Frances R. Balkwill

Cancer and the chemokine network

A complex network of chemokines and their receptors influences the development of primary tumours and metastases. New information about the biological role of chemokines in these processes is providing insights into host–tumour interactions, such as the role of the leukocyte infiltrate, and into the mechanisms that determine the metastatic potential and site-specific spread of cancer cells. Chemokine-receptor antagonists are showing promise in animal models of inflammation and autoimmune disease. Could manipulating the local chemokine network have therapeutic benefits in malignant disease?

Mice deficient in tumor necrosis factor-alpha are resistant to skin carcinogenesis.

Given the associations between chronic inflammation and epithelial cancer we studied susceptibility to skin carcinogenesis in mice deficient for the pro-inflammatory cytokine TNF-α (refs. 5,6). TNF-α–/– mice were resistant to development of benign and malignant skin tumors, whether induced by initiation with DMBA and promotion with TPA or by repeated dosing with DMBA. TNF-α–/– mice developed 5–10% the number of tumors developed by wild-type mice during initiation/promotion and 25% of those in wild-type mice after repeated carcinogen treatment. TNF-α could influence tumor and stromal cells during tumor development. The early stages of TPA promotion are characterized by keratinocyte hyperproliferation and inflammation. These were diminished in TNF-α–/– mice. TNF-α was extensively induced in the epidermis, but not the dermis, in TPA-treated wild-type skin, indicating that dermal inflammation is controlled by keratinocyte TNF-α production. Deletion of a TNF-α inducible chemokine also conferred some resistance to skin tumor development. TNF-α has little influence on later stages of carcinogenesis, as tumors in wild-type and TNF-α–/– mice had similar rates of malignant progression. These data provide evidence that a pro-inflammatory cytokine is required for de novo carcinogenesis and that TNF-α is important to the early stages of tumor promotion. Strategies that neutralize TNF-α production may be useful in cancer treatment and prevention.

Guidelines for the welfare and use of animals in cancer research

Animal experiments remain essential to understand the fundamental mechanisms underpinning malignancy and to discover improved methods to prevent, diagnose and treat cancer. Excellent standards of animal care are fully consistent with the conduct of high quality cancer research. Here we provide updated guidelines on the welfare and use of animals in cancer research. All experiments should incorporate the 3Rs: replacement, reduction and refinement. Focusing on animal welfare, we present recommendations on all aspects of cancer research, including: study design, statistics and pilot studies; choice of tumour models (e.g., genetically engineered, orthotopic and metastatic); therapy (including drugs and radiation); imaging (covering techniques, anaesthesia and restraint); humane endpoints (including tumour burden and site); and publication of best practice.

Rethinking ovarian cancer: recommendations for improving outcomes.

There have been major advances in our understanding of the cellular and molecular biology of the human malignancies that are collectively referred to as ovarian cancer. At a recent Helene Harris Memorial Trust meeting, an international group of researchers considered actions that should be taken to improve the outcome for women with ovarian cancer. Nine major recommendations are outlined in this Opinion article.

Cancer: An inflammatory link

The NF-κB protein is a key player in inflammation. It now seems that it might also activate signalling pathways, in both cancer cells and tumour-associated inflammatory cells, that promote malignancy.

“Re-educating” tumor-associated macrophages by targeting NF-κB

The nuclear factor κB (NF-κB) signaling pathway is important in cancer-related inflammation and malignant progression. Here, we describe a new role for NF-κB in cancer in maintaining the immunosuppressive phenotype of tumor-associated macrophages (TAMs). We show that macrophages are polarized via interleukin (IL)-1R and MyD88 to an immunosuppressive “alternative” phenotype that requires IκB kinase β–mediated NF-κB activation. When NF-κB signaling is inhibited specifically in TAMs, they become cytotoxic to tumor cells and switch to a “classically” activated phenotype; IL-12high, major histocompatibility complex IIhigh, but IL-10low and arginase-1low. Targeting NF-κB signaling in TAMs also promotes regression of advanced tumors in vivo by induction of macrophage tumoricidal activity and activation of antitumor activity through IL-12–dependent NK cell recruitment. We provide a rationale for manipulating the phenotype of the abundant macrophage population already located within the tumor microenvironment; the potential to “re-educate” the tumor-promoting macrophage population may prove an effective and novel therapeutic approach for cancer that complements existing therapies.

Tumor necrosis factor or tumor promoting factor

The cytokine tumor necrosis factor (TNF) alpha is a major mediator of inflammation, with actions directed towards both tissue destruction and recovery from damage [1]. TNF is a key member of a large family of cytokines and receptors that are crucial to cellular organization in metazoans [2]. Individual members of this cytokine family generate interand intracellular signals that orchestrate multi-cellular structures. Some of these structures are permanent, such as lymphoid organs, hair follicles and brain; others are impermanent but long-lived such as the mammary gland; whereas a third group are transient, such as inflammatory and wound healing responses. Several receptors of the TNF family are also ‘death receptors’ signaling apoptosis in a variety of cells and many ligands induce or modulate cell death [2]. TNF is a 17 kDa polypeptide that acts biologically in a trimeric form. TNF binds to two distinct cell surface receptors. The p55 TNF receptor is ubiquitously expressed on mammalian cells, p75 receptor expression is more restricted, being commonly found in haemopoietic cells. TNF is particularly important in organizing reversible microenvironments, and its production can stimulate dramatic cellular change and tissue modeling. Induction of TNF by pathogenic stimuli, often via Toll-like receptors, induces a cascade of other inflammatory cytokines, chemokines, growth factors and endothelial adhesins which recruit and activate a range of cells at the site of infection or tissue damage [1]. The inflammatory cascade induced by TNF and its receptors is modulated by feedback inhibition, up and down-regulation of receptor expression, soluble processing

TNF-α in promotion and progression of cancer

Tumour necrosis factor alpha is a member of the TNF/TNFR cytokine superfamily. In common with other family members, TNF-α is involved in maintenance and homeostasis of the immune system, inflammation and host defence. However, there is a ‘dark side’ to this powerful cytokine; it is now clear that, especially in middle and old age, TNF-α is involved in pathological processes such as chronic inflammation, autoimmunity and, in apparent contradiction to its name, malignant disease. This article will discuss the involvement of TNF-α in the inflammatory network that contributes to all stages of the malignant process, and consider the possibility that TNF-α may be a target for cancer therapy.

EVIDENCE FOR TUMOUR NECROSIS FACTOR/CACHECTIN PRODUCTION IN CANCER

Labile tumour-necrosis-factor-like (TNF) activity was detected by means of an enzyme-linked immunosorbent assay in 50% of 226 freshly obtained serum samples from cancer patients with active disease. In contrast, only 3% of 32 samples from normal subjects and 18% of 39 samples from cancer patients with no clinically evident disease were positive for this factor, with low levels of activity. Greater proportions of serum samples from patients with ovarian or oat-cell carcinoma were positive (69% and 63%) than those from patients with lymphoma (26%). RNA preparations from peripheral-blood mononuclear cells and solid tumours were probed with TNF complementary DNA; evidence of TNF messenger RNA was found in 8 of 11 samples of peripheral-blood mononuclear cells from cancer patients, but only 1 of 8 normal subjects, and in 2 of 6 colorectal tumours. As yet the inducing stimulus and the clinical significance of TNF production in cancer are not understood.

Macrophages Induce Invasiveness of Epithelial Cancer Cells Via NF-κB and JNK

Tumor-associated macrophages may influence tumor progression, angiogenesis and invasion. To investigate mechanisms by which macrophages interact with tumor cells, we developed an in vitro coculture model. Previously we reported that coculture enhanced invasiveness of the tumor cells in a TNF-α- and matrix metalloprotease-dependent manner. In this report, we studied intracellular signaling pathways and induction of inflammatory genes in malignant cells under the influence of macrophage coculture. We report that coculture of macrophages with ovarian or breast cancer cell lines led to TNF-α-dependent activation of JNK and NF-κB pathways in tumor cells, but not in benign immortalized epithelial cells. Tumor cells with increased JNK and NF-κB activity exhibited enhanced invasiveness. Inhibition of the NF-κB pathway by TNF-α neutralizing Abs, an NF-κB inhibitor, RNAi to RelA, or overexpression of IκB inhibited tumor cell invasiveness. Blockade of JNK also significantly reduced invasiveness, but blockade of p38 MAPK or p42 MAPK had no effect. Cocultured tumor cells were screened for the expression of 22 genes associated with inflammation and invasion that also contained an AP-1 and NF-κB binding site. EMMPRIN and MIF were up-regulated in cocultured tumor cells in a JNK- and NF-κB-dependent manner. Knocking down either MIF or EMMPRIN by RNAi in the tumor cells significantly reduced tumor cell invasiveness and matrix metalloprotease activity in the coculture supernatant. We conclude that TNF-α, via NF-κB, and JNK induces MIF and EMMPRIN in macrophage to tumor cell cocultures and this leads to increased invasive capacity of the tumor cells.