Blockade of hedgehog signaling inhibits pancreatic cancer invasion and metastases: a new paradigm for combination therapy in solid cancers

In the context of pancreatic cancer, metastasis remains the most critical determinant of resectability, and hence survival. The objective of this study was to determine whether Hedgehog (Hh) signaling plays a role in pancreatic cancer invasion and metastasis because this is likely to have profound clinical implications. In pancreatic cancer cell lines, Hh inhibition with cyclopamine resulted in down-regulation of snail and up-regulation of E-cadherin, consistent with inhibition of epithelial-to-mesenchymal transition, and was mirrored by a striking reduction of in vitro invasive capacity (P < 0.0001). Conversely, Gli1 overexpression in immortalized human pancreatic ductal epithelial cells led to a markedly invasive phenotype (P < 0.0001) and near total down-regulation of E-cadherin. In an orthotopic xenograft model, cyclopamine profoundly inhibited metastatic spread; only one of seven cyclopamine-treated mice developed pulmonary micrometastases versus seven of seven mice with multiple macrometastases in control animals. Combination of gemcitabine and cyclopamine completely abrogated metastases while also significantly reducing the size of "primary" tumors. Gli1 levels were up-regulated in tissue samples of metastatic human pancreatic cancer samples compared with matched primary tumors. Aldehyde dehydrogenase (ALDH) overexpression is characteristic for both hematopoietic progenitors and leukemic stem cells; cyclopamine preferentially reduced "ALDH-high" cells by approximately 3-fold (P = 0.048). We confirm pharmacologic Hh pathway inhibition as a valid therapeutic strategy for pancreatic cancer and show for the first time its particular efficacy against metastatic spread. By targeting specific cellular subpopulations likely involved in tumor initiation at metastatic sites, Hh inhibitors may provide a new paradigm for therapy of disseminated malignancies, particularly when used in combination with conventional antimetabolites that reduce "bulk" tumor size.

An in vivo platform for translational drug development in pancreatic cancer

Effective development of targeted anticancer agents includes the definition of the optimal biological dose and biomarkers of drug activity. Currently available preclinical models are not optimal to this end. We aimed at generating a model for translational drug development using pancreatic cancer as a prototype. Resected pancreatic cancers from 14 patients were xenografted and expanded in successive groups of nude mice to develop cohorts of tumor-bearing mice suitable for drug therapy in simulated early clinical trials. The xenografted tumors maintain their fundamental genotypic features despite serial passages and recapitulate the genetic heterogeneity of pancreatic cancer. The in vivo platform is useful for integrating drug screening with biomarker discovery. Passages of tumors in successive cohorts of mice do not change their susceptibility to anticancer agents and represent a perpetual live bank, facilitating the application of new technologies that will result in the creation of an integrated stable database of tumor-drug response data and biomarkers.

Restitution of tumor suppressor microRNAs using a systemic nanovector inhibits pancreatic cancer growth in mice

Mis-expression of microRNAs (miRNA) is widespread in human cancers, including in pancreatic cancer. Aberrations of miRNA include overexpression of oncogenic miRs (Onco-miRs) or downregulation of so-called tumor suppressor TSG-miRs. Restitution of TSG-miRs in cancer cells through systemic delivery is a promising avenue for pancreatic cancer therapy. We have synthesized a lipid-based nanoparticle for systemic delivery of miRNA expression vectors to cancer cells (nanovector). The plasmid DNA-complexed nanovector is approximately 100 nm in diameter and shows no apparent histopathologic or biochemical evidence of toxicity upon intravenous injection. Two miRNA candidates known to be downregulated in the majority of pancreatic cancers were selected for nanovector delivery: miR-34a, which is a component of the p53 transcriptional network and regulates cancer stem cell survival, and the miR-143/145 cluster, which together repress the expression of KRAS2 and its downstream effector Ras-responsive element binding protein-1 (RREB1). Systemic intravenous delivery with either miR-34a or miR-143/145 nanovectors inhibited the growth of MiaPaCa-2 subcutaneous xenografts (P < 0.01 for miR-34a; P < 0.05 for miR-143/145); the effects were even more pronounced in the orthotopic (intrapancreatic) setting (P < 0.0005 for either nanovector) when compared with vehicle or mock nanovector delivering an empty plasmid. Tumor growth inhibition was accompanied by increased apoptosis and decreased proliferation. The miRNA restitution was confirmed in treated xenografts by significant upregulation of the corresponding miRNA and significant decreases in specific miRNA targets (SIRT1, CD44 and aldehyde dehydrogenase for miR34a, and KRAS2 and RREB1 for miR-143/145). The nanovector is a platform with potential broad applicability in systemic miRNA delivery to cancer cells.

An orally bioavailable small-molecule inhibitor of Hedgehog signaling inhibits tumor initiation and metastasis in pancreatic cancer

Recent evidence suggests that blockade of aberrant Hedgehog signaling can be exploited as a therapeutic strategy for pancreatic cancer. Our previous studies using the prototype Hedgehog small-molecule antagonist cyclopamine had shown the striking inhibition of systemic metastases on Hedgehog blockade in spontaneously metastatic orthotopic xenograft models. Cyclopamine is a natural compound with suboptimal pharmacokinetics, which impedes clinical translation. In the present study, a novel, orally bioavailable small-molecule Hedgehog inhibitor, IPI-269609, was tested using in vitro and in vivo model systems. In vitro treatment of pancreatic cancer cell lines with IPI-269609 resembled effects observed using cyclopamine (i.e., Gli-responsive reporter knockdown, down-regulation of the Hedgehog target genes Gli1 and Ptch, as well as abrogation of cell migration and colony formation in soft agar). Single-agent IPI-269609 profoundly inhibited systemic metastases in orthotopic xenografts established from human pancreatic cancer cell lines, although Hedgehog blockade had minimal effect on primary tumor volume. The only discernible phenotype observed within the treated primary tumor was a significant reduction in the population of aldehyde dehydrogenase-bright cells, which we have previously identified as a clonogenic tumor-initiating population in pancreatic cancer. Selective ex vivo depletion of aldehyde dehydrogenase-bright cells with IPI-269609 was accompanied by significant reduction in tumor engraftment rates in athymic mice. Pharmacologic blockade of aberrant Hedgehog signaling might prove to be an effective therapeutic strategy for inhibition of systemic metastases in pancreatic cancer, likely through targeting subsets of cancer cells with tumor-initiating ("cancer stem cell") properties.

Tumor engraftment in nude mice and enrichment in stroma- related gene pathways predict poor survival and resistance to gemcitabine in patients with pancreatic cancer

PURPOSE

The goal of this study was to evaluate prospectively the engraftment rate, factors influencing engraftment, and predictability of clinical outcome of low-passage xenografts from patients with resectable pancreatic ductal adenocarcinoma (PDA) and to establish a bank of PDA xenografts.

EXPERIMENTAL DESIGN

Patients with resectable PDA scheduled for resection at the Johns Hopkins Hospital were eligible. Representative pieces of tumor were implanted in nude mice. The status of the SMAD4 gene and content of tumor-generating cells were determined by immunohistochemistry. Gene expression was carried out by using a U133 Plus 2.0 array. Patients were followed for progression and survival.

RESULTS

A total of 94 patients with PDA were resected, 69 tumors implanted in nude mice, and 42 (61%) engrafted. Engrafted carcinomas were more often SMAD4 mutant, and had a metastatic gene expression signature and worse prognosis. Tumors from patients resistant to gemcitabine were enriched in stroma-related gene pathways. Tumors sensitive to gemcitabine were enriched in cell cycle and pyrimidine gene pathways. The time to progression for patients who received treatment with gemcitabine for metastatic disease (n = 7) was double in patients with xenografts sensitive to gemcitabine.

CONCLUSION

A successful xenograft was generated in 61% of patients attempted, generating a pool of 42 PDA xenografts with significant biological information and annotated clinical data. Patients with PDA and SMAD4 inactivation have a better engraftment rate. Engraftment is a poor prognosis factor, and engrafted tumors have a metastatic gene expression signature. Tumors from gemcitabine-resistant patients were enriched in stromal pathways.

Epigenetic silencing of MicroRNA miR-107 regulates cyclin-dependent kinase 6 expression in pancreatic cancer

Aberrant expression of microRNAs (miRNAs) has emerged as an important hallmark of cancer. However, the putative mechanisms regulating miRNAs per se are only partially known. It is well established that many tumor suppressor genes in human cancers are silenced by chromatin alterations, including promoter methylation and histone deacetylation. We postulated that miRNAs undergo similar epigenetic inactivation in pancreatic cancer. Two human pancreatic cancer cell lines - MiaPACA-2 and PANC-1 - were treated with the demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-dC) or the histone deacetylase inhibitor, trichostatin A, as well as the combination of the two. Expression of miRNAs in control and treated cell lines was assessed using a custom microarray platform. Fourteen miRNAs were upregulated two-fold or greater in each of the cell lines following exposure to both chromatin-modifying agents, including 5 that were in common (miR-107, miR-103, miR-29a, miR-29b, and miR-320) to both MiaPACA-2 and PANC-1. The differential overexpression of miR-107 in the treated cancer cell lines was confirmed by Northern blot assays. Methylation-specific PCR assays for assessment of CpG island methylation status in the 5' promoter region of the miR-107 primary transcript demonstrated complete loss of methylation upon exposure to 5-Aza-dC. Enforced expression of miR-107 in MiaPACA-2 and PANC-1 cells downregulated in vitro growth, and this was associated with repression of the putative miR-107 target, cyclin-dependent kinase 6, thereby providing a functional basis for the epigenetic inactivation of this miRNA in pancreatic cancer.

Array-based comparative genomic hybridization identifies localized DNA amplifications and homozygous deletions in pancreatic cancer

Pancreatic cancer, the fourth leading cause of cancer death in the United States, is frequently associated with the amplification and deletion of specific oncogenes and tumor-suppressor genes (TSGs), respectively. To identify such novel alterations and to discover the underlying genes, we performed comparative genomic hybridization on a set of 22 human pancreatic cancer cell lines, using cDNA microarrays measuring approximately 26,000 human genes (thereby providing an average mapping resolution of <60 kb). To define the subset of amplified and deleted genes with correspondingly altered expression, we also profiled mRNA levels in parallel using the same cDNA microarray platform. In total, we identified 14 high-level amplifications (38-4934 kb in size) and 15 homozygous deletions (46-725 kb). We discovered novel localized amplicons, suggesting previously unrecognized candidate oncogenes at 6p21, 7q21 (SMURF1, TRRAP), 11q22 (BIRC2, BIRC3), 12p12, 14q24 (TGFB3), 17q12, and 19q13. Likewise, we identified novel polymerase chain reaction-validated homozygous deletions indicating new candidate TSGs at 6q25, 8p23, 8p22 (TUSC3), 9q33 (TNC, TNFSF15), 10q22, 10q24 (CHUK), 11p15 (DKK3), 16q23, 18q23, 21q22 (PRDM15, ANKRD3), and Xp11. Our findings suggest candidate genes and pathways, which may contribute to the development or progression of pancreatic cancer.

The Axl receptor tyrosine kinase confers an adverse prognostic influence in pancreatic cancer and represents a new therapeutic target

BACKGROUND

Pancreatic cancer is a near uniformly lethal disease and a better understanding of the molecular basis of this malignancy may lead to improved therapeutics. The Axl receptor tyrosine kinase is implicated in cellular transformation and tumor progression, although its role in pancreatic cancer has not been previously documented.

RESULTS

Axl labeling was present in 54 of 99 (55%), and was absent in 45 of 99 (45%) cases, respectively. Axl expression in pancreatic cancer was significantly associated with lymph node metastases (p < 0.01), and a shorter median survival (12 versus 18 months, p < 0.01), than in tumors with negative labeling. Stable knockdown of Axl resulted in significant reduction in cell viability (p < 0.001), anchorage independent growth (p = 0.0031), as well as attenuation of migratory (p < 0.001) and invasive properties (p < 0.005), compared to vector-transfected cells. Profound inhibition of p42/p44 MAP kinase and PI-3kinase/Akt effector pathways was observed in MIAPaCa-2 cells with loss of Axl function. The reduction in invasion and migration upon Axl knockdown was mirrored by a decrease in the amounts of activated (GTP-bound) GTPase proteins Rho and Rac, significant downregulation in transcript levels of the epithelial mesenchymal transition (EMT)-associated transcription factors slug, snail and twist, and significant decrease in matrix metalloproteinase MMP-9 mRNA levels.

MATERIALS

The immunohistochemical expression of Axl protein was assessed in a panel of 99 archival pancreatic cancers. Endogenous Axl expression was stably downregulated by lentiviral short hairpin shRNA directed against AXL mRNA in MIAPaCa-2 cells, and the effects on cell viability, anchorage independent growth, invasion, migration and intracellular effector pathways was assessed, by comparing to lentiviral vector-transfected cells.

CONCLUSION

Expression of Axl tyrosine kinase in pancreatic cancers confers an adverse prognostic influence, and represents a new therapeutic target in this malignancy.

Hedgehog inhibition prolongs survival in a genetically engineered mouse model of pancreatic cancer

BACKGROUND AND AIMS

Pancreatic cancer is among the most dismal of human malignancies. Current therapeutic strategies are virtually ineffective in controlling advanced, metastatic disease. Recent evidence suggests that the Hedgehog signalling pathway is aberrantly reactivated in the majority of pancreatic cancers, and that Hedgehog blockade has the potential to prevent disease progression and metastatic spread.

METHODS

Here it is shown that the Hedgehog pathway is activated in the Pdx1-Cre;LsL-Kras(G12D);Ink4a/Arf(lox/lox) transgenic mouse model of pancreatic cancer. The effect of Hedgehog pathway inhibition on survival was determined by continuous application of the small molecule cyclopamine, a smoothened antagonist. Microarray analysis was performed on non-malignant human pancreatic ductal cells overexpressing Gli1 in order to screen for downstream Hedgehog target genes likely to be involved in pancreatic cancer progression.

RESULTS

Hedgehog inhibition with cyclopamine significantly prolonged median survival in the transgenic mouse model used here (67 vs 61 days; p = 0.026). In vitro data indicated that Hedgehog activation might at least in part be ascribed to oncogenic Kras signalling. Microarray analysis identified 26 potential Hedgehog target genes that had previously been found to be overexpressed in pancreatic cancer. Five of them, BIRC3, COL11A1, NNMT, PLAU and TGM2, had been described as upregulated in more than one global gene expression analysis before.

CONCLUSION

This study provides another line of evidence that Hedgehog signalling is a valid target for the development of novel therapeutics for pancreatic cancer that might be worth evaluating soon in a clinical setting.

Systemic administration of polymeric nanoparticle-encapsulated curcumin (NanoCurc) blocks tumor growth and metastases in preclinical models of pancreatic cancer

Curcumin or diferuloylmethane is a yellow polyphenol extracted from the rhizome of turmeric (Curcuma longa). A large volume (several hundreds) of published reports has established the anticancer and chemopreventative properties of curcumin in preclinical models of every known major cancer type. Nevertheless, the clinical translation of curcumin has been significantly hampered due to its poor systemic bioavailability, which mandates that patients consume up to 8 to 10 g of the free drug orally each day to achieve detectable levels in circulation. We have engineered a polymeric nanoparticle encapsulated curcumin formulation (NanoCurc) that shows remarkably higher systemic bioavailability in plasma and tissues compared with free curcumin upon parenteral administration. In xenograft models of human pancreatic cancer established in athymic mice, administration of parenteral NanoCurc significantly inhibits primary tumor growth in both subcutaneous and orthotopic settings. The combination of parenteral NanoCurc with gemcitabine results in enhanced tumor growth inhibition versus either single agent, suggesting an additive therapeutic influence in vivo. Furthermore, this combination completely abrogates systemic metastases in orthotopic pancreatic cancer xenograft models. Tumor growth inhibition is accompanied by significant reduction in activation of nuclear factor-kappaB, as well as significant reduction in expression of matrix metalloproteinase-9 and cyclin D1, in xenografts treated with NanoCurc and gemcitabine. NanoCurc is a promising new formulation that is able to overcome a major impediment for the clinical translation of curcumin to cancer patients by improving systemic bioavailability, and by extension, therapeutic efficacy.

Aberrant MicroRNA-155 expression is an early event in the multistep progression of pancreatic adenocarcinoma

BACKGROUND/AIMS

Pancreatic intraepithelial neoplasia (PanIN) is the most common noninvasive precursor to invasive pancreatic adenocarcinoma. Misexpression of microRNAs (miRNAs) is commonly encountered in invasive neoplasia; however, miRNA abnormalities in PanIN lesions have not been documented.

METHODS

Three candidate miRNAs (miR-21, miR-155, and miR-221) previously reported as overexpressed in pancreatic cancers were assessed in 31 microdissected PanINs (14 PanIN-1, 9 PanIN-2, 8 PanIN-3) using quantitative reverse transcription PCR (qRT-PCR). Subsequently, miR-155 was evaluated by locked nucleic acid in situ hybridization (LNA-ISH) in PanIN tissue microarrays.

RESULTS

Relative to microdissected non-neoplastic ductal epithelium, significant overexpression of miR-155 was observed in both PanIN-2 (2.6-fold, p = 0.02) and in PanIN-3 (7.4-fold, p = 0.014), while borderline significant overexpression of miR-21 (2.5-fold, p = 0.049) was observed in PanIN-3 only. In contrast, no significant differences in miR-221 levels were observed between ductal epithelium and PanIN lesions by qRT-PCR. LNA-ISH confirmed the aberrant expression of miR-155 in PanIN-2 (9 of 20, 45%) and in PanIN-3 (8 of 13, 62%), respectively, when compared with normal ductal epithelium (0 of 10) (p < 0.01).

CONCLUSIONS

Abnormalities of miRNA expression are observed in the multistep progression of pancreatic cancer, with miR-155 aberrations demonstrable at the stage of PanIN-2, and miR-21 abnormalities at the stage of PanIN-3 lesions. and IAP.

Cyclin-dependent kinase inhibitor Dinaciclib (SCH727965) inhibits pancreatic cancer growth and progression in murine xenograft models

Pancreatic cancer is one of the most lethal of human malignancies, and potent therapeutic options are lacking. Inhibition of cell cycle progression through pharmacological blockade of cyclin-dependent kinases (CDK) has been suggested as a potential treatment option for human cancers with deregulated cell cycle control. Dinaciclib (SCH727965) is a novel small molecule multi-CDK inhibitor with low nanomolar potency against CDK1, CDK2, CDK5 and CDK9 that has shown favorable toxicity and efficacy in preliminary mouse experiments, and has been well tolerated in Phase I clinical trials. In the current study, the therapeutic efficacy of SCH727965 on human pancreatic cancer cells was tested using in vitro and in vivo model systems. Treatment with SCH727965 significantly reduced in vitro cell growth, motility and colony formation in soft agar of MIAPaCa-2 and Pa20C cells. These phenotypic changes were accompanied by marked reduction of phosphorylation of Retinoblastoma (Rb) and reduced activation of RalA. Single agent therapy with SCH727965 (40 mg/kg i.p. twice weekly) for 4 weeks significantly reduced subcutaneous tumor growth in 10/10 (100%) of tested low-passage human pancreatic cancer xenografts. Treatment of low passage pancreatic cancer xenografts with a combination of SCH727965 and gemcitabine was significantly more effective than either agent alone. Gene Set Enrichment Analysis identified overrepresentation of the Notch and Transforming Growth Factor-β (TGF-β) signaling pathways in the xenografts least responsive to SCH727965 treatment. Treatment with the cyclin-dependent kinase inhibitor SCH727965 alone or in combination is a highly promising novel experimental therapeutic strategy against pancreatic cancer.

The Axl receptor tyrosine kinase is an adverse prognostic factor and a therapeutic target in esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) arises in the backdrop of reflux-induced metaplastic phenomenon known as Barrett esophagus. The prognosis of advanced EAC is dismal, and there is an urgent need for identifying molecular targets for therapy. Serial Analysis of Gene Expression (SAGE) was performed on metachronous mucosal biopsies from a patient who underwent progression to EAC during endoscopic surveillance. SAGE confirmed significant upregulation of Axl "tags" during the multistep progression of Barrett esophagus to EAC. In a cohort of 92 surgically resected EACs, Axl overexpression was associated with shortened median survival on both univariate (p < 0.004) and multivariate (p < 0.036) analysis. Genetic knockdown of Axl receptor tyrosine kinase (RTK) function was enabled in two EAC lines (OE33 and JH-EsoAd1) using lentiviral short hairpin RNA (shRNA). Genetic knockdown of Axl in EAC cell lines inhibited invasion, migration, and in vivo engraftment, which was accompanied by downregulation in the activity of the Ral GTPase proteins (RalA and RalB). Restoration of Ral activation rescued the transformed phenotype of EAC cell lines, suggesting a novel effector mechanism for Axl in cancer cells. Pharmacological inhibition of Axl was enabled using a small molecule antagonist, R428 (Rigel Pharmaceuticals). Pharmacological inhibition of Axl with R428 in EAC cell lines significantly reduced anchorage-independent growth, invasion and migration. Blockade of Axl function abrogated phosphorylation of ERBB2 (Her-2/neu) at the Tyr877 residue, indicative of receptor crosstalk. Axl RTK is an adverse prognostic factor in EAC. The availability of small molecule inhibitors of Axl function provides a tractable strategy for molecular therapy of established EAC.

A composite polymer nanoparticle overcomes multidrug resistance and ameliorates doxorubicin-associated cardiomyopathy

Acquired chemotherapy resistance is a major contributor to treatment failure in oncology. For example, the efficacy of the common anticancer agent doxorubicin (DOX) is limited by the emergence of multidrug resistance (MDR) phenotype in cancer cells. While dose escalation of DOX can circumvent such resistance to a degree, this is precluded by the appearance of cardiotoxicity, a particularly debilitating condition in children. In vitro studies have established the ability of the natural phytochemical curcumin to overcome MDR; however, its widespread clinical application is restricted by poor solubility and low bioavailability. Building upon our recently developed polymer nanoparticle of curcumin (NanoCurc or NC) that significantly enhances the systemic bioavailability of curcumin, we synthesized a doxorubicin-curcumin composite nanoparticle formulation called NanoDoxCurc (NDC) for overcoming DOX resistance. Compared to DOX alone, NDC inhibited the MDR phenotype and caused striking growth inhibition both in vitro and in vivo in several models of DOX-resistant cancers (multiple myeloma, acute leukemia, prostate and ovarian cancers, respectively). Notably, NDC-treated mice also demonstrated complete absence of cardiac toxicity, as assessed by echocardiography, or any bone marrow suppression, even at cumulative dosages where free DOX and pegylated liposomal DOX (Doxil®) resulted in demonstrable attenuation of cardiac function and hematological toxicities. This improvement in safety profile was achieved through a reduction of DOX-induced intracellular oxidative stress, as indicated by total glutathione levels and glutathione peroxidase activity in cardiac tissue. A composite DOX-curcumin nanoparticle that overcomes both MDR-based DOX chemoresistance and DOX-induced cardiotoxicity holds promise for providing lasting and safe anticancer therapy.

A polymeric nanoparticle encapsulated small-molecule inhibitor of Hedgehog signaling (NanoHHI) bypasses secondary mutational resistance to Smoothened antagonists

Aberrant activation of the hedgehog (Hh) signaling pathway is one of the most prevalent abnormalities in human cancer. Tumors with cell autonomous Hh activation (e.g., medulloblastomas) can acquire secondary mutations at the Smoothened (Smo) antagonist binding pocket, which render them refractory to conventional Hh inhibitors. A class of Hh pathway inhibitors (HPI) has been identified that block signaling downstream of Smo; one of these compounds, HPI-1, is a potent antagonist of the Hh transcription factor Gli1 and functions independent of upstream components in the pathway. Systemic administration of HPI-1 is challenging due to its minimal aqueous solubility and poor bioavailability. We engineered a polymeric nanoparticle from [poly(lactic-co-glycolic acid); (PLGA)] conjugated with polyethylene glycol (PEG), encapsulating HPI-1 (NanoHHI). NanoHHI particles have an average diameter of approximately 60 nm, forms uniform aqueous suspension, and improved systemic bioavailability compared with the parent compound. In contrast to the prototype targeted Smo antagonist, HhAntag (Genentech), NanoHHI markedly inhibits the growth of allografts derived from Ptch(-/+); Trp53(-/-) mouse medulloblastomas that harbor a Smo(D477G) binding site mutation (P < 0.001), which is accompanied by significant downregulation of mGli1 as well as bona fide Hh target genes (Akna, Cltb, and Olig2). Notably, NanoHHI combined with gemcitabine also significantly impedes the growth of orthotopic Pa03C pancreatic cancer xenografts that have a ligand-dependent, paracrine mechanism of Hh activation when compared with gemcitabine alone. No demonstrable hematologic or biochemical abnormalities were observed with NanoHHI administration. NanoHHI should be amenable to clinical translation in settings where tumors acquire mutational resistance to current Smo antagonists.

Targeting the apoptotic machinery in pancreatic cancers using small-molecule antagonists of the X-linked inhibitor of apoptosis protein

Resistance to apoptosis is a hallmark of many solid tumors, including pancreatic cancers, and may be the underlying basis for the suboptimal response to chemoradiation therapies. Overexpression of a family of inhibitor of apoptosis proteins (IAP) is commonly observed in pancreatic malignancies. We determined the therapeutic efficacy of recently described small-molecule antagonists of the X-linked IAP (XIAP) in preclinical models of pancreatic cancer. Primary pancreatic cancers were assessed for XIAP expression by immunohistochemistry, using a pancreatic cancer tissue microarray. XIAP small-molecule antagonists ("XAntag"; compounds 1396-11 and 1396-12) and the related compound 1396-28 were tested in vitro in a panel of human pancreatic cancer cell lines (Panc1, Capan1, and BxPC3) and in vivo in s.c. xenograft models for their ability to induce apoptosis and impede neoplastic growth. In addition, pancreatic cancer cell lines were treated with XAntags in conjunction with either tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or with radiation to determine potential synergy for such dual targeting of the apoptotic machinery. XIAP was overexpressed in 14 of 18 (77%) of primary pancreatic cancers. The XAntags1396-11 and 1396-12, but not the inactive isomer 1396-28, induced profound apoptosis in multiple pancreatic cancer cell lines tested in vitro, with a IC(50) in the range of 2 to 5 mumol/L. Mechanistic specificity of the XAntags for the baculoviral IAP repeat-2 domain of XIAP was shown by preferential activation of downstream "effector" caspases (caspase-3 and caspase-7) versus the upstream "initiator" caspase-9. S.c. BxPC3 xenograft growth in athymic mice was significantly inhibited by monotherapy with XAntags; treated xenografts showed marked apoptosis and increased cleavage of caspase-3. Notably, striking synergy was demonstrable when XAntags were combined with either TRAIL or radiation therapy, as measured by growth inhibition in vitro and reduced colony formation in soft agar of pancreatic cancer cell lines, at dosages where these therapeutic modalities had minimal to modest effects when used alone. Finally, XAntags in combination with the standard-of-care agent for advanced pancreatic cancer, gemcitabine, resulted in significantly greater inhibition of in vitro growth than gemcitabine alone. Our results confirm that pharmacologic inhibition of XIAP is a potent therapeutic modality in pancreatic cancers. These antagonists are independently capable of inducing pancreatic cancer cell death and also show synergy when combined with proapoptotic ligands (TRAIL), with radiation, and with a conventional antimetabolite, gemcitabine. These preclinical results suggest that targeting of the apoptotic machinery in pancreatic cancers with XAntags is a promising therapeutic option that warrants further evaluation.

The Ape-1/Ref-1 redox antagonist E3330 inhibits the growth of tumor endothelium and endothelial progenitor cells: therapeutic implications in tumor angiogenesis

The apurinic/apyrimidinic endonuclease 1/redox factor-1 (Ape-1/Ref-1) is a multi-functional protein, involved in DNA repair and the activation of redox-sensitive transcription factors. The Ape-1/Ref-1 redox domain acts as a cytoprotective element in normal endothelial cells, mitigating the deleterious effects of apoptotic stimuli through induction of survival signals. We explored the role of the Ape-1/Ref-1 redox domain in the maintenance of tumor-associated endothelium, and of endothelial progenitor cells (EPCs), which contribute to tumor angiogenesis. We demonstrate that E3330, a small molecule inhibitor of the Ape-1/Ref-1 redox domain, blocks the in vitro growth of pancreatic cancer-associated endothelial cells (PCECs) and EPCs, which is recapitulated by stable expression of a dominant-negative redox domain mutant. Further, E3330 blocks the differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) into CD31(+) endothelial progeny. Exposure of PCECs to E3330 results in a reduction of H-ras expression and intracellular nitric oxide (NO) levels, as well as decreased DNA-binding activity of the hypoxia-inducible transcription factor, HIF-1alpha. E3330 also reduces secreted and intracellular vascular endothelial growth factor expression by pancreatic cancer cells, while concomitantly downregulating the cognate receptor Flk-1/KDR on PCECs. Inhibition of the Ape-1/Ref-1 redox domain with E3330 or comparable angiogenesis inhibitors might be a potent therapeutic strategy in solid tumors.

In vivo characterization of a polymeric nanoparticle platform with potential oral drug delivery capabilities

Nanotechnology has enabled significant advances in the areas of cancer diagnosis and therapy. The field of drug delivery is a sterling example, with nanoparticles being increasingly used for generating therapeutic formulations of poorly water-soluble, yet potent anticancer drugs. Whereas a number of nanoparticle-drug combinations are at various stages of preclinical or clinical assessment, the overwhelming majorities of such systems are injectable formulations and are incapable of being partaken orally. The development of an oral nano-delivery system would have distinct advantages for cancer chemotherapy. We report the synthesis and physicochemical characterization of orally bioavailable polymeric nanoparticles composed of N-isopropylacrylamide, methylmethacrylate, and acrylic acid in the molar ratios of 60:20:20 (designated NMA622). Amphiphilic NMA622 nanoparticles show a size distribution of <100 nm (mean diameter of 80 +/- 34 nm) with low polydispersity and can readily encapsulate a number of poorly water-soluble drugs such as rapamycin within the hydrophobic core. No apparent systemic toxicities are observed in mice receiving as much as 500 mg/kg of the orally administered void NMA622 for 4 weeks. Using NMA622-encapsulated rapamycin ("nanorapamycin") as a prototype for oral nano-drug delivery, we show favorable in vivo pharmacokinetics and therapeutic efficacy in a xenograft model of human pancreatic cancer. Oral nanorapamycin leads to robust inhibition of the mammalian target of rapamycin pathway in pancreatic cancer xenografts, which is accompanied by significant growth inhibition (P < 0.01) compared with control tumors. These data indicate that NMA622 nanoparticles provide a suitable platform for oral delivery of water-insoluble drugs like rapamycin for cancer therapy.

SMURF1 amplification promotes invasiveness in pancreatic cancer

Pancreatic cancer is a deadly disease, and new therapeutic targets are urgently needed. We previously identified DNA amplification at 7q21-q22 in pancreatic cancer cell lines. Now, by high-resolution genomic profiling of human pancreatic cancer cell lines and human tumors (engrafted in immunodeficient mice to enrich the cancer epithelial fraction), we define a 325 Kb minimal amplicon spanning SMURF1, an E3 ubiquitin ligase and known negative regulator of transforming growth factor β (TGFβ) growth inhibitory signaling. SMURF1 amplification was confirmed in primary human pancreatic cancers by fluorescence in situ hybridization (FISH), where 4 of 95 cases (4.2%) exhibited amplification. By RNA interference (RNAi), knockdown of SMURF1 in a human pancreatic cancer line with focal amplification (AsPC-1) did not alter cell growth, but led to reduced cell invasion and anchorage-independent growth. Interestingly, this effect was not mediated through altered TGFβ signaling, assayed by transcriptional reporter. Finally, overexpression of SMURF1 (but not a catalytic mutant) led to loss of contact inhibition in NIH-3T3 mouse embryo fibroblast cells. Together, these findings identify SMURF1 as an amplified oncogene driving multiple tumorigenic phenotypes in pancreatic cancer, and provide a new druggable target for molecularly directed therapy.

Allele-specific expression in the germline of patients with familial pancreatic cancer: an unbiased approach to cancer gene discovery

Physiologic allele-specific expression (ASE) in germline tissues occurs during random X-chromosome inactivation and in genomic imprinting, wherein the two alleles of a gene in a heterozygous individual are not expressed equally. Recent studies have confirmed the existence of ASE in apparently non-imprinted autosomal genes; however, the extent of ASE in the human genome is unknown. We explored ASE in lymphoblastoid cell lines of 145 individuals using an oligonucleotide array based assay. ASE of autosomal genes was found to be a very common phenomenon in approximately 20% of heterozygotes at 78% of SNPs at 84% of the genes examined. Comparison of 100 affected individuals from familial pancreatic cancer kindreds and 45 controls revealed three types of changes in the germline: (a) loss of ASE, (b) gain of ASE, and, (c) rare instances of "extreme" (near monoallelic) ASE. The latter changes identified heterozygous deleterious mutations in a subset of these genes. Consequently, an ASE assay efficiently identifies candidate disease genes with altered germline expression properties as compared to controls, and provides insights into mechanisms that confer an inherited disease risk for pancreatic cancer.

The HMGA1-COX-2 axis: a key molecular pathway and potential target in pancreatic adenocarcinoma

CONTEXT

Although pancreatic cancer is a common, highly lethal malignancy, the molecular events that enable precursor lesions to become invasive carcinoma remain unclear. We previously reported that the high-mobility group A1 (HMGA1) protein is overexpressed in >90% of primary pancreatic cancers, with absent or low levels in early precursor lesions.

METHODS

Here, we investigate the role of HMGA1 in reprogramming pancreatic epithelium into invasive cancer cells. We assessed oncogenic properties induced by HMGA1 in non-transformed pancreatic epithelial cells expressing activated K-RAS. We also explored the HMGA1-cyclooxygenase (COX-2) pathway in human pancreatic cancer cells and the therapeutic effects of COX-2 inhibitors in xenograft tumorigenesis.

RESULTS

HMGA1 cooperates with activated K-RAS to induce migration, invasion, and anchorage-independent cell growth in a cell line derived from normal human pancreatic epithelium. Moreover, HMGA1 and COX-2 expression are positively correlated in pancreatic cancer cell lines (r(2) = 0.93; p < 0.001). HMGA1 binds directly to the COX-2 promoter at an AT-rich region in vivo in three pancreatic cancer cell lines. In addition, HMGA1 induces COX-2 expression in pancreatic epithelial cells, while knock-down of HMGA1 results in repression of COX-2 in pancreatic cancer cells. Strikingly, we also discovered that Sulindac (a COX-1/COX-2 inhibitor) or Celecoxib (a more specific COX-2 inhibitor) block xenograft tumorigenesis from pancreatic cancer cells expressing high levels of HMGA1.

CONCLUSIONS

Our studies identify for the first time an important role for the HMGA1-COX-2 pathway in pancreatic cancer and suggest that targeting this pathway could be effective to treat, or even prevent, pancreatic cancer.

Homozygous deletions of methylthioadenosine phosphorylase in human biliary tract cancers

The p16(INK4A)/CDKN2A gene on chromosome 9p21 is a site of frequent allelic loss in human cancers, and in a subset of cases, homozygous deletions at this locus encompass the telomeric methylthioadenosine phosphorylase (MTAP) gene. The MTAP gene product is the principal enzyme involved in purine synthesis via the salvage pathway, such that MTAP-negative cancers are solely dependent on de novo purine synthesis mechanisms. Inhibitors of the de novo pathway can then be used to selectively blockade purine synthesis in cancer cells while causing minimal collateral damage to normal cells. In this study, we determine that 10 of 28 (35%) biliary tract cancers show complete lack of Mtap protein expression. In vitro analysis using a selective inhibitor of the de novo purine synthesis pathway, L-alanosine, shows robust growth inhibition in MTAP-negative biliary cancer cell lines CAK-1 and GBD-1 accompanied by striking depletion of intracellular ATP and failure to rescue this depletion via addition of exogenous methylthioadenosine, the principal substrate of the MTAP gene product; in contrast, no significant effects were observed in MTAP-expressing HuCCT1 and SNU308 cell lines. Colony formation studies confirmed that L-alanosine reduced both number and size of CAK-1 colonies in soft agar assays. Knockdown of Mtap protein by RNA interference in L-alanosine-resistant HuCCT1 cells conferred sensitivity to this agent, confirming that intracellular Mtap protein levels determine response to L-alanosine. Inhibitors of de novo purine synthesis can be a potential mechanism-based strategy for treatment of biliary tract cancers, one third of which show complete loss of MTAP function.

Mitochondrial DNA mutations in pancreatic cancer

BACKGROUND

Somatic mutations of mitochondrial DNA (mtDNA) are increasingly being recognized in many human cancers, but automated sequencing of 16.5 kb of DNA poses an onerous task. We have recently described an oligonucleotide microarray (MitoChip) for rapid and accurate sequencing of the entire mitochondrial genome (Zhou et al., J Mol Diagnostics, 8: 9_14, 2006), greatly facilitating the analysis of mtDNA mutations in cancer. In this report, we perform a comprehensive cataloging of somatic mutations in the mitochondrial genome of human pancreatic cancers using our novel array-based approach.

MATERIALS AND METHODS

MitoChip analysis was performed on DNA isolated from 15 histologically confirmed resection specimens of pancreatic ductal adenocarcinomas. In all cases, matched nonneoplastic pancreatic tissue was obtained as germline control for mtDNA sequence. DNA was extracted from snap-frozen cryostat-embedded specimens and hybridized to the sequencing microarray after appropriate polymerase chain reaction amplification and labeling steps. The vast majority of somatic mutational analyses of mtDNA in human cancers utilize lymphocyte DNA as germline control, without excluding the potential for organ-specific polymorphisms. Therefore, we also examined a series of 15 paired samples of DNA obtained from nonneoplastic pancreata and corresponding EBV-immortalized lymphoblastoid cell lines to determine whether lymphocyte DNA provides an accurate surrogate for the mtDNA sequence of pancreatic tissue.

RESULTS

We sequenced 497,070 base pairs of mtDNA in the 15 matched samples of pancreatic cancer and nonneoplastic pancreatic tissue, and 467,269 base pairs (94.0%) were assigned by the automated genotyping software. All 15 pancreatic cancers demonstrated at least one somatic mtDNA mutation compared to the control germline DNA with a range of 1-14 alterations. Of the 71 somatic mutations observed in our series, 18 were nonsynonymous coding region alterations (i.e., resulting in an amino acid change), 22 were synonymous coding region alterations, and 31 involved noncoding mtDNA segments (including ribosomal and transfer RNAs). Overall, somatic mutations in the coding region most commonly involved the ND4, COI, and CYTB genes; of note, an A-G transition at nucleotide position 841 in the 12sRNA was observed in three independent samples. In the paired analysis of nonneoplastic pancreata and lymphoblastoid cell line DNA, 14 nucleotide discrepancies were observed out of 226,876 nucleotide sequences (a concordance rate of 99.99%), with 9 samples demonstrating a perfect match across all bases assigned.

CONCLUSIONS

Our findings confirm that somatic mtDNA mutations are common in pancreatic cancers, and therefore, have the potential to be a clinically useful biomarker for early detection. Further, our studies confirm that lymphocyte DNA is an excellent, albeit not perfect, surrogate for nonneoplastic pancreatic tissues in terms of being utilized as a germline control. Finally, our report confirms the utility of a high-throughput array-based platform for mtDNA mutational analyses of human cancers.

Sex-specific development of cortical monoamine levels in mouse

Several mental health disorders exhibit sex differences in monoamine levels associated with dimorphic cortical ontogeny. Studies in rodents support the notion that monoamines can profoundly modulate morphogenesis. Here, we show significant sex and hemisphere differences in BALB/cByJ mice on postnatal day 3 for dopamine (DA) and serotonin (5-TH), supporting the notion that sex differences in early monoaminergic ontogeny may result in dimorphic cortical development. Such sex differences may also influence differential behavioral and/or clinical outcomes.

Frequent detection of infectious xenotropic murine leukemia virus (XMLV) in human cultures established from mouse xenografts

PURPOSE

To investigate the frequency of xenotropic murine leukemia virus (MLV) presence in human cell lines established from mouse xenografts and to search for the evidence of horizontal viral spread to other cell lines.

RESULTS

Six of 23 (26%) mouse DNA free xenograft cultures were strongly positive for MLV and their sequences had greater than 99% homology to known MLV strains. Four of five available supernatant fluids from these viral positive cultures were strongly positive for RT activity. Three of these supernatant fluids were studied to confirm the infectivity of the released virions for other human culture cells. Of the 78 non-xenograft derived cell lines maintained in the xenograft culture-containing facilities, 13 (17%) were positive for MLV, including XMRV, a virus strain first identified in human tissues. By contrast, all 50 cultures maintained in a xenograft culture-free facility were negative for viral sequences.

METHODOLOGY

We examined xenograft tumor cell lines from seven independent laboratories and 128 non-xenografted tumor cell lines. Cell line DNA was examined for mouse DNA contamination, and by 3 Taqman qPCR assays targeting the gag, env or pol regions of MLV. Sequencing was used for viral strain identification. Supernatant fluids were tested for reverse transcriptase (RT) activity.

CONCLUSIONS

Human cultures derived after mouse xenografting frequently contain and release highly infectious xenotropic MLV viruses. Laboratories working with xenograft-derived human cultures should be aware of the risk of contamination with potentially biohazardous human-tropic mouse viruses and their horizontal spread to other cultures.