Carrier-free Nanomedicines Research Articles

Carrier-free supramolecular nanomedicines assembled by small-molecule therapeutics for cancer treatment

Nanomedicines have shown great promise in cancer therapy, but are challenged by limited drug loading, safety concerns of drug carriers, and complexity of function integration. Recently, carrier-free nanomedicines produced by supramolecular assembly of small-molecule therapeutic functionalities and their conjugates were proposed to address these issues. These nanomedicines achieve very high drug loading, enhanced tumor accumulation and improved therapeutic efficiency, and avoid carrier-related safety problems. In this review article, the applications of these nanomedicines in chemotherapy, photodynamic therapy, photothermal therapy as well as combination therapies will be reviewed. The concept of nanomedicine design and mechanism of supramolecular assembly will be discussed. Finally, future perspectives of carrier-free supramolecular nanomedicines for cancer therapy will be highlighted.

Carrier-Free Nanomedicine for Cancer Immunotherapy.

With the rapid development of nanotechnology, carrier-based nano-drug delivery systems (DDSs) have been widely studied due to their advantages in optimizing pharmacokinetic and distribution profiles. However, despite those merits, some carrier-related limitations, such as low drug-loading capacity, systematic toxicity and unclear metabolism, usually prevent their further clinical transformation. Carrier-free nanomedicines with non-therapeutic excipients, are considered as an excellent paradigm to overcome these obstacles, owing to their superiority in improving both drug delivery efficacy and safety concern. In recent years, carrier-free nanomedicines have opened new horizons for cancer immunotherapy, and have already made outstanding progress. Herein, in this review, we are focusing on making an integrated and exhaustive overview of lately reports about them. Firstly, the major synthetic strategies of carrier-free nanomedicines are introduced, such as nanocrystals, prodrug-, amphiphilic drug-drug conjugates (ADDCs)-, polymer-drug conjugates-, and peptide-drug conjugates (PepDCs)-assembled nanomedicines. Afterwards, the typical applications of carrier-free nanomedicines in cancer immunotherapy are well-discussed, including cancer vaccines, cytokine therapy, enhancing T-cell checkpoint inhibition, as well as modulating tumor microenvironment (TME). After that, both the advantages and the potential challenges, as well as the future prospects of carrier-free nanomedicines in cancer immunotherapy, were discussed. And we believe that it would be of great potential practiced and reference value to the relative fields.

Carrier Free O2 -Economizer for Photodynamic Therapy Against Hypoxic Tumor by Inhibiting Cell Respiration.

Abnormal tumor metabolism causes the hypoxic microenvironment, which greatly limits the efficacy of photodynamic therapy (PDT). In this work, a strategy of metabolic reprogramming is proposed to economize O2 for enhanced PDT against hypoxic tumors. The carrier-free O2 -economizer (designated as LonCe) is prepared based on the metabolic antitumor drug of Lonidamine (Lon) and the photosensitizer of chlorin e6 (Ce6). By virtue of intermolecular interactions, Lon and Ce6 self-assemble into nanosized LonCe with favorable stability and high drug contents. Compared with Ce6, LonCe exhibits an improved cellular uptake and photodynamic property for tumor treatment. Moreover, LonCe is capable of inhibiting cell metabolism and mitochondrial respiration to remit the tumor hypoxia, which would promote reactive oxygen species (ROS) production and elevate the PDT efficacy on tumor suppression. In vivo experiments indicate that intravenously injected LonCe prefers to accumulate at the tumor site for highly efficient PDT regardless of the hypoxic environment. Besides, the self-delivery LonCe is fabricated without any carriers, which avoids the excipients induced system toxicity and immunogenicity in vivo. This carrier-free nanomedicine with cell respiratory inhibition mechanism would expedite the development and clinical translation of photodynamic nanoplatforms in tumor treatment.

Photodynamic therapy initiated immunotherapy of self-delivery re-educator by inducing immunogenic cell death and macrophage polarization

Immunotherapy is a promising clinical treatment strategy against malignant tumor metastasis, however, it often shows an inadequate efficacy owing to the immunosuppressive tumor microenvironment (ITM). Herein, we develop a self-delivery re-educator to induce immunogenic cell death (ICD) and macrophage polarization for photodynamic therapy (PDT) and immunotherapy against breast cancer. To be specific, the self-delivery re-educator (designated as PyroR) is prepared by the self-assembly of the photosensitizer pyropheophorbide-a (Pyro) and TLR agonist resiquimod (R848). Without any carriers, nanosized PyroR exhibits high drug contents and could avoid the side effects raised by excipients. After intravenous administration, PyroR could generate a lot of reactive oxygen species (ROS) for PDT against primary tumor in the presence of light irradiation. Meanwhile, PDT triggered ICD cascade would promote dendritic cells (DCs) maturation and activate cytotoxic T lymphocytes (CTLs) for immunotherapy against distant and metastatic tumors. More importantly, R848 is able to polarize macrophages from M2 to M1 phenotype, which would improve the ITM to enhance antitumor immunity. Consequently, the PDT-initiated immunotherapy of PyroR demonstrates significant inhibition effects on primary, distant and metastatic tumors while causes a minimal system toxicity. This self-delivery re-educating strategy would shed light on constructing carrier-free nanomedicine for treatment of malignant tumors.

Ruthenium-based antitumor drugs and delivery systems from monotherapy to combination therapy.

Ruthenium complex is an important compound group for antitumor drug research and development. NAMI-A, KP1019, TLD1433 and other ruthenium complexes have entered clinical research. In recent years, the research on ruthenium antitumor drugs has not been limited to single chemotherapy drugs; other applications of ruthenium complexes have emerged such as in combination therapy. During the development of ruthenium complexes, drug delivery forms of ruthenium antitumor drugs have also evolved from single-molecule drugs to nanodrug delivery systems. The review summarizes the following aspects: (1) ruthenium complexes from monotherapy to combination therapy, including the development of single-molecule compounds, carrier nanomedicine, and self-assembly of carrier-free nanomedicine; (2) ruthenium complexes in the process of ADME in terms of absorption, distribution, metabolism and excretion; (3) the applications of ruthenium complexes in combination therapy, including photodynamic therapy (PDT), photothermal therapy (PTT), photoactivated chemotherapy (PACT), immunotherapy, and their combined application; (4) the future prospects of ruthenium-based antitumor drugs.

Carrier-free nanomedicine for enhanced photodynamic tumor therapy through glutathione S-transferase inhibition

A chlorine e6 and coniferyl ferulate-based self-delivery nanomedicine is developed to inhibit intracellular glutathione S-transferase (GST) and enhance the photodynamic therapy (PDT)-mediated oxidative damage on tumor cells.

Carrier‐Free Delivery of Ultrasmall π‐Conjugated Oligomer Nanoparticles with Photothermal Conversion over 80% for Cancer Theranostics

High-performance photothermal theranostics is urgently desired for cancer therapy because of their good controllability and noninvasive features. The relatively low photothermal conversion efficiency is still at the drawbacks because of the absence of efficient extraneous carriers. Herein, a carrier-free nanomedicine is developed to in vivo self-deliver organic photothermal agents for efficient cancer phototheranostics. By a facile self-assembly strategy, the near-infrared (NIR)-absorbing conjugated oligomer IDIC-4F is fabricated into a carrier-free nanoparticle (DCF-P), showing ultrasmall size of nearly 4.0nm with a nearly 100% of drug loading capacity. Notably, DCF-P achieves a superhigh photothermal conversion efficiency of 80.5% that is far greater than that of IDIC-4F-loaded nanomicelle DCF-M (57.3%). With the guidance of NIR fluorescence and photoacoustic dual-imaging, it is verified that DCF-P could well achieve tumor-preferential accumulation and retention at 4 h postinjection, and meanwhile shows highly efficient in vivo tumor elimination with good biosafety. This study thus contributes a novel concept for designing ultrasmall nanoparticle characteristics of preferential accumulation in tumors, and also provides a strategy for creating high-performance carrier-free nanomedicine via highly ordered molecular stacking.

A nanosensitizer self-assembled from oleanolic acid and chlorin e6 for synergistic chemo/sono-photodynamic cancer therapy

BackgroundSono-photodynamic therapy (SPDT) which is the combination of photodynamic therapy (PDT) and sonodynamic therapy (SDT), could exert much better anti-cancer effects than monotherapy. The combination of chemotherapy and PDT or SDT has shown great potential for cancer treatment. However, the combination of SPDT and chemotherapy for cancer treatment is rarely explored. PurposeWe utilized a natural hydrophobic anti-cancer drug oleanolic acid (OA) and a photosensitizer chlorin e6 (Ce6) through self-assembly technology to form a carrier-free nanosensitizer OC for combined chemotherapy and SPDT for cancer treatment. No studies involving using carrier-free nanomedicine for combined chemotherapy/SPDT have been reported yet. Study designAfter fully characterization of OC, the in vitro and in vivo anti-cancer activities of OC were investigated and the mechanisms of the synergistic therapeutic effects were studied. MethodsOC were synthesized through self-assembly technology and characterized by dynamic light scattering (DLS) and an atomic force microscope (AFM). Confocal microscope was used to investigate the intracellular uptake efficiency and the penetration ability of OC. The cell viability of PC9 and 4T1 cells treated with OC under laser and ultrasound (US) irradiation was determined by MTT assay. Furthermore, flow cytometry was performed to detect the reactive oxygen species (ROS) generation, loss of mitochondrial membrane potential (MMP), cell apoptosis and cell cycle arrest. Finally, the anti-tumor therapeutic efficacy of OC was investigated in orthotopic 4T1 breast tumor-bearing mouse model. ResultsOC showed an average particle size of around 100 nm with excellent light stability. OC increased more than 23 times accumulation of Ce6 in cancer cells and had strong tumor penetration ability in three-dimensional (3D) multicellular tumor spheroids (MCTSs). Compared with other therapeutic options, OC showed obvious synergistic inhibitory effects under light and US irradiation in PC9 and 4T1 cells with a significant decrease in IC50 values. Mechanism studies showed that OC could generate high ROS, induce MMP loss, and cause apoptosis and cell cycle arrest. In vivo studies also approved the synergistic therapeutic effects of OC in 4T1 mouse models. ConclusionSelf-assembled carrier-free nanosensitizer OC could be a promising therapeutic agent for synergistic chemo/sono-photodynamic therapy for cancer treatment.

Carrier-free prodrug nanoparticles based on dasatinib and cisplatin for efficient antitumor in vivo

Carrier-free drug self-delivery systems consisting of amphiphilic drug-drug conjugate (ADDC) with well-defined structure and nanoscale features have drawn much attention in tumor drug delivery. Herein, we report a simple and effective strategy to prepare ADDC using derivatives of cisplatin (CP) and dasatinib (DAS), which further self-assembled to form reduction-responsive nanoparticles (CP-DDA NPs). DAS was modified with succinic anhydride and then connected with CP derivative by ester bonds. The size, micromorphology and in vitro drug release of CP-DDA NPs were characterized. The biocompatibility and bioactivity of these carrier-free nanoparticles were then investigated by HepG2 cells and H22-tumor bearing mice. In vitro and in vivo experiments proved that CP-DDA NPs had excellent anti-tumor activity and significantly reduced toxicities. This study provides a new strategy to design the carrier-free nanomedicine composed of CP and DAS for synergistic tumor treatment.

Brain-targeting delivery of MMB4 DMS using carrier-free nanomedicine CRT-MMB4@MDZ

Brain-targeting delivery of 1,1′-methylenebis[4-[(hydroxyimino)methyl]-pyridinium] dimethanesulfonate (MMB4 DMS) is limited by its hydrophilic property and chemical instability. In order to solve this problem, herein, we develop a facile protocol through combining antisolvent precipitation and emulsion-solvent evaporation method to synthesize midazolam (MDZ) coated MMB4 DMS (MMB4@MDZ) nanoparticles. The as-prepared MMB4@MDZ had a MMB4 DMS nanocrystal (MMB4-NC) core and a MDZ shell. The MDZ shell prevented the MMB4-NC core from contacting the aqueous environment, and thus, guaranteed the chemical stability of MMB4 DMS. Most charmingly, the iron mimic cyclic peptide CRTIGPSVC (CRT) was modified on MMB4@MDZ surfaces to produce CRT-MMB4@MDZ which was endowed with ability to absorb transferrin (Tf)-abundant corona. Taking advantages of the Tf-abundant corona, CRT-MMB4@MDZ achieved transferrin receptor (TfR)-mediated brain-targeting delivery. With the fascinating chemical stability and brain-targeting delivery effect, CRT-MMB4@MDZ showed great clinical transform prospect as a brand-new nanomedicine. Of particular importance, this work promised not only a core–shell carrier-free nanomedicine platform for effective delivery of unstable water-soluble drug, but also a protein corona-manipulating strategy for targeting delivery.

Carrier-Free Platinum Nanomedicine for Targeted Cancer Therapy.

Numerous nanomedicines have been developed to improve the efficiency and safety of conventional anticancer drugs; however, the complexities in carrier materials and functional integration make it challenging to promote these candidates for clinical translation. In this study, a facile method to prepare carrier-free anticancer nanodrug with inherent bone targeting and osteoclastogenesis inhibition capabilities is reported. Phytic acid, a naturally occurring and nontoxic product, is reacted with cisplatin to form uniform nanoparticles of different sizes. The prepared nanoparticles possess high drug loading and pH-responsive drug release behaviors. Phytic acid in the nanomedicine ensures high bone targeting and osteoclastogenesis inhibition, and the released platinum drugs triggered by tumor extracellular acidity eradicate tumor cells. The nanomedicine around 100nm shows high anticancer activity and much reduced side effects in a subcutaneous breast cancer model when compared with cisplatin. In addition, it shows high accumulation at osteolytic lesions, and efficiently inhibits tumor growth and tumor-associated osteolysis in a bone metastatic breast cancer model. Here, a facile and efficient strategy to prepare carrier-free nanomedicines with high anticancer drug loading, inherent bone targeting, and osteoclast inhibitory activities for cancer therapy is provided.

Emerging carrier-free nanosystems based on molecular self-assembly of pure drugs for cancer therapy.

The potential toxicity of nanocarrier excipients and complicated preparation technologies have impeded the clinical application of nanomedicine. Recently, pure drug-assembled nanosystems (PDANS) have been widely investigated, due to the unique self-assembly characteristics of pure drug molecules. PDANS provides a facile nanoplatform for developing carrier-free nanomedicine. Herein, the recent trends in PDANS for cancer therapy are outlined. First, the emerging strategies to develop single pure drug-based nanoassemblies are discussed. Second, co-assembly of two or more pure drugs for efficient combination therapy is overviewed. Then, the functional self-assembly of non-cytotoxic agents in tumor sites is presented. Finally, the rational design and self-assembly mechanisms of these unique nanoplatforms are highlighted.

Selenium-Containing Carrier-Free Assemblies with Aggregation-Induced Emission Property Combine Cancer Radiotherapy with Chemotherapy.

Developing multifunctional carrier-free nanomedicine with high efficacy attracts tremendous attention in cancer treatment. Here, we develop selenium-containing carrier-free assemblies with aggregation-induced emission (AIE) property, which achieve the combination of cancer radiotherapy with chemotherapy. Under γ-radiation, diselenide bonds in the assemblies can be cleaved to form seleninic acid, which exhibits anticancer activity by upregulating the reactive oxygen species (ROS) levels in cancer cells. The incorporation of AIE groups further endows the selenium-containing assemblies with the ability of bioimaging. Their self-assembly behavior change under γ-radiation can be consequently observed in situ. The system combines cancer radiotherapy with chemotherapy, which exhibits improved anticancer activity.

PH and redox dual responsive carrier-free anticancer drug nanoparticles for targeted delivery and synergistic therapy

Advanced drug delivery systems often employ nanomaterials as carriers to deliver drugs to desirable disease sites for enhanced efficacy. However, most systems have low drug loading capacity and cause safety concerns. Therefore, many anticancer therapeutics have recently been assembled to NPs form without using any additional nanocarrier to achieve high drug loading. However, carrier-free nanomedicines are often constrained by limitations such as inadequate stability and lack of control in drug release. Therefore, we synthesize carrier-free drug NPs containing cis-aconitic anhydride-modified doxorubicin and paclitaxel (CAD-PTX) and coating with crosslinked (CL) surfactant based on hyaluronic acid (HA) segment. With this design, the pure drug NPs possess pH and redox dual responsive release characteristic and could target CD44 overexpressed cancer cells. Our studies demonstrate that these CAD-PTX-CLHA NPs display high stability, excellent active targeting effect and controllable intracellular drug release, and ultimately achieve significantly better anti-cancer efficiency than individual doxorubicin and paclitaxel.

Small Molecular Theranostic Assemblies Functionalized by Doxorubicin-Hyaluronic Acid-Methotrexate Prodrug for Multiple Tumor Targeting and Imaging-Guided Combined Chemo-Photothermal Therapy.

Because of high drug payload and minimized burden of foreign materials in the course of metabolism and excretion, carrier-free nanomedicine based on self-assembly of small-molecule therapeutic agents has attracted considerable attention in cancer therapy. However, obstacles still remained, such as lack of targeting efficiency, poor physiological stability, and serious drug burst release. Herein, we developed a self-dual-targeting prodrug conjugate by coupling methotrexate (MTX) and doxorubicin (DOX) to a hyaluronic acid (HA) backbone which enveloped the small molecular drug coassemblies of DOX and indocyanine green for specific targeting and imaging-guided chemo-photothermal therapy (PTT). The constructed nanosystems exhibited a diameter of ∼200 nm, superior physiological stability, and improved photothermal effect. Taking advantage of functionality of MTX-HA-DOX conjugate, the nanosystems remarkably enhanced the accumulation in the tumor regions by enhanced penetration and retention effect and CD44/folate receptor-mediated endocytosis. Upon the stimuli of acid, the nanosystems showed the rapid disassembly followed by the accelerated drug release. Consequently, the nanosystems demonstrated highly efficient apoptosis in cancer cells and remarkable tumor ablation by synergy between chemotherapy and PTT upon the irradiation of near-infrared laser. The multifunctional nanosystems based on small molecular theranostic assemblies could provide a promising potential in developing dual-targeting drug delivery and imaging-guided combinational therapy.

Light/pH-Triggered Biomimetic Red Blood Cell Membranes Camouflaged Small Molecular Drug Assemblies for Imaging-Guided Combinational Chemo-Photothermal Therapy.

Nanoparticles camouflaged by red blood cell (RBC) membranes have attracted considerable attention owing to reservation of structure of membrane and surface proteins, endowing prominent cell-specific function including biocompatibility, prolonged circulation lifetime, and reduced reticular endothelial system (RES) uptake ability. Considering the drawbacks of carrier-free nanomedicine including the serious drug burst release, poor stability, and lack of immune escape function, herein we developed and fabricated a novel RBC membranes biomimetic combinational therapeutic system by enveloping the small molecular drug coassemblies of 10-hydroxycamptothecin (10-HCPT) and indocyanine green (ICG) in the RBC membranes for prolonged circulation, controlled drug release, and synergistic chemo-photothermal therapy (PTT). The self-reorganized RBCs@ICG-HCPT nanoparticles (NPs) exhibited a diameter of ∼150 nm with core-shell structure, high drug payload (∼92 wt %), and reduced RES uptake function. Taking advantage of the stealth functionality of RBC membranes, RBCs@ICG-HCPT NPs remarkably enhanced the accumulation at the tumor sites by passive targeting followed by cellular endocytosis. Upon the stimuli of near-infrared laser followed by acidic stimulation, RBCs@ICG-HCPT NPs showed exceptional instability by heat-mediated membrane disruption and pH change, thereby triggering the rapid disassembly and accelerated drug release. Consequently, compared with individual treatment, RBCs@ICG-HCPT NPs under dual-stimuli accomplished highly efficient apoptosis in cancer cells and remarkable ablation of tumors by chemo-PTT. This biomimetic nanoplatform based on carrier-free, small molecular drug coassemblies integrating imaging capacity as a promising theranostic system provides potential for cancer diagnosis and combinational therapy.

Facile Engineering of Indomethacin-Induced Paclitaxel Nanocrystal Aggregates as Carrier-Free Nanomedicine with Improved Synergetic Antitumor Activity.

Carrier-free nanomedicines mainly composed of drug nanocrystals are considered as promising candidates for next-generation nanodrug formulations. However, such nanomedicines still need to be stabilized by additive surfactants, synthetic polymers, or biologically based macromolecules. Based on the strong intermolecular interactions between indomethacin (IDM, a COX-2 inhibitor) and paclitaxel (PTX, a chemotherapy drug), we herein successfully engineered a novel kind of carrier-free nanomedicines that organized as IDM-induced PTX nanocrystal aggregates via one-pot self-assembly without any nonactive excipients. In the assemblies of IDM and PTX (IDM/PTX assemblies), PTX nanocrystals were casted with amorphous IDM molecules, like a "brick-cement" architecture. In serum, these nanoassemblies could rapidly collapse into a great number of smaller nanoparticles, thus targeting the tumor site through the EPR effect. Under the assistance of IDM on immunotherapy, the IDM/PTX assemblies showed obviously improved synergetic antitumor effects of immunotherapy and chemotherapy. The self-assembly of two synergistic active substances into nanomedicines without any nonactive excipients might open an alternative avenue and give inspiration to fabricate novel carrier-free nanomedicines in many fields.

Multifunctional Cargo-Free Nanomedicine for Cancer Therapy.

Nanocarriers encapsulating multiple chemotherapeutics are a promising strategy to achieve combinational chemotherapy for cancer therapy; however, they generally use exotic new carriers without therapeutic effect, which usually suffer from carrier-related toxicity issues, as well as having to pass extensive clinical trials to be drug excipients before any clinical applications. Cargo-free nanomedicines, which are fabricated by drugs themselves without new excipients and possess nanoscale characteristics to realize favorable pharmacokinetics and intracellular delivery, have been rapidly developed and drawn much attention to cancer treatment. Herein, we discuss recent advances of cargo-free nanomedicines for cancer treatment. After a brief introduction to the major types of carrier-free nanomedicine, some representative applications of these cargo-free nanomedicines are discussed, including combination therapy, immunotherapy, as well as self-monitoring of drug release. More importantly, this review draws a brief conclusion and discusses the future challenges of cargo-free nanomedicines from our perspective.

Docetaxel prodrug self-assembled nanosystem: Synthesis, formulation and cytotoxicity

Conventional drug delivery systems of docetaxel (DTX) are challenged with low drug loading efficiency and potential carriers-induced toxicity. In this work, a docetaxel prodrug self-assembled nanosystem was designed and synthesized by conjugating docetaxel with oleic acid (OA) exploring a thioether as the linker, which is redox-sensitive to the redox environment within tumor cells. Notably, the carrier-free nanomedicine which does not need any carrier has obviously high drug loading that reaches 58%. Moreover, the cytotoxicity of DTX-S-OA maintains an equal level with DTX. The novel prodrug conjugate therefore has a promising perspective as carrier-free nanomedicine for cancer therapy due to its high drug loading property, redox-sensitive release and long circulation mechanism.

High drug-loading nanomedicines: progress, current status, and prospects.

Drug molecules transformed into nanoparticles or endowed with nanostructures with or without the aid of carrier materials are referred to as “nanomedicines” and can overcome some inherent drawbacks of free drugs, such as poor water solubility, high drug dosage, and short drug half-life in vivo. However, most of the existing nanomedicines possess the drawback of low drug-loading (generally less than 10%) associated with more carrier materials. For intravenous administration, the extensive use of carrier materials might cause systemic toxicity and impose an extra burden of degradation, metabolism, and excretion of the materials for patients. Therefore, on the premise of guaranteeing therapeutic effect and function, reducing or avoiding the use of carrier materials is a promising alternative approach to solve these problems. Recently, high drug-loading nanomedicines, which have a drug-loading content higher than 10%, are attracting increasing interest. According to the fabrication strategies of nanomedicines, high drug-loading nanomedicines are divided into four main classes: nanomedicines with inert porous material as carrier, nanomedicines with drug as part of carrier, carrier-free nanomedicines, and nanomedicines following niche and complex strategies. To date, most of the existing high drug-loading nanomedicines belong to the first class, and few research studies have focused on other classes. In this review, we investigate the research status of high drug-loading nanomedicines and discuss the features of their fabrication strategies and optimum proposal in detail. We also point out deficiencies and developing direction of high drug-loading nanomedicines. We envision that high drug-loading nanomedicines will occupy an important position in the field of drug-delivery systems, and hope that novel perspectives will be proposed for the development of high drug-loading nanomedicines.