Promoting tumor penetration of nanoparticles for cancer stem cell therapy by TGF-β signaling pathway inhibition

A nano-based thermotherapy for cancer stem cell-targeted therapy

Cancer stem cells (CSCs) exhibit high resistance to conventional therapy and are responsible for cancer metastasis and tumor relapse.

Dual pH-Responsive Polymer Nanogels with a Core-Shell Structure for Improved Cell Association

We report the fabrication of polymer nanogels with a pH-responsive core and a pH-sheddable shell and investigate the pH-dependent cell association of the pH-responsive polymer nanogels. The pH-responsive core composed of poly(2-diisopropylaminoethyl methacrylate) (PDPA) with a pK_a ≈ 6.2 was synthesized by using polymerization in emulsion droplets. The pH-sheddable poly(ethylene glycol) (PEG) shell was coated on the amine-modified PDPA nanogels by an acid-degradable amide bond. The PEG shell is cleavable in response to the acidic tumor microenvironment, and subsequently, the surface charge of the nanogels can be reversed, which effectively enhances cellular association of these nanogels. The reported pH-responsive polymer nanogels provide a promising way for the better understanding of bio-nano interactions and potentially enrich the application of therapeutic delivery for cancer therapy.

Therapeutic Strategies Targeting Cancer Stem Cells and Their Microenvironment

Cancer stem cells (CSCs) have been demonstrated in a variety of tumors and are thought to act as a clonogenic core for the genesis of new tumor growth. This small subpopulation of cancer cells has been proposed to help drive tumorigenesis, metastasis, recurrence and conventional therapy resistance. CSCs show self-renewal and flexible clonogenic properties and help define specific tumor microenvironments (TME). The interaction between CSCs and TME is thought to function as a dynamic support system that fosters the generation and maintenance of CSCs. Investigation of the interaction between CSCs and the TME is shedding light on the biologic mechanisms underlying the process of tumor malignancy, metastasis, and therapy resistance. We summarize recent advances in CSC biology and their environment, and discuss the challenges and future strategies for targeting this biology as a new therapeutic approach.

Recent advances in polymeric materials for the delivery of RNA therapeutics

Introduction: The delivery of nucleic acid therapeutics through non-viral carriers face multiple biological barriers that reduce their therapeutic efficiency. Despite great progress, there remains a significant technological gap that continues to limit clinical translation of these nanocarriers. A number of polymeric materials are being exploited to efficiently deliver nucleic acids and achieve therapeutic effects. Areas covered: We discuss the recent advances in the polymeric materials for the delivery of nucleic acid therapeutics. We examine the use of common polymer architectures and highlight the challenges that exist for their development from bench side to clinic. We also provide an overview of the most notable improvements made to circumvent such challenges, including structural modification and stimuli-responsive approaches, for safe and effective nucleic acid delivery. Expert opinion: It has become apparent that a universal carrier that follows 'one-size' fits all model cannot be expected for delivery of all nucleic acid therapeutics. Carriers need to be designed to exhibit sensitivity and specificity toward individual targets diseases/indications, and relevant subcellular compartments, each of which possess their own unique challenges. The ability to devise synthetic methods that control the molecular architecture enables the future development that allow for the construction of 'intelligent' designs.

Application of Nanotechnology in Targeting of Cancer Stem Cells: A Review

Cancer is increasingly apparent as a systems-level, network happening. The central tendency of malignant alteration can be described as a two-phase procedure, where an initial increase of network plasticity is followed by reducing plasticity at late stages of tumor improvement. Cancer stem cells (CSCs) are cancer cells that take characteristics associated with normal stem cells. Cancer therapy has been based on the concept that most of the cancer cells have a similar ability to separate metastasise and kill the host. In this review, we addressed the use of nanotechnology in the treatment of cancer stem cells.

Role of Nanoparticle Mechanical Properties in Cancer Drug Delivery

The physicochemical properties of nanoparticles play critical roles in regulating nano-bio interactions. Whereas the effects of the size, shape, and surface charge of nanoparticles on their biological performances have been extensively investigated, the roles of nanoparticle mechanical properties in drug delivery, which have only been recognized recently, remain the least explored. This review article provides an overview of the impacts of nanoparticle mechanical properties on cancer drug delivery, including (1) basic terminologies of the mechanical properties of nanoparticles and techniques for characterizing these properties; (2) current methods for fabricating nanoparticles with tunable mechanical properties; (3) in vitro and in vivo studies that highlight key biological performances of stiff and soft nanoparticles, including blood circulation, tumor or tissue targeting, tumor penetration, and cancer cell internalization, with a special emphasis on the underlying mechanisms that control those complicated nano-bio interactions at the cellular, tissue, and organ levels. The interesting research and findings discussed in this review article will offer the research community a better understanding of how this research field evolved during the past years and provide some general guidance on how to design and explore the effects of nanoparticle mechanical properties on nano-bio interactions. These fundamental understandings, will in turn, improve our ability to design better nanoparticles for enhanced drug delivery.

The softness of tumour-cell-derived microparticles regulates their drug-delivery efficiency

Extracellular microparticles (MPs) can function as drug-delivery vehicles for anticancer drugs. Here, we show that the softness of MPs derived from tumour-repopulating cells (TRCs) isolated from three-dimensional fibrin gels enhances the MPs' drug-delivery efficiency. We found that, compared with MPs derived from tumour cells cultured in conventional tissue-culture plastic, TRC-derived MPs intravenously injected in tumour-xenograft-bearing mice showed enhanced accumulation in tumour tissues, enhanced blood-vessel crossing and penetration into tumour parenchyma, and preferential uptake by highly tumorigenic TRCs. We also show that the cytoskeleton-related protein cytospin-A plays a critical role in the regulation of TRC-derived MP softness. The modulation of the mechanical properties of TRC-derived MPs could aid the efficiency of delivery of anticancer drugs.

The Evolving Landscape of Cancer Stem Cells and Ways to Overcome Cancer Heterogeneity

Cancer stem cells (CSCs) with therapeutic resistance and plasticity can be found in various types of tumors and are recognized as attractive targets for treatments. As CSCs are derived from tissue stem or progenitor cells, and/or dedifferentiated mature cells, their signal transduction pathways are critical in the regulation of CSCs; chronic inflammation causes the accumulation of genetic mutations and aberrant epigenetic changes in these cells, potentially leading to the production of CSCs. However, the nature of CSCs appears to be stronger than the treatments of the past. To improve the treatments targeting CSCs, it is important to inhibit several molecules on the signaling cascades in CSCs simultaneously, and to overcome cancer heterogeneity caused by the plasticity. To select suitable target molecules for CSCs, we have to explore the landscape of CSCs from the perspective of cancer stemness and signaling systems, based on the curated databases of cancer-related genes. We have been studying the integration of a broad range of knowledge and experiences from cancer biology, and also from other interdisciplinary basic sciences. In this review, we have introduced the concept of developing novel strategies targeting CSCs.

Development of "CLAN" Nanomedicine for Nucleic Acid Therapeutics

Nucleic acid-based macromolecules have paved new avenues for the development of therapeutic interventions against a spectrum of diseases; however, their clinical translation is limited by successful delivery to the target site and cells. Therefore, numerous systems have been developed to overcome delivery challenges to nucleic acids. From the viewpoint of clinical translation, it is highly desirable to develop systems with clinically validated materials and controllability in synthesis. With this in mind, a cationic lipid assisted PEG-b-PLA nanoparticle (CLAN) is designed that is capable of protecting nucleic acids via encapsulation inside the aqueous core, and delivers them to target cells, while maintaining or improving nucleic acid function. The system is formulated from clinically validated components (PEG-b-PLA and its derivatives) and can be scaled-up for large scale manufacturing, offering potential for its future use in clinical applications. Here, the development and working mechanisms of CLANs, the ways to improve its delivery efficacy, and its application in various disease treatments are summarized. Finally, a prospective for the further development of CLAN is also discussed.

Engineering Nanoparticles for Targeted Delivery of Nucleic Acid Therapeutics in Tumor

In the past 10 years, with the increase of investment in clinical nano-gene therapy, there are many trials that have been discontinued due to poor efficacy and serious side effects. Therefore, it is particularly important to design a suitable gene delivery system. In this paper, we introduce the application of liposomes, polymers, and inorganics in gene delivery; also, different modifications with some stimuli-responsive systems can effectively improve the efficiency of gene delivery and reduce cytotoxicity and other side effects. Besides, the co-delivery of chemotherapy drugs with a drug tolerance-related gene or oncogene provides a better theoretical basis for clinical cancer gene therapy.

Targeting stem cells in the realm of drug-resistant breast cancer

Since its first documentation, breast cancer (BC) has been a conundrum that ails millions of women every year. This cancer has been well studied by researchers all over the world, which has improved the patient outcome significantly. There are many diagnostic markers to identify the disease, but early detection and then subclassification of this cancer remain dubious. Even after the correct diagnosis, more than half the patients come back with a more aggressive and metastatic tumor. The underpinning mechanism that governs the resistance includes over-amplification of receptors, mutations in key gene targets, and activation of different signaling. A plethora of drugs have been devised that have shown promising results in clinical settings. However, in recent times, the role played by cancer stem cells in disease progression and their interaction in mediating the resistance to cellular insults have come into the limelight. As breast cancer stem cells (BCSCs) are dormant in nature, it is highly likely that they fail to directly respond to the cytotoxic drugs which are meant for ablating rapidly proliferating cells. Furthermore, the absence of well-characterized, drug-able surface markers to date, has limited the application of targeted therapies in complete eradication of the disease. In this review, our intent is to discuss versatile therapeutics in practice followed by discussing the upcoming therapy strategies in the pipeline for BC. Furthermore, we focus on the roles played by BCSCs in mediating the resistance, and therefore, the aspects of new therapeutics against BCSCs under development that may ease the burden in future has also been discussed.

Nanotechnology in metastatic cancer treatment: Current Achievements and Future Research Trends

The systemic spread of malignant cells from a primary site, a process termed metastasis represents a global challenge in cancer treatment. There is a real need to develop novel therapy strategies and nanomedicine may have remarkable and valuable contribution through specific and selective delivery of chemotherapeutic agents, through its intrinsic cytotoxic activity or through imaging applications, appealing also in the context of cancer personalized therapy. This review is focused on the applications of nanoparticles in the treatment of metastatic cancer, particularly on the possible effect on cell stabilization, growth inhibition, eventual interaction with adhesion molecules and antiangiogenic effect.

Nucleus-targeted nano delivery system eradicates cancer stem cells by combined thermotherapy and hypoxia-activated chemotherapy

Many efforts have focused on the cancer stem cell (CSC) targeting nano delivery system, however, the anticancer therapy efficacy is relative low due to the highly drug-resistance and drug efflux. Nucleus-targeted drug delivery is a promising strategy for reverse the drug resistance and drug efflux of CSCs, but in vivo nucleus-targeted drug delivery has been challenging. Herein, we designed a mesoporous silica nanoparticle (MSN)-based nucleus-targeted system, which could directly target the CSCs and further enter the nucleus by the surface modification of anti-CD133 and thermal-triggered exposure of TAT peptides under an alternating magnetic field (AMF). The nucleus-targeted drug release ultimately leads to an exhaustive apoptosis of the CSCs through combined thermotherapy and hypoxia-activated chemotherapy. In vivo, the nucleus-targeted nano delivery system efficiently inhibits the tumor growth without notable side effects during the course of treatment. Molecular mechanism study illustrates that the system effectively eliminates the CSCs by blocking the hypoxia signaling pathway. This designed nucleus-targeted nano delivery system is expected to provide new insights for developing efficient platforms for CSC-targeted cancer therapy.

Designing nanoparticles with improved tumor penetration: surface properties from the molecular architecture viewpoint

Cancer is the second most common cause of death, and nanomedicine is regarded as one of the strategies that may revolutionize cancer treatments. However, the tumor microenvironment (e.g., increased interstitial fluid pressure and dense extracellular matrix) hinders the penetration of nanomedicine into tumor cells, which leads to a short acting time and low drug concentration with tumors, eventually leading to a high recurrence rate and therapeutic failure in clinics. Developing a delivery system with deep penetration ability into the tumor has always been pursued and highly desirable for cancer treatments. Inspired by the high cellular uptake efficiency of enveloped viruses with rough and nanoscale surfaces, we constructed polystyrene nanoparticles (NPs) with similar sizes and charges, but with different surface topologies at the molecular level, by conjugating poly(propylene imine) (PPI) dendrimers with different generations onto the NPs. We found that subtle changes made to the surficial chemical properties led to changes in surface roughness and wettability, which considerably influenced the cellular internalization, endocytosis mechanism, and penetration into the tumor model both in vitro and in vivo. This will shed light on the future design of drug delivery vehicles and facilitate understanding the interactions between NP surfaces and cells, as well as tumor penetration.

Hydrophobicity-Adaptive Nanogels for Programmed Anticancer Drug Delivery

Reconciling the conflicting needs for a prolonged circulation time, enhanced cellular uptake by bulk tumor cells and cancer stem cells (CSCs), and extensive tumor tissue penetration remains a major challenge for current nano drug delivery systems. Here we describe smart poly( N-isopropylacrylamide)-based nanogels with a fast adaptive hydrophobicity to solve these contradictory requirements for enhanced cancer chemotherapy. The nanogels are hydrophilic in the blood to prolong their circulation time. Once they accumulate at tumor sites, they rapidly become hydrophobic in response to tumor extracellular acidity. The adaptive hydrophobicity of the nanogels facilitates tumor accumulation, deep tumor penetration, and efficient uptake by bulk tumor cells and CSCs, resulting in a greater in vivo enrichment in tumor cells and side population cells. Together with lysosomal pH-regulated charge reversal and redox-responsive intracellular drug release, the nanogels escape from lysosomes and release their cargo doxorubicin. Thus, the nanogels significantly improve the in vivo anticancer efficacy and decrease side effects of doxorubicin. Strikingly, the ratio of CSCs is greatly decreased after treatment with the nanogels loaded with doxorubicin. Our current study provides new insights into designing effective anticancer drug delivery systems.

Deep Tumor-Penetrated Nanocages Improve Accessibility to Cancer Stem Cells for Photothermal-Chemotherapy of Breast Cancer Metastasis

Cancer stem cells (CSCs) are proposed to account for the initiation of cancer metastasis, but their accessibility remains a great challenge. This study reports deep tumor-penetrated biomimetic nanocages to augment the accessibility to CSCs fractions in tumor for anti-metastasis therapy. The nanocages can load photothermal agent of 1,1-dioctadecyl-3,3,3,3-tetramethylindotricarbocyanine iodide (DBN) and chemotherapeutic epirubicin (EBN) to eradicate CSCs for photothermal-chemotherapy of breast cancer metastasis. In metastatic 4T1-indcued tumor model, both DBN and EBN can efficiently accumulate in tumor sites and feasibly permeate throughout the tumor mass. These biomimetic nanosystems can be preferentially internalized by cancer cells and effectively accessed to CSCs fractions in tumor. The DBN+laser/EBN treatment produces considerable depression of primary tumor growth, drastically eradicates around 80% of CSCs fractions in primary tumor, and results in 95.2% inhibition of lung metastasis. Thus, the biomimetic nanocages can be a promising delivery nanovehicle with preferential CSCs-accessibility for effective anti-metastasis therapy.

Breast cancer stem cells: Features, key drivers and treatment options

The current view is that breast cancer is a stem cell disease characterized by the existence of cancer cells with stem-like features and tumor-initiating potential. These cells are made responsible for tumor dissemination and metastasis. Common therapies by chemotherapeutic drugs fail to eradicate these cells and rather increase the pool of cancer stem cells in tumors, an effect that may increase the likelyhood of recurrence. Fifteen years after the first evidence for a small stem-like subpopulation playing a major role in breast cancer initiation has been published a large body of knowledge has been accumulated regarding the signaling cascades and proteins involved in maintaining stemness in breast cancer. Differences in the stem cell pool size and in mechanisms regulating stemness in the different breast cancer subtypes have emerged. Overall, this knowledge offers new approaches to intervene with breast cancer stem cell activity. New options are particularly needed for the treatment of triple-negative breast cancer subtype, which is particularly rich in cancer stem cells and is also the subtype for which specific therapies are still not available.

Emerging functional markers for cancer stem cell-based therapies: Understanding signaling networks for targeting metastasis

Metastasis is one of the most challenging issues in cancer patient management, and effective therapies to specifically target disease progression are missing, emphasizing the urgent need for developing novel anti-metastatic therapeutics. Cancer stem cells (CSCs) gained fast attention as a minor population of highly malignant cells within liquid and solid tumors that are responsible for tumor onset, self-renewal, resistance to radio- and chemotherapies, and evasion of immune surveillance accelerating recurrence and metastasis. Recent progress in the identification of their phenotypic and molecular characteristics and interactions with the tumor microenvironment provides great potential for the development of CSC-based targeted therapies and radical improvement in metastasis prevention and cancer patient prognosis. Here, we report on newly uncovered signaling mechanisms controlling CSC's aggressiveness and treatment resistance, and CSC-specific agents and molecular therapeutics, some of which are currently under investigation in clinical trials, gearing towards decisive functional CSC intrinsic or surface markers. One special research focus rests upon subverted regulatory pathways such as insulin-like growth factor 1 receptor signaling and its interactors in metastasis-initiating cell populations directly related to the gain of stem cell- and EMT-associated properties, as well as key components of the E2F transcription factor network regulating metastatic progression, microenvironmental changes, and chemoresistance. In addition, the study provides insight into systems biology tools to establish complex molecular relationships behind the emergence of aggressive phenotypes from high-throughput data that rely on network-based analysis and their use to investigate immune escape mechanisms or predict clinical outcome-relevant CSC receptor signaling signatures. We further propose that customized vector technologies could drastically enhance systemic drug delivery to target sites, and summarize recent progress and remaining challenges. This review integrates available knowledge on CSC biology, computational modeling approaches, molecular targeting strategies, and delivery techniques to envision future clinical therapies designed to conquer metastasis-initiating cells.

Size shrinkable drug delivery nanosystems and priming the tumor microenvironment for deep intratumoral penetration of nanoparticles

The penetration of nanomedicine into solid tumor still constitutes a great challenge for cancer therapy, which lead to the failure of thorough clearance of tumor cells. Aiming at solving this issue, lots of encouraging progress has been made in the development of multistage nanoparticles triggered by various stimuli in the past few years. Besides, the therapeutical effects of nanoagents are also greatly impacted by the complex tumor microenvironment, and remodeling tumor microenvironment has become another important approach for promoting nanoparticles penetration. In this review, we summarize and analyze recent research progress and challenges in promoting nanoparticle penetration based on two kinds of different strategies, which include size shrinkable nanoparticles and priming tumor microenvironments. Especially, many recent reported multi-strategy approaches based on particle size reduction in conjugated with other therapeutic strategies are discussed. And we expect to provide some useful enlightenments and proposals on nanotechnology-based drug delivery systems for more effective therapy of solid tumors.

Amphiphilic poly(α)glutamate polymeric micelles for systemic administration of siRNA to tumors

RNAi therapeutics carried a great promise to the area of personalized medicine: the ability to target "undruggable" oncogenic pathways. Nevertheless, their efficient tumor targeting via systemic administration had not been resolved yet. Amphiphilic alkylated poly(α)glutamate amine (APA) can serve as a cationic carrier to the negatively-charged oligonucleotides. APA polymers complexed with siRNA to form round-shaped, homogenous and reproducible nano-sized polyplexes bearing ~50 nm size and slightly negative charge. In addition, APA:siRNA polyplexes were shown to be potent gene regulators in vitro. In light of these preferred physico-chemical characteristics, their performance as systemically-administered siRNA nanocarriers was investigated. Intravenously-injected APA:siRNA polyplexes accumulated selectively in tumors and did not accumulate in the lungs, heart, liver or spleen. Nevertheless, the polyplexes failed to induce specific mRNA degradation, hence neither reduction in tumor volume nor prolonged mice survival was seen.

A Distinct Endocytic Mechanism of Functionalized-Silica Nanoparticles in Breast Cancer Stem Cells

Nanoparticles provide new fields for life medical science application, including targeted-drug delivery and cancer treatment. To maximize the delivery efficiency of nanoparticle, one must understand the uptake mechanism of nanoparticle in cells, which may determine their ultimate fate and localization in cells. Recently, the proposed-cancer stem cell (CSC) theory has been attracted great attention and regarded as new targets for the new nanodrug developmet and cancer therapies. The interaction between nanoparticles and cancer cells has been extensively studied, but the uptake mechanism of nanoparticles in CSCs has received little attention. Here, we use the pharmacological inhibitors of major endocytic pathways to study the silica nanoparticle (SiNP) uptake mechanisms in the human breast adenocarcinoma cell line (MCF-7) and MCF-7-derived breast cancer stem cells (BCSCs). The results demonstrate that the uptake of SiNPs, particularly amino-functionalized SiNPs, in MCF-7 cells is strongly affected by the actin depolymerization, whereas BCSCs more strongly inhibit the amino-functionalized SiNP uptake after the scavenger receptor disruption. These findings indicate a distinct endocytic mechanism of functionalized SiNPs in BCSCs, which is significant for designing ideal nanosized drug delivery systems and improving the selectivity for CSC-targeted therapy.

EGFR-targeting PLGA-PEG nanoparticles as a curcumin delivery system for breast cancer therapy

Poor bioavailability and non-specificity of chemotherapeutic agents are major challenges in breast cancer treatment. Antibodies and small molecules that block cell signaling pathways have shown promise in the clinic, but their application is also limited by the high costs and treatment dosages required. Novel therapies that aim to rapidly and specifically target malignant cells with long-lasting impact in the tumor microenvironment may ultimately improve clinical outcome in cancer patients. Here, we demonstrate that epidermal growth factor receptor (EGFR)-targeting GE11 peptides conjugated with PEGylated polylactic-co-glycolic acid (PLGA) nanoparticles can be used to effectively deliver an anti-cancer agent, curcumin, into EGFR-expressing MCF-7 cells in vitro and in vivo. Treatment of breast cancer cells and tumor-bearing mice with these curcumin-loaded nanoparticles gave rise to reduced phosphoinositide 3-kinase signaling, decreased cancer cell viability, attenuated drug clearance from the circulation, and suppressed tumor burden compared with free curcumin or non-EGFR targeting nanoparticles. The targeted nanoscale drug delivery system we describe here may provide a new strategy for the design of targeted cancer therapy vectors. Our study provides evidence that the efficacy of pharmacologic anti-cancer agents can be enhanced through their delivery in the form of modified nanoparticles that effectively target specific malignant cell types.

Advances in cancer stem cell targeting: How to strike the evil at its root

Cancer progression to metastatic stages is still unmanageable and the promise of effective anti-metastatic therapy remains largely unmet, emphasizing the need to develop novel therapeutics. The special focus here is on cancer stem cells (CSC) as the seed of tumor initiation, epithelial-mesenchymal transition, chemoresistance and, as a consequence, drivers of metastatic dissemination. We report on targeted therapies gearing towards the CSC's internal and membrane-anchored markers using agents such as antibody derivatives, nucleic therapeutics, small molecules and genetic payloads. Another emphasis lies on novel proceedings envisaged to deliver current and prospective therapies to the target sites using newest viral and non-viral vector technologies. In this review, we summarize recent progress and remaining challenges in therapeutic strategies to combat CSC.

Single-walled carbon nanotube: One specific inhibitor of cancer stem cells in osteosarcoma upon downregulation of the TGFβ1 signaling

Cancer stem cells (CSCs) are believed to have a critical role in tumorigenesis, metastasis, therapeutic resistance or recurrence. Therefore, strategies designed to specifically target and eliminate CSCs have become one of the most promising and desirable ways for tumor treatment. Osteosarcoma stem cells (OSCs), the CSCs in osteosarcoma (OS), are critically associated with OS progression. Here, we show that single-walled carbon nanotubes (SWCNTs), including unmodified SWCNT (SWCNT-Raw) and SWCNT-COOH, have the ability to specifically inhibit the process of TGFβ1-induced OS cells dedifferentiation, prevent the stem cell phenotypes acquisition in OS cells and reduce the OSC viability under conditions which mimic the OS microenvironment. Concurrently, SWCNT treatment significantly down-regulates the expression of OSC markers in OS, and markedly reduces the tumor microvessel density and tumor growth. Furthermore, we found that SWCNT could suppress the TGFβ1-induced activation of TGFβ type I receptor and downstream signaling, which are key for the OSC formation and maintenance. Our results reveal an unexpected function of SWCNT in negative modulation of OSCs, and provide significant implications for the potential CSCs-targeted therapeutic applications of SWCNT.

Nanocarrier based approaches for targeting breast cancer stem cells

Breast cancer stem cells (BCSCs) are heterogeneous subpopulation of tumour initiating cells within breast tumours. They are spared even after chemotherapy and responsible for tumour relapse. Targeting BCSCs is, therefore, necessary to achieve radical cure in breast cancer. Despite the availability of agents targeting BCSCs, their clinical application is limited due to their off-target effects and bioavailability issues. Nanotechnology based drug carriers (nanocarriers) offer various advantages to deliver anti-BCSCs agents specifically to their target sites by overcoming their bioavailability issues. In this review, we describe various strategies for targeting BCSCs using nanocarriers.

Nonviral cancer gene therapy: Delivery cascade and vector nanoproperty integration

Gene therapy represents a promising cancer treatment featuring high efficacy and limited side effects, but it is stymied by a lack of safe and efficient gene-delivery vectors. Cationic polymers and lipid-based nonviral gene vectors have many advantages and have been extensively explored for cancer gene delivery, but their low gene-expression efficiencies relative to viral vectors limit their clinical translations. Great efforts have thus been devoted to developing new carrier materials and fabricating functional vectors aimed at improving gene expression, but the overall efficiencies are still more or less at the same level. This review analyzes the cancer gene-delivery cascade and the barriers, the needed nanoproperties and the current strategies for overcoming these barriers, and outlines PEGylation, surface-charge, size, and stability dilemmas in vector nanoproperties to efficiently accomplish the cancer gene-delivery cascade. Stability, surface, and size transitions (3S Transitions) are proposed to resolve those dilemmas and strategies to realize these transitions are comprehensively summarized. The review concludes with a discussion of the future research directions to design high-performance nonviral gene vectors.

Rational Design of Cancer Nanomedicine: Nanoproperty Integration and Synchronization

Current cancer nanomedicines can only mitigate adverse effects but fail to enhance therapeutic efficacies of anticancer drugs. Rational design of next-generation cancer nanomedicines should aim to enhance their therapeutic efficacies. Taking this into account, this review first analyzes the typical cancer-drug-delivery process of an intravenously administered nanomedicine and concludes that the delivery involves a five-step CAPIR cascade and that high efficiency at every step is critical to guarantee high overall therapeutic efficiency. Further analysis shows that the nanoproperties needed in each step for a nanomedicine to maximize its efficiency are different and even opposing in different steps, particularly what the authors call the PEG, surface-charge, size and stability dilemmas. To resolve those dilemmas in order to integrate all needed nanoproperties into one nanomedicine, stability, surface and size nanoproperty transitions (3S transitions for short) are proposed and the reported strategies to realize these transitions are comprehensively summarized. Examples of nanomedicines capable of the 3S transitions are discussed, as are future research directions to design high-performance cancer nanomedicines and their clinical translations.

A novel double-targeted nondrug delivery system for targeting cancer stem cells

Instead of killing cancer stem cells (CSCs), the conventional chemotherapy used for cancer treatment promotes the enrichment of CSCs, which are responsible for tumor growth, metastasis, and recurrence. However, most therapeutic agents are only able to kill a small proportion of CSCs by targeting one or two cell surface markers or dysregulated CSC pathways, which are usually shared with normal stem cells (NSCs). In this study, we developed a novel nondrug delivery system for the dual targeting of CSCs by conjugating hyaluronic acid (HA) and grafting the doublecortin-like kinase 1 (DCLK1) monoclonal antibody to the surface of poly(ethylene glycol) (PEG)–poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles (NPs), which can specifically target CD44 receptors and the DCLK1 surface marker – the latter was shown to possess the capacity to distinguish between CSCSs and NSCs. The size and morphology of these NPs were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). This was followed by studies of NP encapsulation efficiency and in vitro drug release properties. Then, the cytotoxicity of the NPs was tested via Cell Counting Kit-8 assay. Finally, the 4T1 CSCs were obtained from the alginate-based platform, which we developed as an in vitro tumor model. Tumor-bearing nude mice were used as in vivo models to systematically detect the ability of NPs to target CSCs. Our results showed that the DCLK1–HA–PEG–PLGA NPs exhibited a targeting effect toward CSCs both in vitro and in vivo. These findings have important implications for the rational design of drug delivery systems that target CSCs with high efficacy.

Nanomedicine-Mediated Therapies to Target Breast Cancer Stem Cells

Accumulating evidences have suggested the existence of breast cancer stem cells (BCSCs), which possess the potential of both self-renewal and differentiation. The origin of BCSCs might have relationship to the development of normal mammary stem cells. BCSCs are believed to play a key role in the initiation, recurrence and chemo-/radiotherapy resistances of breast cancer. Therefore, elimination of BCSCs is crucial for breast cancer therapy. However, conventional chemo and radiation therapies cannot eradicate BCSCs effectively. Fortunately, nanotechnology holds great potential for specific and efficient anti-BCSCs treatment. “Smart” nanocarriers can distinguish BCSCs from the other breast cancer cells and selectively deliver therapeutic agents to the BCSCs. Emerging findings suggest that BCSCs in breast cancer could be successfully inhibited and even eradicated by functionalized nanomedicines. In this review, we focus on origin of BCSCs, strategies used to target BCSCs, and summarize the nanotechnology-based delivery systems that have been applied for eliminating BCSCs in breast cancer.

Combined cancer therapy with hyaluronan-decorated fullerene-silica multifunctional nanoparticles to target cancer stem-like cells

Cancer stem-like cells (CSCs) are resistant to chemotherapy and highly tumorigenic, which contributes to tumor occurrence and post-treatment relapse. We developed a novel C60 fullerene-silica nanoparticle system surface-decorated with hyaluronan (HA) to target the variant CD44 overexpressed on breast CSCs. Furthermore, doxorubicin hydrochloride (DOX) and indocyanine green (ICG) can be encapsulated in the nanoparticles with ultrahigh encapsulation efficiency (>90%) and loading content (e.g., 48.5% at a drug-to-nanoparticle feeding ratio of 1:1, compared to the commonly used drug-to-nanoparticle feeding ratio of 1:20 with a drug loading content of less than 5%). As a result, the DOX and ICG-laden nanoparticles can be used as a single nanoplatform to achieve combined chemo, photodynamic, and photothermal therapy under near infrared laser irradiation for effective destruction of the breast CSCs both in vitro and in vivo, with no evident systemic toxicity. Moreover, we found the nanoparticles with a higher drug loading content (e.g., 48.5 versus 4.6%) also have significantly higher antitumor efficacy, given the same total drug dose. These results demonstrate the great potential of the multifunctional hybrid nanoparticle system for augmenting cancer therapy by eliminating the CSCs.

Drug Delivery Using Nanoparticles for Cancer Stem-Like Cell Targeting

The theory of cancer stem-like cell (or cancer stem cell, CSC) has been established to explain how tumor heterogeneity arises and contributes to tumor progression in diverse cancer types. CSCs are believed to drive tumor growth and elicit resistance to conventional therapeutics. Therefore, CSCs are becoming novel target in both medical researches and clinical studies. Emerging evidences showed that nanoparticles effectively inhibit many types of CSCs by targeting various specific markers (aldehyde dehydrogenases, CD44, CD90, and CD133) and signaling pathways (Notch, Hedgehog, and TGF-β), which are critically involved in CSC function and maintenance. In this review, we briefly summarize the current status of CSC research and review a number of state-of-the-art nanomedicine approaches targeting CSC. In addition, we discuss emerging therapeutic strategies using epigenetic drugs to eliminate CSCs and inhibit cancer cell reprogramming.

Activated Charge-Reversal Polymeric Nano-System: The Promising Strategy in Drug Delivery for Cancer Therapy

Various polymeric nanoparticles (NPs) with optimal size, tumor-targeting functionalization, or microenvironment sensitive characteristics have been designed to solve several limitations of conventional chemotherapy. Nano-sized polymeric drug carrier systems have remarkably great advantages in drug delivery and cancer therapy, which are still plagued with severe deficiencies, especially insufficient cellular uptake. Recently, surface charge of medical NPs has been demonstrated to play an important role in cellular uptake. NPs with positive charge show higher affinity to anionic cell membranes such that with more efficient cellular internalization, but otherwise cause severe aggregation and fast clearance in circulation. Thus, surface charge-reversal NPs, specifically activated at the tumor site, have shown to elegantly resolve the enhanced cellular uptake in cancer cells vs. non-specific protein adsorption dilemma. Herein, this review mainly focuses on the effect of tumor-site activated surface charge reversal NPs on tumor treatment, including the activated mechanisms and various applications in suppressing cancer cells, killing cancer stem cell and overcoming multidrug resistance, with the emphasis on recent research in these fields. With the comprehensive and in-depth understanding of the activated surface charge reversal NPs, this approach might arouse great interest of scientific research on enhanced efficient polymeric nano-carriers in cancer therapy.