Enhanced permeability and retention effect for selective targeting of anticancer nanomedicine: are we there yet?

Nanomedicine: is it lost in translation?

By the end of 2017 more than 200,000 scientific research articles had been published about nanomedicine. Out of this vast number only a few of the reported nanoconstructs reached clinical trials for various applications, including the diagnosis and treatment of several cancers, and the treatment of infections and other non-cancerous diseases. 30 years after the pioneering work in this field of research, the low product yield at the end of research pipeline leads to a question that is asked by many: 'had nanomedicine been lost in translation?' In this review, we will discuss the landscape of nanomedicine regarding cancer treatment and miscellaneous applications as well as some obstacles toward full utilization of this powerful therapeutic tool and suggest a few solutions to improve the current translational value of nanomedicine research.

Sildenafil citrate improves the delivery and anticancer activity of doxorubicin formulations in a mouse model of breast cancer

Sildenafil is an approved drug for the treatment of erectile dysfunction. The drug exerts its action through the relaxation of smooth muscles and the modulation of vascular endothelial permeability. In this work, we tested whether the aforementioned effects of sildenafil on tumour vasculatures could result in an improvement of anticancer drug concentration in tumour tissues and hence improves its anticancer effect. Sildenafil when added to doxorubicin showed synergistic anticancer activity against 4T1 breast cancer cells in vitro. Adding 1, 30 and 100 μM of Viagra to 1 μM of doxorubicin resulted in 1.8-fold, 6.2-fold and 21-fold statistically significant increases in its cytotoxic effect, respectively. As a result, 4T1 tumour-bearing mice showed up to 2.7-fold increase in drug concentrations of the fluorescent Dye DiI and doxorubicin in tumour tissues, as well as their nanoformulations. Animals treated with the combinations of both Sildenafil citrate and doxorubicin showed a statistically significant 4.7-fold reduction in tumour size compared to doxorubicin alone. This work highlights the effect of Sildenafil on tumour vasculatures and provides a rational for further testing the combination on breast cancer patients.

Vincristine liposomes with smaller particle size have stronger diffusion ability in tumor and improve tumor accumulation of vincristine significantly

The passive targeting is the premise of active targeting that could make nanocarrier detained in tumor tissue. The particle size is the most important factor that influences the diffusion and distribution of nanoparticle both in vivo and in vitro. In order to investigate the relationship between particle size and diffusion ability, two kinds of liposome loaded with Vincristine (VCR-Lip) were prepared. The diffusion behavior of VCR-Lip with different particle size and free VCR was compared through diffusion stability study. The diffusion ability from 12-well culture plate to Millipore transwell of each formulation reflected on HepG-2 cytotoxicity results. Different cell placement methods and drug adding positions were used to study the VCR-Lip diffusion behaviors, which influenced the apoptosis of HepG-2 cell. The different cell uptake of Nile red–Lip and free Nile red was compared when changed the adding way of fluorescent fluorescein. To study the penetration ability in HepG-2 tumor spheroids, we constructed 30 nm and 100 nm Cy5.5-Lip to compare with free Cy5.5. Then the anti-tumor effect, tissue distribution of free VCR injection, 30 nm and 100 nm VCR-Lip were further investigated on the HepG-2 tumor bearing nude mice. The results of these study showed that the diffusion ability of free drug and fluorescent fluorescein was remarkable stronger than which encapsulated in liposomes. Moreover, diffusion ability of smaller liposome was stronger than larger one. In this way, 30 nm liposome had not only faster and stronger tumor distribution than 100 nm liposome, but also higher tumor drug accumulation than free drug as well. Our study provided a new thinking to improve the targeting efficiency of nano drug delivery system, no matter passive or active targeting.

Fabrication and Cytotoxicity of Gemcitabine-Functionalized Magnetite Nanoparticles

Nanotechnology has been successfully used for the fabrication of targeted anti-cancer drug carriers. This study aimed to obtain Fe₃O₄ nanoparticles functionalized with Gemcitabine to improve the cytotoxic effects of the chemotherapeutic substance on cancer cells. The (un) functionalized magnetite nanoparticles were synthesized using a modified co-precipitation method. The nanoconjugate characterization was performed by XRD, SEM, SAED and HRTEM; the functionalizing of magnetite with anti-tumor substances has been highlighted through TGA. The interaction with biologic media has been studied by means of stability and agglomeration tendency (using DLS and Zeta Potential); also, the release kinetics of the drug in culture media was evaluated. Cytotoxicity of free-Gemcitabine and the obtained nanoconjugate were evaluated on human BT 474 breast ductal carcinoma, HepG2 hepatocellular carcinoma and MG 63 osteosarcoma cells by MTS. In parallel, cellular morphology of these cells were examined through fluorescence microscopy and SEM. The localization of the nanoparticles related to the cells was studied using SEM, EDX and TEM. Hemolysis assay showed no damage of erythrocytes. Additionally, an in vivo biodistribution study was made for tracking where Fe₃O₄@Gemcitabine traveled in the body of mice. Our results showed that the transport of the drug improves the cytotoxic effects in comparison with the one produced by free Gemcitabine for the BT474 and HepG2 cells. The in vivo biodistribution test proved nanoparticle accumulation in the vital organs, with the exception of spleen, where black-brown deposits have been found. These results indicate that our Gemcitabine-functionalized nanoparticles are a promising targeted system for applications in cancer therapy.

Recent advances in hyaluronic acid-decorated nanocarriers for targeted cancer therapy

The cluster-determinant 44 (CD44) receptor has a high affinity for hyaluronic acid (HA) binding and is a desirable receptor for active targeting based on its overexpression in cancer cells compared with normal body cells. The nanocarrier affinity can be increased by conjugating drug-loaded carriers with HA, allowing enhanced cancer cell uptake via the HA-CD44 receptor-mediated endocytosis pathway. In this review, we discuss recent advances in HA-based nanocarriers and micelles for cancer therapy. In vitro and in vivo experiments have repeatedly indicated HA-based nanocarriers to be a target-specific drug and gene delivery platform with great promise for future applications in clinical cancer therapy.

Self-Assembling Doxorubicin Prodrug Forming Nanoparticles and Effectively Reversing Drug Resistance In Vitro and In Vivo

Doxorubicin (DOX) is a widely used chemotherapeutic drug to treat a range of cancers. However, its unfavorable effects, particularly the cardiotoxicity and the induction of multidrug resistance (MDR), significantly limit its clinical applications. Herein, a novel doxorubicin prodrug, PEG_2K -DOX, is synthesized by conjugating a deprotonated doxorubicin molecule with the polyethylene glycol (PEG, MW: 2K) chain via pH-responsive hydrazone bond, and its potential as a better alternative than doxorubicin is evaluated. The data show that the amphiphilic PEG_2K -DOX can self-assemble into stable nanoparticles with a high and fixed doxorubicin loading content (≈20 wt%), a favorable size of 91.5 nm with a narrow polydispersity (PDI = 0.14), good stability, and pH-dependent release behavior due to the acid-cleavable linkage between PEG and doxorubicin. Although doxorubicin hardly accumulates in MDR cells, PEG_2K -DOX nanoparticles significantly increase the cellular uptake and cell-killing activity of doxorubicin in two MDR cancer cell lines MCF-7/ADR and KBv200, with the IC₅₀ values dropped to 1.130% and 42.467% of doxorubicin, respectively. More impressively, PEG_2K -DOX nanoparticles exhibit significantly improved plasma pharmacokinetics, increased in vivo therapeutic efficacy against MDR xenograft tumors, and better in vivo safety compared with doxorubicin. PEG_2K -DOX nanoparticles hold the promise to become a better alternative than doxorubicin for cancer treatment, especially for MDR tumors.

Tumor cell-specific photothermal killing by SELEX-derived DNA aptamer-targeted gold nanorods

Despite widespread availability of cytotoxic chemotherapeutic agents, the killing of tumour cells without affecting healthy surrounding tissue remains elusive, although recent developments in terms of plasmonic nanoparticles capable of photothermal killing have some promise. Here we describe novel DNA aptamer-tethered gold nanorods (GNRs) that act as efficient photothermal therapeutics against tumour cells, but not their isogenic normal cell counterparts. A modified Cell-SELEX process was developed to select a novel DNA aptamer (KW16-13) that specifically recognised and was internalised by cells of the MCF10CA1h human breast ductal carcinoma line but not by those of its isogenic normal counterpart (MCF10A). GNRs conjugated to KW16-13 were readily internalized by the MCF10CA1h tumour cells with minimal uptake by MCF10A normal cells. Upon near infrared (NIR) light irradiation, tumour cell death of >96%, could be effected, compared to <1% in the normal cells or cells incubated with GNRs alone, our KW16-13 aptamer-targeted GNRs thus showing >71-fold tumor cell death than GNRs-targeted with a previously described aptamer. This demonstrates the significant potential for aptamer functionalised-GNRs to be used effective and above all selective anti-cancer photothermal therapeutics.

Tumor therapy: targeted drug delivery systems

The review highlights the main targeted drug delivery systems for tumor therapy, including the targeting sites, strategies, mechanisms and preclinical/clinical trials.

Preparation and cellular targeting study of VEGF-conjugated PLGA nanoparticles

Vascular endothelial growth factor receptor (VEGFR) is over-expressed on a variety of tumour cells and tumour neovasculature, and so becomes well-documented target for cancer treatment. This study was designed to evaluate the cellular targeting and anti-tumor potency of VEGF-conjugated nanoparticles (VEGF-NPs). The poly-lactic-co-glycolic acid nanoparticles were prepared using the emulsion-solvent evaporation method and the VEGF was conjugated on surface of nanoparticles by covalent coupling method. The obtained particles were found to be of spherical shape exhibiting a size of 710 nm and VEGF conjugation efficiency was 16.6%. The results in vitro test showed that VEGF-NPs were more associated to Human Umbilical Vein Endothelial Cells by binding to VEGFR. In vitro cell proliferation test, IC50 showed the superior antiproliferative activity of paclitaxel-loaded VEGF-NPs over unconjugated nanoparticles and native paclitaxel due to higher cellular association on tumour cells. So, the VEGF-NPs offer a promising active targeting carrier for tumour selective treatment.

Targeting strategies for delivery of anti-HIV drugs

Human Immunodeficiency Virus (HIV) infection remains a significant cause of mortality globally. Though antiretroviral therapy has significantly reduced AIDS-related morbidity and mortality, there are several drawbacks in the current therapy, including toxicity, drug–drug interactions, development of drug resistance, necessity for long-term drug therapy, poor bio-availability and lack of access to tissues and reservoirs. To circumvent these problems, recent anti-HIV therapeutic research has focused on improving drug delivery systems through drug delivery targeted specifically to host cells infected with HIV or could potentially get infected with HIV. In this regard, several surface molecules of both viral and host cell origin have been described in recent years, that would enable targeted drug delivery in HIV infection. In the present review, we provide a comprehensive overview of the need for novel drug delivery systems, and the successes and challenges in the identification of novel viral and host-cell molecules for the targeted drug delivery of anti-HIV drugs. Such targeted anti-retroviral drug delivery approaches could pave the way for effective treatment and eradication of HIV from the body.