HPMA-hydrogels result in prolonged delivery of anticancer drugs and are a promising tool for the treatment of sensitive and multidrug resistant leukaemia

Prospects of Delivering Natural Compounds by Polymer-Drug Conjugates in Cancer Therapeutics

Synthetic chemotherapeutics have played a crucial role in minimizing mostly palliative symptoms associated with cancer; however, they have also created other problems such as system toxicity due to a lack of specificity. This has led to the development of polymer-drug conjugates amongst other novel drug delivery systems. Most of the formulations designed using delivery systems consist of synthetic drugs and face issues such as drug resistance, which has already rendered drugs such as antibiotics ineffective. This is further exacerbated by toxicity due to long term use. Given these problems and the fact that conjugation of synthetic compounds to polymers has been relatively slow with no formulation on the market after a decade of extensive studies, the focus has shifted to using this platform with medicinal plant extracts to improve solubility, specificity and increase drug release of medicinal and herbal bioactives. In recent years, various plant extracts such as flavonoids, tannins and terpenoids have been studied extensively using this approach. The success of formulations developed using novel drug-delivery systems is highly dependent on the tumour microenvironment especially on the enhanced permeability and retention effect. As a result, the compromised lymphatic network and 'leaky' vasculature exhibited by tumour cells act as a guiding principle in the delivering of these formulations. This review focuses on the state of the polymer-drug conjugates and their exploration with natural compounds, the progress and difficulties thus far, and future directions concerning cancer treatment.

Antitumor Activity of Thermosensitive Hydrogels Packaging Gambogic Acid Nanoparticles and Tumor-Penetrating Peptide iRGD Against Gastric Cancer

Introduction

Gambogic acid (GA) is proved to have anti-tumor effects on gastric cancer. Due to poor solubility, non-specific biological distribution, toxicity to normal tissues and short half-life, it is hard to be applied into the clinic. To overcome these issues, we developed a thermosensitive and injectable hydrogel composed of hydroxypropyl cellulose, silk fibroin and glycerol, with short gelling time, good compatibility and sustained release, and demonstrated that the hydrogel packaged with gambogic acid nanoparticles (GA-NPs) and tumor-penetrating peptide iRGD could improve the anti-tumor activity.

Methods

The Gelling time and micropore size of the hydrogels were regulated through different concentrations of glycerol. Controlled release characteristics of the hydrogels were evaluated with a real-time near-infrared fluorescence imaging system. Location of nanoparticles from different carriers was traced by confocal laser scanning microscopy. The in vivo antitumor activity of the hydrogels packaging GA-NPs and iRGD was evaluated by investigating tumor volume and tumor size.

Results

The thermo-sensitive properties of hydrogels were characterized by 3-4 min, 37°C, when glycerol concentration was 20%. The hydrogels physically packaged with GA-NPs and iRGD showed higher fluorescence intensity than other groups. The in vivo study indicated that the co-administration of GA-NPs and iRGD by hydrogels had higher antitumor activity than the GA-loaded hydrogels and free GA combining with iRGD. Free GA group showed few antitumor effects. Compared with the control group, the body weight in other groups had no obvious change, and the count of leukocytes and hemoglobin was slightly decreased.

Discussion

The hydrogel constructed iRGD and GA-NPs exerted an effective anti-tumor effect possibly due to retention effect, local administration and continuous sustained release of iRGD promoting the penetration of nanoparticles into a deep part of tumors. The delivery system showed little systemic toxicity and would provide a promising strategy to improve anti-gastric cancer efficacy.

Incorporation of Synthetic mRNA in Injectable Chitosan-Alginate Hybrid Hydrogels for Local and Sustained Expression of Exogenous Proteins in Cells

The application of synthetic messenger RNA (mRNA) exhibits various advantages, such as expression of desired proteins in cells without genomic integration. In the field of tissue engineering, synthetic mRNAs could be also used to modulate the protein expression in implanted cells. Therefore, in this study, we incorporated synthetic humanized Gaussia luciferase (hGLuc) mRNA into alginate, chitosan, or chitosan-alginate hybrid hydrogels and analyzed the release of hGLuc mRNA from these hydrogels. After 3 weeks, 79% of the incorporated mRNA was released from alginate hydrogels, approximately 42% was released from chitosan hydrogels, and about 70% was released from chitosan-alginate hydrogels. Due to the injectability, chitosan-alginate hybrid hydrogels were selected for further investigation of the bioactivity of embedded hGLuc mRNA and the stability of these hydrogels was examined after the incorporation of synthetic mRNA by rheometric analysis. Therefore, HEK293 cells were incorporated into chitosan-alginate hydrogels containing mRNA transfection complexes and the luciferase activity in the supernatants was detected for up to 3 weeks. These results showed that the biodegradable chitosan-alginate hybrid hydrogels are promising delivery systems for sustained delivery of synthetic mRNAs into cells. Since chitosan-alginate hybrid hydrogels are injectable, the hydrogels can be simultaneously loaded with cells and the desired synthetic mRNA for exogenous protein synthesis and can be administered by minimally invasive local injection for tissue engineering applications.

Overcoming multidrug resistance in Dox-resistant neuroblastoma cell lines via treatment with HPMA copolymer conjugates containing anthracyclines and P-gp inhibitors

Water-soluble N-(2-hydroxypropyl)methacrylamide copolymer conjugates bearing the anticancer drugs doxorubicin (Dox) or pirarubicin (THP), P-gp inhibitors derived from reversin 121 (REV) or ritonavir (RIT)), or both anticancer drug and P-gp inhibitor were designed and synthesized. All biologically active molecules were attached to the polymer carrier via pH-sensitive spacer enabling controlled release in mild acidic environment modeling endosomes and lysosomes of tumor cells. The cytotoxicity of the conjugates against three sensitive and Dox-resistant neuroblastoma (NB) cell lines, applied alone or in combination, was studied in vitro. All conjugates containing THP displayed higher cytotoxicity against all three Dox-resistant NB cell lines compared with the corresponding Dox-containing conjugates. Furthermore, the cytotoxicity of conjugates containing both drug and P-gp inhibitor was up to 10 times higher than that of the conjugate containing only drug. In general, the polymer-drug conjugates showed higher cytotoxicity when conjugates containing inhibitors were added 8 or 16h prior to treatment compared with conjugates bearing both the inhibitor and the drug. The difference in cytotoxicity was more pronounced at the 16-h time point. Moreover, higher inhibitor:drug ratios resulted in higher cytotoxicity. The cytotoxicity of the polymer-drug used in combination with polymer P-gp inhibitor was up to 84 times higher than that of the polymer-drug alone.

Nanotherapeutics With Anthracyclines: Methods of Determination and Quantification of Anthracyclines in Biological Samples

Anthracyclines, e.g. doxorubicin, pirarubicin, are widely used as cytostatic agents in the polymer nanotherapeutics designed for the highly effective antitumor therapy with reduced side effects. However, their precise dosage scheme needs to be optimized, which requires an accurate method for their quantification on the cellular level in vitro during nanocarrier development and in body fluids and tissues during testing in vivo. Various methods detecting the anthracycline content in biological samples have already been designed. Most of them are highly demanding and they differ in exactness and reproducibility. The cellular uptake and localization is predominantly observed and determined by microscopy techniques, the anthracycline content is usually quantified by chromatographic analysis using fluorescence detection. We reviewed and compared published methods concerning the detection of anthracycline nanocarriers.

Synergistic antitumor effects of doxorubicin-loaded carboxymethyl cellulose nanoparticle in combination with endostar for effective treatment of non-small-cell lung cancer

The multi-modal combination therapy is proved powerful and successful to enhance the antitumor efficacy in clinics as compared with single therapy modes. In this study, the potential of combining chemotherapy with antiangiogenic therapy for the treatment of non-small-cell lung cancer is explored. Towards this aim, OEGylated carboxymethyl cellulose-(2-(2-(2-methoxyethoxy)ethoxy)methyl)oxirane (CMC-ME2MO) is prepared by treating CMC with ME2MO in the alkaline aqueous solution, and used to efficiently carry doxorubicin (DOX) with high drug-loading content (16.64%) and encapsulation efficiency (99.78%). As compared to free DOX, the resulting nanoparticles show not only the favorable stability in vitro but also the prolonged blood circulation, improved safety and tolerability, optimized biodistribution, reduced systemic toxicity, and enhanced antitumor efficacy in vivo, indicates a potential utility in cancer chemotherapy. Furthermore, the combination of the DOX-loaded polysaccharide nanoparticles and antiangiogenic drug endostar provides synergistic effects of chemotherapy and antiangiogenic therapy, which shows the highest efficiency in tumor suppression. The combination approach of the DOX-containing nanomedicine and endostar for efficient treatment of non-small-cell lung cancer is first proposed to demonstrate the synergistic therapeutic effect. This synergistic combination proves to be a promising therapeutic regimen in cancer therapy and holds great potential for clinical application.

Hydrogels and scaffolds for immunomodulation

For over two decades, immunologists and biomaterials scientists have co-existed in parallel world with the rationale of understanding the molecular profile of immune responses to vaccination, implantation, and treating incurable diseases. Much of the field of biomaterial-based immunotherapy has relied on evaluating model antigens such as chicken egg ovalbumin in mouse models but their relevance to humans has been point of much discussion. Nevertheless, such model antigens have provided important insights into the mechanisms of immune regulation and served as a proof-of-concept for plethora of biomaterial-based vaccines. After years of extensive development of numerous biomaterials for immunomodulation, it is only recently that an experimental scaffold vaccine implanted beneath the skin has begun to use the human model to study the immune responses to cancer vaccination by co-delivering patient-derived tumor lysates and immunomodulatory proteins. If successful, this scaffold vaccine will change the way we approached untreatable cancers, but more importantly, will allow a faster and more rational translation of therapeutic regimes to other cancers, chronic infections, and autoimmune diseases. Most materials reviews have focused on immunomodulatory adjuvants and micro-nano-particles. Here we provide an insight into emerging hydrogel and scaffold based immunomodulatory approaches that continue to demonstrate efficacy against immune associated diseases.

Cucumber mosaic virus as drug delivery vehicle for doxorubicin

Taking advantage of the unique structure feature of cucumber mosaic virus (CMV), we have anchored folic acid (FA) as targeting moiety on the rigid CMV capsid and loaded significant amount of doxorubicin (Dox) into the interior cavity of CMV through the formation of Dox-RNA conjugate to provide a nanosized control delivery system for cancer therapy. The FA-CMV-Dox assemblies were characterized using transmission electron microscopy and size exclusion chromatography, which disclose that they have comparable size and morphology to the native CMV particles. The Dox-loaded viral particles exhibit sustained in vitro Dox release profile over 5 days at physiological pH but can be liberated from the conjugates with the presence of elevated level of RNase. The in vitro effects of folate receptor (FR)-targeted CMV-Dox nanoconjugates on cellular internalization and cell proliferation were evaluated by live-cell imaging, MTT and TUNEL assay, respectively, in mouse cardiomyocytes and FR over expression OVCAR-3 tumor cells. The in vivo efficacy was also investigated in the OVCAR-3 BALB/c nude mouse xenograft model through histological alterations and TUNEL assessment. The FA-CMV-Dox particles significantly decrease the accumulation of Dox in the nuclei of mouse myocardial cells and improve the uptake of Dox in the ovarian cancer, leading to less cardiotoxicity and enhanced antitumor effect. We believe that CMV offers a new way to fabricate nanosized drug delivery vehicles.

Partially biodegradable temperature- and pH-responsive poly(N-isopropylacrylamide)/dextran-maleic acid hydrogels: formulation and controlled drug delivery of doxorubicin

A new family of partially biodegradable temperature- and pH-responsive hydrogels, poly(N-isopropylacrylamide)/dextran-maleic acid (PNIPAAm/Dex-MA), was synthesized and its application as a drug carrier was investigated. The PNIPAAm/Dex-MA hydrogels were synthesized by UV cross-linking over a wide range of mixed solvent ratios of dimethyl formamide (DMF) to water. PNIPAAm and Dex-MA precursors were chosen as thermo-sensitive and pH-sensitive components, respectively. Dex-MA was also used as a cross-linker. An anti-tumor drug, doxorubicin, was used to examine the effects of network structures of PNIPAAm/Dex-MA hydrogels on the release of drug. These PNIPAAm/Dex-MA hybrid hydrogels exhibited a wide range of porous network structures and sizes due to the effect of the mixed solvent during the gelation reaction. This variation in porous network structure of NDF hydrogels led to a wide range of swelling, deswelling and biodegradation processes. The distinctive porous structure of the PNIPAAm/Dex-MA hydrogels was correlated to the release of doxorubicin from the hydrogels. A larger and faster release of doxorubicin was found in those hydrogels having a large pore size. This new family of PNIPAAm/Dex-MA hydrogels may have a great potential as drug carriers because of their combined stimuli-response capability, as well as partial biodegradability.

In vivo evaluation of doxorubicin-loaded polymeric micelles targeting folate receptors and early endosomal pH in drug-resistant ovarian cancer

The second generation of pH-sensitive micelles composed of poly(l-histidine-co-l-phenlyalanine(16 mol %))(MW:5K)-b-PEG(MW:2K) and poly(l-lactic acid)(MW:3K)-b-PEG(MW:2K)-folate (80/20 wt/wt %) was previously optimized by physicochemical and in vitro tests for both folate receptor and early endosomal pH targeting (pH approximately 6.0). In this study, the therapeutic efficacy of the doxorubicin (DOX)-loaded micelles (DOX loading content: 20 wt %) was evaluated using in vivo tests. Multidrug-resistant (MDR) ovarian tumor-xenografted mouse models were employed. The skin-fold dorsal window chamber model was applied for visualization of extravasation and drug retention for the initial one hour after iv injection. Noninvasive imaging followed, providing evidence of drug accumulation in the tumor after the first hour. The biodistribution study further supported the long circulation of the drug carrier, tumor-selective accumulation and intracellular drug delivery. Comprehensive tumor growth inhibition experiments examined the collective efficacy of the pH-sensitive micelles. The micelle formulation effectively suppressed the growth of existing MDR tumors in mice for at least 50 days by three iv injections at a 3-day interval at a dose of 10 mg of DOX/kg. The body weight of the animals treated with the test micelle formulation gradually increased over the experimental time period, rather than decreasing. The micelle formulation was superior to its first generation, which targeted pH 6.8 and folate receptor.

HYDROGELS FROM SOFT CONTACT LENSES AND IMPLANTS TO SELF-ASSEMBLED NANOMATERIALS

Hydrogels were the first biomaterials designed for clinical use. Their discovery and applications as soft contact lenses and implants are presented. This early hydrogel research served as a foundation for the expansion of biomedical polymers research into new directions: design of stimuli sensitive hydrogels that abruptly change their properties upon application of an external stimulus (pH, temperature, solvent, electrical field, biorecognition) and hydrogels as carriers for the delivery of drugs, peptides, and proteins. Finally, pathways to self-assembly of block and graft copolymers into hydrogels of precise 3D structures are introduced.

Pharmacokinetic and pharmacodynamic evaluation of a novel in situ forming poly(ethylene glycol)-based hydrogel for the controlled delivery of the camptothecins

Inadequate drug delivery, due to problems associated with achieving constant therapeutic blood levels, has hampered the use of anticancer agents of the camptothecin (CPT) class. The objective of the current studies was to develop a depot delivery system for the water-soluble analog of CPT, topotecan (TPT). In this study, a 2-phase drug depot consisting of TPT-loaded liposomes entrapped in a poly(ethylene glycol) hydrogel was designed. Physically entrapped unaltered TPT displayed a rapid release rate from the hydrogel. Controlled release was demonstrated in vitro and in vivo from the 2-phase system with constant blood levels being achieved for several days in rats. Cytotoxicity and antitumor activity were also evaluated in rats inoculated with syngeneic MAT B III breast cancer cells. Rats treated with the liposome-loaded hydrogel displayed significantly longer tumor growth suppression and did not exhibit body weight loss compared to those treated with other delivery modes. These experiments constitute a proof-of-principle of the 2-phase depot concept and its potential value for enhancing safety and efficacy in chemotherapy.