Analysis on the current status of targeted drug delivery to tumors

Designing sub-20 nm self-assembled nanocarriers for small molecule delivery: Interplay among structural geometry, assembly energetics, and cargo release kinetics

Biological constraints in diseased tissues have motivated the need for small nanocarriers (10-30 nm) to achieve sufficient vascular extravasation and pervasive tumor penetration. This particle size limit is only an order of magnitude larger than small molecules, such that cargo loading is better described by co-assembly processes rather than simple encapsulation. Understanding the structural, kinetic, and energetic contributions of carrier-cargo co-assembly is thus critical to achieve molecular-level control towards predictable in vivo behavior. These interconnected set of properties were systematically examined using sub-20 nm self-assembled nanocarriers known as three-helix micelles (3HM). Both hydrophobicity and the "geometric packing parameter" dictate small molecule compatibility with 3HM's alkyl tail core. Planar obelisk-like apomorphine and doxorubicin (DOX) molecules intercalated well within the 3HM core and near the core-shell interface, forming an integral component to the co-assembly, as corroborated by small-angle X-ray and neutron-scattering structural studies. DOX promoted crystalline alkyl tail ordering, which significantly increased (+63%) the activation energy of 3HM subunit exchange. Subsequently, 3HM-DOX displayed slow-release kinetics (t_1/2 = 40 h) at physiological temperatures, with ~50× greater cargo preference for the micelle core as described by two drug partitioning coefficients (micellar core/shell K_p1 ~ 24, and shell/bulk solvent K_p2 ~ 2). The geometric and energetic insights between nanocarrier and their small molecule cargos developed here will aid in broader efforts to deconvolute the interconnected properties of carrier-drug co-assemblies. Adding this knowledge to pharmacological and immunological explorations will expand our understanding of nanomedicine behavior throughout all the physical and in vivo processes they are intended to encounter.

Design of 18 nm Doxorubicin-Loaded 3-Helix Micelles: Cellular Uptake and Cytotoxicity in Patient-Derived GBM6 Cells

The fate of nanocarrier materials at the cellular level constitutes a critical checkpoint in the development of effective nanomedicines, determining whether tissue level accumulation results in therapeutic benefit. The cytotoxicity and cell internalization of ∼18 nm 3-helix micelle (3HM) loaded with doxorubicin (DOX) were analyzed in patient-derived glioblastoma (GBM) cells in vitro. The half-maximal inhibitory concentration (IC₅₀) of 3HM-DOX increased to 6.2 μg/mL from <0.5 μg/mL for free DOX in patient-derived GBM6 cells, to 15.0 μg/mL from 6.5 μg/mL in U87MG cells, and to 21.5 μg/mL from ∼0.5 μg/mL in LN229 cells. Modeling analysis of previous 3HM biodistribution results predicts that these cytotoxic concentrations are achievable with intravenous injection in rodent GBM models. 3HM-DOX formulations were internalized intact and underwent intracellular trafficking distinct from free DOX. 3HM was quantified to have an internalization half-life of 12.6 h in GBM6 cells, significantly longer than that reported for some liposome and polymer systems. 3HM was found to traffic through active endocytic processes, with clathrin-mediated endocytosis being the most involved of the pathways studied. Inhibition studies suggest substantial involvement of receptor recognition in 3HM uptake. As the 3HM surface is PEG-ylated with no targeting functionalities, protein corona-cell surface interactions, such as the apolipoprotein-low-density lipoprotein receptor, are expected to initiate internalization. The present work gives insights into the cytotoxicity, pharmacodynamics, and cellular interactions of 3HM and 3HM-DOX relevant for ongoing preclinical studies. This work also contributes to efforts to develop predictive mathematical models tracking the accumulation and biodistribution kinetics at a systemic level.

Distinct Proteins in Protein Corona of Nanoparticles Represent a Promising Venue for Endogenous Targeting - Part II: In vitro and in vivo Kinetics Study

Introduction

Nanoparticles (NPs), upon introduction to the biological systems, become wrapped by serum and cellular proteins constituting the protein corona (PC). This PC contributes largely to the NPs’ interaction with the biological systems and their subsequent functions. On the one hand, PC can decrease the efficiency of targeting by directing the NPs to the reticuloendothelial system (RES) or by masking the active targeting moieties and decreasing their ability to bind to their target receptors. On the other hand, some components of PC have offered hopes for achieving endogenous targeting.

Methods

In this study, we aimed at the investigation of the role of the PC in determining the behavior of cRGDyk peptide-unconjugated and -conjugated NPs (uNPs and cNPs) exhibiting different physicochemical properties and their interaction with melanoma on in vitro and in vivo levels. Mathematical modeling has been utilized to understand the kinetics of the interaction of NPs with the tumor cells and different organs, respectively.

Results

Endocytosis and exocytosis were reported to occur simultaneously for the utilized NPs. The balance was largely dependent on the NPs’ physicochemical properties and the role of the PC. In addition, distinct proteins present in the PC (illustrated in the results of the PC analysis in part I) have also determined the patterns of the NPs’ distribution in different organs and tissues of the vascular system, the RES system and the target tumot tissue. Vitronectin (VN) was found to mediate higher accumulation in integrin receptor-expressing melanoma cells, while complement 3 protein (C3) and clusterin (CLU), as an opsonin and dysopsonin, respectively, regulated the balance between the RES uptake and blood circulation.

Discussion

PC, if properly modulated by tuning NPs’ physicochemical properties, can serve as a potential venue for optimum utilization of NPs in cancer therapy.

Lipid-oligonucleotide conjugates for bioapplications

Lipid-oligonucleotide conjugates (LONs) are powerful molecular-engineering materials for various applications ranging from biosensors to biomedicine. Their unique amphiphilic structures enable the self-assembly and the conveyance of information with high fidelity. In particular, LONs present remarkable potential in measuring cellular mechanical forces and monitoring cell behaviors. LONs are also essential sensing tools for intracellular imaging and have been employed in developing cell-surface-anchored DNA nanostructures for biomimetic-engineering studies. When incorporating therapeutic oligonucleotides or small-molecule drugs, LONs hold promise for targeted therapy. Moreover, LONs mediate the controllable assembly and fusion of vesicles based on DNA-strand displacements, contributing to nanoreactor construction and macromolecule delivery. In this review, we will summarize the general synthesis strategies of LONs, provide some characterization analysis and emphasize recent advances in bioanalytical and biomedical applications. We will also consider the relevant challenges and suggest future directions for building better functional LONs in nanotechnology and materials-science applications.

Nucleic Acid Aptamers as a Potential Nucleus Targeted Drug Delivery System

BACKGROUND

Nucleus targeted drug delivery provides several opportunities for the treatment of fatal diseases such as cancer. However, the complex nucleocytoplasmic barriers pose significant challenges for delivering a drug directly and efficiently into the nucleus. Aptamers representing singlestranded DNA and RNA qualify as next-generation highly advanced and personalized medicinal agents that successfully inhibit the expression of certain proteins; possess extraordinary gene-expression for manoeuvring the diseased cell's fate with negligible toxicity. In addition, the precisely directed aptamers to the site of action present a tremendous potential to reach the nucleus by escaping the ensuing barriers to exhibit a better drug activity and gene expression.

OBJECTIVE

This review epigrammatically highlights the significance of targeted drug delivery and presents a comprehensive description of the principal barriers faced by the nucleus targeted drug delivery paradigm and ensuing complexities thereof. Eventually, the progress of nucleus targeting with nucleic acid aptamers and success achieved so far have also been reviewed.

METHODS

Systematic literature search was conducted of research published to date in the field of nucleic acid aptamers.

CONCLUSION

The review specifically points out the contribution of individual aptamers as the nucleustargeting agent rather than aptamers in conjugated form.

The role of tumor-associated macrophages (TAMs) in tumor progression and relevant advance in targeted therapy

Macrophages have a leading position in the tumor microenvironment (TME) which paves the way to carcinogenesis. Initially, monocytes and macrophages are recruited to the sites where the tumor develops. Under the guidance of different microenvironmental signals, macrophages would polarize into two functional phenotypes, named as classically activated macrophages (M1) and alternatively activated macrophages (M2). Contrary to the anti-tumor effect of M1, M2 exerts anti-inflammatory and tumorigenic characters. In progressive tumor, M2 tumor-associated macrophages (TAMs) are in the majority, being vital regulators reacting upon TME. This review elaborates on the role of TAMs in tumor progression. Furthermore, prospective macrophage-focused therapeutic strategies, including drugs not only in clinical trials but also at primary research stages, are summarized followed by a discussion about their clinical application values. Nanoparticulate systems with efficient drug delivery and improved antitumor effect are also summed up in this article.

Optimization and efficacy study of synergistic vincristine coloaded liposomal doxorubicin against breast and lung cancer

Aim: To improve the efficacy of poly-ethylene glycol (PEG)ylated liposomes coloaded with doxorubicin and vincristine against triple-negative breast cancer (TNBC) and non-small-cell lung cancer (NSCLC). Methods: The combinatorial index of the drugs was established using the Chou-Talalay method in MDA-MB-231 and A549 cell lines. The most effective ratio was co-encapsulated in factorial design optimized nanoliposomes which were characterized for similarity to clinical standard and evaluated in vitro and in vivo for therapeutic efficacy. Results & conclusion: The formulation exhibited more than 95% co-encapsulation, a size of 95.74 ± 2.65 nm and zeta potential of -9.17 ± 1.19 mV while having no significant differences in physicochemical and biochemical characteristics as compared with the clinical standard. Efficacy evaluation studies showed significantly improved cytotoxicity and tumor regression compared with liposomal doxorubicin indicating improvement in efficacy against TNBC and NSCLC.

Correlation between in vitro stability and pharmacokinetics of poly(ε-caprolactone)-based micelles loaded with a photosensitizer

Polymeric micelles are extensively investigated as drug delivery systems for hydrophobic drugs including photosensitizers (PSs). In order to benefit from micelles as targeted delivery systems for PS, rather than only solubilizers, the stability and cargo retention of the (PS-loaded) micelles should be properly assessed in biologically relevant media to get insight into the essential parameters predicting their in vivo performance (i.e., pharmacokinetics). In the present study, asymmetric flow field-flow fractionation (AF4) was used to investigate the in vitro stability in human plasma of empty and meta-tetra(hydroxyphenyl)chlorin (mTHPC)-loaded dithiolane-crosslinked micelles based on poly(ɛ-caprolactone)-co-poly(1,2-dithiolane‑carbonate)-b-poly(ethylene glycol) (p(CL-co-DTC)-PEG) and non (covalently)-crosslinked micelles composed of poly(ε-caprolactone)-b-poly(ethylene glycol) (pCL-PEG). AF4 allows separation of the micelles from plasma proteins, which showed that small non (covalently)-crosslinked pCL₉-PEG (17 nm) and pCL₁₅-PEG (22 nm) micelles had lower stability in plasma than pCL₂₃-PEG micelles with larger size (43 nm) and higher degree of crystallinity of pCL, and had also lower stability than covalently crosslinked p(CL₉-DTC_3.9)-PEG and p(CL₁₈-DTC_7.5)-PEG micelles with similar small sizes (~20 nm). In addition, PS (re)distribution to specific plasma proteins was observed by AF4, giving strong indications for the (in)stability of PS-loaded micelles in plasma. Nevertheless, fluorescence spectroscopy in human plasma showed that the retention of mTHPC in non (covalently)-crosslinked but semi-crystalline pCL₂₃-PEG micelles (>8 h) was much longer than that in covalently crosslinked p(CL₁₈-DTC_7.5)-PEG micelles (~4 h). In line with this, in vivo circulation kinetics showed that pCL₂₃-PEG micelles loaded with mTHPC had significantly longer half-life values (t½-β of micelles and mTHPC was 14 and 18 h, respectively) than covalently crosslinked p(CL₁₈-DTC_7.5)-PEG micelles (t½-β of both micelles and mTHPC was ~2 h). As a consequence, long circulating pCL₂₃-PEG micelles resulted in significantly higher tumor accumulation of both the micelles and loaded mTHPC as compared to short circulating p(CL₁₈-DTC_7.5)-PEG micelles. These in vivo data were in good agreement with the in vitro stability studies. In conclusion, the present study points out that AF4 and fluorescence spectroscopy are excellent tools to evaluate the (in)stability of nanoparticles in biological media and thus predict the (in)stability of drug loaded nanoparticles after i.v. administration, which is favorable to screen promising delivery systems with reduced experimental time and costs and without excessive use of animals.

Synergistic co-loading of vincristine improved chemotherapeutic potential of pegylated liposomal doxorubicin against triple negative breast cancer and non-small cell lung cancer

The current work aims to explore the biological characteristics of vincristine synergistic co-loading into pegylated liposomal doxorubicin in non-indicated modalities of non-small cell lung cancer (NSCLC) and triple negative breast cancer (TNBC). The combinatorial liposome prepared by active co-loading of the drugs against modified ammonium ion gradient exhibited 95% encapsulation of both drugs. The cellular uptake studies using confocal microscopy and flow cytometry showed significantly increased uptake of dual drug formulation as against liposomal doxorubicin. The co-loaded liposome formulation had significantly increased cell cycle arrest in G₂/M phase with subsequent apoptosis and reduced cell viability in both tumor cell lines than doxorubicin liposome. This carrier exhibited similar acute toxicity, pharmacokinetic and tissue distribution profiles with significant increase in tumor regression as compared to liposomal doxorubicin. These results indicate that co-encapsulation of vincristine into clinically used pegylated liposomal doxorubicin significantly improved in-vitro and in-vivo therapeutic efficacy against NSCLC and TNBC.

Anti-CD206 antibody-conjugated Fe3O4-based PLGA nanoparticles selectively promote tumor-associated macrophages to polarize to the pro-inflammatory subtype

M2 macrophages serve roles in inhibiting inflammation and promoting tumor development. Reversing tumor-associated macrophages (TAMs) from M2- to M1-type polarization may provide an important strategy for tumor immunotherapy. The present study aimed to enhance antitumor immunity by targeting the concentration of iron in macrophages. Fe₃O₄-based poly(lactic-co-glycolic) acid (PLGA) nanoparticles surface-modified with an anti-CD206 monoclonal antibody were prepared using the oil in water single-emulsion technique. Particle size was measured using a particle size analyzer, the ζ potential was determined using a ζ potential analyzer and the carrier rate of Fe₃O₄ was measured using an iron assay kit. The conjugation of anti-CD206, and the ability to target M2 macrophages were studied via immunofluorescence. Polarization indexes of the macrophages were detected using both western blotting and reverse transcription-quantitative PCR (RT-qPCR), and a mouse model with subcutaneous tumors was established to verify the antitumor effects of the nanoparticles in vivo. Nanoparticles had a mean diameter in the range of 260–295 nm, and the ζ potential values were between −19 and −33 mV. The Fe₃O₄ association efficiency ranged from 65–75%, whereas the anti-CD206 conjunction efficiency ranged from 65–70%. The immunofluorescence experiments were able to demonstrate the successful targeting of the M2 macrophages. The western blotting and RT-qPCR experiments identified that CD206-Fe₃O₄-PLGA and Fe₃O₄-PLGA promoted the expression of TNF-α, inducible nitric oxide synthase (iNOS) and IL-1β in the macrophages. The in vivo studies indicated that CD206-Fe₃O₄-PLGA nanoparticles were able to promote CD86 expression in TAMs, with CD86 being a specific marker of the M1 subtype. In summary, nanoparticles were characterized in the present study by their mean particle size, polydispersity index, ζ potential and morphology, as well as by their association with Fe₃O₄ and conjugation with the anti-CD206 monoclonal antibody. Collectively, the present results suggested that the nanoparticles were able to both target M2 macrophages and reverse the M2 polarization of the macrophages to the M1 phenotype via the release of coated iron-oxide particles.

Glutamine-β-cyclodextrin for targeted doxorubicin delivery to triple-negative breast cancer tumors via the transporter ASCT2

Chemotherapy is the primary therapy for triple-negative breast cancer (TNBC) and the tumor-targeted delivery of chemotherapeutic drugs is necessary to minimize their side effects on normal tissues. TNBC cells display addictions to glutamine in culture, and the levels of the glutamine transporter, alanine-serine-cysteine transporter 2 (ASCT2), are elevated in many types of cancer. However, glutamine- or ASCT2-based carriers have not been used in tumor-targeted drug delivery. In this study, a novel derivative of β-cyclodextrin (β-CD), glutamine-β-cyclodextrin (GLN-CD), was developed by conjugating glutamine with the 6-hydroxy of β-CD, and GLN-CD was then used to prepare doxorubicin (DOX) inclusion complexes (DOX@GLN-CD) for TNBC treatment. GLN-CD and glutamine have similar ASCT2-binding sites, and GLN-CD has the potential to enter cells through ASCT2-dependent facilitated diffusion. An increase in the degree of substitution did not promote binding between GLN-CD and ASCT2. GLN-CD and DOX formed inclusion complexes at a molar ratio of 1 : 1. DOX@GLN-CD specifically accumulated in TNBC cells, including MDA-MB-231 and BT549 cells, where it subsequently induced G2/M blockade and apoptosis, but hardly affected nontumorigenic MCF10A cells. l-γ-Glutamyl-p-nitroanilide (GPNA), which is a specific inhibitor of ASCT2, antagonistically decreased the cellular uptake of DOX@GLN-CD by TNBC cells, which further confirmed the role of ASCT2 in DOX@GLN-CD transport. In vivo, DOX@GLN-CD accumulated specifically in tumors, achieved improved outcomes and minimized the toxic effects on main organs at the same dose as DOX. As a novel derivative of β-CD, GLN-CD is an effective carrier that can specifically deliver DOX to TNBC cells via targeting ASCT2 and minimize its uptake by normal cells.

Nitric Oxide Nano-Delivery Systems for Cancer Therapeutics: Advances and Challenges

Nitric oxide (NO) plays important roles in various physiological and pathological functions and processes in the human body. Therapeutic application of NO molecules has been investigated in various diseases, including cardiovascular disease, cancer, and infections. However, the extremely short half-life of NO, which limits its clinical use considerably, along with non-specific distribution, has resulted in a low therapeutic index and undesired adverse effects. To overcome the drawbacks of using this gaseous signaling molecule, researchers in the last several decades have focused on innovative medical technologies, specifically nanoparticle-based drug delivery systems (DDSs), because these systems alter the biodistribution of the therapeutic agent through controlled release at the target tissues, resulting in a significant therapeutic drug effect. Thus, the application of nano-systems for NO delivery in the field of biomedicine, particularly in the development of new drugs for cancer treatment, has been increasing worldwide. In this review, we discuss NO delivery nanoparticle systems, with the aim of improving drug delivery development for conventional chemotherapies and controlling multidrug resistance in cancer treatments.

Multiplexed non-invasive tumor imaging of glucose metabolism and receptor-ligand engagement using dark quencher FRET acceptor

Rationale: Following an ever-increased focus on personalized medicine, there is a continuing need to develop preclinical molecular imaging modalities to guide the development and optimization of targeted therapies. Near-Infrared (NIR) Macroscopic Fluorescence Lifetime Förster Resonance Energy Transfer (MFLI-FRET) imaging offers a unique method to robustly quantify receptor-ligand engagement in live intact animals, which is critical to assess the delivery efficacy of therapeutics. However, to date, non-invasive imaging approaches that can simultaneously measure cellular drug delivery efficacy and metabolic response are lacking. A major challenge for the implementation of concurrent optical and MFLI-FRET in vivo whole-body preclinical imaging is the spectral crowding and cross-contamination between fluorescent probes. Methods: We report on a strategy that relies on a dark quencher enabling simultaneous assessment of receptor-ligand engagement and tumor metabolism in intact live mice. Several optical imaging approaches, such as in vitro NIR FLI microscopy (FLIM) and in vivo wide-field MFLI, were used to validate a novel donor-dark quencher FRET pair. IRDye 800CW 2-deoxyglucose (2-DG) imaging was multiplexed with MFLI-FRET of NIR-labeled transferrin FRET pair (Tf-AF700/Tf-QC-1) to monitor tumor metabolism and probe uptake in breast tumor xenografts in intact live nude mice. Immunohistochemistry was used to validate in vivo imaging results. Results: First, we establish that IRDye QC-1 (QC-1) is an effective NIR dark acceptor for the FRET-induced quenching of donor Alexa Fluor 700 (AF700). Second, we report on simultaneous in vivo imaging of the metabolic probe 2-DG and MFLI-FRET imaging of Tf-AF700/Tf-QC-1 uptake in tumors. Such multiplexed imaging revealed an inverse relationship between 2-DG uptake and Tf intracellular delivery, suggesting that 2-DG signal may predict the efficacy of intracellular targeted delivery. Conclusions: Overall, our methodology enables for the first time simultaneous non-invasive monitoring of intracellular drug delivery and metabolic response in preclinical studies.

Molecularly Imprinted Polymers: Antibody Mimics for Bioimaging and Therapy

Molecularly imprinted polymers (MIPs) are tailor-made chemical receptors that recognize and bind target molecules with a high affinity and selectivity. MIPs came into the spotlight in 1993 when they were dubbed "antibody mimics," and ever since, they have been widely studied for the extraction or trapping of chemical pollutants, in immunoassays, and for the design of sensors. Owing to novel synthesis strategies resulting in more biocompatible MIPs in the form of soluble nanogels, these synthetic antibodies have found favor in the biomedical domain since 2010, when for the first time, they were shown to capture and eliminate a toxin in live mice. This review, covering the years 2015-2020, will first describe the rationale behind these antibody mimics, and the different synthesis methods that have been employed for the preparation of MIPs destined for in vitro and in vivo targeting and bioimaging of cancer biomarkers, an emerging and fast-growing area of MIP applications. MIPs have been synthesized for targeting and visualizing glycans and protein-based cell receptors overexpressed in certain diseases, which are well-known biomarkers for example for tumors. When loaded with drugs, the MIPs could locally kill the tumor cells, making them efficient therapeutic agents. We will end the review by reporting how MIPs themselves can act as therapeutics by inhibiting cancer growth. These works mark a new opening in the use of MIPs for antibody therapy and even immunotherapy, as materials of the future in nanomedicine.

Micro/Nanorobot: A Promising Targeted Drug Delivery System

Micro/nanorobot, as a research field, has attracted interest in recent years. It has great potential in medical treatment, as it can be applied in targeted drug delivery, surgical operation, disease diagnosis, etc. Differently from traditional drug delivery, which relies on blood circulation to reach the target, the designed micro/nanorobots can move autonomously, which makes it possible to deliver drugs to the hard-to-reach areas. Micro/nanorobots were driven by exogenous power (magnetic fields, light energy, acoustic fields, electric fields, etc.) or endogenous power (chemical reaction energy). Cell-based micro/nanorobots and DNA origami without autonomous movement ability were also introduced in this article. Although micro/nanorobots have excellent prospects, the current research is mainly based on in vitro experiments; in vivo research is still in its infancy. Further biological experiments are required to verify in vivo drug delivery effects of micro/nanorobots. This paper mainly discusses the research status, challenges, and future development of micro/nanorobots.

Drug-internalized bacterial swimmers for magnetically manipulable tumor-targeted drug delivery

Tumor-targeted drug carriers are becoming attractive for precise drug delivery in anti-tumor therapy. However, a lot of the reported drug delivery systems are complicatedly designed and their destiny in vivo is beyond our control, which limited their clinical applications. Hence, it is urgently needed to develop spatio-manipulable self-propelled nanosystems for drug delivery in a facile way. Here, we have successfully constructed drug-internalized bacterial swimmers, whose movement can be manually controlled by an external magnetic field (MF). We demonstrate that the swimmers maintain the mobility to align and swim along MF lines. Further studies reveal that the doxorubicin (DOX-) internalized bacterial swimmers are able to navigate toward tumor sites under the guidance of MF, rendering enhanced anti-tumor efficacy compared with that of dead ones and free DOX. Therefore, the MF-guided bacterial swimmers hold great promise for spatio-manipulable drug delivery in precision medicine.

Photocontrolled miR-148b nanoparticles cause apoptosis, inflammation and regression of Ras induced epidermal squamous cell carcinomas in mice

Despite evidence that microRNAs (miRNAs) are essential in modulating tumorigenesis, a major challenge in cancer treatment is to achieve tumor-specific selectivity and efficient yet safe delivery of miRNAs in vivo. In this study, we have developed a light-inducible silver nanoparticle nucleic acid delivery system that demonstrates precise spatiotemporal control, high cellular uptake, low cytotoxicity, escape from endosomes and release of functional miRNA into the cytosol. Using this approach, we delivered exogenous miR-148b to induce apoptosis in Ras-expressing keratinocytes and murine squamous cell carcinoma cells while avoiding cytotoxicity in untransformed keratinocytes. When administered to transgenic mice with HRas^G12V-driven skin tumors, a single dose of silver nanoparticle conjugates followed by 415 nm LED irradiation at the tumor site caused a rapid and sustained reduction in tumor volume by 92.8%, recruited T cells to the tumor site, and acted as a potent immunomodulator by polarizing the cytokine balance toward Th1 both locally and systemically. In summary, our results demonstrate that spatiotemporal controlled miR-148b mimic delivery can promote tumor regression efficiently and safely.

Exploiting the dynamics of the EPR effect and strategies to improve the therapeutic effects of nanomedicines by using EPR effect enhancers

The enhanced permeability and retention (EPR) effect is a unique phenomenon of solid tumors that is related to their particular anatomical and pathophysiological characteristics, e.g. defective vascular architecture; large gaps between endothelial cells in blood vessels; abundant vascular mediators such as bradykinin, nitric oxide, carbon monoxide, and vascular endothelial growth factor; and impaired lymphatic recovery. These features lead to tumor tissues showing considerable extravasation of plasma components and nanomedicines. These data comprise the basic theory underlying the development of macromolecular agents or nanomedicines. The EPR effect is not necessarily valid for all solid tumors, because tumor blood flow and vascular permeability vary greatly. Tumor blood flow is frequently obstructed as tumor size increases, as often seen clinically; early stage, small tumors show a more uniform EPR effect, whereas advanced large tumor show heterogeneity in EPR effect. Accordingly, it would be very important to apply enhancers of EPR effect in clinical setting to make EPR effect more uniform. In this review, we discuss the EPR effect: its history, factors involved, and dynamics and heterogeneity. Strategies to overcome the EPR effect's heterogeneity may guarantee better therapeutic outcomes of drug delivery to advanced cancers.

[Anti-CD206 antibody-conjugated Fe3O4-based PLGA nanoparticles selectively promotes M1 polarization of tumorassociated macrophages in mice]

OBJECTIVE

To enhance the anti-tumor immunity of macrophages by increasing iron concentration in the macrophages using nanospheres.

METHODS

Anti-CD206 antibody-conjugated Fe₃O₄-based polylactic acid glycolic acid (CD206- Fe₃O₄-PLGA) nanoparticles were prepared with the W/O/W method. The particle diameter was measured using Malvern particle size detector, the Zeta potential was determined using Zeta potentiometry, and the encapsulation efficiency of Fe₃O₄ was determined using an iron determination kit. The macrophage-binding and targeting abilities of the conjugated nanoparticles were evaluated using immunofluorescence assay, and the polarization index of macrophages was determined with Western blotting and qRT-PCR. BALB/C-57 mouse models bearing subcutaneous tumors were used to verify the efficacy of the nanoparticles to promote polarization of the tumor-associated macrophages (TAMs).

RESULTS

The conjugated nanoparticles had a mean diameter of 260-295 nm with Zeta potential values ranging from -19 mV to -33 mV, encapsulation efficiency of Fe₃O₄ ranging from 65% to 75%, and anti-CD206 conjunction efficiency of 65%-70%. Immunofluorescence assay verified the targeted binding ability of the nanoparticles with M2 macrophages. Western blotting and qRT-PCR confirmed that both CD206-Fe₃O₄-PLGA and Fe₃O₄-PLGA nanoparticles promoted the expression of TNF-α, iNOS and IL-1β (P < 0.05). In the tumor-bearing mouse models, CD206-Fe₃O₄-PLGA nanoparticles were confirmed to promote CD86 expression in the TAMs.

CONCLUSIONS

CD206-Fe₃O₄-PLGA nanoparticles are capable of targeted binding to M2 macrophages and reversing the M2 macrophages to M1 phenotype by releasing coated iron oxide particles.

Recent advances of drug delivery nanocarriers in osteosarcoma treatment

Osteosarcoma is the most common primary malignant bone tumor mainly occurred in children and adolescence, and chemotherapy is limited for the side effects and development of drug resistance. Advances in nanotechnology and knowledge of cancer biology have led to significant improvements in developing tumor-targeted drug delivery nanocarriers, and some have even entered clinically application. Delivery of chemotherapeutic agents by functionalized smart nanocarriers could protect the drugs from rapid clearance, prolong the circulating time, and increase the drug concentration at tumor sites, thus enhancing the therapeutic efficacy and reducing side effects. Various drug delivery nanocarriers have been designed and tested for osteosarcoma treatment, but most of them are still at experimental stage, and more further studies are needed before clinical application. In this present review, we briefly describe the types of commonly used nanocarriers in osteosarcoma treatment, and discuss the strategies for osteosarcoma-targeted delivery and controlled release of drugs. The application of nanoparticles in the management of metastatic osteosarcoma is also briefly discussed. The purpose of this article is to present an overview of recent progress of nanoscale drug delivery platforms in osteosarcoma, and inspire new ideas to develop more effective therapeutic options.

Micro/nano-bubble-assisted ultrasound to enhance the EPR effect and potential theranostic applications

Drug delivery for tumor theranostics involves the extensive use of the enhanced permeability and retention (EPR) effect. Previously, various types of nanomedicines have been demonstrated to accumulate in solid tumors via the EPR effect. However, EPR is a highly variable phenomenon because of tumor heterogeneity, resulting in low drug delivery efficacy in clinical trials. Because ultrasonication using micro/nanobubbles as contrast agents can disrupt blood vessels and enhance the specific delivery of drugs, it is an effective approach to improve the EPR effect for the passive targeting of tumors. In this review, the basic thermal effect, acoustic streaming, and cavitation mechanisms of ultrasound, which are characteristics that can be utilized to enhance the EPR effect, are briefly introduced. Second, micro/nanobubble-enhanced ultrasound imaging is discussed to understand the validity and variability of the EPR effect. Third, because the tumor microenvironment is complicated owing to elevated interstitial fluid pressure and the deregulated extracellular matrix components, which may be unfavorable for the EPR effect, few new trends in smart bubble drug delivery systems, which may improve the accuracy of EPR-mediated passive drug targeting, are summarized. Finally, the challenging and major concerns that should be considered in the next generation of micro/nanobubble-contrast-enhanced ultrasound theranostics for EPR-mediated passive drug targeting are also discussed.

Thirty Years of Cancer Nanomedicine: Success, Frustration, and Hope

Starting with the enhanced permeability and retention (EPR) effect discovery, nanomedicine has gained a crucial role in cancer treatment. The advances in the field have led to the approval of nanodrugs with improved safety profile and still inspire the ongoing investigations. However, several restrictions, such as high manufacturing costs, technical challenges, and effectiveness below expectations, raised skeptical opinions within the scientific community about the clinical relevance of nanomedicine. In this review, we aim to give an overall vision of the current hurdles encountered by nanotherapeutics along with their design, development, and translation, and we offer a prospective view on possible strategies to overcome such limitations.

Size-Optimized Ultrasmall Porous Silica Nanoparticles Depict Vasculature-Based Differential Targeting in Triple Negative Breast Cancer

Rapid sequestration and prolonged retention of intravenously injected nanoparticles by the liver and spleen (reticuloendothelial system (RES)) presents a major barrier to effective delivery to the target site and hampers clinical translation of nanomedicine. Inspired by biological macromolecular drugs, synthesis of ultrasmall (diameter ≈12-15 nm) porous silica nanoparticles (UPSNs), capable of prolonged plasma half-life, attenuated RES sequestration, and accelerated hepatobiliary clearance, is reported. The study further investigates the effect of tumor vascularization on uptake and retention of UPSNs in two mouse models of triple negative breast cancer with distinctly different microenvironments. A semimechanistic mathematical model is developed to gain mechanistic insights into the interactions between the UPSNs and the biological entities of interest, specifically the RES. Despite similar systemic pharmacokinetic profiles, UPSNs demonstrate strikingly different tumor responses in the two models. Histopathology confirms the differences in vasculature and stromal status of the two models, and corresponding differences in the microscopic distribution of UPSNs within the tumors. The studies demonstrate the successful application of multidisciplinary and complementary approaches, based on laboratory experimentation and mathematical modeling, to concurrently design optimized nanomaterials, and investigate their complex biological interactions, in order to drive innovation and translation.

Smart Targeting To Improve Cancer Therapeutics

Cancer is the second largest cause of death worldwide with the number of new cancer cases predicted to grow significantly in the next decades. Biotechnology and medicine can and should work hand-in-hand to improve cancer diagnosis and treatment efficacy. However, success has been frequently limited, in particular when treating late-stage solid tumors. There still is the need to develop smart and synergistic therapeutic approaches to achieve the synthesis of strong and effective drugs and delivery systems. Much interest has been paid to the development of smart drug delivery systems (drug-loaded particles) that utilize passive targeting, active targeting, and/or stimulus responsiveness strategies. This review will summarize some main ideas about the effect of each strategy and how the combination of some or all of them has shown to be effective. After a brief introduction of current cancer therapies and their limitations, we describe the biological barriers that nanoparticles need to overcome, followed by presenting different types of drug delivery systems to improve drug accumulation in tumors. Then, we describe cancer cell membrane targets that increase cellular drug uptake through active targeting mechanisms. Stimulus-responsive targeting is also discussed by looking at the intra- and extracellular conditions for specific drug release. We include a significant amount of information summarized in tables and figures on nanoparticle-based therapeutics, PEGylated drugs, different ligands for the design of active-targeted systems, and targeting of different organs. We also discuss some still prevailing fundamental limitations of these approaches, eg, by occlusion of targeting ligands.

Complexation of methotrexate via ligand diffusion molecular dynamic simulations under neutral, basic, and acidic conditions

Methotrexate (MTX), an FDA-approved drug employed in the treatment of several types of cancer and autoimmune diseases, is characterized by its poor solubility. Therefore, new strategies have been implemented such as coupling to nanocarriers to increase its solubility. Previous experimental studies have demonstrated complexation of MTX to polyamidoamine of a generation four (PAMAM-G4) dendrimer with a complex stoichiometry of 19/22:1 under neutral conditions, providing important information that can be used to further elucidate the structural and energetic basis of the molecular binding of MTX and PAMAM-G4. In this study, we performed ligand diffusion molecular dynamic simulations (LDMDSs), using 3 μs combined with the molecular mechanics generalized surface area (MMGBSA) approach employing saturating concentrations of MTX to explore the mechanism through which MTX is complexed by PAMAM-G4 at neutral, basic, and acidic conditions. Our results reproduce the reported complex stoichiometry between MTX and PAMAM-G4 in neutral conditions. Binding free energy values suggest a much slower release in neutral and acidic conditions, consistent with the controlled rate of drug release into the bloodstream and when reaching the acidic environment of tumor tissues. Altogether, the methodology employed and the results may be useful in the evaluation of other drugs of pharmaceutical interest.

A Simple, Yet Multifunctional, Nanoformulation for Eradicating Tumors and Preventing Recurrence with Safely Low Administration Dose

Designing simple-structured nanomedicine without lacking key functionalities, thereby avoiding incomplete damage or relapse of tumor with the administration of a safe dose, is pivotal for successful cancer nanotherapy. We herein presented a nanomedicine of photodynamic therapy (PDT) that simply assembled amphiphilic macromolecules of poly-l-lysine conjugating with photosensitizers onto hydrophobic upconverting nanoparticles. We demonstrated that the nanoformulation, despite its simple structure and synthesis, simultaneously possesses multiple features, including substantial payload of photosensitizers, avid cellular internalization both in vitro and in vivo, efficient diffusion and broad distribution in tumor lesion, and potent fatality for cancer stem cells that are refractory to other therapy modalities. Because of the combination of these functionalities, the tumors in mice were eradicated and no relapse was observed after at least 40 days, just with an extremely low intraperitoneal injection dose of 5.6 mg/kg. Our results suggested a strategy for designing multifunctional nanomedicines with simple construct and efficacious therapeutic response and presented the promising potential of PDT for a radical cure of cancer.

Responses of Chlorella vulgaris exposed to boron: Mechanisms of toxicity assessed by multiple endpoints

Boron (B) has been widely used and contaminated the aquatic ecosystem. However, knowledge of the effects of sodium pentaborate pentahydrate (SPP) on algae remains limited. This study aimed to assess SPP toxicity using multiple endpoints, specially detecting the intracellular metal ion concentrations, malondialdehyde (MDA) content and extracellular polymeric substance (EPS) classes for the very first time during SPP exposure to Chlorella vulgaris (C. vulgaris). Our findings indicated that the inhibitory effects of SPP on C. vulgaris may be related to nutrient absorption and utilization. The changes in intracellular starch grains, MDA and the protein-like substances in EPS probably acted as a defense mechanism, helping to alleviate the toxic effects. This work may contribute to the understanding of the mechanism of SPP toxicity in algae. Further studies may focus on the effects of B on speciation of metallic ions and the interaction of B with metallic ions on aquatic organisms.

Augmentation of EPR Effect and Efficacy of Anticancer Nanomedicine by Carbon Monoxide Generating Agents

One obstacle to the successful delivery of nanodrugs into solid tumors is the heterogeneity of an enhanced permeability and retention (EPR) effect as a result of occluded or embolized tumor blood vessels. Therefore, the augmentation of the EPR effect is critical for satisfactory anticancer nanomedicine. In this study, we focused on one vascular mediator involved in the EPR effect, carbon monoxide (CO), and utilized two CO generating agents, one is an extrinsic CO donor (SMA/CORM2 micelle) and another is an inducer of endogenous CO generation via heme oxygenase-1 (HO-1) induction that is carried out using pegylated hemin. Both agents generated CO selectively in solid tumors, which resulted in an enhanced EPR effect and a two- to three-folds increased tumor accumulation of nanodrugs. An increase in drug accumulation in the normal tissue did not occur with the treatment of CO generators. In vivo imaging also clearly indicated a more intensified fluorescence of macromolecular nanoprobe in solid tumors when combined with these CO generators. Consequently, the combination of CO generators with anticancer nanodrugs resulted in an increased anticancer effect in the different transplanted solid tumor models. These findings strongly warrant the potential application of these CO generators as EPR enhancers in order to enhance tumor detection and therapy using nanodrugs.

Bacterial magnetosomes loaded with doxorubicin and transferrin improve targeted therapy of hepatocellular carcinoma

High metastatic rate and recurrence of tumor because of tumor circulating cells are seriously hinders for clinical tumor therapy. Herein, we develop a novel, active-targeting nanotherapeutic by simultaneously loading doxorubicin (DOX) and transferrin (Tf) onto bacterial magnetosomes (Tf-BMs-DOX) and investigate its antitumor efficacy in vitro and in vivo. Drug release profiles indicated that Tf-BMs/BMs loaded with DOX were capable of sustained drug release, suggesting that reduce drugs required frequency of administration and enhance their therapeutic effect. The results of cellular uptake revealed that Tf-BMs-DOX recognized hepatocellular carcinoma HepG2 cells more specifically compared to HL-7702 normal hepatocytes because of high expression of transferrin receptor (TfR) on the surface of HepG2 cells. Tf-BMs-DOX increased tumor cytotoxicity and apoptosis more significantly than free DOX or BMs-DOX by regulating the expression of tumor-related and apoptosis-related genes. Following intravenous injection in HepG2 cell-bearing mice, Tf-BMs-DOX displayed tumor suppression rate of 56.78%, significantly higher than that of the BMs-DOX (41.53%) and free DOX (31.26%) groups. These results suggest that Tf-BMs-DOX have the potential to actively target to tumor sites, as well as the ability to kill circulating tumor cells via intravenous injection. Our findings provide a promising candidate for the clinical treatment of metastatic cancer.

Organotropic drug delivery: Synthetic nanoparticles and extracellular vesicles

Most clinically approved drugs (primarily small molecules or antibodies) are rapidly cleared from circulation and distribute throughout the body. As a consequence, only a small portion of the dose accumulates at the target site, leading to low efficacy and adverse side effects. Therefore, new delivery strategies are necessary to increase organ and tissue-specific delivery of therapeutic agents. Nanoparticles provide a promising approach for prolonging the circulation time and improving the biodistribution of drugs. However, nanoparticles display several limitations, such as clearance by the immune systems and impaired diffusion in the tissue microenvironment. To overcome common nanoparticle limitations various functionalization and targeting strategies have been proposed. This review will discuss synthetic nanoparticle and extracellular vesicle delivery strategies that exploit organ-specific features to enhance drug accumulation at the target site.

Ligand density on nanoparticles: A parameter with critical impact on nanomedicine

Nanoparticles modified with ligands for specific targeting towards receptors expressed on the surface of target cells are discussed in literature towards improved delivery strategies. In such concepts the ligand density on the surface of the nanoparticles plays an important role. How many ligands per nanoparticle are best for the most efficient delivery? Importantly, this number may be different for in vitro and in vivo scenarios. In this review first viruses as "biological" nanoparticles are analyzed towards their ligand density, which is then compared to the ligand density of engineered nanoparticles. Then, experiments are reviewed in which in vitro and in vivo nanoparticle delivery has been analyzed in terms of ligand density. These results help to understand which ligand densities should be attempted for better targeting. Finally synthetic methods for controlling the ligand density of nanoparticles are described.

Free radical-mediated targeting and immobilization of coupled payloads

Targeted drug delivery is a promising approach to enhance the accumulation of therapies in diseased tissues while limiting off-site effects. Ligand-receptor interactions are traditionally identified to deliver therapies, and although specific, this can be costly and often suffers from limited sensitivity. An emerging approach is to target intermediary species that modulate disease progression. Here, we propose novel methods of targeting therapies by using native free radicals as a homing signal. Elevated concentrations of free radicals are a characteristic comorbidity of many different diseases. In polymer chemistry, free radicals are frequently used to initiate crosslinking reactions. We proposed that free radicals elevated in injury sites are capable of inducing crosslinking of acrylate groups on polymer chains. Coupling payloads to the polymer then allow for specific targeting of therapies to areas with elevated free radicals. We demonstrate in vitro proof-of-principle of this approach. Reactive oxygen species (ROS) initiated crosslinking of acrylated PEGs, which immobilized a fluorescent payload within tissue mimics. The cross-linking efficiency and immobilization potential varied with the polymer chain length, suggesting that a tuneable platform can be achieved. Together these results provide promising proof-of-concept for using free radicals to specifically target and sustain nearly endless payloads to disease sites.

Cancer-targeted and glutathione-responsive micellar carriers for controlled delivery of cabazitaxel

Novel type of multifunctional polymeric micelles (PMs) designated as HM-PMss/CTX micelles were developed in the present study for tumor-targeted and glutathione (GSH)-responsive delivery of cabazitaxel (CTX). The surface of the vehicles was modified with piloting molecules (HM-3 peptide), which targets α _v β ₃ integrin overexpressed on cancer cells, and the micelle core was cross-linked by GSH-disintegrable disulfide linkages for controlled drug release. HM-PMss/CTX micelles were prepared using a mixture of two functionalized amphiphilic block copolymers and found to physically encapsulate CTX with excellent entrapment efficiency (93.94 ± 4.19%), drug-loading capacity (8.39 ± 2.28%), and a narrow size distribution. In vitro release profiles showed that CTX remained stably entrapped in the micelles in a release medium without GSH or with GSH of low concentration, while undergoing a rapid release in a highly reductive environment. Cellular uptake experiments showed that the conjugation of the targeting peptide, containing an arginine-glycine-aspartate sequence, enhanced the cellular uptake of HM-PMss/CTX micelles via α _v β ₃ integrin-mediated endocytosis. In vitro cell viability measurements revealed that blank micelles were biocompatible, while HM-PMss/CTX micelles, owing to their tumor-targeting ability and GSH sensitivity, effectively inhibited the proliferation of MDA-MB-231 breast cancer cells. These results indicate that HM-PMss/CTX micelles could be a promising platform for future intelligent drug delivery in cancer therapy.

A novel method for conjugating the terminal amine of peptide ligands to cholesterol: synthesis iRGD-cholesterol

AIM

Conventional conjugation reactions often involve the use of activated PEG as a linker, but concerns about PEG-mediated reduction in intracellular delivery and enhanced immunogenicity have generated interest in developing methods that eliminate the need for a PEG linker.

MATERIALS & METHODS

Reaction conditions were identified that specifically couples the terminal amine of a cyclic iRGD peptide (CRGDRGPDC) to the hydroxyl moiety of cholesterol through a short carbamate linker.

RESULTS & CONCLUSION

Using this method for synthesizing iRGD-cholesterol, peptide ligands can be incorporated into lipid-based delivery systems, thereby eliminating concerns about adverse reactions to PEG. Toxicity and stability data indicate low toxicity and adequate serum stability at low ligand levels.

Stimuli-responsive graphene-incorporated multifunctional chitosan for drug delivery applications: a review

INTRODUCTION

Recently, the use of chitosan (CS) in the drug delivery has reached an acceptable maturity. Graphene-based drug delivery is also increasing rapidly due to its unique physical, mechanical, chemical, and electrical properties. Therefore, the combination of CS and graphene can provide a promising carrier for the loading and controlled release of therapeutic agents.

AREAS COVERED

In this review, we will outline the advantages of this new drug delivery system (DDS) in association with CS and graphene alone and will list the various forms of these carriers, which have been studied in recent years as DDSs. Finally, we will discuss the application of this hybrid composite in other fields.

EXPERT OPINION

The introducing the GO amends the mechanical characteristics of CS, which is a major problem in the use of CS-based carriers in drug delivery due to burst release in a CS-based controlled release system through the poor mechanical strength of CS. Many related research on this area are still not fully unstated and occasionally they seem inconsistent in spite of the intent to be complementary. Therefore, a sensitive review may be needed to understand the role of graphene in CS/graphene carriers for future drug delivery applications.

P-glycoprotein-targeted photodynamic therapy boosts cancer nanomedicine by priming tumor microenvironment

Cancer nanomedicines only modestly improve the overall survival of patients because their anticancer activity is limited by biological barriers posed by the tumor microenvironment. Currently, all the drugs in FDA-approved cancer nanomedicines are substrates for P-glycoprotein (Pgp), and thus, Pgp-mediated multidrug resistance (MDR) remains a hurdle for cancer nanomedicines.

Methods: In this study, Pgp-targeted photodynamic therapy (PDT) was developed to enhance the anticancer efficacy of nanomedicines by depleting MDR cancer cells as well as enhancing tumor penetration of nanomedicines. We first examined the Pgp specificity of our targeted PDT approach, and then tested combination therapy of PDT with Doxil in mixed tumor models of MDR cancer cells and stromal cells, mimicking human heterogeneous tumors.

Results: In vitro studies showed that the antibody-photosensitizer conjugates produced Pgp-specific cytotoxicity towards MDR cancer cells upon irradiation with a near-infrared light. The studies with a co-culture model of MDR cancer cells and stromal cells revealed synergistic effects in the combination therapy of PDT with Doxil. Using a mouse model of mixed tumors containing MDR cancer cells and stroma cells, we observed markedly enhanced tumor delivery of Doxil after PDT in vivo. We further examined the effects of the two modalities on individual cell populations and their synergism using an in vivo dual substrate bioluminescence assay. The results indicated that Pgp-targeted PDT specifically depleted MDR cancer cells and further enhanced Doxil's actions on both MDR cancer cells and stromal cells.

Conclusion: We conclude that our targeted PDT approach markedly enhances anticancer actions of nanomedicines by depleting MDR cancer cells and increasing their tumor penetration, and thereby, may provide an effective approach to facilitate translation of cancer nanomedicines.

Tat-functionalized Ag-Fe3O4 nano-composites as tissue-penetrating vehicles for tumor magnetic targeting and drug delivery

In this paper, we prepared a dual functional system based on dextrin-coated silver nanoparticles which were further attached with iron oxide nanoparticles and cell penetrating peptide (Tat), producing Tat-modified Ag-Fe₃O₄ nanocomposites (Tat-FeAgNPs). To load drugs, an –SH containing linker, 3-mercaptopropanohydrazide, was designed and synthesized. It enabled the silver carriers to load and release doxorubicin (Dox) in a pH-sensitive pattern. The delivery efficiency of this system was assessed in vitro using MCF-7 cells, and in vivo using null BalB/c mice bearing MCF-7 xenograft tumors. Our results demonstrated that both Tat and externally applied magnetic field could promote cellular uptake and consequently the cytotoxicity of doxorubicin-loaded nanoparticles, with the IC₅₀ of Tat-FeAgNP-Dox to be 0.63 µmol/L. The in vivo delivery efficiency of Tat-FeAgNP carrying Cy5 to the mouse tumor was analyzed using the in vivo optical imaging tests, in which Tat-FeAgNP-Cy5 yielded the most efficient accumulation in the tumor (6.7±2.4% ID of Tat-FeAgNPs). Anti-tumor assessment also demonstrated that Tat-FeAgNP-Dox displayed the most significant tumor-inhibiting effects and reduced the specific growth rate of tumor by 29.6% (P = 0.009), which could be attributed to its superior performance in tumor drug delivery in comparison with the control nanovehicles.

Augmentation of the Enhanced Permeability and Retention Effect with Nitric Oxide-Generating Agents Improves the Therapeutic Effects of Nanomedicines

Enhanced permeability and retention (EPR) effect-based nanomedicine is a promising strategy for successful anticancer therapy. The EPR effect is based on tumor blood flow. Because advanced large tumors, as frequently seen in clinical settings, are heterogeneous, with regions of defective vasculature and blood flow, achieving the desired tumor drug delivery is difficult. Here, we utilized the EPR effect to increase drug delivery. To augment the EPR effect for improved therapeutic effects of nanomedicine, we exploited vascular mediators-the nitric oxide (NO) generators nitroglycerin (NG), hydroxyurea, and l-arginine. These compounds generate NO in tumors with relatively high selectivity. Using different nanosized drugs in our protocol significantly increased (1.5-2 times) delivery of nanomedicines to different solid tumor models, along with markedly improving (2-3-fold) the antitumor effects of these drugs. Also, in 7,12-dimethylbenz[a]anthracene-induced advanced end-stage breast cancer, often seen in clinical settings, 2 mg/kg polymer-conjugated pirarubicin (P-THP) with NG (0.2 mg/mouse) showed better effects than did 5 mg/kg P-THP, and 5 mg/kg P-THP used with NG resulted in cures or stable tumors (no tumor growth) for up to 120 days. Moreover, in a murine autochthonous azoxymethane/dextran sulfate sodium-induced colon cancer model, NO donors markedly improved the therapeutic effects of P-THP even after just one injection, results that were comparable with those achieved with three weekly P-THP treatments. These findings strongly suggest the potential usefulness of NO donors as EPR effect enhancers to improve the therapeutic efficacy of nanomedicines.

P-glycoprotein targeted and near-infrared light-guided depletion of chemoresistant tumors

Drug resistance remains a formidable challenge to cancer therapy. P-glycoprotein (Pgp) contributes to multidrug resistance in numerous cancers by preventing accumulation of anticancer drugs in cancer cells. Strategies to overcome this resistance have been vigorously sought for over 3 decades, yet clinical solutions do not exist. The main reason for the failure is lack of cancer specificity of small-molecule Pgp inhibitors, thus causing severe toxicity in normal tissues. In this study, Pgp-targeted photodynamic therapy (PDT) was developed to achieve superior cancer specificity through antibody targeting plus locoregional light activation. Thus, a Pgp monoclonal antibody was chemically modified with IR700, a porphyrin photosensitizer. In vitro studies showed that the antibody-photosensitizer conjugates specifically bind to Pgp-expressing drug resistant cancer cells, and caused dramatic cytotoxicity upon irradiation with a near infrared light. We then tested our Pgp-targeted approach in mouse xenograft models of chemoresistant ovarian cancer and head and neck cancer. In both models, targeted PDT produced rapid tumor shrinkage, and significantly prolonged survival of tumor-bearing mice. We conclude that our targeted PDT approach produces molecularly targeted and spatially selective ablation of chemoresistant tumors, and thereby provides an effective approach to overcome Pgp-mediated multidrug resistance in cancer, where conventional approaches have failed.