https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1538-7836.2005.01377.x

Protease-activated receptors in hemostasis, thrombosis and vascular biology.

We examined the in vivo behavior of liver natural killer T cells (NKT cells) by intravital fluorescence microscopic imaging of mice in which a green fluorescent protein cDNA was used to replace the gene encoding the chemokine receptor CXCR6. NKT cells, which account for most CXCR6(+) cells in liver, were found to crawl within hepatic sinusoids at 10-20 microm/min and to stop upon T cell antigen receptor activation. CXCR6-deficient mice exhibited a selective and severe reduction of CD1d-reactive NKT cells in the liver and decreased susceptibility to T-cell-dependent hepatitis. CXCL16, the cell surface ligand for CXCR6, is expressed on sinusoidal endothelial cells, and CXCR6 deficiency resulted in reduced survival, but not in altered speed or pattern of patrolling of NKT cells. Thus, NKT cells patrol liver sinusoids to provide intravascular immune surveillance, and CXCR6 contributes to liver-based immune responses by regulating their abundance.

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Intravascular immune surveillance by CXCR6+ NKT cells patrolling liver sinusoids.

Recommendations for the use of common outcome measures in traumatic brain injury research

Unexpected side effects and problems experienced in clinical trials have created a difficult environment for those developing new pharmaceuticals and, as a consequence, the number of new chemical entities being registered has fallen to a historic low. Those developing metal-based therapeutics will face the same difficulties, but this environment also provides many opportunities for creative solutions to be applied to overcoming the problems and concerns. In this perspective, these challenges and opportunities are considered in the context of examples of a number of classes of metal-based therapeutics.

Developing new metal-based therapeutics: challenges and opportunities.

Glycolysis in cancer: A potential target for therapy

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Screening: Fingerprinting cancer cells

URLs The role of circulating endothelial progenitors (CEPs; bone-marrow derived endothelial progenitor cells that enter the circulation and migrate to sites of angiogenesis) in tumours has been controversial. Their contribution to tumour endothelium has been estimated to be as low as 5% or less in many studies of tumours from untreated hosts. However, Robert Kerbel and colleagues have now shown that if CEPs are acutely mobilized in tumour-bearing mice using vascular disrupting agents (VDAs), treatment with anti-angiogenic agents disrupts this spike in CEP numbers, and thereby reduces tumour cell growth at the viable tumour periphery that remains after VDA treatments. The use of VDAs combined with anti-angiogenic agents might therefore be an efficacious combination to treat solid tumours. VDAs cause the acute occlusion of existing blood vessels and rapid tumour necrosis — unlike antiangiogenic agents that mainly inhibit new blood vessel formation. The authors proposed that the rapid mobilization of CEPs as a consequence of treatment with VDAs might contribute to the rapid regrowth that is seen at the tumour periphery after VDA treatment. First, the authors showed that the treatment of non-tumour-bearing mice with the VDA combretastine-A4 phosphate or its more potent derivative OXi-4503 did cause a CEP spike of about three times normal levels. If the anti-angiogenic agent DC101 was injected into tumour-bearing mice 24 hours before giving OXi-4503, the size of the viable tumour rim was reduced threefold compared with that seen in mice treated with OXi-4503 alone. In addition, the combination of the VDA and anti-angiogenic agent led to markedly decreased perfusion, increased hypoxia and necrosis of the tumours. So, does the VDA-induced spike in CEPs lead to preferential homing of the cells to the viable tumour rim? To investigate this, Kerbel and colleagues used lethally irradiated mice transplanted with green fluorescent protein (GFP+) bone marrow cells before allowing syngeneic Lewis lung carcinomas to establish. Although untreated and DC101-treated mice showed only some modest homing of the bone marrow cells to the tumour rim, mice treated with OXi-4503 alone showed greater homing and incorporation of some of the GFP+ cells into the peripheral tumou vasculature. Mice treated with both drugs had a reduced number of GFP+ cells at the tumour periphery. If mice that are incapable of mobilizing CEPs (Idmut mice) are treated with OXi-4503 no CEP spike is seen. When these mice bear Lewis lung tumours and are treated with OXi-4503, the viable tumour rim and perfusion are reduced, confirming the significant role of therapy-induced mobilization and tumour-homing of CEPs in tumour regrowth. The authors conclude that CEPs are a key contributor to the growth of the viable tumour rim after treatment with VDAs, and suggest that treatment with cytotoxic chemotherapy drugs at maximum tolerated doses might have the same effect. If so, the combination of an anti-angiogenic drug given with chemotherapy might be one way the anti-tumour efficacy of chemotherapy can be improved.

Blunting the spikes

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Apoptosis: Escaping the rays

Studies in cultured cell lines have shown that oncogene-induced senescence is an important guardian against transformation, but the role of senescence in in vivo tumour formation has not been established. Four papers published in Nature have laid this issue to rest, demonstrating that senescence protects against tumour progression in animal models and in human tissues. Characterized by the stable growth arrest that occurs in response to various cell stressors, including oncogene induction, senescence is known to be regulated by the ARF–p53 and also the INK4A–RB (retinoblastoma protein) signalling pathways. Chrysilis Michaloglou et al. investigated senescence in human naevi (moles), which are benign tumours of melanocytes that frequently carry activating mutations in the oncogene BRAF. Naevi remain in a growth-arrested state for decades, and only rarely progress into malignancy (melanoma). Michaloglou et al. showed that mutant BRAF-expressing naevi also express high levels of senescence markers and do not proliferate. This is because activated BRAF cannot fully transform human melanocytes — additional mutations are required to disable the senescence machinery, allowing melanomas to arise. Not all naevi cells upregulate INK4A, ARF or p53, however, indicating that other, undiscovered senescenceinducing mechanisms exist in human melanocytes. In another article, Zhenbang Chen et al. showed that senescent cells are also present in early-stage prostate cancers of both humans and mice. In mouse prostate cells, inactivation of the tumour-suppressor PTEN (phosphate and tensin homologue) leads to senescence through a p53-dependent pathway, both in vitro and in vivo. Loss of both PTEN and p53, however, results in the rapid formation of invasive prostate cancer. So p53mediated senescence induction seems to be a protective mechanism against prostate tumour progression. One of the limitations of studying senescent cells in tumours has been the limited number of markers available. Using a microarray screen, Manuel Collado et al. identified a small set of genes for which the expression level was correlated with senescence induction. Using a combined panel of markers, his group analyzed the distribution of senescent cells in various activated RAS-induced tumours in mice. They showed that senescent cells uniformly exist in premalignant tumours, but not in malignant ones, and conclude that oncogene-induced senescence helps to restrict tumour progression. Melanie Braig et al. investigated a novel mechanism of senescence induction in response to oncogenic RAS. Transgenic mice that express activated RAS in their haematopoietic cell compartment (Eμ-NRas mice) develop non-lymphoid neoplasia after long periods of time, with most cells undergoing senescence through an RB-mediated pathway. Previous reports of the presence of heterochromatin foci in senescent cells indicated that histone modifications were associated with growth arrest. Since the histone methyltransferase SUV39H1 binds to RB, the authors investigated whether these two proteins function together to regulate senescence. Indeed, Eμ-NRas mice with targeted deletions of Suv39h1 rapidly succumbed to invasive T-cell lymphomas, indicating that this protein is an important inhibitor of lymphoma progression. The authors propose that SUV39H1 and RB might somehow regulate the DNA packaging required for senescence. Together, these studies show that although senescence induction is a highly heterogenous process, it seems to be a universal barrier against tumour progression. Further studies are required to determine the exact pathways that trigger senescence when oncogenes become activated, and how some cells escape senescence to progress into highly invasive, metastatic tumours. Kristine Novak

Ezzie Hutchinson

Papers

Screening: Fingerprinting cancer cells

Blunting the spikes

Apoptosis: Escaping the rays

Be sun-smart

A taxing problem