Next-generation nanocarriers for precision antitumor therapy: from passive targeting to intelligent response

Nanostructured lipid carriers in cancer therapy: Advances in passive and active targeting strategies.

Nanocarriers can penetrate the tumour vasculature through its leaky endothelium and, in this way, accumulate in several solid tumours. This is called the enhanced permeation and retention (EPR) effect. Together with nanocarriers whose surface is tailored for prolonged blood circulation times, the concept is referred to as passive targeting. Targeting ligands, which bind to specific receptors on the tumour cells and endothelium, can be attached on the nanocarrier surface. This active targeting increases the selectivity of the delivery of drugs. Passive and active drug targeting with nanocarriers to tumours reduce toxic side-effects, increase efficacy, and enhance delivery of poorly soluble or sensitive therapeutic molecules. In this review, currently studied and used passive and active targeting strategies in cancer therapy are presented.

Nanoparticle-mediated drug targeting is an active area of cancer research and hold enormous potential in improving anticancer efficacy by providing tumor tissue specificity. Herein, tumor targeting capabilities of nanoparticles between passive targeting approach via the enhanced permeability and retention (EPR ) effect and active targeting approach via the biotin receptors were compared to determine targeting efficiency rates. For this reason, Fe 3 O 4 @SiO 2 (FITC)-DOX (for passive targeting) and Fe 3 O 4 @SiO 2 (FITC)-BTN/DOX (for active targeting) multifunctional nanoparticles combining imaging and therapy were used. Fluorescence microscopy and flow cytometry were employed to both visualize and quantify the accumulation of nanoparticles into the tumor cells. The results demonstrated that active targeting strategy considerably enhanced nanoparticle accumulation in the cervical carcinoma HeLa cells with a 2-fold increase in comparison to passive targeting. Targeted nanoparticles exhibited higher cytotoxicity in cancer cells with an approximately 2.5-fold better half maximal inhibitory concentration (IC 50 ) value than untargeted nanoparticles. Moreover, it was found that targeted nanoparticles increased the number of apoptotic cells by nearly 21.1% as compared to untargeted nanoparticles. These observations show that active tumor targeting drug delivery systems could be more promising for enhancing the chemotherapeutic effects of anticancer drugs as compared to passive tumor targeting drug delivery systems.

Various types of nanoparticles, such as liposomes, polymeric micelles, dendrimers, superparamagnetic iron oxide crystals, and colloidal gold, have been employed in targeted therapies for cancer. Both passive and active targeting strategies can be utilized for nano-drug delivery. Passive targeting is based on the enhanced permeability and retention (EPR) effect of the vasculature surrounding tumors. Active targeting relies on ligand-directed binding of nanoparticles to receptors expressed by tumor cells. Release of loaded drugs from nanoparticles may be controlled in response to changes in environmental condition such as temperature and pH. Biodistribution profiles and anticancer efficacy of nano-drugs in vivo would be different depending upon their size, surface charge, PEGylation and other biophysical properties. This review focuses on the recent development of nanoparticles for tumor targeted therapies, including physicochemical properties, tumor targeting, control of drug release, pharmacokinetics, anticancer efficacy and safety. Future perspectives are discussed as well.

According to the World Health Organisation (WHO), cancer is the second leading cause of death globally, accounting for an estimated 9.6 million deaths in 2018.1 This is attributed to the several disadvantages and limitations of currently available diagnostic and treatment options such as lacking in sensitivity, targeting-specificity and poor resolution. The application of nanotechnology in medicine, termed “nanomedicine”, has shown tremendous potential in enhancing various conventional diagnostic and therapeutic techniques and the development of new novel ones. In particular, the development of nanoparticles (NPs) as specific and targeted drug delivery systems for various diseases including different types of cancers.2 NPs are defined as material with overall dimensions in the nanoscale (1-100nm). Particles on a nanoscale behave like nothing on large scales, as they have to satisfy the laws of quantum mechanics rather than semi-classical physics for microstructure/bulk materials. NPs have several unique properties in terms of their large surface to volume ratios giving them a very high chemical reactivity, quantisation of energy/quantum confinement allowing to be used as bioimaging agents and biological mobility, which are not present in macroscopic materials. NPs can be classified into different classes based on their properties, shapes and sizes. These include metallic NPs, polymeric NPs, lipid-based NPs and more recently polymer-lipid hybrid NPs.2,3 In targeted drug delivery, NPs protects the drugs from non-specific binding and allows for better tumour accumulation via passive and/or active targeting. Passive targeting is primarily driven by the enhanced permeability and retention (EPR) effect. Active targeting, on the other hand, relies on site-specific ligands (e.g. antibodies) used to functionated the surface of NPs. Alternatively, an on-site injection can be used for superficial tumours. Once at the tumour site, NPs can undergo cellular internalisation and intracellular drug release triggered by site-specific internal stimuli such as overexpressed proteolytic enzymes and acidic pH. NP formulations are being developed to deliver traditional chemotherapy drugs as well as non-toxic sensitising agents that only elicits a cytotoxic effect when they are activated by an external stimulus such as light, radiofrequency and low-intensity ultrasound.2 It has also offered the ability to develop non-invasive and effective theragnostic systems allowing for both diagnosis and treatment with a single agent such as photosensitive cyanine dyes.4 Another form of nanotechnology-based cancer treatment being developed is localised magnetic hyperthermia using magnetic NPs and more recently thermo-chemotherapy, where traditional chemotherapy agents are combined with magnetic NPs in the same formulation. Ferrite NPs or iron oxide NPs are the most explored magnetic NPs up to date. Once these particles are reduced to the nanoscale, they become superparamagnets, which means they only exhibit magnetic behaviour when an external magnetic field is applied. This, in theory, allows for magnetic targeting of the tumour site as an alternative to passive/active targeting but it has certain practical limitations such as possible damage to the blood vessels and surrounding tissues/organs. Once at the tumour site, these NPs can be made to vibrate by applying an alternating magnetic field. The heat is generated from the conversion of magnetic energy into heat energy.2 We still need to better understand the in-vivo nanoparticle-tissue interactions. In particular, the formation of protein corona (a coating of proteins adsorbed from plasma and/or intracellular fluid) around the nanoparticles that not only changes their overall shape and size but also eliminates the functionality of any surface modalities.5 A retrospective study (2005-2015) of NP targeting efficacy revealed a median NP delivery of 0.7% to solid tumours.6 Furthermore, there is a lack of research being carried out in nanotoxicity – toxic side-effects arising from particles on a nanoscale. Only an estimated 5% and 4% of EU's and US nanotechnology research budget is being spent on “nanotoxicity or impact on humans and the environment”.7 Generally, the toxicity studies rarely go beyond the weight loss and the histology of organs. Since the idea is to improve therapies, side-effects need to be investigated thoroughly – even at preclinical stages. Nevertheless, if these issues are addressed properly, nanotechnology does offer a lot of potential for developing novel cancer diagnostic and therapeutic techniques with high tumour-targeting specificity and sensitivity.

Active targeting redox-responsive mannosylated prodrug nanocolloids promote tumor recognition and cell internalization for enhanced colon cancer chemotherapy

Background The liver, a central organ in human metabolism, is often the primary target for drugs. However, conditions such as viral hepatitis, cirrhosis, non-alcoholic fatty liver disease (NAFLD), and hepatocellular carcinoma (HCC) present substantial health challenges worldwide. Existing treatments, which suffer from the non-specific distribution of drugs, frequently fail to achieve desired efficacy and safety, risking unnecessary liver harm and systemic side effects. Purpose The aim of this review is to synthesise the latest progress in the design of liver-targeted prodrugs, with a focus on passive and active targeting strategies, providing new insights into the development of liver-targeted therapeutic approaches. Methods This study conducted an extensive literature search through databases like Google Scholar, PubMed, Web of Science, and China National Knowledge Infrastructure (CNKI), systematically collecting and selecting recent research on liver-targeted prodrugs. The focus was on targeting mechanisms, including the Enhanced Permeability and Retention (EPR) effect, the unique microenvironment of liver cancer, and active targeting through specific transporters and receptors. Results Active targeting strategies achieve precise drug delivery by binding specific ligands to liver surface receptors. Passive targeting takes advantage of the EPR effect and tumour characteristics to enrich drugs in liver tumours. The review details successful cases of using small molecule ligands, peptides, antibodies and nanoparticles as drug carriers. Conclusion Liver-targeted prodrug strategies show great potential in enhancing the efficacy of drug treatment and reducing side effects for liver diseases. Future research should balance the advantages and limitations of both targeting strategies, focusing on optimising drug design and targeting efficiency, especially for clinical application. In-depth research on liver-specific receptors and the development of innovative targeting molecules are crucial for advancing the field of liver-targeted prodrugs.

Inadequate drug absorption, poor tumor selectivity, and the widespread emergence of chemoresistance are some of the ongoing issues facing modern cancer treatments. A paradigm change, targeted nanocarrier technologies allow for regulated release and site-specific drug accumulation while reducing systemic toxicity. The current mechanistic understanding of advanced nanocarrier platforms is summarized in this review, which explains how active targeting uses ligand-receptor interactions to promote receptor-mediated cellular internalization, while passive targeting takes advantage of the enhanced permeability and retention (EPR) phenomenon. In addition to biomimetic and immune cell-derived nanocarriers that exhibit superior biocompatibility and immune evasion, we look at current developments in stimuli-responsive nanosystems, such as pH-sensitive, redox-responsive, and externally-triggered platforms. Multifunctional theranostic systems that combine therapeutic and diagnostic capabilities are given special attention for applications in precision medicine. There includes a full discussion of mechanistic insights into drug release kinetics, intracellular trafficking pathways, and nanocarrier interactions with the tumor microenvironment. Additionally, we highlight new technologies including programmable and self-assembling nanocarrier platforms while addressing important translational challenges like immunological clearance, manufacturing scalability, regulatory complexity, and unfavorable bioaccumulation. The synergistic efficacy of integration with modern therapeutic methods, such as immunotherapy, gene editing, and combination chemotherapy, is assessed. In addition to identifying critical tactics to close the translational gap between preclinical innovation and clinical implementation, this thorough analysis establishes the fundamental mechanisms underlying next-generation nanomedicines, ultimately advancing accessible, individualized cancer therapies.

Despite the significant progress in the development of anticancer technology, there is still no common cure for patients with malignant diseases. Conventional anticancer treatments are nonspecific to target killing of tumor cells, and always lead to systemic toxicity, causing undesirable severe side effects such as hair loss, damages to liver, kidney, and bone marrow. In order to achieve therapeutic levels of drug at the tumor site without damaging healthy organs and tissues, it is important to recognize the physiological differences between diseased and normal sites. Targeting drug delivery system is attracting increasing interest in research field to remove severe side effects and to increase reorganization of physiological differences. Polymeric nanoparticles can accumulate and extravasate within tumor tissue since their prolonged circulation by enhanced permeation and retention (EPR) effect, passive targeting system, which is achieved due to disorganized vascularization and defective vascular architecture induced in rapidly growing cancers. Even though passive targeting system shows moderate tumor therapeutic efficacy, active targeting drug delivery system has recently gained considerable attention to improve specificity. Especially, ligand/receptor-medicated targeting has emerged as a novel paradigm in the active targeting. Here, we have investigated active targeted polymeric nanoparticles by conjugation of tumor-specific homing peptide, AP-1 peptide, with modified glycol chitosan nanoparticles. Selection of peptides which show preferential binding to the target can be achieved by biopanning phage-displayed peptide libraries. Phage display technique is a promising tool for selecting peptides or proteins with specific binding properties from a lot of variants. AP-1 peptide can bind with interleukin-4 receptor which expressed on surface of several human cancer cells like H226 and MDA-MB231. Developed peptide-guided targetable polymeric nanoparticles show more specific binding and uptake as well as better therapeutic efficacy than net polymeric nanoparticles, passive targeted nanoparticles, which were confirmed with flowcytometry, immunofluorescence, histology, immunohitochemistry studies and animal experiments. In addition, they are better candidate as an imaging probe for cancer imaging and diagnosis than net polymeric nanoparticles. In conclusion, AP-1 peptide-conjugated chitosan nanoparticles are effective candidate as drug carrier and imaging probe for cancer therapy and imaging since AP-1 peptide induces the improvement of cell binding and uptake of nanoparticles. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5487.

A variety of active pharmaceutical ingredients (APIs) currently used for cancer treatment are cytotoxic, and show nonspecific distribution when administered systemically resulting in toxicity to normal tissues, hence limiting their clinical application. To overcome these challenges, nanocarriers such as liposomes and micelles have been widely used to deliver APIs for cancer chemotherapy. Delivery of nanocarriers is achieved either via “passive targeting” owing to the enhanced permeability and retention (EPR) effect or via “active targeting” due to the presence of various ligands on the surface of nanocarriers, such as antibodies, peptides, etc. Numerous factors are involved in successful delivery of chemotherapeutic agents; these depend on the tumor microenvironment, formulation factors such as choice of ligand use, physiochemical properties of the nanocarriers, and the choice of target. In this chapter, we discuss the fundamentals of EPR effect, factors affecting passive and active targeting, and current clinical update of various actively and passively targeted liposomes and micelles.

Despite continuous improvement and significant progress made in diagnostic and therapeutic approaches for cancer, it is still the leading cause of death worldwide. Although conventional chemotherapy has made significant advances in improving patient survival the indiscriminate destruction of normal cells leads to severe side effects and poor clinical outcomes. Thus, there is a need for effective delivery of drugs to the tumor site avoiding normal tissues to reduce toxicity in the rest of the body. For this reason, a novel multidisciplinary field called Nanotechnology has evolved in recent years and advances in this field have contributed to the development of nanoscale materials to overcome the lack of specificity of conventional chemotherapeutic agents for optimized cancer therapy. Nanoparticles can be designed to preferentially target the tumor site and deliver high drug payloads by either passive or active targeting. Passive targeting exploits the preferential drug accumulation in tumor cells through enhanced permeability and retention (EPR) effect. On the other hand, active targeting uses functionalized nanoparticles to carry a drug to the specific site. This targeting strategy is becoming a new standard in cancer treatment. A selective and tumor site-specific treatment can be achieved by using various ligands such as aptamers, antibodies, peptides, and small molecules. Targeting nanocarriers serve as a highly promising strategy for effective cancer treatment, as shown by encouraging results in many recent studies. This thesis highlights the diversity of nanoparticle types, targeting mechanisms and active targeting strategies. I will also discuss an emerging field of nano drug delivery using biological nanovesicles called exosomes. Finally, I will discuss the current clinical status of nanoparticle formulations.

INNOVATIONS IN CONTROLLED AND TARGETED DRUG DELIVERY SYSTEMS Despite remarkable advances in pharmaceutical sciences, the clinical performance of many drugs remains constrained by suboptimal delivery strategies. Conventional dosage forms frequently release therapeutic agents at rates that are either excessive or insufficient, compromising both efficacy and safety. Immediate adverse reactions and long-term toxicities often arise not solely from the drug itself, but from the manner in which it is administered (1). Thus, drug delivery is no longer a passive component of therapy; it is a determinant of therapeutic success. The distribution of a drug across tissues and receptor sites directly influences its therapeutic index and overall clinical outcome. Recognizing this, researchers have increasingly shifted their focus to controlled, targeted drug delivery systems designed to optimize pharmacokinetics and pharmacodynamics while minimizing systemic exposure (2,3). As illustrated in Figure1a, innovative carrier platforms have transformed traditional administration approaches, enhancing both drug stability and therapeutic precision. Modern delivery systems—including liposomes, nanoparticles, micelles, microspheres, and hydrogels—aim to improve bioavailability by directing the drug moiety specifically to its site of action. Targeted delivery fundamentally relies on two coordinated processes: accurate target recognition and effective pharmacological action at the diseased site (4). The overarching objective is clear: to maximize therapeutic activity while reducing off-target toxicity, thereby improving patient outcomes and safety profiles. In contemporary pharmaceutical development, innovation is no longer limited to discovering new molecules; it increasingly lies in redefining how those molecules are delivered (5). ACTIVE AND PASSIVE TARGETING STRATEGIES The development of targeted drug delivery has fundamentally reshaped the therapeutic landscape. Active targeting involves functionalizing carrier systems with specific ligands that selectively recognize pathological sites, enhancing both accumulation and cellular uptake (Figure 1b). This approach has demonstrated significant promise in hematological malignancies such as leukemia and lymphomas, where receptor overexpression can be exploited to improve therapeutic precision (4,6). By directing drugs to their intended targets, active strategies minimize systemic exposure and reduce off-target toxicity. In contrast, passive targeting relies on the inherent pathophysiological characteristics of diseased tissues. Nanocarriers preferentially accumulate at sites such as the tumor interstitium due to the enhanced permeability and retention (EPR) effect, which arises from leaky vasculature and impaired lymphatic drainage (6,7). While less selective than ligand-mediated approaches, passive targeting remains foundational in nanomedicine and has guided the design of numerous clinically approved nanoformulations.

Glioblastoma, the most common, aggressive brain tumor, ranks among the least curable cancers—owing to its strong tendency for intracranial dissemination, high proliferation potential, and inherent tumor resistance to radiation and chemotherapy. Current glioblastoma treatment strategies are further hampered by a critical challenge: adverse, non-specific treatment effects in normal tissue combined with the inability of drugs to penetrate the blood brain barrier and reach the tumor microenvironment. Thus, the creation of effective therapies for glioblastoma requires development of targeted drug-delivery systems that increase accumulation of the drug in the tumor tissue while minimizing systemic toxicity in healthy tissues. As demonstrated in various preclinical glioblastoma models, macromolecular drug carriers have the potential to improve delivery of small molecule drugs, therapeutic peptides, proteins, and genes to brain tumors. Currently used macromolecular drug delivery systems, such as liposomes and polymers, passively target solid tumors, including glioblastoma, by capitalizing on abnormalities of the tumor vasculature, its lack of lymphatic drainage, and the enhanced permeation and retention (EPR) effect. In addition to passive targeting, active targeting approaches include the incorporation of various ligands on the surface of macromolecules that bind to cell surface receptors expressed on specific cancer cells. Active targeting approaches also utilize stimulus responsive macromolecules which further improve tumor accumulation by triggering changes in the physical properties of the macromolecular carrier. The stimulus can be an intrinsic property of the tumor tissue, such as low pH, or extrinsic, such as local application of ultrasound or heat. This review article explores current preclinical studies and future perspectives of targeted drug delivery to glioblastoma by macromolecular carrier systems, including polymeric micelles, nanoparticles, and biopolymers. We highlight key aspects of the design of diverse macromolecular drug delivery systems through a review of their preclinical applications in various glioblastoma animal models. We also review the principles and advantages of passive and active targeting based on various macromolecular carriers. Additionally, we discuss the potential disadvantages that may prevent clinical application of these carriers in targeting glioblastoma, as well as approaches to overcoming these obstacles.

Enhanced permeability and retention (EPR) and the (over-) expression of angiogenesis-related surface receptors are key features of tumor blood vessels. As a consequence, EPR-mediated passive and Arg-Gly-Asp (RGD) and Asn-Gly-Arg (NGR) based active tumor targeting have received considerable attention in the last couple of years. Using several different in vivo and ex vivo optical imaging techniques, we here visualized and quantified the benefit of RGD- and NGR-based vascular vs EPR-mediated passive tumor targeting. This was done using ∼ 10 nm sized polymeric nanocarriers, which were either labeled with DY-676 (peptide-modified polymers) or with DY-750 (peptide-free polymers). Upon coinjection into mice bearing both highly leaky CT26 and poorly leaky BxPC3 tumors, it was found that vascular targeting did work, resulting in rapid and efficient early binding to tumor blood vessels, but that over time, passive targeting was significantly more efficient, leading to higher overall levels and to more efficient retention within tumors. Although this situation might be different for larger carrier materials, these insights indicate that caution should be taken not to overestimate the potential of active over passive tumor targeting.

Active and passive tumor targeting of a novel poorly soluble cyclin dependent kinase inhibitor, JNJ-7706621