Mind the (guidance) signals! Translational relevance of semaphorins, plexins, and neuropilins in pancreatic cancer

Pancreatic cancer is a major cause of demise worldwide. Although key associated genetic changes have been discovered, disease progression is sustained by pathogenic mechanisms that are poorly understood at the molecular level. In particular, the tissue microenvironment of pancreatic adenocarcinoma (PDAC) is usually characterized by high stromal content, scarce recruitment of immune cells, and the presence of neuronal fibers. Semaphorins and their receptors, plexins and neuropilins, comprise a wide family of regulatory signals that control neurons, endothelial and immune cells, embryo development, and normal tissue homeostasis, as well as the microenvironment of human tumors. We focus on the role of these molecular signals in pancreatic cancer progression, as revealed by experimental research and clinical studies, including novel approaches for cancer treatment.

Breast cancers as ecosystems: a metabolic perspective

Breast cancer (BC) is the most frequently diagnosed cancer and one of the major causes of cancer death. Despite enormous progress in its management, both from the therapeutic and early diagnosis viewpoints, still around 700,000 patients succumb to the disease each year, worldwide. Late recurrency is the major problem in BC, with many patients developing distant metastases several years after the successful eradication of the primary tumor. This is linked to the phenomenon of metastatic dormancy, a still mysterious trait of the natural history of BC, and of several other types of cancer, by which metastatic cells remain dormant for long periods of time before becoming reactivated to initiate the clinical metastatic disease. In recent years, it has become clear that cancers are best understood if studied as ecosystems in which the impact of non-cancer-cell-autonomous events-dependent on complex interaction between the cancer and its environment, both local and systemic-plays a paramount role, probably as significant as the cell-autonomous alterations occurring in the cancer cell. In adopting this perspective, a metabolic vision of the cancer ecosystem is bound to improve our understanding of the natural history of cancer, across space and time. In BC, many metabolic pathways are coopted into the cancer ecosystem, to serve the anabolic and energy demands of the cancer. Their study is shedding new light on the most critical aspect of BC management, of metastatic dissemination, and that of the related phenomenon of dormancy and fostering the application of the knowledge to the development of metabolic therapies.

Mutated axon guidance gene PLXNB2 sustains growth and invasiveness of stem cells isolated from cancers of unknown primary

The genetic changes sustaining the development of cancers of unknown primary (CUP) remain elusive. The whole-exome genomic profiling of 14 rigorously selected CUP samples did not reveal specific recurring mutation in known driver genes. However, by comparing the mutational landscape of CUPs with that of most other human tumor types, it emerged a consistent enrichment of changes in genes belonging to the axon guidance KEGG pathway. In particular, G842C mutation of PlexinB2 (PlxnB2) was predicted to be activating. Indeed, knocking down the mutated, but not the wild-type, PlxnB2 in CUP stem cells resulted in the impairment of self-renewal and proliferation in culture, as well as tumorigenic capacity in mice. Conversely, the genetic transfer of G842C-PlxnB2 was sufficient to promote CUP stem cell proliferation and tumorigenesis in mice. Notably, G842C-PlxnB2 expression in CUP cells was associated with basal EGFR phosphorylation, and EGFR blockade impaired the viability of CUP cells reliant on the mutated receptor. Moreover, the mutated PlxnB2 elicited CUP cell invasiveness, blocked by EGFR inhibitor treatment. In sum, we found that a novel activating mutation of the axon guidance gene PLXNB2 sustains proliferative autonomy and confers invasive properties to stem cells isolated from cancers of unknown primary, in EGFR-dependent manner.

Correction: Ponzo et al. Nucleolin Therapeutic Targeting Decreases Pancreatic Cancer Immunosuppression. Cancers 2022, 14, 4265

In the original publication [...].

Neuropilin 1 and its inhibitory ligand mini-tryptophanyl-tRNA synthetase inversely regulate VE-cadherin turnover and vascular permeability

The formation of a functional blood vessel network relies on the ability of endothelial cells (ECs) to dynamically rearrange their adhesive contacts in response to blood flow and guidance cues, such as vascular endothelial growth factor-A (VEGF-A) and class 3 semaphorins (SEMA3s). Neuropilin 1 (NRP1) is essential for blood vessel development, independently of its ligands VEGF-A and SEMA3, through poorly understood mechanisms. Grounding on unbiased proteomic analysis, we report here that NRP1 acts as an endocytic chaperone primarily for adhesion receptors on the surface of unstimulated ECs. NRP1 localizes at adherens junctions (AJs) where, interacting with VE-cadherin, promotes its basal internalization-dependent turnover and favors vascular permeability initiated by histamine in both cultured ECs and mice. We identify a splice variant of tryptophanyl-tRNA synthetase (mini-WARS) as an unconventionally secreted extracellular inhibitory ligand of NRP1 that, by stabilizing it at the AJs, slows down both VE-cadherin turnover and histamine-elicited endothelial leakage. Thus, our work shows a role for NRP1 as a major regulator of AJs plasticity and reveals how mini-WARS acts as a physiological NRP1 inhibitory ligand in the control of VE-cadherin endocytic turnover and vascular permeability.

Targeting Acute Myelogenous Leukemia Using Potent Human Dihydroorotate Dehydrogenase Inhibitors Based on the 2-Hydroxypyrazolo[1,5-a]pyridine Scaffold: SAR of the Biphenyl Moiety

The connection with acute myelogenous leukemia (AML) of dihydroorotate dehydrogenase (hDHODH), a key enzyme in pyrimidine biosynthesis, has attracted significant interest from pharma as a possible AML therapeutic target. We recently discovered compound 1, a potent hDHODH inhibitor (IC50 = 1.2 nM), able to induce myeloid differentiation in AML cell lines (THP1) in the low nM range (EC50 = 32.8 nM) superior to brequinar's phase I/II clinical trial (EC50 = 265 nM). Herein, we investigate the 1 drug-like properties observing good metabolic stability and no toxic profile when administered at doses of 10 and 25 mg/kg every 3 days for 5 weeks (Balb/c mice). Moreover, in order to identify a backup compound, we investigate the SAR of this class of compounds. Inside the series, 17 is characterized by higher potency in inducing myeloid differentiation (EC50 = 17.3 nM), strong proapoptotic properties (EC50 = 20.2 nM), and low cytotoxicity toward non-AML cells (EC30(Jurkat) > 100 μM).

Albumin nanoformulations as an innovative solution to overcome doxorubicin chemoresistance

Aim: Resistance to chemotherapy is a major limiting factor that hamper the effectiveness of anticancer therapies. Doxorubicin is an antineoplastic agent used in the treatment of a wide range of cancers. However, it presents several limitations such as dose-dependent cardiotoxicity, lack of selectivity for tumor cells, and induced cell resistance. Nanotechnology represents a promising strategy to avoid these drawbacks. In this work, new albumin-based nanoparticles were formulated for the intracellular delivery of doxorubicin with the aim to overcome cancer drug resistance.

Methods: Glycol chitosan-coated and uncoated albumin nanoparticles were prepared with a tuned coacervation method. The nanoformulations were in vitro characterized evaluating the physicochemical parameters, morphology, and in vitro release kinetics. Biological assays were performed on A2780res and EMT6 cells from human ovarian carcinoma and mouse mammary cell lines resistant for doxorubicin, respectively.

Results: Cell viability assays showed that nanoparticles have higher cytotoxicity than the free drug. Moreover, at low concentrations, both doxorubicin-loaded nanoparticles inhibited the cell colony formation in a greater extent than drug solution. In addition, the cell uptake of the different formulations was investigated by confocal microscopy and by the HPLC determination of doxorubicin intracellular accumulation. The nanoparticles were rapidly internalized in greater extent compared to the free drug.

Conclusion: Based on these results, doxorubicin-loaded albumin nanoparticles might represent a novel platform to overcome the mechanism of drug resistance in cancer cell lines and improve the drug efficacy.

HIV Protease Inhibitors Block HPV16-Induced Murine Cervical Carcinoma and Promote Vessel Normalization in Association with MMP-9 Inhibition and TIMP-3 Induction

Antiretrovirals belonging to the human immunodeficiency virus (HIV) protease inhibitor (HIV-PI) class exert inhibitory effects across several cancer types by targeting tumor cells and its microenvironment. Cervical carcinoma represents a leading cause of morbidity and mortality, particularly in women doubly infected with high-risk human papillomaviruses (HR-HPV) and HIV; of note, combined antiretroviral therapy has reduced cervical carcinoma onset and progression in HIV-infected women. We evaluated the effectiveness and mechanism(s) of action of HIV-PI against cervical carcinoma using a transgenic model of HR-HPV-induced estrogen-promoted cervical carcinoma (HPV16/E2) and found that treatment of mice with ritonavir-boosted HIV-PI, including indinavir, saquinavir, and lopinavir, blocked the growth and promoted the regression of murine cervical carcinoma. This was associated with inhibition of tumor angiogenesis, coupled to downregulation of matrix metalloproteinase (MMP)-9, reduction of VEGF/VEGFR2 complex, and concomitant upregulation of tissue inhibitor of metalloproteinase-3 (TIMP-3). HIV-PI also promoted deposition of collagen IV at the epithelial and vascular basement membrane and normalization of both vessel architecture and functionality. In agreement with this, HIV-PI reduced tumor hypoxia and enhanced the delivery and antitumor activity of conventional chemotherapy. Remarkably, TIMP-3 expression gradually decreased during progression of human dysplastic lesions into cervical carcinoma. This study identified the MMP-9/VEGF proangiogenic axis and its modulation by TIMP-3 as novel HIV-PI targets for the blockade of cervical intraepithelial neoplasia/cervical carcinoma development and invasiveness and the normalization of tumor vessel functions. These findings may lead to new therapeutic indications of HIV-PI to treat cervical carcinoma and other tumors in either HIV-infected or uninfected patients.

CAR T cells targeting tumor endothelial marker CLEC14A inhibit tumor growth

Engineering T cells to express chimeric antigen receptors (CARs) specific for antigens on hematological cancers has yielded remarkable clinical responses, but with solid tumors, benefit has been more limited. This may reflect lack of suitable target antigens, immune evasion mechanisms in malignant cells, and/or lack of T cell infiltration into tumors. An alternative approach, to circumvent these problems, is targeting the tumor vasculature rather than the malignant cells directly. CLEC14A is a glycoprotein selectively overexpressed on the vasculature of many solid human cancers and is, therefore, of considerable interest as a target antigen. Here, we generated CARs from 2 CLEC14A-specific antibodies and expressed them in T cells. In vitro studies demonstrated that, when exposed to their target antigen, these engineered T cells proliferate, release IFN-γ, and mediate cytotoxicity. Infusing CAR engineered T cells into healthy mice showed no signs of toxicity, yet these T cells targeted tumor tissue and significantly inhibited tumor growth in 3 mouse models of cancer (Rip-Tag2, mPDAC, and Lewis lung carcinoma). Reduced tumor burden also correlated with significant loss of CLEC14A expression and reduced vascular density within malignant tissues. These data suggest the tumor vasculature can be safely and effectively targeted with CLEC14A-specific CAR T cells, offering a potent and widely applicable therapy for cancer.

T cells expressing a chimeric antigen receptor specific for the tumor vascular marker CLEC14A inhibited tumor growth in three mouse cancer models.

A rationally designed NRP1-independent superagonist SEMA3A mutant is an effective anticancer agent

Vascular normalizing strategies, aimed at ameliorating blood vessel perfusion and lessening tissue hypoxia, are treatments that may improve the outcome of cancer patients. Secreted class 3 semaphorins (SEMA3), which are thought to directly bind neuropilin (NRP) co-receptors that, in turn, associate with and elicit plexin (PLXN) receptor signaling, are effective normalizing agents of the cancer vasculature. Yet, SEMA3A was also reported to trigger adverse side effects via NRP1. We rationally designed and generated a safe, parenterally deliverable, and NRP1-independent SEMA3A point mutant isoform that, unlike its wild-type counterpart, binds PLXNA4 with nanomolar affinity and has much greater biochemical and biological activities in cultured endothelial cells. In vivo, when parenterally administered in mouse models of pancreatic cancer, the NRP1-independent SEMA3A point mutant successfully normalized the vasculature, inhibited tumor growth, curbed metastatic dissemination, and effectively improved the supply and anticancer activity of chemotherapy. Mutant SEMA3A also inhibited retinal neovascularization in a mouse model of age-related macular degeneration. In summary, mutant SEMA3A is a vascular normalizing agent that can be exploited to treat cancer and, potentially, other diseases characterized by pathological angiogenesis.

Therapeutic Silencing of miR-214 Inhibits Tumor Progression in Multiple Mouse Models

We previously demonstrated that miR-214 is upregulated in malignant melanomas and triple-negative breast tumors and promotes metastatic dissemination by affecting a complex pathway including the anti-metastatic miR-148b. Importantly, tumor dissemination could be reduced by blocking miR-214 function or increasing miR-148b expression or by simultaneous interventions. Based on this evidence, with the intent to explore the role of miR-214 as a target for therapy, we evaluated the capability of new chemically modified anti-miR-214, R97/R98, to inhibit miR-214 coordinated metastatic traits. Relevantly, when melanoma or breast cancer cells were transfected with R97/R98, anti-miR-214 reduced miR-214 expression and impaired transendothelial migration were observed. Noteworthy, when the same cells were injected in the tail vein of mice, cell extravasation and metastatic nodule formation in lungs were strongly reduced. Thus, suggesting that R97/R98 anti-miR-214 oligonucleotides were able to inhibit tumor cell escaping through the endothelium. More importantly, when R97/R98 anti-miR-214 compounds were systemically delivered to mice carrying melanomas or breast or neuroendocrine pancreatic cancers, a reduced number of circulating tumor cells and lung or lymph node metastasis formation were detected. Similar results were also obtained when AAV8-miR-214 sponges were used in neuroendocrine pancreatic tumors. Based on this evidence, we propose miR-214 as a promising target for anti-metastatic therapies.

Abstract B069: Temozolomide drives mismatch repair deficiency and fosters neoantigen generation in tumor cells

The tumor mutational burden affects immune surveillance and is associated with response to immune checkpoint blockade. We recently reported that inactivation of the DNA mismatch repair (MMR) pathway in cancer cells increases the mutational burden and modifies the neoantigen landscapes of cancer cells leading to their increased recognition by the immune system. We designed a pharmacologic screening to identify FDA-approved drugs capable of differentially affecting cancer cells MMR proficient and deficient. MMR-deficienT-cells displayed lower sensitivity to the alkylating agent Temozolomide (TMZ) and to the antimetabolite 6-Thioguanine (6-TG). Cells lacking key elements of the MMR pathway such as MutL homolog1, MutS homolog2 (MSH2) or MutS homolog 6 (MSH6), displayed an increased resistance to both TMZ and 6-TG. Next we treated two mouse colorectal cancer cell lines (MC38 and CT26) with TMZ until resistant populations emerged. MC38 cells acquired TMZ resistance through inactivation of the MMR pathway. Bioinformatic analysis revealed that these cells had higher numbers of neoantigens compared to parental cells. Importantly, when MC38 MMRd cells were injected in syngeneic mice, they were unable to form tumors. On the contrary, CT26 cells that acquired TMZ-resistance through other mechanisms, efficiently formed tumors in mice. Therefore, TMZ-induced MMR inactivation, and not TMZ treatment per se, triggered immune surveillance. To assess whether results obtained in mouse cancer models might translate to human disease, we tested TMZ in 47 molecularly annotated colorectal cancer (CRC) cancer cell lines. Only MMR-proficienT-cells and cells in which O6-methylguanine-DNA- methyltransferase (MGMT, the enzyme responsible for repairing the DNA adducts formed by TMZ) was not expressed were sensible to TMZ. Ten sensitive cell lines were chronically treated with TMZ until resistant populations emerged; we found that MGMT re-expression and loss of MMR genes were the main mechanisms of acquired resistance. In agreement with in vitro observations, analysis of biopsies from eight patients relapsing upon TMZ-based therapeutic regimens revealed MGMT re-expression (5 patients) and MMR genes mutations (i.e., MSH2 or MSH6) as main resistance mechanism. In both cell lines and biopsies, MMR inactivation led to increased mutational load and, consequently, to higher levels of predicted neo-antigens, suggesting an augmented immunogenicity. These preclinical data led to the clinical trial Arethusa (NCT03519412; https://clinicaltrials.gov/ct2/show/NCT03519412). Within Arethusa MMR-proficient patients will be tested for (MGMT) expression (IHC) and then for MGMT promoter methylation. MGMT negative patients will be treated with temozolomide (TMZ). Patients progressing under temozolomide will be tested for tumor mutational burden (TMB) and proceed to pembrolizumab if TMB is > 20 mutations/Mb. The primary study hypothesis is that tumors with acquired resistance to temozolomide might become hypermutated and could be sensitive to the anti PD-1 antibody, pembrolizumab.

Citation Format: Vito Amodio, Giovanni Grmano, Ludovic Barault, Simona Lamba, Giuseppe Rospo, Alessandro Magrì, Federica Maione, Giovanni Crisafulli, Carlotta Cancelliere, Giulia Lerda, Alice Bartolini, Giulia Siravegna, Benedetta Mussolin, Roberta Frappolli, Monica Montone, Giovanni Randon, Filippo de Braud, Nabil Amirouchene Angelozzi, Silvia Marsoni, Maurizio D'Incalci, Armando Orlandi, Enrico Giraudo, Andrea Satore-Bianchi, Salvatore Siena, Filippo Pietrantonio, Federica Di Nicolantonio, Alberto Bardelli. Temozolomide drives mismatch repair deficiency and fosters neoantigen generation in tumor cells [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B069.

α-ketoglutarate dehydrogenase inhibition counteracts breast cancer-associated lung metastasis

Metastasis formation requires active energy production and is regulated at multiple levels by mitochondrial metabolism. The hyperactive metabolism of cancer cells supports their extreme adaptability and plasticity and facilitates resistance to common anticancer therapies. In spite the potential relevance of a metastasis metabolic control therapy, so far, limited experience is available in this direction. Here, we evaluated the effect of the recently described α-ketoglutarate dehydrogenase (KGDH) inhibitor, (S)-2-[(2,6-dichlorobenzoyl) amino] succinic acid (AA6), in an orthotopic mouse model of breast cancer 4T1 and in other human breast cancer cell lines. In all conditions, AA6 altered Krebs cycle causing intracellular α-ketoglutarate (α-KG) accumulation. Consequently, the activity of the α-KG-dependent epigenetic enzymes, including the DNA demethylation ten-eleven translocation translocation hydroxylases (TETs), was increased. In mice, AA6 injection reduced metastasis formation and increased 5hmC levels in primary tumours. Moreover, in vitro and in vivo treatment with AA6 determined an α-KG accumulation paralleled by an enhanced production of nitric oxide (NO). This epigenetically remodelled metabolic environment efficiently counteracted the initiating steps of tumour invasion inhibiting the epithelial-to-mesenchymal transition (EMT). Mechanistically, AA6 treatment could be linked to upregulation of the NO-sensitive anti-metastatic miRNA 200 family and down-modulation of EMT-associated transcription factor Zeb1 and its CtBP1 cofactor. This scenario led to a decrease of the matrix metalloproteinase 3 (MMP3) and to an impairment of 4T1 aggressiveness. Overall, our data suggest that AA6 determines an α-KG-dependent epigenetic regulation of the TET-miR200-Zeb1/CtBP1-MMP3 axis providing an anti-metastatic effect in a mouse model of breast cancer-associated metastasis.

Inflammatory Cytokines Induce Podoplanin Expression at the Tumor Invasive Front

Tumor invasion is a critical first step in the organismic dissemination of cancer cells and the formation of metastasis in distant organs, the most important prognostic factor and the actual cause of death in most of the cancer patients. We report herein that the cell surface protein podoplanin (PDPN), a potent inducer of cancer cell invasion, is conspicuously expressed by the invasive front of squamous cell carcinomas (SCCs) of the cervix in patients and in the transgenic human papillomavirus/estrogen mouse model of cervical cancer. Laser capture microscopy combined with gene expression profiling reveals that the expression of interferon-responsive genes is up-regulated in PDPN-expressing cells at the tumor invasive front, which are exposed to CD45-positive inflammatory cells. Indeed, PDPN expression can be induced in cultured SCC cell lines by single or combined treatments with interferon-γ, transforming growth factor-β, and/or tumor necrosis factor-α. Notably, shRNA-mediated ablation of either PDPN or STAT1 in A431 SCC cells repressed cancer cell invasion on s.c. transplantation into immunodeficient mice. The results highlight the induction of tumor cell invasion by the inflammatory cytokine-stimulated expression of PDPN in the outermost cell layers of cervical SCC.

Inactivation of DNA repair triggers neoantigen generation and impairs tumour growth

Molecular alterations in genes involved in DNA mismatch repair (MMR) promote cancer initiation and foster tumour progression. Cancers deficient in MMR frequently show favourable prognosis and indolent progression. The functional basis of the clinical outcome of patients with tumours that are deficient in MMR is not clear. Here we genetically inactivate MutL homologue 1 (MLH1) in colorectal, breast and pancreatic mouse cancer cells. The growth of MMR-deficient cells was comparable to their proficient counterparts in vitro and on transplantation in immunocompromised mice. By contrast, MMR-deficient cancer cells grew poorly when transplanted in syngeneic mice. The inactivation of MMR increased the mutational burden and led to dynamic mutational profiles, which resulted in the persistent renewal of neoantigens in vitro and in vivo, whereas MMR-proficient cells exhibited stable mutational load and neoantigen profiles over time. Immune surveillance improved when cancer cells, in which MLH1 had been inactivated, accumulated neoantigens for several generations. When restricted to a clonal population, the dynamic generation of neoantigens driven by MMR further increased immune surveillance. Inactivation of MMR, driven by acquired resistance to the clinical agent temozolomide, increased mutational load, promoted continuous renewal of neoantigens in human colorectal cancers and triggered immune surveillance in mouse models. These results suggest that targeting DNA repair processes can increase the burden of neoantigens in tumour cells; this has the potential to be exploited in therapeutic approaches.

Multivalent cationic pseudopeptide polyplexes as a tool for cancer therapy

In this study, a novel anticancer reagent based on polyplexes nanoparticles was developed. These nanoparticles are obtained by mixing negatively charged polyelectrolytes with the antitumour cationically-charged pseudopeptide N6L. Using two in vivo experimental tumor pancreatic models based upon PANC-1 and mPDAC cells, we found that the antitumour activity of N6L is significantly raised via its incorporation in polyplexed nanoparticles. Study of the mechanism of action using affinity isolation and si-RNA experiments indicated that N6L-polyplexes are internalized through their interaction with nucleolin. In addition, using a very aggressive model of pancreatic cancer in which gemcitabine, a standard of care for this type of cancer, has a weak effect on tumour growth, we observed that N6L-polyplexes administration has a stronger efficacy than gemcitabine. Biodistribution studies carried out in tumour-bearing mice indicated that N6L-polyplexes localises in tumour tissue, in agreement with its antitumour effect. These results support the idea that N6L nanoparticles could develop into a promising strategy for the treatment of cancer, especially hard-to-treat pancreatic cancers.

Sema3F (Semaphorin 3F) Selectively Drives an Extraembryonic Proangiogenic Program

OBJECTIVE

Molecular pathways governing blood vessel patterning are vital to vertebrate development. Because of their ability to counteract proangiogenic factors, antiangiogenic secreted Sema3 (class 3 semaphorins) control embryonic vascular morphogenesis. However, if and how Sema3 may play a role in the control of extraembryonic vascular development is presently unknown.

APPROACH AND RESULTS

By characterizing genetically modified mice, here, we show that surprisingly Sema3F acts instead as a selective extraembryonic, but not intraembryonic proangiogenic cue. Both in vivo and in vitro, in visceral yolk sac epithelial cells, Sema3F signals to inhibit the phosphorylation-dependent degradation of Myc, a transcription factor that drives the expression of proangiogenic genes, such as the microRNA cluster 17/92. In Sema3f-null yolk sacs, the transcription of Myc-regulated microRNA 17/92 cluster members is impaired, and the synthesis of Myc and microRNA 17/92 foremost antiangiogenic target Thbs1 (thrombospondin 1) is increased, whereas Vegf (vascular endothelial growth factor) signaling is inhibited in yolk sac endothelial cells. Consistently, exogenous recombinant Sema3F inhibits the phosphorylation-dependent degradation of Myc and the synthesis of Thbs1 in mouse F9 teratocarcinoma stem cells that were in vitro differentiated in visceral yolk sac epithelial cells. Sema3f-/- mice placentas are also highly anemic and abnormally vascularized.

CONCLUSIONS

Sema3F functions as an unconventional Sema3 that promotes extraembryonic angiogenesis by inhibiting the Myc-regulated synthesis of Thbs1 in visceral yolk sac epithelial cells.

Abstract PR13: Inactivation of DNA repair triggers dynamic neoantigen evolution and impairs cancer growth

Colorectal, ovarian, endometrial and other tumors carrying defects in DNA mismatch repair often show favorable prognosis and indolent progression. The genomes of these tumors -also known as microsatellite unstable (MSI) cancers- bear hundreds of thousands of somatic mutations, a feature which fosters cancer progression and rapid evolution of resistance to targeted therapies. The molecular bases for the favorable outcome of MMR deficient cancers have long remained a mystery. Recent evidences that a subset of MSI tumors respond prominently to immune checkpoint blockade led to the seminal hypothesis that the presence of high number of somatic mutations may be responsible for effective immune-surveillance. However, several reports indicate that a relevant fraction of hyper-mutated tumors have unfavorable prognosis and do not respond to immune-modulators. Intrigued by these contradictory findings, we used the CRISPR system to genetically inactivated MutL homolog 1 (MLH1) in colorectal, breast and pancreatic mouse cancer cells. The growth of MMR deficient cells was comparable to their proficient counterparts in vitro and upon transplantation in immune-compromised mice. Strikingly however, isogenic MMR deficient colorectal, breast and pancreatic cancer cells were largely unable to form tumors when injected subcutaneously or orthotopically in syngeneic mouse models. MMR deficient tumors initially established in immune-deficient mice continued to grow exponentially when transplanted in syngeneic animals but regressed promptly when immune checkpoint inhibitors (anti PD-1 and anti CTLA-4) were administered. Exome sequencing of MMR proficient cells revealed mutational loads and neo-antigen profiles that were stable over time. MMR inactivation further increased the mutation burden and led to highly dynamic mutational profiles, resulting in persistent renewal of neoantigens. These results led us hypothesize that enforced increase of the number of mutations in cancer cells could be paradoxically- beneficial for therapeutic purposes. We therefore performed a pharmacological screen to identify agents capable of permanent inactivation of MMR in colorectal, breast and PDAC cancer cells. We found that temozolomide triggers MLH1 inactivation and leads to rapid clonal evolution and dynamic neoantigen profiles. Temozolomide-treated cells were unable to form tumors in syngeneic animals, while cells treated with other alkylating agents did. Genomic analysis of these tumor models revealed that fluctuating levels of neoantigens, rather than the absolute number of mutations is critical to provoke immune surveillance. These results provide the rationale for developing innovative anticancer therapies that target DNA repair proteins.

This abstract is also being presented as Poster B11.

Citation Format: Giovanni Germano, Simona Lamba, Giuseppe Rospo, Alessandro Magrì, Federica Maione, Mariangela Russo, Nabil Amirouchene Angelozzi, Ludovuc Barault, Monica Montone, Federica Di Nicolantonio, Enrico Giraudo, Alberto Bardelli. Inactivation of DNA repair triggers dynamic neoantigen evolution and impairs cancer growth. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr PR13.

Nucleolin Targeting Impairs the Progression of Pancreatic Cancer and Promotes the Normalization of Tumor Vasculature

Pancreatic cancer is a highly aggressive tumor, mostly resistant to the standard treatments. Nucleolin is overexpressed in cancers and its inhibition impairs tumor growth. Herein, we showed that nucleolin was overexpressed in human specimens of pancreatic ductal adenocarcinoma (PDAC) and that the overall survival significantly increased in patients with low levels of nucleolin. The nucleolin antagonist N6L strongly impaired the growth of primary tumors and liver metastasis in an orthotopic mouse model of PDAC (mPDAC). Similar antitumor effect of N6L has been observed in a highly angiogenic mouse model of pancreatic neuroendocrine tumor RIP-Tag2. N6L significantly inhibited both human and mouse pancreatic cell proliferation and invasion. Notably, the analysis of tumor vasculature revealed a strong increase of pericyte coverage and vessel perfusion both in mPDAC and RIP-Tag2 tumors, in parallel to an inhibition of tumor hypoxia. Nucleolin inhibition directly affected endothelial cell (EC) activation and changed a proangiogenic signature. Among the vascular activators, nucleolin inhibition significantly decreased angiopoietin-2 (Ang-2) secretion and expression in ECs, in the tumor and in the plasma of mPDAC mice. As a consequence of the observed N6L-induced tumor vessel normalization, pre-treatment with N6L efficiently improved chemotherapeutic drug delivery and increased the antitumor properties of gemcitabine in PDAC mice. In conclusion, nucleolin inhibition is a new anti-pancreatic cancer therapeutic strategy that dually blocks tumor progression and normalizes tumor vasculature, improving the delivery and efficacy of chemotherapeutic drugs. Moreover, we unveiled Ang-2 as a potential target and suitable response biomarker for N6L treatment in pancreatic cancer. Cancer Res; 76(24); 7181-93. ©2016 AACR.

Activation of P2X7 and P2Y11 purinergic receptors inhibits migration and normalizes tumor-derived endothelial cells via cAMP signaling

Purinergic signaling is involved in inflammation and cancer. Extracellular ATP accumulates in tumor interstitium, reaching hundreds micromolar concentrations, but its functional role on tumor vasculature and endothelium is unknown. Here we show that high ATP doses (>20 μM) strongly inhibit migration of endothelial cells from human breast carcinoma (BTEC), but not of normal human microvascular EC. Lower doses (1–10 mm result ineffective. The anti-migratory activity is associated with cytoskeleton remodeling and is significantly prevented by hypoxia. Pharmacological and molecular evidences suggest a major role for P2X7R and P2Y11R in ATP-mediated inhibition of TEC migration: selective activation of these purinergic receptors by BzATP mimics the anti-migratory effect of ATP, which is in turn impaired by their pharmacological or molecular silencing. Downstream pathway includes calcium-dependent Adenilyl Cyclase 10 (AC10) recruitment, cAMP release and EPAC-1 activation. Notably, high ATP enhances TEC-mediated attraction of human pericytes, leading to a decrease of endothelial permeability, a hallmark of vessel normalization. Finally, we provide the first evidence of in vivo P2X7R expression in blood vessels of murine and human breast carcinoma. In conclusion, we have identified a purinergic pathway selectively acting as an antiangiogenic and normalizing signal for human tumor-derived vascular endothelium.

Class 3 semaphorins in cardiovascular development

Secreted class 3 semaphorins (Sema3), which signal through holoreceptor complexes that are formed by different subunits, such as neuropilins (Nrps), proteoglycans, and plexins, were initially characterized as fundamental regulators of axon guidance during embryogenesis. Subsequently, Sema3A, Sema3C, Sema3D, and Sema3E were discovered to play crucial roles in cardiovascular development, mainly acting through Nrp1 and Plexin D1, which funnels the signal of multiple Sema3 in vascular endothelial cells. Mechanistically, Sema3 proteins control cardiovascular patterning through the enzymatic GTPase-activating-protein activity of the cytodomain of Plexin D1, which negatively regulates the function of Rap1, a small GTPase that is well-known for its ability to drive vascular morphogenesis and to elicit the conformational activation of integrin adhesion receptors.

Abstract 3372: Semaphorin 3A normalizes the tumor vasculature and impairs tumor progression in a Nrp-1-independent manner

It is widely described that tumor vessel normalization, occurring in response to certain anti-angiogenic therapies, represents a remarkably advantageous anti-cancer strategy (1). We have demonstrated that Semaphorin 3A (Sema3A), an axon guidance cue part of class 3 semaphorins family, is an endogenous angiogenic inhibitor able to efficiently impair tumor progression, prolong the survival and normalize the tumor vasculature in different mouse models of spontaneous tumorigenesis (2). Moreover, we recently showed that Sema3A, by extending the normalization window and abrogating tumor hypoxia, overcame the resistance to the anti-angiogenic therapy inhibiting metastasis dissemination (3).

Stemming from these findings we sought to investigate the molecular mechanisms of vessel normalization and metastasis inhibition induced by Sema3A. Interestingly, by confocal microscope and western blot analysis, in a co-culture systems of human endothelial cells (ECs) and pericytes grown in contact, we observed that Sema3A dramatically down-modulated its receptor Nrp-1 in both cell types, with the consequent over-expression of PDGF-B and Ang-1, known to promote vessel maturation. Moreover, a wide screening of different genes and pathways modulated in the ECs/pericyte co-cultures revealed that the most modulated was the HGF/Met pathway. In fact, we observed that c-Met phosphorylation was impaired in FACS-sorted ECs co-cultured with human pericytes, compared to ECs grown as single layer. To better investigate the specific role of Sema3A in modulating HGF/Met activation in vessels, we detected a strong inhibition of HGF-induced Met phosphorylation in Nrp-1 silenced ECs induced by Sema3A, suggesting that this semaphorin could directly interfere with Met signaling. Notably, Sema3A impaired HGF-induced Met phosphorylation, not only in ECs, but also in several Nrp-1-silenced gastric, lung and pancreatic tumor cell lines, inducing apoptosis and blocking the invasiveness. Finally, treating an orthotopic mouse model of pancreatic ductal adenocarcinoma (PDAC) with adeno-associate virus (AAV)-8 expressing Sema3A, we observed a strong inhibition of tumor growth, a dramatic reduction of liver metastasis and a normalized and perfused tumor vessels phenotype. Remarkably, we found that Sema3A strongly and specifically inhibited Met activation in both tumor cells and vessels, in parallel to a down-modulation of Nrp-1.

We conclude that Sema3A normalizes the tumor vasculature and blocks cancer progression in a Nrp-1-independent manner, in part by inhibiting HGF/Met pathway.

References

1. Jain RK, et al. Cancer Cell. 2014; 26:605-22.

2. Maione F., et al. J. Clin. Invest. 2009; 119:3356-72.

3. Maione F., et al. J. Clin Invest. 2012; 122:1832-48.

Citation Format: Federica Maione, Cristina Basilico, Elisa Vigna, Mauro Giacca, Guido Serini, Enrico Giraudo. Semaphorin 3A normalizes the tumor vasculature and impairs tumor progression in a Nrp-1-independent manner. [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 3372.

Abstract 3366: NCL targeting impairs the progression of pancreatic ductal adenocarcinoma and promotes tumor vessel normalization through Ang-2 inhibition

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive tumor, mostly resistant to the standard treatments. NCL is overexpressed in cancers and its inhibition impairs tumor growth. Herein we described, that NCL was overexpressed in human specimens of PDAC, and low NCL staining patients had increased overall survival. Previously, we described a family of multivalent pseudopeptides binding to NCL and inhibiting tumour growth. Here, NCL antagonist N6L, strongly impaired tumor growth, liver metastasis formation and angiogenesis in an orthothopic mouse model of PDAC. N6L inhibited both human and mouse tumor cell proliferation and invasion. Proteome analysis of endothelial cell secreted proteins showed that NCL inhibition decreased Ang-2 levels and switched a pro-angiogenic signature. Importantly, Ang-2 levels were decreased in plasma of N6L-treated PDAC mice. The analysis of tumor vasculature revealed a strong increase of pericyte coverage and vessel perfusion in parallel to an inhibition of tumor hypoxia. As consequence of N6L-induced tumor vessel normalization, pre-treatment with N6L efficiently improved chemotherapeutic drug delivery and increased the anti-tumor properties of gemcitabine in PDAC mice.

In conclusion, NCL inhibition is a new anti-tumor therapeutic strategy that dually blocks tumor progression and normalizes tumor vessels improving the delivery and efficacy of chemotherapeutic drugs in PDAC cancers. Moreover, we identified Ang-2 as a potential target and suitable response biomarker for N6L treatment in PDAC.

Citation Format: Maud-Emmanuelle Gilles, Federica Maione, Mélissande Cossutta, Gilles Carpentier, Laure Caruana, Silvia Di Maria, Damien Destouches, Ksenya Shchors, Christopher Prochasson, Anne Couvelard, José Courty, Enrico Giraudo, Ilaria Cascone. NCL targeting impairs the progression of pancreatic ductal adenocarcinoma and promotes tumor vessel normalization through Ang-2 inhibition. [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 3366.

Lenalidomide normalizes tumor vessels in colorectal cancer improving chemotherapy activity

Background

Angiogenesis inhibition is a promising approach for treating metastatic colorectal cancer (mCRC). Recent evidences support the seemingly counterintuitive ability of certain antiangiogenic drugs to promote normalization of residual tumor vessels with important clinical implications. Lenalidomide is an oral drug with immune-modulatory and anti-angiogenic activity against selected hematologic malignancies but as yet little is known regarding its effectiveness for solid tumors. The aim of this study was to determine whether lenalidomide can normalize colorectal cancer neo-vessels in vivo, thus reducing tumor hypoxia and improving the benefit of chemotherapy.

Methods

We set up a tumorgraft model with NOD/SCID mice implanted with a patient-derived colorectal cancer liver metastasis. The mice were treated with oral lenalidomide (50 mg/Kg/day for 28 days), intraperitoneal 5-fluorouracil (5FU) (20 mg/Kg twice weekly for 3 weeks), combination (combo) of lenalidomide and 5FU or irrelevant vehicle. We assessed tumor vessel density (CD146), pericyte coverage (NG2; alphaSMA), in vivo perfusion capability of residual vessels (lectin distribution essay), hypoxic areas (HP2-100 Hypoxyprobe) and antitumor activity in vivo and in vitro.

Results

Treatment with lenalidomide reduced tumor vessel density (p = 0.0001) and enhanced mature pericyte coverage of residual vessels (p = 0.002). Perfusion capability of tumor vessels was enhanced in mice treated with lenalidomide compared to controls (p = 0.004). Accordingly, lenalidomide reduced hypoxic tumor areas (p = 0.002) and enhanced the antitumor activity of 5FU in vivo. The combo treatment delayed tumor growth (p = 0.01) and significantly reduced the Ki67 index (p = 0.0002). Lenalidomide alone did not demonstrate antitumor activity compared to untreated controls in vivo or against 4 different mCRC cell lines in vitro.

Conclusions

We provide the first evidence of tumor vessel normalization and hypoxia reduction induced by lenalidomide in mCRC in vivo. This effect, seemingly counterintuitive for an antiangiogenic compound, translates into indirect antitumor activity thus enhancing the therapeutic index of chemotherapy. Our findings suggest that further research should be carried out on synergism between lenalidomide and conventional therapies for treating solid tumors that might benefit from tumor vasculature normalization.

Abstract A16: Semaphorin 3A normalizes the tumor vasculature and impairs cancer progression in a Nrp-1-independent manner

It is widely described that tumor vessel normalization, occurring in response to certain anti-angiogenic therapies, represents a remarkably advantageous anti-cancer strategy (1). We have demonstrated that Semaphorin 3A (Sema3A), an axon guidance cue part of class 3 semaphorins family, is an endogenous angiogenic inhibitor able to efficiently impair tumor progression, prolong the survival and normalize the tumor vasculature in different mouse models of spontaneous tumorigenesis (2). Moreover, we recently showed that Sema3A, by extending the normalization window and abrogating tumor hypoxia, overcame the resistance to the anti-angiogenic therapy inhibiting metastasis dissemination (3).

Stemming from these findings we sought to investigate the molecular mechanisms of vessel normalization and metastasis inhibition induced by Sema3A. Interestingly, by confocal microscope and western blot analysis, in a co-culture systems of human endothelial cells (ECs) and pericytes grown in contact, we observed that Sema3A dramatically down-modulated its receptor Nrp-1 in both cell types, with the consequent over-expression of PDGF-B and Ang-1, known to promote vessel maturation. Moreover, a wide screening of different genes and pathways modulated in the ECs/pericyte co-cultures, revealed that the most modulated was the HGF/Met pathway. In fact, we observed that c-Met phosphorylation was impaired in FACS-sorted ECs co-cultured with human pericytes, compared to ECs grown as single layer. To better investigate the specific role of Sema3A in modulating HGF/Met activation in vessels, we detected a strong inhibition of HGF-induced Met phosphorylation in Nrp-1 silenced ECs induced by Sema3A, suggesting that this semaphorin could directly interfere with Met signaling. Finally, treating an orthotopic mouse model of pancreatic ductal adenocarcinoma (PDAC) with adeno-associate virus (AAV)-8 expressing Sema3A, we observed a strong inhibition of tumor growth, a dramatic reduction of liver metastasis and a normalized and perfused tumor vessels phenotype. Remarkably, we found that Sema3A strongly and specifically inhibited Met activation in both tumor cells and vessels, in parallel to a down-modulation of Nrp-1 in normalized vasculature.

We conclude that Sema3A normalizes the tumor vasculature and blocks cancer progression by acting on Nrp-1 and HGF/Met pathway.

References:

1. Goel S, et al. Physiol Rev. 2011; 91(3):1071–1121.

2. Maione F., et al. J. Clin. Invest. 2009; 119(11):3356-72.

3. Maione F., et al. J. Clin Invest. 2012; 122(5):1832-48.

Citation Format: Federica Maione, Cristina Basilico, Mauro Giacca, Guido Serini, Enrico Giraudo. Semaphorin 3A normalizes the tumor vasculature and impairs cancer progression in a Nrp-1-independent manner. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr A16.

Abstract A02: Nucleolin antagonist peptide N6L, normalizes tumor vasculature by decreasing Ang-2 secretion and inhibits pancreatic ductal adenocarcinoma growth and metastasis

Nucleolin (NCL) is a nucleolar protein regulating ribogenesis and cell cycle progression, and is overexpressed in tumor cells. Shuttling to the cell surface of tumor cells and tumor vessels NCL is a marker of tumor tissues and a target for cancer therapy. Recently, we developed a family of nucleolin antagonist pseudopeptides (NucANT). The N6L peptide, strongly inhibits human tumor growth by inducing apoptosis of tumor cells (1), and is currently in clinical trial for cancer. Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human malignancies, and an explanation of the failure of treatments is that chemotherapies are poorly delivered to the tumor because of a deficient and pathologic vasculature. We investigated the possibility that N6L could dually target tumor cells and tumor vasculature and be a promising new option for the treatment of PDAC.

NCL targeting by N6L inhibited pancreatic tumor cell proliferation and pancreatic tumor cell motility similarly to other tumor cell types (1). Concerning endothelial cells (EC), N6L inhibited EC proliferation, motility, adhesion and tubulogenesis. We screened proteins involved in vascular stability and showed that N6L treatment or NCL depletion regulated the secretion of Ang-2. This N6L effect was specific of NCL targeting because NCL depletion rescued the inhibition of Ang-2 secretion induced by N6L.

We investigated the effect of N6L on the growth and metastasis of a PDAC orthotopic mouse model that was deficient in vasculature such as the human tumors and NCL was highly expressed in tumor ductal epithelial cells. We showed that N6L strongly inhibited the tumor growth by inhibiting NCL expression, tumor cell proliferation, and increasing tumor cell apoptosis. Coherently with the in vitro data, N6L decreased Ang-2 plasma concentration of PDAC mice. By characterizing the PDAC tumor vasculature after treatment, we demonstrated that N6L induced both vessel pruning and normalization of tumor vasculature by improving pericyte coverage and tumor blood vessel perfusion. Moreover, N6L-induced tumor vessel normalization was accompanied by an improved efficiency of chemotherapeutic drugs delivery to cancer tissues and an inhibition of liver metastasis incidence.

We conclude that NCL inhibition by N6L normalizes pancreatic tumor vasculature and suggest Ang-2 as a target and a biomarker of N6L response. N6L-induced PDAC vessel normalization promotes drug delivery and contributes to decrease metastasis formation.

1. Destouches D, et al. (2011) A simple approach to cancer therapy afforded by multivalent pseudopeptides that target cell-surface nucleoproteins. Cancer Res 71(9):3296-3305.

Citation Format: Maud-Emmanuelle Gilles, Federica Maione, Gilles Carpentier, damien Destouches, José Courty, Enrico Giraudo, Ilaria Cascone. Nucleolin antagonist peptide N6L, normalizes tumor vasculature by decreasing Ang-2 secretion and inhibits pancreatic ductal adenocarcinoma growth and metastasis. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr A02.

Abstract B17: In-depth proteomics unveils fatty acid oxidation role in controlling vascular permeability

Endothelial cells (ECs) play a key role in maintaining vascular functionality. Alterations in vessel stability and permeability are hallmarks of tumor angiogenesis and may affect the efficacy of anti-cancer therapy. Modulating EC metabolism has emerged as a promising strategy to target angiogenesis in pathological conditions, but so far, little is known about the role of EC metabolism in the regulation of vessel stability and permeability.

In this work we took advantage of a simplified in-vitro model of angiogenesis, where HUVECs (human umbilical vein endothelial cells) form a vascular-like network on a tridimensional matrix, to elucidate the role of EC metabolism during this process.

By integrating high resolution proteomic data with a human genome scale metabolic model we built up the first predictive model of metabolic fluxes occurring in ECs forming a complex network and identified increased fluxes for reactions involving fatty acid oxidation (FAO) enzymes when ECs are assembled into a fully formed network. Upon inhibition of CPT1, the FAO rate-limiting enzyme, we disrupted the network and reduced cellular ATP levels and oxygen consumption, which were restored by replenishing the tricarboxylic acid cycle (TCAc). Remarkably, phosphoproteomic changes measured upon CPT1A inhibition evoked those triggered by thrombin, a potent inducer of EC permeability through calcium signaling. Indeed, acute CPT1A inhibition increased EC permeability in-vitro and leakage of fully formed blood vessel in-vivo, which were restored by replenishing the TCAc or inhibiting calcium influx.

FAO emerges as central regulator of blood vessel stability, revealing the possibility of targeting FAO to interfere with tumor vessel permeability.

Citation Format: Francesca Patella, Zachary T. Schug, Erez Persi, Lisa J. Neilson, Zahra Erami, Daniele Avanzato, Federica Maione, Juan R. Hernandez-Fernaud, Gillian Mackay, Liang Zheng, Steven Reid, Christian Frezza, Enrico Giraudo, Alessandra Fiorio Pla, Kurt Anderson, Eytan Ruppin, Eyal Gottlieb, Sara Zanivan. In-depth proteomics unveils fatty acid oxidation role in controlling vascular permeability. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Angiogenesis and Vascular Normalization: Bench to Bedside to Biomarkers; Mar 5-8, 2015; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl):Abstract nr B17.

Proteomics-based metabolic modeling reveals that fatty acid oxidation (FAO) controls endothelial cell (EC) permeability

Endothelial cells (ECs) play a key role to maintain the functionality of blood vessels. Altered EC permeability causes severe impairment in vessel stability and is a hallmark of pathologies such as cancer and thrombosis. Integrating label-free quantitative proteomics data into genome-wide metabolic modeling, we built up a model that predicts the metabolic fluxes in ECs when cultured on a tridimensional matrix and organize into a vascular-like network. We discovered how fatty acid oxidation increases when ECs are assembled into a fully formed network that can be disrupted by inhibiting CPT1A, the fatty acid oxidation rate-limiting enzyme. Acute CPT1A inhibition reduces cellular ATP levels and oxygen consumption, which are restored by replenishing the tricarboxylic acid cycle. Remarkably, global phosphoproteomic changes measured upon acute CPT1A inhibition pinpointed altered calcium signaling. Indeed, CPT1A inhibition increases intracellular calcium oscillations. Finally, inhibiting CPT1A induces hyperpermeability in vitro and leakage of blood vessel in vivo, which were restored blocking calcium influx or replenishing the tricarboxylic acid cycle. Fatty acid oxidation emerges as central regulator of endothelial functions and blood vessel stability and druggable pathway to control pathological vascular permeability.

Abstract 4807: Zoledronic acid overcomes the resistance to the anti-angiogenic therapy and normalizes tumor vessels by switching from a M2- to a M1-like macrophages phenotype in a mouse model of spontaneous cervical cancer

Recent studies described a resistance to the anti-angiogenic therapy both in pre-clinical and clinical settings. Several mechanisms that contribute to this resistance has been so far proposed and, among these, the recruitment of bone marrow-derived cells to the tumors, seems to be critical.

We have previously showed that an amino-bisphosphonate, Zoledronic acid (ZA), in a mouse model of spontaneous cervical carcinogenesis (HPV16/E2) by targeting MMP-9+ tumor-associated macrophages (TAM), strongly inhibited cancer progression and angiogenesis. Stemming from these data we sought to investigate whether ZA by acting on TAM, was able to overcome the resistance to anti-angiogenic treatments.

We treated tumor-bearing HPV16/E2 mice with ZA alone or combined with the small molecule tyrosine kinase inhibitor Sunitinib or with an anti-VEGFR-2 antibody, DC101, to assess the ability of ZA to block metastasis dissemination. Notably ZA synergized with Sunitinib and DC101 to inhibit primary tumor growth. Interestingly, while these compounds increased the incidence and the number of liver and lung metastasis, ZA alone inhibited basal tumor metastasis in parallel to angiogenesis inhibition. ZA combined with Sunitinib or DC101 showed a greater effect in impairing liver and lung metastasis formation. Confocal analysis of the vasculature revealed that while Sunitinib- or DC101-treated cancers displayed poorly functional vessels, both ZA alone or combined with Sunitinib or DC101 efficiently induced a normalized vasculature highly covered by pericytes and better perfused. Remarkably, gene and protein expression analysis of FACS-sorted macrophages derived from tumors of the different treatment groups, showed that ZA alone or combined with Sunitinib or DC101 inhibited the expression of M2-markers such as MRC-1, Il-10, CCL22 and MMP-9 and simultaneously enhanced the levels of M1-markers such as Il12 and CXCL9 in these cells.

We conclude that ZA, by promoting a M1-like macrophages phenotype in HPV16/E2 cervical cancers and consequently inducing a normalized vasculature, efficiently overcomes the resistance to angiogenesis inhibition by blocking metastasis dissemination.

Citation Format: Stefania Capano, Federica Maione, Oriol Casanovas, Federico Bussolino, Enrico Giraudo. Zoledronic acid overcomes the resistance to the anti-angiogenic therapy and normalizes tumor vessels by switching from a M2- to a M1-like macrophages phenotype in a mouse model of spontaneous cervical cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4807. doi:10.1158/1538-7445.AM2014-4807

Semaphorins in cardiovascular medicine

During organogenesis, patterning is primarily achieved by the combined actions of morphogens. Among these, semaphorins represent a general system for establishing the appropriate wiring architecture of biological nets. Originally discovered as evolutionarily conserved steering molecules for developing axons, subsequent studies on semaphorins expanded their functions to the cardiovascular and immune systems. Semaphorins participate in cardiac organogenesis and control physiological vasculogenesis and angiogenesis, which result from a balance between pro- and anti-angiogenic signals. These signals are altered in several diseases. In this review, we discuss the role of semaphorins in vascular biology, emphasizing the mechanisms by which these molecules control vascular patterning and lymphangiogenesis, as well as in genetically inherited and degenerative vascular diseases.

Peptide-functionalized nanoparticles for selective targeting of pancreatic tumor

Chemotherapy for pancreatic cancer is hampered by the tumor's physio-pathological complexity. Here we show a targeted nanomedicine using a new ligand, the CKAAKN peptide, which had been identified by phage display, as an efficient homing device within the pancreatic pathological microenvironment. Taking advantage of the squalenoylation platform, the CKAAKN peptide was conjugated to squalene (SQCKAAKN) and then co-nanoprecipitated with the squalenoyl prodrug of gemcitabine (SQdFdC) giving near monodisperse nanoparticles (NPs) for safe intravenous injection. By interacting with a novel target pathway, the Wnt-2, the CKAAKN functionalization enabled nanoparticles: (i) to specifically interact with both tumor cells and angiogenic vessels and (ii) to simultaneously promote pericyte coverage, thus leading to the normalization of the vasculature likely improving the tumor accessibility for therapy. All together, this approach represents a unique targeted nanoparticle design with remarkable selectivity towards pancreatic cancer and multiple mechanisms of action.

SILAC-based proteomics of human primary endothelial cell morphogenesis unveils tumor angiogenic markers

Proteomics has been successfully used for cell culture on dishes, but more complex cellular systems have proven to be challenging and so far poorly approached with proteomics. Because of the complexity of the angiogenic program, we still do not have a complete understanding of the molecular mechanisms involved in this process, and there have been no in depth quantitative proteomic studies. Plating endothelial cells on matrigel recapitulates aspects of vessel growth, and here we investigate this mechanism by using a spike-in SILAC quantitative proteomic approach. By comparing proteomic changes in primary human endothelial cells morphogenesis on matrigel to general adhesion mechanisms in cells spreading on culture dish, we pinpoint pathways and proteins modulated by endothelial cells. The cell-extracellular matrix adhesion proteome depends on the adhesion substrate, and a detailed proteomic profile of the extracellular matrix secreted by endothelial cells identified CLEC14A as a matrix component, which binds to MMRN2. We verify deregulated levels of these proteins during tumor angiogenesis in models of multistage carcinogenesis. This is the most in depth quantitative proteomic study of endothelial cell morphogenesis, which shows the potential of applying high accuracy quantitative proteomics to in vitro models of vessel growth to shed new light on mechanisms that accompany pathological angiogenesis. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium with the data set identifier PXD000359.

Preclinical activity of lenalidomide in metastatic colorectal cancer

e14654

Background: Metastatic colorectal cancer (mCRC) is currently considered incurable. Recent evidences support the importance of micro-environment and angiogenesis on survival and propagation of mCRC. Lenalidomide is a derivative of thalidomide, effective in several hematologic disorders, whose activity includes modulation on tumor microenvironment and inhibition of angiogenesis. We investigated the preclinical activity of lenalidomide against mCRC in vitro and in vivo. Methods: CRC cell lines and primary mCRC cells were treated with scalar concentrations of lenalidomide (10 to 150 µM). Two cohorts of NOD/SCID mice (n=8) implanted with mCRC xenografts derived from two different patients were treated orally for 21 consecutive days with Lenalidomide (50 mg/Kg/die). Results: In vivo a significant reduction of tumor growth was observed in one cohort compared to untreated controls (n=8), 247±118 mm3 vs. 567±216 mm3 (P=0.02), while no significant differences occurred in the second cohort. Pathology review on tumor samples removed from the mice revealed a trend toward the restoration of normal colon tissue morphology and architecture in lenalidomide treated samples compared to untreated controls. Quantitative evaluation of tumor angiogenesis on the responsive cohort, by immunohistochemistry for factor VIII, revealed a tumor-vessel reduction of 49% with lenalidomide compared to controls. Moreover, necrotic-hypoxic areas were reduced by 6 fold in lenalidomide treated xenografts compared to untreated controls (P<0.001). Treatment in vitro did not result in any direct antitumor effect. The average rate of cell death in treated samples was 15.5±2.1%, 15.3±6.7%, and 11.5±3.4% at lenalidomide doses of 10, 40 and 150 µM respectively, compared to 14.6±2.6% of untreated controls. Conclusions: Our data indicate a potential activity of lenalidomide against mCRC. The beneficial effect was limited in-vivo, supporting the hypothesis that the main activity of lenalidomide is exerted through modulation of tumor microenvironment and angiogenesis rather than a direct antitumor effect. Our findings may be of clinical relevance and support further investigations to explore the benefit of lenalidomide in the challenging setting of mCRC.

The role of semaphorins and their receptors in vascular development and cancer

Semaphorins (Semas) are a large family of traditional axon guidance molecules. Through interactions with their receptors, Plexins and Neuropilins, Semas play critical roles in a continuously growing list of diverse biological systems. In this review, we focus on their function in regulating vascular development. In addition, over the past few years a number of findings have shown the crucial role that Semas and their receptors play in the regulation of cancer progression and tumor angiogenesis. In particular, Semas control tumor progression by directly influencing the behavior of cancer cells or, indirectly, by modulating angiogenesis and the function of other cell types in the tumor microenvironment (i.e., inflammatory cells and fibroblasts). Some Semas can activate or inhibit tumor progression and angiogenesis, while others may have the opposite effect depending on specific post-translational modifications. Here we will also discuss the diverse biological effects of Semas and their receptor complexes on cancer progression as well as their impact on the tumor microenvironment.

Class 3 semaphorins: physiological vascular normalizing agents for anti-cancer therapy

Findings from preclinical and clinical studies show that vascular normalization represents a novel strategy to enhance the efficacy of and overcome the acquired resistance to anti-angiogenic therapies in cancer. Several mechanisms of tumour vessel normalization have been revealed. Amongst them, secreted class 3 semaphorins (Sema3), which regulate axon guidance and angiogenesis, have been recently identified as novel vascular normalizing agents that inhibit metastatic dissemination by restoring vascular function. Here, we discuss the different biological functions and mechanisms of action of Sema3 in the context of tumour vascular normalization, and their impact on the different cellular components of the tumour microenvironment.

Neuropilin-1 identifies a subset of bone marrow Gr1- monocytes that can induce tumor vessel normalization and inhibit tumor growth

Improving tumor perfusion, thus tempering tumor-associated hypoxia, is known to impair cancer progression. Previous work from our laboratory has shown that VEGF-A165 and semaphorin 3A (Sema3A) promote vessel maturation through the recruitment of a population of circulating monocytes expressing the neuropilin-1 (Nrp1) receptor (Nrp1-expressing monocytes; NEM). Here, we define the characteristics of bone marrow NEMs and assess whether these cells might represent an exploitable tool to induce tumor vessel maturation. Gene expression signature and surface marker analysis have indicated that NEMs represent a specific subset of CD11b+ Nrp1+ Gr1- resident monocytes, distinctively recruited by Sema3A. NEMs were found to produce several factors involved in vessel maturation, including PDGFb, TGF-β, thrombospondin-1, and CXCL10; consistently, they were chemoattractive for vascular smooth muscle cells in vitro. When directly injected into growing tumors, NEMs, isolated either from the bone marrow or from Sema3A-expressing muscles, exerted antitumor activity despite having no direct effects on the proliferation of tumor cells. NEM inoculation specifically promoted mural cell coverage of tumor vessels and decreased vascular leakiness. Tumors treated with NEMs were smaller, better perfused and less hypoxic, and had a reduced level of activation of HIF-1α. We conclude that NEMs represent a novel, unique population of myeloid cells that, once inoculated into a tumor, induce tumor vessel normalization and inhibit tumor growth.

IL-12-dependent innate immunity arrests endothelial cells in G0-G1 phase by a p21(Cip1/Waf1)-mediated mechanism

Innate immunity may activate paracrine circuits able to entail vascular system in the onset and progression of several chronic degenerative diseases. In particular, interleukin (IL)-12 triggers a genetic program in lymphomononuclear cells characterized by the production of interferon-γ and specific chemokines resulting in an angiostatic activity. The aim of this study is to identify molecules involved in the regulation of cell cycle in endothelial cells co-cultured with IL-12-stimulated lymphomonuclear cells. By using a transwell mediated co-culture system we demonstrated that IL-12-stimulated lymphomonuclear cells induce an arrest of endothelial cells cycle in G1, which is mainly mediated by the up-regulation of p21(Cip1/Waf1), an inhibitor of cyclin kinases. This effect requires the activation of STAT1, PKCδ and p38 MAPK, while p53 is ineffective. In accordance, siRNA-dependent silencing of these molecules in endothelial cells inhibited the increase of p21(Cip1/Waf1) and the modification in cell cycle promoted by IL-12-stimulated lymphomonuclear cells. These results indicate that the angiostatic action of IL-12-stimulated lymphomononuclear cells may lie in the capability to arrest endothelial cells in G1 phase through a mechanisms mainly based on the specific up-regulation of p21(Cip1/Waf1) induced by the combined activity of STAT1, PKCδ and p38 MAPK.

Abstract SY41-04: Targeting Semaphorin 3A: A new tool to normalize tumor vasculature and to overcome the evasive resistance to the anti-angiogenic therapy

The critical role of angiogenesis in tumor development, progression and metastatization has long been appreciated and several anti-angiogenic inhibitors are approved for use in cancer therapy. Recently it has been reported in pre-clinical mouse models that angiogenesis inhibitors, induced transient primary tumor shrinkage followed by an evasive resistance to the therapy eliciting tumor invasiveness and increased distal metastasis formation (1). Therefore it is crucial to identify new angiogenic modulators and uncover the underlying mechanisms in order to design more effective anti-angiogenic combinatory regimens. A growing body of evidences demonstrated an important role of class3 Semaphorins (Sema3s), that act via receptor complexes binding neuropilins 1 and 2 (Nrp1/2) and transducing the signal by plexins, in regulating angiogenesis and tumor growth (2).

We have recently demonstrated that Sema3A is an endogenous inhibitor that is lost during tumor progression and its reintroduction into a mouse model of pancreatic neuroendocrine tumors (RIP-Tag2), resulted in reduced vascular density, blood vessel normalization, restoration of cancer normoxia, and inhibition of tumor growth (3).

Herein, we show that the treatment of RIP-Tag2 mice and of a mouse model of cervical cancer (HPV16/E2) with Sema3A by somatic gene transfer employing adeno-associated virus (AAV)-8, induced a dramatic reduction of tumor invasiveness, of metastases formation and a modulation of several epithelial-mesenchymal transition (EMT) genes. Then, we sought to investigate whether the administration of Sema3A in tumors was able to overcome the evasive resistance observed upon treatment with Sunitinib, an anti-angiogenic tyrosine kinase receptors inhibitor (1). Notably, we observed a dramatic reduction of cancer invasiveness and distal metastases formation in both RIP-Tag2 and HPV16/E2 mice simultaneously treated with Sema3A and Sunitinib for 4 weeks, compared to Sunitinib-treated controls. Moreover, while Sunitinib-treated tumors were highly hypoxic and displayed few pericyte-covered vessels, the combinatorial regimen of Sema3A with Sunitinib normalized the vasculature and restored tumor normoxia. Remarkably, Real-Time RT-PCR and confocal microscopy, revealed a strong modulation of EMT genes and a dramatic inhibition of several hypoxia-induced molecules in tumors treated with Sema3A and Sunitinib compared to Sunitinib-treated cancers.

Thus, treatment of tumors with Sema3A may safely improve the therapeutic potential of anti-angiogenic drugs, by normalizing the vasculature, inhibiting tumor hypoxia, and modulating the expression of hypoxic-induced genes activated by anti-angiogenic treatments.

References

1) Paez-Ribes M. et al. Cancer Cell, 2009. 15:220-31

2) Neufeld G. et al. Nat Rev Cancer 2008. 8:632-45

3) Maione F. et al. J.Clin.Invest, 2009. 119:3356-72

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 SY41-04. doi:1538-7445.AM2012-SY41-04

Semaphorin 3A overcomes cancer hypoxia and metastatic dissemination induced by antiangiogenic treatment in mice

Cancer development, progression, and metastasis are highly dependent on angiogenesis. The use of antiangiogenic drugs has been proposed as a novel strategy to interfere with tumor growth, but cancer cells respond by developing strategies to escape these treatments. In particular, animal models show that antiangiogenic drugs currently used in clinical settings reduce tumor tissue oxygenation and trigger molecular events that foster cancer resistance to therapy. Here, we show that semaphorin 3A (Sema3A) expression overcomes the proinvasive and prometastatic resistance observed upon angiogenesis reduction by the small-molecule tyrosine inhibitor sunitinib in both pancreatic neuroendocrine tumors (PNETs) in RIP-Tag2 mice and cervical carcinomas in HPV16/E2 mice. By improving cancer tissue oxygenation and extending the normalization window, Sema3A counteracted sunitinib-induced activation of HIF-1α, Met tyrosine kinase receptor, epithelial-mesenchymal transition (EMT), and other hypoxia-dependent signaling pathways. Sema3A also reduced tumor hypoxia and halted cancer dissemination induced by DC101, a specific inhibitor of the VEGF pathway. As a result, reexpressing Sema3A in cancer cells converts metastatic PNETs and cervical carcinomas into benign lesions. We therefore suggest that this strategy could be developed to safely harnesses the therapeutic potential of the antiangiogenic treatment.

Semaphorin 4A exerts a proangiogenic effect by enhancing vascular endothelial growth factor-A expression in macrophages

The axon guidance cues semaphorins (Semas) and their receptors plexins have been shown to regulate both physiological and pathological angiogenesis. Sema4A plays an important role in the immune system by inducing T cell activation, but to date, the role of Sema4A in regulating the function of macrophages during the angiogenic and inflammatory processes remains unclear. In this study, we show that macrophage activation by TLR ligands LPS and polyinosinic-polycytidylic acid induced a time-dependent increase of Sema4A and its receptors PlexinB2 and PlexinD1. Moreover, in a thioglycollate-induced peritonitis mouse model, Sema4A was detected in circulating Ly6C(high) inflammatory monocytes and peritoneal macrophages. Acting via PlexinD1, exogenous Sema4A strongly increased macrophage migration. Of note, Sema4A-activated PlexinD1 enhanced the expression of vascular endothelial growth factor-A, but not of inflammatory chemokines. Sema4A-stimulated macrophages were able to activate vascular endothelial growth factor receptor-2 and the PI3K/serine/threonine kinase Akt pathway in endothelial cells and to sustain their migration and in vivo angiogenesis. Remarkably, in an in vivo cardiac ischemia/reperfusion mouse model, Sema4A was highly expressed in macrophages recruited at the injured area. We conclude that Sema4A activates a specialized and restricted genetic program in macrophages able to sustain angiogenesis and participates in their recruitment and activation in inflammatory injuries.

Tumour growth inhibition and anti-metastatic activity of a mutated furin-resistant Semaphorin 3E isoform

Secreted Semaphorin 3E (Sema3E) promotes cancer cell invasiveness and metastatic spreading. The pro-metastatic activity of Sema3E is due to its proteolytic fragment p61, capable of transactivating the oncogenic tyrosine kinase ErbB2 that associates with the Sema3E receptor PlexinD1 in cancer cells. Here, we show that a mutated, uncleavable variant of Sema3E (Uncl-Sema3E) binds to PlexinD1 like p61-Sema3E, but does not promote the association of PlexinD1 with ErbB2 nor activates the ensuing signalling cascade leading to metastatic spreading. Furthermore, Uncl-Sema3E competes with endogenous p61-Sema3E produced by tumour cells, thereby hampering their metastatic ability. Uncl-Sema3E also acts independently as a potent anti-angiogenic factor. It activates a PlexinD1-mediated signalling cascade in endothelial cells that leads to the inhibition of adhesion to extracellular matrix, directional migration and cell survival. The putative therapeutic potential of Uncl-Sema3E was validated in multiple orthotopic or spontaneous tumour models in vivo, where either local or systemic delivery of Uncl-Sema3E-reduced angiogenesis, growth and metastasis, even in the case of tumours refractory to treatment with a soluble vascular endothelial growth factor trap. In summary, we conclude that Uncl-Sema3E is a novel inhibitor of tumour angiogenesis and growth that concomitantly hampers metastatic spreading.

A model of vascular tumour growth in mice combining longitudinal tumour size data with histological biomarkers

Optimising the delivery of antiangiogenic drugs requires the development of drug-disease models of vascular tumour growth that incorporate histological data indicative of cytostatic action. In this study, we formulated a model to analyse the dynamics of tumour progression in nude mice xenografted with HT29 or HCT116 colorectal cancer cells. In 30 mice, tumour size was periodically measured, and percentages of hypoxic and necrotic tissue were assessed using immunohistochemistry techniques on tumour samples after euthanasia. The simultaneous analysis of histological data together with longitudinal tumour size data prompted the development of a semi-mechanistic model integrating random effects of parameters. In this model, the peripheral non-hypoxic tissue proliferates according to a generalised-logistic equation where the maximal tumour size is represented by a variable called 'carrying capacity'. The ratio of the whole tumour size to the carrying capacity was used to define the hypoxic stress. As this stress increases, non-hypoxic tissue turns hypoxic. Hypoxic tissue does not stop proliferating, but hypoxia constitutes a transient stage before the tissue becomes necrotic. As the tumour grows, the carrying capacity increases owing to the process of angiogenesis. The model is shown to correctly predict tumour growth dynamics as well as percentages of necrotic and hypoxic tissues within the tumour. We show how the model can be used as a theoretical tool to investigate the effects of antiangiogenic treatments on tumour growth. This model provides a tool to analyse tumour size data in combination with histological biomarkers such as the percentages of hypoxic and necrotic tissue and is shown to be useful for gaining insight into the effects of antiangiogenic drugs on tumour growth and composition.

Increased expression of alpha6 integrin in endothelial cells unveils a proangiogenic role for basement membrane

The integrin alpha6 subunit is part of the alpha6beta1 and alpha6beta4 integrin complexes, which are known to be receptors for laminins and to mediate several biological activities such as embryogenesis, organogenesis, and invasion of carcinoma cells. However, the precise role of alpha6 integrin in angiogenesis has not yet been addressed. We observed that both vascular endothelial growth factor-A and fibroblast growth factor-2 strongly upregulate alpha6 integrin in human endothelial cells. Moreover, alpha6 integrin was positively modulated in angiogenic vessels in pancreatic neuroendocrine carcinoma. In this transgenic mouse model of spontaneous tumorigenesis, alpha6 integrin expression increased in the angiogenic stage, while being expressed at low levels in normal and hyperplastic tissue. We studied the functional role of alpha6 integrin during angiogenesis by lentivirus-mediated gene silencing and blocking antibody. Cell migration and morphogenesis on basement membrane extracts, a laminin-rich matrix, was reduced in endothelial cells expressing low levels of alpha6 integrin. However, we did not observe any differences in collagen matrices. Similar results were obtained in the aortic ring angiogenesis assay. alpha6 integrin was required for vessel sprouting on basement membrane gels but not on collagen gels, as shown by stably silencing this integrin in the murine aorta. Finally, a neutralizing anti-alpha6 integrin antibody inhibited in vivo angiogenesis in chicken chorioallantoic membrane and transgenic tumor mouse model. In summary, we showed that the alpha6 integrin participated in vascular endothelial growth factor-A and fibroblast growth factor-2-driven angiogenesis in vitro and in vivo, suggesting that it might be an attractive target for therapeutic approaches in angiogenesis-dependent diseases such as tumor growth.

Semaphorin 3A is an endogenous angiogenesis inhibitor that blocks tumor growth and normalizes tumor vasculature in transgenic mouse models

Tumor growth and progression rely upon angiogenesis, which is regulated by pro- and antiangiogenic factors, including members of the semaphorin family. By analyzing 3 different mouse models of multistep carcinogenesis, we show here that during angiogenesis, semaphorin 3A (Sema3A) is expressed in ECs, where it serves as an endogenous inhibitor of angiogenesis that is present in premalignant lesions and lost during tumor progression. Pharmacologic inhibition of endogenous Sema3A during the angiogenic switch, the point when pretumoral lesions initiate an angiogenic phase that persists throughout tumor growth, enhanced angiogenesis and accelerated tumor progression. By contrast, when, during the later stages of carcinogenesis following endogenous Sema3A downmodulation, Sema3A was ectopically reintroduced into islet cell tumors by somatic gene transfer, successive waves of apoptosis ensued, first in ECs and then in tumor cells, resulting in reduced vascular density and branching and inhibition of tumor growth and substantially extended survival. Further, long-term reexpression of Sema3A markedly improved pericyte coverage of tumor blood vessels, something that is thought to be a key property of tumor vessel normalization, and restored tissue normoxia. We conclude, therefore, that Sema3A is an endogenous and effective antiangiogenic agent that stably normalizes the tumor vasculature.

AP-2alpha and AP-2gamma regulate tumor progression via specific genetic programs

The events occurring during tumor formation and progression display similarities to some of the steps in embryonic morphogenesis. The family of AP-2 proteins consists of five different transcription factors (alpha, beta, gamma, delta, and epsilon) that play relevant roles in embryonic development, as demonstrated by the phenotypes of the corresponding knockout mice. Here, we show that AP-2alpha and AP-2gamma proteins play an essential role in tumorigenesis. Down-modulation of AP-2 expression in tumor cells by RNA interference (RNAi) led to enhanced tumor growth and reduced chemotherapy-induced cell death, as well as migration and invasion. Most of these biological modulations were rescued by AP-2 overexpression. We observed that increased xenotransplant growth was mostly due to highly enhanced proliferation of the tumor cells together with reduced innate immune cell recruitment. Moreover, we showed that migration impairment was mediated, at least in part, by secreted factors. To identify the genetic programs involved in tumorigenesis, we performed whole genome microarray analysis of AP-2alpha knockdown cells and observed that AP-2alpha regulates specific genes involved in cell cycle, cell death, adhesion, and migration. In particular, we showed that ESDN, EREG, and CXCL2 play a major role in AP-2 controlled migration, as ablation of any of these genes severely altered migration.