Folate and CD44 Receptors Dual-Targeting Hydrophobized Hyaluronic Acid Paclitaxel-Loaded Polymeric Micelles for Overcoming Multidrug Resistance and Improving Tumor Distribution

Therapeutic Approaches of Dual-targeted Nanomedicines for Tumor Multidrug Resistance

Currently, the main cause of cancer chemotherapy failure is multi-drug resistance (MDR), which involves a variety of complex mechanisms. Compared with traditional small-molecule chemotherapy, targeted nanomedicines offer promising alternative strategies as an emerging form of therapy, especially active targeted nanomedicines. However, although single-targeted nanomedicines have made some progress in tumor therapy, the complexity of tumor microenvironment and tumor heterogeneity limits their efficacy. Dual-targeted nanomedicines can simultaneously target two tumor-specific factors that cause tumor MDR, which have the potential in overcoming tumor MDR superior to single-targeted nanomedicines by further enhancing cell uptake and cytotoxicity in new forms, as well as the effectiveness of tumor-targeted delivery. This review discusses tumor MDR mechanisms and the latest achievements applied to dual-targeted nanomedicines in tumor MDR.

Hyaluronidase and pH Dual-Responsive Nanoparticles for Targeted Breast Cancer Stem Cells

pH-responsive and CD44 receptor-mediated targeted nanoparticles for eliminating cancer stem cells (CSCs) were developed based on complexes of PEG-poly(β-amino ester) (PEG-PBAE) micelles (PPM) coated with hyaluronic acid (HA) (HA-coated PPM complex, or HPPMc). Thioridazine (Thz) was loaded into HPPMc with a decent drug loading content. The release results of the drug in vitro showed that Thz was released from the HPPMc, which was stimulated by both the acidic pH and specific enzymes. Cytotoxicity studies on mammospheres (MS) revealed that the toxicity potential of Thz-loaded HPPMc (Thz–HPPMc) at pH 5.5 was better than drug solutions. Compared with that at pH 7.4, a higher cellular uptake of a coumarin-6 (C6)-labeled complex at pH 5.5 was observed, which demonstrated that complexes were efficiently taken up in MS. Meanwhile, free HA competitively inhibited the cellular uptake of HPPMc, which revealed that the uptake mechanism was CD44 receptor-mediated endocytosis. Within the acidic endolysosomal environment, the protonation of PBAE facilitated the escape of the complex from the lysosome and releases the drug. The results of in vivo distribution studies and tumor suppression experiments showed that HPMMc could stay in the tumor site of BALB/c nude mice for a longer period of time, and Thz–HPPMc could significantly improve the tumor-suppressing effect. All these results demonstrated the great potential of the multifunctional nanoparticle system for eliminating CSCs.

Lauroyl hyaluronan films for local drug delivery: Preparation and factors influencing the release of small molecules

Lauroyl derivatives of hyaluronan are safe and biodegradable materials that seem promising for application in medicine. However, their potential in the field of drug delivery was not yet explored. We thus prepared lauroyl hyaluronan films loaded with various drugs and studied the effects of lauroyl hyaluronan properties, drug hydrophobicity and medium composition on the drug release. Since biomolecules will always be present in real clinical applications, media supplemented by albumin were also included. The amphiphilic character of lauroyl hyaluronan enabled convenient loading of the films by both hydrophilic and hydrophobic drugs. Dominant factors influencing drug release were drug hydrophobicity and the presence of albumin. Hydrophilic diclofenac was released rapidly in all cases, while triclosan with medium hydrophobicity exhibited slower release sensitive to other parameters, reaching equilibrium values in the used experimental setup. The release of hydrophobic octenidine into pure buffer was almost negligible, but the addition of albumin did promote its release. The strong effect of albumin highlights the importance of considering biomolecules in the design of release experiments.

Single- versus Dual-Targeted Nanoparticles with Folic Acid and Biotin for Anticancer Drug Delivery

Cancer is one of the major causes of death worldwide and its treatment remains very challenging. The effectiveness of cancer therapy significantly depends upon tumour-specific delivery of the drug. Nanoparticle drug delivery systems have been developed to avoid the side effects of the conventional chemotherapy. However, according to the most recent recommendations, future nanomedicine should be focused mainly on active targeting of nanocarriers based on ligand-receptor recognition, which may show better efficacy than passive targeting in human cancer therapy. Nevertheless, the efficacy of single-ligand nanomedicines is still limited due to the complexity of the tumour microenvironment. Thus, the NPs are improved toward an additional functionality, e.g., pH-sensitivity (advanced single-targeted NPs). Moreover, dual-targeted nanoparticles which contain two different types of targeting agents on the same drug delivery system are developed. The advanced single-targeted NPs and dual-targeted nanocarriers present superior properties related to cell selectivity, cellular uptake and cytotoxicity toward cancer cells than conventional drug, non-targeted systems and single-targeted systems without additional functionality. Folic acid and biotin are used as targeting ligands for cancer chemotherapy, since they are available, inexpensive, nontoxic, nonimmunogenic and easy to modify. These ligands are used in both, single- and dual-targeted systems although the latter are still a novel approach. This review presents the recent achievements in the development of single- or dual-targeted nanoparticles for anticancer drug delivery.

Recent Development of Copolymeric Nano-Drug Delivery System for Paclitaxel

Background:

Paclitaxel (PTX) has been clinically used for several years due to its good therapeutic effect against cancers. Its poor water-solubility, non-selectivity, high cytotoxicity to normal tissue and worse pharmacokinetic property limit its clinical application.

Objective:

To review the recent progress on the PTX delivery systems.

Methods:

In recent years, the copolymeric nano-drug delivery systems for PTX are broadly studied. It mainly includes micelles, nanoparticles, liposomes, complexes, prodrugs and hydrogels, etc. They were developed or further modified with target molecules to investigate the release behavior, targeting to tissues, pharmacokinetic property, anticancer activities and bio-safety of PTX. In the review, we will describe and discuss the recent progress on the nano-drug delivery system for PTX since 2011.

Results:

The water-solubility, selective delivery to cancers, tissue toxicity, controlled release and pharmacokinetic property of PTX are improved by its encapsulation into the nano-drug delivery systems. In addition, its activities against cancer are also comparable or high when compared with the commercial formulation.

Conclusion:

Encapsulating PTX into nano-drug carriers should be helpful to reduce its toxicity to human, keeping or enhancing its activity and improving its pharmacokinetic property.

Dual-Targeted Delivery of Nanoparticles Encapsulating Paclitaxel and Everolimus: a Novel Strategy to Overcome Breast Cancer Receptor Heterogeneity

PURPOSE

The intratumoral heterogeneity observed in breast cancer (BC), in particular with regard to cell surface receptor expression, can hinder the success of many targeted cancer therapies. The development of novel therapeutic agents that target more than one receptor can overcome this inherent property of tumors and can facilitate their selective internalization in cancer cells. The goal of this study is to develop a drug combination-loaded nanoparticle (NP) formulation that is actively-targeted to HER2 and EGFR receptors on BC cells.

METHODS

A polymeric NP formulation was prepared which co-encapsulated a synergistic combination of the chemotherapeutic agent, paclitaxel (PTX), and the mTOR inhibitor, everolimus (EVER), and is targeted to HER2 and EGFR receptors on BC cells using antibody Fab fragments as the targeting moieties. The physicochemical characteristics of the dual-targeted formulation (Dual-NP) were evaluated, along with its cytotoxic profile (in both, monolayer and 3D BC models), as well as the degree of cellular uptake in HER2_high/EGFR_mod and HER2_neg/EGFR_low BC cells.

RESULTS

Dual-NPs were found to have significantly higher cytotoxicity relative to HER2 mono-targeted (T-NPs) and untargeted NPs (UT-NPs) in HER2_high/EGFR_mod monolayer BC cells after 72 h exposure, while no significant difference was observed in HER2_neg/EGFR_low cells. However, in the HER2_high/EGFR_mod spheroids, the cytotoxicity of Dual-NPs was comparable to that of T-NPs. This was thought to be attributed to the previously reported downregulation of EGFR in 3D in comparison to 2D BC models. Dual-NPs had significantly higher cellular uptake relative to UT-NPs and T-NPs in HER2_high/EGFR_mod BC cells after 24 h exposure, whereas in the HER2_neg/EGFR_low cells, the increase in cellular uptake of the Dual-NPs was not as high as the level achieved in the HER2_high/EGFR_mod cells. Blocking HER2 and EGFR significantly reduced the uptake of T-NPs and Dual-NPs in the HER2_high/EGFR_mod BC cells, demonstrating specific binding to both EGFR and HER2.

CONCLUSIONS

The dual-targeting strategy developed in this study in conjunction with a potentially promising delivery vector for a synergistic combination therapy can overcome receptor heterogeneity, yielding significant improvements in the cytotoxicity and cellular uptake in BC cells.

Bioresponsive albumin-conjugated paclitaxel prodrugs for cancer therapy

The efficacy of traditional chemotherapy often suffers from rapid clearance and off-target toxicity. Drug delivery systems and controlled release are applied to improve the therapeutic efficiencies of small-molecule drugs. In this work, two novel oxidative/reductive (Ox/Re) -sensitive and one non-sensitive Paclitaxel (PTX) prodrugs were synthesized with a maleimide group, which rapidly conjugates with albumin in vivo. Albumin serves as a good vehicle to deliver more prodrug to tumors due to the enhanced permeation and retention (EPR) effect. PTX was then released from the prodrugs in glutathione(GSH)/ reactive oxygen species(ROS)-rich tumor microenvironments. This bioresponsive prodrug strategy demonstrates potent chemotherapeutic efficiency in vivo and may be utilized in clinical cancer therapy.

Redox-sensitive micelles for targeted intracellular delivery and combination chemotherapy of paclitaxel and all-trans-retinoid acid

The application of paclitaxel (PTX) in clinic has been restricted due to its poor solubility. Several traditional nano-medicines have been developed to improve this defect, while they are still lack of tumor targeting ability and rapid drug release. In this work, an amphiphilic polymeric micelle of hyaluronic acid (HA) – all-trans-retinoid acid (ATRA) with a disulfide bond, was developed successfully for the co-delivery of PTX and ATRA. The combination chemotherapy of PTX and ATRA can strengthen the anti-tumor activity. Along with self-assembling to micelles in water, the delivery system displayed satisfying drug loading capacities for both PTX (32.62% ± 1.39%) and ATRA, due to directly using ATRA as the hydrophobic group. Rapid drug release properties of the PTX-loaded redox-sensitive micelles (HA-SS-ATRA) in vitro were confirmed under reducing condition containing GSH. Besides, HA-CD44 mediated endocytosis promoted the uptake of HA-SS-ATRA micelles by B16F10 cells. Due to these properties, cytotoxicity assay verified that PTX-loaded HA-SS-ATRA micelles showed concentration-dependent cytotoxicity and displayed obvious combination therapy of PTX and ATRA. Importantly, HA-SS-ATRA micelles could remarkably prolong plasma circulation time after intravenously administration. Therefore, redox-sensitive HA-SS-ATRA micelles could be utilized and explored as a promising drug delivery system for cancer combination chemotherapy.

Triphenylphosphonium-modified mitochondria-targeted paclitaxel nanocrystals for overcoming multidrug resistance

Mitochondria are currently known as novel targets for treating cancer, especially for tumors displaying multidrug resistance (MDR). This present study aimed to develop a mitochondria-targeted delivery system by using triphenylphosphonium cation (TPP⁺)-conjugated Brij 98 as the functional stabilizer to modify paclitaxel (PTX) nanocrystals (NCs) against drug-resistant cancer cells. Evaluations were performed on 2D monolayer and 3D multicellular spheroids (MCs) of MCF-7 cells and MCF-7/ADR cells. In comparison with free PTX and the non-targeted PTX NCs, the targeted PTX NCs showed the strongest cytotoxicity against both 2D MCF-7 and MCF-7/ADR cells, which was correlated with decreased mitochondrial membrane potential. The targeted PTX NCs exhibited deeper penetration on MCF-7 MCs and more significant growth inhibition on both MCF-7 and MCF-7/ADR MCs. The proposed strategy indicated that the TPP⁺-modified NCs represent a potentially viable approach for targeted chemotherapeutic molecules to mitochondria. This strategy might provide promising therapeutic outcomes to overcome MDR.

Synergetic Combinations of Dual-Targeting Ligands for Enhanced In Vitro and In Vivo Tumor Targeting

The concept of dual-ligand targeting has been around for quite some time, but remains controversial due to the intricate interplay between so many different factors such as the choice of dual ligands, their densities, ratios and length matching, etc. Herein, the synthesis of a combinatorial library of single and dual-ligand nanoparticles with systematically varied properties (ligand densities, ligand ratios, and lengths) for tumor targeting is reported. Folic acid (FA) and hyaluronic acid (HA) are used as two model targeting ligands. It is found that the length matching and ligand ratio play critical roles in achieving the synergetic effect of the dual-ligand targeting. When FA is presented on the nanoparticle surface through a 5K polyethylene glycol (PEG) chain, the dual ligand formulations using the HA with either 5K or 10K length do not show any targeting effect, but the right length of HA (7K) with a careful selection of the right ligand ratio do enhance the targeting efficiency and specificity significantly. Further in vitro 3D tumor spheroid models and in vivo xenograft mice models confirm the synergetic targeting efficiency of the optimal dual-ligand formulation (5F2H_7K ). This work provides a valuable insight into the design of dual-ligand targeting nanosystems.

Reduction-sensitive CD44 receptor-targeted hyaluronic acid derivative micelles for doxorubicin delivery

Introduction

A reduction-sensitive CD44-positive tumor-targetable drug delivery system for doxorubicin (DOX) delivery was developed based on hyaluronic acid (HA)-grafted polymers.

Materials and methods

HA was conjugated with folic acid (FA) via a reduction-sensitive disulfide linkage to form an amphiphilic polymer (HA-ss-FA). The chemical structure of HA-ss-FA was analyzed by ultraviolet spectroscopy, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance (NMR) spectroscopy. The molecular weight of HA-ss-FA was determined by high-performance gel permeation chromatography. Blank HA-ss-FA micelles and DOX-loaded micelles were prepared and characterized. The reduction responsibility, cellular uptake, and in vivo biodistribution of HA-ss-FA micelles were investigated.

Results

DOX-loaded micelles were of high encapsulation efficiency (88.09%), high drug-loading content (22.70%), appropriate mean diameter (100-120 nm), narrow size distribution, and negative zeta potential (-6.7 to -31.5 mV). The DOX release from the micelles was significantly enhanced in reduction environment compared to normal environment. The result of in vitro cytotoxicity assay indicated that the blank micelles were of low toxicity and good biocompatibility and the cell viabilities were >100% with the concentration of HA-ss-FA from 18.75 to 600.00 μg/mL. Cellular uptake and in vivo biodistribution studies showed that DOX-loaded micelles were tumor-targetable and could significantly enhance cellular uptake by CD44 receptor-mediated endocytosis, and the cellular uptake of DOX in CD44-positve A549 cells was 1.6-fold more than that in CD44-negative L02 cells. In vivo biodistribution of HA-ss-FA micelles showed that micelles were of good in vivo tumor targetability and the fluorescence of indocyanine green (ICG)-loaded micelles was 4- to 6.6-fold stronger than free ICG within 6 h in HCCLM3 tumor-bearing nude mice.

Conclusion

HA-ss-FA is a promising nanocarrier with excellent biocompatibility, tumor targetability, and controlled drug release capability for delivery of chemotherapy drugs in cancer therapy.

Paclitaxel delivered by CD44 receptor-targeting and endosomal pH sensitive dual functionalized hyaluronic acid micelles for multidrug resistance reversion

The drug efflux mediated by P-glycoprotein (P-gp) transporter is a major factor responsible for multidrug resistance (MDR) of paclitaxel (PTX). The efficient intracellular PTX delivery is a promising strategy for overcoming the MDR of tumor cells. A CD44 receptor targeting and endosome-pH sensitive dual functionalized hyaluronic acid-deoxycholic acid-histidine (HA-DOCA-His) micellar formulation was developed to overcome MDR, and a CD44 receptor targeting hyaluronic acid-deoxycholic acid (HA-DOCA) micelles was used as a comparison. Compared with Taxol solution and HA-DOCA micelles, the cytotoxicity of PTX loaded in HA-DOCA-His micelles against drug-resistant tumor cells was improved significantly and possessed superior MDR-overcoming performance; this phenomenon is due to the increased intracellular PTX delivery by CD44 receptor-mediated endocytosis pathway and endosome-pH sensitivity-mediated PTX triggering release. Upon pharmacokinetic study, PTX/HA-DOCA-His micelles demonstrated longer blood circulation time, larger AUC, decreased V_d and CL than the Taxol solution. More importantly, PTX/HA-DOCA-His micelles were more effective in tumor growth inhibition in MCF-7/Adr tumor-bearing mice compared with PTX/HA-DOCA micelles and Taxol solution. Dual targeting strategy-functionalized HA-DOCA-His micelles demonstrated excellent MDR-reversing ability for therapeutic efficacy and improvement on MDR tumors, thereby providing an effective targeting strategy for PTX delivery of nano-drug delivery system in MDR cancer chemotherapy.

Antibody-modified liposomes for tumor-targeting delivery of timosaponin AIII

Introduction

Timosaponin AIII (TAIII), as a steroid saponin in Anemarrhena asphodeloides, has favorable potential as an antitumor candidate. However, its hydrophobicity and low bioavailability severely limit its in vivo antitumor efficacy.

Methods

To overcome this drawback, TAIII-loaded liposomes (LP) were prepared to improve TAIII solubility and extend its circulation time. Furthermore, anti-CD44 antibody-modified LP (CD44-LP) was prepared to enhance the therapeutic index of TAIII. The LP and CD44-LP were also characterized through their biological activity, target selective binding and uptake, and in vivo pharmacokinetics.

Results

Compared with free TAIII, both LP and CD44-LP possessed a desirable sustained-release profile in vitro, with ~14.2- and 10.7-fold longer TAIII half-life, respectively, and 1.7- and 1.9-fold larger area under the curve, respectively. LP and CD44-LP enhanced TAIII antitumor activity against HepG2 cells and in a xenograft mouse model without detectable toxicity. In particular, CD44-LP exhibited notably higher cytotoxicity than did LP, with a lower half-maximal inhibitory concentration (48 h). CD44-LP exhibited stronger tumor inhibition, and the tumor inhibitory effect was 1.3-fold that of LP. Furthermore, confocal laser scanning microscopy and in vivo near-infrared imaging of a xenograft mouse model revealed that compared with LP, CD44-LP could effectively enhance tumor accumulation.

Conclusion

Taken together, the results indicate that both CD44-LP and LP can considerably extend TAIII circulation time, increase tumor-targeted accumulation, and enhance antitumor activity. Thus, the anti-CD44 antibody-modified liposome is a promising candidate for treating CD44-positive cancer with considerable antitumor effects.

Targeted Delivery of siRNA Therapeutics to Malignant Tumors

Over the past 20 years, a diverse group of ligands targeting surface biomarkers or receptors has been identified with several investigated to target siRNA to tumors. Many approaches to developing tumor-homing peptides, RNA and DNA aptamers, and single-chain variable fragment antibodies by using phage display, in vitro evolution, and recombinant antibody methods could not have been imagined by researchers in the 1980s. Despite these many scientific advances, there is no reason to expect that the ligand field will not continue to evolve. From development of ligands based on novel or existing biomarkers to linking ligands to drugs and gene and antisense delivery systems, several fields have coalesced to facilitate ligand-directed siRNA therapeutics. In this review, we discuss the major categories of ligand-targeted siRNA therapeutics for tumors, as well as the different strategies to identify new ligands.

Recent advances in hyaluronic acid-decorated nanocarriers for targeted cancer therapy

The cluster-determinant 44 (CD44) receptor has a high affinity for hyaluronic acid (HA) binding and is a desirable receptor for active targeting based on its overexpression in cancer cells compared with normal body cells. The nanocarrier affinity can be increased by conjugating drug-loaded carriers with HA, allowing enhanced cancer cell uptake via the HA-CD44 receptor-mediated endocytosis pathway. In this review, we discuss recent advances in HA-based nanocarriers and micelles for cancer therapy. In vitro and in vivo experiments have repeatedly indicated HA-based nanocarriers to be a target-specific drug and gene delivery platform with great promise for future applications in clinical cancer therapy.

Development and evaluation of targeting ligands surface modified paclitaxel nanocrystals

To overcome the toxicity of excipient or blank nanoparticles for drug delivery nano-system, the surface modified paclitaxel nanocrystals (PTX-NC) have been developed. PTX-NCs were prepared by nano-precipitation method. The surface of PTX-NCs were modified by grafting with apo-transferrin (Tf) or hyaluronic acid (HA). The physical properties of PTX-NCs were evaluated by field emission scanning electron microscope (FE-SEM), zeta-sizer, zeta-potential, differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectrometry. In vitro drug release study was performed in phosphate buffered saline (PBS) with or without 0.5% (w/v) Tween 80 for 24h. Cellular uptake was studied at time intervals of 0.5, 1, and 2h in MCF-7 cells, and cell growth inhibition study was performed for 24h using MCF-7 cells (cancer cells), and HaCaT cells (normal cells). Three different types of PTX-NCs with a mean size of 236.0±100.6nm (PTX-NC), 302.0±152.0nm (Tf-PTX-NC) and 339±180.6nm (HA-PTX-NC) were successfully prepared. The drug release profiles showed 29.1%/6.9% (PTX (pure)), 40.7%/23.9% (PTX-NC), 50.5%/25.1% (Tf-PTX-NC) and 46.8/24.8% (HA-PTX-NC) in PBS with/without 0.5% (w/v) Tween 80 for 24h, respectively. As per the results, the drug release of PTX-NCs showed the faster release as compared to that of PTX (pure). Surface modified PTX-NCs exhibited higher values for cell permeability than unmodified PTX-NC in the cellular uptake study. Surface modified PTX-NCs inhibited the cell growth approximately to 60% in MCF-7 cells, however effect of surface modified PTX-NCs on normal cell line was lower than the PTX-NC and PTX (pure). In conclusion, biological macromolecules (Tf or HA) surface modified PTX-NC enhanced the cellular uptake and the cell growth inhibition.

The effect of dual-functional hyaluronic acid-vitamin E succinate micelles on targeting delivery of doxorubicin

Tumor-targeted delivery system has been developed as an attractive strategy for effective tumor therapy. In this study, in order to enhance the antitumor effects of doxorubicin (DOX), amphiphilic hyaluronic acid (HA)-conjugated vitamin E succinate (VES) copolymers (HA-VES) with different degrees of substitution (DS) were prepared with synergistic antitumor effects and active targeting activities, and utilized as nanocarriers for the efficient delivery of DOX. DOX-loaded HA-VES polymeric micelles (HA-VES/DOX) self-assembled from dual-functional HA-VES copolymer and exhibited excellent loading efficiency and superior colloidal stability. In vitro, HA-VES/DOX displayed enhanced cytotoxicity with synergistic anticancer effects of HA-VES copolymer, high apoptosis-inducing activities of tumor cells, and reversal effects of DOX on multidrug resistance, in comparison with DOX. Also, in vitro cellular uptake and subcellular localization studies revealed that HA-VES/DOX could more efficiently internalize into cancer cells and selectively release DOX within lysosomes, thereby enhancing the distribution of DOX in nuclei and facilitating its interactions with DNA. Specifically, HA-VES/DOX decreased the activity of CD44 mRNA and improved the targeting efficiency on MCF-7 cells, based on the active recognition between HA and CD44 receptor. More importantly, HA-VES/DOX displayed better tumor accumulation and targeting, and enhanced antitumor efficacy with reduced systemic toxicity in 4T1 tumor-bearing mice. In summary, the developed HA-VES-based drug delivery system, which increased drug targeting on the tumor site and exhibited preferable anticancer activity, could hold great potential as an effective and promising strategy for efficient tumor therapy.

Targeting cancer with hyaluronic acid-based nanocarriers: recent advances and translational perspectives

Hyaluronic acid is a natural polysaccharide that has been widely explored for the development of anticancer therapies due to its ability to target cancer cells. Moreover, advances made in the last decade have revealed the versatility of this biomaterial in the design of multifunctional carriers, intended for the delivery of a variety of bioactive molecules, including polynucleotides, immunomodulatory drugs and imaging agents. In this review, we aim to provide an overview of the major recent achievements in this field, highlighting the application of the newly developed nanostructures in combination therapies, immunomodulation and theranostics. Finally, we will discuss the main challenges and technological advances that will allow these carriers to be considered as candidates for clinical development.

A review of the ligands and related targeting strategies for active targeting of paclitaxel to tumours

It has been 30 years since the discovery of the anti-tumour property of paclitaxel (PTX), which has been successfully applied in clinic for the treatment of carcinomas of the lungs, breast and ovarian. However, PTX is poorly soluble in water and has no targeting and selectivity to tumour tissue. Recent advances in active tumour targeting of PTX delivery vehicles have addressed some of the issues related to lack of solubility in water and non-specific toxicities associated with PTX. These PTX delivery vehicles are designed for active targeting to specific cancer cells by the addition of ligands for recognition by specific receptors/antigens on cancer cells. This article will focus on various ligands and related targeting strategies serving as potential tools for active targeting of PTX to tumour tissues, illustrating their use in different tumour models. This review also highlights the need of further studies on the discovery of receptors in different cells of specific organ and ligands with binding efficiency to these specific receptors.

Hyaluronic acid for anticancer drug and nucleic acid delivery

Hyaluronic acid (HA) is widely used in anticancer drug delivery, since it is biocompatible, biodegradable, non-toxic, and non-immunogenic; moreover, HA receptors are overexpressed on many tumor cells. Exploiting this ligand-receptor interaction, the use of HA is now a rapidly-growing platform for targeting CD44-overexpressing cells, to improve anticancer therapies. The rationale underlying approaches, chemical strategies, and recent advances in the use of HA to design drug carriers for delivering anticancer agents, are reviewed. Comprehensive descriptions are given of HA-based drug conjugates, particulate carriers (micelles, liposomes, nanoparticles, microparticles), inorganic nanostructures, and hydrogels, with particular emphasis on reports of preclinical/clinical results.

Hyaluronic acid-coated poly(β-amino) ester nanoparticles as carrier of doxorubicin for overcoming drug resistance in breast cancer cells

Hyaluronic acid-coated poly(β-amino) ester nanoparticles used as carrier for doxorubicin could efficiently overcome the drug resistance in breast cancer cells.

Engineered Nanoparticles Against MDR in Cancer: The State of the Art and its Prospective

Cancer is a highly heterogeneous disease at intra/inter patient levels and known as the leading cause of death worldwide. A variety of mono and combinational therapies including chemotherapy have been evolved over the years for its effective treatment. However, advent of chemotherapeutic resistance or multidrug resistance (MDR) in cancer is a major challenge researchers are facing in cancer chemotherapy. MDR is a complex process having multifaceted non-cellular or cellular-based mechanisms. Research in the area of cancer nanotechnology over the past two decade has now proven that the smartly designed nanoparticles help in successful chemotherapy by overcoming the MDR and preferentially accumulate in the tumor region by means of active and passive targeting therefore reducing the offtarget accumulation of payload. Many of such nanoparticles are in different stages of clinical trials as nanomedicines showing promising result in cancer therapy including the resistant cases. Nanoparticles as chemotherapeutics carriers offer the opportunity to have multiple payload of drug and or imaging agents for combinational and theranostics therapy. Moreover, nanotechnology further bring in notice the new treatment strategies such as combining the NIR, MRI and HIFU in cancer chemotherapy and imaging. Here, we discussed the cellular/non-cellular factors constituting the MDR in cancer and the role of nanomedicines in effective chemotherapy of MDR cases of cancers. Moreover, recent advancements like combinational payload delivery and combined physical approach with nanotechnology in cancer therapy have also been discussed.

Intracellular delivery and antitumor effects of a redox-responsive polymeric paclitaxel conjugate based on hyaluronic acid

Polymer-drug conjugates have demonstrated application potentials in optimizing chemotherapeutics. In this study a new bioconjugate, HA-ss-PTX, was designed and synthesized with cooperative dual characteristics of active tumor targeting and selective intracellular drug release. Paclitaxel (PTX) was covalently attached to hyaluronic acid (HA) with various sizes (MW 9.5, 35, 770 kDa); a cross-linker containing disulfide bond was also used to shield drug leakage in blood circulation and to achieve rapid drug release in tumor cells in response to glutathione. Incorporation of HA to the conjugate enhanced the capabilities of drug loading, intracellular endocytosis and tumor targeting of micelles in comparison to mPEG. HA molecular weight showed significant effect on properties and antitumor efficacy of the synthesized conjugates. Intracellular uptake of HA-ss-PTX toward MCF-7 cells was mediated by CD44-caveolae-mediated endocytosis. Compared to Taxol and mPEG-ss-PTX, HA9.5-ss-PTX demonstrated improved tumor growth inhibition in vivo with a TIR of 83.27 ± 5.20%. It was concluded that HA9.5-ss-PTX achieved rapid intracellular release of PTX and enhanced its therapeutic efficacy, thus providing a platform for specific drug targeting and controlled intracellular release in chemotherapeutics.

STATEMENT OF SIGNIFICANCE

Polymer-drug conjugates, promising nanomedicines, still face some technical challenges including a lack of specific targeting and rapid intracellular drug release at the target site. In this manuscript we designed and constructed a novel bioconjugate HA-ss-PTX, which possessed coordinated dual characteristics of active tumor targeting and selective intracellular drug release. Redox-responsive disulfide bond was introduced to the conjugate to shield drug leakage in blood circulation and to achieve rapid drug release at tumor site in response to reductant like glutathione. Paclitaxel was selected as a model drug to be covalently attached to hyaluronic acid (HA) with various sizes to elucidate the structure-activity relationship and to address whether HA could substitute PEG as a carrier for polymeric conjugates. Based on a series of in vitro and in vivo experiments, HA-ss-PTX performed well in drug loading, cellular internalization, tumor targeting by entering tumor cells via CD44-caveolae-mediated endocytosis and rapidly release drug at target in the presence of GSH. One of the key issues in clinical oncology is to enhance drug delivery efficacy while minimizing side effects. The study indicated that this new polymeric conjugate system would be useful in delivering anticancer agents to improve therapeutic efficacy and to minimize adverse effects, thus providing a platform for specific drug targeting and controlled intracellular release in chemotherapeutics.

Micro- and nanotechnologies for intracellular delivery

The majority of drugs and biomolecules need to be delivered into cells to be effective. However, the cell membranes, a biological barrier, strictly resist drugs or biomolecules entering cells, resulting in significantly reduced intracellular delivery efficiency. To overcome this barrier, a variety of intracellular delivery approaches including chemical and physical ways have been developed in recent years. In this review, the focus is on summarizing the nanomaterial routes involved in making use of a collection of receptors for the targeted delivery of drugs and biomolecules and the physical ways of applying micro- and nanotechnologies for high-throughput intracellular delivery.