Tumor targeting with a selective gelatinase inhibitor

[Advances in the molecular mechanisms of perineural invasion in salivary adenoid cystic carcinoma]

Salivary adenoid cystic carcinoma is a very common malignant neoplasm in the salivary glands. One of the most important features of salivary cystic carcinoma is perineural invasion, which renders its complete removal is very difficult through clinical surgery. Consequently, tumor recurrence occurs easily after clinical surgery. Therefore, the molecular mechanisms of perineural invasion in salivary adenoid cystic carcinoma are necessary to explore. These mechanisms are reviewed in this paper.

Application of Bld-1-Embedded Elastin-Like Polypeptides in Tumor Targeting

Expression of various molecules on the surface of cancer cells compared to normal cells creates a platform for the generation of various drug vehicles for targeted therapy. Multiple interactions between ligands and their receptors mediated by targeting peptide-modified polymer could enable simultaneous delivery of a drug selectively to target tumor cells, thus limiting side effects resulting from non-specific drug delivery. In this study, we synthesized a novel tumor targeting system by using two key elements: (1) Bld-1 peptide (SNRDARRC), a recently reported bladder tumor targeting peptide identified by using a phage-displayed peptide library, and (2) ELP, a thermally responsive polypeptide. B5V60 containing five Bld-1 peptides and non-targeted ELP77 with a thermal phase-transition over 37 °C were analyzed to determine their bioactivities. Further studies confirmed the superior binding ability of B5V60 to bladder tumor cells and the cellular accumulation of B5V60 in cancer cells was dependent on the expression level of sialyl-Tn antigen (STn), a tumor-associated carbohydrate antigen. Additionally, B5V60 displayed excellent localization in bladder tumor xenograft mice after intravenous injection and was strictly confined to sialyl-Tn antigen-overexpressing tumor tissue. Thus, our newly designed B5V60 showed high potential as a novel carrier for STn-specific targeted cancer therapy or other therapeutic applications.

Nanoplatform Assembled from a CD44-Targeted Prodrug and Smart Liposomes for Dual Targeting of Tumor Microenvironment and Cancer Cells

The tumor microenvironment (TME) plays a critical role in tumor initiation, progression, invasion, and metastasis. Therefore, a therapy that combines chemotherapeutic drugs with a TME modulator could be a promising route for cancer treatment. This paper reports a nanoplatform self-assembled from a hyaluronic acid (HA)-paclitaxel (PTX) (HA-PTX) prodrug and marimastat (MATT)-loaded thermosensitive liposomes (LTSLs) (MATT-LTSLs) for the dual targeting of the TME and cancer cells. Interestingly, the prodrug HA-PTX can self-assemble on both positively and negatively charged liposomes, forming hybrid nanoparticles (HNPs, 100 nm). Triggered by mild hyperthermia, HA-PTX/MATT-LTSLs HNPs rapidly release their payloads into the extracellular environment, and the released HA-PTX quickly enters 4T1 cells through a CD44-HA affinity. The HNPs possess promoted tumor accumulation (1.6-fold), exhibit deep tumor penetration, and significantly inhibit the tumor growth (10-fold), metastasis (100%), and angiogenesis (10-fold). Importantly, by targeting the TME and maintaining its integrity via inhibiting the expression and activity of matrix metalloproteinases (>5-fold), blocking the fibroblast activation by downregulating the TGF-β1 expression (5-fold) and suppressing the degradation of extracellular matrix, the HNPs allow for significant metastasis inhibition. Overall, these findings indicate that a prodrug of an HA-hydrophobic-active compound and liposomes can be self-assembled into a smart nanoplatform for the dual targeting of the TME and tumor cells and efficient combined treatment; additionally, the co-delivery of MATT and HA-PTX with the HNPs is a promising approach for the treatment of metastatic cancer. This study creates opportunities for fabricating multifunctional nanodevices and offers an efficient strategy for disease therapy.

Recent opportunities in matrix metalloproteinase inhibitor drug design for cancer

INTRODUCTION

The overexpression of matrix metalloproteinase (MMP) plays an important role in the context of tumor invasion and metastasis, and MMP-2 has been characterized as the most validated target for cancer. Therefore, it is necessary to design matrix metalloproteinase inhibitors (MMPIs) that would be active and selective against MMP-2 but non-selective toward other MMPs. Areas covered: This article clearly describes the structural character of MMP-2 followed by a review of the recent development of selective MMP-2 inhibitors based on their basic structures. Expert opinion: Over the past 30 years, MMPs have been considered to be attractive cancer targets, and several different types of synthetic inhibitors have been identified as anticancer agents, but only a small number of small MMPIs have been examined in clinical trials, and none of these molecules has been established as anticancer drugs due to their adverse effects. One major possibility is that the MMPIs used in clinical trials were broad-spectrum drugs that also inhibited the anti-tumor effects and influenced the mediation of the normal physiological processes of MMPs. MMP-2 has recently been characterized as the most validated target for cancer. Therefore, the design and synthesis of selective MMP-2 inhibitors would be helpful for the treatment of cancer.

HGF potentiates extracellular matrix-driven migration of human myoblasts: involvement of matrix metalloproteinases and MAPK/ERK pathway

Background

The hepatocyte growth factor (HGF) is required for the activation of muscle progenitor cells called satellite cells (SC), plays a role in the migration of proliferating SC (myoblasts), and is present as a soluble factor during muscle regeneration, along with extracellular matrix (ECM) molecules. In this study, we aimed at determining whether HGF is able to interact with ECM proteins, particularly laminin 111 and fibronectin, and to modulate human myoblast migration.

Methods

We evaluated the expression of the HGF-receptor c-Met, laminin, and fibronectin receptors by immunoblotting, flow cytometry, or immunofluorescence and used Transwell assays to analyze myoblast migration on laminin 111 and fibronectin in the absence or presence of HGF. Zymography was used to check whether HGF could modulate the production of matrix metalloproteinases by human myoblasts, and the activation of MAPK/ERK pathways was evaluated by immunoblotting.

Results

We demonstrated that human myoblasts express c-Met, together with laminin and fibronectin receptors. We observed that human laminin 111 and fibronectin have a chemotactic effect on myoblast migration, and this was synergistically increased when low doses of HGF were added. We detected an increase in MMP-2 activity in myoblasts treated with HGF. Conversely, MMP-2 inhibition decreased the HGF-associated stimulation of cell migration triggered by laminin or fibronectin. HGF treatment also induced in human myoblasts activation of MAPK/ERK pathways, whose specific inhibition decreased the HGF-associated stimulus of cell migration triggered by laminin 111 or fibronectin.

Conclusions

We demonstrate that HGF induces ERK phosphorylation and MMP production, thus stimulating human myoblast migration on ECM molecules. Conceptually, these data state that the mechanisms involved in the migration of human myoblasts comprise both soluble and insoluble moieties. This should be taken into account to optimize the design of therapeutic cell transplantation strategies by improving the migration of donor cells within the host tissue, a main issue regarding this approach.

Electronic supplementary material

The online version of this article (10.1186/s13395-017-0138-6) contains supplementary material, which is available to authorized users.

Seek & Destroy, use of targeting peptides for cancer detection and drug delivery

Accounting for 16 million new cases and 9 million deaths annually, cancer leaves a great number of patients helpless. It is a complex disease and still a major challenge for the scientific and medical communities. The efficacy of conventional chemotherapies is often poor and patients suffer from off-target effects. Each neoplasm exhibits molecular signatures - sometimes in a patient specific manner - that may completely differ from the organ of origin, may be expressed in markedly higher amounts and/or in different location compared to the normal tissue. Although adding layers of complexity in the understanding of cancer biology, this cancer-specific signature provides an opportunity to develop targeting agents for early detection, diagnosis, and therapeutics. Chimeric antibodies, recombinant proteins or synthetic polypeptides have emerged as excellent candidates for specific homing to peripheral and central nervous system cancers. Specifically, peptide ligands benefit from their small size, easy and affordable production, high specificity, and remarkable flexibility regarding their sequence and conjugation possibilities. Coupled to imaging agents, chemotherapies and/or nanocarriers they have shown to increase the on-site delivery, thus allowing better tumor mass contouring in imaging and increased efficacy of the chemotherapies associated with reduced adverse effects. Therefore, some of the peptides alone or in combination have been tested in clinical trials to treat patients. Peptides have been well-tolerated and shown absence of toxicity. This review aims to offer a view on tumor targeting peptides that are either derived from natural peptide ligands or identified using phage display screening. We also include examples of peptides targeting the high-grade malignant tumors of the central nervous system as an example of the complex therapeutic management due to the tumor's location. Peptide vaccines are outside of the scope of this review.

Sustained Release of a Peptide-Based Matrix Metalloproteinase-2 Inhibitor to Attenuate Adverse Cardiac Remodeling and Improve Cardiac Function Following Myocardial Infarction

Following myocardial infarction (MI), degradation of extracellular matrix (ECM) by upregulated matrix metalloproteinases (MMPs) especially MMP-2 decreases tissue mechanical properties, leading to cardiac function deterioration. Attenuation of cardiac ECM degradation at the early stage of MI has the potential to preserve tissue mechanical properties, resulting in cardiac function increase. Yet the strategy for efficiently preventing cardiac ECM degradation remains to be established. Current preclinical approaches have shown limited efficacy because of low drug dosage allocated to the heart tissue, dose-limiting side effects, and cardiac fibrosis. To address these limitations, we have developed a MMP-2 inhibitor delivery system that can be specifically delivered into infarcted hearts at early stage of MI to efficiently prevent MMP-2-mediated ECM degradation. The system was based on an injectable, degradable, fast gelation, and thermosensitive hydrogel, and a MMP-2 specific inhibitor, peptide CTTHWGFTLC (CTT). The use of fast gelation hydrogel allowed to completely retain CTT in the heart tissue. The system was able to release low molecular weight CTT over 4 weeks possibly due to the strong hydrogen bonding between the hydrogel and CTT. The release kinetics was modulated by amount of CTT loaded into the hydrogel, and using chondroitin sulfate and heparin that can interact with CTT and the hydrogel. Both glycosaminoglycans augmented CTT release, while heparin more greatly accelerated the release. After it was injected into the infarcted hearts for 4 weeks, the released CTT efficiently prevented cardiac ECM degradation as it not only increased tissue thickness but also preserved collagen composition similar to that in the normal heart tissue. In addition, the delivery system significantly improved cardiac function. Importantly, the delivery system did not induce cardiac fibrosis. These results demonstrate that the developed MMP-2 inhibitor delivery system has potential to efficiently reduce adverse myocardial remodeling and improve cardiac function.

Vascular-homing peptides for cancer therapy

In the past 30 years, a variety of phage libraries have been extensively utilized to identify and develop tumor homing peptides (THPs). THPs specifically bind to tumor cells or elements of the tumor microenvironment while no or low affinity to normal cells. In this regard, the efficacy of therapeutic agents in cancer therapy can be enhanced by targeting strategies based on coupling with THPs that recognize receptors expressed by tumor cells or tumor vasculature. Especially, vascular-homing peptides, targeting tumor vasculature, have their receptors expressed on or around the blood vessel including pro-angiogenic factors, metalloproteinase, integrins, fibrin-fibronectin complexes, etc. This review briefly summarizes recent studies on identification and therapeutic applications of vascular-homing peptides targeting common angiogenic markers or with unknown vascular targets in some certain types of cancers. These newly discovered vascular-homing peptides are promising candidates which could provide novel strategies for cancer therapy.

Tumor Microenvironment Targeting and Responsive Peptide-Based Nanoformulations for Improved Tumor Therapy

The tumor microenvironment participates in all stages of tumor progression and has emerged as a promising therapeutic target for cancer therapy. Rapid progress in the field of molecular self-assembly using various biologic molecules has resulted in the fabrication of nanoformulations that specifically target and regulate microenvironment components to inhibit tumor growth. This inhibition process is based on differentiating between biophysicochemical cues guiding tumor and normal tissue microenvironments. Peptides and peptide derivatives, owing to their biocompatibility, chemical versatility, bioactivity, environmental sensitivity, and biologic recognition abilities, have been widely used as building blocks to construct multifunctional nanostructures for targeted drug delivery and controlled release. Several groups of peptides have been identified as having the ability to penetrate plasma membranes, regulate the essential signaling pathways of angiogenesis and immune reactions, and recognize key components in the tumor microenvironment (such as vascular systems, stromal cells, and abnormal tumor biophysicochemical features). Thus, using different modules, various functional peptides, and their derivatives can be integrated into nanoformulations specifically targeting the tumor microenvironment with increased selectivity, on-demand response, elevated cellular uptake, and improved tumor therapy. In this review, we introduce several groups of functional peptides and highlight peptide-based nanoformulations that specifically target the tumor microenvironment. We also provide our perspective on the development of smart drug-delivery systems with enhanced therapeutic efficacy.

High-Throughput Approaches to the Development of Molecular Imaging Agents

Molecular imaging allows for the visualization of changes at the cellular level in diseases such as cancer. A successful molecular imaging agent must rely on disease-selective targets and ligands that specifically interact with those targets. Unfortunately, the translation of novel target-specific ligands into the clinic has been frustratingly slow with limitations including the complex design and screening approaches for ligand identification, as well as their subsequent optimization into useful imaging agents. This review focuses on combinatorial library approaches towards addressing these two challenges, with particular focus on phage display and one-bead one-compound (OBOC) libraries. Both of these peptide-based techniques have proven successful in identifying new ligands for cancer-specific targets and some of the success stories will be highlighted. New developments in screening methodology and sequencing technology have pushed the bounds of phage display and OBOC even further, allowing for even faster and more robust discovery of novel ligands. The combination of multiple high-throughput technologies will not only allow for more accurate identification, but also faster affinity maturation, while overall streamlining the process of translating novel ligands into clinical imaging agents.

Tumor-targeting peptides from combinatorial libraries

Cancer is one of the major and leading causes of death worldwide. Two of the greatest challenges in fighting cancer are early detection and effective treatments with no or minimum side effects. Widespread use of targeted therapies and molecular imaging in clinics requires high affinity, tumor-specific agents as effective targeting vehicles to deliver therapeutics and imaging probes to the primary or metastatic tumor sites. Combinatorial libraries such as phage-display and one-bead one-compound (OBOC) peptide libraries are powerful approaches in discovering tumor-targeting peptides. This review gives an overview of different combinatorial library technologies that have been used for the discovery of tumor-targeting peptides. Examples of tumor-targeting peptides identified from each combinatorial library method will be discussed. Published tumor-targeting peptide ligands and their applications will also be summarized by the combinatorial library methods and their corresponding binding receptors.

Matrix-metalloproteinases as targets for controlled delivery in cancer: An analysis of upregulation and expression

While commonly known for degradation of the extracellular matrix, matrix metalloproteinases (MMPs) exhibit broad potential for use in targeting of bioactive and imaging agents in cancer treatment. MMPs are upregulated at all stages of expression in cancers. A comprehensive analysis of published literature on expression of all MMP subtypes at the genetic, protein, and activity levels in normal and diseased tissues indicate targeting applicability in a variety of cancers. This expression significantly increases at advanced cancer stages, providing an improved opportunity for controlled release in higher-stage patients. Since MMPs are integral at every stage of metastasis, MMP roles in cancer are discussed with a focus on MMP distribution and mobility within cells and tumors for cancer targeting applications. Several strategies for MMP utilization in targeting - such as matrix degradation, MMP cleavage, MMP binding, and MMP-induced environmental changes - are addressed.

Short peptides interfering with signaling pathways as new therapeutic tools for cancer treatment

Short peptides have many advantages, such as low molecular weight, selectivity for a specific target, organelles or cells with minimal toxicity. We describe properties of short peptides, which interfere with communication networks in tumor cells and within microenvironment of malignant gliomas, the most common brain tumors. We focus on ligand/receptor axes and intracellular signaling pathways critical for gliomagenesis that could be targeted with interfering peptides. We review structures and efficacy of organelle-specific and cell-penetrating peptides and describe diverse chemical modifications increasing proteolytic stability and protecting synthetic peptides against degradation. We report results of application of short peptides in glioma therapy clinical trials, their rises and falls. The most advanced examples of therapeutics such as short interfering peptides combined with cell-penetrating peptides that show good effectiveness in disease models are presented. It is foreseen that identification of peptides with better clinical properties may improve their success rates in clinical trials.

Zymography as a Research Tool in the Study of Matrix Metalloproteinase Inhibitors

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade various components of the extracellular matrix (ECM) and play a role in tissue remodeling. Changes in MMPs have been observed in cancer, connective tissue disorders, and vascular disease, and both endogenous tissue inhibitors of MMPs (TIMPs) and synthetic MMP inhibitors (MMPIs) have been evaluated as modulators of MMP activity in various biological systems. Zymography is a simple technique that is commonly used to assess MMP activity and the efficacy of MMPIs. Also, reverse zymography is a modified technique to study the activity of endogenous TIMPs. However, problems are often encountered during the zymography procedure, which could interfere with accurate assessment of MMP activity in control specimens, and thus make it difficult to determine the pathological changes in MMPs and their responsiveness to MMPIs. Simplified protocols for preparation of experimental solutions, tissue preparation, regular and reverse zymography procedures, and zymogram analysis are presented. Additional helpful tips to troubleshoot problems in the zymography technique and to enhance the quality of the zymograms should make it more feasible to determine the changes in MMPs and assess the efficacy of MMPIs in modulating MMP activity in various biological systems and pathological conditions.

Generation of inhibitory monoclonal antibodies targeting matrix metalloproteinase-14 by motif grafting and CDR optimization

Matrix metalloproteinase-14 (MMP-14) plays important roles in cancer metastasis, and the failures of broad-spectrum MMP compound inhibitors in clinical trials suggested selectivity is critical. By grafting an MMP-14 specific inhibition motif into complementarity determining region (CDR)-H3 of antibody scaffolds and optimizing other CDRs and the sequences that flank CDR-H3, we isolated a Fab 1F8 showing a binding affinity of 8.3 nM with >1000-fold enhancement on inhibition potency compared to the peptide inhibitor. Yeast surface display and fluorescence-activated cell sorting results indicated that 1F8 was highly selective to MMP-14 and competed with TIMP-2 on binding to the catalytic domain of MMP-14. Converting a low-affinity peptide inhibitor into a high potency antibody, the described methods can be used to develop other inhibitory antibodies of therapeutic significance.

Ligand-targeted theranostic nanomedicines against cancer

Nanomedicines have significant potential for cancer treatment. Although the majority of nanomedicines currently tested in clinical trials utilize simple, biocompatible liposome-based nanocarriers, their widespread use is limited by non-specificity and low target site concentration and thus, do not provide a substantial clinical advantage over conventional, systemic chemotherapy. In the past 20years, we have identified specific receptors expressed on the surfaces of tumor endothelial and perivascular cells, tumor cells, the extracellular matrix and stromal cells using combinatorial peptide libraries displayed on bacteriophage. These studies corroborate the notion that unique receptor proteins such as IL-11Rα, GRP78, EphA5, among others, are differentially overexpressed in tumors and present opportunities to deliver tumor-specific therapeutic drugs. By using peptides that bind to tumor-specific cell-surface receptors, therapeutic agents such as apoptotic peptides, suicide genes, imaging dyes or chemotherapeutics can be precisely and systemically delivered to reduce tumor growth in vivo, without harming healthy cells. Given the clinical applicability of peptide-based therapeutics, targeted delivery of nanocarriers loaded with therapeutic cargos seems plausible. We propose a modular design of a functionalized protocell in which a tumor-targeting moiety, such as a peptide or recombinant human antibody single chain variable fragment (scFv), is conjugated to a lipid bilayer surrounding a silica-based nanocarrier core containing a protected therapeutic cargo. The functionalized protocell can be tailored to a specific cancer subtype and treatment regimen by exchanging the tumor-targeting moiety and/or therapeutic cargo or used in combination to create unique, theranostic agents. In this review, we summarize the identification of tumor-specific receptors through combinatorial phage display technology and the use of antibody display selection to identify recombinant human scFvs against these tumor-specific receptors. We compare the characteristics of different types of simple and complex nanocarriers, and discuss potential types of therapeutic cargos and conjugation strategies. The modular design of functionalized protocells may improve the efficacy and safety of nanomedicines for future cancer therapy.

Peptidic Biomaterials: From Self-Assembling to Regenerative Medicine

Peptidic biomaterials represent a particularly exciting topic in regenerative medicine. Peptidic scaffolds can be specifically designed for biomimetic customization for targeted therapy. The field is at a pivotal point where preclinical research is being translated into clinics, so it is crucial to understand the theory and describe the status of this rapidly developing technology. In this review, we highlight major advantages and current limitations of self-assembling peptide-based biomaterials, and we discuss the most widely used classes of assembling peptides, describing recent and promising approaches in tissue engineering, drug delivery, and clinics. We also suggest design strategies and hurdles that still need to be overcome to fully exploit their therapeutic potential.

Mechanisms of Renal Vasodilation and Hyperfiltration During Pregnancy

Glomerular filtration rate (GFR) and renal plasma flow (RPF) increase by 40-65% and 50-85%, respectively, during normal pregnancy in women. Studies using the gravid rat as a model have greatly enhanced our understanding of mechanisms underlying these remarkable changes in the renal circulation during gestation. Hyperfiltration appears to be almost completely due to the increase in RPF, the latter attributable to profound reductions in both the renal afferent and efferent arteriolar resistances. The major pregnancy hormone involved is relaxin. The mediators downstream from relaxin include endothelin (ET) and nitric oxide (NO). New evidence indicates that relaxin increases vascular gelatinase activity during pregnancy, thereby converting big ET to ET(1-32), which leads to renal vasodilation, hyperfiltration, and reduced myogenic reactivity of small renal arteries via the endothelial ET(B) receptor and NO. Whether the chronic volume expansion characteristic of pregnancy contributes to the maintenance of gestational renal changes requires further investigation. Additional studies are also needed to further delineate the molecular basis of these mechanisms and, importantly, to investigate whether they apply to women.

Regulation and involvement of matrix metalloproteinases in vascular diseases

Matrix metalloproteinases (MMPs) are a family of zinc dependent endopeptidases whose main function is to degrade and deposit structural proteins within the extracellular matrix (ECM). A dysregulation of MMPs is linked to vascular diseases. MMPs are classified into collagenases, gelatinases, membrane-type, metalloelastase, stromelysins, matrilysins, enamelysins, and unclassified subgroups. The production of MMPs is stimulated by factors such as oxidative stress, growth factors and inflammation which lead to its up- or down-regulation with subsequent ECM remodeling. Normally, excess activation of MMPs is controlled by their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMPs). An imbalance of MMPs and TIMPs has been implicated in hypertension, atherosclerotic plaque formation and instability, aortic aneurysms and varicose vein wall remodeling. Also, recent evidence suggests epigenetic regulation of some MMPs in angiogenesis and atherosclerosis. Over the years, pharmacological inhibitors of MMPs have been used to modify or prevent the development of the disease with some success. In this review, we discuss recent advances in MMP biology, and their involvement in the manifestation of vascular disease.

Development of a Novel PET Tracer [18F]AlF-NOTA-C6 Targeting MMP2 for Tumor Imaging

Background and Objective

The overexpression of gelatinases, that is, matrix metalloproteinase MMP2 and MMP9, has been associated with tumor progression, invasion, and metastasis. To image MMP2 in tumors, we developed a novel ligand termed [¹⁸F]AlF-NOTA-C6, with consideration that: c(KAHWGFTLD)NH₂ (herein, C6) is a selective gelatinase inhibitor; Cy5.5-C6 has been visualized in many in vivo tumor models; positron emission tomography (PET) has a higher detection sensitivity and a wider field of view than optical imaging; fluorine-18 (¹⁸F) is the optimal PET radioisotope, and the creation of a [¹⁸F]AlF-peptide complex is a simple procedure.

Methods

C6 was conjugated to the bifunctional chelator NOTA (1, 4, 7-triazacyclononanetriacetic acid) for radiolabeling [¹⁸F]AlF conjugation. The MMP2-binding characteristics and tumor-targeting efficacy of [¹⁸F]AlF-NOTA-C6 were tested in vitro and in vivo.

Results

The non-decay corrected yield of [¹⁸F]AlF-NOTA-C6 was 46.2–64.2%, and the radiochemical purity exceeded 95%. [¹⁸F]AlF-NOTA-C6 was favorably retained in SKOV3 and PC3 cells, determined by cell uptake. Using NOTA-C6 as a competitive ligand, the uptake of [¹⁸F]AlF-NOTA-C6 in SKOV3 cells decreased in a dose-dependent manner. In biodistribution and PET imaging studies, higher radioactivity concentrations were observed in tumors. Pre-injection of C6 caused a marked reduction in tumor tissue uptake. Immunohistochemistry showed MMP2 in tumor tissues.

Conclusions

[¹⁸F]AlF-NOTA-C6 was easy to synthesize and has substantial potential as an imaging agent that targets MMP2 in tumors.

Role of Matrix Metalloproteinases 2 and 9 in Lacrimal Gland Disease in Animal Models of Sjögren's Syndrome

PURPOSE

Chronic inflammation of the lacrimal gland results in changes in the composition of the extracellular matrix (ECM), which is believed to compromise tissue repair. We hypothesized that increased production/activity of matrix metalloproteinases (MMPs), especially MMP-2 and -9, in inflamed lacrimal glands modifies the ECM environment, therefore disrupting tissue repair.

METHODS

The lacrimal glands from female MRL/lpr and male NOD mice along with their respective control strains were harvested and divided into three pieces and processed for histology, immunohistochemistry, zymography, Western blotting, and RNA analyses. In another study, MRL/lpr mice were treated for 5 weeks with a selective MMP2/9 inhibitor peptide or a control peptide. At the end of treatment, the lacrimal glands were excised and the tissue was processed as described above.

RESULTS

There was a 2.5- and 2.7-fold increase in MMP2 gene expression levels in MRL/lpr and NOD mice, respectively. Matrix metalloproteinase 2 and 9 enzymatic activities and protein expression levels were significantly upregulated in the lacrimal glands of MRL/lpr and NOD mice compared to controls. Treatment with the MMP2/9 inhibitor resulted in decreased activity of MMP-2 and -9 both in vitro and in vivo. Importantly, MMP2/9 inhibitor treatment of MRL/lpr mice improved aqueous tear production and resulted in reduced number and size of lymphocytic foci in diseased lacrimal glands.

CONCLUSIONS

We conclude that MMP2/9 expression and activity are elevated in lacrimal glands of two murine models of Sjögren's syndrome, suggesting that manipulation of MMP2/9 activity might be a potential therapeutic target in chronically inflamed lacrimal glands.

Amphipathic tail-anchoring peptide is a promising therapeutic agent for prostate cancer treatment

Amphipathic tail-anchoring peptide (ATAP) derived from the human anti-apoptotic protein Bfl-1 is a potent inducer of apoptosis by targeting mitochondria permeability transition. By linking ATAP to an internalizing RGD peptide (iRGD), selective targeting for ATAP to tumor cell was achieved. Confocal fluorescence microscopy showed that ATAP-iRGD could penetrate into cancer cells and distribute along the mitochondria network. ATAP-iRGD triggered mitochondria-dependent cell death through release of cytochrome c. In an effort to promote ATAP-iRGD physiochemical properties to approach clinic application, amino acid substitution and chemical modification were made with ATAP-iRGD to improve its bioactivity. One of these modified peptides, ATAP-iRGD-M8, was with improved stability and aqueous solubility without compromising in vitro cytotoxicity in cultured cancer cells. In vivo xenograft studies with multiple prostate cancer cell lines showed that intravenous administration of ATAP-iRGD-M8 suppressed tumor growth. Toxicological studies revealed that repetitive intravenous administration of ATAP-iRGD-M8 did not produce significant toxicity in the SV129 mice. Our data suggest that ATAP-iRGD-M8 is a promising agent with high selectivity and limited systemic toxicity for prostate cancer treatment.

Targeting of MMP2 activity in malignant tumors with a 68Ga-labeled gelatinase inhibitor cyclic peptide

INTRODUCTION

Elevated levels of gelatinases (matrix metalloproteinases 2/9, i.e., MMP2 and MMP9) are associated with tumor progression, invasion and metastasis, so these enzymes are potential targets for tumor imaging. The peptide c(KAHWGFTLD)NH2 (herein, C6) is a selective gelatinase inhibitor. Cy5.5-C6 has been visualized in many tumor models in vivo. However, the sensitivity and penetrance of optical imaging are poor. It is well known that positron emission tomography (PET) has a high detection sensitivity and Gallium-68 ((68)Ga) is an optimal PET radioisotope. Thus, in the present study, we developed a novel ligand, (68)Ga-NOTA-C6, to image MMP2 activity in tumors.

METHODS

C6 was conjugated with the bifunctional chelator NOTA (1,4,7-triazacyclononanetriacetic acid) and labeled with (68)Ga. In vitro uptake and binding analyses were performed by using SKOV3 cell lines, coincubating with or without the MMP inhibitor doxycycline. The biodistribution and PET imaging were conducted on SKOV3 ovarian tumor models. MMP2 expression in tumors was analyzed by immunohistochemistry (IHC).

RESULTS

The non-decay corrected yield of (68)Ga-NOTA-C6 was 61.8%-63.3%. (68)Ga-NOTA-C6 was stable in both physiological saline and human serum. The uptake of (68)Ga-NOTA-C6 in SKOV3 cells increased with time, and could be blocked by doxycycline in a dose dependent manner. The results of biodistribution and PET imaging showed that high radioactivity concentrations of (68)Ga-NOTA-C6 occurred in tumors. The ratios of tumor to blood, muscle and ovary and oviduct at 30, 60 and 120min p.i. were 2.78±0.54, 3.86±0.65, 0.48±0.14, and 1.73±0.36, 10.31±3.12, 1.22±0.10, and 2.50±0.78, 7.03±1.85, 0.97±0.25, respectively. The tracer was excreted mainly through the renal system, as evidenced by high levels of radioactivity in the kidneys. These data support the possibility of using (68)Ga-NOTA-C6 in PET to visualize tumors that overexpress MMP2.

CONCLUSIONS

(68)Ga-NOTA-C6 is a potential radiopharmaceutical for the imaging of in vivo MMP2 activity in tumors.

BubR1 Acts as a Promoter in Cellular Motility of Human Oral Squamous Cancer Cells through Regulating MMP-2 and MMP-9

BubR1 is a critical component of spindle assembly checkpoint, ensuring proper chromatin segregation during mitosis. Recent studies showed that BubR1 was overexpressed in many cancer cells, including oral squamous cell carcinomas (OSCC). However, the effect of BubR1 on metastasis of OSCC remains unclear. This study aimed to unravel the role of BubR1 in the progression of OSCC and confirm the expression of BubR1 in a panel of malignant OSCC cell lines with different invasive abilities. The results of quantitative real-time PCR showed that the mRNA level of BubR1 was markedly increased in four OSCC cell lines, Ca9-22, HSC3, SCC9 and Cal-27 cells, compared to two normal cells, normal human oral keratinocytes (HOK) and human gingival fibroblasts (HGF). Moreover, the expression of BubR1 in these four OSCC cell lines was positively correlated with their motility. Immunofluorescence revealed that BubR1 was mostly localized in the cytosol of human gingival carcinoma Ca9-22 cells. BubR1 knockdown significantly decreased cellular invasion but slightly affect cellular proliferation on both Ca9-22 and Cal-27 cells. Consistently, the activities of metastasis-associated metalloproteinases MMP-2 and MMP-9 were attenuated in BubR1 knockdown Ca9-22 cells, suggesting the role of BubR1 in promotion of OSCC migration. Our present study defines an alternative pathway in promoting metastasis of OSCC cells, and the expression of BubR1 could be a prognostic index in OSCC patients.

Advances in phage display technology for drug discovery

INTRODUCTION

Over the past decade, several library-based methods have been developed to discover ligands with strong binding affinities for their targets. These methods mimic the natural evolution for screening and identifying ligand-target interactions with specific functional properties. Phage display technology is a well-established method that has been applied to many technological challenges including novel drug discovery.

AREAS COVERED

This review describes the recent advances in the use of phage display technology for discovering novel bioactive compounds. Furthermore, it discusses the application of this technology to produce proteins and peptides as well as minimize the use of antibodies, such as antigen-binding fragment, single-chain fragment variable or single-domain antibody fragments like VHHs.

EXPERT OPINION

Advances in screening, manufacturing and humanization technologies demonstrate that phage display derived products can play a significant role in the diagnosis and treatment of disease. The effects of this technology are inevitable in the development pipeline for bringing therapeutics into the market, and this number is expected to rise significantly in the future as new advances continue to take place in display methods. Furthermore, a widespread application of this methodology is predicted in different medical technological areas, including biosensing, monitoring, molecular imaging, gene therapy, vaccine development and nanotechnology.

The DNA hypomethylating agent, 5-aza-2'-deoxycytidine, enhances tumor cell invasion through a transcription-dependent modulation of MMP-1 expression in human fibrosarcoma cells

In diseases such as cancer, cells need to degrade the extracellular matrix (ECM) and therefore require high protease levels. Thus, aberrant tissue degradation is associated to matrix metalloproteinases (MMPs) overexpression resulting from different mechanisms including epigenetic events. One of the most characterized epigenetic mechanisms is DNA methylation causing changes in chromatin conformation, thereby decreasing the accessibility to the transcriptional machinery and resulting in a robust gene silencing. Modulation of DNA methylation by DNA hypomethylating agents such as 5-aza-2'-deoxycytidine (5-azadC) is widely used in epigenetic anticancer treatments. Here, we focus on the effects of this drug on the expression level of MMP-1, -2, and -9 in human HT1080 fibrosarcoma cells. We demonstrate that 5-azadC increases MMP expression at both mRNA and protein levels, and promotes invasion potential of HT1080 cells. Using broad-spectrum and specific MMP inhibitors, we establish that MMP-1, but not MMP-2 and -9, plays a key role in 5-azadC-enhanced cell invasion. We show that 5-azadC induces MMP-1 expression through a transcriptional mechanism without affecting MMP-1 promoter methylation status. Finally, we demonstrate that 5-azadC treatment increases the nuclear levels of Sp1 and Sp3 transcription factors, and modulates their recruitment to the MMP-1 promoter, resulting in chromatin remodeling associated to 5-azadC-induced MMP-1 expression. All together, our data indicate that the hypomethylating agent 5-azadC modulates, mainly via Sp1 recruitment, MMP-1 expression resulting in an increased invasive potential of HT1080 cells.

Systemic delivery of protein nanocages bearing CTT peptides for enhanced imaging of MMP-2 expression in metastatic tumor models

Matrix metalloproteinase 2 (MMP-2) in metastatic cancer tissue, which is associated with a poor prognosis, is a potential target for tumor imaging in vivo. Here, we describe a metastatic cancer cell-targeted protein nanocage. An MMP-2-binding peptide, termed CTT peptide (CTTHWGFTLC), was conjugated to the surface of a naturally occurring heat shock protein nanocage by genetic modification. The engineered protein nanocages showed a binding affinity for MMP-2 and selective uptake in cancer cells that highly expressed MMP-2 in vitro. In near-infrared fluorescence imaging, the nanocages showed specific and significant accumulation in tumor tissue after intravenous injection in vivo. These protein nanocages conjugated with CTT peptide could be potentially applied to a noninvasive near-infrared fluorescence detection method for imaging gelatinase activity in metastatic tumors in vivo.

Potent tumor targeting drug release system comprising MMP-2 specific peptide fragment with self-assembling characteristics

Self-assembling peptides are capable of forming a complex containing a cavity where cytotoxic agents can be wrapped in a self-assembling manner. These complexes are beneficial for improving the pharmacological properties and pharmacokinetics of cytotoxic agents, such as doxorubicin and paclitaxel. In the present study, this self-assembling feature was successfully integrated into a hexapeptide with matrix metalloproteinase (MMP)-2 specific targeting activity, producing a supramolecule possessing controlled drug release characteristics. The MMP-2 specific substrate fragment, PVGLIG, makes this supramolecule disassociate in the presence of MMP-2, and this system is considered to be a powerful tool for the treatment of tumors with high expression of MMP-2 or tumor metastasis. Our findings show that this modified self-assembling peptide with the PVGLIG fragment was able to significantly enhance specificity against HT1080 cells, a tumor cell line with high expression of MMP-2. In addition, residence time of the complex in blood was prolonged since paclitaxel was wrapped into the supramolecule. Our results suggest that the modified MMP-2 specific substrate, SAMTA7, could act as a controlled and sustained drug carrier for treatment of tumors with high expression of MMP-2 and for tumor metastasis.

Matrix metalloproteinases are involved in cardiovascular diseases

This MiniReview describes the essential biochemical and molecular aspects of matrix metalloproteinases (MMPs) and briefly discusses how they engage in different diseases, with particular emphasis on cardiovascular diseases. There is compelling scientific evidence that many MMPs, especially MMP-2, play important roles in the development of cardiovascular diseases; inhibition of these enzymes is beneficial to many cardiovascular conditions, sometimes precluding or postponing end-organ damage and fatal outcomes. Conducting comprehensive discussions and further studies on how MMPs participate in cardiovascular diseases is important, because inhibition of these enzymes may be an alternative or an adjuvant for current cardiovascular disease therapy.

Selection of pancreatic cancer cell-binding landscape phages and their use in development of anticancer nanomedicines

It is hypothesized that the use of targeted drug delivery systems can significantly improve the therapeutic index of small molecule chemotherapies by enhancing accumulation of the drugs at the site of disease. Phage display offers a high-throughput approach for selection of the targeting ligands. We have successfully isolated phage fusion proteins selective and specific for PANC-1 pancreatic cancer cells. Doxorubicin liposomes (Lipodox) modified with tumor-specific phage fusion proteins enhanced doxorubicin uptake specifically in PANC-1 cells as compared with unmodified Lipodox and also compared with normal breast epithelial cells. Phage protein-targeted Lipodox substantially increased the concentration of doxorubicin in the nuclei of PANC-1 cells in spite of P-glycoprotein-mediated drug efflux. The in vitro cytotoxic activity obtained with pancreatic cell-targeted Lipodox was greater than that of unmodified Lipodox. We present a novel and straightforward method for preparing pancreatic tumor-targeted nanomedicines by anchoring pancreatic cancer-specific phage proteins within the liposome bilayer.

Peptide-based cancer therapy: opportunity and challenge

Cancer is one of the leading causes of death worldwide. Conventional cancer therapies mainly focus on mass cell killing without high specificity and often cause severe side effects and toxicities. Peptides are a novel class of anticancer agents that could specifically target cancer cells with lower toxicity to normal tissues, which will offer new opportunities for cancer prevention and treatment. Anticancer peptides face several therapeutic challenges. In this review, we present the sources and mechanisms of anticancer peptides and further discuss modification strategies to improve the anticancer effects of bioactive peptides.

Matrix metalloproteinase-9: Many shades of function in cardiovascular disease

Matrix metalloproteinase (MMP)-9, one of the most widely investigated MMPs, regulates pathological remodeling processes that involve inflammation and fibrosis in cardiovascular disease. MMP-9 directly degrades extracellular matrix (ECM) proteins and activates cytokines and chemokines to regulate tissue remodeling. MMP-9 deletion or inhibition has proven overall beneficial in multiple animal models of cardiovascular disease. As such, MMP-9 expression and activity is a common end point measured. MMP-9 cell-specific overexpression, however, has also proven beneficial and highlights the fact that little information is available on the underlying mechanisms of MMP-9 function. In this review, we summarize our current understanding of MMP-9 physiology, including structure, regulation, activation, and downstream effects of increased MMP-9. We discuss MMP-9 roles during inflammation and fibrosis in cardiovascular disease. By concentrating on the substrates of MMP-9 and their roles in cardiovascular disease, we explore the overall function and discuss future directions on the translational potential of MMP-9 based therapies.

Design of (99m) Tc-DTPA-CLP and preliminary evaluation in rats

Radiopharmaceuticals are localized in (malignant) tumor tissues by different mechanisms. One of these mechanisms, gelatinase enzyme activity, is associated with poor prognosis in cancer patients and potential targets for tumor imaging. There are some gelatinases to be associated with metastatic potential for tumor imaging to possibly predict metastases. In this study, a cyclic decapeptide conjugate, DTPA-CLP (DTPA-Cys-Leu-Pro-Gly-His-Trp-Gly-Phe-Pro-Ser-Cys), was selected as a peptide conjugate because of its selective inhibitory activity toward gelatinases. Peptide-conjugated DTPA-CLP was labeled with (99m) Tc with a radiolabeling efficiency of 97.0 ± 2.8%. After determining optimization conditions for radiolabeling, a biodistribution study of radiolabeled peptide in albino Wistar rats was performed. According to biodistribution data, (99m) Tc-DTPA-CLP showed high uptake in the lung, liver, uterus, and spleen. These results show that (99m) Tc-DTPA-CLP may be used for the imaging of gelatinase activity in metastatic tumors.

Nano delivers big: designing molecular missiles for cancer therapeutics

Current first-line treatments for most cancers feature a short-list of highly potent and often target-blind interventions, including chemotherapy, radiation, and surgical excision. These treatments wreak considerable havoc upon non-cancerous tissue and organs, resulting in deleterious and sometimes fatal side effects for the patient. In response, this past decade has witnessed the robust emergence of nanoparticles and, more relevantly, nanoparticle drug delivery systems (DDS), widely touted as the panacea of cancer therapeutics. While not a cure, nanoparticle DDS can successfully negotiate the clinical payoff between drug dosage and side effects by encompassing target-specific drug delivery strategies. The expanding library of nanoparticles includes lipoproteins, liposomes, dendrimers, polymers, metal and metal oxide nano-spheres and -rods, and carbon nanotubes, so do the modes of delivery. Importantly, however, the pharmaco-dynamics and –kinetics of these nano-complexes remain an urgent issue and a serious bottleneck in the transition from bench to bedside. This review addresses the rise of nanoparticle DDS platforms for cancer and explores concepts of gene/drug delivery and cytotoxicity in pre-clinical and clinical contexts.

Phage protein-targeted cancer nanomedicines

Nanoencapsulation of anticancer drugs improves their therapeutic indices by virtue of the enhanced permeation and retention effect which achieves passive targeting of nanoparticles in tumors. This effect can be significantly enhanced by active targeting of nanovehicles to tumors. Numerous ligands have been proposed and used in various studies with peptides being considered attractive alternatives to antibodies. This is further reinforced by the availability of peptide phage display libraries which offer an unlimited reservoir of target-specific probes. In particular landscape phages with multivalent display of target-specific peptides which enable the phage particle itself to become a nanoplatform creates a paradigm for high throughput selection of nanoprobes setting the stage for personalized cancer management. Despite its promise, this conjugate of combinatorial chemistry and nanotechnology has not made a significant clinical impact in cancer management due to a lack of using robust processes that facilitate scale-up and manufacturing. To this end we proposed the use of phage fusion protein as the navigating modules of novel targeted nanomedicine platforms which are described in this review.

Mapping proteolytic processing in the secretome of gastric cancer-associated myofibroblasts reveals activation of MMP-1, MMP-2, and MMP-3

Cancer progression involves changes in extracellular proteolysis, but the contribution of stromal cell secretomes to the cancer degradome remains uncertain. We have now defined the secretome of a specific stromal cell type, the myofibroblast, in gastric cancer and its modification by proteolysis. SILAC labeling and COFRADIC isolation of methionine containing peptides allowed us to quantify differences in gastric cancer-derived myofibroblasts compared with myofibroblasts from adjacent tissue, revealing increased abundance of several proteases in cancer myofibroblasts including matrix metalloproteinases (MMP)-1 and -3. Moreover, N-terminal COFRADIC analysis identified cancer-restricted proteolytic cleavages, including liberation of the active forms of MMP-1, -2, and -3 from their inactive precursors. In vivo imaging confirmed increased MMP activity when gastric cancer cells were xenografted in mice together with gastric cancer myofibroblasts. Western blot and enzyme activity assays confirmed increased MMP-1, -2, and -3 activity in cancer myofibroblasts, and cancer cell migration assays indicated stimulation by MMP-1, -2, and -3 in cancer-associated myofibroblast media. Thus, cancer-derived myofibroblasts differ from their normal counterparts by increased production and activation of MMP-1, -2, and -3, and this may contribute to the remodelling of the cancer cell microenvironment.

Role of matrix metalloproteinase-2 in recovery after tubular damage in acute kidney injury in mice

BACKGROUND/AIMS

Matrix metalloproteinases (MMPs) are zinc endopeptidases that degrade extracellular matrix and are involved in the pathogenesis of ischemic damage in acute kidney injury (AKI). In the present study, we analyzed the role of MMP-2 in the repair process in ischemic AKI.

METHODS

AKI was induced in MMP-2 wild-type (MMP-2(+/+)) and MMP-2-deficient (MMP-2(-/-)) mice by 90-min renal artery clamping followed by reperfusion. Renal histology and the activity and distribution of MMP-2 were examined from day 1 to day 14. During the recovery from AKI, MMP-2(+/+) mice were also treated with MMP-2/MMP-9 inhibitor.

RESULTS

In both MMP-2(+/+) and MMP-2(-/-) mice, AKI developed on day 1 after ischemia/reperfusion with widespread acute tubular injury, but subsequent epithelial cell proliferation was evident on days 3-7. During the repair process, active MMP-2 and MMP-9 increased in regenerating tubular epithelial cells in MMP-2(+/+) mice on days 7-14, and the tubular repair process was almost complete by day 14. On the other hand, in MMP-2(-/-) mice, less prominent proliferation of tubular epithelial cells was evident on days 3 and 7, and damaged tubules that were covered with elongated and immature regenerated epithelial cells were identified on days 7 and 14. Incomplete recovery of injured microvasculature was also noted with persistent macrophage infiltration. Similarly, treatment with MMP-2/MMP-9 inhibitor resulted in impaired recovery in MMP-2(+/+) mice.

CONCLUSION

MMP-2 is involved in tubular repair after AKI. The use of the MMP-2/MMP-9 inhibitor was a disadvantage when it was administered during the repair stage of ischemic AKI. Treatment with MMP inhibitor for AKI needs to be modified to enhance recovery from AKI.

Recent trends in multifunctional liposomal nanocarriers for enhanced tumor targeting

Liposomes are delivery systems that have been used to formulate a vast variety of therapeutic and imaging agents for the past several decades. They have significant advantages over their free forms in terms of pharmacokinetics, sensitivity for cancer diagnosis and therapeutic efficacy. The multifactorial nature of cancer and the complex physiology of the tumor microenvironment require the development of multifunctional nanocarriers. Multifunctional liposomal nanocarriers should combine long blood circulation to improve pharmacokinetics of the loaded agent and selective distribution to the tumor lesion relative to healthy tissues, remote-controlled or tumor stimuli-sensitive extravasation from blood at the tumor's vicinity, internalization motifs to move from tumor bounds and/or tumor intercellular space to the cytoplasm of cancer cells for effective tumor cell killing. This review will focus on current strategies used for cancer detection and therapy using liposomes with special attention to combination therapies.

Nanoparticles for Improving Cancer Diagnosis

Despite the progress in developing new therapeutic modalities, cancer remains one of the leading diseases causing human mortality. This is mainly attributed to the inability to diagnose tumors in their early stage. By the time the tumor is confirmed, the cancer may have already metastasized, thereby making therapies challenging or even impossible. It is therefore crucial to develop new or to improve existing diagnostic tools to enable diagnosis of cancer in its early or even pre-syndrome stage. The emergence of nanotechnology has provided such a possibility. Unique physical and physiochemical properties allow nanoparticles to be utilized as tags with excellent sensitivity. When coupled with the appropriate targeting molecules, nanoparticle-based probes can interact with a biological system and sense biological changes on the molecular level with unprecedented accuracy. In the past several years, much progress has been made in applying nanotechnology to clinical imaging and diagnostics, and interdisciplinary efforts have made an impact on clinical cancer management. This article aims to review the progress in this exciting area with emphases on the preparation and engineering techniques that have been developed to assemble "smart" nanoprobes.

Fluctuating roles of matrix metalloproteinase-9 in oral squamous cell carcinoma

One hallmark of cancer is the degradation of the extracellular matrix (ECM), which is caused by proteinases. In oral cancers, matrix metalloproteinases (MMPs), especially MMP-9, are associated with this degradation. MMPs break down the ECM allowing cancer to spread; they also release various factors from their cryptic sites, including cytokines. These factors modulate cell behavior and enhance cancer progression by regulating angiogenesis, migration, proliferation, and invasion. The development of early metastases is typical for oral cancer, and increased MMP-9 expression is associated with a poor disease prognosis. However, many studies fail to relate MMP-9 expression with metastasis formation. Contrary to earlier models, recent studies show that MMP-9 plays a protective role in oral cancers. Therefore, the role of MMP-9 is complicated and may fluctuate throughout the different types and stages of oral cancers.

Challenges in design and characterization of ligand-targeted drug delivery systems

Targeting of therapeutic agents to molecular markers expressed on the surface of cells requiring clinical intervention holds promise to improve specificity of delivery, enhancing therapeutic effects while decreasing potential damage to healthy tissues. Drug targeting to cellular receptors involved in endocytic transport facilitates intracellular delivery, a requirement for a number of therapeutic goals. However, after several decades of experimental design, there is still considerable controversy on the practical outcome of drug targeting strategies. The plethora of factors contributing to the relative efficacy of targeting makes the success of these approaches hardly predictable. Lack of fully specific targets, along with selection of targets with spatial and temporal expression well aligned to interventional requirements, pose difficulties to this process. Selection of adequate sub-molecular target epitopes determines accessibility for anchoring of drug conjugates and bulkier drug carriers, as well as proper signaling for uptake within the cell. Targeting design must adapt to physiological variables of blood flow, disease status, and tissue architecture by accommodating physicochemical parameters such as carrier composition, functionalization, geometry, and avidity. In many cases, opposite features need to meet a balance, e.g., sustained circulation versus efficient targeting, penetration through tissues versus uptake within cells, internalization within endocytic compartment to avoid efflux pumps versus accessibility to molecular targets within the cytosol, etc. Detailed characterization of these complex physiological factors and design parameters, along with a deep understanding of the mechanisms governing the interaction of targeted drugs and carriers with the biological environment, are necessary steps toward achieving efficient drug targeting systems.