Eva L. Lund

Regulation of YKL-40 expression during genotoxic or microenvironmental stress in human glioblastoma cells

YKL‐40 is a 40 kDa secreted glycoprotein belonging to the family of ‘mammalian chitinase‐like proteins’, but without chitinase activity. YKL‐40 has a proliferative effect on fibroblasts, chondrocytes and synoviocytes, and chemotactic effect on endothelium and vascular smooth muscle cells. Elevated YKL‐40 levels are found in serum of patients with diseases characterized by inflammation, fibrosis and tissue remodeling. Several studies have reported that high serum YKL‐40 levels in patients with cancer are associated with poor prognosis. YKL‐40 expression is strongly elevated in serum and biopsy material from glioblastomas patients. We investigated the expression of YKL‐40 in three human malignant glioma cell lines exposed to different types of stress. Whereas a polymerase chain reaction transcript was detectable in all three cell lines, only U87 produced measurable amounts of YKL‐40 protein. In U87, hypoxia and ionizing radiation induced a significant increase in YKL‐40 after 24–48 h. The hypoxic induction of YKL‐40 was independent of HIF1. Etoposide, ceramide, serum depletion and confluence all led to elevated YKL‐40. Inhibition of p53 augmented the YKL‐40 expression indicating that YKL‐40 is attenuated by p53. In contrast, both basic fibroblast growth factor and tumor necrosing factor‐α repressed YKL‐40. These are the first data on regulation of YKL‐40 in cancer cells. Diverse types of stress resulted in YKL‐40 elevation, which strongly supports an involvement of YKL‐40 in the malignant phenotype as a cellular survival factor in an adverse microenvironment. (Cancer Sci 2005; 96: 183–190)

Tumor angiogenesis ‐ a new therapeutic target in gliomas

Tumor growth is critically dependent on angiogenesis, which is sprouting of new vessels from pre‐existing vasculature. This process is regulated by inducers and inhibitors released from tumor cells, endothelial cells, and macrophages. Brain tumors, especially glioblastoma multiforme, have significant angiogenic activity primarily by the expression of the angiogenic factor VEGE Anti‐angiogenic therapy represents a new promising therapeutic modality in solid tumors. Several agents are currently under evaluation in clinical trials. The present review describes the principal inducers and inhibitors of angiogenesis in tumors and summarizes what is known about their mechanisms of action in relation to CNS tumors. Potential areas for clinical use are also discussed.

Differential regulation of VEGF, HIF1α and angiopoietin‐1, ‐2 and ‐4 by hypoxia and ionizing radiation in human glioblastoma

We examined how ionizing radiation (IR) delivered under either severe hypoxia (< 0.1% O2) or normoxia affects the expression of hypoxia inducible factor 1α (HIF‐1α) and the angiogenic factors vascular endothelial growth factor (VEGF) and angiopoietins 1, 2 and 4 in U87 human glioblastoma cells. IR was delivered as single doses of 0, 2, 5, 10 and 20 Gy after 6‐hr hypoxic incubation and in normoxic controls. Irradiation at any dose did not affect the cellular protein levels of any of the angiopoietins, whereas hypoxia led to increasing levels of both angiopoietin‐4 and angiopoietin‐2. Levels of angiopoietin‐1 protein were unaltered throughout the observation period. A dose‐dependent increase in levels of secreted VEGF in the medium occurred after IR at doses from 5–20 Gy. In hypoxic cells, 20 Gy IR induced an additional significant increase in VEGF relative to nonirradiated hypoxic control cells with elevated baseline VEGF levels induced by hypoxia. HIF‐1α and glucose transporter‐1 (Glut‐1) were not correspondingly upregulated by IR. Blocking HIF‐1α by antisense treatment induced a reduced baseline VEGF at normoxia, while the relative upregulation of VEGF by IR was unaffected. These data provide evidence that VEGF is upregulated by IR by mechanisms independent of HIF‐1 transactivation.

Hypoxia-induced secretion of macrophage migration-inhibitory factor from MCF-7 breast cancer cells is regulated in a hypoxia-inducible factor-independent manner.

The cytokine MIF is over-expressed in tumors and is associated with tumor proliferation, angiogenesis and metastasis. Hypoxia, a hallmark feature of tumors, increases MIF expression from tumor cells. We examined the role of hypoxia-inducible transcription factors on MIF secretion from MCF-7 breast carcinoma cells. Secretion of MIF was induced by hypoxia after 24h but up-regulation of MIF mRNA was minimal. Inhibition of HIF-1alpha, HIF-2alpha, NF-kappaB and C/EBPbeta using siRNA had no effect on hypoxia-induced MIF secretion. However, inhibition of transcription and translation significantly decreased MIF production, suggesting that hypoxia-induced secretion of MIF in MCF-7 cells is via an alternative pathway.

Improved Effect of an Antiangiogenic Tyrosine Kinase Inhibitor (SU5416) by Combinations with Fractionated Radiotherapy or Low Molecular Weight Heparin

The effect of combining SU5416 with fractionated radiotherapy or with low molecular weight (LMW) heparin (dalteparin) was studied in U87 human glioblastoma xenografts in nude mice. SU5416 is antiangiogenic by a specific inhibition of the vascular endothelial growth factor receptor 2 (VEGFR-2), and heparins are assumed to bind VEGF. Both SU5416 (100 mg/kg every second day in 5 days) and 3 Gyx5 produced moderate, yet significant, growth inhibition. Tumors treated with concomitant irradiation and short-term SU5416 maintained a lower growth rate during regrowth than the other treatment groups (P=.007). Dalteparin (1000 IE/kg subcutaneously once a day) had no growth-inhibitory effect on its own, but when this LMW heparin was added to the SU5416 schedule, a significantly enhanced growth inhibition was obtained. VEGF protein content in tumors was not significantly altered by SU5416, but a significant decrease in VEGF levels was found in tumors treated with concomitant dalteparin and SU5416 compared with controls (P=.03). We conclude that: 1) an additive growth-inhibitory effect is obtained by combining SU5416 and fractionated radiotherapy; and 2) LMW heparin (dalteparin), in combination with SU5416, decreases the level of VEGF in tumors and increases the growth-inhibitory effect of SU5416.

Effect of Radiation Therapy on Small-Cell Lung Cancer Is Reduced by Ubiquinone Intake

The effect of oral ubiquinone (Q10) intake on thein vivo response of tumors to single dose radiotherapy was examined. The human small-cell lung cancer (SCLC) line CPH 054A, which is sensitive to relatively low doses of X-radiation, was grown as subcutaneous transplants in the flanks of nude nu/nu mice. When macroscopical growth was established, groups of mice received either 10, 20 or 40 mg/kg Q10 in 30 mL soy oil intragastrically daily on 4 consecutive days. Controls received either 30 mL of pure soy oil or nothing. Three h after the last dose half of the tumors in each group received a single radiation dose of 5 Gy, using a 300 kV therapeutic unit. The macroscopic growth pre- and posttreatment was analyzed according to a transformed Gompertz algorithm using the software program GROWTH. Treatment with Q10 or soy oil alone had no effect on tumor growth compared with untreated controls. Groups of tumors that received Q10 and radiotherapy had a significantly lower specific growth delay (SGD) than the radiotherapy-only groups. This effect was significant at 40 mg/kg and borderline at 20 mg/kg, whereas at 10 mg/kg no radioprotection was seen. We conclude that systemic Q10 reduces the response to single dose tumor irradiation inxenotransplanted human SCLC tumors.

Interactions between HIF-1 and Jab1: balancing apoptosis and adaptation. Outline of a working hypothesis.

When cells experience hypoxia, they either die by apoptosis or adapt to the hypoxic conditions by a series of compensatory mechanisms. Hypoxia inducible factor-1 (HIF-1) is a transcription factor involved in both processes, but the exact mechanisms regulating whether the cells survive (adapt) or perish by apoptosis are largely unknown. We hypothesize that the balancing between apoptosis and adaptation is governed by a triangular feedback system involving the alpha-subunit of HIF-1, p53, and jun activating binding protein 1 (Jab1). Jab1 and p53 bind competitively to the same domain on HIF-1alpha resulting in either stabilization or degradation of HIF-1alpha, respectively. Moreover, p53 is stabilized by binding to HIF-1alpha, whereas its interaction with Jab1 targets p53 for degradation. Thus as a consequence we propose that the ratio between p53 and Jab1 determine whether a hypoxic induction of HIF-1 results in apoptosis or adaptation, with Jab1 as the factor promoting adaptation. On this background we consider Jab1 an interesting molecular target for anticancer therapy.