Combination therapy: opportunities and challenges for polymer-drug conjugates as anticancer nanomedicines

Systemic delivery of sticky siRNAs targeting the cell cycle for lung tumor metastasis inhibition

RNA interference allows the design of new inhibitors that target deregulated pathways in cancer. However systemic delivery of siRNA for the treatment of solid tumors still remains an issue. In our study, in order to suppress the progression of lung cancer metastasis in mice, we developed sticky siRNA (ssiRNA) to inhibit survivin and cyclin B1, two candidates involved in cell survival and proliferation. We exploited the linear polyethylenimine (PEI) as potent non-viral carrier to efficiently deliver our inhibitors. As a proof of concept, we have chosen a very aggressive mammary adenocarcinoma model (TSA-Luc cells), which forms lung metastases upon systemic cell injection. We confirmed in vitro, that the ssiRNAs delivered with PEI are not only able to inhibit our target genes at the mRNA and protein levels, but are also able to block the cell cycle and cell proliferation through a mechanism of RNA interference. More importantly, we showed in vivo by luciferase dosage, bioimaging and tissue section, an inhibition of lung tumor metastases after systemic delivery of cyclin B1 and survivin ssiRNA complexed with PEI. Alternating treatment with cisplatin and ssiRNA/PEI showed an additive effect between the two anticancer drugs on lung tumor inhibition leading to a significant increase in animal survival. Moreover a promising window between activity (IC₅₀) and toxicity (LD₅₀), essential for therapeutic application, was observed. Our data show that systemic delivery of ssiRNA/PEI complexes targeting the cell cycle is a valuable strategy for the treatment of lung tumor metastasis and that it can be combined with chemotherapy.

Combined modality doxorubicin-based chemotherapy and chitosan-mediated p53 gene therapy using double-walled microspheres for treatment of human hepatocellular carcinoma

The therapeutic efficiency of combined chemotherapy and gene therapy on human hepatocellular carcinoma HepG2 cells was investigated using double-walled microspheres that consisted of a poly(D,L-lactic-co-glycolic acid) (PLGA) core surrounded by a poly(L-lactic acid) (PLLA) shell layer and fabricated via the precision particle fabrication (PPF) technique. Here, double-walled microspheres were used to deliver doxorubicin (Dox) and/or chitosan-DNA nanoparticles containing the gene encoding the p53 tumor suppressor protein (chi-p53), loaded in the core and shell phases, respectively. Preliminary studies on chi-DNA nanoparticles were performed to optimize gene transfer to HepG2 cells. The transfection efficiency of chi-DNA nanoparticles was optimal at an N/P ratio of 7. In comparison to the 25-kDa branched polyethylenimine (PEI), chitosan showed no inherent toxicity towards the cells. Next, the therapeutic efficiencies of Dox and/or chi-p53 in microsphere formulations were compared to free drug(s) and evaluated in terms of growth inhibition, and cellular expression of tumor suppressor p53 and apoptotic caspase 3 proteins. Overall, the combined Dox and chi-p53 treatment exhibited enhanced cytotoxicity as compared to either Dox or chi-p53 treatments alone. Moreover, the antiproliferative effect was more substantial when cells were treated with microspheres than those treated with free drugs. High p53 expression was maintained during a five-day period, and was largely due to the controlled and sustained release of the microspheres. Moreover, increased activation of caspase 3 was observed, and was likely to have been facilitated by high levels of p53 expression. Overall, double-walled microspheres present a promising dual anticancer delivery system for combined chemotherapy and gene therapy.

pH-responsive complexes using prefunctionalized polymers for synchronous delivery of doxorubicin and siRNA to cancer cells

A nanocarrier delivery system that can simultaneously deliver a chemotherapeutic drug and siRNA to the tumor is emerging as a promising treatment strategy for cancer treatment. In this study, a multifunctional PHD/PPF/siRNA complexes was developed by one-step assembly of prefunctionalized polymers: PEI-HZ-DOX (PHD) and PEI-PEG-Folate (PPF) with siRNA. The PHD, a conjugate of PEI (polyethylenimine) with doxorubicin (DOX) via a pH-responsive hydrazone linkage, enables pH-controlled drug release. The PPF, a tumor-targeting folate ligand conjugated to PEI using polyethyleneglycol (PEG) as a linker, enables immune evasion and cell-specific targeting. The prefunctionalized PHD and PPF as well as the self-assembly complexes reveals advantage on safety in further application for siRNA delivery. By exploiting distinct triple ratios of PHD, PPF and siRNA during nanocomplexes formulation, the folate surface density, DOX loading amount and siRNA complexation can be precisely and reproducibly changed. The studies showed that the complexes was capable of delivering siRNA and DOX to cancerous cells and release synchronously in cell by acid-triggered manner, i.e. hydrazone bond cleavage and endosome/lysosome escape using flow cytometry and confocal laser scanning microscopy analysis. The results highlight the potential for therapeutic gene silencing in vitro and in vivo using RT-PCR and non-invasive in vivo imaging systems. The PHD/PPF/siRNA complexes can increase DOX and siRNA accumulation in cancerous cells and decrease the nonspecific distribution in normal tissues by the combination of EPR effect of nanocarriers, pH-triggered drug release, folate-mediated targeted delivery, and synergistic action of DOX and siRNA.

Functionalized graphene oxide mediated adriamycin delivery and miR-21 gene silencing to overcome tumor multidrug resistance in vitro

Multidrug resistance (MDR) is a major impediment to successful cancer chemotherapy. Co-delivery of novel MDR-reversing agents and anticancer drugs to cancer cells holds great promise for cancer treatment. MicroRNA-21 (miR-21) overexpression is associated with the development and progression of MDR in breast cancer, and it is emerging as a novel and promising MDR-reversing target. In this study, a multifunctional nanocomplex, composed of polyethylenimine (PEI)/poly(sodium 4-styrenesulfonates) (PSS)/graphene oxide (GO) and termed PPG, was prepared using the layer-by-layer assembly method to evaluate the reversal effects of PPG as a carrier for adriamycin (ADR) along with miR-21 targeted siRNA (anti-miR-21) in cancer drug resistance. ADR was firstly loaded onto the PPG surface (PPG_ADR) by physical mixing and anti-miR-21 was sequentially loaded onto PPG_ADR through electric absorption to form ^anti-miR-21PPG_ADR. Cell experiments showed that PPG significantly enhanced the accumulation of ADR in MCF-7/ADR cells (an ADR resistant breast cancer cell line) and exhibited much higher cytotoxicity than free ADR, suggesting that PPG could effectively reverse ADR resistance of MCF-7/ADR. Furthermore, the enhanced therapeutic efficacy of PPG could be correlated with effective silencing of miR-21 and with increased accumulation of ADR in drug-resistant tumor cells. The endocytosis study confirmed that PPG could effectively carry drug molecules into cells via the caveolae and clathrin-mediated endocytosis pathways. These results suggest that this PPG could be a potential and efficient non-viral vector for reversing MDR, and the strategy of combining anticancer drugs with miRNA therapy to overcome MDR could be an attractive approach in cancer treatment.

Lipid raft modulation by Rp1 reverses multidrug resistance via inactivating MDR-1 and Src inhibition

Multidrug resistance (MDR) is a major obstacle to effective cancer therapy. The membrane transporter MDR-1 (P-gp, ABCB1), a member of the ATP-binding cassette (ABC) transporter family, effluxes anti-cancer drugs from cancer cells. Increased activity of MDR-1 is known to be the main mechanism for multidrug resistance. MDR-1 is known to be localized in the cholesterol- and sphingolipid-enriched plasma membrane microdomains, known as lipid rafts. Disruption of lipid rafts by cholesterol depletion alters lipid raft functions, indicating that cholesterol is critical for raft function. Because ginsenosides are structurally similar to cholesterol, in this study, we investigated the effect of Rp1, a novel ginsenoside derivative, on drug resistance using drug-sensitive OVCAR-8 and drug-resistant NCI/ADR-RES and DXR cells. Rp1 treatment resulted in an accumulation of doxorubicin or rhodamine 123 by decreasing MDR-1 activity in doxorubicin-resistant cells. Rp1 synergistically induced cell death with actinomycin D in DXR cells. Rp1 appeared to redistribute lipid rafts and MDR-1 protein. Moreover, Rp1 reversed resistance to actinomycin D by decreasing MDR-1 protein levels and Src phosphorylation with modulation of lipid rafts. Addition of cholesterol attenuated Rp1-induced raft aggregation and MDR-1 redistribution. Rp1 and actinomycin D reduced Src activity, and overexpression of active Src decreased the synergistic effect of Rp1 with actinomycin D. Rp1-induced drug sensitization was also observed with several anti-cancer drugs, including doxorubicin. These data suggest that lipid raft-modulating agents can be used to inhibit MDR-1 activity and thus overcome drug resistance.

Drug-initiated ring-opening polymerization of O-carboxyanhydrides for the preparation of anticancer drug-poly(O-carboxyanhydride) nanoconjugates

We report a novel synthetic strategy of polymer-drug conjugates for nanoparticulate drug delivery: hydroxyl-containing drug (e.g., camptothecin, paclitaxel, doxorubicin and docetaxel) can initiate controlled polymerization of phenyl O-carboxyanhydride (Phe-OCA) to afford drug-poly(Phe-OCA) conjugated nanoparticles, termed drug-PheLA nanoconjugates (NCs). Our new NCs have well-controlled physicochemical properties, including high drug loading, quantitative drug loading efficiency, controlled particle size with narrow particle size distribution, and sustained drug release profile over days without "burst" release effect as observed in conventional polymer/drug encapsulates. Compared with polylactide NCs, the PheLA NCs have increased noncovalent hydrophobic interchain interactions and thereby result in remarkable stability in human serum with negligible particle aggregation. Such distinctive properties can reduce the premature disassembly of NCs upon dilution in the bloodstream and prolong NCs' in vivo circulation with the enhancement of intratumoral accumulation of NCs, which has a bearing on therapeutic effectiveness.

Galactosylated chitosan-polycaprolactone nanoparticles for hepatocyte-targeted delivery of curcumin

Galactosylated chitosan-polycaprolactone (Gal-CH-PCL) copolymers with a galactosylation degree of around 10% and varied PCL percentages less than 40 wt% were synthesized and used to produce nanoparticles for delivering curcumin. Some nanoparticles with encapsulation efficiency of 70% or higher and sizes changing from 100 to 250 nm were able to deliver curcumin in a controlled manner. PCL content in Gal-CH-PCLs was found to be a key factor for governing the release behavior of nanoparticles. Hepatocyte-targeted characteristic of nanoparticles was confirmed using human hepatocellular carcinoma (HepG2) cells. In comparison to free curcumin, curcumin-loaded Gal-CH-PCL nanoparticles well retained its anticancer activity. At an equivalent curcumin-dose of around 20 μg/mL that was found to be relatively safe to human normal liver cells, the results obtained from flow-cytometry revealed that some optimized Gal-CH-PCL nanoparticles showed more than 6-fold increasing abilities to induce the apoptosis and necrosis of HepG2 cells during 72 h treatment compared to free curcumin.

Immunoconjugates and long circulating systems: origins, current state of the art and future directions

Significant progress has been made recently in the area of immunoconjugated drugs and drug delivery systems (DDS). The immuno-modification of either the drug or DDS has proven to be a very promising approach that has significantly improved the targeted accumulation in pathological sites while decreasing its undesirable side effects in healthy tissues. The arrangement for both prolonged life in the circulation and specific target recognition represents another potent strategy in the development of immuno-targeted systems. The longevity of immuno-targeted DDS such as immunoliposomes and immunomicelles improves their targetability even in the presence of the additional passive accumulation in areas with a compromised vasculature. The added use of the immuno-targeted systems takes advantage of the specific microenvironment of pathological sites including lowered pH, increased temperature, and variation in the enzymatic activity. "Smart" stimulus-responsive systems combine different valuable functionalities including PEG-protection, targeting antibody, cell-penetration, and stimulus-sensitive functions. In this review we examined the evolution, current status and future directions in the area of therapeutical immunoconjugates and long-circulating immuno-targeted DDS.

Polymer therapeutics-prospects for 21st century: the end of the beginning

The term "polymer therapeutics" was coined to describe polymeric drugs, polymer conjugates of proteins, drugs and aptamers, together with those block copolymer micelles and multicomponent non-viral vectors which contain covalent linkages. These often complex, multicomponent constructs are actually "drugs" and "macromolecular prodrugs" in contrast to drug delivery systems that simply entrap (non-covalently) therapeutic agents. They have also been described as nanomedicines. First polymer-protein conjugates entered routine clinical use in 1990 and a growing number of polymeric drugs/sequestrants and PEGylated proteins/aptamers have since come into the market. Valuable lessons have been learnt over >3 decades of clinical development, especially in relation to critical product attributes governing safety and efficacy, the validated methods needed for product characterisation. Not least there has been improved understanding of polymer therapeutic-specific biomarkers that will in future enable improved selection of patients for therapy. Advances in synthetic polymer chemistry (including control of 3D architecture), the move towards greater use of biodegradable polymers, polymers delivering combination therapy, increased understanding of polymer therapeutic critical product attributes to guide pharmaceutical development, and advances in understanding of endocytosis and intracellular trafficking pathways in health and disease are opening new opportunities for design and clinical use of polymer-based therapeutics in the decades to come.

Use of Nanotechnology to Develop Multi-Drug Inhibitors For Cancer Therapy

Therapeutic agents that inhibit a single target often cannot combat a multifactorial disease such as cancer. Thus, multi-target inhibitors (MTIs) are needed to circumvent complications such as the development of resistance. There are two predominant types of MTIs, (a) single drug inhibitor (SDIs) that affect multiple pathways simultaneously, and (b) combinatorial agents or multi-drug inhibitors (MDIs) that inhibit multiple pathways. Single agent multi-target kinase inhibitors are amongst the most prominent class of compounds belonging to the former, whereas the latter includes many different classes of combinatorial agents that have been used to achieve synergistic efficacy against cancer. Safe delivery and accumulation at the tumor site is of paramount importance for MTIs because inhibition of multiple key signaling pathways has the potential to lead to systemic toxicity. For this reason, the development of drug delivery mechanisms using nanotechnology is preferable in order to ensure that the MDIs accumulate in the tumor vasculature, thereby increasing efficacy and minimizing off-target and systemic side effects. This review will discuss how nanotechnology can be used for the development of MTIs for cancer therapy and also it concludes with a discussion of the future of nanoparticle-based MTIs as well as the continuing obstacles being faced during the development of these unique agents.’

Hypocrellin-loaded gold nanocages with high two-photon efficiency for photothermal/photodynamic cancer therapy in vitro

A new bioconjugate nanostructure was constructed by using photosensitizer-incorporated mixed lipid-coated gold nanocages for two-photon photothermal/photodynamic cancer therapy in vitro with high efficiency. Scanning electron microscopic and transmission electron microscopic images reveal that the precursors and bioconjugate nanostructure as-prepared are narrowly dispersed and possess uniform morphologies. The relevant energy dispersion X-ray analysis and UV-vis spectra indicate that the bioconjugate nanostructure above was assembled successfully and has a strong absorption in the near-infrared region. Fluorescence and electronic spin resonance results show that the gold nanocage in the bioconjugate nanostructure can dramatically quench the photosensitizer and inhibit the production of singlet oxygen, which is supposed to alleviate the photosensitizers' unwanted side effects originating from their nontargeted distribution. We have demonstrated that as the nanocomplex is internalized by cancer cells, under two-photon illumination, photodynamic anticancer treatment is dramatically enhanced by the photothermal effect.

Nanoparticle-assisted combination therapies for effective cancer treatment

Combination chemotherapy and nanoparticle drug delivery are two areas that have shown significant promise in cancer treatment. Combined therapy of two or more drugs promotes synergism among the different drugs against cancer cells and suppresses drug resistance through distinct mechanisms of action. Nanoparticle drug delivery, on the other hand, enhances therapeutic effectiveness and reduces side effects of the drug payloads by improving their pharmacokinetics. These two active research fields have been recently merged to further improve the efficacy of cancer therapeutics. This review article summarizes the recent efforts in developing nanoparticle platforms to concurrently deliver multiple types of drugs for combination chemotherapy. We also highlight the challenges and design specifications that need to be considered in optimizing nanoparticle-based combination chemotherapy.

Drug targeting to tumors: principles, pitfalls and (pre-) clinical progress

Many different systems and strategies have been evaluated for drug targeting to tumors over the years. Routinely used systems include liposomes, polymers, micelles, nanoparticles and antibodies, and examples of strategies are passive drug targeting, active drug targeting to cancer cells, active drug targeting to endothelial cells and triggered drug delivery. Significant progress has been made in this area of research both at the preclinical and at the clinical level, and a number of (primarily passively tumor-targeted) nanomedicine formulations have been approved for clinical use. Significant progress has also been made with regard to better understanding the (patho-) physiological principles of drug targeting to tumors. This has led to the identification of several important pitfalls in tumor-targeted drug delivery, including I) overinterpretation of the EPR effect; II) poor tumor and tissue penetration of nanomedicines; III) misunderstanding of the potential usefulness of active drug targeting; IV) irrational formulation design, based on materials which are too complex and not broadly applicable; V) insufficient incorporation of nanomedicine formulations in clinically relevant combination regimens; VI) negligence of the notion that the highest medical need relates to metastasis, and not to solid tumor treatment; VII) insufficient integration of non-invasive imaging techniques and theranostics, which could be used to personalize nanomedicine-based therapeutic interventions; and VIII) lack of (efficacy analyses in) proper animal models, which are physiologically more relevant and more predictive for the clinical situation. These insights strongly suggest that besides making ever more nanomedicine formulations, future efforts should also address some of the conceptual drawbacks of drug targeting to tumors, and that strategies should be developed to overcome these shortcomings.

Advanced materials for co-delivery of drugs and genes in cancer therapy

With cancer being the major cause of mortality worldwide, the continued development of safe and efficacious treatments is warranted. A better understanding of the molecular mechanism and genetic basis of tumor initiation and progression, coupled with advances in chemistry, molecular biology and engineering have led to discovery of a wide range of therapeutic agents for cancer therapy. However, multidrug-resistance, which is mainly caused by malfunction of genes, has become a major problem in chemotherapy. To overcome this problem, the simultaneous delivery of genes to cancer cells has been proposed to correct the malfunctioned genes to sensitize the cells to chemotherapeutics. This progress report summarizes key advances in drug and gene delivery with focus on the development of polymers, peptides, liposomes and inorganic materials as nanocarriers for co-delivery of small molecular drugs and macromolecular genes or proteins. In addition, challenges and future perspectives in the design of nanocarriers for the co-delivery of therapeutic drugs and genes are discussed.

Design, synthesis and evaluation of N-acetyl glucosamine (NAG)-PEG-doxorubicin targeted conjugates for anticancer delivery

Efficacy of anticancer drug is limited by the severe adverse effects induced by drug; therefore the crux is in designing delivery systems targeted only to cancer cells. Toward this objectives, we propose, synthesis of poly(ethylene glycol) (PEG)-doxorubicin (DOX) prodrug conjugates consisting N-acetyl glucosamine (NAG) as a targeting moiety. Multicomponent system proposed here is characterized by (1)H NMR, UV spectroscopy, and HPLC. The multicomponent system is evaluated for in vitro cellular kinetics and anticancer activity using MCF-7 and MDA-MB-231 cells. Molecular modeling study demonstrated sterically stabilized conformations of polymeric conjugates. Interestingly, PEG-DOX conjugate with NAG ligand showed significantly higher cytotoxicity compared to drug conjugate with DOX. In addition, the polymer drug conjugate with NAG and DOX showed enhanced internalization and retention effect in cancer cells, compared to free DOX. Thus, with enhanced internalization and targeting ability of PEG conjugate of NAG-DOX has implication in targeted anticancer therapy.

Single-injection HPLC method for rapid analysis of a combination drug delivery system

Developing combination drug delivery systems (CDDS) is a challenging but necessary task to meet the needs of complex therapy regimes for patients. As the number of multi-drug regimens being administered increases, so does the difficulty of characterizing the CDDS as a whole. We present a single-step method for quantifying three model therapeutics released from a model hydrogel scaffold using high-performance liquid chromatography (HPLC). Poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogel tablets were fabricated via photoinitiated crosslinking and subsequently loaded with model active pharmaceutical ingredients (APIs), namely, porcine insulin (PI), fluorescein isothiocyanate-labeled bovine serum albumin (FBSA), prednisone (PSE), or a combination of all three. The hydrogel tablets were placed into release chambers and sampled over 21 days, and APIs were quantified using the method described herein. Six compounds were isolated and quantified in total. Release kinetics based on chemical properties of the APIs did not give systematic relationships; however, PSE was found to have improved device loading versus PI and FBSA. Rapid analysis of three model APIs released from a PEGDMA CDDS was achieved with a direct, single-injection HPLC method. Development of CDDS platforms is posited to benefit from such analytical approaches, potentially affording innovative solutions to complex disease states.

Nanotechnology-based combinational drug delivery: an emerging approach for cancer therapy

Combination therapy for the treatment of cancer is becoming more popular because it generates synergistic anticancer effects, reduces individual drug-related toxicity and suppresses multi-drug resistance through different mechanisms of action. In recent years, nanotechnology-based combination drug delivery to tumor tissues has emerged as an effective strategy by overcoming many biological, biophysical and biomedical barriers that the body stages against successful delivery of anticancer drugs. The sustained, controlled and targeted delivery of chemotherapeutic drugs in a combination approach enhanced therapeutic anticancer effects with reduced drug-associated side effects. In this article, we have reviewed the scope of various nanotechnology-based combination drug delivery approaches and also summarized the current perspective and challenges facing the successful treatment of cancer.

Dextran-catechin conjugate: a potential treatment against the pancreatic ductal adenocarcinoma

PURPOSE

A polysaccharide-flavonoid conjugate was developend and proposed for the treatment of pancreatic ductal adenocarcinoma (PDAC).

METHODS

The conjugate was synthesized by free radical grafting reaction between catechin and dextran. The chemical characterization of the conjugate was obtained by UV-Vis, 1H-NMR, FT-IR and GPC analyses, while the functionalization degree was determined by the Folin-Ciocalteu assay. The biological activity of the catechin-dextran conjugate was tested on two different cell lines derived from human pancreatic cancer (MIA PaCa-2 and PL45 cells), and the toxicity towards human pancreatic nestin-expressing cells evaluated.

RESULTS

Both the cancer cell lines are killed when exposed to the conjugate, and undergo apoptosis after the incubation with catechin-dextran which resulted more effective in killing pancreatic tumor cells compared to the catechin alone. Moreover, our experimental data indicate that the conjugate was less cytotoxic to human pancreatic nestin-expressing cells which are considered a good model of non-neoplastic pancreatic cells.

CONCLUSION

The suitability of newly synthesized Dextran-Catechin conjugate in the treatment of PDAC was proved confirming the high potential application of the proposed macromolecula system in the cancer therapy.

Combination drug delivery approaches in metastatic breast cancer

Disseminated metastatic breast cancer needs aggressive treatment due to its reduced response to anticancer treatment and hence low survival and quality of life. Although in theory a combination drug therapy has advantages over single-agent therapy, no appreciable survival enhancement is generally reported whereas increased toxicity is frequently seen in combination treatment especially in chemotherapy. Currently used combination treatments in metastatic breast cancer will be discussed with their challenges leading to the introduction of novel combination anticancer drug delivery systems that aim to overcome these challenges. Widely studied drug delivery systems such as liposomes, dendrimers, polymeric nanoparticles, and water-soluble polymers can concurrently carry multiple anticancer drugs in one platform. These carriers can provide improved target specificity achieved by passive and/or active targeting mechanisms.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Multifunctional nanocapsules for simultaneous encapsulation of hydrophilic and hydrophobic compounds and on-demand release

Cocktail therapy by delivering multiple drugs to diseased cells can elicit synergistic therapeutic effects and better modulate the complex cell-signaling network. Besides selection of drug combinations, a difficulty in delivery is how to encapsulate drugs with various solubility into a common vehicle, particularly when both hydrophobic and hydrophilic compounds are involved. Furthermore, it is highly desirable that the drug release profile can be controlled in an on-demand fashion for balanced therapeutic and side effects. On the basis of a simple and scalable double emulsion approach, we report a new class of nanocapsules that can solve these problems simultaneously. Further linking the nanocapsules with peptides targeting cell surface integrins leads to significantly enhanced cell uptake of the nanocapsules. Intracellular drug release triggered by external stimuli has also been achieved without affecting cell viability. Further development of this technology should open exciting opportunities in treating tough diseases such as cancer, cardiovascular diseases, neurological disorders, and infectious diseases.

Folate decorated dual drug loaded nanoparticle: role of curcumin in enhancing therapeutic potential of nutlin-3a by reversing multidrug resistance

Retinoblastoma is the most common intraocular tumor in children. Malfunctioning of many signaling pathways regulating cell survival or apoptosis, make the disease more vulnerable. Notably, resistance to chemotherapy mediated by MRP-1, lung-resistance protein (LRP) is the most challenging aspect to treat this disease. Presently, much attention has been given to the recently developed anticancer drug nutlin-3a because of its non-genotoxic nature and potency to activate tumor suppressor protein p53. However, being a substrate of multidrug resistance protein MRP1 and Pgp its application has become limited. Currently, research has step towards reversing Multi drug resistance (MDR) by using curcumin, however its clinical relevance is restricted by plasma instability and poor bioavailability. In the present investigation we tried to encapsulate nutlin-3a and curcumin in PLGA nanoparticle (NPs) surface functionalized with folate to enhance therapeutic potential of nutlin-3a by modulating MDR. We document that curcumin can inhibit the expression of MRP-1 and LRP gene/protein in a concentration dependent manner in Y79 cells. In vitro cellular cytotoxicity, cell cycle analysis and apoptosis studies were done to compare the effectiveness of native drugs (single or combined) and single or dual drug loaded nanoparticles (unconjugated/folate conjugated). The result demonstrated an augmented therapeutic efficacy of targeted dual drug loaded NPs (Fol-Nut-Cur-NPs) over other formulation. Enhanced expression or down regulation of proapoptotic/antiapoptotic proteins respectively and down-regulation of bcl2 and NFκB gene/protein by Fol-Nut-Cur-NPs substantiate the above findings. This is the first investigation exploring the role of curcumin as MDR modulator to enhance the therapeutic potentiality of nutlin-3a, which may opens new direction for targeting cancer with multidrug resistance phenotype.

Drug-Initiated, Controlled Ring-Opening Polymerization for the Synthesis of Polymer-Drug Conjugates

Paclitaxel, a polyol chemotherapeutic agent, was covalently conjugated through its 2'-OH to polylactide with 100% regioselectivity via controlled polymerization of lactide mediated by paclitaxel/(BDI-II)ZnN(TMS)(2) (BDI-II = 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene). The steric bulk of the substituents on the N-aryl groups of the BDI ligand drastically affected the regiochemistry of coordination of the metal catalysts to paclitaxel and the subsequent ring-opening polymerization of lactide. The drug-initiated, controlled polymerization of lactide was extended, again with 100% regioselectivity, to docetaxel, a chemotherapeutic agent that is even more structurally complex than paclitaxel. Regioselective incorporation of paclitaxel (or docetaxel) to other biopolymers (i.e., poly(δ-valerolactone), poly(trimethylene carbonate), and poly(ε-caprolactone)), was also achieved through drug/(BDI-II)ZnN(TMS)(2)-mediated controlled polymerization. These drug-polylactide conjugates with precisely controlled structures are expected to be excellent building blocks for drug delivery, coating, and controlled-release applications.

pH- and redox-responsive polysaccharide-based microcapsules with autofluorescence for biomedical applications

Autofluorescent microcapsules were assembled by covalent cross-linking of polysaccharide alginate dialdehyde (ADA) derivative and cystamine dihydrochloride (CM) through a layer-by-layer (LBL) technique. The formulated Schiff base and disulfide bonds render capsules with pH- and redox-responsive properties for pinpointed intracellular delivery based on the physiological difference between intracellular and extracellular environments. This simple and versatile method could be extended to other polysaccharide derivatives for the fabrication of autofluorescent nano- and micromaterials with dual stimuli response for biomedical applications.

Protease-activated drug development

In this extensive review, we elucidate the importance of proteases and their role in drug development in various diseases with an emphasis on cancer. First, key proteases are introduced along with their function in disease progression. Next, we link these proteases as targets for the development of prodrugs and provide clinical examples of protease-activatable prodrugs. Finally, we provide significant design considerations needed for the development of the next generation protease-targeted and protease-activatable prodrugs.