A novel aminopeptidase N/CD13 inhibitor selectively targets an endothelial form of CD13 after coupling to proteins

Aminopeptidase N/CD13, a membrane-bound enzyme upregulated in tumor vasculature and involved in angiogenesis, can be used as a receptor for the targeted delivery of drugs to tumors through ligand-directed targeting approaches. We describe a novel peptide ligand (VGCARRYCS, called "G4") that recognizes CD13 with high affinity and selectivity. Enzymological and computational studies showed that G4 is a competitive inhibitor that binds to the catalytic pocket of CD13 through its N-terminal region. Fusing the peptide C-terminus to tumor necrosis factor-alpha (TNF) or coupling it to a biotin/avidin complex causes loss of binding and inhibitory activity against different forms of CD13, including natural or recombinant ectoenzyme and a membrane form expressed by HL60 promyelocytic leukemia cells (likely due to steric hindrance), but not binding to a membrane form of CD13 expressed by endothelial cells (ECs). Furthermore, G4-TNF systemically administered to tumor-bearing mice exerted anticancer effects through a CD13-targeting mechanism, indicating the presence of a CD13 form in tumor vessels with an accessible binding site. Biochemical studies showed that most CD13 molecules expressed on the surface of ECs are catalytically inactive. Other functional assays showed that these molecules can promote endothelial cell adhesion to plates coated with G4-avidin complexes, suggesting that the endothelial form of CD13 can exert catalytically independent biological functions. In conclusion, ECs express a catalytically inactive form of CD13 characterized by an accessible conformation that can be selectively targeted by G4-protein conjugates. This form of CD13 may represent a specific target receptor for ligand-directed targeted delivery of therapeutics to tumors.

A simple and robust nanosystem for photoacoustic imaging of bladder cancer based on α5β1-targeted gold nanorods

BACKGROUND

Early detection and removal of bladder cancer in patients is crucial to prevent tumor recurrence and progression. Because current imaging techniques may fail to detect small lesions of in situ carcinomas, patients with bladder cancer often relapse after initial diagnosis, thereby requiring frequent follow-up and treatments.

RESULTS

In an attempt to obtain a sensitive and high-resolution imaging modality for bladder cancer, we have developed a photoacoustic imaging approach based on the use of PEGylated gold nanorods (GNRs) as a contrast agent, functionalized with the peptide cyclic [CphgisoDGRG] (Iso4), a selective ligand of α5β1 integrin expressed by bladder cancer cells. This product (called GNRs@PEG-Iso4) was produced by a simple two-step procedure based on GNRs activation with lipoic acid-polyethyleneglycol(PEG-5KDa)-maleimide and functionalization with peptide Iso4. Biochemical and biological studies showed that GNRs@PEG-Iso4 can efficiently recognize purified integrin α5β1 and α5β1-positive bladder cancer cells. GNRs@PEG-Iso4 was stable and did not aggregate in urine or in 5% sodium chloride, or after freeze/thaw cycles or prolonged exposure to 55 °C, and, even more importantly, do not settle after instillation into the bladder. Intravesical instillation of GNRs@PEG-Iso4 into mice bearing orthotopic MB49-Luc bladder tumors, followed by photoacoustic imaging, efficiently detected small cancer lesions. The binding to tumor lesions was competed by a neutralizing anti-α5β1 integrin antibody; furthermore, no binding was observed to healthy bladders (α5β1-negative), pointing to a specific targeting mechanism.

CONCLUSION

GNRs@PEG-Iso4 represents a simple and robust contrast agent for photoacoustic imaging and diagnosis of small bladder cancer lesions.

Abstract 2381: Gold nanorods functionalized with an alpha5beta1 ligand: a simple and robust nanosystem for early bladder cancer detection

Early detection and removal of bladder cancer (BC) is crucial to prevent tumor recurrence and progression. Various imaging modalities have been used to diagnose BC, including computed tomography urography, intravenous urography, ultrasound echography, multiparametric magnetic resonance imaging, cystoscopy, and cystoscopy in conjunction with intravesical instillation of hexaminolaevulinic acid, a photodynamic diagnostic agent. However, all these imaging techniques show a very poor detection rate of small (<5mm) and flattened cancer lesions. Because of this limitation, patients with BC frequently relapse after initial diagnosis and need frequent follow-ups and treatments, resulting in a poor quality of life. For the same reason, BC has the highest cost/patient among all cancers. We have recently developed a new methodology to detect bladder cancer lesions based on bladder instillation with GNRs@Chit-Iso4, a nanosystem consisting of gold nanorods (GNRs) decorated with chitosan and functionalized with the head-to-tail cyclized [CphgisoDGRG] peptide (Iso4, a selective ligand of alpha5beta1-integrin expressed by BC cells), followed by low-frequency ultrasound-assisted shaking of nanoparticles necessary to prevent their sedimentation, and photoacoustic imaging of targeted tumor lesions. In murine models, this procedure can detect orthotopic BC lesions <0.5 mm, undetectable by standard imaging modalities (Alchera et al., Photoacoustic, 2022). In the attempt to develop a simpler and more effective imaging modality of BC, we have produced and preclinically evaluated new GNRs decorated with lipoic acid-polyethylene glycol (PEG -5KDa) and functionalized with Iso4. The resulting product, obtained by a simple 2-step procedure and called GNRs@PEG5K-Iso4, efficiently recognized alpha5beta1- and alpha5beta1-expressing cells, was stable in 90% urine, and was resistant to freezing- or salt-induced aggregation.GNRs@PEG5K-Iso4 did not undergo sedimentation after instillation into the bladder, thereby avoiding the need of the complex ultrasound-assisted shaking of nanoparticles and could efficiently detect BC lesions smaller than <0.5 mm in murine models. These results suggest that GNRs@PEG5K-Iso4 represents a simple and robust contrast agent for photoacoustic imaging and early diagnosis of small BC lesions.

Citation Format: Massimo Alfano, Elisa Alchera, Angelina Sacchi, Alessandro Gori, Irene Locatelli, Anna Maria Gasparri, Barbara Colombo, Giulia Anderluzzi, Paolo Armanetti, Luca Minichetti, Andrea Salonia, Angelo Corti, Flavio Curnis. Gold nanorods functionalized with an alpha5beta1 ligand: a simple and robust nanosystem for early bladder cancer detection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2381.

A stapled chromogranin A-derived peptide homes in on tumors that express αvβ6 or αvβ8 integrins

Rationale: The αvβ6- and αvβ8-integrins, two cell-adhesion receptors upregulated in many tumors and involved in the activation of the latency associated peptide (LAP)/TGFβ complex, represent potential targets for tumor imaging and therapy. We investigated the tumor-homing properties of a chromogranin A-derived peptide containing an RGDL motif followed by a chemically stapled alpha-helix (called "5a"), which selectively recognizes the LAP/TGFβ complex-binding site of αvβ6 and αvβ8. Methods: Peptide 5a was labeled with IRDye 800CW (a near-infrared fluorescent dye) or with ¹⁸F-NOTA (a label for positron emission tomography (PET)); the integrin-binding properties of free peptide and conjugates were then investigated using purified αvβ6/αvβ8 integrins and various αvβ6/αvβ8 single - or double-positive cancer cells; tumor-homing, biodistribution and imaging properties of the conjugates were investigated in subcutaneous and orthotopic αvβ6-positive carcinomas of the pancreas, and in mice bearing subcutaneous αvβ8-positive prostate tumors. Results: In vitro studies showed that 5a can bind both integrins with high affinity and inhibits cell-mediated TGFβ activation. The 5a-IRDye and 5a-NOTA conjugates could bind purified αvβ6/αvβ8 integrins with no loss of affinity compared to free peptide, and selectively recognized various αvβ6/αvβ8 single- or double-positive cancer cells, including cells from pancreatic carcinoma, melanoma, oral mucosa, bladder and prostate cancer. In vivo static and dynamic optical near-infrared and PET/CT imaging and biodistribution studies, performed in mice with subcutaneous and orthotopic αvβ6-positive carcinomas of the pancreas, showed high target-specific uptake of fluorescence- and radio-labeled peptide by tumors and low non-specific uptake in other organs and tissues, except for excretory organs. Significant target-specific uptake of fluorescence-labeled peptide was also observed in mice bearing αvβ8-positive prostate tumors. Conclusions: The results indicate that 5a can home to αvβ6- and/or αvβ8-positive tumors, suggesting that this peptide can be exploited as a ligand for delivering imaging or anticancer agents to αvβ6/αvβ8 single- or double-positive tumors, or as a tumor-homing inhibitor of these TGFβ activators.

Quantification of Chromogranin A and Its Fragments in Biological Fluids

Human chromogranin A (CgA), a 439-residue long neurosecretory protein, can serve as a circulating biomarker for a wide range of neuroendocrine tumors. Increased levels of immunoreactive CgA are also present in the blood of patients with cardiovascular, gastrointestinal, or inflammatory diseases with, in certain cases, important diagnostic and prognostic implications. A growing body of evidence suggest that CgA and various CgA-derived fragments have complex roles in the regulation of cardiovascular system, metabolism, innate immunity, angiogenesis, and tissue repair, sometime with opposite biological effects. For example, while full-length CgA (CgA_1-439) inhibits angiogenesis, the CgA_1-373 fragment, at certain doses, is proangiogenic. Thus, the selective quantification of CgA and its fragments in the blood of patients (and in other biological fluids) is of great experimental and clinical interest. Here, we describe methods to produce CgA_1-439 and CgA_1-373 and to develop ELISAs capable of detecting these polypeptides in a very selective manner. The same approach can be used, in principle, also for developing assays for other fragments.

Early diagnosis of bladder cancer by photoacoustic imaging of tumor-targeted gold nanorods

Detection and removal of bladder cancer lesions at an early stage is crucial for preventing tumor relapse and progression. This study aimed to develop a new technological platform for the visualization of small and flat urothelial lesions of high-grade bladder carcinoma in situ (CIS). We found that the integrin α5β1, overexpressed in bladder cancer cell lines, murine orthotopic bladder cancer and human bladder CIS, can be exploited as a receptor for targeted delivery of GNRs functionalized with the cyclic CphgisoDGRG peptide (Iso4). The GNRs@Chit-Iso4 was stable in urine and selectively recognized α5β1 positive neoplastic urothelium, while low frequency ultrasound-assisted shaking of intravesically instilled GNRs@Chit-Iso4 allowed the distribution of nanoparticles across the entire volume of the bladder. Photoacoustic imaging of GNRs@Chit-Iso4 bound to tumor cells allowed for the detection of neoplastic lesions smaller than 0.5 mm that were undetectable by ultrasound imaging and bioluminescence.

Neuropilin-1 and Integrins as Receptors for Chromogranin A-Derived Peptides

Human chromogranin A (CgA), a 439 residue-long member of the "granin" secretory protein family, is the precursor of several peptides and polypeptides involved in the regulation of the innate immunity, cardiovascular system, metabolism, angiogenesis, tissue repair, and tumor growth. Despite the many biological activities observed in experimental and preclinical models for CgA and its most investigated fragments (vasostatin-I and catestatin), limited information is available on the receptor mechanisms underlying these effects. The interaction of vasostatin-1 with membrane phospholipids and the binding of catestatin to nicotinic and b2-adrenergic receptors have been proposed as important mechanisms for some of their effects on the cardiovascular and sympathoadrenal systems. Recent studies have shown that neuropilin-1 and certain integrins may also work as high-affinity receptors for CgA, vasostatin-1 and other fragments. In this case, we review the results of these studies and discuss the structural requirements for the interactions of CgA-related peptides with neuropilin-1 and integrins, their biological effects, their mechanisms, and the potential exploitation of compounds that target these ligand-receptor systems for cancer diagnosis and therapy. The results obtained so far suggest that integrins (particularly the integrin avb6) and neuropilin-1 are important receptors that mediate relevant pathophysiological functions of CgA and CgA fragments in angiogenesis, wound healing, and tumor growth, and that these interactions may represent important targets for cancer imaging and therapy.

Targeting the Blood–Brain Tumor Barrier with Tumor Necrosis Factor-α

The blood–brain tumor barrier represents a major obstacle for anticancer drug delivery to brain tumors. Thus, novel strategies aimed at targeting and breaching this structure are of great experimental and clinical interest. This review is primarily focused on the development and use of a derivative of tumor necrosis factor-α (TNF) that can target and alter the blood–brain-tumor-barrier. This drug, called NGR-TNF, consists of a TNF molecule fused to the Cys-Asn-Gly-Arg-Cys-Gly (CNGRCG) peptide (called NGR), a ligand of aminopeptidase N (CD13)-positive tumor blood vessels. Results of preclinical studies suggest that this peptide-cytokine fusion product represents a valuable strategy for delivering TNF to tumor vessels in an amount sufficient to break the biological barriers that restrict drug penetration in cancer lesions. Moreover, clinical studies performed in patients with primary central nervous system lymphoma, have shown that an extremely low dose of NGR-TNF (0.8 µg/m²) is sufficient to promote selective blood–brain-tumor-barrier alteration, increase the efficacy of R-CHOP (a chemo-immunotherapy regimen) and improve patient survival. Besides reviewing these findings, we discuss the potential problems related to the instability and molecular heterogeneity of NGR-TNF and review the various approaches so far developed to obtain more robust and homogeneous TNF derivatives, as well as the pharmacological properties of other peptide/antibody-TNF fusion products, muteins and nanoparticles that are potentially useful for targeting the blood–brain tumor barrier. Compared to other TNF-related drugs, the administration of extremely low-doses of NGR-TNF or its derivatives appear as promising non-immunogenic approaches to overcome TNF counter-regulatory mechanism and systemic toxicity, thereby enabling safe breaking of the BBTB.

DIPG-21. DIPG cells alter the permeability of the blood-brain barrier in the brainstem leading to treatment failure

Diffuse Intrinsic Pontine Glioma (DIPG) is an aggressive paediatric high-grade glioma with no effective therapies. The blood-brain barrier (BBB) presents a significant obstacle for delivery of therapeutics into the brain, especially in the brainstem. This study aims to investigate the effect of DIPG cells on the BBB in the brainstem. We hypothesized that the location of DIPG may result in a less permeable BBB than other brain regions. We compared two independent orthotopic models with the same DIPG cells injected in the cortical region or brainstem. We found that treatment with mTOR inhibitor, temsirolimus, significantly extended survival for cortical tumors compared with the same tumor in the brainstem (p=0.0097). Immunohistochemical analysis showed significant reduction of mTOR target, P-p70S6K, in the cortical region compared to brainstem in treated animals, with pharmacokinetic analysis confirming significantly higher temsirolimus levels in the cortical region. These findings suggest that cortical tumors respond better than brainstem tumors, and that a less permeable BBB in brainstem tumors contributes to treatment failure. To understand whether DIPG cells affect the BBB in the brainstem, single-cell RNA sequencing experiments were conducted on vasculature isolated from DIPG and matrigel-injected mice. Gene-ontology overrepresentation analyses identified downregulation in the P38MAPK pathway in endothelial cells from DIPG-injected mice, suggesting the potential for therapeutic manipulation with cytokines. Treatment with SNGR-TNFα, a derivative of an agent successfully used in improving drug penetration in CNS lymphoma patients, in an in vitro BBB/DIPG model significantly reduced transendothelial resistance, and further exploration into the effects on the BBB in vivo is currently being undertaken. Our studies indicate that the intact BBB in the brainstem in DIPG is a major reason for treatment failure, and DIPG cells directly influence the vasculature and response to treatment. This may lead to a novel DIPG treatment strategy and for other brain tumors.

A Novel RGD-4C-Saporin Conjugate Inhibits Tumor Growth in Mouse Models of Bladder Cancer

Although toxin may have some advantages compared to chemotherapeutic drugs in cancer therapy, e.g. a potent cytotoxic activity and a reduced risk of resistance, their successful application in the treatments to solid tumors still remains to be fully demonstrated. In this study, we genetically modified the structure of the plant-derived single-chain ribosome inactivating protein saporin (SAP) by fusing its N-terminus to the ACDCRGDCFCG peptide (RGD-4C), an αv-integrin ligand, and explored the anti-tumor activity of the resulting protein (called RGD-SAP) in vitro and in vivo, using a model of muscle invasive bladder cancer. We found that the RGD-4C targeting domain enhances the cytotoxic activity of SAP against various tumor cell lines, in a manner dependent on αv-integrin expression levels. In a subcutaneous syngeneic model of bladder cancer, RGD-SAP significantly reduced tumor growth in a dose-dependent manner. Furthermore, systemic administration of RGD-SAP in combination with mitomycin C, a chemotherapeutic drug currently used to treat patients with bladder cancer, increased the survival of mice bearing orthotopic bladder cancer with no evidence of systemic toxicity. Overall, the results suggest that RGD-SAP represents an efficient drug that could be exploited, either alone or in combination with the state-of-the-art therapies, for the treatment of bladder cancer and, potentially, of other solid tumors.

Oxidized/deamidated-ceruloplasmin dysregulates choroid plexus epithelial cells functionality and barrier properties via RGD-recognizing integrin binding

Choroid plexus epithelial cells (CPEpiCs) determine the composition of cerebrospinal fluid (CSF) and constitute the blood-CSF barrier (BCSFB), functions that are altered in neurodegenerative diseases. In Parkinson's disease (PD) the pathological environment oxidizes and deamidates the ceruloplasmin, a CSF-resident ferroxidase, which undergoes a gain of RGD-recognizing integrin binding property, that may result in signal transduction. We investigated the effects that oxidized/deamidated ceruloplasmin (Cp-ox/de) may exert on CPEpiCs functions. Through RGD-recognizing integrins binding, Cp-ox/de mediates CPEpiCs adhesion and intracellular signaling, resulting in cell proliferation inhibition and alteration of the secretome profile in terms of proteins related to cell-extracellular matrix interaction. Oxidative conditions, comparable to those found in the CSF of PD patients, induced CPEpiCs barrier leakage, allowing Cp-ox/de to cross it, transducing integrins-mediated signal that further worsens BCSFB integrity. This mechanism might contribute to PD pathological processes altering CSF composition and aggravating the already compromised BCSFB function.

Nanogold Functionalized With Lipoamide-isoDGR: A Simple, Robust and Versatile Nanosystem for αvβ3-Integrin Targeting

Gold nanoparticles functionalized with isoDGR, a tripeptide motif that recognizes αvβ3 integrin overexpressed in tumor vessels, have been used as nano-vectors for the delivery of cytokines to tumors. Functionalization of nanogold with this peptide has been achieved by coating nanoparticles with a peptide-albumin conjugate consisting of heterogeneous molecules with a variable number of linkers and peptides. To reduce nanodrug heterogeneity we have designed, produced and preclinically evaluated a homogeneous and well-defined reagent for nanogold functionalization, consisting of a head-to-tail cyclized CGisoDGRG peptide (iso1) coupled via its thiol group to maleimide-PEG₁₁-lipoamide (LPA). The resulting iso1-PEG₁₁-LPA compound can react with nanogold via lipoamide to form a stable bond. In vitro studies have shown that iso1, after coupling to nanogold, maintains its capability to bind purified αvβ3 and αvβ3-expressing cells. Nanogold functionalized with this peptide can also be loaded with bioactive tumor necrosis factor-α (TNF) to form a bi-functional nanodrug that can be stored for three days at 37°C or >1 year at low temperatures with no loss αvβ3-binding properties and TNF-cytolytic activity. Nanoparticles functionalized with both iso1 and TNF induced tumor eradication in WEHI-164 fibrosarcoma-bearing mice more efficiently than nanoparticles lacking the iso1 targeting moiety. These results suggest that iso1-PEG₁₁-LPA is an efficient and well-defined reagent that can be used to produce robust and more homogeneous nano-vectors for the delivery of TNF and other cytokines to αvβ3 positive cells.

Enhancement of doxorubicin anti-cancer activity by vascular targeting using IsoDGR/cytokine-coated nanogold

Background

Gold nanospheres tagged with peptides containing isoDGR (isoAsp-Gly-Arg), an αvβ3 integrin binding motif, represent efficient carriers for delivering pro-inflammatory cytokines to the tumor vasculature. We prepared bi- or trifunctional nanoparticles bearing tumor necrosis factor-α (TNF) and/or interleukin-12 (IL12) plus a peptide containing isoDGR, and we tested their anti-cancer effects, alone or in combination with doxorubicin, in tumor-bearing mice.

Results

In vitro biochemical studies showed that both nanodrugs were monodispersed and functional in terms of binding to TNF and IL12 receptors and to αvβ3. In vivo studies performed in a murine model of fibrosarcoma showed that low doses of bifunctional nanoparticles bearing isoDGR and TNF (corresponding to few nanoparticles per cell) delayed tumor growth and increased the efficacy of doxorubicin without worsening its toxicity. Similar effects were obtained using trifunctional nanoparticles loaded with isoDGR, TNF and IL12. Mechanistic studies showed that nanoparticles bearing isoDGR and TNF could increase doxorubicin penetration in tumors a few hours after injection and caused vascular damage at later time points.

Conclusion

IsoDGR-coated gold nanospheres can be exploited as a versatile platform for single- or multi-cytokine delivery to cells of the tumor vasculature. Extremely low doses of isoDGR-coated nanodrugs functionalized with TNF or TNF plus IL12 can enhance doxorubicin anti-tumor activity.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00871-y.

Circulating Chromogranin A Is Cleaved Into Vasoregulatory Fragments in Patients With Pancreatic Ductal Adenocarcinoma

Chromogranin A (CgA), a secretory protein released in the blood by the neuroendocrine system, consists of a mixture of full-length molecules and fragments endowed of vasoregulatory activity. The extent and the role of CgA fragmentation were investigated in patients with locally advanced or metastatic pancreatic ductal adenocarcinoma (PDAC, n=172). Multivariate analysis showed that full-length CgA was associated with better progression free and overall survival, whereas CgA C-terminal fragmentation was associated with worse prognosis. In vitro studies showed that PDAC cells can promote the cleavage of CgA C-terminal region by activating plasminogen to plasmin. Limited digestion of full-length CgA with plasmin abolished its anti-angiogenic activity and generated pro-angiogenic molecules. The fragmentation of CgA C-terminal region was increased also in murine models of PDAC. In these models, the inhibition of CgA fragmentation with aprotinin, an inhibitor of plasmin and other serine proteases, or the blockade of pro-angiogenic fragments with specific antibodies inhibited the growth of PDAC implanted subcutaneously in mice. Finally, administration of full-length CgA to mice bearing orthotopic PDAC reduced tumor perfusion, as measured by contrast-enhanced ultrasound. These findings suggest that PDAC can promote the cleavage of circulating CgA C-terminal region to generate fragments that regulate the tumor vascular biology and that may represent new potential therapeutic targets.

NGR-TNF Engineering with an N-Terminal Serine Reduces Degradation and Post-Translational Modifications and Improves Its Tumor-Targeting Activity

The therapeutic index of cytokines in cancer therapy can be increased by targeting strategies based on protein engineering with peptides containing the CNGRC (NGR) motif, a ligand that recognizes CD13-positive tumor vessels. We show here that the targeting domain of recombinant CNGRC-cytokine fusion proteins, such as NGR-TNF (a CNGRC-tumor necrosis factor-α (TNF) conjugate used in clinical studies) and NGR-EMAP-II, undergoes various post-translational modification and degradation reactions that lead to the formation of markedly heterogeneous products. These modifications include N-terminal cysteine acetylation or the formation of various asparagine degradation products, the latter owing to intramolecular interactions of the cysteine α-amino group with asparagine and/or its succinimide derivative. Blocking the cysteine α-amino group with a serine (SCNGRC) reduced both post-translational and degradation reactions. Furthermore, the serine residue reduced the asparagine deamidation rate to isoaspartate (another degradation product) and improved the affinity of NGR for CD13. Accordingly, genetic engineering of NGR-TNF with the N-terminal serine produced a more stable and homogeneous drug (called S-NGR-TNF) with improved antitumor activity in tumor-bearing mice, either when used alone or in combination with chemotherapy. In conclusion, the targeting domain of NGR-cytokine conjugates can undergo various untoward modification and degradation reactions, which can be markedly reduced by fusing a serine to the N-terminus. The SCNGRC peptide may represent a ligand for cytokine delivery to tumors more robust than conventional CNGRC. The S-NGR-TNF conjugate (more stable, homogeneous, and active than NGR-TNF) could be rapidly developed for clinical trials.

A stapled chromogranin A-derived peptide is a potent dual ligand for integrins αvβ6 and αvβ8

Combining 2D STD-NMR, computation, biochemical assays and click-chemistry, we have identified a chromogranin-A derived compound (5) that has high affinity and bi-selectivity for αvβ6 and αvβ8 integrins and is stable in microsomal preparations. 5 is suitable for nanoparticle functionalization and delivery to cancer cells, holding promise for diagnostic and/or therapeutic applications.

Boosting Interleukin-12 Antitumor Activity and Synergism with Immunotherapy by Targeted Delivery with isoDGR-Tagged Nanogold

The clinical use of interleukin-12 (IL12), a cytokine endowed with potent immunotherapeutic anticancer activity, is limited by systemic toxicity. The hypothesis is addressed that gold nanoparticles tagged with a tumor-homing peptide containing isoDGR, an αvβ3-integrin binding motif, can be exploited for delivering IL12 to tumors and improving its therapeutic index. To this aim, gold nanospheres are functionalized with the head-to-tail cyclized-peptide CGisoDGRG (Iso1) and murine IL12. The resulting nanodrug (Iso1/Au/IL12) is monodispersed, stable, and bifunctional in terms of αvβ3 and IL12-receptor recognition. Low-dose Iso1/Au/IL12, equivalent to 18-75 pg of IL12, induces antitumor effects in murine models of fibrosarcomas and mammary adenocarcinomas, with no evidence of toxicity. Equivalent doses of Au/IL12 (a nanodrug lacking Iso1) fail to delay tumor growth, whereas 15 000 pg of free IL12 is necessary to achieve similar effects. Iso1/Au/IL12 significantly increases tumor infiltration by innate immune cells, such as NK and iNKT cells, monocytes, and neutrophils. NK cell depletion completely inhibits its antitumor effects. Low-dose Iso1/Au/IL12 can also increase the therapeutic efficacy of adoptive T-cell therapy in mice with autochthonous prostate cancer. These findings indicate that coupling IL12 to isoDGR-tagged nanogold is a valid strategy for enhancing its therapeutic index and sustaining adoptive T-cell therapy.

Overcoming Biological Barriers in Neuroblastoma Therapy: The Vascular Targeting Approach with Liposomal Drug Nanocarriers

Neuroblastoma is a rare pediatric cancer characterized by a wide clinical behavior and adverse outcome despite aggressive therapies. New approaches based on targeted drug delivery may improve efficacy and decrease toxicity of cancer therapy. Furthermore, nanotechnology offers additional potential developments for cancer imaging, diagnosis, and treatment. Following these lines, in the past years, innovative therapies based on the use of liposomes loaded with anticancer agents and functionalized with peptides capable of recognizing neuroblastoma cells and/or tumor-associated endothelial cells have been developed. Studies performed in experimental orthotopic models of human neuroblastoma have shown that targeted nanocarriers can be exploited for not only decreasing the systemic toxicity of the encapsulated anticancer drugs, but also increasing their tumor homing properties, enhancing tumor vascular permeability and perfusion (and, consequently, drug penetration), inducing tumor apoptosis, inhibiting angiogenesis, and reducing tumor glucose consumption. Furthermore, peptide-tagged liposomal formulations are proved to be more efficacious in inhibiting tumor growth and metastatic spreading of neuroblastoma than nontargeted liposomes. These findings, herein reviewed, pave the way for the design of novel targeted liposomal nanocarriers useful for multitargeting treatment of neuroblastoma.

Spatiotemporal Regulation of Tumor Angiogenesis by Circulating Chromogranin A Cleavage and Neuropilin-1 Engagement

The unbalanced production of pro- and antiangiogenic factors in tumors can lead to aberrant vasculature morphology, angiogenesis, and disease progression. In this study, we report that disease progression in various murine models of solid tumors is associated with increased cleavage of full-length chromogranin A (CgA), a circulating vasoregulatory neurosecretory protein. Cleavage of CgA led to the exposure of the highly conserved PGPQLR site, which corresponds to residues 368-373 of human CgA_1-373, a fragment that has proangiogenic activity. Antibodies against this site, unable to bind full-length CgA, inhibited angiogenesis and reduced tumor perfusion and growth. The PGPQLR sequence of the fragment, but not of the precursor, bound the VEGF-binding site of neuropilin-1; the C-terminal arginine (R₃₇₃) of the sequence was crucial for binding. The proangiogenic activity of the CgA_1-373 was blocked by anti-neuropilin-1 antibodies as well as by nicotinic acetylcholine receptor antagonists, suggesting that these receptors, in addition to neuropilin-1, play a role in the proangiogenic activity of CgA_1-373. The R₃₇₃ residue was enzymatically removed in plasma, causing loss of neuropilin-1 binding and gain of antiangiogenic activity. These results suggest that cleavage of the R₃₇₃R₃₇₄ site of circulating human CgA in tumors and the subsequent removal of R₃₇₃ in the blood represent an important "on/off" switch for the spatiotemporal regulation of tumor angiogenesis and may serve as a novel therapeutic target. SIGNIFICANCE: This work reveals that the interaction between fragmented chromogranin A and neuropilin-1 is required for tumor growth and represents a novel potential therapeutic target.

Enhancement of Tumor Homing by Chemotherapy-Loaded Nanoparticles

Targeted delivery of anticancer drugs with nanocarriers can reduce side effects and ameliorate therapeutic efficacy. However, poorly perfused and dysfunctional tumor vessels limit the transport of the payload into solid tumors. The use of tumor-penetrating nanocarriers might enhance tumor uptake and antitumor effects. A peptide containing a tissue-penetrating (TP) consensus motif, capable of recognizing neuropilin-1, is here fused to a neuroblastoma-targeting peptide (pep) previously developed. Neuroblastoma cell lines and cells derived from both xenografts and high-risk neuroblastoma patients show overexpression of neuropilin-1. In vitro studies reveal that TP-pep binds cell lines and cells derived from neuroblastoma patients more efficiently than pep. TP-pep, after coupling to doxorubicin-containing stealth liposomes (TP-pep-SL[doxorubicin]), enhances their uptake by cells and cytotoxic effects in vitro, while increasing tumor-binding capability and homing in vivo. TP-pep-SL[doxorubicin] treatment enhances the Evans Blue dye accumulation in tumors but not in nontumor tissues, pointing to selective increase of vascular permeability in tumor tissues. Compared to pep-SL[doxorubicin], TP-pep-SL[doxorubicin] shows an increased antineuroblastoma activity in three neuroblastoma animal models mimicking the growth of neuroblastoma in humans. The enhancement of drug penetration in tumors by TP-pep-targeted nanoparticles may represent an innovative strategy for neuroblastoma.

A critical assessment of force field accuracy against NMR data for cyclic peptides containing β-amino acids

Hybrid cyclic α/β-peptides, in which one or more β-amino acids are incorporated into the backbone, are gaining increasing interest as potential therapeutics, thanks to their ability to achieve enhanced binding affinities for a biological target through pre-organization in solution. The in silico prediction of their three dimensional structure through strategies such as MD simulations would substantially advance the rational design process. However, whether the molecular mechanics force fields are accurate in sampling highly constrained cyclopeptides containing β-amino acids remains to be verified. Here, we present a systematic assessment of the ability of 8 widely used force fields to reproduce 79 NMR observables (including chemical shifts and 3J scalar couplings) on five cyclic α/β-peptides that contain the integrin recognition motif isoDGR. Most of the investigated force fields, which include force fields from AMBER, OPLS, CHARMM and GROMOS families, display very good agreement with experimental 3J(HN,Hα), suggesting that MD simulations could be an appropriate tool in the rational design of therapeutic cyclic α-peptides. However, for NMR observables directly related to β-amino acids, we observed a poor agreement with experiments and a remarkable dependence of our evaluation on the choice of Karplus parameters. The force field weaknesses herein unveiled might constitute a source of inspiration for further force field optimization.

Abstract 3879: Enhancement of tumor penetration by drug-loaded nanoparticles: An innovative targeted strategy for neuroblastoma

Background: Anti-cancer drugs-loaded targeted nanocarriers can reduce side-effects and improve therapeutic efficacy in preclinical studies. However, poorly perfused and dysfunctional tumour vessels limit the transport of the payload into the parenchyma of solid tumours. The use of tumour-penetrating nanocarriers might enhance tumour penetration and anti-tumour effects.

Methods: A consensus motif, mediator of tissue penetration (TP) was added to a previously characterized neuroblastoma (NB)-targeting peptide (pep). In vitro NB cell association and internalization of TP-pep, either free or coupled to Stealth Liposomes (SL), were tested by FACS and confocal microscopy. In vitro cytotoxic potential of a novel doxorubicin (DXR)-loaded liposomal (TP-pep-SL[DXR]) was evaluated by MTS assay. Three mouse xenograft models mimicking the growth and spread of NB in humans (injection routes: subcutaneous; adrenal gland; tail vein) were enrolled to examine in vivo penetration, vascular permeability, tumour glucose consumption and sensitivity in response to TP-pep-SL[DXR].

Results: Compared to pep, TP-pep increases its cellular association in vitro on cell lines and cells derived from NB patients. When coupled to SL, TP-pep enhances liposomes penetration and cytotoxic effects in vitro and increases binding and penetration in a mouse model of NB. Moreover, in vivo accumulation of Evans Blue dye within the tumour mass reveals that TP-pep-SL[DXR] increases the tumour vascular permeability into NB tumour mass, but not in non-tumour tissues. Compared to pep-targeted liposomes, TP-pep-SL[DXR] leads to an increased anti-NB effect towards all the animal models tested.

Conclusion: Our findings demonstrate that the enhancement of tumour penetration by drug-loaded nanoparticles might represent an innovative targeted strategy for NB.

Citation Format: Mirco Ponzoni, Chiara Brignole, Laura Emionite, Silvia Bruno, Daniela Guarnieri, Leopoldo Sitia, Matteo Bauckneht, Ambra Buschiazzo, Andrea Rossi, Daniela Di Paolo, Patrizia Perri, Flavio Curnis, Alessandro Gori, Angela Rita Sementa, Michele Cilli, Pier Paolo Pompa, Gianmario Sambuceti, Angelo Corti, Fabio Pastorino. Enhancement of tumor penetration by drug-loaded nanoparticles: An innovative targeted strategy for neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3879.

Succinimide-Based Conjugates Improve IsoDGR Cyclopeptide Affinity to αvβ3 without Promoting Integrin Allosteric Activation

The isoDGR sequence is an integrin-binding motif that has been successfully employed as a tumor-vasculature-homing molecule or for the targeted delivery of drugs and diagnostic agents to tumors. In this context, we previously demonstrated that cyclopeptide 2, the product of the conjugation of c(CGisoDGRG) (1) to 4-( N-maleimidomethyl)cyclohexane-1-carboxamide, can be successfully used as a tumor-homing ligand for nanodrug delivery to neoplastic tissues. Here, combining NMR, computational, and biochemical methods, we show that the succinimide ring contained in 2 contributes to stabilizing interactions with α_vβ₃, an integrin overexpressed in the tumor vasculature. Furthermore, we demonstrate that various cyclopeptides containing the isoDGR sequence embedded in different molecular scaffolds do not induce α_vβ₃ allosteric activation and work as pure integrin antagonists. These results could be profitably exploited for the rational design of novel isoDGR-based ligands and tumor-targeting molecules with improved α_vβ₃-binding properties and devoid of adverse integrin-activating effects.

Regulation of tumor growth by circulating full-length chromogranin A

Chromogranin A (CgA), a neuroendocrine secretory protein, and its fragments are present in variable amounts in the blood of normal subjects and cancer patients. We investigated whether circulating CgA has a regulatory function in tumor biology and progression. Systemic administration of full-length CgA, but not of fragments lacking the C-terminal region, could reduce tumor growth in murine models of fibrosarcoma, mammary adenocarcinoma, Lewis lung carcinoma, and primary and metastatic melanoma, with U-shaped dose-response curves. Tumor growth inhibition was associated with reduction of microvessel density and blood flow in neoplastic tissues. Neutralization of endogenous CgA with antibodies against its C-terminal region (residues 410-439) promoted tumor growth. Structure-function studies showed that the C-terminal region of CgA contains a bioactive site and that cleavage of this region causes a marked loss of anti-angiogenic and anti-tumor potency. Mechanistic studies showed that full-length CgA could induce, with a U-shaped dose-response curve, the production of protease nexin-1 in endothelial cells, a serine protease inhibitor endowed of anti-angiogenic activity. Gene silencing or neutralization of protease nexin-1 with specific antibodies abolished both anti-angiogenic and anti-tumor effects of CgA. These results suggest that circulating full-length CgA is an important inhibitor of angiogenesis and tumor growth, and that cleavage of its C-terminal region markedly reduces its activity. Pathophysiological changes in CgA blood levels and/or its fragmentation might regulate disease progression in cancer patients.

Glycine N-methylation in NGR-Tagged Nanocarriers Prevents Isoaspartate formation and Integrin Binding without Impairing CD13 Recognition and Tumor Homing

NGR (asparagine-glycine-arginine) is a tumor vasculature-homing peptide motif widely used for the functionalization of drugs, nanomaterials and imaging compounds for cancer treatment and diagnosis. Unfortunately, this motif has a strong propensity to undergo rapid deamidation. This reaction, which converts NGR into isoDGR, is associated with receptor switching from CD13 to integrins, with potentially important manufacturing, pharmacological and toxicological implications. It is found that glycine N-methylation of NGR-tagged nanocarriers completely prevents asparagine deamidation without impairing CD13 recognition. Studies in animal models have shown that the methylated NGR motif can be exploited for delivering radiolabeled compounds and nanocarriers, such as tumor necrosis factor-α (TNF)-bearing nanogold and liposomal doxorubicin, to tumors with improved selectivity. These findings suggest that this NGR derivative is a stable and efficient tumor-homing ligand that can be used for delivering functional nanomaterials to tumor vasculature.

Abstract 5130: Tumor-penetrating peptide-coated nanoparticles as a novel strategy for the targeted therapy of neuroblastoma

Anticancer drugs loaded into tumor- and vasculature-targeted nanocarriers (NC) can reduce side-effects and improve therapeutic efficacy in pre-clinical studies. However, poorly perfused and dysfunctional tumor vessels and lymphatics limit the transport of the payload into the parenchyma of solid tumors. The use of NC decorated with tumor-penetrating peptides (TPPs) might enhance tumor penetration and antitumor effects.

A previously characterized neuroblastoma (NB)-targeting peptide ligand was here modified (now referred as TPP-NB) by adding a consensus motif as a mediator of cell, vascular and tissue penetration via neuropilin-1 (NRP-1) receptor recognition. NPR-1 expression was validated by FACS analysis in NB cell lines and by IHC staining in tumor cells and tumor stroma from NB-bearing mice. Recombinant NRP-1 was used to validate TPP-NB specificity. In vitro and in vivo cell association and internalization of TPP-NB, either free or coupled to Liposomes (L) were tested by FACS and confocal microscopy. Vascular permeability assay after treatment with TPP-NB-targeted, doxorubicin-loaded Liposomes (TPP-NB-L[DXR]) was performed evaluating the in vivo accumulation of Evans Blue dye within the tumor mass. Therapeutic experiments with TPP-NB-L[DXR] were performed in mice orthotopically injected with human NB cells.

NRP-1 expression is validated in a panel of NB cells and in tumors from NB-bearing mice. Differently from the original peptide and some control ones, TPP-NB is able to recognize recombinant NRP-1. The addition of the NRP-1-recognizing sequence to the original peptide significantly increases its NB cellular association in vitro. Interestingly, the results seem to indicate that the enhanced capability by TPP-NB in binding NB cells is related to the combination of the NRP-1-recognizing and the original sequence. Importantly, TPP-NB coupled at the external surfaces of L[DXR] significantly increases their cellular association on NB cells in vitro. Competitive binding assay reveals that binding of TPP-NB is specific and can be inhibited by an excess of the unlabeled free peptide. The localization and the cellular distribution of L evaluated by confocal microscopy in vitro and in mouse models of NB, confirm the binding specificity, showing an increased selective internalization of TPP-NB-L-FITC compared to that obtained with either untargeted L or L decorated with the scrambled peptide. Moreover, TPP-NB-L[DXR] further increases the vascular permeability into the NB tumor mass, but not in non-tumor tissues. The therapeutic efficacy of TPP-NB-L[DXR] has been investigating in terms of overall survival. On running results indicate that the novel NC exerts an increased anti-NB effect compared to DXR-loaded L decorated with the original peptide.

Our findings demonstrate that the achieved penetrating features by a NB-targeting peptide might increase liposomal drug binding, homing and antitumor efficacy.

Citation Format: Fabio Pastorino, Chiara Brignole, Laura Emionite, Silvia Bruno, Flavio Curnis, Daniela Di Paolo, Patrizia Perri, Alessandro Gori, Renato Longhi, Michele Cilli, Angelo Corti, Mirco Ponzoni. Tumor-penetrating peptide-coated nanoparticles as a novel strategy for the targeted therapy of neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5130. doi:10.1158/1538-7445.AM2017-5130

T Cells Redirected to a Minor Histocompatibility Antigen Instruct Intratumoral TNFα Expression and Empower Adoptive Cell Therapy for Solid Tumors

Donor-derived allogeneic T cells evoke potent graft versus tumor (GVT) effects likely due to the simultaneous recognition of tumor-specific and host-restricted minor histocompatibility (H) antigens. Here we investigated whether such effects could be reproduced in autologous settings by TCR gene-engineered lymphocytes. We report that T cells redirected either to a broadly expressed Y-encoded minor H antigen or to a tumor-associated antigen, although poorly effective if individually transferred, when simultaneously administered enabled acute autochthonous tumor debulking and resulted in durable clinical remission. Y-redirected T cells proved hyporesponsive in peripheral lymphoid organs, whereas they retained effector function at the tumor site, where in synergy with tumor-redirected lymphocytes, they instructed TNFα expression, endothelial cell activation, and intratumoral T-cell infiltration. While neutralizing TNFα hindered GVT effects by the combined T-cell infusion, a single injection of picogram amounts of NGR-TNF, a tumor vessel-targeted TNFα derivative currently in phase III clinical trials, substituted for Y-redirected cells and enabled tumor debulking by tumor-redirected lymphocytes. Together, our results provide new mechanistic insights into allogeneic GVT, validate the importance of targeting the tumor and its associated stroma, and prove the potency of a novel combined approach suitable for immediate clinical implementation. Cancer Res; 77(3); 658-71. ©2016 AACR.

NGR-tagged nano-gold: A new CD13-selective carrier for cytokine delivery to tumors

Colloidal gold (Au), a well-tolerated nanomaterial, is currently exploited for several applications in nanomedicine. We show that gold nanoparticles tagged with a novel tumor-homing peptide containing Asn-Gly-Arg (NGR), a ligand of CD13 expressed by the tumor neovasculature, can be exploited as carriers for cytokine delivery to tumors. Biochemical and functional studies showed that the NGR molecular scaffold/linker used for gold functionalization is critical for CD13 recognition. Using fibrosarcoma-bearing mice, NGR-tagged nanodrugs could deliver extremely low, yet pharmacologically active doses of tumor necrosis factor (TNF), an anticancer cytokine, to tumors with no evidence of toxicity. Mechanistic studies confirmed that CD13 targeting was a primary mechanism of drug delivery and excluded a major role of integrin targeting consequent to NGR deamidation, a degradation reaction that generates the isoAsp-Gly-Arg (isoDGR) integrin ligand. NGR-tagged gold nanoparticles can be used, in principle, as a novel platform for single- or multi-cytokine delivery to tumor endothelial cells for cancer therapy.

Chromogranin A Is Preferentially Cleaved into Proangiogenic Peptides in the Bone Marrow of Multiple Myeloma Patients

Angiogenesis has been postulated to be critical for the pathogenesis of multiple myeloma, a neoplastic disease characterized by abnormal proliferation of malignant plasma cells in the bone marrow (BM). Cleavage of the N- and C-terminal regions of circulating chromogranin A (CgA, CHGA), classically an antiangiogenic protein, can activate latent antiangiogenic and proangiogenic sites, respectively. In this study, we investigated the distribution of CgA-derived polypeptides in multiple myeloma patients and the subsequent implications for disease progression. We show that the ratio of pro/antiangiogenic forms of CgA is altered in multiple myeloma patients compared with healthy subjects and that this ratio is higher in BM plasma compared with peripheral plasma, suggesting enhanced local cleavage of the CgA C-terminal region. Enhanced cleavage correlated with increased VEGF and FGF2 BM plasma levels and BM microvascular density. Using the Vk*MYC mouse model of multiple myeloma, we further demonstrate that exogenously administered CgA was cleaved in favor of the proangiogenic form and was associated with increased microvessel density. Mechanistic studies revealed that multiple myeloma and proliferating endothelial cells can promote CgA C-terminal cleavage by activating the plasminogen activator/plasmin system. Moreover, cleaved and full-length forms could also counter balance the pro/antiangiogenic activity of each other in in vitro angiogenesis assays. These findings suggest that the CgA-angiogenic switch is activated in the BM of multiple myeloma patients and prompt further investigation of this CgA imbalance as a prognostic or therapeutic target. Cancer Res; 76(7); 1781–91. ©2016 AACR.

Ceruloplasmin functional changes in Parkinson's disease-cerebrospinal fluid

Background

Ceruloplasmin, a ferroxidase present in cerebrospinal fluid (CSF), plays a role in iron homeostasis protecting tissues from oxidative damage. Its reduced enzymatic activity was reported in Parkinson’s disease (PD) contributing to the pathological iron accumulation. We previously showed that ceruloplasmin is modified by oxidation in vivo, and, in addition, in vitro by deamidation of specific NGR-motifs that foster the gain of integrin-binding function. Here we investigated whether the loss of ceruloplasmin ferroxidase activity in the CSF of PD patients was accompanied by NGR-motifs deamidation and gain of function.

Results

We have found that endogenous ceruloplasmin in the CSF of PD patients showed structural changes, deamidation of the ⁹⁶²NGR-motif which is usually hidden within the ceruloplasmin structure, and the gain of integrin-binding function. These effects occur owing to the presence of abnormal levels of hydrogen peroxide we detected in the CSF of PD patients. Interestingly, the pathological CSF's environment of PD patients promoted the same modifications in the exogenously added ceruloplasmin, which in turn resulted in loss of ferroxidase-activity and acquisition of integrin-binding properties.

Conclusions

We show that in pathological oxidative environment of PD-CSF the endogenous ceruloplasmin, in addition to loss-of-ferroxidase function, is modified as to gain integrin-binding function. These findings, beside the known role of ceruloplasmin in iron homeostasis, might have important pathogenic implications due to the potential triggering of signals mediated by the unusual integrin binding in cells of central nervous system. Furthermore, there are pharmacological implications because, based on data obtained in murine models, the administration of ceruloplasmin has been proposed as potential therapeutic treatment of PD, however, the observed CSF's pro-oxidant properties raise the possibility that in human the ceruloplasmin-based therapeutic approach might not be efficacious.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0055-2) contains supplementary material, which is available to authorized users.

Neuroblastoma-targeted nanocarriers improve drug delivery and penetration, delay tumor growth and abrogate metastatic diffusion

Selective tumor targeting is expected to enhance drug delivery and to decrease toxicity, resulting in an improved therapeutic index. We have recently identified the HSYWLRS peptide sequence as a specific ligand for aggressive neuroblastoma, a childhood tumor mostly refractory to current therapies. Here we validated the specific binding of HSYWLRS to neuroblastoma cell suspensions obtained either from cell lines, animal models, or Schwannian-stroma poor, stage IV neuroblastoma patients. Binding of the biotinylated peptide and of HSYWLRS-functionalized fluorescent quantum dots or liposomal nanoparticles was dose-dependent and inhibited by an excess of free peptide. In animal models obtained by the orthotopic implant of either MYCN-amplified or MYCN single copy human neuroblastoma cell lines, treatment with HSYWLRS-targeted, doxorubicin-loaded Stealth Liposomes increased tumor vascular permeability and perfusion, enhancing tumor penetration of the drug. This formulation proved to exert a potent antitumor efficacy, as evaluated by bioluminescence imaging and micro-PET, leading to (i) delay of tumor growth paralleled by decreased tumor glucose consumption, and (ii) abrogation of metastatic spreading, accompanied by absence of systemic toxicity and significant increase in the animal life span. Our findings are functional to the design of targeted nanocarriers with potentiated therapeutic efficacy towards the clinical translation.

Abstract 1778: Characterization and anti-tumor functionality of a neuroblastoma-specific peptide, either free or conjugated to nanocarriers

Introduction. The identification of peptide ligands specific for solid tumors is expected to provide targeting moieties to improve delivery and to decrease toxicity of chemotherapy. We have recently identified the peptide HSYWLRS as a specific ligand for neuroblastoma (NB), a childhood tumor mostly refractory to current therapies.

Experimental procedures. The capability of peptide HSYWLRS to recognize NB cells was evaluated by coupling Qdot fluorescent nanoparticles with HSYWLRS or its scrambled version (SCR). NB cell association and internalization of HSYWLRS-targeted liposomes were tested by FACS and confocal microscopy studies. We further evaluated a potential role of this peptide in perturbing tumor-stroma interactions and tumor growth. NB cell lines stably transfected with eGFP were mixed with endothelial cells in the presence of either SCR or HSYWLRS peptides. Cell morphology and reciprocal cellular interactions were evaluated by optical and fluorescence microscopy. We finally performed therapeutic experiments with mice orthotopically injected with luc-trasfected NB cells and treated with HSYWLRS-targeted, doxorubicin-loaded liposomes (HSYWLRS-SL[DXR]). Anti-tumor efficacy was evaluated by BLI imaging. In vivo imaging was also performed by injecting mice with a bolus of fluorodeoxyglucose during a list mode acquisition lasting one hour using a dedicated micro-PET system. After framing rate optimization, tumor glucose consumption was measured using Patlak graphical approach and normalizing the slope of regression line for serum glucose level.

Results. FACS analysis showed that HSYWLRS-Qdot and SCR-Qdot bound NB cells in a dose-dependent manner, however with different intensity, being HSYWLRS-Qdot the more potent. The binding of HSYWLRS-Qdot was efficiently inhibited by an excess of HSYWLRS, but not by control SCR peptide. In contrast, the binding of SCR-Qdot was not inhibited neither by an excess of SCR nor by HSYWLRS peptide, suggesting that the binding of SCR-Qdot is not specific. Again, the specific peptide-driven binding of HSYWLRS-SL to NB cells was inhibited by an excess of HSYWLRS peptide. In all cases, HSYWLRS specifically altered in vitro the interactions of NB cells with endothelium. Similarly, this peptide statistically decreased tumor take and growth when co-injected with tumor cells in the adrenal gland of nude mice.

Preliminary in vivo results obtained by BLI and micro-PET devises indicated that HSYWLRS-SL[DXR] decrease tumor growth through a reduction of tumor glucose consumption, leading to an enhanced life span in treated mice.

Conclusion. Our findings demonstrate that HSYWLRS peptide recognizes NB cells and is functional in the design of nanocarriers with therapeutic efficacy paving the way to its clinical development.

Citation Format: Alice Bartolini, Monica Loi, Daniela Di Paolo, Laura Emionite, Angelina Sacchi, Flavio Curnis, Gianluca Bottoni, Michela Massollo, Cristina Gagliani, Silvia Bruno, Alessandro Gori, Renato Longhi, Michele Cilli, Carlo Tacchetti, Angelo Corti, Gianmario Sambuceti, Mirco Ponzoni, Serena Marchiò, Fabio Pastorino. Characterization and anti-tumor functionality of a neuroblastoma-specific peptide, either free or conjugated to nanocarriers. [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 1778. doi:10.1158/1538-7445.AM2014-1778

Oxidation-induced structural changes of ceruloplasmin foster NGR motif deamidation that promotes integrin binding and signaling

Asparagine deamidation occurs spontaneously in proteins during aging; deamidation of Asn-Gly-Arg (NGR) sites can lead to the formation of isoAsp-Gly-Arg (isoDGR), a motif that can recognize the RGD-binding site of integrins. Ceruloplasmin (Cp), a ferroxidase present in the cerebrospinal fluid (CSF), contains two NGR sites in its sequence: one exposed on the protein surface ((568)NGR) and the other buried in the tertiary structure ((962)NGR). Considering that Cp can undergo oxidative modifications in the CSF of neurodegenerative diseases, we investigated the effect of oxidation on the deamidation of both NGR motifs and, consequently, on the acquisition of integrin binding properties. We observed that the exposed (568)NGR site can deamidate under conditions mimicking accelerated Asn aging. In contrast, the hidden (962)NGR site can deamidate exclusively when aging occurs under oxidative conditions, suggesting that oxidation-induced structural changes foster deamidation at this site. NGR deamidation in Cp was associated with gain of integrin-binding function, intracellular signaling, and cell pro-adhesive activity. Finally, Cp aging in the CSF from Alzheimer disease patients, but not in control CSF, causes Cp deamidation with gain of integrin-binding function, suggesting that this transition might also occur in pathological conditions. In conclusion, both Cp NGR sites can deamidate during aging under oxidative conditions, likely as a consequence of oxidative-induced structural changes, thereby promoting a gain of function in integrin binding, signaling, and cell adhesion.

Peptide-mediated targeting of cytokines to tumor vasculature: the NGR-hTNF example

A growing body of evidence suggests that the efficacy of cytokines in cancer therapy can be increased by targeting strategies based on conjugation with ligands that recognize receptors expressed by tumor cells or elements of the tumor microenvironment, including the tumor vasculature. The targeting approach is generally conceived to permit administration of low, yet pharmacologically active, doses of drugs, thereby avoiding toxic reactions. However, it is becoming clear that, in the case of cytokines, this strategy has another inherent advantage, i.e. the possibility of administering extremely low doses that do not activate systemic counter-regulatory mechanisms, which may limit their potential therapeutic effects. This review is focused on the use of tumor vasculature-homing peptides as vehicles for targeted delivery of cytokines to tumor blood vessel. In particular, we provide an overview of peptide-cytokine conjugates made with peptides containing the NGR, RGD, isoDGR or RGR sequences and describe, in more details, the biological and pharmacological properties of NGR-hTNF, a peptide-tumor necrosis factor-α conjugate that is currently being tested in phase II and III clinical studies. The results of preclinical and clinical studies performed with these products suggest that peptide-mediated vascular-targeting is indeed a viable strategy for delivering bioactive amounts of cytokines to tumor endothelial cells without causing the activation of counter-regulatory mechanisms and toxic reactions.

Selective imaging of the angiogenic relevant integrins α5β1 and αvβ3

Pattern seekers: For the two angiogenic relevant integrins α5β1 and αvβ3, functionalized derivatives of the selective antagonists 1 and 2 could target and discriminate between tumor cells in vivo based on their different integrin patterns and also delay tumor growth in vivo. In addition, the first α5β1-selective integrin antagonist that enables specific molecular imaging by positron emission tomography was developed.

Novel phage display-derived neuroblastoma-targeting peptides potentiate the effect of drug nanocarriers in preclinical settings

Molecular targeting of drug delivery nanocarriers is expected to improve their therapeutic index while decreasing their toxicity. Here we report the identification and characterization of novel peptide ligands specific for cells present in high-risk neuroblastoma (NB), a childhood tumor mostly refractory to current therapies. To isolate such targeting moieties, we performed combined in vitro/ex-vivo phage display screenings on NB cell lines and on tumors derived from orthotopic mouse models of human NB. By designing proper subtractive protocols, we identified phage clones specific either for the primary tumor, its metastases, or for their respective stromal components. Globally, we isolated 121 phage-displayed NB-binding peptides: 26 bound the primary tumor, 15 the metastatic mass, 57 and 23 their respective microenvironments. Of these, five phage clones were further validated for their specific binding ex-vivo to biopsies from stage IV NB patients and to NB tumors derived from mice. All five clones also targeted tumor cells and vasculature in vivo when injected into NB-bearing mice. Coupling of the corresponding targeting peptides with doxorubicin-loaded liposomes led to a significant inhibition in tumor volume and enhanced survival in preclinical NB models, thereby paving the way to their clinical development.

Abstract 5620: Novel phage display-derived neuroblastoma-targeting peptides potentiate the effect of drug nanocarriers in preclinical settings

Purpose: Molecular targeting of drug delivery nanocarriers is expected to improve their therapeutic index while decreasing their toxicity. The identification of novel peptide ligands specific for cells present in high-risk neuroblastoma, a childhood tumor mostly refractory to current therapies, is needed.

Experimental design: We performed combined in vitro/ex-vivo phage display screenings on human neuroblastoma cell lines and on tumors derived from orthotopic mouse models of human neuroblastoma. Binding validation and homing in vivo of selected phage clones were tested by immunohistochemistry/immunofluorescent analyses. Cell association experiments in vitro with the corresponding synthetic biotin-labeled peptides were performed. In vitro cytotoxicity and in vivo tumor accumulation and therapeutic experiments were performed using peptide-targeted, doxorubicin-loaded, nanocarriers.

Results: By designing proper subtractive protocols, we identified phage clones specific either for the primary tumor, its metastases, or for the stromal components. Globally, we isolated 121 phage-displayed neuroblastoma-binding peptides; of these, 26 bound the primary tumor, 15 the metastatic mass, 57 and 23 their respective microenvironments. Of these, five phage clones were further validated for their specific binding ex-vivo to biopsies from stage IV neuroblastoma patients and to neuroblastoma tumors derived from mice. All five clones also targeted tumor cells and vasculature in vivo when injected into neuroblastoma-bearing mice. Coupling of the corresponding targeting peptides with doxorubicin-loaded nanocarriers led to a significant inhibition in tumor volume and enhanced survival in preclinical neuroblastoma models.

Conclusions: Our findings demonstrate that novel ligands of neuroblastoma-associated markers are functional in the design of nanocarriers with therapeutic efficacy paving the way to their clinical development.

Citation Format: Monica Loi, Daniela Di Paolo, Marco Soster, Chiara Brignole, Alice Bartolini, Laura Emionite, Jessica Sun, Pamela Becherini, Flavio Curnis, Andrea Petretto, Monica Sani, Alessandro Gori, Claudio Gambini, Renato Longhi, Michele Cilli, Theresa M. Allen, Federico Bussolino, Wadih Arap, Renata Pasqualini, Angelo Corti, Mirco Ponzoni, Serena Marchiò, Fabio Pastorino. Novel phage display-derived neuroblastoma-targeting peptides potentiate the effect of drug nanocarriers in preclinical settings. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5620. doi:10.1158/1538-7445.AM2013-5620

Abstract 5617: A new alphaV/beta3 integrin selective carrier for nanodrug delivery to tumors based on isoDGR-tagged albumin

Albumin is emerging as a versatile drug carrier in a number of applications in cancer therapy and diagnosis. Basically, albumin can be exploited to enhance the tumor uptake of peptides and low molecular-weight compounds, owing its tendency to accumulate in tumors, and for the preparation of nanoparticles that encapsulate anti-cancer drugs or diagnostic agents.

We have addressed the hypothesis that coupling albumin with a peptide containing the isoAsp-Gly-Arg (isoDGR) sequence, a tumor-vasculature targeting motif discovered by our group, might enhance its tumor-homing properties. IsoDGR is a mimetic of Arg-Gly-Asp (RGD), an integrin-recognition motif. Accordingly, isoDGR can recognize RGD-dependent integrins with different affinity and selectivity depending on isoDGR conformation and molecular scaffold. To have at hand isoDGR peptides that can be easily coupled to albumin we designed various head-to-tail-cyclized exapeptides containing free thiol groups, to enable chemical coupling to proteins, and analyzed their integrin binding properties before and after coupling to albumin. We have identified a peptide (c(CGisoDGRG)) that, after coupling to human serum albumin, has a very good selectivity for alphaV/beta3 and alphaV/beta5, two integrins overexpressed in the tumor vasculature. In vitro and in vivo studies showed that isoDGR-tagged albumin binds to endothelial cells, inhibits their adhesion properties, homes in on tumor vessels and inhibits tumor growth, with no evidence of toxicity. IsoDGR-tagged albumin was exploited as a carrier for the preparation of a new nano-gold systems capable of delivering tumor necrosis factor α (TNF), a well known vascular damaging agent, to tumor vessels. In vivo studies, performed with mice bearing WEHI-fibrosarcomas, showed that intravenous administration of gold nanoparticles loaded with isoDGR-tagged albumin and TNF (equivalent 5 pg of bioactive TNF/mouse) could induce stronger anti-tumor effects than nanoparticles loaded with albumin and TNF. These findings support the concept that isoDGR-tagged albumin is superior to albumin as a vector system for targeted delivery of nanomedicines to tumor vessels. Because of its good selectivity for tumor vessels and its inherent anticancer activity isoDGR-tagged albumin might be exploited as a novel and versatile material for the preparation of a wide range of tumor vasculature-selective drugs and nanoparticles for cancer therapy and diagnosis.

Citation Format: Flavio Curnis, Angelina Sacchi, Renato Longhi, Barbara Colombo, Anna Gasparri, Angelo Corti. A new alphaV/beta3 integrin selective carrier for nanodrug delivery to tumors based on isoDGR-tagged albumin. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5617. doi:10.1158/1538-7445.AM2013-5617

IsoDGR-tagged albumin: a new αvβ3 selective carrier for nanodrug delivery to tumors

A new cyclic peptide containing the isoDGR motif that, after coupling to albumin, selectively binds αvβ3, an integrin overexpressed in the tumor vasculature. IsoDGR-tagged albumin binds tumor vessels and can be exploited as a carrier for the preparation of tumor vasculature-selective nanomedicines, such as gold nanoparticles (Au) carrying tumor necrosis factor α (TNF), a potent vascular damaging agent.

Chromogranin A binds to αvβ6-integrin and promotes wound healing in mice

Chromogranin A (CgA), a secretory protein expressed by many neuroendocrine cells, neurons, cardiomyocytes, and keratinocytes, is the precursor of various peptides that regulate the carbohydrate/lipid metabolism and the cardiovascular system. We have found that CgA, locally administered to injured mice, can accelerate keratinocyte proliferation and wound healing. This biological activity was abolished by the Asp(45)Glu mutation. CgA and its N-terminal fragments, but not the corresponding Asp(45)Glu mutants, could selectively recognize the αvβ6-integrin on keratinocytes (a cell-adhesion receptor that is up-regulated during wound healing) and regulate keratinocyte adhesion, proliferation, and migration. No binding was observed to other integrins such as αvβ3, αvβ5, αvβ8, α5β1, α1β1, α3β1, α6β4, α6β7 and α9β1. Structure-activity studies showed that the entire CgA(39-63) region is crucial for αvβ6 recognition (K(i) = 7 nM). This region contains an RGD site (residues CgA(43-45)) followed by an amphipathic α-helix (residues CgA(47-63)), both crucial for binding affinity and selectivity. These results suggest that the interaction of the RGD/α-helix motif of CgA with αvβ6 regulates keratinocyte physiology in wound healing.

Targeting TNF-α to neoangiogenic vessels enhances lymphocyte infiltration in tumors and increases the therapeutic potential of immunotherapy

Abnormal tumor vasculature impairs T lymphocyte adhesion to endothelial cells and lymphocyte extravasation into neoplastic tissues, limiting the therapeutic potential of both active and adoptive immunotherapies. We have found that treatment of tumor-bearing mice with NGR-TNF, a Cys-Asn-Gly-Arg-Cys peptide-TNF fusion product capable of altering the endothelial barrier function and improving drug penetration in tumors, associated with the intratumor upregulation of leukocyte-endothelial cell adhesion molecules, the release of proinflammatory cytokines and chemokines, and the infiltration of tumor-specific effector CD8(+) T cells. As a result, NGR-TNF enhanced the therapeutic activity of adoptive and active immunotherapy, delaying tumor growth and prolonging survival. Furthermore, we have found that therapeutic effects of these combinations can be further increased by the addition of chemotherapy. Thus, these findings might be relevant for the design of novel immunotherapeutic approaches for cancer patients.

Tumor vasculature targeting through NGR peptide-based drug delivery systems

Various peptide sequences have been discovered by selecting peptide-phage display libraries in vitro against specific receptors or in vivo in tumor-bearing animals. One class of these peptides is characterized by the presence of Asn-Gly-Asp (NGR), a structural motif that can recognize the endothelium and other cells of neoangiogenic vessels. Because of this property these peptides have been used by several investigators to deliver a variety of drugs, cytokines, nanoparticles, viruses and imaging agents to tumor blood vessels. Here we review the reports on these conjugates and discuss the structural, functional and stability properties of NGR embedded into different molecular scaffolds.

Chromogranin A restricts drug penetration and limits the ability of NGR-TNF to enhance chemotherapeutic efficacy

NGR-TNF is a derivative of TNF-α that targets tumor blood vessels and enhances penetration of chemotherapeutic drugs. Because of this property, NGR-TNF is being tested in combination with chemotherapy in various phase II and III clinical trials. Here we report that chromogranin A (CgA), a protein present in variable amounts in the blood of normal subjects and cancer patients, inhibits the synergism of NGR-TNF with doxorubicin and melphalan in mouse models of lymphoma and melanoma. Pathophysiologically relevant levels of circulating CgA blocked NGR-TNF-induced drug penetration by enhancing endothelial barrier function and reducing drug extravasation in tumors. Mechanistic investigations done in endothelial cell monolayers in vitro showed that CgA inhibited phosphorylation of p38 MAP kinase, disassembly of VE-cadherin-dependent adherence junctions, paracellular macromolecule transport, and NGR-TNF-induced drug permeability. In this system, the N-terminal fragment of CgA known as vasostatin-1 also inhibited drug penetration and NGR-TNF synergism. Together, our results suggest that increased levels of circulating CgA and its fragments, as it may occur in certain cancer patients with nonneuroendocrine tumors, may reduce drug delivery to tumor cells particularly as induced by NGR-TNF. Measuring CgA and its fragments may assist the selection of patients that can respond better to NGR-TNF/chemotherapy combinations in clinical trials.

Isoaspartate-dependent molecular switches for integrin-ligand recognition

Integrins are cell-adhesion receptors that mediate cell-extracellular-matrix (ECM) and cell-cell interactions by recognizing specific ligands. Recent studies have shown that the formation of isoaspartyl residues (isoAsp) in integrin ligands by asparagine deamidation or aspartate isomerization could represent a mechanism for the regulation of integrin-ligand recognition. This spontaneous post-translational modification, which might occur in aged proteins of the ECM, changes the length of the peptide bond and, in the case of asparagine, also of the charge. Although these changes typically have negative effects on protein function, recent studies suggested that isoAsp formation at certain Asn-Gly-Arg (NGR) sites in ECM proteins have a gain-of-function effect, because the resulting isoAsp-Gly-Arg (isoDGR) sequence can mimic Arg-Gly-Asp (RGD), a well-known integrin-binding motif. Substantial experimental evidence suggests that the NGR-to-isoDGR transition can occur in vitro in natural proteins and in drugs containing this motif, thereby promoting integrin recognition and cell adhesion. In this Commentary, we review these studies and discuss the potential effects that isoAsp formation at NGR, DGR and RGD sites might have in the recognition of integrins by natural ligands and by drugs that contain these motifs, as well as their potential biological and pharmacological implications.

Abstract 3625: Novel phage-display derived peptides for tumor- and vasculature-targeted therapies in neuroblastoma

Disseminated neuroblastoma (NB) is refractory to most current therapeutic regimens. The therapeutic index of anticancer drugs is increased by liposome encapsulation and further improvements is obtained by coupling tumor-targeting ligands to the surface of the lipidic envelop. Phage display technology is a powerful tool in discovering novel ligands specific to receptors on the surface of tumor epithelial and endothelial cells. Therapeutic targeting to tumor blood vessels combines blood vessel destruction with the expected anti-tumor activities of the drug, resulting in increased efficacy and reduced toxicity.

To find NB-specific targeting moieties, we established a protocol for the isolation of heterogeneous cell populations by tissue fractionation of primary tumors and metastases from two models of human NB (with tumor cells injected either intravenously, to mimic minimal residual disease, or orthotopically in the adrenal gland of mice, to reflect the growth of advanced NB in children with large adrenal gland tumors and small metastatic lesions) and from stage IV, stroma poor, NB-derived specimens immediately after surgical removal. Cells extracted from corresponding healthy organs from mice and patients were used both in a negative pre-selection step and as a negative control for specific phage enrichment. The NB cell suspensions were subjected to multi-step screenings with the phage-displayed peptide library CX7C (where C = cysteine and X = any aminoacid). We globally isolated 135 NB-binding peptides. Of these, 31 were selected for binding to the primary tumor mass, 16 to the metastatic mass, 63 to tumor endothelial cells, and 25 to endothelial cells of metastases. Several proteins presenting sequence homology with the discovered peptides have been identified by BLAST analysis and were evaluated for their expression in NB tumors, derived from both mouse xenogratfs and patient specimens. Specifically, 5 novel phage display derived-peptides showed specific binding on NB specimens and homing to tumor cells and tumor vasculature, 10 minutes and 24 hours after injection through the tail vein of NB-bearing mice. We are testing the new molecular, tumor- and vasculature-specific peptides for generating novel tumor-specific liposomal therapies against NB. The availability of novel ligands binding to additional tumor-associated antigens and to targets on both endothelial and perivascular tumor cells will allow to design more sophisticated liposomal targeted anticancer strategies that exhibit high levels of selective toxicity for the cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3625. doi:10.1158/1538-7445.AM2011-3625