Discovery of cell active macrocyclic peptides with on-target inhibition of KRAS signaling

Macrocyclic peptides have the potential to address intracellular protein–protein interactions (PPIs) of high value therapeutic targets that have proven largely intractable to small molecules. Here, we report broadly applicable lessons for applying this modality to intracellular targets and specifically for advancing chemical matter to address KRAS, a protein that represents the most common oncogene in human lung, colorectal and pancreatic cancers yet is one of the most challenging targets in human disease. Specifically, we focused on KRpep-2d, an arginine-rich KRAS-binding peptide with a disulfide-mediated macrocyclic linkage and a protease-sensitive backbone. These latter redox and proteolytic labilities obviated cellular activity. Extensive structure–activity relationship studies involving macrocyclic linker replacement, stereochemical inversion, and backbone α-methylation, gave a peptide with on-target cellular activity. However, we uncovered an important generic insight – the arginine-dependent cell entry mechanism limited its therapeutic potential. In particular, we observed a strong correlation between net positive charge and histamine release in an ex vivo assay, thus making this series unsuitable for advancement due to the potentially fatal consequences of mast cell degranulation. This observation should signal to researchers that cationic-mediated cell entry – an approach that has yet to succeed in the clinic despite a long history of attempts – carries significant therapy-limiting safety liabilities. Nonetheless, the cell-active molecules identified here validate a unique inhibitory epitope on KRAS and thus provide valuable molecular templates for the development of therapeutics that are desperately needed to address KRAS-driven cancers – some of the most treatment-resistant human malignancies.

Targeting undruggable intracellular proteins with peptides: novel on-target macrocyclic peptide inhibitors of KRAS with broad inhibition of proliferation of multiple KRAS-dependent cancer cell lines.

Discovery and characterization of novel peptide inhibitors of the NRF2/MAFG/DNA ternary complex for the treatment of cancer

Pathway activating mutations of the transcription factor NRF2 and its negative regulator KEAP1 are strongly correlative with poor clinical outcome with pemetrexed/carbo(cis)platin/pembrolizumab (PCP) chemo-immunotherapy in lung cancer. Despite the strong genetic support and therapeutic potential for a NRF2 transcriptional inhibitor, currently there are no known direct inhibitors of the NRF2 protein or its complexes with MAF and/or DNA. Herein we describe the design of a novel and high-confidence homology model to guide a medicinal chemistry effort that resulted in the discovery of a series of peptides that demonstrate high affinity, selective binding to the Antioxidant Response Element (ARE) DNA and thereby displace NRF2-MAFG from its promoter, which is an inhibitory mechanism that to our knowledge has not been previously described. In addition to their activity in electrophoretic mobility shift (EMSA) and TR-FRET-based assays, we show significant dose-dependent ternary complex disruption of NRF2-MAFG binding to DNA by SPR, as well as cellular target engagement by thermal destabilization of HiBiT-tagged NRF2 in the NCI-H1944 NSCLC cell line upon digitonin permeabilization, and SAR studies leading to improved cellular stability. We report the characterization and unique profile of lead peptide 18, which we believe to be a useful in vitro tool to probe NRF2 biology in cancer cell lines and models, while also serving as an excellent starting point for additional in vivo optimization toward inhibition of NRF2-driven transcription to address a significant unmet medical need in non-small cell lung cancer (NSCLC).

De-risking Drug Discovery of Intracellular Targeting Peptides: Screening Strategies to Eliminate False-Positive Hits

Nonspecific promiscuous compounds can mislead researchers and waste significant resources. This phenomenon, though well-documented for small molecules, has not been widely explored for the peptide modality. Here we demonstrate that two purported peptide-based KRas inhibitors, SAH-SOS1 _A and cyclorasin 9A5, exemplify false-positive molecules-in terms of both their binding affinities and cellular activities. Through multiple gold-standard biophysical techniques, we unambiguously show that both peptides lack specific binding to KRas and instead induce protein unfolding. Although these peptides inhibited cellular proliferation, the activities appeared to be off-target on the basis of a counterscreen with KRas-independent cell lines. We further demonstrate that their cellular activities are derived from membrane disruption. Accordingly, we propose that to de-risk false-positive molecules, orthogonal binding assays and cellular counterscreens are indispensable.

High Levels of Expression of P-glycoprotein/Multidrug Resistance Protein Result in Resistance to Vintafolide

Targeting surface receptors overexpressed on cancer cells is one way to specifically treat cancer versus normal cells. Vintafolide (EC145), which consists of folate linked to a cytotoxic small molecule, desacetylvinblastine hydrazide (DAVLBH), takes advantage of the overexpression of folate receptor (FR) on cancer cells. Once bound to FR, vintafolide enters the cell by endocytosis, and the reducing environment of the endosome cleaves the linker, releasing DAVLBH to destabilize microtubules. Vintafolide has shown efficacy and improved tolerability compared with DAVLBH in FR-positive preclinical models. As the first FR-targeting drug to reach the clinic, vintafolide has achieved favorable responses in phase II clinical trials in FR-positive ovarian and lung cancer. However, some FR-positive patients in these clinical trials do not respond to vintafolide. We sought to identify potential biomarkers of resistance to aid in the future development of this and other FR-targeting drugs. Here, we confirm that high P-glycoprotein (P-gp) expression was the strongest predictor of resistance to DAVLBH in a panel of 359 cancer cell lines. Furthermore, targeted delivery of DAVLBH via the FR, as in vintafolide, fails to overcome P-gp-mediated efflux of DAVLBH in both in vitro and in vivo preclinical models. Therefore, we suggest that patients whose tumors express high levels of P-gp be excluded from future clinical trials for vintafolide as well as other FR-targeted therapeutics bearing a P-gp substrate. Mol Cancer Ther; 15(8); 1998-2008. ©2016 AACR.

Abstract B65: High levels of expression of P-glycoprotein/multidrug resistance protein result in resistance to vintafolide

Targeting surface receptors overexpressed on cancer cells is one way to specifically treat cancer versus normal cells. Vintafolide (EC145), which consists of folate linked to a cytotoxic small molecule, desacetylvinblastine hydrazide (DAVLBH), takes advantage of the overexpression of folate receptor (FR) on cancer cells. Once bound to FR, vintafolide enters the cell by endocytosis, and the reducing environment of the endosome cleaves the linker, releasing DAVLBH to destabilize microtubules. Vintafolide has shown efficacy and improved tolerability compared to DAVLBH in FR-positive preclinical models. As the first FR-targeting drug to reach the clinic, vintafolide has achieved favorable responses in Phase II clinical trials in FR-positive ovarian and lung cancer. However, some FR-positive patients in these clinical trials do not respond to vintafolide. We sought to identify potential biomarkers of resistance to aid in the future development of this and other FR-targeting drugs. Here, we confirm in both in vitro and in vivo preclinical models that high P-glycoprotein (P-gp) expression was the strongest predictor of resistance to DAVLBH in a panel of 359 cancer cell lines. Furthermore, targeted delivery of DAVLBH via the FR as in vintafolide fails to overcome P-gp mediated efflux of DAVLBH as seen in FR-expressing engineered cell lines and in vivo models. Therefore, we suggest that patients whose tumors express high levels of P-gp be excluded from future clinical trials for vintafolide as well as other FR-targeted therapeutics bearing a P-gp substrate.

Citation Format: Amy D. Guertin, Jennifer O'Neil, Alexander Stoeck, Joseph A. Reddy, Razvan Cristescu, Brian B. Haines, Marlene C. Hinton, Ryan Dorton, Alicia Bloomfield, Melissa Nelson, Marilynn Vetzel, Serguei Lejnine, Michael Nebozhyn, Theresa Zhang, Andrey Loboda, Kristen L. Picard, Emmett V. Schmidt, Isabelle Dussault, Christopher P. Leamon. High levels of expression of P-glycoprotein/multidrug resistance protein result in resistance to vintafolide. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B65.

Discovery of biomarkers predictive of GSI response in triple-negative breast cancer and adenoid cystic carcinoma

Next-generation sequencing was used to identify Notch mutations in a large collection of diverse solid tumors. NOTCH1 and NOTCH2 rearrangements leading to constitutive receptor activation were confined to triple-negative breast cancers (TNBC; 6 of 66 tumors). TNBC cell lines with NOTCH1 rearrangements associated with high levels of activated NOTCH1 (N1-ICD) were sensitive to the gamma-secretase inhibitor (GSI) MRK-003, both alone and in combination with paclitaxel, in vitro and in vivo, whereas cell lines with NOTCH2 rearrangements were resistant to GSI. Immunohistochemical staining of N1-ICD in TNBC xenografts correlated with responsiveness, and expression levels of the direct Notch target gene HES4 correlated with outcome in patients with TNBC. Activating NOTCH1 point mutations were also identified in other solid tumors, including adenoid cystic carcinoma (ACC). Notably, ACC primary tumor xenografts with activating NOTCH1 mutations and high N1-ICD levels were sensitive to GSI, whereas N1-ICD-low tumors without NOTCH1 mutations were resistant.

SIGNIFICANCE

NOTCH1 mutations, immunohistochemical staining for activated NOTCH1, and HES4 expression are biomarkers that can be used to identify solid tumors that are likely to respond to GSI-based therapies.

Gauging NOTCH1 Activation in Cancer Using Immunohistochemistry

Fixed, paraffin-embedded (FPE) tissues are a potentially rich resource for studying the role of NOTCH1 in cancer and other pathologies, but tests that reliably detect activated NOTCH1 (NICD1) in FPE samples have been lacking. Here, we bridge this gap by developing an immunohistochemical (IHC) stain that detects a neoepitope created by the proteolytic cleavage event that activates NOTCH1. Following validation using xenografted cancers and normal tissues with known patterns of NOTCH1 activation, we applied this test to tumors linked to dysregulated Notch signaling by mutational studies. As expected, frequent NICD1 staining was observed in T lymphoblastic leukemia/lymphoma, a tumor in which activating NOTCH1 mutations are common. However, when IHC was used to gauge NOTCH1 activation in other human cancers, several unexpected findings emerged. Among B cell tumors, NICD1 staining was much more frequent in chronic lymphocytic leukemia than would be predicted based on the frequency of NOTCH1 mutations, while mantle cell lymphoma and diffuse large B cell lymphoma showed no evidence of NOTCH1 activation. NICD1 was also detected in 38% of peripheral T cell lymphomas. Of interest, NICD1 staining in chronic lymphocytic leukemia cells and in angioimmunoblastic lymphoma was consistently more pronounced in lymph nodes than in surrounding soft tissues, implicating factors in the nodal microenvironment in NOTCH1 activation in these diseases. Among carcinomas, diffuse strong NICD1 staining was observed in 3.8% of cases of triple negative breast cancer (3 of 78 tumors), but was absent from 151 non-small cell lung carcinomas and 147 ovarian carcinomas. Frequent staining of normal endothelium was also observed; in line with this observation, strong NICD1 staining was also seen in 77% of angiosarcomas. These findings complement insights from genomic sequencing studies and suggest that IHC staining is a valuable experimental tool that may be useful in selection of patients for clinical trials.

Identification of PBX1 target genes in cancer cells by global mapping of PBX1 binding sites

PBX1 is a TALE homeodomain transcription factor involved in organogenesis and tumorigenesis. Although it has been shown that ovarian, breast, and melanoma cancer cells depend on PBX1 for cell growth and survival, the molecular mechanism of how PBX1 promotes tumorigenesis remains unclear. Here, we applied an integrated approach by overlapping PBX1 ChIP-chip targets with the PBX1-regulated transcriptome in ovarian cancer cells to identify genes whose transcription was directly regulated by PBX1. We further determined if PBX1 target genes identified in ovarian cancer cells were co-overexpressed with PBX1 in carcinoma tissues. By analyzing TCGA gene expression microarray datasets from ovarian serous carcinomas, we found co-upregulation of PBX1 and a significant number of its direct target genes. Among the PBX1 target genes, a homeodomain protein MEOX1 whose DNA binding motif was enriched in PBX1-immunoprecipicated DNA sequences was selected for functional analysis. We demonstrated that MEOX1 protein interacts with PBX1 protein and inhibition of MEOX1 yields a similar growth inhibitory phenotype as PBX1 suppression. Furthermore, ectopically expressed MEOX1 functionally rescued the PBX1-withdrawn effect, suggesting MEOX1 mediates the cellular growth signal of PBX1. These results demonstrate that MEOX1 is a critical target gene and cofactor of PBX1 in ovarian cancers.

Abstract 815: The role of spleen tyrosine kinase (SYK) in paclitaxel resistant ovarian cancer

The development of resistance to paclitaxel represents a general challenge in clinical oncology, particularly in ovarian serous carcinomas (OSCs), the most common and lethal form of ovarian cancer. Initial treatment with a taxane and platinum combination regimen is standard and while the majority of women will achieve a major response to this treatment, the mortality of ovarian cancer is directly related to the tumor's development of chemoresistance. Using a proteomic approach to comprehensively compare the protein expression profiles of primary and recurrent OSC clinical samples, our laboratory previously identified several novel candidate proteins associated with the development of recurrent OSC. In this study, we focus on evaluating one of these proteins, spleen tyrosine kinase (SYK), a non-receptor tyrosine kinase, and its role in the maintenance of paclitaxel resistance in OSC. We have determined that increased expression of SYK in OSC tumor cells obtained from ascites and/or pleural effusion fluid is associated with a poorer response to chemotherapy. Using a cell culture system, we found that two OSC cell lines show an increased expression of SYK after development of in vitro resistance to paclitaxel treatment. More importantly, we demonstrate that SYK small compound inhibitors significantly resensitize the tumor cells to paclitaxel. Our results suggest that SYK plays a role in maintaining paclitaxel resistance in OSC. Recently an oral SYK inhibitor was found to be safe and effective in treating rheumatoid arthritis and non-Hodgkin lymphoma; our results suggest a potential translational use for this inhibitor as a chemosensitizing agent in patients with OSC.

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 815. doi:1538-7445.AM2012-815

Defining NOTCH3 target genes in ovarian cancer

NOTCH3 gene amplification plays an important role in the progression of many ovarian and breast cancers, but the targets of NOTCH3 signaling are unclear. Here, we report the use of an integrated systems biology approach to identify direct target genes for NOTCH3. Transcriptome analysis showed that suppression of NOTCH signaling in ovarian and breast cancer cells led to downregulation of genes in pathways involved in cell-cycle regulation and nucleotide metabolism. Chromatin immunoprecipitation (ChIP)-on-chip analysis defined promoter target sequences, including a new CSL binding motif (N1) in addition to the canonical CSL binding motif, that were occupied by the NOTCH3/CSL transcription complex. Integration of transcriptome and ChIP-on-chip data showed that the ChIP target genes overlapped significantly with the NOTCH-regulated transcriptome in ovarian cancer cells. From the set of genes identified, we showed that the mitotic apparatus organizing protein DLGAP5 (HURP/DLG7) was a critical target. Both the N1 motif and the canonical CSL binding motif were essential to activate DLGAP5 transcription. DLGAP5 silencing in cancer cells suppressed tumorigenicity and inhibited cellular proliferation by arresting the cell cycle at the G(2)-M phase. In contrast, enforced expression of DLGAP5 partially counteracted the growth inhibitory effects of a pharmacologic or RNA interference-mediated NOTCH inhibition in cancer cells. Our findings define direct target genes of NOTCH3 and highlight the role of DLGAP5 in mediating the function of NOTCH3.

Sequential and gamma-secretase-dependent processing of the betacellulin precursor generates a palmitoylated intracellular-domain fragment that inhibits cell growth

Betacellulin (BTC) belongs to the family of epidermal growth factor (EGF)-like growth factors that are expressed as transmembrane precursors and undergo proteolytic ectodomain shedding to release soluble mature ligands. BTC is a dual-specificity ligand for ErbB1 and ErbB4 receptors, and can activate unique signal-transduction pathways that are beneficial for the function, survival and regeneration of pancreatic beta-cells. We have previously shown that BTC precursor (proBTC) is cleaved by ADAM10 to generate soluble ligand and a stable, transmembrane remnant (BTC-CTF). In this study, we analyzed the fate of the BTC-CTF in greater detail. We demonstrated that proBTC is cleaved by ADAM10 to produce BTC-CTF, which then undergoes intramembrane processing by presenilin-1- and/or presenilin-2-dependent gamma-secretase to generate an intracellular-domain fragment (BTC-ICD). We found that the proBTC cytoplasmic domain is palmitoylated and that palmitoylation is not required for ADAM10-dependent cleavage but is necessary for the stability and gamma-secretase-dependent processing of BTC-CTF to generate BTC-ICD. Additionally, palmitoylation is required for nuclear-membrane localization of BTC-ICD, as demonstrated by the redistribution of non-palmitoylated BTC-ICD mutant to the nucleoplasm. Importantly, a novel receptor-independent role for BTC-ICD signaling is suggested by the ability of BTC-ICD to inhibit cell growth in vitro.

ADAM10 as a target for anti-cancer therapy

There is a great unmet medical need in the area of cancer treatment. A potential therapeutic target for intervention in cancer is ADAM10. ADAM10 is a disintegrin-metalloproteinase that processes membrane bound proteins from the cell surface to yield soluble forms. Pharmaceutical companies are actively seeking out inhibitors of ADAM10 for treatments in cancer as the enzyme is known to release the ErbB receptor, HER2/ErbB2 from the cell membrane, an event that is necessary for HER2 positive tumor cells to proliferate. ADAM10 is also capable of processing betacellulin indicating that an inhibitor could be used against EGFR/ErbB1 and/or HER4/ErbB4 receptor positive tumor cells that are betacellulin-dependent. ADAM10 is the principle sheddase for several other molecules associated with cancer proliferation, differentiation, adhesion and migration such as Notch, E-cadherin, CD44 and L1 adhesion molecule indicating that targeting ADAM10 with specific inhibitors could be beneficial.

Malignant ascites-derived exosomes of ovarian carcinoma patients contain CD24 and EpCAM

OBJECTIVE

CD24 is an established marker for poor prognosis in ovarian and other carcinomas. Acquisition of cytoplasmic CD24, as opposed to membranous expression, has been correlated with a higher invasiveness of tumor cells. Exosomes are small vesicles of endosomal origin that are often secreted by tumor cells. Given the emerging role of exosomes in tumor progression, we investigated whether cytoplasmic CD24 expression is correlated with the secretion of CD24 in exosomes.

METHODS

We used CD24 transfected carcinoma cell lines, ovarian carcinoma cell lines and malignant ascites fluid of ovarian carcinoma patients. Exosomes were isolated via ultracentrifugation and sucrose density fractionation and subsequently examined by Western blot analysis and gelatine zymography. In tissue sections CD24 was detected by immunohistochemical staining.

RESULTS

We show that CD24 is released by transfected as well as endogenously expressing cells in vesicles that represent exosomes. CD24 was also identified in exosomes isolated from ascites fluid of ovarian carcinoma patients. In 16 ovarian carcinomas analyzed no correlation between CD24 in tumor tissue sections and the appearance of CD24 in exosomes was detected. Furthermore, we provide evidence that the epithelial cell adhesion molecule (EpCAM), known to be overexpressed in ovarian carcinomas, is secreted in exosomes. The ascites exosomes contain gelatinolytic enzymes.

CONCLUSIONS

Our study identifies CD24 and EpCAM as cargo proteins of exosomes of cultured cell lines and malignant ascites. The exosome-associated proteolytic activity in the tumor vicinity might augment tumor invasion into the stroma.

The ADAM10 prodomain is a specific inhibitor of ADAM10 proteolytic activity and inhibits cellular shedding events

ADAM10 is a disintegrin metalloproteinase that processes amyloid precursor protein and ErbB ligands and is involved in the shedding of many type I and type II single membrane-spanning proteins. Like tumor necrosis factor-alpha-converting enzyme (TACE or ADAM17), ADAM10 is expressed as a zymogen, and removal of the prodomain results in its activation. Here we report that the recombinant mouse ADAM10 prodomain, purified from Escherichia coli, is a potent competitive inhibitor of the human ADAM10 catalytic/disintegrin domain, with a K(i) of 48 nM. Moreover, the mouse ADAM10 prodomain is a selective inhibitor as it only weakly inhibits other ADAM family proteinases in the micromolar range and does not inhibit members of the matrix metalloproteinase family under similar conditions. Mouse prodomains of TACE and ADAM8 do not inhibit their respective enzymes, indicating that ADAM10 inhibition by its prodomain is unique. In cell-based assays we show that the ADAM10 prodomain inhibits betacellulin shedding, demonstrating that it could be of potential use as a therapeutic agent to treat cancer.

CD24 is a marker of exosomes secreted into urine and amniotic fluid

Exosomes are small membrane vesicles that are secreted from a variety of cell types into various body fluids including the blood and urine. These vesicles are thought to play a role in cell-cell interactions. CD24 is a small but extensively glycosylated protein linked to the cell surface by means of a glycosyl-phosphatidylinositol anchor. In this study we found that CD24 is present in membrane vesicles characterized as exosomes that were isolated from the urine of normal individuals. CD24 was expressed by both tubule cells and podocytes and treatment of the latter with a cholesterol-extracting agent, but not with a calcium ionophore, caused the release of CD24-containing exosomes. Using CD24 as a marker, we found exosomes in the urine of newborn infants and in the amniotic fluid of pregnant women with similar findings made in mice. Interestingly, studies with CD24 knockout mice showed that the exosomes are released from the fetus but not from the mother; however, exosome release was similar from both the knockout and the wild-type mice. This indicates that CD24 is not essential for exosome formation or release but may be a convenient exosome marker. Our studies suggest that exosomal secretion from the embryonic kidney could play a biological role at the fetal-maternal interphase.

Exosomes: from biogenesis and secretion to biological function

Exosomes are small microvesicles that are released from late endosomal compartments of cultured cells. Recent work has shown that exosome-like vesicles are also found in many body fluids such as blood, urine, ascites and amnionic fluid. Although the biological function of exosomes is far from being fully understood, exosomes may have general importance in cell biology and immunology. The present review aims to address some of the facets of exosome research with particular emphasis on the immunologist's perspective: (i) exosomes as a novel platform for the ectodomain shedding of membrane proteins by ADAMs and (ii) recent findings on the role of exosomes in tumor biology and immune regulation.

L1-CAM in a membrane-bound or soluble form augments protection from apoptosis in ovarian carcinoma cells

OBJECTIVE

Apoptosis resistance is a hallmark of cancer progression, a phenomenon frequently observed in ovarian carcinoma. We reported previously, that L1 adhesion molecule (CD171) is overexpressed in ovarian and endometrial carcinomas and that L1 expression is a predictor of poor outcome. We investigated a possible role of L1 in apoptosis resistance.

METHODS

We used L1 transfectants and ovarian carcinoma cell lines and induced apoptosis by different stimuli such as C2-ceramide, staurosporine, cisplatin or hypoxia.

RESULTS

We found that cells expressing L1 are more resistant against apoptosis. In HEK293 cells, L1-expresssion leads to a sustained ERK, FAK and PAK phosphorylation. Soluble L1 only partially rescued HEK293 cells from apoptosis. Treatment with apoptotic stimuli upregulated the anti-apoptotic molecule Bcl-2 to a greater extend in HEK293 cells expressing L1. In the ovarian carcinoma cell line OVMz, the depletion of L1 by RNA interference sensitized cells for apoptosis induction. No changes in activation of ERK or FAK were observed after L1 knockdown. The selection of m130 ovarian carcinoma or SW707 colon carcinoma cells with cisplatin leads to upregulated expression of L1.

CONCLUSIONS

Our results suggest a link between L1 expression and chemoresistance of ovarian carcinomas. Upregulation of L1 after cisplatin treatment might indicate a more malignant tumor phenotype given the established role of L1 in cell motility and invasion.

Different expression levels of alpha3/4 fucosyltransferases and Lewis determinants in ovarian carcinoma tissues and cell lines

Ovarian carcinoma is the leading cause of death from gynecological cancers in many countries. Fucosylated glycoconjugates have been associated with various carcinomas. In the present study, we have characterized the expression of alpha3/4 fucosyltransferases transcripts and their products, the Lewis carbohydrate determinants, and their in vitro specificity towards synthetic acceptors using ovarian carcinoma cell lines OVM, m130, GG and SKOV3. We found different expression patterns: GG cells expressed mostly Lewisx (Lex), Lewisy (Ley), sLea and Leb, and m130 cells expressed mostly Lex and Ley. The detection was on the plasma membrane and in intracellular vesicles. OVM and SKOV3 cells had very low amounts of staining. From RT-PCR studies, enzyme specificity of cellular extracts towards a panel of synthetic carbohydrate acceptors and Western blot analysis we concluded that Lea, sLea and Leb were synthesised by FUT3, whereas Lex and Ley were synthesized by FUT4 and FUT9 in both cell lines. The GG and m130 cell lines are adequate models to investigate the role of Lex, Ley, sLea and Leb in ovarian carcinoma development.

A role for exosomes in the constitutive and stimulus-induced ectodomain cleavage of L1 and CD44

Ectodomain shedding is a proteolytic mechanism by which transmembrane molecules are converted into a soluble form. Cleavage is mediated by metalloproteases and proceeds in a constitutive or inducible fashion. Although believed to be a cell-surface event, there is increasing evidence that cleavage can take place in intracellular compartments. However, it is unknown how cleaved soluble molecules get access to the extracellular space. By analysing L1 (CD171) and CD44 in ovarian carcinoma cells, we show in the present paper that the cleavage induced by ionomycin, APMA (4-aminophenylmercuric acetate) or MCD (methyl-beta-cyclodextrin) is initiated in an endosomal compartment that is subsequently released in the form of exosomes. Calcium influx augmented the release of exosomes containing functionally active forms of ADAM10 (a disintegrin and metalloprotease 10) and ADAM17 [TACE (tumour necrosis factor a-converting enzyme)] as well as CD44 and L1 cytoplasmic cleavage fragments. Cleavage could also proceed in released exosomes, but only depletion of ADAM10 by small interfering RNA blocked cleavage under constitutive and induced conditions. In contrast, cleavage of L1 in response to PMA occurred at the cell surface and was mediated by ADAM17. We conclude that different ADAMs are involved in distinct cellular compartments and that ADAM10 is responsible for shedding in vesicles. Our findings open up the possibility that exosomes serve as a platform for ectodomain shedding and as a vehicle for the cellular export of soluble molecules.

L1 on ovarian carcinoma cells is a binding partner for Neuropilin-1 on mesothelial cells

The progression of ovarian cancer is driven by a variety of cellular factors that are incompletely understood. Binding of tumor cells to normal cells and to soluble factors influence tumor growth, angiogenesis and the stimulation of vascular permeability leading to ascites production. L1 adhesion molecule is overexpressed in ovarian carcinoma and is associated with bad prognosis. One receptor for L1 is Neuropilin-1 (NRP-1) that is also known as a receptor for VEGF(165). In the nervous system a complex of NRP-1 and L1 transmits signals by the neurorepellant Sem3A that is critical for the control of neurite outgrowth. NRP-1 has also been detected in human carcinomas but its function remains unknown. Here, we have examined NRP-1 expression in ovarian carcinoma cell lines and tissue. We report that little NRP-1 protein was detected in primary ovarian carcinoma tissues or established cell lines although mRNA for soluble and transmembrane NRP-1 were detected by RT-PCR. Instead, we observed strong expression of NRP-1 in mesothelial cells, which form the lining of the peritoneum. NRP-1 could serve as an isolation marker for primary mesothelial cells present in ascites fluid. We demonstrate that ovarian cancer cells expressing L1 can bind to NRP-1 overexpressing cells and mesothelial cells. Likewise, soluble L1 isolated from ascites of patients or produced as a fusion protein could bind to NRP-1 overexpressing cells and a direct interaction was demonstrated at the protein level. These findings suggest that L1 can support the binding of ovarian carcinoma cells to mesothelial cells via NRP-1. The L1-NRP-1 binding pathway could contribute to the growth of ovarian carcinomas and to reciprocal signalling between mesothelial cells and tumors.

L1 augments cell migration and tumor growth but not beta3 integrin expression in ovarian carcinomas

L1 is a neural cell adhesion molecule involved in cell migration, axon growth and guidance. Recent data have shown that L1 is overexpressed in ovarian and endometrial tumors and is associated with bad prognosis. How L1 promotes tumor progression is presently unknown. Here we show that L1 expression is predominantly confined to the invasive front of ovarian carcinomas. Overexpression of L1 in carcinoma cell lines by adenovirus-mediated gene transfer enhanced the haptotactic cell migration on extracellular matrix proteins. Expression of L1 augmented tumor growth of carcinomas xenografted in nonobese diabetic/severe combined immunodeficient mice (NOD/SCID). A recent report has demonstrated L1-dependent upregulation of beta3 integrin involving activation of the extracellular signal-regulated kinase (erk) pathway. We find that L1 and beta3 integrin are not coexpressed in ovarian carcinoma tissues. Overexpression of L1 did not upregulate beta3 integrin in ovarian carcinoma cell lines but could do so in HEK293 cells. Our results suggest that L1 could drive progression by enhancing cell migration and tumor growth but that L1 dependent and erk-regulated gene expression requires cell-type specific elements.

Cleavage of L1 in exosomes and apoptotic membrane vesicles released from ovarian carcinoma cells

PURPOSE

The L1 adhesion molecule (CD171) is overexpressed in human ovarian and endometrial carcinomas and is associated with bad prognosis. Although expressed as a transmembrane molecule, L1 is released from carcinoma cells in a soluble form. Soluble L1 is present in serum and ascites of ovarian carcinoma patients. We investigated the mode of L1 cleavage and the function of soluble L1.

EXPERIMENTAL DESIGN

We used ovarian carcinoma cell lines and ascites from ovarian carcinoma patients to analyze soluble L1 and L1 cleavage by Western blot analysis and ELISA.

RESULTS

We find that in ovarian carcinoma cells the constitutive cleavage of L1 proceeds in secretory vesicles. We show that apoptotic stimuli like C2-ceramide, staurosporine, UV irradiation, and hypoxic conditions enhance L1-vesicle release resulting in elevated levels of soluble L1. Constitutive cleavage of L1 is mediated by a disintegrin and metalloproteinase 10, but under apoptotic conditions multiple metalloproteinases are involved. L1 cleavage occurs in two types of vesicles with distinct density features: constitutively released vesicles with similarity to exosomes and apoptotic vesicles. Both types of L1-containing vesicles are present in the ascites fluids of ovarian carcinoma patients. Soluble L1 from ascites is a potent inducer of cell migration and can trigger extracellular signal-regulated kinase phosphorylation.

CONCLUSIONS

We suggest that tumor-derived vesicles may be an important source for soluble L1 that could regulate tumor cell function in an autocrine/paracrine fashion.

Brain development in mice lacking L1-L1 homophilic adhesion

A new mouse line has been produced in which the sixth Ig domain of the L1 cell adhesion molecule has been deleted. Despite the rather large deletion, L1 expression is preserved at normal levels. In vitro experiments showed that L1–L1 homophilic binding was lost, along with L1-α5β1 integrin binding. However, L1–neurocan and L1–neuropilin binding were preserved and sema3a responses were intact. Surprisingly, many of the axon guidance defects present in the L1 knockout mice, such as abnormal corticospinal tract and corpus callosum, were not observed. Nonetheless, when backcrossed on the C57BL/6 strain, a severe hydrocephalus was observed and after several generations, became an embryonic lethal. These results imply that L1 binding to L1, TAG-1, or F3, and L1-α5β1 integrin binding are not essential for normal development of a variety of axon pathways, and suggest that L1–L1 homophilic binding is important in the production of X-linked hydrocephalus.

L1 expression as a predictor of progression and survival in patients with uterine and ovarian carcinomas

BACKGROUND

Ovarian and uterine carcinomas are the most common cause of cancer-related deaths in gynecological malignant diseases. We aimed to assess whether the L1 adhesion molecule, an important mediator for cell migration for neural and tumour cells, is expressed in these carcinomas.

METHODS

We investigated L1 expression by immunohistochemistry, RT-PCR, and Western blot analysis of tumour samples. Soluble L1 in the serum was detected by ELISA and immunoprecipitation.

FINDINGS

We detected the L1 adhesion molecule in ovarian and uterine tumours in a stage-dependent manner. In a retrospective study L1 was found in 46 of 58 ovarian carcinomas and 20 of 72 uterine adenocarcinomas. L1 expression was an excellent predictor of poor outlook (p<0.00001). Patients with L1 positive uterine tumours were at high risk for progression even in the endometrioid-type tumours, which usually have a favourable prognosis. In uterine tumours, expression of L1 in curettage samples enabled us to identify aggressive tumours before the operation. Soluble L1 was specifically detected in serum samples from patients with ovarian and uterine tumours. ADAM10, which was implicated in previous studies as L1 sheddase, was expressed in tumours in which soluble L1 was present in the serum.

INTERPRETATION

L1 is overexpressed in ovarian and uterine carcinomas and is associated with short survival. L1 can serve as a new marker for prediction of clinical outcome and could be helpful to identify patients with uterine tumours who are at high risk for recurrent disease. L1 expression and cleavage could promote dissemination of tumours by facilitating cell migration.

ADAM10-mediated cleavage of L1 adhesion molecule at the cell surface and in released membrane vesicles

Cells can release membrane components in a soluble form and as membrane vesicles. L1, an important molecule for cell migration of neural and tumor cells, is released by membrane-proximal cleavage, and soluble L1 promotes cell migration. Release of L1 is enhanced by shedding inducers such as phorbol ester and pervanadate, but it is also enhanced by depletion of cellular cholesterol with methyl-beta-cyclodextrin (MCD). How such different compounds can induce shedding is presently unknown. We show here that ADAM10 is involved in L1 cleavage, which occurs at the cell surface and in the Golgi apparatus. MCD and pervanadate treatment induced the release of microvesicles containing full-length L1 and the active form of ADAM10. L1 cleavage occurred in isolated vesicles. L1-containing microvesicles could trigger haptotactic cell migration. Only the neural L1 form carrying the RSLE signal for clathrin-dependent endocytosis was recruited and cleaved in vesicles. Phorbol ester treatment activated L1 cleavage predominantly at the cell surface. Our results provide evidence for two pathways of L1 cleavage, based on ADAM10 localization, that can be activated differentially: 1) direct cleavage at the cell surface, and 2) release and cleavage in secretory vesicles most likely derived from the Golgi apparatus. The findings establish a novel role for ADAM10 as a vesicle-based protease.

Ectodomain shedding of L1 adhesion molecule promotes cell migration by autocrine binding to integrins

The L1 adhesion molecule plays an important role in axon guidance and cell migration in the nervous system. L1 is also expressed by many human carcinomas. In addition to cell surface expression, the L1 ectodomain can be released by a metalloproteinase, but the biological function of this process is unknown. Here we demonstrate that membrane-proximal cleavage of L1 can be detected in tumors and in the developing mouse brain. The shedding of L1 involved a disintegrin and metalloproteinase (ADAM)10, as transfection with dominant-negative ADAM10 completely abolishes L1 release. L1-transfected CHO cells (L1-CHO) showed enhanced haptotactic migration on fibronectin and laminin, which was blocked by antibodies to alpha v beta 5 and L1. Migration of L1-CHO cells, but not the basal migration of CHO cells, was blocked by a metalloproteinase inhibitor, indicating a role for L1 shedding in the migration process. CHO and metalloproteinase-inhibited L1-CHO cells were stimulated to migrate by soluble L1-Fc protein. The induction of migration was blocked by alpha v beta 5-specific antibodies and required Arg-Gly-Asp sites in L1. A 150-kD L1 fragment released by plasmin could also stimulate CHO cell migration. We propose that ectodomain-released L1 promotes migration by autocrine/paracrine stimulation via alpha v beta 5. This regulatory loop could be relevant for migratory processes under physiological and pathophysiological conditions.