p38 MAPK mediates gamma-irradiation-induced endothelial cell apoptosis, and vascular endothelial growth factor protects endothelial cells through the phosphoinositide 3-kinase-Akt-Bcl-2 pathway

Phosphatidylinositol ether lipid analogues that inhibit AKT also independently activate the stress kinase, p38alpha, through MKK3/6-independent and -dependent mechanisms

Previously, we identified five active phosphatidylinositol ether lipid analogues (PIAs) that target the pleckstrin homology domain of Akt and selectively induce apoptosis in cancer cells with high levels of Akt activity. To examine specificity, PIAs were screened against a panel of 29 purified kinases. No kinase was inhibited, but one isoform of p38, p38alpha, was uniformly activated 2-fold. Molecular modeling of p38alpha revealed the presence of two regions that could interact with PIAs, one in the activation loop and a heretofore unappreciated region in the upper lobe that resembles a pleckstrin homology domain. In cells, two phases of activation were observed, an early phase that was independent of the upstream kinase MKK3/6 and inhibited by the p38 inhibitor SB203580 and a latter phase that was coincident with MKK3/6 activation. In short term xenograft experiments that employed immunohistochemistry and immunoblotting, PIA administration increased phosphorylation of p38 but not MKK3/6 in tumors in a statistically significant manner. Although PIAs rapidly activated p38 with similar time and dose dependence as Akt inhibition, p38 activation and Akt inhibition were independent events induced by PIAs. Using SB203580 or p38alpha(-/-) cells, we showed that p38alpha is not required for PIA-induced apoptosis but is required for H(2)O(2)- and anisomycin-induced apoptosis. Nonetheless, activation of p38a contributes to PIA-induced apoptosis, because reconstitution of p38a into p38alpha(-/-) cells increased apoptosis. These studies indicate that p38alpha is activated by PIAs through a novel mechanism and show that p38alpha activation contributes to PIA-induced cell death. Independent modulation of Akt and p38alpha could account for the profound cytotoxicity of PIAs.

Different signaling responses to anti-proliferative agents in human aortic and venous smooth muscle cells

Proliferation of smooth muscle cells (SMCs) contributes to the stenosis of coronary arteries and vascular grafts. Local delivery of anti-proliferative drugs can prevent vascular stenosis. To understand the cellular responses to anti-proliferative agents, we investigated the signaling events in cultured human aortic SMCs (ASMCs), saphenous venous SMCs (VSMCs), and dermal fibroblasts (DFs) in response to paclitaxel or etoposide. Cellular mitochondrial and proliferative activities were examined with the methylthiazoletetrazolium (MTT) dye reduction and the bromodeoxyuridine (BrdU) incorporation assay, respectively. Cell proliferation was almost completely suppressed by paclitaxel or etoposide, but apoptosis was achieved in only about 50% of cells at the highest drug concentrations, suggesting the presence of compensatory mechanisms to prevent apoptosis. Examination of three important signaling pathways revealed significant differences between ASMCs, VSMCs, and DFs. Treatment with either paclitaxel or etoposide caused a transient phosphorylation/activation of p42 MAPK in ASMCs and DFs, but had no effect on phospho-p42/44 MAPK in VSMCs. High-dose etoposide enhanced p38 MAPK activation in ASMCs, but not in VSMCs. The p38 inhibitor, PD169316, partially inhibited etoposide-induced ASMC apoptosis, but induced apoptosis in VSMCs. The effects of etoposide and paclitaxel on Akt also differed between ASMCs and VSMCs. These observations indicate that ASMCs and VSMCs differ in the response of signaling pathways to anti-proliferative agents. In ASMCs, p42/44 MAPK appears to serve a pro-survival role, whereas p38 MAPK is a pro-apoptotic regulator. In contrast, p38 MAPK is an important pro-survival regulator in VSMCs and p42/44 MAPK appears to play a minor role in responding to anti-proliferative drugs.

Regional and global protective effects of tissue kallikrein gene delivery to the peri-infarct myocardium

BACKGROUND

The kallikrein-kinin system participates in the maintenance of the cardiovascular phenotype. We previously demonstrated that human tissue kallikrein gene (hTK) transfer promotes the healing of ischemic limbs. The present investigation aimed to test the original hypothesis that hTK delivery to the peri-infarct myocardium would prevent post-ischemic heart failure.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in anesthetized mice by permanently occluding the left coronary descendant. hTK was delivered to the peri-infarct myocardium via an adenoviral vector (Ad.hTK). Controls received Ad.Null or saline. Survival rate was similar among groups. Ad.hTK increased the number of circulating endothelial progenitor cells and promoted the growth of capillaries and arterioles in the peri-infarct myocardium. In addition, Ad.hTK increased the abundance of cardiac progenitor cells (CPCs) in the peri-infarct and suppressed the apoptotic death of peri-infarct cardiomyocytes in vivo and ex vivo. As a consequence of these beneficial effects, at 5 weeks from MI, hTK-transduced hearts were protected from post-MI ventricular dilatation and showed better systolic and diastolic functions.

CONCLUSIONS

Ad.hTK benefits the neovascularization and viability of peri-infarct myocardium and increases CPC abundance, thereby decreasing ventricular dysfunction. Our study significantly adds to the knowledge of the protective effects of TK gene transfer on ischemic diseases and opens new avenues for the treatment of post-MI cardiac failure.

Dose scheduling of the dual VEGFR and EGFR tyrosine kinase inhibitor vandetanib (ZD6474, Zactima) in combination with radiotherapy in EGFR-positive and EGFR-null human head and neck tumor xenografts

PURPOSE

Vandetanib (ZD6474, Zactima) is a novel, orally available inhibitor of vascular endothelial growth factor receptor-2 (VEGFR2) tyrosine kinase activity with additional activity against epidermal growth factor receptor (EGFR) tyrosine kinase. Vandetanib has demonstrated enhanced efficacy in combination with radiation therapy (RT) in human tumor models. This study aimed to evaluate the schedule-dependent interaction of clinically relevant dosing of vandetanib with RT in human head and neck cancer models that had been characterized as EGFR positive (EGFR+) or negative (EGFR-) in order to begin differentiating vandetanib and RT interactions at the level of antitumor (EGFR) or antivascular (VEGFR2) activities.

METHODS

The human head and neck squamous cell carcinoma (HNSCC) cell lines UMSCC2 (EGFR+) and UMSCC10 (EGFR(-)) are sensitive and resistant to EGFR inhibitors, respectively, while having similar sensitivity to ionizing radiation. Nude mice with UMSCC2 or UMSCC10 tumor xenografts were treated with vandetanib or RT alone, or with combinations of concomitant and sequential therapy. Vandetanib was dosed at 30 mg kg(-1) day(-1) based on pharmacokinetic studies in nude mice showing that this dose results in drug exposure similar to that seen in humans at clinical doses. RT was dosed at 3 Gy twice a week for two consecutive weeks for a total dose of 12 Gy.

RESULTS

Vandetanib alone caused regression in EGFR+ but not EGFR- tumors and RT therapy alone was similar in both tumor types. Combinations of vandetanib and RT showed concomitant use of vandetanib and RT was superior to RT followed by vandetanib or visa versa in EGFR- tumors. Therapeutic response of EGFR+ tumors was similar regardless of treatment sequencing.

CONCLUSIONS

The combination of vandetanib and RT is active in both EGFR+ and EGFR- HNSCC tumor xenografts, however, vandetanib alone is only active in EGFR+ xenografts. EGFR+ tumor response to vandetanib and RT was independent of treatment sequencing, but concomitant treatment was superior to sequencing in EGFR- tumors. These results suggest that the anti-VEGFR2 antitumor activity of vandetanib is enhanced by RT as presumably the activity seen in EGFR- tumors is due to antiangiogenic activity, whereas the anti-EGFR antitumor activity dominates in EGFR+ tumors such that RT enhancement is not observed.

Cytochrome P-450 epoxygenases protect endothelial cells from apoptosis induced by tumor necrosis factor-alpha via MAPK and PI3K/Akt signaling pathways

Endothelial cells play a vital role in the maintenance of cardiovascular homeostasis. Epoxyeicosatrienoic acids (EETs), cytochrome P-450 (CYP) epoxygenase metabolites of arachidonic acid in endothelial cells, possess potent and diverse biological effects within the vasculature. We evaluated the effects of overexpression of CYP epoxygenases on tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis in bovine aortic endothelial cells. CYP epoxygenase overexpression significantly increased endothelial cell viability and inhibited TNF-alpha induction of endothelial cell apoptosis as evaluated by morphological analysis of nuclear condensation, DNA laddering, and fluorescent-activated cell sorting (FACS) analysis. CYP epoxygenase overexpression also significantly inhibited caspase-3 activity and downregulation of Bcl-2 expression induced by TNF-alpha. The antiapoptotic effects of CYP epoxygenase overexpression were significantly attenuated by inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt and MAPK signaling pathways; however, inhibition of endothelial nitric oxide synthase activity had no effect. Furthermore, CYP epoxygenase overexpression significantly attenuated the extent of TNF-alpha-induced ERK1/2 dephosphorylation in a time-dependent manner and significantly increased PI3K expression and Akt phosphorylation in both the presence and absence of TNF-alpha. Collectively, these results suggest that CYP epoxygenase overexpression, which is known to increase EET biosynthesis, significantly protects endothelial cells from apoptosis induced by TNF-alpha. This effect is mediated, at least in part, through inhibition of ERK dephosphorylation and activation of PI3K/Akt signaling.

Interaction of vascular endothelial growth factor 165 with neuropilin-1 protects rheumatoid synoviocytes from apoptotic death by regulating Bcl-2 expression and Bax translocation

Rheumatoid arthritis (RA) synoviocytes are resistant to apoptosis and exhibit a transformed phenotype, which might be caused by chronic exposure to genotoxic stimuli including reactive oxygen species and growth factors. In this study, we investigated the role of vascular endothelial growth factor165 (VEGF165), a potent angiogenic factor, and its receptor in the apoptosis of synoviocytes. We demonstrated here that neuropilin-1, rather than fms-like tyrosine kinase-1 and kinase insert domain-containing receptor, is the major VEGF165 receptor in the fibroblast-like synoviocytes. Neuropilin-1 was highly expressed in the lining layer, infiltrating leukocytes, and endothelial cells of rheumatoid synovium. The production of VEGF165, a ligand for neuropilin, was significantly higher in the RA synoviocytes than in the osteoarthritis synoviocytes. The ligation of recombinant VEGF165 to its receptor prevented the apoptosis of synoviocytes induced by serum starvation or sodium nitroprusside (SNP). VEGF165 rapidly triggered phospho-Akt and phospho-ERK activity and then induced Bcl-2 expression in the rheumatoid synoviocytes. The Akt or ERK inhibitor cancelled the protective effect of VEGF165 on SNP-induced synoviocyte apoptosis. Moreover, VEGF165 blocks SNP-induced Bcl-2 down-regulation as well as SNP-induced Bax translocation from the cytosol to the mitochondria. The down-regulation of the neuropilin-1 transcripts by short interfering RNA caused spontaneous synoviocyte apoptosis, which was associated with both the decrease in Bcl-2 expression and the increase in Bax translocation to mitochondria. Collectively, our data suggest that the interaction of VEGF165 with neuropilin-1 is crucial to the survival of rheumatoid synoviocytes and provide important implications for the abnormal growth of synoviocytes and therapeutic intervention in RA.

Bcl-2 Protects Endothelial Cells against γ-Radiation via a Raf-MEK-ERK-Survivin Signaling Pathway That Is Independent of CytochromecRelease

The Bcl-2 oncoprotein is a potent inhibitor of apoptosis and is overexpressed in a wide variety of malignancies. Until recently, it was generally accepted that Bcl-2 primarily mediates its antiapoptotic function by regulating cytochrome c release from mitochondria. However, more recent studies have shown that Bcl-2 is present on several intracellular membranes and mitochondria may not be the only site where Bcl-2 exercises its survival function. In this study, we investigated if Bcl-2 can protect endothelial cells against gamma-radiation by a cytochrome c-independent signaling pathway. Human dermal microvascular endothelial cells (HDMEC), when exposed to gamma-radiation, exhibited a time-dependent activation of caspase-3 that was associated with increased cytochrome c release from mitochondria. Bcl-2 expression in endothelial cells (HDMEC-Bcl-2) significantly inhibited irradiation-induced caspase-3 activation. However, Bcl-2-mediated inhibition of caspase-3 was significantly reversed by inhibition of the Raf-mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK pathway. Interestingly, caspase-3 activation in HDMEC-Bcl-2 cells was not associated with cytochrome c release. We also observed that endothelial cell Bcl-2 expression significantly increased the expression of survivin and murine double minute-2 (Mdm2) via the Raf-MEK-ERK pathway. Endothelial cells expressing Bcl-2 also inhibited gamma-radiation-induced activation of p38 MAPK and p53 accumulation. Inhibition of p53 accumulation in HDMEC-Bcl-2 could be due to the enhanced expression of Mdm2 in these cells. Taken together, these results show three mechanisms by which Bcl-2 may mediate endothelial cell cytoprotection independently of cytochrome c release: (a) increased survivin expression, (b) inhibition of p53 accumulation, and (c) inhibition of p38 MAPK.

Fractionated and acute irradiation induced signaling in a murine tumor

The effect of fractionated doses of Co(60) gamma-irradiation (2 Gy per fraction over 5 days), as is delivered in cancer radiotherapy, was compared with acute doses of 10 and 2 Gy, in a serially transplanted mouse fibrosarcoma grown in Swiss mice. The aspects that were studied included the three major mitogen-activated protein (MAP) kinases, namely p44 MAP kinase, p38 MAP kinase, and stress-activated protein (SAP) kinase, which are known to be involved in determining the cell fate following exposure to ionizing radiation. The response of dual specificity phosphatase PAC1 which is involved in the dephosphorylation of MAP kinases was also looked at. There were significant differences in the response to different dose regimens for all the factors studied. Fractionated irradiation elicited an adaptive response with a sustained activation over 7 days of prosurvival p44 MAP kinase which was balanced by the increased activation of proapoptotic p54 SAP kinase up to 1 day post-irradiation, whereas, phosphorylated p38 MAP kinase showed a decrease at most time points. PAC1 was induced following fractionated irradiation and may be acting as a feed back regulator of p44 MAP kinase. The activation of SAP kinase after fractionated irradiation may be a stress response, whereas, constitutively activated p44 MAP kinase may play an important role in the induction of radioresistance during fractionated radiotherapy of cancer and may serve as a promising target for specific inhibitors to enhance the efficacy of radiotherapy.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

Does the tumor microenvironment influence radiation-induced apoptosis?

Cytotoxic anti-cancer agents induce apoptosis in tumor and normal tissues. Therefore, it is important to investigate which factors determine these apoptotic processes and hence their likely impact on therapeutic gain. Radiation-induced apoptosis in tumors may be inhibited due to mutations of apoptotic elements or to tumor microenvironmental conditions arising from vascular insufficiency. Tumors typically contain regions of hypoxia, low glucose and acidosis. Hypoxic cells compromise treatment partly because of reduced fixation of damage during radiotherapy and partly because they promote a more malignant phenotype. There is also evidence that hypoxia may inhibit apoptosis. For some cell types, concurrent hypoxia may modulate radiation-induced apoptosis while, for others, post-irradiation hypoxia may be required. This may reflect the activity of different apoptotic pathways. Pathways involving mitochondrial components as well as regulation of SAPK and Fas have been implicated. In addition, several key stages in apoptosis are sensitive to depletion of cellular energy reserves, which results from hypoxia and low glucose conditions. There is also evidence that low pH in tumors can interfere with radiation-induced apoptosis, partly through cell cycle arrest and other undefined mechanisms.

CONCLUSIONS

Hypoxia, low glucose and acidosis influence radiation-induced apoptosis and thus may be detrimental to radiotherapy.

VEGF, a prosurvival factor, acts in concert with TGF-beta1 to induce endothelial cell apoptosis

VEGF and TGF-beta1 are potent angiogenesis inducers with opposing effects on endothelial cells. TGF-beta1 induces apoptosis; VEGF protects endothelial cells from apoptosis. We found that TGF-beta1 promotes endothelial cell expression of FGF-2, which up-regulates VEGF synthesis. Inhibition of VEGF signaling through VEGF receptor 2 (flk-1) abrogates TGF-beta1-induced apoptosis and p38(MAPK) activation. Inhibition of p38(MAPK) blocks TGF-beta1-induced apoptosis, showing that VEGF/flk-1-mediated activation of p38(MAPK) is required for TGF-beta1 induction of apoptosis. In the absence of TGF-beta1, VEGF activates p38(MAPK) and promotes endothelial cell survival. However, in context with TGF-beta1, VEGF/flk-1-mediated activation of p38(MAPK) results in apoptosis. Thus, cross-talk between TGF-beta1 and VEGF signaling converts VEGF/flk-1-activated p38(MAPK) into a proapoptotic signal. This finding illustrates an unexpected role of VEGF and indicates that VEGF can be pharmacologically converted into an apoptotic factor, a novel approach to antiangiogenesis therapy.

Human in vivo dose-response to controlled, low-dose low linear energy transfer ionizing radiation exposure

PURPOSE

The effect of low doses of low-linear energy transfer (photon) ionizing radiation (LDIR, <10 cGy) on human tissue when exposure is under normal physiologic conditions is of significant interest to the medical and scientific community in therapeutic and other contexts. Although, to date, there has been no direct assessment of the response of human tissue to LDIR when exposure is under normal physiologic conditions of intact three-dimensional architecture, vasculature, and cell-cell contacts (between epithelial cells and between epithelial and stromal cells).

EXPERIMENTAL DESIGN

In this article, we present the first data on the response of human tissue exposed in vivo to LDIR with precisely controlled and calibrated doses. We evaluated transcriptomic responses to a single exposure of LDIR in the normal skin of men undergoing therapeutic radiation for prostate cancer (research protocol, Health Insurance Portability and Accountability Act-compliant, Institutional Review Board-approved). Using newly developed biostatistical tools that account for individual splice variants and the expected variability of temporal response between humans even when the outcome is measured at a single time, we show a dose-response pattern in gene expression in a number of pathways and gene groups that are biologically plausible responses to LDIR.

RESULTS

Examining genes and pathways identified as radiation-responsive in cell culture models, we found seven gene groups and five pathways that were altered in men in this experiment. These included the Akt/phosphoinositide-3-kinase pathway, the growth factor pathway, the stress/apoptosis pathway, and the pathway initiated by transforming growth factor-beta signaling, whereas gene groups with altered expression included the keratins, the zinc finger proteins and signaling molecules in the mitogen-activated protein kinase gene group. We show that there is considerable individual variability in radiation response that makes the detection of effects difficult, but still feasible when analyzed according to gene group and pathway.

CONCLUSIONS

These results show for the first time that low doses of radiation have an identifiable biosignature in human tissue, irradiated in vivo with normal intact three-dimensional architecture, vascular supply, and innervation. The genes and pathways show that the tissue (a) does detect the injury, (b) initiates a stress/inflammatory response, (c) undergoes DNA remodeling, as suggested by the significant increase in zinc finger protein gene expression, and (d) initiates a "pro-survival" response. The ability to detect a distinct radiation response pattern following LDIR exposure has important implications for risk assessment in both therapeutic and national defense contexts.

Resveratrol-caused apoptosis of human prostate carcinoma LNCaP cells is mediated via modulation of phosphatidylinositol 3′-kinase/Akt pathway and Bcl-2 family proteins

Prostate cancer is a major health problem in the U.S. and the available treatment and surgical options have proven to be inadequate in controlling the mortality and morbidity associated with this disease. It is therefore necessary to intensify our efforts to better understand this disease and develop novel approaches for its prevention and treatment. This study was conducted to evaluate the chemopreventive/antiproliferative potential of resveratrol (trans-3,4',5,-trihydroxystilbene) against prostate cancer and its mechanism of action. Treatment with resveratrol (0-50 micromol/L for 24 hours) resulted in a significant (a) decrease in cell viability, (b) decrease of clonogenic cell survival, (c) inhibition of androgen (R1881)-stimulated growth, and (d) induction of apoptosis in androgen-responsive human prostate carcinoma (LNCaP) cells. Interestingly, at similar concentrations, resveratrol treatment did not affect the viability or rate of apoptosis in normal human prostate epithelial cells. Furthermore, our data showed that resveratrol-treatment resulted in significant dose-dependent inhibition in the constitutive expression of phosphatidylinositol 3'-kinase and phosphorylated (active) Akt in LNCaP cells. Resveratrol treatment for LNCaP cells was also found to result in a significant (a) loss of mitochondrial membrane potential, (b) inhibition in the protein level of antiapoptotic Bcl-2, and (c) increase in proapoptotic members of the Bcl-2 family, i.e., Bax, Bak, Bid, and Bad. Taken together, our data suggested that resveratrol causes an inhibition of phosphatidylinositol 3'-kinase/Akt activation that, in turn, results in modulations in Bcl-2 family proteins in such a way that the apoptosis of LNCaP cells is promoted. Based on these studies, we suggest that resveratrol could be developed as an agent for the management of prostate cancer.

Combining radiotherapy and angiogenesis inhibitors: clinical trial design

Radiotherapy (RT) plays a vital role in the multimodality treatment of cancer. Recent advances in RT have primarily involved improvements in dose delivery. Future improvements in tumor control and disease outcomes will likely involve the combination of RT with targeted therapies. Preclinical evaluations of angiogenesis inhibitors in combination with RT have yielded promising results with increased tumor "cure." It remains to be seen whether these improvements in tumor control in the laboratory will translate into improved outcomes in the clinic. Multiple differences between these agents and cytotoxic chemotherapy must be taken into account when designing clinical trials evaluating their effectiveness in combination with RT. We discuss important considerations for designing clinical trials of angiogenesis inhibitors with RT.

Epstein-Barr virus lytic infection is required for efficient production of the angiogenesis factor vascular endothelial growth factor in lymphoblastoid cell lines

Although Epstein-Barr virus (EBV)-associated malignancies are primarily composed of cells with one of the latent forms of EBV infection, a small subset of tumor cells containing the lytic form of infection is often observed. Whether the rare lytically infected tumor cells contribute to the growth of the latently infected tumor cells is unclear. Here we have investigated whether the lytically infected subset of early-passage lymphoblastoid cell lines (LCLs) could potentially contribute to tumor growth through the production of angiogenesis factors. We demonstrate that supernatants from early-passage LCLs infected with BZLF1-deleted virus (Z-KO LCLs) are highly impaired in promoting endothelial cell tube formation in vitro compared to wild-type (WT) LCL supernatants. Furthermore, expression of the BZLF1 gene product in trans in Z-KO LCLs restored angiogenic capacity. The supernatants of Z-KO LCLs, as well as supernatants from LCLs derived with a BRLF1-deleted virus (R-KO LCLs), contained much less vascular endothelial growth factor (VEGF) in comparison to WT LCLs. BZLF1 gene expression in Z-KO LCLs restored the VEGF level in the supernatant. However, the cellular level of VEGF mRNA was similar in Z-KO, R-KO, and WT LCLs, suggesting that lytic infection may enhance VEGF translation or secretion. Interestingly, a portion of the vasculature in LCL tumors in SCID mice was derived from the human LCLs. These results suggest that lytically infected cells may contribute to the growth of EBV-associated malignancies by enhancing angiogenesis. In addition, as VEGF is a pleiotropic factor with effects other than angiogenesis, lytically induced VEGF secretion may potentially contribute to viral pathogenesis.

Anaplasma phagocytophilum delay of neutrophil apoptosis through the p38 mitogen-activated protein kinase signal pathway

Human granulocytic anaplasmosis is caused by the obligate intracellular bacterium Anaplasma phagocytophilum. The bacterium avoids host innate defenses in part by infecting, surviving in, and propagating in neutrophils, as well as by inhibiting neutrophil apoptosis. However, the mechanisms of A. phagocytophilum survival in neutrophils and the inhibition of spontaneous apoptosis are not well understood. In this study, we demonstrated that antiapoptotic Mcl-1 protein (Bcl-2 family) expression is maintained and that inhibition of procaspase-3 processing occurs in A. phagocytophilum-infected human neutrophils. An evaluation of p38 mitogen-activated protein kinase (MAPK) showed evidence of increased phosphorylation with infection. Moreover, antagonism of p38 MAPK by the inhibitor SB203580 reversed apoptosis inhibition in live or heat-killed A. phagocytophilum-infected neutrophils. A role for the autocrine or paracrine production of antiapoptotic interleukin 8 (IL-8) expressed with A. phagocytophilum infection was excluded by the use of IL-8-, IL-8R1 (CXCR1)-, and IL-8R2 (CXCR2)-blocking antibodies. As previously demonstrated, the antiapoptotic effect was initially mediated by exposure to A. phagocytophilum components in heat-killed bacteria. However, an important role for active infection is demonstrated by the additional delay in apoptosis with intracellular growth and the refractory abrogation of this response by the p38 MAPK inhibitor 3 to 6 h after neutrophil infection. These results suggest that the initial activation of the p38 MAPK pathway leading to A. phagocytophilum-delayed neutrophil apoptosis is bypassed with active intracellular infection. Moreover, active intracellular infection contributes more to the overall delay in apoptosis than do components of heat-killed A. phagocytophilum alone.

Stabilization of Hypoxia-inducible Factor-1α by Prostacyclin under Prolonged Hypoxia via Reducing Reactive Oxygen Species Level in Endothelial Cells

Hypoxia-inducible factor-1 (HIF-1) takes part in the transcriptional activation of hypoxia-responsive genes. HIF-1alpha, a subunit of HIF-1, is rapidly degraded under normoxic conditions by the ubiquitin-proteosome system. Hypoxia up-regulates HIF-1alpha by inhibiting its degradation, thereby allowing it to accumulate to high levels with 3-6 h of hypoxia treatment and decreasing thereafter. In vascular tissues, prostacyclin (prostaglandin I(2) (PGI(2))) is a potent vasodilator and inhibitor of platelet aggregation and is known as a vasoprotective molecule. However, the role of PGI(2) in HIF-1 activation has not been studied. In the present study, we investigated the effect of PGI(2) on HIF-1 regulation in human umbilical vein endothelial cells under prolonged hypoxia (12 h). Augmentation of PGI(2) via adenovirus-mediated gene transfer of both cyclooxygenase-1 and PGI(2) synthase activated HIF-1 by stabilizing HIF-1alpha in cells under prolonged hypoxia or the hypoxia-normoxia transition but not under normoxia. Exogenous H(2)O(2) abolished PGI(2)- and catalase-induced HIF-1alpha up-regulation, which suggests that degradation of HIF-1alpha under prolonged hypoxia is through a reactive oxygen species-dependent pathway. Moreover, PGI(2) attenuated NADPH oxidase activity by suppressing Rac1 and p47(phox) expression under hypoxia. These data demonstrate a novel function of PGI(2) in down-regulating reactive oxygen species production by attenuating NADPH oxidase activity, which stabilizes HIF-1alpha in human umbilical vein endothelial cells exposed to prolonged hypoxia.

Antitumor activity of orally bioavailable farnesyltransferase inhibitor, ABT-100, is mediated by antiproliferative, proapoptotic, and antiangiogenic effects in xenograft models

PURPOSE

To evaluate the preclinical pharmacokinetics, antitumor efficacy, and mechanism of action of a novel orally active farnesyltransferase inhibitor, ABT-100.

EXPERIMENTAL DESIGN

In vitro sensitivity of a panel of human cell lines was determined using proliferation and clonogenic assays. In vivo efficacy of ABT-100 was evaluated in xenograft models (flank or orthotopic) by assessing angiogenesis, proliferation, and apoptosis in correlation with pharmacokinetics. Efficacy of the racemate of ABT-100 (A-367074) was also compared with R115777 (tipifarnib).

RESULTS

ABT-100 inhibited proliferation of cells in vitro carrying oncogenic H-Ras (EJ-1 bladder; IC(50) 2.2 nmol/L), Ki-Ras (DLD-1 colon, MDA-MB-231 breast, HCT-116 colon, and MiaPaCa-2 pancreatic; IC(50) range, 3.8-9.2 nmol/L), and wild-type Ras (PC-3 and DU-145; IC(50), 70 and 818 nmol/L, respectively) as well as clonogenic potential. ABT-100 shows 70% to 80% oral bioavailability in mice. ABT-100 regressed EJ-1 tumors (2-12.5 mg/kg/d s.c., every day for 21 days) and showed significant efficacy in DLD-1, LX-1, MiaPaCa-2, or PC-3 tumor-bearing mice (6.25-50 mg/kg/d s.c. once daily or twice daily orally). A-367074 showed equivalent efficacy to R115777 given at approximately one-fourth the total dose of R115777 for a shorter duration (EJ-1 and LX-1). Antitumor activity was associated with decreased cell proliferation (Ki-67), increased apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling), and decreased angiogenesis. A reduction in tumor angiogenic cytokine levels (vascular endothelial growth factor, basic fibroblast growth factor, and interleukin-8) correlated with a reduction in tumor vascularity (CD31).

CONCLUSIONS

Overall, ABT-100 has an acceptable pharmacokinetic profile, is well tolerated, and possesses broad-spectrum antitumor activity against a series of xenograft models similar to farnesyltransferase inhibitors in clinical development; therefore, it is an attractive candidate for clinical evaluation.

Crosstalk between tumor and endothelial cells promotes tumor angiogenesis by MAPK activation of Notch signaling

While significant progress has been made in understanding the induction of tumor vasculature by secreted angiogenic factors, little is known regarding contact-dependent signals that promote tumor angiogenesis. Here, we report that the Notch ligand Jagged1 induced by growth factors via mitogen-activating protein kinase (MAPK) in head and neck squamous cell carcinoma (HNSCC) cells triggered Notch activation in neighboring endothelial cells (ECs) and promoted capillary-like sprout formation. Jagged1-expressing HNSCC cells significantly enhanced neovascularization and tumor growth in vivo. Moreover, the level of Jagged1 was significantly correlated with tumor blood vessel content and associated with HNSCC development. Our results elucidate a novel mechanism by which the direct interplay between tumor cells and ECs promotes angiogenesis through MAPK and Notch signaling pathways.

The inhibitory effect of dibutyryl cyclic AMP on docosahexaenoic acid-induced apoptosis in HL-60 cells through activation of the phosphatidylinositol-3 kinase pathway

OBJECTIVE

Docosahexaenoic acid (DHA) is known as a chemopreventive substance for cancers. Previously we reported that DHA induces apoptosis in HL-60 cells. The aim of this study was to clarify the role of phosphatidylinositol 3-kinase (PI3-kinase)/Akt signaling during DHA-induced apoptosis in HL-60 cells.

METHODS

The inhibitory effects of dibutyryl cAMP (db-cAMP) or LY294002 (a specific inhibitor of the PI3-kinase/Akt pathway) on DHA-induced apoptosis in HL-60 cells were evaluated by the appearance of apoptosis, and from the activities of caspases (3 and 8), the phospholylation of Akt, and cleavage of Bid using DNA indexes, emzymatic measurement of fragmented substrates, and Western blotting, respectively.

RESULTS

The pre-incubation of db-cAMP reduced the activation of caspasses (3 and 8) during the occurrence of DHA-induced apoptosis in HL-60. However, the inhibition of PI3-kinase/Akt signaling by LY294002 resulted in recovery of the caspases' activities, appearance of apoptotic cells, and cleavage of the Bid molecule when LY294002 was co-treated with db-cAMP before the occurrence of DHA-induced apoptosis in HL-60. It was also confirmed that LY294002 strongly inhibited phospholylation of Akt during db-cAMP induced-reduction of DHA-induced apoptosis in HL-60.

CONCLUSION

We demonstrated that DHA-induced apoptosis was sensitive to the modulation of PI3-kinase activity by treatment with db-cAMP or LY294002. These results may provide new insights into the mechanisms of the anti-cancer activity of DHA.

p38 MAPK regulates phosphorylation of Bad via PP2A-dependent suppression of the MEK1/2-ERK1/2 survival pathway in TNF-alpha induced endothelial apoptosis

We recently reported that p38 MAPK regulates TNF-induced endothelial apoptosis via phosphorylation and downregulation of Bcl-xL. Here, we describe that such apoptosis includes p38 MAPK-mediated, protein phosphatase 2A (PP2A)-dependent, downregulation of the MEK-ERK pathway. Inhibition of PP2A with fostriecin or calyculin A significantly increased MEK phosphorylation, as did exposure to the p38 MAPK inhibitor SB203580. Inhibition of MEK potentiated TNF-induced caspase-3 activity and cell death, and both those events were suppressed by treatment with fostriecin or calyculin A. Immunoprecipitation experiments revealed an association between p38 MAPK, PP2A and MEK, and the results of a phosphatase assay suggested that PP2A is a downstream target of p38 MAPK. Importantly, phosphorylation of Bad at Ser-112 was found to be regulated by p38 MAPK and PP2A. In summary, the present findings indicate a novel p38 MAPK-mediated apoptosis pathway, involving activation of Bad via PP2A-dependent inhibition of the MEK-ERK pathway.

Combination treatment significantly enhances the efficacy of antitumor therapy by preferentially targeting angiogenesis

Radiotherapy is one of the most widely used cancer treatments, but it is often unsuccessful due to the development of radioresistance by tumor cells and endothelial cells (ECs) lining the tumor blood vessels. We have previously shown that ECs are protected against ionizing irradiation primarily via the activation of the phosphoinositide 3-kinase (PI3 K)-Akt-Bcl-2 survival pathway. Here we report that combination treatment with low doses of PI3 K inhibitor (LY294002), cisplatin and gamma-irradiation resulted in significantly higher (61%) EC death as compared to each agent used alone (17, 17 and 11%, respectively). This combination treatment was equally effective in inducing tumor cell death (72%). Combination treatment also significantly inhibited EC tube formation in Matrigel (75%) as compared to each of the agents used alone (8, 8 and 18% for LY294002, cisplatin and gamma-irradiation, respectively). In our in vivo severe combined immunodeficient mouse model of human tumor growth and angiogenesis, combination treatment with low doses of LY294002, cisplatin and irradiation significantly inhibited the growth of human oral squamous carcinoma (OSCC-3) as well as prostate cancer (LnCap). The combination therapy was also very effective in inhibiting tumor angiogenesis where it showed a greater than 90% decrease in neovascularization. In contrast, combination treatment showed only a 29% inhibition of physiological angiogenesis. Taken together, these results suggest a potentially novel strategy to overcome the resistance in ECs lining tumor blood vessels, thereby enhancing the effectiveness of the radiation and chemotherapy. Moreover, this strategy of using a combination of low doses of PI3K/Akt inhibitor, cisplatin and radiation has the potential of significantly decreasing untoward side effects associated with the maximum tolerated doses of radiation and chemotherapy while maintaining their therapeutic efficacy.