Unbiased Phenotype-Based Screen Identifies Therapeutic Agents Selective for Metastatic Prostate Cancer

In American men, prostate cancer is the second leading cause of cancer-related death. Dissemination of prostate cancer cells to distant organs significantly worsens patients' prognosis, and currently there are no effective treatment options that can cure advanced-stage prostate cancer. In an effort to identify compounds selective for metastatic prostate cancer cells over benign prostate cancer cells or normal prostate epithelial cells, we applied a phenotype-based in vitro drug screening method utilizing multiple prostate cancer cell lines to test 1,120 different compounds from a commercial drug library. Top drug candidates were then examined in multiple mouse xenograft models including subcutaneous tumor growth, experimental lung metastasis, and experimental bone metastasis assays. A subset of compounds including fenbendazole, fluspirilene, clofazimine, niclosamide, and suloctidil showed preferential cytotoxicity and apoptosis towards metastatic prostate cancer cells in vitro and in vivo. The bioavailability of the most discerning agents, especially fenbendazole and albendazole, was improved by formulating as micelles or nanoparticles. The enhanced forms of fenbendazole and albendazole significantly prolonged survival in mice bearing metastases, and albendazole-treated mice displayed significantly longer median survival times than paclitaxel-treated mice. Importantly, these drugs effectively targeted taxane-resistant tumors and bone metastases - two common clinical conditions in patients with aggressive prostate cancer. In summary, we find that metastatic prostate tumor cells differ from benign prostate tumor cells in their sensitivity to certain drug classes. Taken together, our results strongly suggest that albendazole, an anthelmintic medication, may represent a potential adjuvant or neoadjuvant to standard therapy in the treatment of disseminated prostate cancer.

Adjuvant-pulsed mRNA vaccine nanoparticle for immunoprophylactic and therapeutic tumor suppression in mice

Synthetic mRNA represents an exciting cancer vaccine technology for the implementation of effective cancer immunotherapy. However, inefficient in vivo mRNA delivery along with a requirement for immune co-stimulation present major hurdles to achieving anti-tumor therapeutic efficacy. Here, we demonstrate a proof-of-concept adjuvant-pulsed mRNA vaccine nanoparticle (NP) that is composed of an ovalbumin-coded mRNA and a palmitic acid-modified TLR7/8 agonist R848 (C16-R848), coated with a lipid-polyethylene glycol (lipid-PEG) shell. This mRNA vaccine NP formulation retained the adjuvant activity of encapsulated C16-R848 and markedly improved the transfection efficacy of the mRNA (>95%) and subsequent MHC class I presentation of OVA mRNA derived antigen in antigen-presenting cells. The C16-R848 adjuvant-pulsed mRNA vaccine NP approach induced an effective adaptive immune response by significantly improving the expansion of OVA-specific CD8+ T cells and infiltration of these cells into the tumor bed in vivo, relative to the mRNA vaccine NP without adjuvant. The approach led to an effective anti-tumor immunity against OVA expressing syngeneic allograft mouse models of lymphoma and prostate cancer, resulting in a significant prevention of tumor growth when the vaccine was given before tumor engraftment (84% reduction vs. control) and suppression of tumor growth when given post engraftment (60% reduction vs. control). Our findings indicate that C16-R848 adjuvant pulsation to mRNA vaccine NP is a rational design strategy to increase the effectiveness of synthetic mRNA vaccines for cancer immunotherapy.

Abstract 508: A novel orally available Wnt-pathway inhibitor for the treatment of metastatic cancers

We have developed a novel drug compound (OBD9) which blocks growth of metastatic cancer cells both in vitro and in vivo. We now identify OBD9 as an effective Wnt-signaling inhibitor targeting TNIK (TRAF2 And NCK Interacting Kinase) and we hypothesize that OBD9 represent a novel therapeutic option for patients with tumors that have an activated Wnt signaling pathway.

To find novel drug candidates that selectively inhibit metastatic tumor cell viability, a drug screen was firstly performed and results of the screen identified members of the FDA-approved benzimidazole methylcarbamate family (e.g. mebendazole (MBZ) and albendazole (ALB)) as potential therapies for metastatic cancer. Earlier work also supports a role for this chemical family in the potential treatment of multiple cancers, but progress has been stalled by their poor water solubility and poor bioavailability for systemic delivery to disseminated tumors. We therefore synthesized a novel compound (OBD9) containing the scaffold of MBZ coupled to an oxetane group to enhance aqueous solubility to 361μM. OBD9 demonstrates significant cytotoxicity toward a variety of cancer cell types including colon, lung, and prostate cancers (IC50: 0.9-2μM). In a mouse xenograft model using highly aggressive PCMLN3 prostate cancer cells, OBD9 at 30 mg/kg significantly repressed growth of established tumors with no visible toxicity. In a mouse xenograft model of human A549 lung cancer cell line, orally delivered OBD9 also dramatically inhibited the growth of established tumors at 30 or 90μM without noticeable toxicity.

Mechanistically, we find that OBD9 treatment significantly reduces TNIK levels as early as 4 hours at 1uM via an autophagy-dependent protein degradation pathway. TNIK functions as an activator of Wnt signaling pathway via phosphorylation of the beta-catenin/TCF4 complex that regulates Wnt downstream targets. We show that OBD9 treatment inhibits colon cancer cell growth and both qPCR and Western blot data suggest that Wnt signaling downstream targets, such as TCF4, AXIN2 and cMyc, are all significantly suppressed by OBD9 via the inhibition of TNIK. Overall, our in vitro and in vivo data suggest that OBD9 potentially represents a novel therapeutic option for multiple cancers including but not limit to colon, lung and prostate cancer.

Citation Format: Kun Zhou, Jae Eun Cheong, Catherine Alix-Panabières, Lijun Sun, Bruce R. Zetter. A novel orally available Wnt-pathway inhibitor for the treatment of metastatic cancers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 508.

Lipidation Approaches Potentiate Adjuvant-Pulsed Immune Surveillance: A Design Rationale for Cancer Nanovaccine

Adjuvant-pulsed peptide vaccines hold great promise for the prevention and treatment of different diseases including cancer. However, it has been difficult to maximize vaccine efficacy due to numerous obstacles including the unfavorable tolerability profile of adjuvants, instability of peptide antigens, limited cellular uptake, and fast diffusion from the injection site, as well as systemic adverse effects. Here we describe a robust lipidation approach for effective nanoparticle co-delivery of low-molecular weight immunomodulators (TLR7/8 agonists) and peptides (SIINFEKL) with a potent in vivo prophylactic effect. The lipidation approaches (C₁₆-R848 and C₁₆-SIINFEKL) increased their hydrophobicity that is intended not only to improve drug encapsulation efficiency but also to facilitate the membrane association, intracellular trafficking, and subcellular localization. The polymer-lipid hybrid nanoparticles (PLNs) are designed to sustain antigen/adjuvant levels with less systemic exposure. Our results demonstrated that a lipidated nanovaccine can induce effective immunity by enhancing the expansion and activation of antigen-specific CD8⁺ T cells. This adaptive immune response led to substantial tumor suppression with improved overall survival in a prophylactic setting. Our new methodology enhances the potential of nanovaccines for anti-tumor therapy.

Developing a novel FRET assay, targeting the binding between Antizyme-AZIN

Antizyme inhibitor (AZIN) stimulates cell proliferation by binding to and sequestering the cell cycle suppressor antizyme. Despite the important role of the antizyme-AZIN protein-protein interaction (PPI) in cell cycle regulation, there are no assays for directly measuring the binding of AZIN to antizyme that are amenable to high throughput screening. To address this problem, we developed and validated a novel antizyme-AZIN intramolecular FRET sensor using clover and mRuby2 fluorescent proteins. By introducing alanine mutations in the AZIN protein, we used this sensor to probe the PPI for key residues governing the binding interaction. We found that like many PPIs, the energy of the antizyme-AZIN binding interaction is distributed across many amino acid residues; mutation of individual residues did not have a significant effect on disrupting the PPI. We also examined the interaction between Clover-AZIN and antizyme-mRuby2 in cells. Evidence of a direct interaction between Clover-AZIN and antizyme-mRuby2 was observed within cells, validating the use of this FRET sensor for probing intracellular antizyme-AZIN PPI. In conclusion, we have developed and optimized a FRET sensor which can be adapted for high throughput screening of either in vitro or intracellular activity.

Restoration of tumour-growth suppression in vivo via systemic nanoparticle-mediated delivery of PTEN mRNA

PTEN is a well-characterized tumour-suppressor gene that is lost or mutated in about half of metastatic castration-resistant prostate cancers and in many other human cancers. The restoration of functional PTEN as a treatment for prostate cancer has however proven difficult. Here, we show that PTEN mRNA can be reintroduced into PTEN-null prostate cancer cells in vitro and in vivo via its encapsulation in polymer-lipid hybrid nanoparticles coated with a poly(ethylene glycol) shell. The nanoparticles are stable in serum, elicit low toxicity, enable high PTEN mRNA transfection in prostate cancer cells, and lead to significant inhibition of tumour growth when delivered systemically in multiple mouse models of prostate cancer. We also show that the restoration of PTEN function in PTEN-null prostate cancer cells inhibits the PI3K-AKT pathway and enhances apoptosis. Our findings provide proof-of-principle evidence of the restoration of mRNA-based tumour suppression in vivo.

Abstract LB-311: Characterization of the antizyme/antizyme inhibitor protein-protein interaction using a novel FRET sensor

The protein-protein interaction (PPI) between the tumor suppressor antizyme (AZ) and its endogenous regulator antizyme inhibitor (AZIN) has recently been demonstrated to be important in several human cancers. AZIN siRNA treatment reduces AZIN expression and slows prostate cancer cell growth in vitro and in vivo but is not currently a viable therapeutic strategy. To further probe the AZ/AZIN PPI and to screen for potential small molecule inhibitors, we have developed a FRET assay (Z score >0.7) utilizing the Clover (donor) and mRuby2 (acceptor) fluorescent proteins linked to AZIN and AZ, respectively. An alanine mutant screen of 43 amino acid positions in the AZIN protein revealed 2 hotspots that dramatically affect the affinity for the AZ protein, thereby identifying key regions for disruption by potential therapeutics. Furthermore, mutating the N327 and Y331 positions in ornithine decarboxylase (ODC) to equivalent residues in the homologous AZIN protein, increased the affinity of ODC for AZ, providing evidence for key residues that contribute to AZ/AZIN PPI. In addition, the S367G AZIN mutation, which is associated with an mRNA editing event in hepatocellular carcinoma, further increases the affinity of AZIN for AZ and supports a mechanism of AZ sequestration as an important driver in cancer cell growth. Taken together, this data expands our current understanding of the contribution of different amino acid residues to the AZ/AZIN binding interaction. The development of small molecule inhibitors to target these regions of the AZIN protein would rescue the tumor suppressive activity of AZ and present a novel therapeutic opportunity for the treatment of prostate cancer and hepatocellular carcinoma.

Note: This abstract was not presented at the meeting.

Citation Format: James M. Rice, Michael S. Rogers, Bruce R. Zetter. Characterization of the antizyme/antizyme inhibitor protein-protein interaction using a novel FRET sensor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-311. doi:10.1158/1538-7445.AM2017-LB-311

Abstract 1231: Restoration of tumor suppression in vivo by systemic delivery of PTEN mRNA nanoparticles

PTEN (phosphatase and tensin homolog on chromosome ten) is one of the most common lost or mutated tumor suppressor genes in human cancers, including ~50% of metastatic castration-resistant prostate cancer (mCRPC). By catalyzing PIP3 dephosphorylation, PTEN negatively regulates the PI3K-AKT-mTOR pathway, which is frequently altered in mCRPC. Reintroduction of functional PTEN for mCRPC treatment has proven difficult. By employing self-assembled lipid-polymer hybrid nanoparticle platforms, we successfully reintroduced PTEN mRNA to PTEN-null prostate cancer cells both in vitro and in vivo. These mRNA-loaded nanoparticles demonstrate high protein expression efficiency, low toxicity and good stability in serum and tumor accumulation. We confirmed that restoration of PTEN in PTEN-null prostate cancer cells inhibits the PI3k-AKT pathway, reduces cell viability and enhances apoptosis in vitro. Systemic delivery of PTEN mRNA-loaded nanoparticles in prostate xenograft tumors results in ~85% inhibition of tumor growth and leads to tumor cell death without toxic side effects in vivo. In summary, this work provides proof of concept of mRNA-based gene therapy for systemic restoration of functional PTEN for tumor suppression in vivo. It represents a novel approach to PI3K-AKT pathway inhibition, with the potential to specifically target cancers with loss of PTEN function.

Citation Format: Yingjie Xu, Mohammad Ariful Islam, Harshal Zope, Morteza Mahmoudi, Robert S. Langer, Jinjun Shi, Bruce R. Zetter, Omid C. Farokhzad. Restoration of tumor suppression in vivo by systemic delivery of PTEN mRNA nanoparticles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1231. doi:10.1158/1538-7445.AM2017-1231

Restoration of tumor suppression in vivo by systemic delivery of chemically-modified PTEN mRNA nanoparticles

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Background: The onset and maintenance of cancer frequently involves gain of oncogenic function along with loss of tumor suppression. PTEN is a well-characterized tumor suppressor gene that is lost or mutated in many human cancers including ~50% of metastatic castration-resistant prostate cancer (mCRPC). Reintroduction of functional PTEN for mCRPC treatment has proven difficult. Methods: PTEN mRNA was synthesized by in vitro transcription method and modified with ARCA capping and enzymatic polyadenylation, and then substituted with Pseudo-UTP, 5’-Methyl-CTP. A robust self-assembly approach was employed to prepare PTEN mRNA nanoparticles (NPs) using cationic lipid-like compound G0-C14 and PLGA polymer coated with lipid-PEG shell. PTEN expression in tumors and PI3K-AKT pathway were confirmed by IHC and western blot, respectively. Apoptosis was checked by flow cytometry and Tunel assays. In vivo toxicity was studied by hematologic and histologic tests, and immune response. Results: We successfully restored PTEN mRNA to PTEN-null prostate cancer (PCa) cells via systemic delivery of mRNA NPs. These mRNA NPs are stable in serum, demonstrate minimal toxicity, and provide highly effective transfection in PCa cells (substantially higher HA-PTEN expression than plasmid PTEN transfection) and PCa xenograft tumors, leading to ~85% inhibition of tumor cell growth in vitro and in vivo. We also confirm mRNA NP-mediated systemic restoration of PTEN function in PTEN-null PCa and delineate its tumor suppression through inhibition of the PI3K-AKT pathway and enhancement of apoptosis. Conclusions: The work provides proof of principle for the systemic reintroduction of mRNA-based tumor suppressor genes to tumors in vivo. Because PTEN loss is frequent in late-stage PCa, this approach may have feasibility in this patient population. Considering the strong potential of mRNA therapy and the lack of systemic studies of in vivo mRNA transfection of tumors, this study sheds light on the useful application of NP-mediated mRNA delivery for validating tumor suppressors (e.g., PTEN) as a therapeutic target in cancer treatment where loss of a tumor suppressor contributes to the underlying genetic mechanism of cancer.

Abstract 4565: Antizyme inhibitor regulates the expression of proteins involved in mitosis and affects prostate cancer cell growth

Upregulation of polyamine biosynthesis is a requirement for cell growth and proliferation. Increases in polyamine levels are mediated by the enzyme ornithine decarboxylase (ODC), which is inhibited by antizyme (AZ). Rescue of ODC activity is accomplished by expression of antizyme inhibitor (AZI), which prevents binding of AZ to ODC. Increases in AZI gene copy number, mRNA transcripts, protein expression and AZI nuclear localization are all associated with prostate cancer. Furthermore, knockdown of AZI expression prevents prostate cancer cell growth in vitro and in vivo. To determine if AZI regulation affects prostate cancer cell growth via mechanisms that are independent of polyamide levels, we conducted a proteomic analysis of the AZI interactome by co-IP and MS/MS. This resulted in the identification of 29 high-confidence interacting proteins (HCIPs), 10 of which are associated with microtubules or with the mitotic spindle including TPX2 and KIFC1. Constitutive overexpression of AZI in PC3M-LN4 prostate cancer cells leads to a decrease in expression of the microtubule associated protein KIFC1, further supporting an interaction between AZI and KIFC1. Silencing of AZI gene expression using siRNA nanoparticles results in a decrease in prostate cancer cell proliferation and altered expression of proteins involved in mitosis. Taken together, this data suggests that AZI may influence prostate cancer cell proliferation via mechanisms that are independent of polyamine regulation.

Citation Format: James M. Rice, Amanda Kusztos, Bruce R. Zetter. Antizyme inhibitor regulates the expression of proteins involved in mitosis and affects prostate cancer cell growth. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4565.

Biomaterials for mRNA delivery

Messenger RNA (mRNA) has recently emerged with remarkable potential as an effective alternative to DNA-based therapies because of several unique advantages. mRNA does not require nuclear entry for transfection activity and has a negligible chance of integrating into the host genome which excludes the possibility of potentially detrimental genomic alternations. Chemical modification of mRNA has further enhanced its stability and decreased its activation of innate immune responses. Additionally, mRNA has been found to have rapid expression and predictable kinetics. Nevertheless, the ubiquitous application of mRNA remains challenging given its unfavorable attributes, such as large size, negative charge and susceptibility to enzymatic degradation. Further refinement of mRNA delivery modalities is therefore essential for its development as a therapeutic tool. This review provides an exclusive overview of current state-of-the-art biomaterials and nanotechnology platforms for mRNA delivery, and discusses future prospects to bring these exciting technologies into clinical practice.

Abstract 18: Prohibitin 1 regulates apoptosis via its interaction with XIAP

Prohibitin 1 (PHB1) belongs to an evolutionarily highly conserved family of proteins that share the stomatin/prohibitin/flotillin/HflK/C (SPFH) domain. PHB1 has been implicated in the regulation of diverse cellular processes, including cell-cycle progression, transcriptional regulation, apoptosis, mitochondrial biogenesis, and as a cell-surface receptor. To better understand the function of PHB1, we analyzed PHB1 protein interactors using Immunoprecipitation followed by mass spectrometry analysis (IP-MS). We identified the X-linked inhibitor of apoptosis protein (XIAP) as a novel PHB1-binding partner. The interaction of PHB1-XIAP has been confirmed both in vitro and in vivo. Using immunofluorescence staining, We observed that PHB1 and XIAP colocalized upon induction of apoptosis. Using various XIAP mutant constructs, we showed that PHB1 binds principally to the BIR3 domain of XIAP. In addition, silencing of either PHB1 or XIAP sensitized cells to chemotherapeutic drug-induced cell apoptosis and partially rescued the chemosensitivity of resistant cancer cells. The observation that PHB1 silencing decreased XIAP levels with a concomitant increase in XIAP cleavage suggests that the formation of a PHB1-XIAP complex inhibits apoptosis by enhancing XIAP stability. Our findings indicate that the PHB1-XIAP complex promotes an anti-apoptotic response in cancer cells and reinforces the potential of PHB1 as a therapeutic target.

Citation Format: Yingjie Xu, Wen Yang, Virginia Guarani, Jinjun Shi, J. Wade Harper, Bruce R. Zetter. Prohibitin 1 regulates apoptosis via its interaction with XIAP. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 18. doi:10.1158/1538-7445.AM2015-18

Identification of a transcriptional profile associated with in vitro invasion in non-small cell lung cancer cell lines

Although much has been learned about basic mechanisms of cell invasion, the genes whose expression is required for this process by malignant cell lines have remained obscure. We assessed invasion through Matrigel using EGF as a chemoattractant and gene expression profiles using oligonucleotide microarrays for 22 non-small cell lung cancer cell lines. The expression of 22 genes were significantly correlated (p < 0.001) with the measured invasion index. Cluster analysis demonstrated that gene expression profiles classify the cell lines into low and high invasive subgroups. Considering invasiveness as a dichotomous variable, Bayesian analysis was used to identify genes that have the highest probability of being differentially expressed between the high and low invasion groups. This analysis identified 16 genes whose expression was associated with invasiveness. "Leave one out" cross validation was 91% accurate. Nine genes were identified in both correlation and Bayesian analyses. Seven of the nine genes were negatively associated with invasion and four of those genes are plasma membrane proteins. The two genes with the highest inverse association with invasion, TACSTD1 and CLDN3, are involved with cell adhesion and cell-cell interactions, respectively. Interestingly, the gene with the highest positive association with invasion, SERPINE1 (PAI-1), is a protease inhibitor. These and the other genes identified by both analyses represent targets for further study to assess their importance in non-small cell lung cancer invasion and metastasis.

Hybrid lipid-polymer nanoparticles for sustained siRNA delivery and gene silencing

The development of controlled-release nanoparticle (NP) technologies has great potential to further improve the therapeutic efficacy of RNA interference (RNAi), by prolonging the release of small interfering RNA (siRNA) for sustained, long-term gene silencing. Herein, we present an NP platform with sustained siRNA-release properties, which can be self-assembled using biodegradable and biocompatible polymers and lipids. The hybrid lipid-polymer NPs showed excellent silencing efficacy, and the temporal release of siRNA from the NPs continued for over one month. When tested on luciferase-expressed HeLa cells and A549 lung carcinoma cells after short-term transfection, the siRNA NPs showed greater sustained silencing activity than lipofectamine 2000-siRNA complexes. More importantly, the NP-mediated sustained silencing of prohibitin 1 (PHB1) generates more effective tumor cell growth inhibition in vitro and in vivo than the lipofectamine complexes. We expect that this sustained-release siRNA NP platform could be of interest in both fundamental biological studies and clinical applications.

FROM THE CLINICAL EDITOR

Emerging gene silencing applications could be greatly enhanced by prolonging the release of siRNA for sustained gene silencing. This team of scientists presents a hybrid lipid-polymer nanoparticle platform that successfully accomplishes this goal, paving the way to future research studies and potential clinical applications.

Interleukin-6 is required for pancreatic cancer progression by promoting MAPK signaling activation and oxidative stress resistance

Pancreatic cancer, one of the deadliest human malignancies, is almost invariably associated with the presence of an oncogenic form of Kras. Mice expressing oncogenic Kras in the pancreas recapitulate the stepwise progression of the human disease. The inflammatory cytokine interleukin (IL)-6 is often expressed by multiple cell types within the tumor microenvironment. Here, we show that IL-6 is required for the maintenance and progression of pancreatic cancer precursor lesions. In fact, the lack of IL-6 completely ablates cancer progression even in presence of oncogenic Kras. Mechanistically, we show that IL-6 synergizes with oncogenic Kras to activate the reactive oxygen species detoxification program downstream of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling cascade. In addition, IL-6 regulates the inflammatory microenvironment of pancreatic cancer throughout its progression, providing several signals that are essential for carcinogenesis. Thus, IL-6 emerges as a key player at all stages of pancreatic carcinogenesis and a potential therapeutic target.

Abstract 4529: Self-assembled lipid-polymer hybrid nanoparticles for the sustained delivery of siRNA and the treatment of drug-resistant cancers

RNA interference (RNAi), which can selectively knockdown target genes, has shown great potential in the treatment of various diseases including cancer. Thus far, numerous nanoparticle (NP) platforms such as lipoplex and polyplex have been developed to facilitate the safe and effective delivery of small interfering RNA (siRNA), which represents a major hurdle for the clinical applications of RNAi. Nevertheless, these NP systems lack the sustained siRNA release property, and thus can only induce transient gene silencing due to the short lifetime of siRNA. Therefore, the delivery of siRNA using controlled-release NPs would be necessary for achieving sustained gene silencing.

Herein, we will present a novel NP platform for safe and effective siRNA delivery in a sustained manner, which can be developed through the self-assembly of biodegradable and biocompatible polymers and lipids. The lipid-polymer hybrid NPs show excellent in vitro knockdown efficacy at low doses of siRNA, and promising in vivo results for delivering siRNA to xenograft tumors. More importantly, these NPs can control the temporal release of siRNA, with the half-release time of ∼ 9 days, for sustained silencing of target gene expression. Results demonstrate that the luciferase expression is still less than 25% at day 7 when the lucifrease-expressed HeLa cells were transfected with the NPs containing 40 pmol anti-luciferase siRNA. As a comparison, the luciferase expression is largely recovered (∼ 80%) at day 7, after transfection with lipo2000-siRNA complexes. Furthermore, this NP platform has been applied to deliver anti-drug resistance siRNA (e.g., anti-PHB1) and chemotherapeutic drugs (e.g., taxanes) for the effective treatment of drug resistant cancers. We believe that the lipid-polymer hybrid NP platform with the property of sustained siRNA release could hold potential in both fundamental studies and clinical applications.

Citation Format: Jinjun Shi, Yingjie Xu, Xiaoyang Xu, Alexander Votruba, Xi Zhu, Eric Pridgen, Zeyu Xiao, Robert Langer, Bruce R. Zetter, Omid C. Farokhzad. Self-assembled lipid-polymer hybrid nanoparticles for the sustained delivery of siRNA and the treatment of drug-resistant cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4529. doi:10.1158/1538-7445.AM2013-4529

Cytoskeletal stiffness, friction, and fluidity of cancer cell lines with different metastatic potential

We quantified mechanical properties of cancer cells differing in metastatic potential. These cells included normal and H-ras-transformed NIH3T3 fibroblast cells, normal and oncoprotein-overexpressing MCF10A breast cancer cells, and weakly and strongly metastatic cancer cell line pairs originating from human cancers of the skin (A375P and A375SM cells), kidney (SN12C and SN12PM6 cells), prostate (PC3M and PC3MLN4 cells), and bladder (253J and 253JB5 cells). Using magnetic twisting cytometry, cytoskeletal stiffness (g') and internal friction (g″) were measured over a wide frequency range. The dependencies of g' and g″ upon frequency were used to determine the power law exponent x which is a direct measure of cytoskeletal fluidity and quantifies where the cytoskeleton resides along the spectrum of solid-like (x = 1) to fluid-like (x = 2) states. Cytoskeletal fluidity x increased following transformation by H-ras oncogene expression in NIH3T3 cells, overexpression of ErbB2 and 14-3-3-ζ in MCF10A cells, and implantation and growth of PC3M and 253J cells in the prostate and bladder, respectively. Each of these perturbations that had previously been shown to enhance cancer cell motility and invasion are shown here to shift the cytoskeleton towards a more fluid-like state. In contrast, strongly metastatic A375SM and SN12PM6 cells that disseminate by lodging in the microcirculation of peripheral organs had smaller x than did their weakly metastatic cell line pairs A375P and SN12C, respectively. Thus, enhanced hematological dissemination was associated with decreased x and a shift towards a more solid-like cytoskeleton. Taken together, these results are consistent with the notion that adaptations known to enhance metastatic ability in cancer cell lines define a spectrum of fluid-like versus solid-like states, and the position of the cancer cell within this spectrum may be a determinant of cancer progression.

Abstract 391: Insulin-like Growth Factors Promote Vasculogenesis in Embryonic Stem Cells

The ability of embryonic stem cells to differentiate into endothelium and form functional blood vessels has been well established and can potentially be harnessed for therapeutic angiogenesis. However, after almost two decades of investigation in this field, limited knowledge exists for directing endothelial differentiation. A better understanding of the cellular mechanisms regulating vasculogenesis is required for the development of embryonic stem cell-based models and therapies. In this study, we elucidated the mechanistic role of insulin-like growth factors (IGF1 and 2) and IGF receptors (IGFR1 and 2) in endothelial differentiation using an embryonic stem cell embryoid body model. Both IGF1 and IGF2 predisposed embryonic stem to differentiate towards a mesodermal lineage, the endothelial precursor germ layer, as well as increased the generation of significantly more endothelial cells at later stages. Interestingly, differentiation into other mesoderm lineages was not augmented while endothelial cell differentiation was significantly increased. The percentage of endothelial cells within differentiated embryoid bodies was amplified by greater than 7% in embryoid bodies, a substantial increase compared to other characterized vasculogenic factors like VEGF. Inhibition of IGFR1 signaling using neutralizing antibody or a pharmacological inhibitor, picropodophyllin, significantly reduced IGF-induced mesoderm and endothelial precursor cell formation. We confirmed that IGF-IGFR1 signaling stabilizes HIF1[[Unsupported Character - Symbol Font α]] and leads to up-regulation of VEGF during vasculogenesis in embryoid bodies, which may be one of the critical mechanisms of IGF-induced promotion of vasculogenesis. Understanding the mechanisms that

are critical for vasculogenesis in various models will bring us one step closer to enabling cell based therapies for neovascularization.

Abstract 2896: Nanoparticle co-delivery of RNAi and chemotherapy for the treatment of drug-resistant cancers

The emergence of drug resistance has been a critical barrier for effective cancer chemotherapy. Recently, RNA interference (RNAi) has shown promise in suppressing the over-expression of drug resistance-associated proteins such as P-glycoprotein and Prohibitin1, and in treating multidrug resistant cancers through combination with chemotherapy. Nevertheless, the safe and effective delivery of RNAi therapeutics (e.g., siRNA and miRNA) to target cells remains a major hurdle for their clinical applications, and the co-delivery of RNAi and chemotherapeutic agents in a controlled fashion requires specific delivery vehicles. Herein, we present a novel nanoparticle (NP) platform to tackle the challenges associated with the delivery of siRNA and chemotherapeutic drugs, using biodegradable and biocompatible polymers and lipids. The hybrid lipid-polymer NP has a differentially charged hollow core/shell nanostructure which provides the delivery system with three distinct functional features: (i) a positively charged inner hollow core for dense loading of siRNA; (ii) a middle hydrophobic polymer layer for the encapsulation of anti-cancer drugs (e.g., taxanes) and for the controlled release of both siRNA and drug; and (iii) a relatively neutral lipid-polyethylene glycol (PEG) surface to keep the NP stable and prolong its systematic circulation. Moreover, such hybrid NPs can be formulated in a simple and robust way that could facilitate future scale-up. By screening various factors, such as inner cationic lipids, outer PEG chain length, and formulation parameters, the hybrid lipid-polymer NPs show excellent in vitro knockdown efficacy at low doses of siRNA, with greater than 80% luciferase silencing at an siRNA dose of 0.4 pmol (4.0 nM) and ∼ 95% silencing at a dose of 2.0 pmol (20 nM). These NPs can also efficiently reduce the expression of drug resistance-associated proteins (e.g., MDR1 and Prohibitin1), as evidenced by qPCR. Cellular cytotoxicity experiments further confirm that this NP co-delivery strategy can drastically improve the sensitivity of drug-resistant cells to chemotherapy. In addition, these hybrid NPs demonstrate promising in vivo results for co-delivering siRNA and chemotherapeutic drugs to treat drug-resistant cancers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2896. doi:1538-7445.AM2012-2896

Insulin-like growth factors promote vasculogenesis in embryonic stem cells

The ability of embryonic stem cells to differentiate into endothelium and form functional blood vessels has been well established and can potentially be harnessed for therapeutic angiogenesis. However, after almost two decades of investigation in this field, limited knowledge exists for directing endothelial differentiation. A better understanding of the cellular mechanisms regulating vasculogenesis is required for the development of embryonic stem cell-based models and therapies. In this study, we elucidated the mechanistic role of insulin-like growth factors (IGF1 and 2) and IGF receptors (IGFR1 and 2) in endothelial differentiation using an embryonic stem cell embryoid body model. Both IGF1 or IGF2 predisposed embryonic stem to differentiate towards a mesodermal lineage, the endothelial precursor germ layer, as well as increased the generation of significantly more endothelial cells at later stages. Inhibition of IGFR1 signaling using neutralizing antibody or a pharmacological inhibitor, picropodophyllin, significantly reduced IGF-induced mesoderm and endothelial precursor cell formation. We confirmed that IGF-IGFR1 signaling stabilizes HIF1α and leads to up-regulation of VEGF during vasculogenesis in embryoid bodies. Understanding the mechanisms that are critical for vasculogenesis in various models will bring us one step closer to enabling cell based therapies for neovascularization.

Knockdown of antizyme inhibitor decreases prostate tumor growth in vivo

The endogenous protein antizyme inhibitor (AZI) is a potential oncogene which promotes cell growth by both inhibiting antizyme (AZ) activity and releasing ornithine decarboxylase (ODC) from AZ-mediated degradation. High levels of ODC and polyamines are associated with numerous types of neoplastic transformation, and the genomic region including AZI is frequently amplified in tumors of the ovary and prostate. To determine whether AZI functionally promotes prostate tumor growth, we made PC3M-LN4 (human) and AT6.1 (rat) cancer cell lines stably expressing shRNA to knockdown antizyme inhibitor 1 (AZI). AZI knockdown was confirmed by western blot, quantitative real-time PCR, and immunofluorescence. To examine the ability of these cells to form tumors in vivo, 1 × 10(6) cells were injected subcutaneously into nude mice either with (PC3M-LN4) or without (AT6.1) Matrigel. Tumor growth was measured two times per week by caliper. We found that cells in which AZI levels had been knocked down by shRNA formed significantly smaller tumors in vivo in both human and rat prostate cancer cell lines. These results suggest that not only does AZI promote tumor growth, but also that AZI may be a valid therapeutic target for cancer treatment.

Evidence of a role for antizyme and antizyme inhibitor as regulators of human cancer

Antizyme and its endogenous antizyme inhibitor have recently emerged as prominent regulators of cell growth, transformation, centrosome duplication, and tumorigenesis. Antizyme was originally isolated as a negative modulator of the enzyme ornithine decarboxylase (ODC), an essential component of the polyamine biosynthetic pathway. Antizyme binds ODC and facilitates proteasomal ODC degradation. Antizyme also facilitates degradation of a set of cell cycle regulatory proteins, including cyclin D1, Smad1, and Aurora A kinase, as well as Mps1, a protein that regulates centrosome duplication. Antizyme has been reported to function as a tumor suppressor and to negatively regulate tumor cell proliferation and transformation. Antizyme inhibitor binds to antizyme and suppresses its known functions, leading to increased polyamine synthesis, increased cell proliferation, and increased transformation and tumorigenesis. Gene array studies show antizyme inhibitor to be amplified in cancers of the ovary, breast, and prostate. In this review, we summarize the current literature on the role of antizyme and antizyme inhibitor in cancer, discuss how the ratio of antizyme to antizyme inhibitor can influence tumor growth, and suggest strategies to target this axis for tumor prevention and treatment.

miR-135a contributes to paclitaxel resistance in tumor cells both in vitro and in vivo

Cancer cell resistance to paclitaxel continues to be a major clinical problem. In this study, we utilized microRNA (miRNA) arrays to screen for differentially expressed miRNAs in paclitaxel-resistant cell lines established in vitro. We observed concordant upregulation of miR-135a in paclitaxel-resistant cell lines representing three human malignancies. Subsequently, the role of miRNA-135a was evaluated in an in vivo model of paclitaxel resistance. In this model, mice were inoculated subcutaneously with a non-small cell lung carcinoma cell line and treated with paclitaxel for a prolonged period. In paclitaxel-resistant cell lines, established either in vitro or in vivo, blockage of miR-135a sensitized resistant cell lines to paclitaxel-induced cell death. We further demonstrated a correlation between paclitaxel response and miR-135a expression in paclitaxel-resistant subclones that were established in vivo. The paclitaxel-resistant phenotype of these subclones was maintained upon retransplantation in new mice, as shown by decreased tumor response upon paclitaxel treatment compared with controls. Upregulation of miR-135a was associated with reduced expression of the adenomatous polyposis coli gene (APC). APC knockdown increased paclitaxel resistance in parental cell lines. Our results indicate that paclitaxel resistance is associated with upregulation of miR-135a, both in vitro and in vivo, and is in part determined by miR-135a-mediated downregulation of APC.

Regenerative protein thymosin beta-4 is a novel regulator of purinergic signaling

By an unknown mechanism, β-thymosins are extracellular modulators of angiogenesis, inflammation, wound healing, and development. We were interested in identifying β-thymosin interactors and determining their importance in β-thymosins signaling in human vein endothelial cells (HUVECs). We performed pulldown experiments with biotinylated thymosin β-4 (Tβ4) in comparison to neutravidin beads alone and used mass spectrometric analysis to identify differentially interacting proteins. By this method, we identified F1-F0 ATP synthase, a known target of antiangiogenic angiostatin. By surface plasmon resonance, we determined for Tβ4 binding to the β subunit of ATP synthase a K(D) of 12 nM. Blocking antibodies and antagonists (oligomycin, IC(50) ∼1.8 μM; piceatannol, IC(50) ∼1.05 μM; and angiostatin, IC(50) ∼2.9 μg/ml) of ATP synthase inhibited the Tβ4-induced increase in cell surface ATP levels, as measured by luciferase assay, and the Tβ4-induced increase in HUVEC migration, as measured by transwell migration assay. Silencing of the ATP-responsive purinergic receptor P2X4 with siRNA also blocked Tβ4-induced HUVEC migration in a transwell assay. Furthermore, in silico we identified common amphiphilic α-helical structural similarities between β-thymosins and the inhibitory factor 1 (IF1), an inhibitor of ATP synthase hydrolysis. In summary, we have identified an extracellular signaling pathway where Tβ4 increases cell surface ATP levels via ATP synthase and have shown further that ATP-responsive P2X4 receptor is required for Tβ4-induced HUVEC migration.

Quantitative proteomics analysis reveals molecular networks regulated by epidermal growth factor receptor level in head and neck cancer

Epidermal growth factor receptor (EGFR) is overexpressed in up to 90% of head and neck cancer (HNC), where increased expression levels of EGFR correlate with poor prognosis. To date, EGFR expression levels have not predicted the clinical response to the EGFR-targeting therapies. Elucidation of the molecular mechanisms underlying anti-EGFR-induced antitumor effects may shed some light on the mechanisms of HNC resistance to EGFR-targeting therapeutics and provide novel targets for improving the treatment of HNC. Here, we conducted a quantitative proteomics analysis to determine the molecular networks regulated by EGFR levels in HNC by specifically knocking-down EGFR and employing stable isotope labeling with amino acids in cell culture (SILAC). Following data normalization to minimize systematic errors and Western blotting validation, 12 proteins (e.g., p21, stratifin, and maspin) and 24 proteins (e.g., cdc2 and MTA2) were found to be significantly upregulated or downregulated by EGFR knockdown, respectively. Bioinformatic analysis revealed that these proteins were mainly involved in long-chain fatty acid biosynthesis and beta-oxidation, cholesterol biosynthesis, cell proliferation, DNA replication, and apoptosis. Cell cycle analysis confirmed that G(2)/M phase progression was significantly inhibited by EGFR knockdown, a hypothesis generated from network modeling. Further investigation of these molecular networks may not only enhance our understanding of the antitumor mechanisms of EGFR targeting but also improve patient selection and provide novel targets for better therapeutics.

Collagen XXIII: a potential biomarker for the detection of primary and recurrent non-small cell lung cancer

BACKGROUND

Collagen XXIII is a transmembrane collagen previously shown to be upregulated in metastatic prostate cancer. The purpose of this study was to determine the protein expression of collagen XXIII in tumor tissues from a variety of cancers and to assess the utility of collagen XXIII as a biomarker for non-small cell lung cancer (NSCLC).

METHODS

A multicancer tissue microarray was used for the immunohistochemical examination of collagen XXIII protein expression in a variety of cancers. Subsequently, collagen XXIII expression was analyzed in three separate cohorts using tissue microarrays with representative tumor and control lung tissues from NSCLC patients. In addition, NSCLC patient urine samples were analyzed for the presence of collagen XXIII through Western blot.

RESULTS

Collagen XXIII was present in tissue samples from a variety of cancers. Within lung cancer tissues, collagen XXIII staining was enriched in NSCLC subtypes. Collagen XXIII was present in 294 of 333 (88%) lung adenocarcinomas and 97 of 133 (73%) squamous cell carcinomas. In urine, collagen XXIII was present in 23 of 29 (79%) NSCLC patient samples but only in 15 of 54 (28%) control samples. High collagen XXIII staining intensity correlated with shorter recurrence-free survival in NSCLC patients.

CONCLUSIONS

We show the capability of collagen XXIII as a tissue and urinary biomarker for NSCLC, in which positivity in tissue or urine significantly correlates with the presence of NSCLC and high staining intensity is a significant recurrence predictor.

IMPACT

Inclusion of collagen XXIII in a tissue- or urine-based cancer biomarker panel could inform NSCLC patient treatment decisions.

Abstract 2032: MicroRNA control of tumor cell plasticity in a new tumor metastasis model

We have developed a new prostate cancer model to discover the molecular changes underlying metastasis. A series of cell lines were developed by isolating metastatic cells from lymph nodes of nude mice following orthotopic injection of DU145 human prostate cancer cells and expression changes analyzed using gene chips. We found that these DU145-LN cells exhibit a mesenchymal-epithelial transition (MET). Repeated rounds of in vivo metastatic selection progressively increased the expression of epithelial markers including E-cadherin, cytokeratin-18 and EpCAM, and decreased mesenchymal markers such as vimentin. Despite being more epithelial, DU145-LN cells are more migratory and show reduced proliferation in vitro. However, they show increased tumorigenesis when reinjected into nude mice. Interestingly, clinical metastases are frequently epithelial, despite strong evidence that EMT enhances metastasis. To explain this, current models of metastasis invoke EMT with subsequent MET at the secondary site. Our cells appear to demonstrate this plasticity making them an ideal model system for studying MET regulation.

The MET changes in the DU145-LN cells suggested a coordinated mechanism of regulation. MicroRNA arrays revealed several candidates which correlated with the epithelial phenotype. DU145-LN cells showed increased expression of the miR-200 family (a, b, c and miR-141), and treatment with synthetic miR-200 inhibitors resulted in reduced cell-cell interactions and decreased E-cadherin levels. Our data complement recent evidence showing down-regulation of miR-200 by EMT. miR-200 acts in a feedback loop with the transcription factor ZEB1 to regulate EMT. We also observed significantly reduced expression of an additional microRNA not previously linked to cell morphology in the DU145-LN cells. Transfection of precursor miRNA to this target altered the epithelial morphology and reduced E-cadherin levels, suggesting an additional pathway of MET/EMT control. We are currently determining the mechanism of action of this new microRNA target.

Our data support a role for MET in tumor metastasis, and indicate that microRNAs are an important mechanism mediating tumor cell plasticity and EMT/MET.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2032.

Self-assembled gold nanoparticle molecular probes for detecting proteolytic activity in vivo

Target-activatable fluorogenic probes based on gold nanoparticles (AuNPs) functionalized with self-assembled heterogeneous monolayers of dye-labeled peptides and poly(ethylene glycol) have been developed to visualize proteolytic activity in vivo. A one-step synthesis strategy that allows simple generation of surface-defined AuNP probe libraries is presented as a means of tailoring and evaluating probe characteristics for maximal fluorescence enhancement after protease activation. Optimal AuNP probes targeted to trypsin and urokinase-type plasminogen activator required the incorporation of a dark quencher to achieve 5- to 8-fold signal amplification. These probes exhibited extended circulation time in vivo and high image contrast in a mouse tumor model.

Abstract B46: Collagen XXIII: A biomarker for non-small cell lung cancer

Purpose: To determine the protein expression of collagen XXIII in tumor tissues from a variety of cancers and in tumor tissues and urine samples from non-small cell lung cancer (NSCLC) patients and to assess collagen XXIII's utility as a biomarker for NSCLC.

Experimental Design: A multi-cancer tissue microarray (TMA) was used to immunohistologically examine collagen XXIII protein expression in a variety of cancers. Subsequently, collagen XXIII expression was analyzed in three separate cohorts using TMAs with representative tumor and normal control lung tissues from patients with NSCLC. In addition, urine samples from NSCLC patients were analyzed for the presence of collagen XXIII via Western blot.

Results: Collagen XXIII staining was present in tissue samples from a variety of cancers. Within lung cancer tissues, collagen XXIII staining was enriched in the NSCLC subtypes. Tissues from 296 of 335 (81%) lung adenocarcinoma and 99 of 135 (73%) squamous cell carcinoma (SqCC) patients had detectable collagen XXIII. In urine, collagen XXIII was present in 23 of 29 (79%) NSCLC patient samples and only 15 of 54 (28%) of control samples. There was a significant association between collagen XXIII positivity in tissue or urine and presence of NSCLC (p&lt;0.001, Fisher's exact test).

Conclusions: We demonstrate that collagen XXIII staining is increased in a variety of carcinomas. Specifically, collagen XXIII is expressed in a large subset of NSCLC patient tissue and urine samples, suggesting its utility as a potential NSCLC biomarker.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B46.

Cystatin B as a tissue and urinary biomarker of bladder cancer recurrence and disease progression

PURPOSE

Using proteomic techniques, we sought to identify novel protein biomarkers in tissue and urine from patients with transitional cell carcinoma (TCC).

EXPERIMENTAL DESIGN

Urinary and tissue proteomes were analyzed and differentially expressed proteins were identified by mass spectrometry. One of the proteins, cystatin B, was further analyzed in TCC tissue by immunohistochemistry and in urine by semiquantitative Western blot analysis.

RESULTS

Cystatin B tissue staining intensity significantly increased concordantly with TCC grade (P = 0.0008). Elevated urinary cystatin B levels correlated with increasing tumor grade (P = 0.062) and stage (P = 0.0047). Patients with elevated levels of cystatin B had a shorter mean +/- SE time to disease recurrence (12 +/- 1.82 months) compared with patients who had low levels (28.8 +/- 2.26 months; P = 0.0047). Similarly, patients with elevated cystatin B levels had a shorter time to grade/stage progression compared with patients with low urinary cystatin B (P = 0.0007). By multivariate Cox regression analysis, an elevated cystatin B level was the most significant variable predicting disease recurrence (hazard ratio, 3.8; 95% confidence interval, 1.5-9.5; P = 0.0049) and grade/stage progression (hazard ratio, 10.4; 95% confidence interval, 1.6-201.5; P = 0.0104).

CONCLUSIONS

Cystatin B is elevated in tissue and urine of bladder cancer patients. Cystatin B urine levels are positively correlated with tumor grade, stage, and shorter time to disease recurrence and progression. Consequently, cystatin B may be useful as a novel predictive biomarker in TCC of the bladder.

Differential regulation of human thymosin beta 15 isoforms by transforming growth factor beta 1

We recently identified an additional isoform of human thymosin beta 15 (also known as NB-thymosin beta, gene name TMSB15A) transcribed from an independent gene, and designated TMSB15B. The purpose of this study was to investigate whether these isoforms were differentially expressed and functional. Our data show that the TMSB15A and TMSB15B isoforms have distinct expression patterns in different tumor cell lines and tissues. TMSB15A was expressed at higher levels in HCT116, DU145, LNCaP, and LNCaP-LN3 cancer cells. In MCF-7, SKOV-3, HT1080, and PC-3MLN4 cells, TMSB15A and TMSB15B showed approximately equivalent levels of expression, while TMSB15B was the predominant isoform expressed in PC-3, MDA-MB-231, NCI-H322, and Caco-2 cancer cells. In normal human prostate and prostate cancer tissues, TMSB15A was the predominant isoform expressed. In contrast, normal colon and colon cancer tissue expressed predominantly TMSB15B. The two gene isoforms are also subject to different transcriptional regulation. Treatment of MCF-7 breast cancer cells with transforming growth factor beta 1 repressed TMSB15A expression but had no effect on TMSB15B. siRNA specific to the TMSB15B isoform suppressed cell migration of prostate cancer cells to epidermal growth factor, suggesting a functional role for this second isoform. In summary, our data reveal different expression patterns and regulation of a new thymosin beta 15 gene paralog. This may have important consequences in both tumor and neuronal cell motility.

The scientific contributions of M. Judah Folkman to cancer research

Dr Judah Folkman was frequently described as a highly compassionate physician who served his patients not only by performing surgery and offering them comfort and reassurance, but also by working tirelessly in the laboratory to find new approaches to the treatment of disease. His dedication to understanding the role of angiogenesis, the formation of new blood vessels, in human disease has given rise to new treatments for several diseases, including inflammatory diseases, vision-threatening diseases of the eye and, as will be emphasized in this Perspective, cancer.

Antizyme, a mediator of ubiquitin-independent proteasomal degradation and its inhibitor localize to centrosomes and modulate centriole amplification

The potential tumor suppressor antizyme and its endogenous inhibitor (antizyme inhibitor, AZI) have been implicated in the ubiquitin-independent proteasomal degradation of proteins involved in cell proliferation as well as in the regulation of polyamine levels. We show here that both antizyme and AZI concentrate at centrosomes and that antizyme preferentially associates with the maternal centriole. Interestingly, alterations in the levels of these proteins have opposing effects on centrosomes. Depletion of antizyme in various cell lines and primary cells leads to centrosome overduplication, whereas overexpression of antizyme reduces numerical centrosome abnormalities. Conversely, silencing of the antizyme inhibitor, AZI, results in a decrease of numerical centrosome abnormalities, whereas overexpression of AZI leads to centrosome overduplication. We further show that the numerical centrosome abnormalities are due to daughter centriole amplification. In summary, our results demonstrate that alterations in the antizyme/AZI balance cause numerical centrosomal defects and suggest a role for ubiquitin-independent proteasomal degradation in centrosome duplication.

Assessing enzyme activities using stable isotope labeling and mass spectrometry

Activity-based protein profiling has emerged as a valuable technology for labeling, enriching, and assessing protein activities from complex mixtures. This is primarily accomplished via a two-step identification and quantification process. Here we show a highly quantitative and streamlined method, termed catch-and-release activity profiling of enzymes (CAPE), which reduces this procedure to a single step. Furthermore the CAPE approach has the ability to detect small quantitative changes that may have been missed by alternative mass spectrometry-based techniques.

Collagen XXIII expression is associated with prostate cancer recurrence and distant metastases

PURPOSE

We had previously identified a new transmembrane collagen, type XXIII, in metastatic rat prostate carcinoma cells. The purpose of this study was to determine the expression of collagen XXIII in human prostate cancer and investigate its relationship with disease progression.

EXPERIMENTAL DESIGN

We investigated collagen XXIII expression in prostate cancer tissue and did a retrospective analysis of association with prostate-specific antigen (PSA)-defined disease recurrence. The presence of collagen XXIII in prostate cancer patient urine was also assessed before and after prostatectomy.

RESULTS

Collagen XXIII protein was detected at very low levels in benign prostate tissue and was significantly increased in prostate cancer. Distant metastases exhibited significantly higher collagen XXIII levels compared with either localized prostate cancer or regional (lymph node) metastases. Patients with high collagen XXIII levels had a 2.8-fold higher risk of PSA failure with median time to failure of 8.1 months, compared with low collagen XXIII patients with a median time to failure of 5 years. Multivariate Cox regression showed that the presence of collagen XXIII was significantly associated with time to PSA recurrence, independent of other clinical variables. Collagen XXIII was also detected in prostate cancer patient urine, with reduced levels after prostatectomy, indicating potential as a noninvasive fluid biomarker.

CONCLUSIONS

We present the first report demonstrating increased collagen XXIII expression in prostate cancer tissue. We show that collagen XXIII level is a significant independent predictor of PSA-defined disease recurrence, suggesting a potential role as a molecular biomarker of prostate cancer progression and metastasis.

Thymosin beta-NB Is the Human Isoform of Rat Thymosin beta15

Thymosin beta15 is a small actin-binding protein upregulated in highly metastatic rat prostate cancer cells, relative to low metastatic cells. We have previously established an important role for thymosin beta15 as a diagnostic marker in human prostate cancer, with potential as a prognostic indicator. We here review the data supporting increased thymosin beta15 expression in other cancer types, including breast, brain, and lung. Human NB thymosin beta is a beta-thymosin originally found in neuroblastoma. New data demonstrate that NB thymosin beta represents the human homolog of rat thymosin beta15; thus we suggest classification as human thymosin beta15. In addition to the previously described gene, thymosin beta15a, we report the discovery of a new isoform of human thymosin beta15, thymosin beta15b, which is transcribed from an independent gene on human chromosome X. The gene structure of thymosin beta15a and beta15b is conserved and the isoforms show 87% identity across the nucleotide sequence. Across the coding sequence the nucleotide differences are silent, resulting in identical proteins. Other thymosin family members have recently been shown to exert potent clinical effects. The functional data available for thymosin beta15, combined with the tumor expression pattern, suggest that thymosin beta15 may play an important role in tumor development and progression in addition to its value as a biomarker in prostate cancer.

Proteomics in tumor progression and metastasis

With the ultimate goal of systematically identifying and characterizing proteins within an organism, the field of proteomics has generated much excitement in the past few years. Coupled with mass spectrometry, various quantitative and functional techniques are now available that allow for large-scale analyses of proteins implicated in cancer. New techniques are just now being applied to identifying the temporal changes in protein levels associated with tumor development. This review will focus on the use and promise of proteomic technologies as they apply to the study of tumor progression and metastasis.

Regulation of cell proliferation by the antizyme inhibitor: evidence for an antizyme-independent mechanism

The antizyme inhibitor was discovered as a protein that binds to the regulatory protein antizyme and inhibits the ability of antizyme to interact with the enzyme ornithine decarboxylase (ODC). Blocking antizyme activity subsequently leads to increased intracellular levels of ODC and increased ODC enzymatic activity. We now report that antizyme inhibitor is a positive modulator of cell growth. Overexpression of antizyme inhibitor in NIH-3T3 mouse fibroblasts or in AT2.1 Dunning rat prostate carcinoma cells resulted in an increased rate of cell proliferation and an increase in saturation density of the cultured cells. This was accompanied by an increase in intracellular levels of the polyamine putrescine. In AT2.1 cells, antizyme inhibitor overexpression also increased the ability of the cells to form foci when grown under anchorage-independent conditions. In order to determine the role of antizyme on antizyme inhibitor activity we created an antizyme inhibitor mutant, AZI(Delta117-140), which lacks the putative antizyme-binding domain. We show that this mutant fails to bind to antizyme, but remains capable of inducing increased rates of cell proliferation, suggesting that antizyme inhibitor has antizyme-independent functions. Silencing antizyme inhibitor expression leads to diminished levels of cyclin D1 and to reduced cell proliferation. Antizyme inhibitor is capable of preventing cyclin D1 degradation, and this effect is at least partially independent of antizyme. We show that wild-type antizyme inhibitor and the AZI(DeltaY) mutant are capable of direct interaction with cyclin D1 suggesting a potential mechanism for the antizyme-independent effects. Together, our data suggest a novel function for antizyme inhibitor in cellular growth control.

Cancer biomarkers: knowing the present and predicting the future

In recent years the discovery of cancer biomarkers has become a major focus of cancer research. The widespread use of prostate-specific antigen in prostate cancer screening has motivated researchers to identify suitable markers for screening different types of cancer. Biomarkers are also useful for diagnosis, monitoring disease progression, predicting disease recurrence and therapeutic treatment efficacy. With the advent of new and improved genomic and proteomic technologies such as DNA and tissue microarray, two-dimensional gel eletrophoresis, mass spectrometry and protein assays coupled with advanced bioinformatic tools, it is possible to develop biomarkers that are able to reliably and accurately predict outcomes during cancer management and treatment. In years to come, a serum or urine test for every phase of cancer may drive clinical decision making, supplementing or replacing currently existing invasive techniques.

Enhanced Analysis of Metastatic Prostate Cancer Using Stable Isotopes and High Mass Accuracy Instrumentation

The primary goal of proteomics is to gain a better understanding of biological function at the protein expression level. As the field matures, numerous technologies are being developed to aid in the identification, quantification and characterization of protein expression and post-translational modifications on a near-global scale. Stable isotope labeling by amino acids in cell culture is one such technique that has shown broad biological applications. While we have recently shown the application of this technology to a model of metastatic prostate cancer, we now report a substantial improvement in quantitative analysis using a linear ion-trap Fourier transform ion cyclotron resonance mass spectrometer (LTQ FT) and novel quantification software. This resulted in the quantification of nearly 1400 proteins, a greater than 3-fold increase in comparison to our earlier study. This dramatic increase in proteome coverage can be attributed to (1) use of a double-labeling strategy, (2) greater sensitivity, speed and mass accuracy provided by the LTQ FT mass spectrometer, and (3) more robust quantification software. Finally, by using a concatenated target/decoy protein database for our peptide searches, we now report these data in the context of an estimated false-positive rate of one percent.

Development of a sensitive and specific enzyme-linked immunosorbent assay for thymosin beta15, a urinary biomarker of human prostate cancer

OBJECTIVES

In tissue-based assays, thymosin beta15 (Tbeta15) has been shown to correlate with prostate cancer (CaP) malignancy and with future recurrence. To be clinically effective, it must be shown that Tbeta15 is released by the tumor into body fluids in detectable concentrations. Toward this end, we have worked to develop a quantitative high-throughput assay that can accurately measure clinically relevant concentrations of Tbeta15 in human urine.

DESIGN AND METHODS

Sixteen antibodies were raised against recombinant Tbeta15 and/or peptide conjugates. One antibody, having stable characteristics over the wide range of pH and salt concentrations found in urine and minimal cross-reactivity with other beta thymosins, was used to develop a competitive enzyme-linked immunosorbent assay (ELISA). Urinary Tbeta15 concentration was determined for control groups; normal (N = 52), prostate intraepithelial neoplasia (PIN, N = 36), and CaP patients; untreated (N = 7) with subsequent biochemical failure, radiation therapy (N = 17) at risk of biochemical recurrence.

RESULTS

The operating range of the competition ELISA fell between 2.5 and 625 ng/mL. Recoveries exceeded 75%, and the intra- and inter-assay coefficients of variability were 3.3% and 12.9%, respectively. No cross-reactivity with other urine proteins was observed. A stable Tbeta15 signal was recovered from urine specimens stored at -20 degrees C for up to 1 year. At a threshold of 40 (ng/dL)/mug protein/mg creatinine), the assay had a sensitivity of 58% and a specificity of 94%. Relative to the control groups, Tbeta15 levels were greater than this threshold in a significant fraction of the CaP patients (P < 0.001), including 5 of the 7 patients who later experienced PSA recurrence.

CONCLUSIONS

We have established an ELISA that is able to detect Tbeta15 at clinically relevant concentrations in urine from patients with CaP. The assay will provide a tool for future clinical trials to validate urinary Tbeta15 as a predictive marker for recurrent CaP.

Use of thymosin beta15 as a urinary biomarker in human prostate cancer

BACKGROUND

Additional prostate cancer (CaP) biomarkers are needed to increase the accuracy of diagnosis and to identify patients at risk of recurrence. In tissue-based assays, thymosin beta15 (Tbeta15) has been linked to an aggressive CaP phenotype and correlated with future tumor recurrence. We hypothesized that Tbeta15 may have clinical utility in biological fluids.

METHODS

Tbeta15 was measured in urine from CaP patients; untreated (N = 61), prostatectomy (RP, N = 46), androgen deprivation therapy (ADT, N = 14) and control groups; normal (N = 52), genitourinary carcinoma (N = 15), non-malignant prostate disease (N = 81), and other urology (N = 73). We evaluated the utility of urinary Tbeta15 for CaP diagnosis, alone or in combination with prostate-specific antigen (PSA), and the relationship to CaP progression.

RESULTS

A normal threshold of 40 (ng/dl)/(mug_protein/mg_creatinine) was defined using receiver operating characteristic analysis and marked the 19th centile for age-matched controls. The proportion of untreated CaP patients with urinary Tbeta15 above the threshold was significantly higher than normal and genitourinary disease controls (P < 0.001). RP caused urinary Tbeta15 to drop significantly (P = 0.005). Pre-surgery Tbeta15 concentrations greater than the normal threshold may confer greater risk of CaP recurrence. Relative to normal controls, patients receiving ADT for aggressive CaP were 12 times more likely to have elevated urinary Tbeta15 (P = 0.001, 95% CI = 2.8, 51.8). Combining PSA and Tbeta15 (PSA > 4, or PSA > 2.5, Tbeta15 > 40, or PSA = 2.5, Tbeta15 > 90) provided the same sensitivity as a 2.5 ng/ml PSA cutoff, but markedly improved diagnostic specificity.

CONCLUSIONS

We report that Tbeta15 is a urinary biomarker for CaP and suggest that Tbeta15, in combination with PSA, can be used to improve both the sensitivity and specificity of CaP diagnosis.

Inhibition of endothelial cell migration by thrombospondin-1 type-1 repeats is mediated by beta1 integrins

The anti-angiogenic effect of thrombospondin-1 has been shown to be mediated through binding of the type-1 repeat (TSR) domain to the CD36 transmembrane receptor. We now report that the TSR domain can inhibit VEGF-induced migration in human umbilical vein endothelial cells (HUVEC), cells that lack CD36. Moreover, we identified β₁ integrins as a critical receptor in TSR-mediated inhibition of migration in HUVEC. Using pharmacological inhibitors of downstream VEGF receptor effectors, we found that phosphoinositide 3-kinase (PI3k) was essential for TSR-mediated inhibition of HUVEC migration, but that neither PLCγ nor Akt was necessary for this response. Furthermore, β₁ integrins were critical for TSR-mediated inhibition of microvascular endothelial cells, cells that express CD36. Together, our results indicate that β₁ integrins mediate the anti-migratory effects of TSR through a PI3k-dependent mechanism.

Oxidative stress and thioredoxin-interacting protein promote intravasation of melanoma cells

Although intravasation may be a critical rate-limiting step in the metastatic cascade, the role of oxidative stress in intravasation is unknown. We tested the hypothesis that reactive oxygen species (ROS), regulated by thioredoxin interacting protein (Txnip) through the action of thioredoxin (Trx), influence human SK-MEL-28 melanoma cell reverse (basolateral-to-apical) transendothelial migration (TEM) in vitro as a model for intravasation. Reverse transendothelial migration was dose-dependently induced by hydrogen peroxide 2.4-fold for 0.1 microM (P < 0.01) and 3.9-fold for 1 microM (P < 0.001) vs. control, and this effect was blocked by the antioxidant N-acetylcysteine. Overexpression of Txnip by infecting melanoma cells with adenovirus increased TEM 3-fold vs. control (P < 0.001), and this increase was blocked by N-acetylcysteine, indicating a redox-sensitive mechanism. Conversely, thioredoxin overexpression blocked hydrogen peroxide-induced TEM. Exposure to ultraviolet-A radiation increased ROS 1.8-fold (P < 0.01), and this was accompanied by a 45% reduction (P < 0.05) in thioredoxin activity and an 11.4-fold (P < 0.001) increase in Txnip gene expression. These data suggest that TEM of melanoma cells during intravasation is in part mediated by ROS-sensitive cellular signaling cascades, may be controlled by Txnip and its interaction with thioredoxin that in turn modulates cellular levels of oxidative stress, and may be initiated by ultraviolet-A induction of this cascade.

Antizyme targets cyclin D1 for degradation. A novel mechanism for cell growth repression

Overproduction of the ornithine decarboxylase (ODC) regulatory protein ODC-antizyme has been shown to correlate with cell growth inhibition in a variety of different cell types. Although the exact mechanism of this growth inhibition is not known, it has been attributed to the effect of antizyme on polyamine metabolism. Antizyme binds directly to ODC, targeting ODC for ubiquitin-independent degradation by the 26 S proteasome. We now show that antizyme induction also leads to degradation of the cell cycle regulatory protein cyclin D1. We demonstrate that antizyme is capable of specific, noncovalent association with cyclin D1 and that this interaction accelerates cyclin D1 degradation in vitro in the presence of only antizyme, cyclin D1, purified 26 S proteasomes, and ATP. In vivo, antizyme up-regulation induced either by the polyamine spermine or by antizyme overexpression causes reduction of intracellular cyclin D1 levels. The antizyme-mediated pathway for cyclin D1 degradation is independent of the previously characterized phosphorylation- and ubiquitination-dependent pathway, because antizyme up-regulation induces the degradation of a cyclin D1 mutant (T286A) that abrogates its ubiquitination. We propose that antizyme-mediated degradation of cyclin D1 by the proteasome may provide an explanation for the repression of cell growth following antizyme up-regulation.