had low osteogenic and adipogenic differentiation capacity compared to that of healthy volunteers. In contrast, chondrogenic differentiation was increased. Moreover, MSCs from patients had lower expression of CD146. Finally, our data showed higher levels of Dkk-1 in peripheral blood plasma from patients compared with healthy volunteers. Because no patient had any bone disorder by the time of the study we propose that the primary tumour altered the plasticity of MSCs. As over 70 % of advanced breast cancer patients and 30-40 % of lung cancer patients will develop osteolytic bone metastasis for which there is no total cure, our findings could possibly be used as predictive tools indicating the first signs of future bone disease. In addition, as the MSCs present in the BM of these patients may not be able to regenerate bone after the tumour cells invasion into BM/bone, it is possible that they promote the cycle between tumour cell growth and bone destruction.

Cyclophosphamide creates a receptive microenvironment for prostate cancer skeletal metastasis

A number of cancers predominantly metastasize to bone, due to its complex microenvironment and multiple types of constitutive cells. Prostate cancer especially has been shown to localize preferentially to bones with higher marrow cellularity. Using an experimental prostate cancer metastasis model, we investigated the effects of cyclophosphamide, a bone marrow-suppressive chemotherapeutic drug, on the development and growth of metastatic tumors in bone. Priming the murine host with cyclophosphamide before intracardiac tumor cell inoculation was found to significantly promote tumor localization and subsequent growth in bone. Shortly after cyclophosphamide treatment, there was an abrupt expansion of myeloid lineage cells in the bone marrow and the peripheral blood, associated with increases in cytokines with myelogenic potential such as C-C chemokine ligand (CCL)2, interleukin (IL)-6, and VEGF-A. More importantly, neutralizing host-derived murine CCL2, but not IL-6, in the premetastatic murine host significantly reduced the prometastatic effects of cyclophosphamide. Together, our findings suggest that bone marrow perturbation by cytotoxic chemotherapy can contribute to bone metastasis via a transient increase in bone marrow myeloid cells and myelogenic cytokines. These changes can be reversed by inhibition of CCL2.

Intratumoral delivery of CD154 homolog (Ad-ISF35) induces tumor regression: analysis of vector biodistribution, persistence and gene expression

Ad-ISF35 is an adenovirus (Ad) vector that encodes a mouse-human chimeric CD154. Ad-ISF35 induces activation of chronic lymphocytic leukemia (CLL) cells converting them into CLL cells capable of promoting immune recognition and anti-leukemia T-cell activation. Clinical trials in humans treated with Ad-ISF35-transduced leukemia cells or intranodal injection of Ad-ISF35 have shown objective clinical responses. To better understand the biology of Ad-ISF35 and to contribute to its clinical development, we preformed studies to evaluate biodistribution, persistence and toxicity of repeat dose intratumoral administration of Ad-ISF35 in a mouse model. Ad-ISF35 intratumoral administration induced tumor regression in more than 80% of mice bearing A20 tumors. There were no abnormalities in the serum chemistry. Mice receiving Ad-ISF35 presented severe extramedullary hematopoiesis and follicular hyperplasia in the spleen and extramedullary hematopoiesis with lymphoid hyperplasia in lymph nodes. After Ad-ISF35 injection, the vector was found primarily in the injected tumors with a biodistribution pattern that showed a rapid clearance with no evidence of Ad-ISF35 accumulation or persistence in the injected tumor or peripheral organs. Furthermore, pre-existing antibodies against Ad-5 did not abrogate Ad-ISF35 anti-tumor activity. In conclusion, intratumoral administration of Ad-ISF35 induced tumor regression in A20 tumor bearing mice without toxicities and with no evidence of vector accumulation or persistence.

Preclinical orthotopic and intracardiac injection models of human breast cancer metastasis to bone and their use in drug discovery

Breast cancer is the most common malignancy in women, with the development of distant metastases rendering the condition incurable. Relatively little is known about the factors governing the progression from primary tumor to metastasis, in part because of the difficulty in modeling what is a complex series of events. Detailed in this unit are descriptions of two murine models of breast cancer metastasis to bone that can be used to screen the effectiveness of new chemical entities on this disease process.

Cellular senescence and cancer chemotherapy resistance

Innate or acquired resistance to cancer therapeutics remains an important area of biomedical investigation that has clear ramifications for improving cancer specific death rates. Importantly, clues to key resistance mechanisms may lie in the well-orchestrated and highly conserved cellular and systemic responses to injury and stress. Many anti-neoplastic therapies typically rely on DNA damage, which engages potent DNA damage response signaling pathways that culminate in apoptosis or growth arrest at checkpoints to allow for damage repair. However, an alternative cellular response, senescence, can also be initiated when challenged with these internal/external pressures and in ideal situations acts as a self-protecting mechanism. Senescence-induction therapies are an attractive concept in that they represent a normal, highly conserved and commonly invoked tumor-suppressing response to overwhelming genotoxic stress or oncogene activation. Yet, such approaches should ensure that senescence by-pass or senescence re-emergence does not occur, as emergent cells appear to have highly drug resistant phenotypes. Further, cell non-autonomous senescence responses may contribute to therapy-resistance in certain circumstances. Here we provide an overview of mechanisms by which cellular senescence plausibly contributes to therapy resistance and concepts by which senescence responses can be influenced to improve cancer treatment outcomes.

Chemically-induced cancers do not originate from bone marrow-derived cells

BACKGROUND

The identification and characterization of cancer stem cells (CSCs) is imperative to understanding the mechanism of cancer pathogenesis. Growing evidence suggests that CSCs play critical roles in the development and progression of cancer. However, controversy exists as to whether CSCs arise from bone marrow-derived cells (BMDCs).

METHODOLOGY AND PRINCIPAL FINDINGS

In the present study, n-nitrosodiethylamine (DEN) was used to induce tumor formation in female mice that received bone marrow from male mice. Tumor formation was induced in 20/26 mice, including 12 liver tumors, 6 lung tumors, 1 bladder tumor and 1 nasopharyngeal tumor. Through comparison of fluorescence in situ hybridization (FISH) results in corresponding areas from serial tumor sections stained with H&E, we determined that BMDCs were recruited to both tumor tissue and normal surrounding tissue at a very low frequency (0.2-1% in tumors and 0-0.3% in normal tissues). However, approximately 3-70% of cells in the tissues surrounding the tumor were BMDCs, and the percentage of BMDCs was highly associated with the inflammatory status of the tissue. In the present study, no evidence was found to support the existence of fusion cells formed form BMDCs and tissue-specific stem cells.

CONCLUSIONS

In summary, our data suggest that although BMDCs may contribute to tumor progression, they are unlike to contribute to tumor initiation.

Mesenchymal niches of bone marrow in cancer

Over the last decade, genetic and cell biology studies have indicated that tumour growth is not only determined by malignant cancer cells themselves, but also by the tumour microenvironment. Cells present in the tumour microenvironment include fibroblasts, vascular, smooth muscle, adipocytes, immune cells and mesenchymal stem cells (MSC). The nature of the relationship between MSC and tumour cells appears dual and whether MSC are pro- or anti-tumorigenic is a subject of controversial reports. This review is focused on the role of MSC and bone marrow (BM) niches in cancer.

The Role of Cancer Stem Cells in the Organ Tropism of Breast Cancer Metastasis: A Mechanistic Balance between the "Seed" and the "Soil"?

Breast cancer is a prevalent disease worldwide, and the majority of deaths occur due to metastatic disease. Clinical studies have identified a specific pattern for the metastatic spread of breast cancer, termed organ tropism; where preferential secondary sites include lymph node, bone, brain, lung, and liver. A rare subpopulation of tumor cells, the cancer stem cells (CSCs), has been hypothesized to be responsible for metastatic disease and therapy resistance. Current treatments are highly ineffective against metastatic breast cancer, likely due to the innate therapy resistance of CSCs and the complex interactions that occur between cancer cells and their metastatic microenvironments. A better understanding of these interactions is essential for the development of novel therapeutic targets for metastatic disease. This paper summarizes the characteristics of breast CSCs and their potential metastatic microenvironments. Furthermore, it raises the question of the existence of a CSC niche and highlights areas for future investigation.

Hematopoietic derived cell infiltration of the intestinal tumor microenvironment in Apc Min/+ mice

Tumors consist of a heterogeneous population of neoplastic cells infiltrated by an equally heterogeneous collection of nonneoplastic cells that comprise the tumor microenvironment. Tumor growth, invasion, and metastasis depend on multiple interactions between these cells. To assess their potential as therapeutic targets or vehicles for tumor specific delivery of therapeutic agents, we examined the contribution of bone marrow derived cells (BMDCs) to the intestinal tumor microenvironment. Hematopoietic stem cells expressing the enhanced green fluorescent protein (eGFP) were transplanted into lethally irradiated ApcMin/+ mice, and their engraftment was analyzed by confocal microscopy. The results showed abundant infiltration of eGFP cells into the small intestine, colon, and spleen compared to heart, muscle, liver, lung, and kidney. Within the intestine, there was a pronounced gradient of engraftment along the anterior to posterior axis, with enhanced infiltration into adenomas. Immunofluorescence analysis showed that osteopontin was expressed in tumor stromal cells but not in nontumor stromal populations, suggesting that gene expression in these cells is distinct. Tumor vasculature in ApcMin/+ mice was chaotic compared to normal intestinal regions. Our data suggest that BMDCs can be harnessed for tumor-targeted therapies to enhance antitumor efficacy.

Three-dimensional characterization of the vascular bed in bone metastasis of the rat by microcomputed tomography (MicroCT)

Background

Angiogenesis contributes to proliferation and metastatic dissemination of cancer cells. Anatomy of blood vessels in tumors has been characterized with 2D techniques (histology or angiography). They are not fully representative of the trajectories of vessels throughout the tissues and are not adapted to analyze changes occurring inside the bone marrow cavities.

Methodology/Principal Findings

We have characterized the vasculature of bone metastases in 3D at different times of evolution of the disease. Metastases were induced in the femur of Wistar rats by a local injection of Walker 256/B cells. Microfil®, (a silicone-based polymer) was injected at euthanasia in the aorta 12, 19 and 26 days after injection of tumor cells. Undecalcified bones (containing the radio opaque vascular casts) were analyzed by microCT, and a first 3D model was reconstructed. Bones were then decalcified and reanalyzed by microCT; a second model (comprising only the vessels) was obtained and overimposed on the former, thus providing a clear visualization of vessel trajectories in the invaded metaphysic allowing quantitative evaluation of the vascular volume and vessel diameter. Histological analysis of the marrow was possible on the decalcified specimens. Walker 256/B cells induced a marked osteolysis with cortical perforations. The metaphysis of invaded bones became progressively hypervascular. New vessels replaced the major central medullar artery coming from the diaphyseal shaft. They sprouted from the periosteum and extended into the metastatic area. The newly formed vessels were irregular in diameter, tortuous with a disorganized architecture. A quantitative analysis of vascular volume indicated that neoangiogenesis increased with the development of the tumor with the appearance of vessels with a larger diameter.

Conclusion

This new method evidenced the tumor angiogenesis in 3D at different development times of the metastasis growth. Bone and the vascular bed can be identified by a double reconstruction and allowed a quantitative evaluation of angiogenesis upon time.

Adipose tissue-derived progenitor cells and cancer

Recruitment of stem cells and partially differentiated progenitor cells is a process which accompanies and facilitates the progression of cancer. One of the factors complicating the clinical course of cancer is obesity, a progressively widespread medical condition resulting from overgrowth of white adipose tissue (WAT), commonly known as white fat. The mechanisms by which obesity influences cancer risk and progression are not completely understood. Cells of WAT secret soluble molecules (adipokines) that could stimulate tumor growth, although there is no consensus on which cell populations and which adipokines are important. Recent reports suggest that WAT-derived mesenchymal stem (stromal) cells, termed adipose stem cells (ASC), may represent a cell population linking obesity and cancer. Studies in animal models demonstrate that adipokines secreted by ASC can promote tumor growth by assisting in formation of new blood vessels, a process necessary for expansion of tumor mass. Importantly, migration of ASC from WAT to tumors has been demonstrated, indicating that the tumor microenvironment in cancer may be modulated by ASC-derived trophic factors in a paracrine rather than in an endocrine manner. Here, we review possible positive and adverse implications of progenitor cell recruitment into the diseased sites with a particular emphasis on the role in cancer progression of progenitors that are expanded in obesity.

Rapid extravasation and establishment of breast cancer micrometastases in the liver microenvironment

To examine the interplay between tumor cells and the microenvironment during early breast cancer metastasis, we developed a technique for ex vivo imaging of murine tissue explants using two-photon microscopy. Cancer cells in the liver and the lung were compared by imaging both organs at specific time points after the injection of the same polyomavirus middle T-initiated murine mammary tumor cell line. Extravasation was greatly reduced in the lung compared with the liver, with 56% of tumor cells in the liver having extravasated by 24 hours, compared with only 22% of tumor cells in the lung that have extravasated. In the liver, imaged cells continually transitioned from an intravascular location to an extravascular site, whereas in the lung, extravasation rates slowed after 6 hours. Within the liver microenvironment, the average size of the imaged micrometastatic lesions increased 4-fold between days 5 and 12. Histologic analysis of these lesions determined that by day 12, the micrometastases were heterogeneous, consisting of both tumor cells and von Willebrand factor-positive endothelial cells. Further analysis with intravenously administered lectin indicated that vessels within the micrometastatic tumor foci were patent by day 12. These data present the use of two-photon microscopy to directly compare extravasation times in metastatic sites using the same tumor cell line and highlight the differences in early events and metastatic patterns between two important secondary sites of breast cancer progression with implications for future therapy.

Differential baseline and response profile to IFN-gamma gene transduction of IL-6/IL-6 receptor-alpha secretion discriminate primary tumors versus bone marrow metastases of nasopharyngeal carcinomas in culture

BACKGROUND

Understanding of immunobiology of bone marrow metastases (designated BM-NPC) versus primary tumors (P-NPC) of the nasopharynx is far from complete. The aim of this study was to determine if there would be differences between cultured P-NPCs and BM-NPCs with respect to (i) constitutive IL-6 and the IL-6 receptor gp80 subunit (IL-6Ralpha) levels in the spent media of nontransduced cells, and (ii) IL-6 and IL-6Ralpha levels in the spent media of cells transduced with a retroviral vector containing the IFN-gamma gene.

METHODS

A panel of NPC cell lines were transduced with the IFN-gamma gene through a retroviral vector. Four clonal sublines were isolated via limiting dilution methods. Cytofluorometric analysis was performed for the detection of cell surface antigens of HLA class I, HLA class II and ICAM-1. ELISA was used to assay for IFN-gamma, IL-6 and IL-6Ralpha in the spent media of cultured cell lines.

RESULTS

Our results showed that in day 3 culture supernatants, low levels of soluble IL-6 were detected in 5/5 cultured tumors derived from P-NPCs, while much higher constitutive levels of IL-6 were detected in 3/3 metastasis-derived NPC cell lines including one originated from ascites; the difference was significant (p = 0.025). An inverse relationship was found between IL-6Ralpha and IL-6 in their release levels in cultured P-NPCs and metastasis-derived NPCs. In IFN-gamma-transduced-P-NPCs, IL-6 production increased and yet IL-6Ralpha decreased substantially, as compared to nontransduced counterparts. At variance with P-NPC cells, the respective ongoing IL-6 and IL-6Ralpha release patterns of BM-NPC cells were not impeded as much following IFN-gamma transduction. These observations were confirmed by extended kinetic studies with representative NPC cell lines and clonal sublines. The latter observation with the clonal sublines also indicates that selection for high IL-6 or low IL-6Ralpha producing subpopulations did not occur as a result of IFN-gamma-transduction process. P-NPCs, which secreted constitutively only marginal levels of IFN-gamma (8.4 ~ 10.5 pg/ml), could be enhanced to produce higher levels of IFN-gamma (6.8- to 10.3-fold increase) after IFN-gamma transduction. Unlike P-NPCs, BM-NPCs spontaneously released IFN-gamma at moderate levels (83.8 ~ 100.7 pg/ml), which were enhanced by 1.3- to 2.2-fold in the spent media of their IFN-gamma-transduced counterparts.

CONCLUSION

Our results showed that cultured P-NPCs and BM-NPCs could be distinguished from one another on the basis of their differential baseline secretion pattern of IFN-gamma, IL-6 and IL-6Ralpha, and their differential response profiles to IFN-gamma gene transfer of the production of these three soluble molecules. These results suggest that the IL-6 and IFN-gamma pathways in a background of genetic instability be involved in the acquisition of metastatic behaviour in BM-NPCs.