Near-infrared fluorescence imaging of CD13 receptor expression using a novel Cy5.5-labeled dimeric NGR peptide

Reconstruction of TNF-α with specific isoelectric point released from SPIONs basing on variable charge to enhance pH-sensitive controlled-release

The clinical application of tumor necrosis factor-α (TNF-α) is limited by its short half-life, subeffective concentration in the targeted area and severe systemic toxicity. In this study, the recombinant polypeptide S4-TNF-α was constructed and coupled with chitosan-modified superparamagnetic iron oxide nanoparticles (S4-TNF-α-SPIONs) to achieve pH-sensitive controlled release and active tumor targeting activity. The isoelectric point (pI) of S4-TNF-α was reconstructed to approach the pH of the tumor microenvironment. The negative-charge S4-TNF-α was adsorbed to chitosan-modified superparamagnetic iron oxide nanoparticles (CS-SPIONs) with a positive charge through electrostatic adsorption at physiological pH. The acidic tumor microenvironment endowed S4-TNF-α with a zero charge, which accelerated S4-TNF-α release from CS-SPIONs. Our studies showed that S4-TNF-α-SPIONs displayed an ideal pH-sensitive controlled release capacity and improved antitumor effects. Our study presents a novel approach to enhance the pH-sensitive controlled-release of genetically engineered drugs by adjusting their pI to match the pH of the tumor microenvironment.

Imaging methods to evaluate tumor microenvironment factors affecting nanoparticle drug delivery and antitumor response

Standard small molecule and nanoparticulate chemotherapies are used for cancer treatment; however, their effectiveness remains highly variable. One reason for this variable response is hypothesized to be due to nonspecific drug distribution and heterogeneity of the tumor microenvironment, which affect tumor delivery of the agents. Nanoparticle drugs have many theoretical advantages, but due to variability in tumor microenvironment (TME) factors, the overall drug delivery to tumors and associated antitumor response are low. The nanotechnology field would greatly benefit from a thorough analysis of the TME factors that create these physiological barriers to tumor delivery and treatment in preclinical models and in patients. Thus, there is a need to develop methods that can be used to reveal the content of the TME, determine how these TME factors affect drug delivery, and modulate TME factors to increase the tumor delivery and efficacy of nanoparticles. In this review, we will discuss TME factors involved in drug delivery, and how biomedical imaging tools can be used to evaluate tumor barriers and predict drug delivery to tumors and antitumor response.

Cyanine Conjugate-Based Biomedical Imaging Probes

Cyanine is a class of fluorescent dye with meritorious fluorescence properties and has motivated numerous researchers to explore its imaging capabilities by miscellaneous structural modification and functionalization strategies. The covalent conjugation with other functional molecules represents a distinctive design strategy and has shown immense potential in both basic and clinical research. This review article summarizes recent achievements in cyanine conjugate-based probes for biomedical imaging. Particular attention is paid to the conjugation with targeting warheads and other contrast agents for targeted fluorescence imaging and multimodal imaging, respectively. Additionally, their clinical potential in cancer diagnostics is highlighted and some concurrent impediments for clinical translation are discussed.

A Uniquely Modified DKL-based Peptide Probe for Positron Emission Tomography Imaging

Peptides containing the asparagine-glycine-arginine (NGR) motif can target the tumor neovascular biomarker CD13/aminopeptidase N receptor. D-K6L9 is a tumor-selective anti-cancer peptide. To improve the capacity of NGR peptides to target tumors, we joined the NGR and D-K6L9 peptides to form NKL. Next, we linked 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) to NKL and labeled it with gallium 68 (68Ga, t1/2 = 67.7 min) to form 68Ga-DOTA-NKL. This novel probe was characterized in vitro. 68Ga-DOTA-NKL was stable in phosphate buffered saline at room temperature and in human serum at 37°C. We determined that the uptake rate of 68Ga-DOTA-NKL in CD13 receptor-positive 22Rv1 tumor cells was 3.15% ± 0.04 after 2 h, and tested 68Ga-DOTA-NKL using positron emission tomography (PET)/computed tomography imaging in vivo. MicroPET imaging results revealed that 22Rv1 tumor uptake of 68Ga-DOTA-NKL was 8.69 ± 0.20, 6.61 ± 0.22, 3.85 ± 0.06, and 1.41 ± 0.23 percentage injected dose per gram of tissue (%ID/g) at 0.5, 1, 2, and 3 h postinjection (pi), respectively. The tumor-to-background contrast in the subcutaneous human prostate cancer 22Rv1 mouse model was 9.97 ± 1.90. The 68Ga-DOTA-NKL probe has combined tumor-targeting and tumor-selective properties, and may be used to diagnose CD13-positive tumors.

SPION decorated exosome delivery of TNF-α to cancer cell membranes through magnetism

Tumor necrosis factor (TNF-α) is capable of inducing apoptosis and is a promising candidate for genetic engineering drugs in cancer therapy; however, the serious side-effects of TNF-α hinder their clinical application. In the present study, a method for preparing fusion proteins of cell-penetrating peptides (CPP) and TNF-α (CTNF-α)-anchored exosomes coupled with superparamagnetic iron oxide nanoparticles (CTNF-α-exosome-SPIONs) with membrane targeting anticancer activity has been demonstrated. To acquire exosomes with TNF-α anchored in its membrane, a CTNF-α expression vector was constructed and a stable mesenchymal stem cell cell line that expressed CTNF-α was established. Conjugating transferrin-modified SPIONs (Tf-SPIONs) onto CTNF-α-exosomes through transferrin-transferrin receptor (Tf-TfR) interaction yields CTNF-α-exosome-SPIONs with good water dispersibility. The incorporation of TNF-α into exosomes and the conjugation of SPIONs significantly enhanced the binding capacity of TNF-α to its membrane-bound receptor TNFR I, thus increasing the therapeutic effects. CTNF-α-exosome-SPIONs significantly enhanced tumor cell growth inhibition via induction of the TNFR I-mediated apoptotic pathway. In vivo studies using murine melanoma subcutaneous cancer models showed that TNF-α-loaded exosome-based vehicle delivery enhanced cancer targeting under an external magnetic field and suppressed tumor growth with mitigating toxicity. Taken together, our results suggest that CTNF-α-exosome-SPIONs showed great potential in membrane targeting therapy.

Near infra-red polymeric nanoparticle based optical imaging in Cancer diagnosis

Cancer disease is a foremost health concern and top basis of death in comparison with many diseases including cardiovascular disorders. During initial diagnosis (usually late diagnosis), a majority of cancer patients suffer from metastatic and advanced cancer stages which resulted in limited therapeutic modalities based interventions and effectiveness. Though considerable advancement has been made in combating the disease, continuous and intense efforts are ongoing for early diagnosis and development of therapies. Generally applied treatment options for cancer are surgery, chemotherapy and radiotherapy, which are restricted by failure to early diagnose, insufficient on-targeted drug delivery, systemic toxicity, and lack of real-time monitoring of therapeutic responses in cancer. Noninvasive imaging or minimally invasive imaging methodology is valuable in clinical diagnostic settings. Specifically, noninvasive optical imaging integrated with polymeric nanomaterial have been extensively investigated in the field of cancer diagnostics and therapy. Currently, optical imaging methods go together with polymer-based fluorescent nanoparticles in accomplishing the molecular level detection of tumor boundaries. NIR probe tagged polymeric nanoparticles have potential to provide an advantage in the early cancer detection, therapeutic monitoring and image guided surgery procedures. This article review the recent progress in state-of-the-art NIRF polymeric nanoparticles used for optical imaging particularly on cancer diagnosis.

Emerging Fluorescent Molecular Tracers to Guide Intra-Operative Surgical Decision-Making

Fluorescence imaging is an emerging technology that can provide real-time information about the operating field during cancer surgery. Non-specific fluorescent agents, used for the assessment of blood flow and sentinel lymph node detection, have so far dominated this field. However, over the last decade, several clinical studies have demonstrated the great potential of targeted fluorescent tracers to visualize tumor lesions in a more specific way. This has led to an exponential growth in the development of novel molecular fluorescent contrast agents. In this review, the design of fluorescent molecular tracers will be discussed, with particular attention for agents and approaches that are of interest for clinical translation.

Near-Infrared Fluorescent Peptides with High Tumor Selectivity: Novel Probes for Image-Guided Surgical Resection of Orthotopic Glioma

The complete excision of glioblastomas with maximal retention of surrounding normal tissues can have a positive effect on the survival status and quality of life of patients. Near-infrared fluorescence (NIRF) optical imaging of the tumor vasculature offers a noninvasive method for detection of early stage glioblastoma and efficient monitoring of therapeutic responses. The aim of this study was to develop a novel NIRF imaging probe as a visualization tool for image-guided surgical resection of orthotopic glioblastoma. In this study, Cy5.5-RKL, Cy5.5-NKL, and Cy5.5-DKL probes were successfully synthesized, and their properties were investigated in vitro and in vivo. In vivo, Cy5.5-RKL and Cy5.5-NKL were able to detect U87MG xenografts for at least 8 h post injection. The maximum tumor-to-muscle ratios of Cy5.5-RKL and Cy5.5-NKL were 7.65 ± 0.72 and 5.43 ± 0.72, respectively. Of the probes, Cy5.5-RKL displayed the best delineation of the boundaries between orthotopic glioblastomas and normal brain tissue at 8 h p.i. In conclusion, NIRF imaging using Cy5.5-RKL is promising not only for diagnostic purposes but also for use in image-guided surgery for orthotopic glioblastoma or other superficial tumors.

IR-783 Labeling of a Peptide Receptor for 'Turn-On' Fluorescence Based Sensing

In this study, we examine a means for developing near-IR fluorescent sensors through streamlined, site-specific coupling with peptide-based receptors. As the penultimate step of solid-phase synthesis of a peptide-based receptor, we show a simple means of labeling the N' terminus with the near IR fluorophore IR-783 to afford a viable fluorescent sensor after cleavage from the resin. The proof-of-concept probe utilized a biotin mimetic peptide sequence as the receptive moiety. Here we revealed a "turn-on" fluorescence enhancement upon binding of the biotin mimetic probe to its intended streptavidin target. Not all peptide-receptive moieties tested were able to generate such an enhancement upon target binding, and as such, the rationale for the observed fluorescence response properties is discussed.

Aminopeptidase N (CD13) targeted MR and NIRF dual-modal imaging of ovarian tumor xenograft

The development of tumor-specific imaging nanoprobes with the potential to improve the accuracy of cancer diagnosis has become an area of intense research. Aminopeptidase N (CD13) predominantly expresses on the surface of ovarian tumor cells and can be specifically recognized by Asn-Gly-Arg (NGR) peptide. The applicability of CD13 as a target for specific ovarian tumor imaging, however, remains unexploited so far. In this study, Cy5.5-labeled, NGR-conjugated iron oxide nanoparticles (Cy5.5-NGR-Fe₃O₄ NPs) were prepared as an ovarian tumor specific bimodal imaging nanoprobe. It is demonstrated that the conjugation of NGR targeting moiety leads to a higher cellular uptake toward ES-2 cells, the human ovarian carcinoma cells that highly express CD13. Moreover, magnetic resonance imaging of ovarian tumor xenograft reveals that the Fe₃O₄-Cy5.5-NGR NPs results in a significant T₂* signal reduction in the tumor. Meanwhile, near infrared fluorescence imaging indicates a higher accumulation of Fe₃O₄-Cy5.5-NGR NPs in the tumor xenograft. Therefore, CD13 could be applied as a novel and efficient target for constructing ovarian tumor specific nanoprobes with improved accuracy for ovarian tumor diagnosis.

A CD44-specific peptide, RP-1, exhibits capacities of assisting diagnosis and predicting prognosis of gastric cancer

Early diagnosis and evaluation of prognosis are both crucial for preventing poor prognosis of patients with gastric cancer (GC), a leading cause of cancer-related deaths worldwide. Cluster of differentiation 44 (CD44), an indicator of cancer stem cells, can be specifically targeted by molecular probes and detected in tissues of GC in a large quantity. In current study we found that RP-1, a specific peptide binding to CD44 protein, exhibited the potentials of specific binding to CD44 high-expressing cancer cells both in vitro and in vivo, and the capacity of predicting prognosis of human GC in a microarray assay. Results showed that RP-1 was characterized by high affinity, sensitivity and specificity, and low toxicity, suggesting RP-1 could be an ideal bio-probe for accessory diagnosis of GC. Further immunohistochemical studies and statistical analysis of tissue microarray of human GC demonstrated similar sensitivity and specificity of RP-1 with the monoclonal anti-CD44 antibody in the diagnosis of GC, and even proved that positive RP-1 could be an independent risk factor. Therefore, this study suggests RP-1 has the potentials of binding to CD44 protein expressed on the membrane of GC cells, and demonstrates the feasibility and reliability of its further application in molecular diagnosis and prognostic prediction of GC.

Next generation NIR fluorophores for tumor imaging and fluorescence-guided surgery: A review

Cancer is a group of diseases responsible for the major causes of mortality and morbidity among people of all ages. Even though medical sciences have made enormous growth, complete treatment of this deadly disease is still a challenging task. Last few decades witnessed an impressive growth in the design and development of near infrared (NIR) fluorophores with and without recognition moieties for molecular recognitions, imaging and image guided surgeries. The present article reviews recently reported NIR emitting organic/inorganic fluorophores that targets and accumulates in organelle/organs specifically for molecular imaging of cancerous cells. Near infrared (NIR probe) with or without a tumor-targeting warhead have been considered and discussed for their applications in the field of cancer imaging. In addition, challenges persist in this area are also delineated in this review.

In Vivo Tumor Angiogenesis Imaging Using Peptide-Based Near-Infrared Fluorescent Probes

Near-infrared fluorescence (NIRF) imaging is an emerging imaging technique for studying diseases at the molecular level. Optical imaging with a near-infrared emitting fluorophore for targeting tumor angiogenesis offers a noninvasive method for early tumor detection and efficient monitoring of tumor response to anti-angiogenesis therapy. CD13 receptor, a zinc-dependent membrane-bound ectopeptidase, plays important roles in regulating tumor angiogenesis and the growth of new blood vessels. In this chapter, we use CD13 receptor as an example to demonstrate how to construct CD13-specific NGR-containing peptides via bioorthogonal click chemistry for visualizing and quantifying the CD13 receptor expression in vivo by means of NIRF optical imaging.

Cellular Uptake and Photo-Cytotoxicity of a Gadolinium(III)-DOTA-Naphthalimide Complex "Clicked" to a Lipidated Tat Peptide

A new bifunctional macrocyclic chelator featuring a conjugatable alkynyl-naphthalimide fluorophore pendant group has been prepared and its Gd(III) complex coupled to a cell-penetrating lipidated azido-Tat peptide derivative using Cu(I)-catalysed “click” chemistry. The resulting fluorescent conjugate is able to enter CAL-33 tongue squamous carcinoma cells, as revealed by confocal microscopy, producing a very modest anti-proliferative effect (IC₅₀ = 93 µM). Due to the photo-reactivity of the naphthalimide moiety, however, the conjugate’s cytotoxicity is significantly enhanced (IC₅₀ = 16 µM) upon brief low-power UV-A irradiation.

Evaluation of (188)Re-labeled NGR-VEGI protein for radioimaging and radiotherapy in mice bearing human fibrosarcoma HT-1080 xenografts

Vascular endothelial growth inhibitor (VEGI) is an anti-angiogenic protein, which includes three isoforms: VEGI-174, VEGI-192, and VEGI-251. The NGR (asparagine-glycine-arginine)-containing peptides can specifically bind to CD13 (Aminopeptidase N) receptor which is overexpressed in angiogenic blood vessels and tumor cells. In this study, a novel NGR-VEGI fusion protein was prepared and labeled with (188)Re for radioimaging and radiotherapy in mice bearing human fibrosarcoma HT-1080 xenografts. Single photon emission computerized tomography (SPECT) imaging results revealed that (188)Re-NGR-VEGI exhibits good tumor-to-background contrast in CD13-positive HT-1080 tumor xenografts. The CD13 specificity of (188)Re-NGR-VEGI was further verified by significant reduction of tumor uptake in HT-1080 tumor xenografts with co-injection of the non-radiolabeled NGR-VEGI protein. The biodistribution results demonstrated good tumor-to-muscle ratio (4.98 ± 0.25) of (188)Re-NGR-VEGI at 24 h, which is consistent with the results from SPECT imaging. For radiotherapy, 18.5 MBq of (188)Re-NGR-VEGI showed excellent tumor inhibition effect in HT-1080 tumor xenografts with no observable toxicity, which was confirmed by the tumor size change and hematoxylin and eosin (H&E) staining of major mouse organs. In conclusion, these data demonstrated that (188)Re-NGR-VEGI has the potential as a theranostic agent for CD13-targeted tumor imaging and therapy.

The evaluation of cellular uptake efficiency and tumor-targeting ability of MPEG–PDLLA micelles: effect of particle size

The study reported herein describes the cellular uptake efficiency and tumor-targeting ability of MPEG–PDLLA micelles with two different particle sizes.

In vivo NIRF imaging-guided delivery of a novel NGR-VEGI fusion protein for targeting tumor vasculature

Pathological angiogenesis is crucial in tumor growth, invasion and metastasis. Previous studies demonstrated that the vascular endothelial growth inhibitor (VEGI), a member of the tumor necrosis factor superfamily, can be used as a potent endogenous inhibitor of tumor angiogenesis. Molecular probes containing the asparagine-glycine-arginine (NGR) sequence can specifically bind to CD13 receptor which is overexpressed on neovasculature and several tumor cells. Near-infrared fluorescence (NIRF) optical imaging for targeting tumor vasculature offers a noninvasive method for early detection of tumor angiogenesis and efficient monitoring of response to anti-tumor vasculature therapy. The aim of this study was to develop a new NIRF imaging probe on the basis of an NGR-VEGI protein for the visualization of tumor vasculature. The NGR-VEGI fusion protein was prepared from prokaryotic expression, and its function was characterized in vitro. The NGR-VEGI protein was then labeled with a Cy5.5 fluorophore to afford Cy5.5-NGR-VEGI probe. Using the NIRF imaging technique, we visualized and quantified the specific delivery of Cy5.5-NGR-VEGI protein to subcutaneous HT-1080 fibrosarcoma tumors in mouse xenografts. The Cy5.5-NGR-VEGI probe exhibited rapid HT-1080 tumor targeting, and highest tumor-to-background contrast at 8 h post-injection (pi). Tumor specificity of Cy5.5-NGR-VEGI was confirmed by effective blocking of tumor uptake in the presence of unlabeled NGR-VEGI (20 mg/kg). Ex vivo NIRF imaging further confirmed in vivo imaging findings, demonstrating that Cy5.5-NGR-VEGI displayed an excellent tumor-to-muscle ratio (18.93 ± 2.88) at 8 h pi for the non-blocking group and significantly reduced ratio (4.92 ± 0.75) for the blocking group. In conclusion, Cy5.5-NGR-VEGI provided highly sensitive, target-specific, and longitudinal imaging of HT-1080 tumors. As a novel theranostic protein, Cy5.5-NGR-VEGI has the potential to improve cancer treatment by targeting tumor vasculature.

MicroPET imaging of CD13 expression using a (64)Cu-labeled dimeric NGR peptide based on sarcophagine cage

CD13 receptor as a tumor vasculature biomarker has attracted great attention in cancer research. Through phage display screening, NGR-containing peptides have been characterized as specific ligands binding to CD13 receptor. In this study, a (64)Cu-labeled dimeric NGR peptide based on sarcophagine cage was synthesized and evaluated for micropositron emission tomography (PET) imaging of CD13 expression in vivo. Macrocyclic chelating agent (sarcophagine cage) was conjugated with two azide moieties, followed by mixing with an alkyne-containing NGR peptide to rapidly provide the Sar-NGR2 peptide by click chemistry. Radiolabeling of Sar-NGR2 with (64)Cu was achieved in >90% decay-corrected yield with radiochemical purity of >99%. The cell uptake study showed that (64)Cu-Sar-NGR2 binds to CD13-positive HT-1080 cells, but not to CD13-negative MCF-7 cells. MicroPET imaging results revealed that (64)Cu-Sar-NGR2 exhibits good tumor uptake in CD13-positive HT-1080 xenografts and significantly lower tumor uptake in CD13-negative MCF-7 xenografts. The CD13-specific binding of (64)Cu-Sar-NGR2 was further verified by significant reduction of tumor uptake in HT-1080 tumor xenografts with coinjection of a nonradiolabeled NGR peptide. The biodistribution results demonstrated good tumor/muscle ratio (8.28 ± 0.37) of (64)Cu-Sar-NGR2 at 24 h pi in HT-1080 tumor xenografts, which is in agreement with the quantitative analysis of microPET imaging. In conclusion, sarcophagine cage has been successfully applied to the construction of a (64)Cu-labeled dimeric NGR-containing peptide. In vitro and in vivo studies demonstrated that (64)Cu-Sar-NGR2 is a promising PET probe for imaging CD13 expression in living mice.