The role of myeloid cells in breast cancer metastasis

© 2012 Dr. Agnieszka SwierczakMetastasis is the leading cause of death in breast cancer patients. The current methods for predicting likelihood of metastasis are insufficient and treatment options are limited once distant metastasis occurs. Emerging data implicate myeloid cells as active participants in breast cancer metastasis. Myeloid cells in cancer are often studied as Gr-1+CD11b+ myeloid derived suppressor cells. However, this group of cells is comprised of many different cell types, including macrophages and neutrophils. Tumour-associated macrophages (TAMs) can play key roles in metastatic events but little is known about the roles of monocytes, i.e. macrophage precursors, in metastasis, and it has been suggested that monocyte/macrophage subpopulations may have different functions in breast tumour metastasis. Recent data link tumour-associated neutrophils (TANs) to the progression of malignancy in other cancers, but the link between TANs and breast cancer metastasis has not been well studied. This thesis is the first body of work to include a comprehensive analysis of monocytes/macrophages/TAMs and neutrophils/TANs during various stages of mammary tumour metastasis. Utilising three isogenic murine mammary tumour variants, namely 4T1.2 (highly metastatic), 66cl4 (weakly metastatic) and 67NR (non-metastatic), as well as the myeloid cell markers Ly6C (a marker for monocytes and neutrophils) and Ly6G (a marker for neutrophils), it was found that increases in both primary tumour Ly6Clow (non-classical, mature) TAM and TAN numbers, as well as that of circulating Ly6Chigh (classical, immature) monocytes and neutrophils were associated with metastasis. Furthermore, increases in these cells occurred early during tumour progression. Pro-MMP-9 was increased in the serum around this time; hence a model is proposed where increased production of MMP-9, either from the tumour or from the surrounding stroma, enhances mobilisation of monocytes and neutrophils leading to increased TAM and TAN numbers that promote metastasis. Furthermore, preliminary data indicate that co-injection of either TAMs and TANs isolated from highly metastatic tumours may promote the growth of less metastatic tumours. Colony stimulating factor-1 (CSF-1/M-CSF), a key macrophage growth factor, has been implicated in advanced breast cancer. Since inhibition of CSF-1 receptor (CSF-1R) signalling depletes TAMs and reduces metastasis in some mammary tumour models, CSF-1 and CSF-1R are considered targets for the treatment of metastatic disease. It is shown in this thesis, for the first time, that treatment of 4T1.2 tumour-bearing mice with neutralising anti-CSF-1R antibody can increase metastasis to lung and bone, without altering primary tumour growth. Furthermore, CSF-1R blockade leads to increased neutrophils in the primary tumour, metastasis-associated lung and peripheral blood, as well as to increased ‘classical’ Ly6Chigh blood monocytes. These data indicate that neutrophils can also play a critical role in 4T1.2 tumour metastasis. In support of this, it was found that increased expression of a key neutrophil CSF, G-CSF, in weakly metastatic primary tumours enhances circulating neutrophil and Ly6Chigh monocytes and is associated with increased metastasis. Thus, cellular changes in neutrophils and Ly6Chigh monocytes may be linked to metastasis and their subsequent increase upon anti-CSF-1R treatment may be related to the enhanced metastasis observed. The above data indicate that both macrophages and neutrophils may be involved during the early stages of breast tumour metastasis. Further analysis of monocyte/macrophage/TAM subpopulations, as well as neutrophils/TANs, may lead to improved treatment of aggressive breast tumours. Targeting both macrophages and neutrophils may be required for successful treatment of certain breast tumour subtypes. It may also be important to target monocytes and neutrophils both in the circulation and at metastatic sites and, if possible, during early stages of metastasis. Stratification of patients based on primary tumour TAM or TAN numbers may better predict the likelihood of metastasis and also guide treatment strategies

Muc1 mucin limits both Helicobacter pylori colonization of the murine gastric mucosa and associated gastritis

Background & Aims: The MUC1 mucin is expressed on the cell surface of epithelial cells fining the gastric mucosa. Epidemiologic studies suggest that functional allelic variations in the MUC1 gene may play a role in human susceptibility to Helicobacter pylori-associated pathologies, including gastric adenocarcinoma. We have evaluated the impact of Muc1 expression on the colonization and pathogenesis of gastric Helicobacter infections. Methods: Wild-type and Muc1-deficient mice were infected with H pylori and colonization and gastritis levels determined. Primary gastric cells were used to examine the impact of Muc1 expression on bacterial adherence. Results: Mice lacking Muc1 were colonized by 5-fold more H pylori within I day of infection, and this difference was maintained for at least 2 months postinfection. Mice heterozygous for the null Muc1 allele developed intermediate bacterial colonization. Although wild-type mice developed only a mild gastritis when infected for 2 months with H pylori, Muc1(-/-) mice developed an atrophic gastritis marked by loss of parietal. cells. We demonstrate H pylori adhesion to purified MUC1 and significantly increased adhesion to cultured murine Muc1 null gastric epithelial cells, suggesting that Muc1 acts as a decoy limiting binding to the cell surface. Conclusions: Muc1 provides a protective barrier, which limits both acute and chronic colonization by H pylori, as well as playing a major role in limiting the inflammation induced by Helicobacter infection. We propose that Muc1 restricts access of H pylori to the epithelial surface, hence reducing exposure of the host to proinflammatory bacterial products

Did transmission of <it>Helicobacter pylori </it>from humans cause a disease outbreak in a colony of Stripe-faced Dunnarts (<it>Sminthopsis macroura</it>)?

<p>Abstract</p> <p>Since the discovery that <it>Helicobacter pylori </it>causes a range of pathologies in the stomachs of infected humans, it has become apparent that <it>Helicobacters </it>are found in a diverse range of animal species where they are frequently associated with disease. In 2003 and 2004, there were two outbreaks of increased mortality associated with gastric bleeding and weight-loss in a captive colony of the Australian marsupial, the Stripe-faced Dunnart (<it>Sminthopsis macroura</it>). The presence of gastric pathology led to an investigation of potential <it>Helicobacter </it>pathogenesis in these animals. Histological examination revealed the presence of gastritis, and PCR analysis confirmed the presence of <it>Helicobacter </it>infection in the stomachs of these marsupials. Surprisingly, sequencing of 16S rRNA from these bacteria identified the species as <it>H. pylori </it>and PCR confirmed the strain to be positive for the important pathogenesis factor, <it>cagA</it>. We therefore describe, for the first time, an apparent reverse zoonotic infection of Stripe-faced Dunnarts with <it>H. pylori</it>. Already prone to pathological effects of stress (as experienced during breeding season), concomitant <it>H. pylori </it>infection appears to be a possible essential but not sufficient co-factor in prototypic gastric bleeding and weight loss in these marsupials. The Stripe-faced Dunnart could represent a new model for investigating <it>Helicobacter</it>-driven gastric pathology. Infections from their human handlers, specifically of <it>H. pylori</it>, may be a potential risk to captive colonies of marsupials.</p