RGD-Binding Integrins in Prostate Cancer: Expression Patterns and Therapeutic Prospects against Bone Metastasis

TGF-β induces matrisome pathological alterations and EMT in patient-derived prostate cancer tumoroids

Extracellular matrix (ECM) tumorigenic alterations resulting in high matrix deposition and stiffening are hallmarks of adenocarcinomas and are collectively defined as desmoplasia. Here, we thoroughly analysed primary prostate cancer tissues obtained from numerous patients undergoing radical prostatectomy to highlight reproducible structural changes in the ECM leading to the loss of the glandular architecture. Starting from patient cells, we established prostate cancer tumoroids (PCTs) and demonstrated they require TGF-β signalling pathway activity to preserve phenotypical and structural similarities with the tissue of origin. By modulating TGF-β signalling pathway in PCTs, we unveiled its role in ECM accumulation and remodelling in prostate cancer. We also found that TGF-β-induced ECM remodelling is responsible for the initiation of prostate cell epithelial-to-mesenchymal transition (EMT) and the acquisition of a migratory, invasive phenotype. Our findings highlight the cooperative role of TGF-β signalling and ECM desmoplasia in prompting prostate cell EMT and promoting tumour progression and dissemination.

Anoikis in phenotypic reprogramming of the prostate tumor microenvironment

Prostate cancer is one of the most common malignancies in males wherein 1 in 8 men are diagnosed with this disease in their lifetime. The urgency to find novel therapeutic interventions is associated with high treatment resistance and mortality rates associated with castration-resistant prostate cancer. Anoikis is an apoptotic phenomenon for normal epithelial or endothelial cells that have lost their attachment to the extracellular matrix (ECM). Tumor cells that lose their connection to the ECM can die via apoptosis or survive via anoikis resistance and thus escaping to distant organs for metastatic progression. This review discusses the recent advances made in our understanding of the signaling effectors of anoikis in prostate cancer and the approaches to translate these mechanistic insights into therapeutic benefits for reducing lethal disease outcomes (by overcoming anoikis resistance). The prostate tumor microenvironment is a highly dynamic landscape wherein the balance between androgen signaling, cell lineage changes, epithelial-mesenchymal transition (EMT), extracellular matrix interactions, actin cytoskeleton remodeling as well as metabolic changes, confer anoikis resistance and metastatic spread. Thus, these mechanisms also offer unique molecular treatment signatures, exploitation of which can prime prostate tumors to anoikis induction with a high translational significance.

Prostate cancer cells of increasing metastatic potential exhibit diverse contractile forces, cell stiffness, and motility in a microenvironment stiffness-dependent manner

During metastasis, all cancer types must migrate through crowded multicellular environments. Simultaneously, cancers appear to change their biophysical properties. Indeed, cell softening and increased contractility are emerging as seemingly ubiquitous biomarkers of metastatic progression which may facilitate metastasis. Cell stiffness and contractility are also influenced by the microenvironment. Stiffer matrices resembling the tumor microenvironment cause metastatic cells to contract more strongly, further promoting contractile tumorigenic phenotypes. Prostate cancer (PCa), however, appears to deviate from these common cancer biophysics trends; aggressive metastatic PCa cells appear stiffer, rather than softer, to their lowly metastatic PCa counterparts. Although metastatic PCa cells have been reported to be more contractile than healthy cells, how cell contractility changes with increasing PCa metastatic potential has remained unknown. Here, we characterize the biophysical changes of PCa cells of various metastatic potential as a function of microenvironment stiffness. Using a panel of progressively increasing metastatic potential cell lines (22RV1, LNCaP, DU145, and PC3), we quantified their contractility using traction force microscopy (TFM), and measured their cortical stiffness using optical magnetic twisting cytometry (OMTC) and their motility using time-lapse microscopy. We found that PCa contractility, cell stiffness, and motility do not universally scale with metastatic potential. Rather, PCa cells of various metastatic efficiencies exhibit unique biophysical responses that are differentially influenced by substrate stiffness. Despite this biophysical diversity, this work concludes that mechanical microenvironment is a key determinant in the biophysical response of PCa with variable metastatic potentials. The mechanics-oriented focus and methodology of the study is unique and complementary to conventional biochemical and genetic strategies typically used to understand this disease, and thus may usher in new perspectives and approaches.

Enhancing nanoparticle accumulation in two dimensional, three dimensional, and xenograft mouse cancer cell models in the presence of docetaxel

Recent clinical trials show docetaxel (DTX), given in conjunction with radiation therapy (RT) and androgen suppression, improves survival in high-risk prostate cancer. Addition of gold nanoparticles (GNPs) to this current DTX/RT protocol is expected to further improve therapeutic benefits remarkably. However, the foundation for the triple combination of RT, DTX, and GNPs must be elucidated to ensure quicker facilitation to the clinic. In this study, we explored the use of low concentrations of DTX combined with GNPs in two prostate cancer cell lines in a two-dimensional monolayer, a three-dimensional spheroid, and a mouse xenograft model. When used together, DTX and GNPs induced a nearly identical relative increase in uptake of gold in both the spheroid model and the mouse xenograft, which saw a 130% and 126% increase respectively after 24 h, showcasing the benefit of using spheroids as an in vitro model to better optimize in vivo experiments. Further, the benefits of using low concentrations of DTX combined with GNPs extended for over 72 h, allowing for less frequency in dosing when translating to the clinic. Overall, these results highlight the benefits of using DTX combined with GNPs and lays the groundwork for the translation of the triple combination of RT, GNPs, and DTX to the clinic.

Melatonin suppresses the metastatic potential of osteoblastic prostate cancers by inhibiting integrin α2 β1 expression

Advanced prostate cancer often develops into bone metastasis, which is characterized by aberrant bone formation with chronic pain and lower chances of survival. No treatment exists as yet for osteoblastic bone metastasis in prostate cancer. The indolamine melatonin (N-acetyl-5-methoxytryptamine) is a major regulator of the circadian rhythm. Melatonin has shown antiproliferative and antimetastatic activities but has not yet been shown to be active in osteoblastic bone lesions of prostate cancer. Our study investigations reveal that melatonin concentration-dependently decreases the migratory and invasive abilities of two osteoblastic prostate cancer cell lines by inhibiting FAK, c-Src, and NF-κB transcriptional activity via the melatonin MT₁ receptor, which effectively inhibits integrin α₂ β₁ expression. Melatonin therapy appears to offer therapeutic possibilities for reducing osteoblastic bone lesions in prostate cancer.

Breast Cancer Bone Metastasis: A Narrative Review of Emerging Targeted Drug Delivery Systems

Bone is one of the most common metastatic sites among breast cancer (BC) patients. Once bone metastasis is developed, patients' survival and quality of life will be significantly declined. At present, there are limited therapeutic options for BC patients with bone metastasis. Different nanotechnology-based delivery systems have been developed aiming to specifically deliver the therapeutic agents to the bone. The conjugation of targeting agents to nanoparticles can enhance the selective delivery of various payloads to the metastatic bone lesion. The current review highlights promising and emerging advanced nanotechnologies designed for targeted delivery of anticancer therapeutics, contrast agents, photodynamic and photothermal materials to the bone to achieve the goal of treatment, diagnosis, and prevention of BC bone metastasis. A better understanding of various properties of these new therapeutic approaches may open up new landscapes in medicine towards improving the quality of life and overall survival of BC patients who experience bone metastasis.

Distinct roles for the RNA-binding protein Staufen1 in prostate cancer

BACKGROUND

Prostate cancer is one of the most common malignant cancers with the second highest global rate of mortality in men. During the early stages of disease progression, tumour growth is local and androgen-dependent. Despite treatment, a large percentage of patients develop androgen-independent prostate cancer, which often results in metastases, a leading cause of mortality in these patients. Our previous work on the RNA-binding protein Staufen1 demonstrated its novel role in cancer biology, and in particular rhabdomyosarcoma tumorigenesis. To build upon this work, we have focused on the role of Staufen1 in other forms of cancer and describe here the novel and differential roles of Staufen1 in prostate cancer.

METHODS

Using a cell-based approach, three independent prostate cancer cell lines with different characteristics were used to evaluate the expression of Staufen1 in human prostate cancer relative to control prostate cells. The functional impact of Staufen1 on several key oncogenic features of prostate cancer cells including proliferation, apoptosis, migration and invasion were systematically investigated.

RESULTS

We show that Staufen1 levels are increased in all human prostate cancer cells examined in comparison to normal prostate epithelial cells. Furthermore, Staufen1 differentially regulates growth, migration, and invasion in the various prostate cancer cells assessed. In LNCaP prostate cancer cells, Staufen1 regulates cell proliferation through mTOR activation. Conversely, Staufen1 regulates migration and invasion of the highly invasive, bone metastatic-derived, PC3 prostate cells via the activation of focal adhesion kinase.

CONCLUSIONS

Collectively, these results show that Staufen1 has a direct impact in prostate cancer development and further demonstrate that its functions vary amongst the prostate cancer cell types. Accordingly, Staufen1 represents a novel target for the development of much-needed therapeutic strategies for prostate cancer.

Extracellular Vesicle-Based Nucleic Acid Delivery: Current Advances and Future Perspectives in Cancer Therapeutic Strategies

Extracellular vesicles (EVs) are sophisticated and sensitive messengers released by cells to communicate with and influence distant and neighboring cells via selective transfer of bioactive content, including protein lipids and nucleic acids. EVs have therefore attracted broad interest as new and refined potential therapeutic systems in many diseases, including cancer, due to their low immunogenicity, non-toxicity, and elevated bioavailability. They might serve as safe and effective vehicles for the transport of therapeutic molecules to specific tissues and cells. In this review, we focus on EVs as a vehicle for gene therapy in cancer. We describe recent developments in EV engineering to achieve efficient intracellular delivery of cancer therapeutics and avoid off-target effects, to provide an overview of the potential applications of EV-mediated gene therapy and the most promising biomedical advances.

Nanomedicine and chemotherapeutics drug delivery: challenges and opportunities

Cancer is considered as one of the biggest threats to humans worldwide. Researchers suggest that tumour is not just a single mass, it comprises cancerous cells surrounded by noncancerous cells such as immune cells, adipocytes and cancer stem cells (CSCs) in the extracellular matrix (ECM) containing distinct components such as proteins, glycoproteins and enzymes; thus tumour microenvironment (TME) is partially complex. Multiple interactions happen in the dynamic microenvironment (ME) lead to an acidic, hypoxic and stiff ME that is considered as one of the major contributors to cancer progression and metastasis. Furthermore, TME involves in drug resistance mechanisms and affects enhanced permeability and retention (EPR) in tumours. In such a scenario, the first step to accomplish satisfying results is the identification and recognition of this ME. Then designing proper drug delivery systems can perform selectively towards cancerous cells. In this way, several targeting and stimuli/enzyme responsive drug delivery systems have been designed. More importantly, it is necessary to design a drug delivery system that can penetrate deeper into the tumours, efficiently and selectively. Various drug delivery systems such as exosomes and size-switchable nanocarriers (NCs) could decrease side effects and increase tumour treatment results by selective accumulation in tumours. In this review, TME features, current drug delivery approaches, challenges and promising strategies towards cancer treatment are discussed.

Inadequate tissue mineralization promotes cancer cell attachment

Bone metastases are a frequent complication in prostate cancer, and several studies have shown that vitamin D deficiency promotes bone metastases. However, while many studies focus on vitamin D’s role in cell metabolism, the effect of chronically low vitamin D levels on bone tissue, i.e. insufficient mineralization of the tissue, has largely been ignored. To investigate, whether poor tissue mineralization promotes cancer cell attachment, we used a fluorescence based adhesion assay and single cell force spectroscopy to quantify the adhesion of two prostate cancer cell lines to well-mineralized and demineralized dentin, serving as biomimetic bone model system. Adhesion rates of bone metastases-derived PC3 cells increased significantly on demineralized dentin. Additionally, on mineralized dentin, PC3 cells adhered mainly via membrane anchored surface receptors, while on demineralized dentin, they adhered via cytoskeleton-anchored transmembrane receptors, pointing to an interaction via exposed collagen fibrils. The adhesion rate of lymph node derived LNCaP cells on the other hand is significantly lower than that of PC3 and not predominately mediated by cytoskeleton-linked receptors. This indicates that poor tissue mineralization facilitates the adhesion of invasive cancer cells by the exposure of collagen and emphasizes the disease modifying effect of sufficient vitamin D for cancer patients.

Small extracellular vesicles modulated by αVβ3 integrin induce neuroendocrine differentiation in recipient cancer cells

The ability of small extracellular vesicles (sEVs) to reprogram cancer cells is well established. However, the specific sEV components able to mediate aberrant effects in cancer cells have not been characterized. Integrins are major players in mediating sEV functions. We have previously reported that the αVβ3 integrin is detected in sEVs of prostate cancer (PrCa) cells and transferred into recipient cells. Here, we investigate whether sEVs from αVβ3-expressing cells affect tumour growth differently than sEVs from control cells that do not express αVβ3. We compared the ability of sEVs to stimulate tumour growth, using sEVs isolated from PrCa C4-2B cells by iodixanol density gradient and characterized with immunoblotting, nanoparticle tracking analysis, immunocapturing and single vesicle analysis. We incubated PrCa cells with sEVs and injected them subcutaneously into nude mice to measure in vivo tumour growth or analysed in vitro their anchorage-independent growth. Our results demonstrate that a single treatment with sEVs shed from C4-2B cells that express αVβ3, but not from control cells, stimulates tumour growth and induces differentiation of PrCa cells towards a neuroendocrine phenotype, as quantified by increased levels of neuroendocrine markers. In conclusion, the expression of αVβ3 integrin generates sEVs capable of reprogramming cells towards an aggressive phenotype.

ROS-Responsive Nanoparticles Formed from RGD-Epothilone B Conjugate for Targeted Cancer Therapy

The targeted nanoagents have shown great potential clinically for cancer therapy. Traditional targeted nanodrugs are usually prepared through surface postmodification. Herein, a nanodrug is self-assembled from the amphiphilic precursor of targeting peptide RGD conjugated with cytotoxin epothilone B (Epo B) through a linker containing the thioketal (tk) group that is sensitive to reactive oxygen species (ROS). The obtained RGD-tk-Epo B conjugate nanoparticles (RECNs) are stable and uniform, which facilitates improving tumor-targeting capacity and accumulation of the drug because of the large number of RGD on the surface of the RECN. After internalization by cancer cells, the blood-inert tk group between RGD and Epo B can be cleaved in the presence of high level of ROS to release Epo B, exhibiting a markedly tumor selectivity and excellent anticancer efficiency in vitro and in vivo.

Materials-Based Approach for Interrogating Human Prostate Cancer Cell Adhesion and Migratory Potential Using a Fluoroalkylsilica Culture Surface

OPCT-1 is a heterogeneous prostate cancer cell line derived from primary (rather than metastatic) disease which contains epithelial, mesenchymal, and CD44^high/CD24^low cancer stem cell (CSC) subpopulations and from which we have previously generated and characterized stable mesenchymal (P4B6B) and epithelial (P5B3) cell subpopulations. In this contribution, we explore the effect of tissue culture surface chemistry (standard tissue culture plastic (TCP) and a fluoroalkylsilica (FS) culture surface with inherently low surface energy) on the phenotype and adherent capacity of mesenchymal and epithelial cell populations. We demonstrate that OPCT-1 cells adherent to FS surfaces comprise both epithelial- and mesenchymal-like populations; a mesenchymal subpopulation derived from OPCT1 (P4B6B) poorly adheres to FS and formed spheroids, whereas an epithelial subpopulation derived from OPCT1 (P5B3) forms an adherent monolayer. In contrast, P4B6B cells do adhere to FS when cocultured with P5B3 cells. Taken together, these findings demonstrate that EMT/cell differentiation status dictates cell adhesive capacity and provide a novel insight into the relationship between epithelial and mesenchymal cell populations in metastasis. Importantly, the differences in adherence capacity between P4B6B and P5B3 are not apparent using standard TCP-based culture, thereby highlighting the value of using alternative culture surfaces for studying cell surface interaction/adhesion phenomena and interrogating mechanisms involved in adhesion and detachment of metastatic tumor cells.

Recent progress in biomedical applications of RGD-based ligand: From precise cancer theranostics to biomaterial engineering: A systematic review

Arginine-glycine-aspartic acid (RGD) peptide family is known as the most prominent ligand for extracellular domain of integrin receptors. Specific expression of these receptors in various tissue of human body and tight association of their expression profile with various pathophysiological conditions made these receptors a suitable targeting candidate for several disease diagnosis and treatment as well as regeneration of various organs. For these reasons, various forms of RGD-based integrins ligands have been greatly used in biomedical studies. Here, we summarized the last decade application progress of RGD for cancer theranostics, control of inflammation, thrombosis inhibition and critically discussed the effect of RGD peptides structure and sequence on the efficacy of gene/drug delivery systems in preclinical studies. Furthermore, we will show recent advances in application of RGD functionalized biomaterials for various tissue regenerations including cornea repair, artificial neovascularization and bone tissue regeneration. Finally, we analyzed clinically translatability of RGD peptides, considering examples of integrin ligands in clinical trials. In conclusion, prospects on using RGD peptide for precise drug delivery and biomaterial engineering are well discussed.

Abi1 loss drives prostate tumorigenesis through activation of EMT and non-canonical WNT signaling

Background

Prostate cancer development involves various mechanisms, which are poorly understood but pointing to epithelial mesenchymal transition (EMT) as the key mechanism in progression to metastatic disease. ABI1, a member of WAVE complex and actin cytoskeleton regulator and adaptor protein, acts as tumor suppressor in prostate cancer but the role of ABI1 in EMT is not clear.

Methods

To investigate the molecular mechanism by which loss of ABI1 contributes to tumor progression, we disrupted the ABI1 gene in the benign prostate epithelial RWPE-1 cell line and determined its phenotype. Levels of ABI1 expression in prostate organoid tumor cell lines was evaluated by Western blotting and RNA sequencing. ABI1 expression and its association with prostate tumor grade was evaluated in a TMA cohort of 505 patients and metastatic cell lines.

Results

Low ABI1 expression is associated with biochemical recurrence, metastasis and death (p = 0.038). Moreover, ABI1 expression was significantly decreased in Gleason pattern 5 vs. pattern 4 (p = 0.0025) and 3 (p = 0.0012), indicating an association between low ABI1 expression and highly invasive prostate tumors. Disruption of ABI1 gene in RWPE-1 cell line resulted in gain of an invasive phenotype, which was characterized by a loss of cell-cell adhesion markers and increased migratory ability of RWPE-1 spheroids. Through RNA sequencing and protein expression analysis, we discovered that ABI1 loss leads to activation of non-canonical WNT signaling and EMT pathways, which are rescued by re-expression of ABI1. Furthermore, an increase in STAT3 phosphorylation upon ABI1 inactivation and the evidence of a high-affinity interaction between the FYN SH2 domain and ABI1 pY421 support a model in which ABI1 acts as a gatekeeper of non-canonical WNT-EMT pathway activation downstream of the FZD2 receptor.

Conclusions

ABI1 controls prostate tumor progression and epithelial plasticity through regulation of EMT-WNT pathway. Here we discovered that ABI1 inhibits EMT through suppressing FYN-STAT3 activation downstream from non-canonical WNT signaling thus providing a novel mechanism of prostate tumor suppression.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0410-y) contains supplementary material, which is available to authorized users.

Integrins, CAFs and Mechanical Forces in the Progression of Cancer

Cells respond to both chemical and mechanical cues present within their microenvironment. Various mechanical signals are detected by and transmitted to the cells through mechanoreceptors. These receptors often contact with the extracellular matrix (ECM), where the external signals are converted into a physiological response. Integrins are well-defined mechanoreceptors that physically connect the actomyosin cytoskeleton to the surrounding matrix and transduce signals. Families of α and β subunits can form a variety of heterodimers that have been implicated in cancer progression and differ among types of cancer. These heterodimers serve as the nexus of communication between the cells and the tumor microenvironment (TME). The TME is dynamic and composed of stromal cells, ECM and associated soluble factors. The most abundant stromal cells within the TME are cancer-associated fibroblasts (CAFs). Accumulating studies implicate CAFs in cancer development and metastasis through their remodeling of the ECM and release of large amounts of ECM proteins and soluble factors. Considering that the communication between cancer cells and CAFs, in large part, takes place through the ECM, the involvement of integrins in the crosstalk is significant. This review discusses the role of integrins, as the primary cell-ECM mechanoreceptors, in cancer progression, highlighting integrin-mediated mechanical communication between cancer cells and CAFs.

Classification of prostate cancer using a protease activity nanosensor library

Improved biomarkers are needed for prostate cancer, as the current gold standards have poor predictive value. Tests for circulating prostate-specific antigen (PSA) levels are susceptible to various noncancer comorbidities in the prostate and do not provide prognostic information, whereas physical biopsies are invasive, must be performed repeatedly, and only sample a fraction of the prostate. Injectable biosensors may provide a new paradigm for prostate cancer biomarkers by querying the status of the prostate via a noninvasive readout. Proteases are an important class of enzymes that play a role in every hallmark of cancer; their activities could be leveraged as biomarkers. We identified a panel of prostate cancer proteases through transcriptomic and proteomic analysis. Using this panel, we developed a nanosensor library that measures protease activity in vitro using fluorescence and in vivo using urinary readouts. In xenograft mouse models, we applied this nanosensor library to classify aggressive prostate cancer and to select predictive substrates. Last, we coformulated a subset of nanosensors with integrin-targeting ligands to increase sensitivity. These targeted nanosensors robustly classified prostate cancer aggressiveness and outperformed PSA. This activity-based nanosensor library could be useful throughout clinical management of prostate cancer, with both diagnostic and prognostic utility.

Phage Therapy in Prostatitis: Recent Prospects

Prostatitis has various etiology including bacterial infection and dysregulated immunity; some of its forms remain a serious therapeutic challenge. Inflammation occurs in all forms of this disorder and is proposed to predispose to the development of prostate cancer (PC). There are reports that phage therapy is effective in chronic bacterial prostatitis. Recent findings suggest that phages not only eliminate bacteria, but also mediate immunomodulating (for example, anti-inflammatory) functions. The immunomodulating effects of phages could be beneficial in treating all forms of prostatitis and play some role in the prevention of the development of PC. As the etiological factors contributing to the majority of prostatitis cases remains largely unknown, and management options are often likewise limited, phage therapy merits further research as an attractive therapeutic option given its immunomodulating effects irrespective of the underlying causative factor(s).

Competition of charge-mediated and specific binding by peptide-tagged cationic liposome-DNA nanoparticles in vitro and in vivo

Cationic liposome-nucleic acid (CL-NA) complexes, which form spontaneously, are a highly modular gene delivery system. These complexes can be sterically stabilized via PEGylation [PEG: poly (ethylene glycol)] into nanoparticles (NPs) and targeted to specific tissues and cell types via the conjugation of an affinity ligand. However, there are currently no guidelines on how to effectively navigate the large space of compositional parameters that modulate the specific and nonspecific binding interactions of peptide-targeted NPs with cells. Such guidelines are desirable to accelerate the optimization of formulations with novel peptides. Using PEG-lipids functionalized with a library of prototypical tumor-homing peptides, we varied the peptide density and other parameters (binding motif, peptide charge, CL/DNA charge ratio) to study their effect on the binding and uptake of the corresponding NPs. We used flow cytometry to quantitatively assess binding as well as internalization of NPs by cultured cancer cells. Surprisingly, full peptide coverage resulted in less binding and internalization than intermediate coverage, with the optimum coverage varying between cell lines. In, addition, our data revealed that great care must be taken to prevent nonspecific electrostatic interactions from interfering with the desired specific binding and internalization. Importantly, such considerations must take into account the charge of the peptide ligand as well as the membrane charge density and the CL/DNA charge ratio. To test our guidelines, we evaluated the in vivo tumor selectivity of selected NP formulations in a mouse model of peritoneally disseminated human gastric cancer. Intraperitoneally administered peptide-tagged CL-DNA NPs showed tumor binding, minimal accumulation in healthy control tissues, and preferential penetration of smaller tumor nodules, a highly clinically relevant target known to drive recurrence of the peritoneal cancer.

Cancer-associated fibroblasts promote directional cancer cell migration by aligning fibronectin

Cancer-associated fibroblasts (CAFs) are major components of the carcinoma microenvironment that promote tumor progression. However, the mechanisms by which CAFs regulate cancer cell migration are poorly understood. In this study, we show that fibronectin (Fn) assembled by CAFs mediates CAF-cancer cell association and directional migration. Compared with normal fibroblasts, CAFs produce an Fn-rich extracellular matrix with anisotropic fiber orientation, which guides the cancer cells to migrate directionally. CAFs align the Fn matrix by increasing nonmuscle myosin II- and platelet-derived growth factor receptor α-mediated contractility and traction forces, which are transduced to Fn through α5β1 integrin. We further show that prostate cancer cells use αv integrin to migrate efficiently and directionally on CAF-derived matrices. We demonstrate that aligned Fn is a prominent feature of invasion sites in human prostatic and pancreatic carcinoma samples. Collectively, we present a new mechanism by which CAFs organize the Fn matrix and promote directional cancer cell migration.

Multivalency Increases the Binding Strength of RGD Peptidomimetic-Paclitaxel Conjugates to Integrin αV β3

This work reports the synthesis of three multimeric RGD peptidomimetic‐paclitaxel conjugates featuring a number of α_Vβ₃ integrin ligands ranging from 2 to 4. These constructs were assembled by conjugation of the integrin α_Vβ₃ ligand cyclo[DKP‐RGD]‐CH₂NH₂ with paclitaxel via a 2′‐carbamate with a self‐immolative spacer, the lysosomally cleavable Val‐Ala dipeptide linker, a multimeric scaffold, a triazole linkage, and finally a PEG spacer. Two monomeric conjugates were also synthesized as reference compounds. Remarkably, the new multimeric conjugates showed a binding affinity for the purified integrin α_Vβ₃ receptor that increased with the number of integrin ligands (reaching a minimum IC₅₀ value of 1.2 nm for the trimeric), thus demonstrating that multivalency is an effective strategy to strengthen the ligand–target interactions.

ROS-Responsive Polyprodrug Nanoparticles for Triggered Drug Delivery and Effective Cancer Therapy

The application of nanoparticles (NPs) to drug delivery has led to the development of novel nanotherapeutics for the treatment of various diseases including cancer. However, clinical use of NP-mediated drug delivery has not always translated into improved survival of cancer patients, in part due to the suboptimal properties of NP platforms, such as premature drug leakage during preparation, storage, or blood circulation, lack of active targeting to tumor tissue and cells, and poor tissue penetration. Herein, an innovative reactive oxygen species (ROS)-responsive polyprodrug is reported that can self-assemble into stable NPs with high drug loading. This new NP platform is composed of the following key components: (i) polyprodrug inner core that can respond to ROS for triggered release of intact therapeutic molecules, (ii) polyethylene glycol (PEG) outer shell to prolong blood circulation; and (iii) surface-encoded internalizing RGD (iRGD) to enhance tumor targeting and tissue penetration. These targeted ROS-responsive polyprodrug NPs show significant inhibition of tumor cell growth both in vitro and in vivo.

Integrins and Exosomes, a Dangerous Liaison in Cancer Progression

Integrin activity and function is classically related to the bi-directional regulation of cell-extracellular matrix (ECM) contacts that regulate a number of cell pathways linked to cell adhesion, cell detachment from ECM, cell migration, and anoikis. Interestingly, emerging data continue to uncover new roles for integrins in cancer-relevant pathways, particularly concerning the regulation of immune cell activity in the tumor niche, like myeloid cell differentiation and function and, very recently, the regulation of metastatic processes by exosomes. Exosomes are deeply involved in cell-cell communication processes and several studies have shown that integrins found in tumor-associated exosomes can promote cancer progression by two novel cooperative mechanisms: horizontal transfer of integrin transcripts as vescicle cargo, and selection of target tissues to form new tumor niches during metastatic spread by integrins carried on the exosome’s surface. In this review we will discuss mounting evidence that contribute to the development of a new picture for integrins in cancer, highlighting the role of integrins in the processes that leads to tumor niche formation. In particular, the role of the periostin pathway in the recruitment of tumor-associated macrophages, and the proposed contribution of exosome-derived integrins in the metastatic spread will be discussed. Finally, in light of the above considerations, an evaluation of integrins as possible therapeutic targets will be conducted.

Tumor Microenvironment-Responsive Multistaged Nanoplatform for Systemic RNAi and Cancer Therapy

While RNA interference (RNAi) therapy has demonstrated significant potential for cancer treatment, the effective and safe systemic delivery of RNAi agents such as small interfering RNA (siRNA) into tumor cells in vivo remains challenging. We herein reported a unique multistaged siRNA delivery nanoparticle (NP) platform, which is comprised of (i) a polyethylene glycol (PEG) surface shell, (ii) a sharp tumor microenvironment (TME) pH-responsive polymer that forms the NP core, and (iii) charge-mediated complexes of siRNA and tumor cell-targeting- and penetrating-peptide-amphiphile (TCPA) that are encapsulated in the NP core. When the rationally designed, long circulating polymeric NPs accumulate in tumor tissues after intravenous administration, the targeted siRNA-TCPA complexes can be rapidly released via TME pH-mediated NP disassembly for subsequent specific targeting of tumor cells and cytosolic transport, thus achieving efficient gene silencing. In vivo results further demonstrate that the multistaged NP delivery of siRNA against bromodomain 4 (BRD4), a recently discovered target protein that regulates the development and progression of prostate cancer (PCa), can significantly inhibit PCa tumor growth.

RGD-Binding Integrins in Head and Neck Cancers

Alterations in integrin expression and function promote tumour growth, invasion, metastasis and neoangiogenesis. Head and neck cancers are highly vascular tumours with a tendency to metastasise. They express a wide range of integrin receptors. Expression of the αv and β1 subunits has been explored relatively extensively and linked to tumour progression and metastasis. Individual receptors αvβ3 and αvβ5 have proved popular targets for diagnostic and therapeutic agents but lesser studied receptors, such as αvβ6, αvβ8, and β1 subfamily members, also show promise. This review presents the current knowledge of integrin expression and function in squamous cell carcinoma of the head and neck (HNSCC), with a particular focus on the arginine-glycine-aspartate (RGD)-binding integrins, in order to highlight the potential of integrins as targets for personalised tumour-specific identification and therapy.

Clinical study of 99mTc-3P-RGD2 peptide imaging in osteolytic bone metastasis

Objective

To investigate the value of integrin α_vβ₃ targeted imaging with ^99mTc-HYNIC-PEG₄-E[PEG₄-c(RGDfk)]₂ (^99mTc-3P-RGD₂) as a radiotracer in dectecting osteolytic bone metastases.

Methods

This is a retrospective study involving a cohort of 69 consecutive patients including 59 with lung cancer and 10 with other cancers. Patients were required to receive whole body scan (WBS) and regional SPECT/CT imaging with ^99mTc-3P-RGD₂ (RGD imaging) and ^99mTc-MDP (MDP imaging) as a radiotracer successively within days. Final diagnosis was based on comprehensive assessment of all available data including case history, CT, MRI, SPECT/CT, PET/CT, histopathology and 6-12 months follow-up. Visual observation and semiquantitative analysis (T/N: tracer uptake ratio of osteolytic metastases to normal bone) of ^99mTc-3P-RGD₂ or ^99mTc-MDP imaging were performed and their detective values for osteolytic metastases were compared.

Results

A total of 131 osteolytic metastatic lesions were retrospectively studied. Osteolytic metastases mainly presented as “hot region”, occasionally as “cool or normal region” on RGD imaging. The detection sensitivity of RGD WBS for osteolytic metastases was significantly higher than that of ^99mTc-MDP WBS (80.9% vs. 46.6%, p<0.01). The sensitivity increased to 96.2% (126/131) when combining with SPECT/CT. ^99mTc-3P-RGD₂ imaging also promoted the detection of unknown primary tumor, lymph node metastases and offered information for clinical staging. T/N of ^99mTc-3P-RGD₂ in lung adenocarcinoma osteolytic metastases showed no statistical difference compared with that in squamous-cell carcinoma (6.84±3.46 vs. 7.33±3.22, t = 0.39, p = 0.71). Whereas, it was higher in osteolytic metastases from lung cancer than that from thyroid cancer (7.05±3.01 vs. 4.11±2.67, p = 0.03).

Conclusion

^99mTc-3P-RGD₂ peptide imaging showed great potential for detection of osteolytic bone metastasis due to high expression level of integrin αvβ3 on osteoclast and most tumor cells.

Recent progress in development of siRNA delivery vehicles for cancer therapy

Recent progress in RNA biology has broadened the scope of therapeutic targets of RNA drugs for cancer therapy. However, RNA drugs, typically small interfering RNAs (siRNAs), are rapidly degraded by RNases and filtrated in the kidney, thereby requiring a delivery vehicle for efficient transport to the target cells. To date, various delivery formulations have been developed from cationic lipids, polymers, and/or inorganic nanoparticles for systemic delivery of siRNA to solid tumors. This review describes the current status of clinical trials related to siRNA-based cancer therapy, as well as the remaining issues that need to be overcome to establish a successful therapy. It, then introduces various promising design strategies of delivery vehicles for stable and targeted siRNA delivery, including the prospects for future design.

On the trail of the glycan codes stored in cancer-related cell adhesion proteins

Changes in the profile of protein glycosylation are a hallmark of ongoing neoplastic transformation. A unique set of tumor-associated carbohydrate antigens expressed on the surface of malignant cells may serve as powerful diagnostic and therapeutic targets. Cell-surface proteins with altered glycosylation affect the growth, proliferation and survival of those cells, and contribute to their acquisition of the ability to migrate and invade. They may also facilitate tumor-induced immunosuppression and the formation of distant metastases. Deciphering the information encoded in these particular glycan portions of glycoconjugates may shed light on the mechanisms of cancer progression and metastasis. A majority of the related review papers have focused on overall changes in the patterns of cell-surface glycans in various cancers, without pinpointing the molecular carriers of these glycan structures. The present review highlights the ways in which particular tumor-associated glycan(s) coupled with a given membrane-bound protein influence neoplastic cell behavior during the development and progression of cancer. We focus on altered glycosylated cell-adhesion molecules belonging to the cadherin, integrin and immunoglobulin-like superfamilies, examined in the context of molecular interactions.

pH-Switch Nanoprecipitation of Polymeric Nanoparticles for Multimodal Cancer Targeting and Intracellular Triggered Delivery of Doxorubicin

Theranostic nanoparticles are emerging as potent tools for noninvasive diagnosis, treatment, and monitoring of solid tumors. Herein, an advanced targeted and multistimuli responsive theranostic platform is presented for the intracellular triggered delivery of doxorubicin. The system consists of a polymeric-drug conjugate solid nanoparticle containing encapsulated superparamagnetic iron oxide nanoparticles (IO@PNP) and decorated with a tumor homing peptide, iRGD. The production of this nanosystem is based on a pH-switch nanoprecipitation method in organic-free solvents, making it ideal for biomedical applications. The nanosystem shows sufficient magnetization saturation for magnetically guided therapy along with reduced cytotoxicity and hemolytic effects. IO@PNP are largely internalized by endothelial and metastatic cancer cells and iRGD decorated IO@PNP moderately enhance their internalization into endothelial cells, while no enhancement is found for the metastatic cancer cells. Poly(ethylene glycol)-block-poly(histidine) with pH-responsive and proton-sponge properties promotes prompt lysosomal escape once the nanoparticles are endocyted. In addition, the polymer-doxorubicin conjugate solid nanoparticles show both intracellular lysosomal escape and efficient translocation of doxorubicin to the nuclei of the cells via cleavage of the amide bond. Overall, IO@PNP-doxorubicin and the iRGD decorated counterpart demonstrate to enhance the toxicity of doxorubicin in cancer cells by improving the intracellular delivery of the drug carried in the IO@PNP.

Designing Peptide Bunches on Nanocage for Bispecific or Superaffinity Targeting

Ferritin cage nanoparticles are promising platforms for targeted delivery of imaging and therapeutic agents because their cage structure can accommodate small molecules and their surfaces can be decorated with multiple functionalities. However, selective targeting is still a challenge for translating ferritin-based nanomedicines into the clinic, especially for heterogeneous diseases such as cancer. Targeting peptides can be genetically fused onto the surface of a ferritin cage, forming peptide bunches on nanocages (PBNCs) that offer synergistic increases in binding avidity. Here, we utilized two sites of the ferritin monomer, the N-terminus and the loop between the fourth and fifth helices, which are exposed on the surface of the assembled 24-subunit ferritin cage, to ligate one or two types of peptides to achieve "super affinity" and bispecificity, respectively. PBNCs formed by ligation of the IL-4 receptor-targeting peptide, AP1, to both sites (48AP1-PBNCs) tethered IL-4R, expressing tumor cells with greater affinity than did PBNCs with AP1 ligated to a single site (24AP1-PBNCs). Moreover, bispecific PBNCs containing 24 RGD peptides and 24 AP1 peptides (24RGD/24AP1-PBNCs) were capable of independently targeting cells expressing the corresponding receptors. Bispecific and superaffinity PBNCs could be useful for efficient targeting of ferritin-based therapeutic/diagnostic agents in a clinical setting.

177Lu-labeled carbon nanospheres: a new entry in the field of targeted radionanomedicine

¹⁷⁷Lu-labeled carbon nanospheres loaded with cRGDfK peptide have been developed as radionanoprobes with favorable pharmacokinetics for integrin α_vβ₃-mediated active targeting.

A new insight into viral proteins as Immunomodulatory therapeutic agents: KSHV vOX2 a homolog of human CD200 as a potent anti-inflammatory protein

The physiologic function of the immune system is defense against infectious microbes and internal tumour cells, Therefore, need to have precise modulatory mechanisms to maintain the body homeostasis. The mammalian cellular CD200 (OX2)/CD200R interaction is one of such modulatory mechanisms in which myeloid and lymphoid cells are regulated. CD200 and CD200R molecules are membrane proteins that their immunomodulatory effects are able to suppress inflammatory responses, particularly in the privilege sites such as CNS and eyes. Kaposi's sarcoma-associated herpesvirus (KSHV), encodes a wide variety of immunoregulatory proteins which play central roles in modulating inflammatory and anti-inflammatory responses in favour of virus dissemination. One such protein is a homologue of the, encoded by open reading frame (ORF) K14 and therefore called vOX2. Based on its gene expression profile during the KSHV life cycle, it is hypothesised that vOX2 modulates host inflammatory responses. Moreover, it seems that vOX2 involves in cell adhesion and modulates innate immunity and promotes Th2 immune responses. In this review the activities of mammalian CD200 and KSHV CD200 in cell adhesion and immune system modulation are reviewed in the context of potential therapeutic agents.

miR-138-Mediated Regulation of KINDLIN-2 Expression Modulates Sensitivity to Chemotherapeutics

Prostate cancer is the second leading cause of cancer-related death in men, second only to lung cancer, mainly due to disease reoccurrence as a result to lack of response to androgen deprivation therapies (ADT) after castration. Patients with metastatic castration-resistant prostate cancer (mCRPC) have very limited treatment options, with docetaxel as the first-line standard of care, for which resistance to this chemotherapeutic ultimately develops. Therefore, finding ways to sensitize tumors to chemotherapies and to limit chemoresistance provides a viable strategy to extend the survival of mCRPC patients. This study investigated the role of Kindlin-2 (FERMT2/K2), a member of the Kindlin family of FERM domain proteins and key regulators of the adhesive functions mediated by integrin, in the sensitization of mCRPC to chemotherapeutics. Loss of K2, which is overexpressed in prostate cancer cells derived from mCRPC tumors, compared with those cells derived from androgen-dependent tumors, significantly enhanced apoptosis and cell death of docetaxel-treated PC3 cells. Furthermore, it was determined that K2-mediated sensitization to docetaxel treatment is the result of inhibition of β1-integrin signaling. Finally, miR-138 specifically targeted K2 and inhibited its expression, thereby regulating a miR-138/K2/β1-integrin signaling axis in mCRPC that is critical for the modulation of sensitivity to chemotherapeutics. Thus, these data identify a novel signaling axis where K2 in combination with chemotherapeutics provides a new target for the treatment of mCRPC.

IMPLICATIONS

Targeted inhibition of Kindlin-2 in combination with chemotherapy represents an effective treatment option for mCRPC.

The Impact of Aspect Ratio on the Biodistribution and Tumor Homing of Rigid Soft-Matter Nanorods

The size and shape of nanocarriers can affect their fate in vivo, but little is known about the effect of nanocarrier aspect ratio on biodistribution in the setting of cancer imaging and drug delivery. The production of nanoscale anisotropic materials is a technical challenge. A unique biotemplating approach based on of rod-shaped nucleoprotein nanoparticles with predetermined aspect ratios (AR 3.5, 7, and 16.5) is used. These rigid, soft-matter nanoassemblies are derived from tobacco mosaic virus (TMV) components. The role of nanoparticle aspect ratio is investigated, while keeping the surface chemistries constant, using either PEGylated stealth nanoparticles or receptor-targeted RGD-displaying formulations. Aspect ratio has a profound impact on the behavior of the nanoparticles in vivo and in vitro. PEGylated nanorods with the lowest aspect ratio (AR 3.5) achieve the most efficient passive tumor-homing behavior because they can diffuse most easily, whereas RGD-labeled particles with a medium aspect ratio (AR 7) are more efficient at tumor targeting because this requires a balance between infusibility and ligand-receptor interactions. The in vivo behavior of nanoparticles can therefore be tailored to control biodistribution, longevity, and tumor penetration by modulating a single parameter: the aspect ratio of the nanocarrier.

To Target or Not to Target: Active vs. Passive Tumor Homing of Filamentous Nanoparticles Based on Potato virus X

Nanoparticles are promising platforms for the diagnosis and treatment of cancer. Diverse classes and shapes of materials have been investigated to establish design principles that achieve the effective partitioning of medical cargos between tumors and healthy tissues. Molecular targeting strategies combined with specific nanoparticle shapes confer tissue-specificity on the carriers, allowing the cell-specific delivery of cargos. We recently developed a filamentous platform technology in which the plant virus Potato virus X (PVX) was used as a scaffold. These particles are flexible 515 × 13 nm filaments that encourage passive tumor homing. Here we sought to advance the PVX platform by including a molecular targeting strategy based on cyclic RGD peptides, which specifically bind to integrins upregulated on tumor cells, neovasculature, and metastatic sites. Although the RGD-targeted filaments outperformed the PEGylated stealth filaments in vitro, enhanced tumor cell targeting did not translate into improved tumor homing in vivo in mouse tumor models. The RGD-PVX and PEG-PVX filaments showed contrasting biodistribution profiles. Both formulations were cleared by the liver and spleen, but only the stealth filaments accumulated in tumors, whereas the RGD-targeted filaments were sequestered in the lungs. These results provide insight into the design principles for virus-based nanoparticles that promote the delivery of medical cargos to the appropriate cell types.

RGD peptide conjugated liposomal drug delivery system for enhance therapeutic efficacy in treating bone metastasis from prostate cancer

Targeting αvβ3 integrin is particularly promising for the treatment of bone metastases by targeting integrin-rich tumor cells and by inhibiting integrin-involved bone metastases. In this work, a liposomal drug delivery system conjugated with cyclic arginine-glycine-aspartic acid-tyrosine-lysine peptide (cRGDyk) as αvβ3 integrin ligand was thus developed to improve therapeutic efficacy in a mice model of bone metastasis from prostate cancer. The resultant liposomes were characterized in terms of size, morphology, zeta potential, stability, drug encapsulation percentage and loading efficiency, and drug release. Compared with free cisplatin and cRGDyk-free liposomes, cRGDyk conjugated liposomes showed significantly higher cellular uptake and higher cytotoxicity of loaded cisplatin, as evidenced by in vitro cell experiments. In vivo results revealed that free cisplatin and free cRGDyk could relieve tumor-induced pain but had no contributions to tumor regression and overall survival improvement. cRGDyk-free liposomal drug system with prolonged blood circulation time could accumulated in the tumor sites in the bone through enhanced permeability and retention (EPR) effects and however, did not exhibit desirable therapeutic efficacy superior to free cisplatin and free cRGDyk. This strongly suggested that ERP effects were not effective in treating metastases. By taking advantages of targeted drug delivery and synergistic antitumor activity of cRGDyk and loaded cisplatin, cRGDyk conjugated liposomal drug system could inhibit osteoclastic and osteoblastic bone lesions, relieve pain, and improve overall survival. Inspired by their enhanced therapeutic efficacy and low organ toxicity, cRGDyk conjugated liposomes could serve as an effective drug system for targeted and synergistic therapy of bone metastases.

Characterization and evaluation of DOTA-conjugated Bombesin/RGD-antagonists for prostate cancer tumor imaging and therapy

INTRODUCTION

Here we present the metallation, characterization, in vivo and in vitro evaluations of dual-targeting, peptide-based radiopharmaceuticals with utility for imaging and potentially treating prostate tumors by virtue of their ability to target the αVβ3 integrin or the gastrin releasing peptide receptor (GRPr).

METHODS

[RGD-Glu-6Ahx-RM2] (RGD: Arg-Gly-Asp; Glu: glutamic acid; 6-Ahx: 6-amino hexanoic acid; RM2: (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2)) was conjugated to a DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) bifunctional chelator (BFCA) purified via reversed-phase high-performance liquid chromatography (RP-HPLC), characterized by electrospray ionization-mass spectrometry (ESI-MS), and radiolabeled with (111)In or (177)Lu. Natural-metallated compounds were assessed for binding affinity for the αVβ3 integrin or GRPr in human glioblastoma U87-MG and prostate PC-3 cell lines and stability prior to in vivo evaluation in normal CF-1 mice and SCID mice xenografted with PC-3 cells.

RESULTS

Competitive displacement binding assays with PC-3 and U87-MG cells revealed high to moderate binding affinity for the GRPr or the αVβ3 integrin (IC50 range of 5.39±1.37 nM to 9.26±0.00 nM in PC-3 cells, and a range of 255±47 nM to 321±85 nM in U87-MG cells). Biodistribution studies indicated high tumor uptake in PC-3 tumor-bearing mice (average of 7.40±0.53% ID/g at 1h post-intravenous injection) and prolonged retention of tracer (mean of 4.41±0.91% ID/g at 24h post-intravenous injection). Blocking assays corroborated the specificity of radioconjugates for each target. Micro-single photon emission computed tomography (microSPECT) confirmed favorable radiouptake profiles in xenografted mice at 20h post-injection.

CONCLUSIONS

[RGD-Glu-[(111)In-DO3A]-6-Ahx-RM2] and [RGD-Glu-[(177)Lu- DO3A]-6-Ahx-RM2] show favorable pharmacokinetic and radiouptake profiles, meriting continued evaluation for molecular imaging in murine U87-MG/PC-3 xenograft models and radiotherapy studies with (177)Lu and (90)Y conjugates.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

These heterovalent, peptide-targeting ligands perform comparably with many mono- and multivalent conjugates with the potential benefit of increased sensitivity for detecting cancer cells exhibiting differential expression of target receptors.

Peptides used in the delivery of small noncoding RNA

RNA interference (RNAi) is an endogenous process in which small noncoding RNAs, including small interfering RNAs (siRNAs) and microRNAs (miRNAs), post-transcriptionally regulate gene expressions. In general, siRNA and miRNA/miRNA mimics are similar in nature and activity except their origin and specificity. Although both siRNAs and miRNAs have been extensively studied as novel therapeutics for a wide range of diseases, the large molecular weight, anionic surface charges, instability in blood circulation, and intracellular trafficking to the RISC after cellular uptake have hindered the translation of these RNAs from bench to clinic. As a result, a great variety of delivery systems have been investigated for safe and effective delivery of small noncoding RNAs. Among these systems, peptides, especially cationic peptides, have emerged as a promising type of carrier due to their inherent ability to condense negatively charged RNAs, ease of synthesis, controllable size, and tunable structure. In this review, we will focus on three major types of cationic peptides, including poly(l-lysine) (PLL), protamine, and cell penetrating peptides (CPP), as well as peptide targeting ligands that have been extensively used in RNA delivery. The delivery strategies, applications, and limitations of these cationic peptides in siRNA/miRNA delivery will be discussed.

Prostate cancer relevant antigens and enzymes for targeted drug delivery

Chemotherapy is one of the most widely used approaches in combating advanced prostate cancer, but its therapeutic efficacy is usually insufficient due to poor specificity and associated toxicity. Lack of targeted delivery to prostate cancer cells is also the primary obstacles in achieving feasible therapeutic effect of other promising agents including peptide, protein, and nucleic acid. Consequently, there remains a critical need for strategies to increase the selectivity of anti-prostate cancer agents. This review will focus on various prostate cancer-relevant antigens and enzymes that could be exploited for prostate cancer targeted drug delivery. Among various targeting strategies, active targeting is the most advanced approach to specifically deliver drugs to their designated cancer cells. In this approach, drug carriers are modified with targeting ligands that can specifically bind to prostate cancer-specific antigens. Moreover, there are several specific enzymes in the tumor microenvironment of prostate cancer that can be exploited for stimulus-responsive drug delivery systems. These systems can specifically release the active drug in the tumor microenvironment of prostate cancer, leading to enhanced tumor penetration efficiency.

A heterodimeric [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] αvβ3/GRPr-targeting antagonist radiotracer for PET imaging of prostate tumors

INTRODUCTION

In the present study, we describe a (64)Cu-radiolabeled heterodimeric peptide conjugate for dual αvβ3/GRPr (αvβ3 integrin/gastrin releasing peptide receptor) targeting of the form [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] (RGD: the amino acid sequence [Arg-Gly-Asp], a nonregulatory peptide used for αvβ3 integrin receptor targeting; Glu: glutamic acid; NO2A: 1,4,7-triazacyclononane-1,4-diacetic acid; 6-Ahx: 6-amino hexanoic acid; and RM2: (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2), an antagonist analogue of bombesin (BBN) peptide used for GRPr targeting).

METHODS

RGD-Glu-6Ahx-RM2] was conjugated to a NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) complexing agent to produce [RGD-Glu-[NO2A]-6-Ahx-RM2], which was purified by reversed-phase high-performance liquid chromatography (RP-HPLC) and characterized by electrospray ionization-mass spectrometry (ESI-MS). Radiolabeling of the conjugate with (64)Cu produced [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2 in high radiochemical yield (≥95%). In vivo behavior of the radiolabeled peptide conjugate was investigated in normal CF-1 mice and in the PC-3 human prostate cancer experimental model.

RESULTS

A competitive displacement receptor binding assay in human prostate PC-3 cells using (125)I-[Tyr(4)]BBN as the radioligand showed high binding affinity of [RGD-Glu-[(nat)Cu-NO2A]-6-Ahx-RM2] conjugate for the GRPr (3.09±0.34 nM). A similar assay in human, glioblastoma U87-MG cells using (125)I-Echistatin as the radioligand indicated a moderate receptor-binding affinity for the αvβ3 integrin (518±37.5 nM). In vivo studies of [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] showed high accumulation (4.86±1.01 %ID/g, 1h post-intravenous injection (p.i.)) and prolonged retention (4.26±1.23 %ID/g, 24h p.i.) of tracer in PC-3 tumor-bearing mice. Micro-positron emission tomography (microPET) molecular imaging studies produced high-quality, high contrast images in PC-3 tumor-bearing mice at 4h p.i.

CONCLUSIONS

The favorable pharmacokinetics and enhanced tumor uptake of (64)Cu-NOTA-RGD-Glu-6Ahx-RM2 warrant further investigations for dual integrin and GRPr-positive tumor imaging and possible radiotherapy.