Autophagy promotes immune evasion of pancreatic cancer by degrading MHC-I.

Immune evasion is a major obstacle for cancer treatment. Common mechanisms of evasion include impaired antigen presentation caused by mutations or loss of heterozygosity of the major histocompatibility complex class I (MHC-I), which has been implicated in resistance to immune checkpoint blockade (ICB) therapy1-3. However, in pancreatic ductal adenocarcinoma (PDAC), which is resistant to most therapies including ICB4, mutations that cause loss of MHC-I are rarely found5 despite the frequent downregulation of MHC-I expression6-8. Here we show that, in PDAC, MHC-I molecules are selectively targeted for lysosomal degradation by an autophagy-dependent mechanism that involves the autophagy cargo receptor NBR1. PDAC cells display reduced expression of MHC-I at the cell surface and instead demonstrate predominant localization within autophagosomes and lysosomes. Notably, inhibition of autophagy restores surface levels of MHC-I and leads to improved antigen presentation, enhanced anti-tumour T cell responses and reduced tumour growth in syngeneic host mice. Accordingly, the anti-tumour effects of autophagy inhibition are reversed by depleting CD8+ T cells or reducing surface expression of MHC-I. Inhibition of autophagy, either genetically or pharmacologically with chloroquine, synergizes with dual ICB therapy (anti-PD1 and anti-CTLA4 antibodies), and leads to an enhanced anti-tumour immune response. Our findings demonstrate a role for enhanced autophagy or lysosome function in immune evasion by selective targeting of MHC-I molecules for degradation, and provide a rationale for the combination of autophagy inhibition and dual ICB therapy as a therapeutic strategy against PDAC.

Antiphospholipid antibodies promote tissue factor-dependent angiogenic switch and tumor progression.

Progression to an angiogenic state is a critical event in tumor development, yet few patient characteristics have been identified that can be mechanistically linked to this transition. Antiphospholipid autoantibodies (aPLs) are prevalent in many human cancers and can elicit proangiogenic expression in several cell types, but their role in tumor biology is unknown. Herein, we observed that the elevation of circulating aPLs among breast cancer patients is specifically associated with invasive-stage tumors. By using multiple in vivo models of breast cancer, we demonstrated that aPL-positive IgG from patients with autoimmune disease rapidly accelerates tumor angiogenesis and consequent tumor progression, particularly in slow-growing avascular tumors. The action of aPLs was local to the tumor site and elicited leukocytic infiltration and tumor invasion. Tumor cells treated with aPL-positive IgG expressed multiple proangiogenic genes, including vascular endothelial growth factor, tissue factor (TF), and colony-stimulating factor 1. Knockdown and neutralization studies demonstrated that the effects of aPLs on tumor angiogenesis and growth were dependent on tumor cell-derived TF. Tumor-derived TF was essential for the development of pericyte coverage of tumor microvessels and aPL-induced tumor cell expression of chemokine ligand 2, a mediator of pericyte recruitment. These findings identify antiphospholipid autoantibodies as a potential patient-specific host factor promoting the transition of indolent tumors to an angiogenic malignant state through a TF-mediated pathogenic mechanism.

Paneth cell marker expression in intestinal villi and colon crypts characterizes dietary induced risk for mouse sporadic intestinal cancer.

Nutritional and genetic risk factors for intestinal tumors are additive on mouse tumor phenotype, establishing that diet and genetic factors impact risk by distinct combinatorial mechanisms. In a mouse model of dietary-induced sporadic small and large intestinal cancer in WT mice in which tumor etiology, lag, incidence, and frequency reflect >90% of intestinal cancer in Western societies, dietary-induced risk altered gene expression profiles predominantly in villus cells of the histologically normal mucosa, in contrast to targeting of crypt cells by inheritance of an Apc(1638N) allele or homozygous inactivation of p21(Waf1/cip1), and profiles induced by each risk factor were distinct at the gene or functional group level. The dietary-induced changes in villus cells encompassed ectopic expression of Paneth cell markers (a lineage normally confined to the bottom of small intestinal crypts), elevated expression of the Wnt receptor Fzd5 and of EphB2 (genes necessary for Paneth cell differentiation and localization to the crypt bottom), and increased Wnt signaling in villus cells. Ectopic elevation of these markers was also present in the colon crypts, which are also sites of sporadic tumors in the nutritional model. Elevating dietary vitamin D(3) and calcium, which prevents tumor development, abrogated these changes in the villus and colon cells. Thus, common intestinal cancer driven by diet involves mechanisms of tumor development distinct from those mechanisms that cause tumors induced by the rare inheritance of a mutant adenomatous polyposis coli (Apc) allele. This is fundamental for understanding how common sporadic tumors arise and in evaluating relative risk in the population.

Targeting pancreatic cancer metabolic dependencies through glutamine antagonism.

Pancreatic ductal adenocarcinoma (PDAC) cells use glutamine (Gln) to support proliferation and redox balance. Early attempts to inhibit Gln metabolism using glutaminase inhibitors resulted in rapid metabolic reprogramming and therapeutic resistance. Here, we demonstrated that treating PDAC cells with a Gln antagonist, 6-diazo-5-oxo-L-norleucine (DON), led to a metabolic crisis in vitro. In addition, we observed a profound decrease in tumor growth in several in vivo models using sirpiglenastat (DRP-104), a pro-drug version of DON that was designed to circumvent DON-associated toxicity. We found that extracellular signal-regulated kinase (ERK) signaling is increased as a compensatory mechanism. Combinatorial treatment with DRP-104 and trametinib led to a significant increase in survival in a syngeneic model of PDAC. These proof-of-concept studies suggested that broadly targeting Gln metabolism could provide a therapeutic avenue for PDAC. The combination with an ERK signaling pathway inhibitor could further improve the therapeutic outcome.

Autophagy supports mitochondrial metabolism through the regulation of iron homeostasis in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) cells maintain a high level of autophagy, allowing them to thrive in an austere microenvironment. However, the processes through which autophagy promotes PDAC growth and survival are still not fully understood. Here, we show that autophagy inhibition in PDAC alters mitochondrial function by losing succinate dehydrogenase complex iron sulfur subunit B expression by limiting the availability of the labile iron pool. PDAC uses autophagy to maintain iron homeostasis, while other tumor types assessed require macropinocytosis, with autophagy being dispensable. We observed that cancer-associated fibroblasts can provide bioavailable iron to PDAC cells, promoting resistance to autophagy ablation. To overcome this cross-talk, we used a low-iron diet and demonstrated that this augmented the response to autophagy inhibition therapy in PDAC-bearing mice. Our work highlights a critical link between autophagy, iron metabolism, and mitochondrial function that may have implications for PDAC progression.

A novel mouse model of inflammatory bowel disease links mammalian target of rapamycin-dependent hyperproliferation of colonic epithelium to inflammation-associated tumorigenesis.

Inflammatory bowel disease (IBD) is a high-risk condition for human colorectal cancer. However, our mechanistic understanding of the link between inflammation and tumorigenesis in the colon is limited. Here we established a novel mouse model of colitis-associated cancer by genetically inactivating signal transducer and activator of transcription 3 (Stat3) in macrophages, with partial deletion in other myeloid and lymphoid cells. Inflammation developed in the colon of mutant mice spontaneously, and tumor lesions, including invasive carcinoma, arose in the inflamed region of the intestine with a frequency similar to that observed in human IBD patients. The development of both inflammation and tumors in the mutant mice required the presence of microflora. Indeed, inflammation was associated with disruption of colonic homeostasis, fulminant epithelial/tumor cell proliferation, and activation of the mammalian target of rapamycin (mTOR)-Stat3 pathway in epithelial and tumor cells. The activation of this pathway was essential for both the excess proliferation of epithelial/tumor cells and the disruption of colonic homeostasis in the mutant mice. Notably, a similar abnormal up-regulation of mTOR-Stat3 signaling was consistently observed in the colonic epithelial cells of human IBD patients with active disease. These studies demonstrate a novel mouse model of IBD-colorectal cancer progression in which disrupted immune regulation, mTOR-Stat3 signaling, and epithelial hyperproliferation are integrated and simultaneously linked to the development of malignancy.

Spontaneous hydrolysis and spurious metabolic properties of α-ketoglutarate esters.

α-ketoglutarate (KG), also referred to as 2-oxoglutarate, is a key intermediate of cellular metabolism with pleiotropic functions. Cell-permeable esterified analogs are widely used to study how KG fuels bioenergetic and amino acid metabolism and DNA, RNA, and protein hydroxylation reactions, as cellular membranes are thought to be impermeable to KG. Here we show that esterified KG analogs rapidly hydrolyze in aqueous media, yielding KG that, in contrast to prevailing assumptions, imports into many cell lines. Esterified KG analogs exhibit spurious KG-independent effects on cellular metabolism, including extracellular acidification, arising from rapid hydrolysis and de-protonation of α-ketoesters, and significant analog-specific inhibitory effects on glycolysis or mitochondrial respiration. We observe that imported KG decarboxylates to succinate in the cytosol and contributes minimally to mitochondrial metabolism in many cell lines cultured in normal conditions. These findings demonstrate that nuclear and cytosolic KG-dependent reactions may derive KG from functionally distinct subcellular pools and sources.

Lung tumor promotion by curcumin.

Curcumin exhibits anti-inflammatory and antitumor activity and is being tested in clinical trials as a chemopreventive agent for colon cancer. Curcumin's chemopreventive activity was tested in a transgenic mouse model of lung cancer that expresses the human Ki-ras(G12C) allele in a doxycycline (DOX) inducible and lung-specific manner. The effects of curcumin were compared with the lung tumor promoter, butylated hydroxytoluene (BHT), and the lung cancer chemopreventive agent, sulindac. Treatment of DOX-induced mice with dietary curcumin increased tumor multiplicity (36.3 +/- 0.9 versus 24.3 +/- 0.2) and progression to later stage lesions, results which were similar to animals that were co-treated with DOX/BHT. Microscopic examination showed that the percentage of lung lesions that were adenomas and adenocarcinomas increased to 66% in DOX/BHT, 66% in DOX/curcumin and 49% in DOX/BHT/curcumin-treated groups relative to DOX only treated mice (19%). Immunohistochemical analysis also showed increased evidence of inflammation in DOX/BHT, DOX/curcumin and DOX/BHT/curcumin mice relative to DOX only treated mice. In contrast, co-treatment of DOX/BHT mice with 200 p.p.m. [DOSAGE ERROR CORRECTED] of sulindac inhibited the progression of lung lesions and reduced the inflammation. Lung tissue from DOX/curcumin-treated mice demonstrated a significant increase (33%; P = 0.01) in oxidative damage, as assessed by the levels of carbonyl protein formation, relative to DOX-treated control mice after 1 week on the curcumin diet. These results suggest that curcumin may exhibit organ-specific effects to enhance reactive oxygen species formation in the damaged lung epithelium of smokers and ex-smokers. Ongoing clinical trials thus may need to exclude smokers and ex-smokers in chemopreventive trials of curcumin.

Western-style diets induce oxidative stress and dysregulate immune responses in the colon in a mouse model of sporadic colon cancer.

A Western-style diet (WD), defined by high-fat, low-calcium, and vitamin D content, is associated with increased risk of human colorectal cancer. Understanding molecular mechanisms altered by the WD is crucial to develop preventive and therapeutic strategies. Effects of a WD on the colonic transcriptome of C57Bl/6J mice, a model for sporadic colon cancer, were studied at endpoints before tumors occur. To assess whether a WD induces inflammatory changes, expression profiles of a broad spectrum of inflammatory proteins were performed and numbers of lamina propria macrophages were determined with semiquantitative morphometry. Transcriptome changes were translated into molecular interaction network maps and pathways. Pathways related to oxidative stress response; lipid, glutathione, and xenobiotic metabolism; and the immune response were perturbed by the WD. Several nuclear factor-erythroid 2-related factor 2- and aryl hydrocarbon receptor-dependent genes, including those coding for enzymes involved in phase 1 and 2 drug metabolism and oxidative stress responses, were induced. Oxidative stress was demonstrated by measurements of endogenous colonic redox-sensitive compound concentrations. Perturbations in immune response-related pathways, expression of inflammatory proteins, and increased numbers of lamina propria macrophages showed that the WD significantly alters the local colonic immune response. Collectively, these data suggest that consumption of a WD interferes with networks of related biological response pathways involving colonic lipid metabolism, oxidative stress, and the immune response. These new findings impact our understanding of links between consumption of WD and colon carcinogenesis, providing additional information for developing preventive means for decreasing colorectal cancer risk.

Tumor-associated macrophages press the angiogenic switch in breast cancer.

The development of a supportive vasculature is essential for tumor progression. In a mouse model of breast cancer, we found that tumor-associated macrophages that are recruited to the tumor just before malignant conversion are essential for the angiogenic switch. These findings establish a causal linkage to explain well-documented clinical correlations between macrophages, microvessel density, and poor prognosis in breast tumors.

Direct visualization of macrophage-assisted tumor cell intravasation in mammary tumors.

Although the presence of macrophages in tumors has been correlated with poor prognosis, until now there was no direct observation of how macrophages are involved in hematogenous metastasis. In this study, we use multiphoton microscopy to show, for the first time, that tumor cell intravasation occurs in association with perivascular macrophages in mammary tumors. Furthermore, we show that perivascular macrophages of the mammary tumor are associated with tumor cell intravasation in the absence of local angiogenesis. These results show that the interaction between macrophages and tumor cells lying in close proximity defines a microenvironment that is directly involved in the intravasation of cancer cells in mammary tumors.

Human Tumor-Associated Macrophage and Monocyte Transcriptional Landscapes Reveal Cancer-Specific Reprogramming, Biomarkers, and Therapeutic Targets.

The roles of tumor-associated macrophages (TAMs) and circulating monocytes in human cancer are poorly understood. Here, we show that monocyte subpopulation distribution and transcriptomes are significantly altered by the presence of endometrial and breast cancer. Furthermore, TAMs from endometrial and breast cancers are transcriptionally distinct from monocytes and their respective tissue-resident macrophages. We identified a breast TAM signature that is highly enriched in aggressive breast cancer subtypes and associated with shorter disease-specific survival. We also identified an auto-regulatory loop between TAMs and cancer cells driven by tumor necrosis factor alpha involving SIGLEC1 and CCL8, which is self-reinforcing through the production of CSF1. Together these data provide direct evidence that monocyte and macrophage transcriptional landscapes are perturbed by cancer, reflecting patient outcomes.

Macrophages regulate the angiogenic switch in a mouse model of breast cancer.

The development of a tumor vasculature or access to the host vasculature is a crucial step for the survival and metastasis of malignant tumors. Although therapeutic strategies attempting to inhibit this step during tumor development are being developed, the biological regulation of this process is still largely unknown. Using a transgenic mouse susceptible to mammary cancer, PyMT mice, we have characterized the development of the vasculature in mammary tumors during their progression to malignancy. We show that the onset of the angiogenic switch, identified as the formation of a high-density vessel network, is closely associated with the transition to malignancy. More importantly, both the angiogenic switch and the progression to malignancy are regulated by infiltrated macrophages in the primary mammary tumors. Inhibition of the macrophage infiltration into the tumor delayed the angiogenic switch and malignant transition whereas genetic restoration of the macrophage population specifically in these tumors rescued the vessel phenotype. Furthermore, premature induction of macrophage infiltration into premalignant lesions promoted an early onset of the angiogenic switch independent of tumor progression. Taken together, this study shows that tumor-associated macrophages play a key role in promoting tumor angiogenesis, an essential step in the tumor progression to malignancy.

Autophagy Sustains Pancreatic Cancer Growth through Both Cell-Autonomous and Nonautonomous Mechanisms.

Autophagy has been shown to be elevated in pancreatic ductal adenocarcinoma (PDAC), and its role in promoting established tumor growth has made it a promising therapeutic target. However, due to limitations of prior mouse models as well as the lack of potent and selective autophagy inhibitors, the ability to fully assess the mechanistic basis of how autophagy supports pancreatic cancer has been limited. To test the feasibility of treating PDAC using autophagy inhibition and further our understanding of the mechanisms of protumor effects of autophagy, we developed a mouse model that allowed the acute and reversible inhibition of autophagy. We observed that autophagy inhibition causes significant tumor regression in an autochthonous mouse model of PDAC. A detailed analysis of these effects indicated that the tumor regression was likely multifactorial, involving both tumor cell-intrinsic and host effects. Thus, our study supports that autophagy inhibition in PDAC may have future utility in the treatment of pancreatic cancer and illustrates the importance of assessing complex biological processes in relevant autochthonous models.Significance: This work demonstrates that autophagy is critical pancreatic tumor maintenance through tumor cell-intrinsic and -extrinsic mechanisms. These results have direct clinical relevance to ongoing clinical trials as well as drug-development initiatives. Cancer Discov; 8(3); 276-87. ©2018 AACR.See related commentary by Noguera-Ortega and Amaravadi, p. 266This article is highlighted in the In This Issue feature, p. 253.

GFP expression in the mammary gland for imaging of mammary tumor cells in transgenic mice.

To examine the behavior of tumor cells in tumors developing directly from mammary tissue in transgenic models, we have evaluated transgenic mice expressing green fluorescent protein (GFP). Using the mouse mammary virus promoter (MMTV) to directly drive expression of GFP, we find low levels of fluorescence in the mammary and salivary glands of transgenic animals. Using MMTV-Cre or WAP-Cre in combination with the Cre-activatable CAG-CAT-EGFP construct, we find stronger expression of GFP that is still tissue specific. These animals provide a range of expression of GFP that is suitable for analysis of transgenic mammary tumors and metastases in vivo at the single cell level of resolution.

A paracrine loop between tumor cells and macrophages is required for tumor cell migration in mammary tumors.

Invasion of tumor cells into the surrounding connective tissue and blood vessels is a key step in the metastatic spread of breast tumors. Although the presence of macrophages in primary tumors is associated with increased metastatic potential, the mechanistic basis for this observation is unknown. Using a chemotaxis-based in vivo invasion assay and multiphoton-based intravital imaging, we show that the interaction between macrophages and tumor cells facilitates the migration of carcinoma cells in the primary tumor. Gradients of either epidermal growth factor (EGF) or colony-stimulating factor 1 (CSF-1) stimulate collection into microneedles of tumor cells and macrophages even though tumor cells express only EGF receptor and macrophages express only CSF-1 receptor. Intravital imaging shows that macrophages and tumor cells migrate toward microneedles containing either EGF or CSF-1. Inhibition of either CSF-1- or EGF-stimulated signaling reduces the migration of both cell types. This work provides the first direct evidence for a synergistic interaction between macrophages and tumor cells during cell migration in vivo and indicates a mechanism for how macrophages may contribute to metastasis.

Treatment with rhenium-188-perrhenate and iodine-131 of NIS-expressing mammary cancer in a mouse model remarkably inhibited tumor growth.

INTRODUCTION: Novel therapeutic modalities are needed for breast cancer patients in whom standard treatments are not effective. Mammary gland sodium/iodide symporter has been identified as a molecular target in breast cancers in humans and in some transgenic mouse models. We report the results of a therapy study with (131)I(-) and (188)ReO(4)(-) of breast cancer in polyoma middle T oncoprotein (PyMT) transgenic mice endogenously expressing the Na(+)/I(-) symporter (NIS). METHODS: PyMT mice (12-13 weeks old) with one palpable tumor of 0.5-0.8 cm in diameter were used. For the therapy studies, PyMT mice were (1) treated with two intraperitoneal injections of 1.5 mCi of (188)ReO(4)(-) 1 week apart, (2) pretreated for 1 week with 5 microg of triiodothyronine (T3) followed by two intraperitoneal injections of 1.5 mCi of (131)I(-) 1 week apart or (3) left untreated. The tumor and normal organ uptakes were assessed by scintigraphic imaging. The thyroid function of treated and control animals was evaluated at the completion of the study by measuring the T3/thyroxine (T4) ratio in their blood. RESULTS: There was significant uptake of (131)I(-) and (188)ReO(4)(-) in the primary palpable tumors as well as in nonpalpable tumors, stomachs and thyroids. The tumor uptake after the second injection was 10 times lower in comparison with the first injection. Tumor growth was significantly inhibited in both the (131)I(-) and (188)ReO(4)(-) groups in comparison with the control group, and tumors in the (188)ReO(4)(-) group increased in size significantly less than in the (131)I(-) group. The T3/T4 ratios were calculated to be 27 and 25 for the control group and the (188)ReO(4)(-) group, respectively; for (131)I(-), both the T3 and T4 levels were below detection limit, demonstrating much less effect on the thyroids of treatment with (188)ReO(4)(-) than with (131)I(-). CONCLUSIONS: These results prove that NIS expression in breast tumors in animal models allows specific, efficient and safe treatment with a variety of radionuclides transported by NIS.

Predicting Outcomes Using the Heart Failure Survival Score in Adults with Moderate or Complex Congenital Heart Disease.

BACKGROUND: Adults with congenital heart disease (CHD) face increased risk for morbidity and mortality with age, but few prognostic models exist. OBJECTIVE: This study aims to assess whether the Heart Failure Survival Score (HFSS), which risk stratifies patients for heart transplantation, predicts outcomes in adults with moderate or complex CHD. METHODS: This was a multicenter, retrospective study which identified 441 patients with moderate or complex CHD between 2005 and 2013, of whom 169 had all the HFSS parameters required to calculate the risk score. Because all study patients were deemed low risk by the HFSS, the score was dichotomized at the median (10.4). Outcomes included death, transplant or ventricular assist device (VAD), arrhythmia requiring treatment, nonelective cardiovascular (CV) hospitalizations, and the composite. Associations of mean HFSS and HFSS <10.4 with each outcome were assessed. RESULTS: The cohort had mean ± standard deviation age of 33.6 ± 12.6 years, peak VO2 21.8 ± 7.5 mL/kg/min, HFSS of 10.45 ± 0.88, and median years follow-up of 2.7 (1.1, 5.2). There were five deaths (2.8%), no transplants or VADs, 25 arrhythmias (14.8%), 22 CV hospitalizations (13%), and 39 composites (23.1%). Lower mean HFSS was observed for patients who died (9.6 ± 0.83 vs. 10.5 ± 0.87, P = .02), arrhythmia requiring treatment (10.0 ± 0.70 vs. 10.5 ± 0.89, P = .005), CV hospitalizations (9.9 ± 0.73 vs. 10.5 ± 0.88, P = .002), and the composite (10.0 ± 0.70 vs. 10.6 ± 0.89, P < .001). The positive and negative predictive values of HFSS <10.4 for the composite were 34% and 88% respectively, with sensitivity and specificity 74% and 56%. CONCLUSIONS: Although a low HFSS was significantly associated with outcomes, it did not adequately risk stratify adults with CHD, whose heterogeneous pathophysiology differs from that of the acquired heart failure population. Further studies are warranted to provide a more accurate prognosis.

Positron emission tomography agent 2-deoxy-2-[18F]fluoro-D-glucose has a therapeutic potential in breast cancer.

BACKGROUND: Novel approaches are needed for breast cancer patients in whom standard therapy is not effective. 2-Deoxy-2-[18F]fluoro-D-glucose (18F-FDG) was evaluated as a potential radiomolecular therapy agent in breast cancer animal models and, retrospectively, in patients with metastatic breast cancer. METHODS: Polyoma middle T antigen (PyMT) and mouse mammary tumor virus-NeuT transgenic mice with tumors 0.5-1 cm in diameter were imaged with 18F-FDG, and tumor to liver ratios (TLRs) were calculated. The radiotoxicity of 18F-FDG administration was determined in healthy mice. PyMT mice with small (0.15-0.17 cm) and large (more than 1 cm) tumors were treated with 2-4 mCi of 18F-FDG, and control C3H/B6 mice with 3 mCi of 18F-FDG. At 10 days after treatment the tumors and control mammary glands were analyzed for the presence of apoptotic and necrotic cells. Five patients with breast cancer and metastatic disease were evaluated and standardized uptake values (SUVs) in tumors, maximum tolerated dose, and the doses to the tumor were calculated. RESULTS: Doses up to 5 mCi proved to be non-radiotoxic to normal organs. The 18F-FDG uptake in mouse tumors showed an average TLR of 1.6. The treatment of mice resulted in apoptotic cell death in the small tumors. Cell death through the necrotic pathway was seen in large tumors, and was accompanied by tumor fragmentation and infiltration with leukocytes. Normal mammary tissues were not damaged. A human 18F-FDG dose delivering 200 rad to the red marrow (less than 5% damage) was calculated to be 4.76 Ci for a 70 kg woman, and the dose to the tumors was calculated to be 220, 1100 and 2200 rad for SUVs of 1, 5 and 10, respectively. CONCLUSION: We have shown that positrons delivered by 18F-FDG to mammary tumors have a tumoricidal effect on cancer cells. The study of breast cancer patients suggests that the tumor and normal organ dosimetry of 18F-FDG makes it suitable for therapy of this malignancy.

Macrophages: modulators of breast cancer progression.

In many solid tumour types the abundance of tumour associated macrophages (TAMs) is correlated with poor prognosis. Macrophages are recruited through the local expression of chemoattractants such as colony stimulating factor 1 (CSF-1) and macrophage chemoattractant protein 1. Over-expression of both of these factors is correlated with poor prognosis in a variety of tumours. Macrophages also play an important physiological role in the development and function of many tissues ranging from the brain to the mammary gland. Thus we hypothesized that TAMs are recruited to tumours through the expression of potent chemoattractants and in this site their normal trophic functions are subverted to promote tumour progression and metastasis. To test this hypothesis we crossed mice deficient in macrophages owing to being homozygous for a null mutation in the CSF-1 gene with mice pre-disposed to mammary cancer due to the epithelial restricted expression of the polyoma middle T oncoprotein. The absence of macrophages did not change the incidence or growth of the primary tumour but decreased its rate of progression and inhibited metastasis. These data are explicable through the known macrophage functions in matrix remodelling, angiogenesis and stimulation of tumour growth and motility through the synthesis of growth and chemotactic factors. Interestingly, these functions are also normally found in wound healing or pathologically during chronic inflammation. This supports the notion that tumours are 'wounds that never heal' and suggests that chronic inflammation through persistent infection or by other means might be an important cofactor in the genesis and promotion of tumours. Macrophages might therefore be important targets for cancer therapies.