p16-induced apoptosis in Ewing's sarcoma

The tumor suppressor p16 is a negative regulator of the cell cycle, and acts by preventing the phosphorylation of RB, which in turn prevents the progression from G1 to S phase of the cell cycle. In addition to its role in the cell cycle, p16 may also be able to induce apoptosis in some tumors. Ewing's sarcoma, a pediatric cancer of the bone and soft tissue, was used to study the ability of p16 to induce apoptosis due to the fact that p16 is often deleted in Ewing's sarcoma tumors and may play a role in the oncogenesis or progression of this disease. The purpose of these studies was to determine whether introduction of p16 into Ewing's sarcoma cells would induce apoptosis. We infected the Ewing's sarcoma cell line TC71, which does not express p16, with adenovirus- p16 (Ad-p16). Ad-p16 infection led to the production of functional p16 as measured by the induction of G1 arrest. Ad-p16 infection induced as much as a 100% increase in G1 arrest compared to untreated cells. As measured by propidium iodide (PI) and Annexin V staining, Ad-p16 was able to induce apoptosis to levels 20–30 fold higher than controls. Furthermore, Ad-p16 infection led to loss of RB protein before apoptosis could be detected. The loss of RB protein was due to post-translational degradation of RB, which was inhibited by the addition of the proteasome inhibitors PS-341 and NPI-0052. Downregulation of RB with si-RNA sensitized cells to Ad-p16-induced apoptosis, indicating that RB protects from apoptosis in this model. This study shows that p16 leads to the degradation of RB by the ubiquitin/proteasome pathway, and that this degradation may be important for the induction of apoptosis. Given that RB may protect from apoptosis in some tumors, apoptosis-inducing therapies may be enhanced in tumors which have lost RB expression, or in which RB is artificially inactivated. ^

Effect of thiazolidinedione, a class of anti-diabetic drugs, on the mouse skin tumorigenesis

Thiazolidinediones (TZDs), a novel class of anti-diabetic drugs, have been known as ligands of peroxisome proliferator-activated receptor γ (PPARγ), a transcription factor that belongs to the nuclear receptor superfamily. These synthetic compounds improve insulin sensitivity in patients with type II diabetes likely through activating PAPRγ. Interestingly, they were also shown to inhibit cell growth and proliferation in a wide variety of tumor cell lines. The aim of this study is to assess the potential use of TZDs in the prevention of carcinogenesis using mouse skin as a model. ^ We found that troglitazone, one of TZD drugs, strongly inhibited cultured mouse skin keratinocyte proliferation as demonstrated by [3H]thymidine incorporation assay. It also induced a cell cycle G1 phase arrest and inhibited expression of cell cycle proteins, including cyclin D1, cdk2 and cdk4. Further experiments showed that PPARγ expression in keratinocytes was surprisingly undetectable in vitro or in vivo. Consistent with this, no endogenous PPARγ function in keratinocytes was found, suggesting that the inhibition of troglitazone on keratinocyte proliferation and cell cycle was PPARγ-independent. We further found that troglitazone inhibited insulin/insulin growth factor I (IGF-1) mitogenic signaling, which may explains, at least partly, its inhibitory effect on keratinocyte proliferation. We showed that troglitazone rapidly inhibited IGF-1 induced phosphorylation of p70S6K by mammalian target of rapamycin (mTOR). However, troglitazone did not directly inhibit mTOR kinase activity as shown by in vitro kinase assay. The inhibition of p70S6K is likely to be the result of strong activation of AMP activated protein kinase (AMPK) by TZDs. Stable expression of a dominant negative AMPK in keratinocytes blocked the inhibitory effect of troglitazone on IGF-1 induced phosphorylation of p70S6K. ^ Finally, we found that dietary TZDs inhibited by up to 73% mouse skin tumor development promoted by elevated IGF-1 signaling in BK5-IGF-1 transgenic mice, while they had no or little effect on skin tumor development promoted by 12-O-tetradecanoylphorbol-13-acetate (TPA) or ultraviolet (UV). Since IGF-1 signaling is frequently found to be elevated in patients with insulin resistance and in many human tumors, our data suggest that TZDs may provide tumor preventive benefit particularly to these patients. ^

The biologic and signaling effects of Tiam1 overexpression in colorectal carcinoma

Cellular migration is essential to many normal cellular processes. In tumor cells, aberrant activation of the normal pathways regulating migration is one of the critical steps in the development of metastasis. Previously, I demonstrated for the first time that overexpression of Tiam1, a guanine nucleotide exchange factor (GNEF) for small G proteins in the Rho family, could alter migration in colorectal tumor cells. ^ This dissertation focuses on the roles of Tiam1 in promoting cell migration, survival, and metastasis of colorectal carcinoma cells, utilizing the model system I developed. To determine the in vivo phenotype of the migratory cell lines, athymic nude mice were injected with cells into the orthotopic site. Several of the mice injected with cells of increased migratory potential had metastases. Thus, the in vitro selection for increased migration resulted in increased metastatic potential in vivo, and therefore, the Tiam1-overexpressing cells provide a model to examine signal transduction pathways important to this process. ^ To examine effects of Tiam1 signaling on small G proteins critical to cellular functions associated with migration, I examined the activation status of the small G proteins Rac, Rho, and Cdc42. The cells of increased migratory potential have increased GTP-bound Rac and Rho, compared to control SW480 cells. Cells that overexpress Tiam1 are more migratory and are resistant to detachment-induced death, or anoikis. To determine which effects and phenotypes were Tiam1-specific, we utilized siRNA to downregulate Tiam1 expression. These results demonstrate that Tiam1 is sufficient but not required for the migration of colorectal carcinoma cells in our model system, and that the biologically selected cells have additional changes that promote migration besides the increase in Tiam1. I also show that Tiam1 protects colorectal carcinoma cells from detachment-induced death, but is not required for anoikis resistance in the biologically selected migratory cells. ^ In summary, my studies demonstrate a heretofore-unknown regulator of phenotypes critical to the development of colorectal carcinoma metastases, overexpression of Tiam1. Understanding the mechanism by which Tiam1 contributes to cellular migration and metastasis is crucial to developing desperately needed new therapies for colorectal carcinoma. ^

Calcium mobilization from the endoplasmic reticulum to the mitochondria during apoptosis in prostate cancer

Previous studies have implicated Ca2+ fluxes in the control of apoptosis but their exact roles in regulating the process remain obscure. Because Ca2+ can serve as a signal for cytochrome c release from isolated mitochondria, we hypothesized that alterations in intracellular Ca2+ compartmentalization might serve as a release signal in whole cells undergoing apoptosis. Exposure of human PC-3 prostate adenocarcinoma cells to staurosporine or DNA damaging agent (doxorubicin) but not to anti-Fas antibody led to early release of Ca2+ from the endoplasmic reticulum and subsequent accumulation of Ca2+ within mitochondria. Both events were blocked in cells stably transfected with Bcl-2 but were not affected by treatment with the pancaspase inhibitor, zVADfmk. The effects of staurosporine were associated with re-localization of Bax from the cytosol to both endoplasmic reticular and mitochondrial membranes. Neither ER Ca 2+ pool depletion nor mitochondrial Ca2+ uptake were observed in DU-145 cells that possess a frameshift mutation in the Bax gene unless wild-type Bax was restored via adenoviral gene transfer. Cytochrome c release and downstream features of apoptosis were attenuated by treatment with an inhibitor of mitochondria) Ca2+ uptake (RU-360). Although, direct pharmacological ER Ca2+ pool emptying in cells treated with thapsigargin did not lead to early cytochrome c release, pretreatment of cells with staurosporine dramatically sensitized mitochondria to thapsigargin-induced cytochrome c release. Together, our data demonstrate that ER-to-mitochondrial Ca2+ fluxes promote cytochrome c release and apoptosis in cells exposed to some (but not all) pro-apoptosic stimuli. ^

Activation of dendritic cells from patients with epithelial ovarian cancer

Dendritic cells (DCs) are the most potent antigen-presenting cells for inducing immune responses to tumor cells. Lin−HLA-DR + DC populations in peripheral blood mononuclear cells (PBMCs) and in ascites mononuclear leukocytes (MNLs) of patients with epithelial ovarian cancer (EOC) are phenotypically immature. Lin−HLA-DR + DCs from PBMCs of normal subjects and EOC patients and MNLs from ascites cells of patients were examined for specific cell surface markers or indicators of differentiation or activation. Separating Lin− HLA-DR+ DCs into subsets based on their HLA-DR intensity provided an additional method for identifying the two major lineages of DCs, myeloid and plasmacytoid. The activation potential of these DCs following exposure to the maturation agents CD40 ligand (CD40L) and lipopolysaccharide (LPS) was examined by measurement of IL-12 and IL-10 concentrations in DC culture supernatants in addition to their ability to stimulate allogeneic T cells. DCs from PBMCs of normal subjects and EOC patients and DCs isolated from ascites MNLs of EOC patients were separated into subsets based on CD11c and CD123 cell surface marker expression identifying the major DC types. These subsets were then compared with cells sorted on the basis of HLA-DR intensity. The in vivo behavior of DCs and DC subsets in peripheral blood and ascites following treatment of peritoneal carcinoma patients with the growth factor fins-like tyrosine kinase 3 ligand (Flt3L) was also examined. Increases in proportions and total numbers of DCs from peripheral blood and ascites were associated with increased secretion of IL-12 and IL-10 following in vitro activation of cultured DCs. There were differences between DCs from PBMCs and ascites and between DC subsets in expression of cell surface markers, cytokine profile, and the ability of Lin−HLA-DR + cells to stimulate proliferation of allogeneic T cells from EOC patients. These Lin−HLA-DR+ cells have certain functional properties that suggest that they could have the potential to facilitate an adaptive anti-tumor immune response. ^

Bortezomib modulates TRAIL sensitivity in human bladder and prostate cancer

Tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) is a member of the TNF superfamily of cytokines that can induce cell death through engagement of cognate death receptors. Unlike other death receptor ligands, it selectively kills tumor cells while sparing normal cells. Preclinical studies in non-human primates have generated much enthusiasm regarding its therapeutic potential. However, many human cancer cell lines exhibit significant resistance to TRAIL-induced apoptosis, and the molecular mechanisms underling this are controversial. Possible explanations are typically cell-type dependent, but include alterations of receptor expression, enhancement of pro-apoptotic intracellular signaling molecules, and reductions in anti-apoptotic proteins. We show here that the proteasome inhibitor bortezomib (Velcade, PS-341) produces synergistic apoptosis in both bladder and prostate cancer cell lines within 4-6 hours when co-treated with recombinant human TRAIL which is associated with accumulation of p21 and cdk1/2 inhibition. Our data suggest that bortezomib's mechanism of action involves a p21-dependent enhancement of caspase maturation. Furthermore, we found enhanced tumor cell death in in vivo models using athymic nude mice. This is associated with increases in caspase-8 and caspase-3 cleavage as well as significant reductions in microvessel density (MVD) and proliferation. Although TRAIL alone had less of an effect, its biological significance as a single agent requires further investigations. Toxicity studies reveal that the combination of bortezomib and rhTRAIL has fatal consequences that can be circumvented by altering treatment schedules. Based on our findings, we conclude that this strategy has significant therapeutic potential as an anti-cancer agent. ^

The role of functional tumor suppressor 15-lipoxygenase 2 (15-LOX2) in normal human prostate epithelial cells and prostate cancer development

15-Lipoxygenase 2 (15-LOX2) is a recently cloned human lipoxygenase that shows tissue-restricted expression in prostate, lung, skin, and cornea. The protein level and enzymatic activity of 15-LOX2 have been shown to be down-regulated in prostate cancers compared with normal and benign prostate tissues. We report the cloning and functional characterization of 15-LOX2 and its three splice variants (termed 15-LOX2sv-a, 15-LOX2sv-b, and 15-LOX2sv-c) from primary prostate epithelial (NHP) cells. Western blotting with multiple NHP cell strains and prostate cancer (PCa) cell lines reveals that the expression of 15-LOX2 is lost in all PCa cell lines, accompanied by decreased enzymatic activity. 15-LOX2 is expressed at multiple subcellular locations, including cytoplasm, cytoskeleton, cell-cell border, and nucleus. Surprisingly, the three splice variants of 15-LOX2 are mostly excluded from the nucleus. To elucidate the relationship between nuclear localization, enzymatic activity, and tumor suppressive functions, we established PCa cell clones stably expressing 15-LOX2 or 15-LOX2sv-b. The 15-LOX2 clones express 15-LOX2 in the nuclei and possess robust enzymatic activity, whereas 15-LOX2sv-b clones show neither nuclear protein localization nor arachidonic acid-metabolizing activity. Interestingly, both 15-LOX2- and 15-LOX2sv-b-stable clones proliferate much slower in vitro when compared with control clones. When orthotopically implanted in nude mouse prostate, both 15-LOX2 and 15-LOX2sv-b suppress PC3 tumor growth in vivo. Finally, cultured NHP cells lose the expression of putative stem/progenitor cell markers, slow down in proliferation, and enter senescence. Several pieces of evidence implicate 15-LOX2 plays a role in replicative senescence of NHP cells: (1) promoter activity and the mRNA and protein levels of 15-LOX2 and its splice variants are upregulated in serially passaged NHP cells, which precede replicative senescence and occur in a cell-autonomous manner; (2) PCa cells stably expressing 15-LOX2 or 15-LOX2sv-b show a passage-related senescence-like phenotype; (3) enforced expression of 15-LOX2 or 15-LOX2sv-b in young NHP cells induce partial cell-cycle arrest and senescence-like phenotypes. Together, these results suggest that 15-LOX2 suppress prostate tumor development and do not necessarily depend on arachidonic acid-metabolizing activity and nuclear localization. Also, 15-LOX2 may serve as an endogenous prostate senescence gene and its tumor-suppressing functions might be associated with its ability to induce cell senescence. ^

The role of interleukin-6 in the angiogenesis of ovarian carcinoma

The purpose of this study was to characterize the effects of IL-6 on endothelial cells and to investigate the role of IL-6 in the angiogenesis of ovarian carcinomas. We evaluated human ovarian carcinoma clinical specimens and determined that high expression of IL-6 was associated with increased tumor vascularization. Additionally, endothelial cells derived from the ovary and mesentery expressed the IL-6 receptor (IL-6R), and their stimulation with the exogenous ligand activated downstream signaling molecules and enhanced cell migration. Dual immunohistochemical staining for CD-31 and IL-6R revealed IL-6R expression on human endothelial cells within normal ovary and ovarian carcinomas. To further investigate the possible proangiogenic function of IL-6, Gelfoam sponges containing IL-6 or bFGF were implanted into the subcutis of BALB/c mice. IL-6 containing sponges were vascularized to the same extent as bFGF containing sponges. ^ Chronic stress can adversely affect disease progression. Stimulation of ovarian carcinoma cell lines with concentrations of catecholamines achieved in individuals experiencing chronic stress resulted in a substantial increase in IL-6 production. It was determined that stress mediators regulate IL-6 expression through the β-adrenergic receptor and Src. These data illustrate one mechanism by which chronic stress may influence tumor progression. ^ To investigate whether IL-6 contributes to the angiogenesis of ovarian carcinomas, we isolated low IL-6 expressing clones from the SKOV3.ip1 cell line and transfected them with a plasmid encoding the IL-6 gene. We observed no difference in tumor weight between high and low IL-6 expressing cells. However, while low IL-6 expressing tumors were highly vascularized, high IL-6 expressing tumors appeared hypervascularized. Immunohistochemical analysis revealed that all tumors exhibited robust expression of additional proangiogenic molecules. ^ Collectively, these studies indicate that IL-6 secreted by ovarian cancer cells is a highly proangiogenic cytokine. However, IL-6 is but one of several proangiogenic molecules produced by ovarian cancer, and its inhibition may not be sufficient to inhibit angiogenesis of ovarian carcinoma. The findings presented in this dissertation provide insight into the function of IL-6 as a regulator of angiogenesis. Understanding of the role of proangiogenic molecules such as IL-6 in ovarian carcinoma may have important implications for therapy directed at the vascular component of this disease. ^

Elucidation of the role of 53BP1 in DNA double strand break (DSB) repair and tumor suppression

The protein p53 binding protein one (53BP1) was discovered in a yeast two-hybrid screen that used the DNA binding domain of p53 as bait. Cloning of full-length 53BP1 showed that this protein contains several protein domains which help make up the protein, which include two tandem BRCT domains and a amino-terminal serine/glutamine cluster domain (SCD). These are two protein domains are often seen in factors that are involved in the cellular response to DNA damage and control of cell cycle checkpoints and we hypothesize that 53BP1 is involved in the cellular response to DNA damage. In support of this hypothesis we observe that 53BP1 is phosphorylated and undergoes a dramatic nuclear re-localization in response to DNA damaging agents. 53BP1 also interacts with several factors that are important in the cellular response to DNA damage, such as the BRCA1 tumor suppressor, ATM and Rad3 related (ATR), and the phosphorylated version of the histone variant H2AX. Mice deficient in 53BP1 display increased sensitivity ionizing radiation (IR), a DNA damaging agent that introduces DNA double strand breaks (DSBs). In addition, 53BP1-deficient mice do not properly undergo the process of class switch recombination (CSR). We also observe that when a defect in 53BP1 is combined with a defect in p53; the resulting mice have an increased rate of formation of spontaneous tumors, notably the formation of B and T lineage lymphomas. The T lineage tumors arise by two distinct mechanisms: one driven by defects in cell cycle regulation and a second driven by defects in the ability to repair DNA DSBs. The B lineage tumors arise by the inability to repair DNA damage and over-expression of the oncogene c-myc. ^ With these observations, we conclude that not only does 53BP1 function in the cellular response to DNA damage, but it also works in concert with p53 to suppress tumor formation. ^

Mechanisms involved in suppression of the elicitation of immune responses by ultraviolet light

The ultraviolet radiation (UVR) present in sunlight is the primary cause of nonmelanoma skin cancer and has been implicated in the development of cutaneous malignant melanoma. Ultraviolet radiation also suppresses the immune response. In the majority of studies investigating the mechanisms regulating UV-induced immune suppression, UV is used to suppress the induction of immune responses. Equally important, is the ability of UVR to suppress established immune responses, such as the recall reaction in humans, which protects against microbial infections. We established a murine model to help elucidate the immunological mechanisms governing UV-induced suppression of the elicitation of immune responses. 80 kJ/m2 of UVR nine days after sensitization consistently suppressed the elicitation of delayed type hypersensitivity reaction to C. albicans . We found ultraviolet A (320±400 nm) radiation was as effective as solar-simulated ultraviolet A + B (290±400 nm) in suppressing the elicitation of an established immune response. The mechanisms involved in UV-induced suppression of the induction & elicitation of the immune response are similar. For example, mice irradiated with UV after immunization generated antigen-specific T suppressor cells. Injection of monoclonal antibodies to IL-10 or recombinant IL-12 immediately after exposure to UVR blocked immune suppression. Liposomes containing bacteriophage T4N5 to the skin of mice also prevented immune suppression, demonstrating an essential role for ultraviolet-induced DNA damage in the suppression of established immune reactions. ^ In addition to damaging DNA, UV initiates immune suppression through the isomerization of urocanic acid in the epidermis. Here we provide evidence that cis-UCA induces systemic immunosuppression via the serotonin (5-hydroxyyryptamine; 5-HT) receptor. Biochemical and immunological analysis indicate that cis-UCA binds to, and activates, the serotonin receptor. Moreover, serotonin specific antibodies block UV- and/or cis-UCA-induced immune suppression. Our findings identify cis-UCA as novel serotonin receptor ligand and indicate that serotonin receptor engagement can activate immune suppression. Cumulatively, our data suggest that similar immune regulatory mechanisms are activated regardless of whether we expose mice to solar-simulated UV (UVA + UVB) radiation or UVA only, and that ultraviolet radiation activates similar immunologic pathways to suppress the induction or the elicitation of the immune response. ^

Tumor heterogeneity dictates sensitivity to gefitinib (Iressa(TM)/ZD1839) in solid tumor models

The epidermal growth factor receptor (EGFR) and its ligands are overexpressed in many human tumors, including bladder and pancreas, correlating with a more aggressive tumor phenotype and poor patient prognosis. We initiated the present study to characterize the heterogeneity of gefitinib responsiveness in a panel of human bladder and pancreatic cancer cell lines in order to identify the biological characteristics of EGFR-dependent proliferation that could be used to prospectively identify drug-sensitive tumors. A second objective was to elucidate how to best exploit these results by utilizing gefitinib in combination therapy. To these ends, we examined the effects of the EGFR antagonist gefitinib on proliferation and apoptosis in a panel of 18 human bladder cancer cell lines and 9 human pancreatic cancer cell lines. Our data confirmed the existence of marked heterogeneity in Iressa responsiveness with less than half of the cell lines displaying significant growth inhibition by clinically relevant concentrations of the drug. Gefitinib responsiveness was found to be p27 kip1 dependent as DNA synthesis was restored following exposure to p27siRNA. Unfortunately, Iressa responsiveness was not closely linked to surface EGFR or TGF-α expression in the bladder cancer cells, however, cellular TGF-α expression correlated directly with Iressa sensitivity in the pancreatic cancer cell lines. These findings provide the potential for prospectively identifying patients with drug-sensitive tumors. ^ Further studies aimed at exploiting gefitinib-mediated cell cycle effects led us to investigate if gefitinib-mediated TRAIL sensitization correlated with increased p27kip1 accumulation. We observed that increased TRAIL sensitivity following gefitinib exposure was not dependent on p27 kip1 expression. Additional studies initiated to examine the role(s) of Akt and Erk signaling demonstrated that exposure to PI3K or MEK inhibitors significantly enhanced TRAIL-induced apoptosis at concentrations that block target phosphorylation. Furthermore, combinations of TRAIL and the PI3K or MEK inhibitors increased procaspase-8 processing above levels observed with TRAIL alone, indicating that the effects were exerted at the level of caspase-8 activation, considered the earliest step in the TRAIL pathway. ^

The transcription factor nuclear factor kappa B (NFkappaB) maintains TRAIL resistance in human pancreatic cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) is a member of the TNF family of cytokines that induces apoptosis in a variety of tumor cells while sparing normal cells. However, many human cancer cell lines display resistance to TRAIL-induced apoptosis and the mechanisms contributing to resistance remain controversial. Previous studies have demonstrated that the dimeric transcription factor Nuclear Factor kappa B (NFκB) is constitutively active in a majority of human pancreatic cancer cell lines and primary tumors, and although its role in tumor progression remains unclear it has been suggested that NFκB contributes to TRAIL resistance. Based on this, I examined the effects of NFκB inhibitors on TRAIL sensitivity in a panel of nine pancreatic cancer cell lines. I show here that inhibitors of NFκB, including two inhibitors of the proteasome (bortezomib (Velcade™, PS-341) and NPI-0052), a small molecule inhibitor of IKK (PS1145), and a novel synthetic diterpene NIK inhibitor (NPI-1342) reverse TRAIL resistance in pancreatic cancer cell lines. Further analysis revealed that the expression of the anti-apoptosic proteins BclXL and XIAP was significantly decreased following exposure to these inhibitors alone and in combination with TRAIL. Additionally, treatment with NPI0052 and TRAIL significantly reduced tumor burden relative to the control tumors in an L3.6pl orthotopic pancreatic xenograft model. This was associated with a significant decrease in proliferation and an increase in caspase 3 and 8 cleavage. Combination therapy employing PS1145 or NPI-1342 in combination with TRAIL also resulted in a significant reduction in tumor burden compared to either agent alone in a Panc1 orthotopic xenograft model. My studies show that combination therapy with inhibitors of NFκB alone and TRAIL is effective in pre-clinical models of pancreatic cancer and suggests that the approach should be evaluated in patients. ^

Insights into the biology of lymphatic metastasis

Recent data suggest that the generation of new lymphatic vessels (i.e. lymphangiogenesis) may be a rate-limiting step in the dissemination of tumor cells to regional lymph nodes. However, efforts to study the cellular and molecular interactions that take place between tumor cells and lymphatic endothelial cells have been limited due to a lack of lymphatic endothelial cell lines available for study. ^ I have used a microsurgical approach to establish conditionally immortalized lymphatic endothelial cell lines from the afferent mesenteric lymphatic vessels of mice. Characterization of lymphatic endothelial cells, and tumor-associated lymphatic vessels revealed high expression levels of VCAM-1, which is known to facilitate adhesion of some tumor cells to vascular endothelial cells. Further investigation revealed that murine melanoma cells selected for high expression of α4, a counter-receptor for VCAM-1, demonstrated enhanced adhesion to lymphatic endothelial cells in vitro, and increased tumorigenicity and lymphatic metastasis in vivo, despite similar lymphatic vessel numbers. ^ Next, I examined the effects of growth factors that regulate lymphangiogenesis, and report that several growth factors are capable of activating survival and proliferation pathways of lymphatic endothelial cells. The dual protein tyrosine kinase inhibitor AEE788 (EGFR and VEGFR-2) inhibited the activation of Akt and MAPK in lymphatic endothelial cells responding to multiple growth factors. Moreover, oral treatment of mice with AEE788 decreased lymphatic vessel density and production of lymphatic metastasis by human colon cancer cells growing in the cecum of nude mice. ^ In the last set of experiments, I investigated the surgical management of lymphatic metastasis using a novel model of sentinel lymphadenectomy in live mice bearing subcutaneous B16-BL6 melanoma. The data demonstrate that this procedure when combined with wide excision of the primary melanoma, significantly enhanced survival of syngeneic C57BL/6 mice. ^ Collectively, these results indicate that the production of lymphatic metastasis depends on lymphangiogenesis, tumor cell adhesion to lymphatic endothelial cells, and proliferation of tumor cells in lymph nodes. Thus, lymphatic metastasis is a multi-step, complex, and active process that depends upon multiple interactions between tumor cells and tumor associated lymphatic endothelial cells. ^

The effects of proteasome inhibition in chronic lymphocytic leukemia and prostate cancer

The use of proteasome inhibitors in cancer has received much attention with the recent FDA approval of bortezomib (Velcade/PS-341). However, in the chronic lymphocytic leukemia (CLL) clinical trial, bortezomib was not as effective as it was in vitro. Accordingly, results in prostate cancer were not remarkable, although regression of lymphadenopathy was observed. This response was also seen in CLL. ^ The proteasome degrades ∼80% of intracellular proteins. Although specific pathways affected by proteasome inhibitors are known, there are still unidentified mechanisms by which they induce apoptosis. The efficacy and mechanism of action of the reversible proteasome inhibitor bortezomib were compared to the novel irreversible inhibitor NPI-0052 in this study, and their mechanisms of action in CLL and prostate cancer were examined. ^ NPI-0052 inhibited proteasome activity and induced apoptosis with more rapid kinetics than bortezomib in CLL. Inhibition of proteasome activity with NPI-0052 was also more durable. Interestingly, bortezomib is cleared from the serum within 15min, which is insufficient time for bortezomib to effectively inhibit the proteasome. However, only 5min exposure was needed for NPI-0052 to produce maximal proteasome inhibition. The data suggest that bortezomib's slow kinetics and reversible nature limit its potential in vivo and the use of NPI-0052 should be considered. ^ In examining the mechanism(s) by which bortezomib and NPI-0052 induce apoptosis in CLL, both were found to elicit the ER stress pathway. A stromal cell co-culture system prevented apoptosis induced by both proteasome inhibitors, suggesting that if such factors in vivo were responsible for reducing bortezomib's efficacy, NPI-0052 would not prove useful either. Finally, Lyn, a Src family kinase (SFK), was decreased in response to bortezomib and NPI-0052 and correlated with apoptosis induction in CLL and prostate cancer. Both proteasome inhibitors specifically targeted Lyn rather than SFKs in general. ^ SFKs are overexpressed in cancer and involved in cell signaling, survival, and metastasis. In prostate cancer cells, both proteasome inhibition and Lyn-silencing significantly inhibited migration. Preliminary evidence also suggested that Lyn downregulation decreases invasion potential. Together, these data suggest that proteasome inhibitors are potential candidates for anti-metastasic therapy and further investigation is warranted for the use of Lyn-targeted therapy to treat metastases. ^

Ligand-directed targeting of malignant gliomas

The dramatic poor survival of patients diagnosed with glioblastoma multiforme (GBM) is a reflection of the struggles that accompany traditional treatments. Thus, the development of molecular-based targeted therapies represents new windows for intervention. In this study, we hypothesized that we could select peptide-ligands that selectively target GBM based on the idea that the glioma microenvironment may induce or modify the expression of cell surface receptors that could be accessed by circulating peptides. To select the peptides we employed two distinct in vivo screenings. First, a random phage-displayed peptide library was injected into mice bearing intracranial tumors. Phage that bound to tumor were recovered and sequenced. We found that the tumor-derived phage CLSYKGRC, CNKVSTKC and CQSSREKC were recovered with the highest frequencies and used for subsequent targeting experiments. Second, the phage peptide library was injected into mice without tumors and phage were recovered from brain and sequenced. A phage-displayed peptide (CRTIGPSVC) with homology to transferrin (Tf) was selected and injected into brain tumor-bearing mice. Results showed that after 6 hours of circulation, the CLSYKGRC, CNKVSTKC and CQSSREKC-phage selectively targeted GBM vasculature. In contrast, Tf-like phage accumulated outside the tumor blood vessels in the cytoplasm of cells located within GBM, suggesting it was internalized in vivo. However, after short periods of circulation this phage was restricted to the tumor vasculature. Importantly, none of the selected phage targeted normal brain cells in animals bearing intracranial tumors. An affinity column coupled to the CNKVSTKC zpeptide was used to identify receptors from GBM. Using mass-spectrometry Vimentin, a marker of glial malignancy, was identified as a potential receptor. Other studies showed that the Tf-like phage bound selectively to Apo-Tf (iron free), with no binding to Holo-Tf (iron loaded) or to Tf receptor (TfR). However, the binding of Tf-like phage to glioma cells that express TfR increased in the presence of Apo-Tf. Thus, the Tf-like phage could indirectly target TfR using the endogenous Tf pathway. We propose that the novel peptides identified in this study could be conjugated to therapeutic or imaging agents for use GBM. ^