cRGD-installed docetaxel-loaded mertansine prodrug micelles: redox-triggered ratiometric dual drug release and targeted synergistic treatment of B16F10 melanoma

Emerging non-antibody‒drug conjugates (non-ADCs) therapeutics of toxins for cancer treatment

The non-selective cytotoxicity of toxins limits the clinical relevance of the toxins. In recent years, toxins have been widely used as warheads for antibody‒drug conjugates (ADCs) due to their efficient killing activity against various cancer cells. Although ADCs confer certain targeting properties to the toxins, low drug loading capacity, possible immunogenicity, and other drawbacks also limit the potential application of ADCs. Recently, non-ADC delivery strategies for toxins have been extensively investigated. To further understand the application of toxins in anti-tumor, this paper provided an overview of prodrugs, nanodrug delivery systems, and biomimetic drug delivery systems. In addition, toxins and their combination strategies with other therapies were discussed. Finally, the prospect and challenge of toxins in cancer treatment were also summarized.

RGD-directed 24 nm micellar docetaxel enables elevated tumor-liver ratio, deep tumor penetration and potent suppression of solid tumors

Nanomedicines while showing a great potential in improving the performance of chemotherapeutics like docetaxel (DTX) are distressed by a high liver deposition and poor tumor penetration, which might not only cause liver toxicity but also moderate therapeutic effect. Herein, we report that cRGD-directed 24 nm disulfide-crosslinked micellar docetaxel (cRGD-MDTX) presents low liver accumulation, high tumor uptake, and deep tumor penetration, leading to the potent suppression of different solid tumors. cRGD-MDTX was optimized with a cRGD density of 4% and DTX loading of 10 wt%. Interestingly, cRGD-MDTX enabled an extraordinary tumor-liver ratio of 2.8/1 with a DTX uptake of 8.3 %ID/g in αvβ3 over-expressing PC3 prostate tumor. The therapeutic studies demonstrated striking antitumor effects of cRGD-MDTX toward PC3 prostate tumor, prostate cancer patient-derived xenografts (PDX), orthotopic A549-Luc lung cancer and orthotopic SKOV3-Luc ovarian tumor models, in which tumor growth was effectually inhibited and 6-8 times better improvement of median survival time over free DTX was observed. This small disulfide-crosslinked micellar drug capable of relegating liver deposition opens a new avenue to nanomedicines for targeted therapy.

An icaritin-loaded microemulsion based on coix oil for improved pharmacokinetics and enhanced antitumor efficacy

Combinational icaritin (IC) and coix seed oil (CSO) holds promising potential in the treatment of hepatocellular carcinoma. However, traditional cocktail therapy is facing difficulties to optimize the synergistic antitumor efficacy due to the asynchronous pharmacokinetics. Therefore, we developed an icaritin-loaded microemulsion based on coix seed oil (IC-MEs) for improved pharmacokinetics and enhanced antitumor efficacy. The preparation technology of IC-MEs was optimized by the Box-Behnken design and the pharmaceutical properties were characterized in detail. IC-MEs show synergistic antiproliferation against HepG2 cells compared with monotherapy. The mechanism is associated with stronger apoptosis induction via enhancing caspases-3 activity. IC-MEs significantly improve the bioavailability of IC due to the encapsulation of coix oil-based microemulsion and also obtain the desired liver accumulation and elimination. More importantly, IC-MEs exhibit the overwhelming antitumor ability among all of the treatments on the HepG2 xenograft-bearing mice. This study verifies the feasibility of using coix oil-based microemulsion to improve the antitumor effect of water-insoluble components.

Immunogenic Cell Death Activates the Tumor Immune Microenvironment to Boost the Immunotherapy Efficiency

Tumor immunotherapy is only effective in a fraction of patients due to a low response rate and severe side effects, and these challenges of immunotherapy in clinics can be addressed through induction of immunogenic cell death (ICD). ICD is elicited from many antitumor therapies to release danger associated molecular patterns (DAMPs) and tumor-associated antigens to facilitate maturation of dendritic cells (DCs) and infiltration of cytotoxic T lymphocytes (CTLs). The process can reverse the tumor immunosuppressive microenvironment to improve the sensitivity of immunotherapy. Nanostructure-based drug delivery systems (NDDSs) are explored to induce ICD by incorporating therapeutic molecules for chemotherapy, photosensitizers (PSs) for photodynamic therapy (PDT), photothermal conversion agents for photothermal therapy (PTT), and radiosensitizers for radiotherapy (RT). These NDDSs can release loaded agents at a right dose in the right place at the right time, resulting in greater effectiveness and lower toxicity. Immunotherapeutic agents can also be combined with these NDDSs to achieve the synergic antitumor effect in a multi-modality therapeutic approach. In this review, NDDSs are harnessed to load multiple agents to induce ICD by chemotherapy, PDT, PTT, and RT in combination of immunotherapy to promote the therapeutic effect and reduce side effects associated with cancer treatment.

One-Step and Facile Synthesis of Poly(phenylalanine) as a Robust Drug Carrier for Enhanced Cancer Therapy

In recent decades, many poly(amino acid)s have been successfully prepared for various biomedical applications. To date, the synthesis and purification procedures used to generate these poly(amino acid)s have generally been complicated and costly. Here, a one-step synthesis strategy was developed and optimized via direct polymerization using thionyl chloride to easily and economically obtain poly(amino acid)s. Phenylalanine (Phe) was selected as a model amino acid to construct a family of biodegradable and biocompatible poly(phenylalanine) (PPhe) molecules with a tunable molecular weight. The prepared PPhe can self-assemble into nanoparticles (PP-NPs) through nanoprecipitation with a particle size of approximately 100 nm. PP-NPs exhibit a high drug-loading capacity (>12 wt %) of paclitaxel (PTX, a commercial antitumor drug) and good therapeutic effects in CT26 cells. The in vivo evaluation of PTX@PP-NPs indicates that it has a prolonged blood circulation time and high tumor aggregation after intravenous injection, resulting in significant antitumor effects in CT26 tumor-bearing mice with minimal toxicity to normal organs. Overall, this study provides a facile and simple strategy for synthesizing poly(amino acids) and a PPhe-based nanoparticle platform for effectively delivering various small-molecule drugs.

Systemic administration of polymersomal oncolytic peptide LTX-315 combining with CpG adjuvant and anti-PD-1 antibody boosts immunotherapy of melanoma

Oncolytic peptide LTX-315 while showing clinical promise in treating solid tumors is limited to intratumoral administration, which is not applicable for inaccessible or metastatic tumors. The cationic and amphipathic nature of oncolytic peptides engenders formidable challenges to developing systems for their systemic delivery. Here, we describe cRGD-functionalized chimaeric polymersomes (cRGD-CPs) as a robust systemic delivery vehicle for LTX-315, which in combination with CpG adjuvant and anti-PD-1 boost immunotherapy of malignant B16F10 melanoma in mice. cRGD-CPs containing 14.9 wt% LTX-315 (cRGD-CPs-L) exhibited a size of 53 nm, excellent serum stability, and strong and selective killing of B16F10 cells (versus L929 fibroblasts) in vitro, which provoked similar immunogenic effects to free LTX-315 as revealed by release of danger-associated molecular pattern molecules. The systemic administration of cRGD-CPs-L gave a notable tumor accumulation of 4.8% ID/g and significant retardation of tumor growth. More interestingly, the treatment of B16F10 tumor-bearing mice was further boosted by co-administration of polymersomal CpG and anti-PD-1 antibody, in which two out of seven mice were cured as a result of strong immune response and long-term immune memory protection. The immunotherapeutic effect was evidenced by secretion of IL-6, IFN-γ and TNF-α, tumor infiltration of CD8⁺ CTLs and T_h, and induction of T_EM and T_CM in spleen. This study opens a new avenue to oncolytic peptides, which enables durable immunotherapy of tumors via systemic administration.

Multicomponent thermosensitive lipid complexes enhance desmoplastic tumor therapy through boosting anti-angiogenesis and synergistic strategy

Currently, the chemotherapy drugs-loaded thermosensitive liposomes have not shown an over standard of clinical effects compared to preclinical trials. In addition to the limiting factors of clinical trial design and heating device, abnormal angiogenesis in desmoplastic tumor is a key factor for unexpected clinical efficacy. Malformed tumor vasculature may result in reduced vascular transport and the heterogeneous distribution of thermosensitive liposomes in tumor. Here, we report an anti-angiogenesis strategy through hypoxia-inducible factors (HIF)-1α-vascular endothelial growth factor (VEGF) axis based on icaritin and coix seed oil dual loaded multicomponent thermosensitive lipid complexes (IC-ML). IC-ML could downregulate the HIF-1α expression in HepG2 cells with a synergetic antitumor effect. In addition, HepG2 + LX-2 cells co-cultured 3D tumor spheres administered IC-ML showed the strongest penetration and inhibition of growth. Accordingly, IC-ML displayed improved tumor penetration and superior synergistic antitumor efficacy with HIF-1α-VEGF downregulation in vivo under mild hyperthermia. The improvement of antitumor efficacy of IC-ML comes from the anti-angiogenesis strategy and comprehensive tumor microenvironment remodeling, including depletion of cancer-associated fibroblasts as well as inhibition of M2-type tumor associated macrophage infiltration in desmoplastic tumor. This study proposes a novel multicomponent synergistic antitumor strategy to improve the therapeutic potential of thermosensitive lipid complexes for hepatocellular carcinoma.

Designed Spider Silk-Based Drug Carrier for Redox- or pH-Triggered Drug Release

Targeted drug delivery and controlled drug release can be obtained using specifically designed polymers as carriers. Due to their biocompatibility and biodegradability and especially the lack of an immune response, materials made of spider silk proteins are promising candidates for use in such applications. Particles made of recombinant spider silk proteins have previously been shown to be suitable drug and gene carriers as they could readily be loaded with various drug substances or biologicals, and subsequent release was observed over a defined period of time. However, the respective substances were bound non-covalently via hydrophobic or charge-charge interactions, and hence, the release of loaded substances could not be spatio-temporally controlled. Here, we present a setup of chemically modified recombinant spider silk protein eADF4 and variants thereof, combining their well-established biocompatible properties with covalent drug binding and triggered release upon changes in the pH or redox state, respectively. The usefulness of the spider silk platform technology was shown with model substances and cytostatic drugs bound to spider silk particles or films via a pH-labile hydrazine linker as one option, and the drugs could be released from the spider silk carriers upon acidification of the environment as seen, e.g., in tumorous tissues or endo/lysosomes. Sulfhydryl-bearing spider silk variants allowed model substance release if exposed to intracellular GSH (glutathione) levels as a second coupling option. The combination of non-immunogenic, nontoxic spider silk materials as drug carriers with precisely triggerable release chemistry presents a platform technology for a wide range of applications.

Soluplus®/TPGS mixed micelles for co-delivery of docetaxel and piperine for combination cancer therapy

In this study, mixed micelles of Soluplus® and TPGS were developed for co-administering docetaxel (DTX) and piperine (PIP) for exerting the synergistic effect, which increased the cytotoxicity and improved the anti-cancer activity in HepG2 cell lines compared to free DTX. These in vitro (MTT assay, intracellular uptake of micelles) and in vivo (pharmacokinetic study, immunostaining, TUNEL analysis) studies exhibited the advantages of co-delivery of anticancer drugs with Soluplus®/TPGS by mixed micelles and furthermore established that co-delivery of DTX and PIP via the mixed micelles of Soluplus®/TPGS could be a promising strategy for the treatment of liver cancer.

IR780-based light-responsive nanocomplexes combining phase transition for enhancing multimodal imaging-guided photothermal therapy

Near-infrared (NIR) light-triggered photothermal therapy (PTT) has been widely applied for treating cancer. The combination of nanotechnology and NIR has shown great promise for promoting the efficacy of PTT. However, PTT alone could not completely ablate the tumors and easily causes tumor recurrence. To overcome this challenge, many studies have been performed to enhance PTT, including combining chemical therapy and radiotherapy, both of which have side effects on the body. To reduce the side effects and enhance PTT, a new infrared IR780-based nanocomplex combining liquid fluorocarbon perfluoropentane (PFP) has been synthesized for enhancing multimodal imaging-guided PTT. Under NIR irradiation, the size changes of PFP-loaded nanobubbles transforming into microbubbles allow ultrasound (US) imaging, showing boundaries and internal information of tumors. The breakup process and cascade reaction of phase transition can improve intratumoral permeation and retention of nanoparticles in nonmicrovascular tissue and damage the cell membranes of tumors, further enhancing PTT to kill tumor cells. The strong absorption in the NIR field of IR780-loaded NPs allows not only photoacoustic (PA) imaging but also NIR fluorescence (NIRF) imaging, which provides more anatomical information about tumors. This nanocomplex exhibits good biocompatibility and nontoxicity, strong PA/US/NIRF imaging contrast, excellent liquid-gas transition and a photothermal effect. This finding provides a new method to enhance multimodal imaging-guided cancer nanotheranostics.

A novel spheroid-based co-culture model mimics loss of keratinocyte differentiation, melanoma cell invasion, and drug-induced selection of ABCB5-expressing cells

Background

Different 3D-cell culture approaches with varying degrees of complexity have been developed to serve as melanoma models for drug testing or mechanistic studies. While these 3D-culture initiatives are already often superior to classical 2D approaches, they are either composed of only melanoma cells or they are so complex that the behavior of individual cell types is hard to understand, and often they are difficult to establish and expensive.

Methods

This study used low-attachment based generation of spheroids composed of up to three cell types. Characterization of cells and spheroids involved cryosectioning, immunofluorescence, FACS, and quantitative analyses. Statistical evaluation used one-way ANOVA with post-hoc Tukey test or Student’s t-test.

Results

The tri-culture model allowed to track cellular behavior in a cell-type specific manner and recapitulated different characteristics of early melanoma stages. Cells arranged into a collagen-IV rich fibroblast core, a ring of keratinocytes, and groups of highly proliferating melanoma cells on the outside. Regularly, some melanoma cells were also found to invade the fibroblast core. In the absence of melanoma cells, the keratinocyte ring stratified into central basal-like and peripheral, more differentiated cells. Conversely, keratinocyte differentiation was clearly reduced upon addition of melanoma cells. Treatment with the cytostatic drug, docetaxel, restored keratinocyte differentiation and induced apoptosis of external melanoma cells. Remaining intact external melanoma cells showed a significantly increased amount of ABCB5-immunoreactivity.

Conclusions

In the present work, a novel, simple spheroid-based melanoma tri-culture model composed of fibroblasts, keratinocytes, and melanoma cells was described. This model mimicked features observed in early melanoma stages, including loss of keratinocyte differentiation, melanoma cell invasion, and drug-induced increase of ABCB5 expression in external melanoma cells.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5606-4) contains supplementary material, which is available to authorized users.

Integrated block copolymer prodrug nanoparticles for combination of tumor oxidative stress amplification and ROS-responsive drug release

In tumor tissues, reactive oxygen species (ROS) level is significantly higher than that in normal tissues, which has been frequently explored as the specific stimulus to trigger drug release. However, the low intrinsic ROS concentration and heterogeneous distribution in tumor tissues hinder the applications as the stimulus for drug delivery. Herein, we developed integrated nanoparticles to remold tumor microenvironment via specific amplification of the tumor oxidative stress and simultaneously realize ROS-responsive drug release. The amphiphilic block copolymer prodrugs composed of poly(ethylene glycol) and polymerized methacrylate monomer containing thioketal-linked camptothecin (CPT) were synthesized and self-assembled to form core-shell micelles for encapsulation of β-lapachone (Lapa@NPs). After tumor accumulation and internalization into tumor cells post systemic administration of Lapa@NPs, Lapa can selectively induce remarkable ROS level increase via the catalysis of NAD(P)H: quinone oxidoreductase-1 (NQO1) enzyme overexpressed in cancer cells. Subsequently, enhanced ROS concentration would trigger the cleavage of thioketal linkers to release drug. The released CPT together with high ROS level achieved a synergistic therapy to suppress tumor growth. Moreover, Lapa@NPs exhibited superior biosafety due to the tumor-specific activation of the cascade reaction. Accordingly, Lapa@NPs represent a novel polymer prodrug design and drug release strategy via tumor-specific oxidative stress amplification and subsequent ROS-responsive drug release.

Redox-responsive nano-carriers as tumor-targeted drug delivery systems

With ever increasing scientific knowledge and awareness, research is underway around the globe to design new types of stimuli (external/internal) responsive nano-carriers for biotechnological applications at large and biomedical/pharmaceutical in particular. Based on literature evidence, stimuli-responsive carriers have been classified into four major categories, i.e. (1) physical, (2) chemical, (3) biological, and (4) dual (combination of any of the first three classes). Among various types, redox-responsive nano-carriers are of supreme interests and discussed here in this review. The difference in redox potential in tumor and normal tissue is considered as a potential target for tumor targeting leading to the development of redox-responsive drug delivery systems (DDS). In this regard, a high concentration of glutathione in tumor/intracellular environment has extensively been exploited. Disulfide bonds were found as a promising tool for designing redox-responsive which tend to cleave in a reductive environment forming sulfhydryl groups. Many nano-carriers have been explored widely to control tumor growth. These systems were used against the tumor xenograft animal model and showed improved tumor targeting with tumor growth inhibition. Herein, an effort has been made to summarize various aspects from design to development of numerous types of redox-responsive DDS including liposomes, micelles, nanoparticles, nanogel and prodrug based nanomedicines. An emphasis is also given on various types of nano-carriers with special reference to the tumor-targeted drug delivery applications. Also, dual responsive nano-carriers (in addition to redox-responsive) have also been briefly discussed. Towards the end of the chapter, the information is also given on their future perspectives.

Reduction-sensitive polymeric nanomedicines: An emerging multifunctional platform for targeted cancer therapy

The development of smart delivery systems that are robust in circulation and quickly release drugs following selective internalization into target cancer cells is a key to precision cancer therapy. Interestingly, reduction-sensitive polymeric nanomedicines showing high plasma stability and triggered cytoplasmic drug release behavior have recently emerged as one of the most exciting platforms for targeted delivery of various anticancer drugs including small chemical drugs, proteins, and nucleic acids. In vivo studies in varying tumor models reveal that these reduction-sensitive multifunctional nanomedicines outperform the currently used clinical formulations and reduction-insensitive counterparts, bringing about not only significantly enhanced tumor selectivity, accumulation and inhibition efficacy but also markedly reduced systemic toxicity and improved therapeutic index. In this review, we will highlight the cutting-edge advancement with a focus on in vivo performances as well as future perspectives on reduction-sensitive polymeric nanomedicines for targeted cancer therapy.

Translation of combination nanodrugs into nanomedicines: lessons learned and future outlook

The concept of nanomedicine is not new. For instance, some nanocrystals and colloidal drug molecules are marketed that improve pharmacokinetic characteristics of single-agent therapeutics. For the past two decades, the number of research publications on single-agent nanoformulations has grown exponentially. However, formulations advancing to pre-clinical and clinical evaluations that lead to therapeutic products has been limited. Chronic diseases such as cancer and HIV/AIDS require drug combinations, not single agents, for durable therapeutic responses. Therefore, development and clinical translation of drug combination nanoformulations could play a significant role in improving human health. Successful translation of promising concepts into pre-clinical and clinical studies requires early considerations of the physical compatibility, pharmacological synergy, as well as pharmaceutical characteristics (e.g. stability, scalability and pharmacokinetics). With this approach and robust manufacturing processes in place, some drug-combination nanoparticles have progressed to non-human primate and human studies. In this article, we discuss the rationale and role of drug-combination nanoparticles, the pre-clinical and clinical research progress made to date and the key challenges for successful clinical translation. Finally, we offer insight to accelerate clinical translation through leveraging robust nanoplatform technologies to enable implementation of personalised and precision medicine.

A multicomponent microemulsion using rational combination strategy improves lung cancer treatment through synergistic effects and deep tumor penetration

Previously, we have developed a multicomponent-based microemulsion composed of etoposide, coix seed oil, and ginsenoside Rh2 (ECG-MEs). In this study, our goal was to validate the feasibility of ECG-MEs in lung cancer treatment and explore the mechanism underling the enhanced antitumor efficacy. The optimal weight ratio of ginsenoside Rh2 (G-Rh2) in ECG-MEs was determined as 3% (wt%), that was capable of forming the microemulsion readily with small particle size and high drug encapsulation efficiency. In cellular studies, the intracellular fluorescence of human non-small cell lung cancer (A549) cells treated with fluorescein isothiocyanate-labeled ECG-MEs (FITC/ECG-MEs) was significantly higher than that of various controls, leading to the obviously synergistic anticancer activities in cytotoxicity and in vitro cell apoptosis induction. The anticancer efficacy in vivo results showed that ECG-MEs markedly inhibited the growth of A549 tumor xenografts, potently induced tumor cells apoptosis, and obviously prolonged the survival time of mice. Of note, the mechanisms of enhanced anticancer efficiency were connected with the small size-mediated deep tumor penetration and increase in serum concentration of T helper 1 (Th1) cytokines. In summary, ECG-MEs exerting the rational drug combination strategy offers a solid evidence for lung cancer treatment, and has a promising potential for clinical application.

αvβ3 integrin-targeted micellar mertansine prodrug effectively inhibits triple-negative breast cancer in vivo

Antibody-mertansine (DM1) conjugates (AMCs) are among the very few active targeting therapeutics that are approved or clinically investigated for treating various cancers including metastatic breast cancer. However, none of the AMCs are effective for the treatment of triple-negative breast cancers (TNBCs). Here, we show that cRGD-decorated, redox-activatable micellar mertansine prodrug (cRGD-MMP) can effectively target and deliver DM1 to α_vβ₃ integrin overexpressing MDA-MB-231 TNBC xenografts in nude mice, resulting in potent tumor growth inhibition. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays showed that cRGD-MMP had obvious targetability to MDA-MB-231 cells with a low half-maximal inhibitory concentration (IC₅₀) of 0.18 μM, which was close to that of free DM1 and 2.2-fold lower than that of micellar mertansine prodrug (MMP; nontargeting control). The confocal microscopy studies demonstrated that cRGD-MMP mediated a clearly more efficient cellular uptake and intracellular release of doxorubicin (used as a fluorescent anticancer drug model) in MDA-MB-231 cells. Notably, cRGD-MMP loaded with 1,1′-dioctadecyltetramethyl indotricarbocyanine iodide (DiR; a hydrophobic near-infrared dye) was shown to quickly accumulate in the MDA-MB-231 tumor with strong DiR fluorescence from 2 to 24 h post injection. MMP loaded with DiR could also accumulate in the tumor, although significantly less than cRGD-MMP. The biodistribution studies revealed a high DM1 accumulation of 8.1%ID/g in the tumor for cRGD-MMP at 12 h post injection. The therapeutic results demonstrated that cRGD-MMP effectively suppressed MDA-MB-231 tumor growth at 1.6 mg DM1 equiv./kg without causing noticeable side effects, as shown by little body weight loss and histological analysis. This MMP has appeared as a promising platform for potent treatment of TNBCs.