Polymer conjugates as anticancer nanomedicines.

The transfer of polymer-protein conjugates into routine clinical use, and the clinical development of polymer-anticancer-drug conjugates, both as single agents and as components of combination therapy, is establishing polymer therapeutics as one of the first classes of anticancer nanomedicines. There is growing optimism that ever more sophisticated polymer-based vectors will be a significant addition to the armoury currently used for cancer therapy.

Endocytosis and intracellular trafficking as gateways for nanomedicine delivery: opportunities and challenges.

More than 40 nanomedicines are already in routine clinical use with a growing number following in preclinical and clinical development. The therapeutic objectives are often enhanced disease-specific targeting (with simultaneously reduced access to sites of toxicity) and, especially in the case of macromolecular biotech drugs, improving access to intracellular pharmacological target receptors. Successful navigation of the endocytic pathways is usually a prerequisite to achieve these goals. Thus a comprehensive understanding of endocytosis and intracellular trafficking pathways in both the target and bystander normal cell type(s) is essential to enable optimal nanomedicine design. It is becoming evident that endocytic pathways can become disregulated in disease and this, together with the potential changes induced during exposure to the nanocarrier itself, has the potential to significantly impact nanomedicine performance in terms of safety and efficacy. Here we overview the endomembrane trafficking pathways, discuss the methods used to determine and quantitate the intracellular fate of nanomedicines, and review the current status of lysosomotropic and endosomotropic delivery. Based on the lessons learned during more than 3 decades of clinical development, the need to use endocytosis-relevant clinical biomarkers to better select those patients most likely to benefit from nanomedicine therapy is also discussed.

Nanomedicine(s) under the microscope.

Depending on the context, nanotechnologies developed as nanomedicines (nanosized therapeutics and imaging agents) are presented as either a remarkable technological revolution already capable of delivering new diagnostics, treatments for unmanageable diseases, and opportunities for tissue repair or highly dangerous nanoparticles, nanorobots, or nanoelectronic devices that will wreak havoc in the body. The truth lies firmly between these two extremes. Rational design of "nanomedicines" began almost half a century ago, and >40 products have completed the complex journey from lab to routine clinical use. Here we critically review both nanomedicines in clinical use and emerging nanosized drugs, drug delivery systems, imaging agents, and theranostics with unique properties that promise much for the future. Key factors relevant to the design of practical nanomedicines and the regulatory mechanisms designed to ensure safe and timely realization of healthcare benefits are discussed.

Polymer coiled-coil conjugates: potential for development as a new class of therapeutic "molecular switch".

Polymer therapeutics, including polymeric drugs and polymer-protein conjugates, are clinically established as first-generation nanomedicines. Knowing that the coiled-coil peptide motif is fundamentally important in the regulation of many cellular and pathological processes, the aim of these studies was to examine the feasibility of designing polymer conjugates containing the coiled-coil motif as a putative therapeutic "molecular switch". To establish proof of concept, we prepared a mPEG-FosW(C) conjugate by reacting mPEG-maleimide (M(w) 5522 g mol(-1), M(w)/M(n) 1.1) with a FosW peptide synthesized to contain a terminal cysteine residue (FosW(C)). Its ability to form a stable coil-coil heterodimer with the target c-Jun sequence of the oncogenic AP-1 transcription factor was investigated using 2D (15)N-HSQC NMR together with a recombinantly prepared (15)N-labeled c-Jun peptide ([(15)N]r-c-Jun). Observation that heterodimerization was achieved and that the polymer did not sterically disadvantage hybridization suggests an important future for this new family of polymer therapeutics.

Cell uptake and trafficking behavior of non-covalent, coiled-coil based polymer-drug conjugates.

This paper reports on the cell uptake and trafficking properties of a series of non-covalent polymer-drug conjugates. These nanomedicines are composed of a poly(N-(2-hydroxypropyl)methacrylamide) backbone functionalized with multiple copies of a drug. The drug moieties are attached to the polymer via a non-covalent, so called coiled coil motif, which is formed by heterodimerization of two complementary peptide strands, one of which is attached to the polymer carrier and the other to the drug. Cytotoxicity and FACS experiments, which were carried out with model anticancer drug or fluorophore conjugates, provided insight into the cell uptake and trafficking behavior of these conjugates.

A comparison of major trauma admissions to Christchurch Hospital during and after COVID-19 lockdown in New Zealand.

AIMS: To describe any change in the volume and mechanisms of injury of major trauma admissions during and after COVID-19 lockdown, and in doing so, to provide information for resource planning and identification of priority areas for injury prevention initiatives. METHODS: A retrospective, descriptive study conducted on Canterbury District Health Board trauma registry data. The study population consisted of all major trauma patients of all age groups admitted to Christchurch Hospital over three 33-day periods: before, during and after COVID-19 lockdown in New Zealand. Broadly speaking, major trauma is defined as having an injury severity score 13 or death following injury. RESULTS: There was a 42% reduction in the volume of major trauma admissions during lockdown. Falls were the most common injury during lockdown, and transport-related injuries after lockdown. Alcohol intoxication was associated with 19 to 33% of all injuries across the study periods. CONCLUSION: Major trauma inevitably occurred during lockdown, although at considerably lower volumes. After lockdown, once restrictions were eased, major trauma admissions reverted to pre-lockdown patterns. Injury prevention strategies can reduce avoidable pressures on hospitals at a time of pandemic. In New Zealand, focus should be placed on reducing alcohol- and transport-related injuries and increasing community awareness on falls prevention.

Studies on the mechanism of action of dextrin-phospholipase A2 and its suitability for use in combination therapy.

The bioresponsive conjugate dextrin-phospholipase A2 (PLA2) is a novel anticancer polymer therapeutic. Dextrin conjugation decreases PLA2 bioactivity, but this can be restored following triggered degradation by alpha-amylase. The conjugate displays reduced hemolytic activity but retains, or shows enhanced, cytotoxicity in vitro that partially correlates with epidermal growth factor receptor (EGFR) expression. Here, we investigate further the mechanism of action of dextrin-PLA2 with the aim of judging its potential for combination with tyrosine kinase inhibitors (TKI) and/or chemotherapy and selecting the first models for in vivo evaluation. The endocytic fate of Oregon Green (OG)-labeled probes was assessed in MCF-7 cells. Whereas PLA2-OG showed greatest membrane binding, the dextrin-PLA2-OG conjugate displayed higher internalization. Moreover, cells incubated with PLA(2)-OG and dextrin-PLA2-OG showed an altered pattern of intracellular vesicle distribution compared to dextrin-OG. When cell lines known to express different levels of EGFR were used to assess cytotoxicity, free PLA2 activity was enhanced by addition of EGF whereas the conjugate was less cytotoxic, perhaps due to differences in their PK/PD profile. Co-incubation of cells with the TKI inhibitor, gefitinib, led to reduced cytotoxicity of both PLA2 and dextrin-PLA2 suggesting a TK-mediated PLA2 mechanism of action. However, the enhanced cytotoxicity seen in the presence of doxorubicin suggested potential for development of a dextrin-PLA2/doxorubicin combination therapy.

Bioresponsive dextrin-rhEGF conjugates: in vitro evaluation in models relevant to its proposed use as a treatment for chronic wounds.

We recently developed a bioresponsive dextrin-recombinant human epidermal growth factor (rhEGF) conjugate as a polymer therapeutic with potential for use in the promotion of tissue repair. The aim of these studies was to use patient-derived wound fluid and fibroblasts to evaluate its potential for further development as a treatment for chronic wounds, such as venous leg ulceration, a growing clinical challenge in the aging population. First, the levels of EGF (ELISA assay), alpha-amylase and elastase (enzyme assays) were measured in patient-derived acute and chronic wound fluid. EGF was detected in acute, but not in chronic wound fluid. alpha-Amylase concentrations were higher in acute (188 IU/L), compared to chronic wound fluid (52 IU/L), but both were in the range of human serum levels. Although elastase was present in chronic wound fluid (2.1 +/- 1.2 RFU/min), none was detected in acute wound fluid. Dextrin-rhEGF incubation in chronic wound fluid led to endogenous alpha-amylase-mediated release of rhEGF (ELISA) that was maximal at 48 h. When the migration of HaCaT keratinocytes and of human fibroblasts (isolated from patient-matched, normal skin and chronic dermal wounds) was studied in vitro using the scratch wound assay, enhanced cell migration was observed in response to both free rhEGF and alpha-amylase-activated dextrin-rhEGF conjugate compared to controls. In addition, fibroblasts displayed increased proliferation (normal dermal fibroblasts approximately 160%; chronic wound fibroblasts approximately 140%) following incubation (72 h) with dextrin-rhEGF that had been exposed to physiological levels of alpha-amylase (93 IU/L). These results suggest further preclinical in vivo evaluation of dextrin-rhEGF is warranted to determine whether conjugate pharmacokinetics and rhEGF liberation into such a complex and aggressive environment can still lead to bioactivity.

Hybrid polymer therapeutics incorporating bioresponsive, coiled coil peptide linkers.

This article reports the design, synthesis and results of first in vitro model studies of a conceptually novel class of polymer therapeutics in which the cargo is attached to a polymer backbone via a noncovalent, biologically inspired coiled coil linker, which is formed by heterodimerization of two complementary peptide sequences that are linked to the polymer carrier and the cargo, respectively. In contrast with the polymer-drug conjugates prepared so far, in which the drug is typically attached via an enzymatically or hydrolytically cleavable linker, the noncovalent polymer therapeutics proposed in this article offer several potential advantages, including facile access to combination therapeutics and rapid production of compound libraries to screen for structure-activity relationships. Furthermore, the coiled coil based peptide linkers may not only be useful to bind and release guests but may also play an active role in enhancing and directing intracellular transport and trafficking, which may make these constructs of particular interest for the cytosolic delivery of biomolecular therapeutics.

Phase II studies of polymer-doxorubicin (PK1, FCE28068) in the treatment of breast, lung and colorectal cancer.

Phase I studies of [N-(2-hydroxypropyl)methacrylamide] (HPMA) copolymer-doxorubicin previously showed signs of activity coupled with 5-fold decreased anthracycline toxicity in chemotherapy-refractory patients. Here we report phase II studies using a similar material (FCE28068) in patients with breast (n=17), non-small cell lung (NSCLC, n=29) and colorectal (n=16) cancer. Up to 8 courses of PK1 (280 mg/m(2) doxorubicin-equivalent) were given i.v., together with 123I-labelled imaging analogue. Toxicities were tolerable, with grade 3 neutropenia more prominent in patients with breast cancer (4/17, 23.5% compared with 5/62, 8.1% overall). Of 14 evaluable patients with breast cancer 3 had partial responses (PR), all anthracycline-naïve patients. In 26 evaluable patients with NSCLC, 3 chemotherapy-naïve patients had PR. In contrast, none of the 16 evaluable patients with colorectal cancer responded. Imaging of 16 patients (5 with breast cancer, 6 NSCLC, 5 colorectal cancer) showed obvious tumour accumulation in 2 metastatic breast cancers, although unfortunately no images were obtained from patients who responded. These results show 6/62 PR with limited side effects, supporting the concept that polymer-bound therapeutics can have modified and improved anticancer activities and suggesting the approach should be explored further for breast cancer and NSCLC.

Dextrin-phospholipase A2: synthesis and evaluation as a bioresponsive anticancer conjugate.

There is still an urgent need for improved treatments for metastatic cancer. Although the phospholipase A(2) (PLA(2)) crotoxin, an antitumor protein that appears to act by interaction with epidermal growth factor receptors (EGFR), has recently shown activity in breast cancer in phase I clinical trials, it also displayed nonspecific neurotoxicity. Therefore, the aim of this study was to apply a novel concept called polymer-masked-unmasked-protein therapy (PUMPT) to give a bioresponsive dextrin-PLA(2) conjugate that would reduce PLA(2) systemic toxicity but retain antitumor activity following alpha-amylase triggered degradation of dextrin in the tumor interstitium. Dextrin (M(w) approximately 60000 g/mol; approximately 22 mol % succinoylation) and PLA(2) (from honey bee venom) were chosen as models for these initial studies, and the conjugates synthesized contained 6.1 wt % PLA(2), with <1% free enzyme. The conjugate showed decreased ( approximately 36%) enzyme activity compared to native PLA(2), but activity was restored to approximately 100% following incubation with alpha-amylase. Whereas dextrin conjugation caused a marked reduction in PLA(2)'s hemolytic activity, the conjugate was cytotoxic toward MCF-7, HT29, and B16F10 cells at a level that was comparable to, or greater than, that seen for free PLA(2). In these cell lines, cytotoxicity showed partial correlation with the level of EGFR expression. The reduced toxicity and alpha-amylase triggered activity of the dextrin-PLA(2) conjugate confirmed the potential of this approach for further development as a novel anticancer treatment.

Approaches for quantifying and managing diffuse phosphorus exports at the farm/small catchment scale.

Quantifying and managing diffuse P losses from small catchments or at the farm scale requires detailed knowledge of farming practices and their interaction with catchment processes. However, detailed knowledge may not be available and hence modeling is required. This paper demonstrates two approaches to developing tools that assist P losses from New Zealand or Australian dairy farms. The first is largely empirical and separates sources of P within a paddock into soil, fertilizer, dung, and treading impacts (including damage to grazed pasture). This information is combined with expert knowledge of hydrological processes and potential point sources (e.g., stream crossings) to create a deterministic model that can be used to evaluate the most cost and labor efficient method of mitigating P losses. For instance, in one example, 45% of annual P lost was attributed to the application of superphosphate just before a runoff event for which a mitigation strategy could be to use a less water soluble P fertilizer. The second approach uses a combination of interviews, expert knowledge and relationships to develop a Bayesian Network that describes P exports. The knowledge integration process helped stakeholders develop a comprehensive understanding of the problem. The Network, presented in the form of a "cause and effect", diagram provided a simple, visual representation of current knowledge that could be easily applied to individual circumstances and isolate factors having the greatest influence on P loss. Both approaches demonstrate that modeling P losses and mitigation strategies does not have to cover every process or permutation and that a degree of uncertainty can be handled to create a working model of P losses at a farm or small catchment scale.

Polymer masked-unmasked protein therapy. 1. Bioresponsive dextrin-trypsin and -melanocyte stimulating hormone conjugates designed for alpha-amylase activation.

Polymer-protein conjugation, particularly PEGylation, is well-established as a means of increasing circulation time, reducing antigenicity, and improving the stability of protein therapeutics. However, PEG has limitations including lack of polymer biodegradability, and conjugation can diminish or modify protein activity. The aim of this study was to explore a novel approach for polymer-protein modification called polymer-masking-unmasking-protein therapy (PUMPT), the hypothesis being that conjugation of a biodegradable polymer to a protein would protect it and mask activity in transit, while enabling controlled reinstatement of activity at the target site by triggered degradation of the polymeric component. To test this hypothesis, dextrin (alpha-1,4 polyglucose, a natural polymer degraded by alpha-amylase) was conjugated to trypsin as a model enzyme or to melanocyte stimulating hormone (MSH) as a model receptor-binding ligand. The effect of dextrin molecular weight (7700, and 47200 g/mol) and degree of succinoylation (9-32 mol %) on its ability to mask/unmask trypsin activity was assessed using N-benzoyl-L-arginine-p-nitroanilide (L-BAPNA). Dextrin conjugation reduced enzyme activity by 34-69% depending on the molecular weight and degree of succinoylation of dextrin. However, incubation with alpha-amylase led to reinstatement of activity to a maximum of 92-115%. The highest molecular dextrin (26 mol % succinoylation) gave optimum trypsin masking-unmasking. This intermediate was used to synthesize a dextrin-MSH conjugate (dextrin Mw = 47200 g/mol; MSH content 37 wt %), and its biological activity (+/-alpha-amylase) was assessed by measuring melanin production by murine melanoma (B16F10) cells. Conjugation reduced melanin production to 11%, but addition of alpha-amylase was able to restore activity to 33% of the control value. These were the first studies to confirm the potential of PUMPT for further application to clinically important protein therapeutics. The choice of masking polymer, activation mechanism, and the rate of unmasking can be tailored to therapeutic application.

Effect of PEG molecular weight and linking chemistry on the biological activity and thermal stability of PEGylated trypsin.

PEGylated proteins are routinely used as therapeutics, but systematic studies of the effect of PEG molecular weight and linking chemistry on the biological activity and particularly the thermal stability of the conjugated protein are rarely made. Here, activated monomethoxypolyethylene glycol (mPEG)s (Mw 1100, 2000 and 5000 g/mol) were prepared using succinic anhydride (SA), cyanuric chloride (CC) or tosyl chloride (TC) and used to synthesise a library of trypsin conjugates. The enzyme activity (KM, Vmax and Kcat) of native trypsin and the mPEG-modified trypsin conjugates was compared using N-benzoyl-l-arginine p-nitroanilide (BAPNA) as a substrate, and their thermal stability determined using both BAPNA and N-alpha-benzoyl-l-arginine ethyl ester hydrochloride (BAEE) as substrates to measure amidase and esterase activity respectively. The effect of conjugate chemistry on trypsin autolysis was also examined at 40 degrees C. PEG-trypsin conjugates containing the higher molecular weight of mPEG (5000 g/mol) were more stable than free trypsin, and the conjugate containing CC-mPEG 5000 g/mol had the best thermal stability.

Comparison of the endocytic properties of linear and branched PEIs, and cationic PAMAM dendrimers in B16f10 melanoma cells.

Many different polymers and architectures are now being developed as polymer therapeutics and non-viral vectors for cytosolic delivery, and cationic dendrimers, and linear and branched poly(ethylenimine)s (PEIs) have been widely used. For rational design and safe transfer into the clinic, it is important to better understand the cellular pharmacokinetics of the carrier, even if this will likely change when it is conjugated to, or complexed with, a targeting residue or therapeutic payload. The aim of these studies was to compare binding, endocytic capture and intracellular trafficking of linear and branched PEIs (Mw 25,000 g/mol) and cationic PAMAM dendrimers (generations (gen) 2- 4) using B16F10 murine melanoma cells. FITC-dextran was used as a control for comparison. All polymers were first conjugated to Oregon Green (OG) and carefully characterised in respect of pH- and concentration-dependence of fluorescence. Throughout, non-toxic concentrations of polymer were used. Flow cytometry showed that all the cationic polymers were internalised by "adsorptive" endocytosis, with maximum uptake seen for PAMAM gen 4>>branched PEI>linear PEI>PAMAM gen 3>PAMAM gen 2. The PAMAM gen 4 uptake rate was 130 fold greater than seen for FITC-dextran. Branched PEI had the highest extracellular binding (accounting for >50% of total cell-associated fluorescence) whereas for the linear PEI, binding was only 13% of the cell-associated fluorescence. Unlike FITC-dextran, all cationic polymers lacked significant exocytosis over the time period studied. Whereas PAMAM gen 4 and the branched PEI were predominately internalised by cholesterol-dependent pathways, internalisation of linear PEI appeared to be independent of clathrin and cholesterol. A perception of the rate and mechanisms of cellular uptake of these vectors will be important in the context of their proposed use as drug delivery systems.

Investigating the mechanism of enhanced cytotoxicity of HPMA copolymer-Dox-AGM in breast cancer cells.

Recently we have described an HPMA copolymer conjugate carrying both the aromatase inhibitor aminoglutethimide (AGM) and doxorubicin (Dox) as combination therapy. This showed markedly enhanced in vitro cytotoxicity compared to the HPMA copolymer-Dox (FCE28068), a conjugate that demonstrated activity in chemotherapy refractory breast cancer patients during early clinical trials. To better understand the superior activity of HPMA copolymer-Dox-AGM, here experiments were undertaken using MCF-7 and MCF-7ca (aromatase-transfected) breast cancer cell lines to: further probe the synergistic cytotoxic effects of AGM and Dox in free and conjugated form; to compare the endocytic properties of HPMA copolymer-Dox-AGM and HPMA copolymer-Dox (binding, rate and mechanism of cellular uptake); the rate of drug liberation by lysosomal thiol-dependant proteases (i.e. conjugate activation), and also, using immunocytochemistry, to compare their molecular mechanism of action. It was clearly shown that attachment of both drugs to the same polymer backbone was a requirement for enhanced cytotoxicity. FACS studies indicated both conjugates have a similar pattern of cell binding and endocytic uptake (at least partially via a cholesterol-dependent pathway), however, the pattern of enzyme-mediated drug liberation was distinctly different. Dox release from PK1 was linear with time, whereas the release of both Dox and AGM from HPMA copolymer-Dox-AGM was not, and the initial rate of AGM release was much faster than that seen for the anthracycline. Immunocytochemistry showed that both conjugates decreased the expression of ki67. However, this effect was more marked for HPMA copolymer-Dox-AGM and, moreover, only this conjugate decreased the expression of the anti-apoptotic protein bcl-2. In conclusion, the superior in vitro activity of HPMA copolymer-Dox-AGM cannot be attributed to differences in endocytic uptake, and it seems likely that the synergistic effect of Dox and AGM is due to the kinetics of intracellular drug liberation which leads to enhanced activity.

Establishment of subcellular fractionation techniques to monitor the intracellular fate of polymer therapeutics II. Identification of endosomal and lysosomal compartments in HepG2 cells combining single-step subcellular fractionation with fluorescent imaging.

As they are often designed for lysosomotropic, endosomotropic and/or transcellular delivery, an understanding of intracellular trafficking pathways is essential to enable optimised design of novel polymer therapeutics. Here, we describe a single-step density gradient subcellular fractionation method combined with fluorescent detection analysis that provides a new tool for characterisation of endocytic traffic of polymer therapeutics. Hepatoma (HepG2) cells were used as a model and cell breakage was optimised using a cell cracker to ensure assay of the whole cell population. After removal of unbroken cells and nuclei, the cell lysate as a post-nuclear supernatant (PNS) was layered onto an iodixanol (OptiPrep) density gradient optimised to 5-20%. Early endosomes, late endosomes and lysosomes were identified from gradient fractions by immunoblotting for marker proteins early endosome antigen 1 (EEA 1) and lysosomal associated membrane protein 1 (LAMP 1) using horseradish peroxidase or fluorescently-labelled secondary antibodies. Lysosomes were also detected using N-acetyl-beta-glucosamindase (Hex A) activity. In addition, cells were incubated with Texas-red labelled transferrin (TxR-Tf) for 5 min to specifically label early endosomes and this was directly detected from SDS-PAGE gels. Internalised macromolecules and colloidal particles can potentially alter vesicle buoyant density. To see if typical macromolecules of interest would alter vesicle density or perturb vesicle traffic, HepG2 cells were incubated with dextran or a polyethyleneglycol (PEG)-polyester dendron G4 (1 mg/ml for 24 h). The PEG-polyester dendron G4 caused a slight redistribution of endocytic structures to lower density fractions but immunofluorescence microscopy showed no obvious dendron effects. In conclusion, the combined subcellular fractionation with fluorescent imaging approach described here can be used as a tool for both fundamental cell biology research and/or the quantitative localisation of polymer therapeutics in the endocytic pathway.

Polyvalent dendrimer glucosamine conjugates prevent scar tissue formation.

Dendrimers are hyperbranched macromolecules that can be chemically synthesized to have precise structural characteristics. We used anionic, polyamidoamine, generation 3.5 dendrimers to make novel water-soluble conjugates of D(+)-glucosamine and D(+)-glucosamine 6-sulfate with immuno-modulatory and antiangiogenic properties respectively. Dendrimer glucosamine inhibited Toll-like receptor 4-mediated lipopolysaccharide induced synthesis of pro-inflammatory chemokines (MIP-1 alpha, MIP-1 beta, IL-8) and cytokines (TNF-alpha, IL-1 beta, IL-6) from human dendritic cells and macrophages but allowed upregulation of the costimulatory molecules CD25, CD80, CD83 and CD86. Dendrimer glucosamine 6-sulfate blocked fibroblast growth factor-2 mediated endothelial cell proliferation and neoangiogenesis in human Matrigel and placental angiogenesis assays. When dendrimer glucosamine and dendrimer glucosamine 6-sulfate were used together in a validated and clinically relevant rabbit model of scar tissue formation after glaucoma filtration surgery, they increased the long-term success of the surgery from 30% to 80% (P = 0.029). We conclude that synthetically engineered macromolecules such as the dendrimers described here can be tailored to have defined immuno-modulatory and antiangiogenic properties, and they can be used synergistically to prevent scar tissue formation.

The dawning era of polymer therapeutics.

As we enter the twenty-first century, research at the interface of polymer chemistry and the biomedical sciences has given rise to the first nano-sized (5-100 nm) polymer-based pharmaceuticals, the 'polymer therapeutics'. Polymer therapeutics include rationally designed macromolecular drugs, polymer-drug and polymer-protein conjugates, polymeric micelles containing covalently bound drug, and polyplexes for DNA delivery. The successful clinical application of polymer-protein conjugates, and promising clinical results arising from trials with polymer-anticancer-drug conjugates, bode well for the future design and development of the ever more sophisticated bio-nanotechnologies that are needed to realize the full potential of the post-genomic age.

Polymer therapeutics at a crossroads? Finding the path for improved translation in the twenty-first century.

Despite the relatively small early investment, first generation 'polymer therapeutics' have been remarkably successful with more than 25 products licenced for human use as polymeric drugs, sequestrants, conjugates, and as an imaging agent. Many exhibit both clinical and commercial success with new concepts already in clinical trials. Nevertheless after four decades of evolution, this field is arriving at an important crossroads. Over the last decade, the landscape has changed rapidly. There are an increasing number of failed clinical trials, the number of 'copy' and 'generic' products is growing (danger of ignoring the biological rationale for design and suppression of innovation), potential drawbacks of PEG are becoming more evident, and the 'nanomedicine' boom has brought danger of loss of scientific focus/hype. Grasping opportunities provided by advances in understanding of the patho-physiology and molecular basis of diseases, new polymer/conjugate synthetic and analytical methods, as well as the large database of clinical experience will surely ensure a successful future for innovative polymer therapeutics. Progress will, however, be in jeopardy if polymer safety is overlooked in respect of the specific route of administration/clinical use, poorly characterised materials/formulations are used to define biological or early clinical properties, and if clinical trial protocols fail to select patients most likely to benefit from these macromolecular therapeutics. Opportunities to improve clinical trial design for polymer-anticancer drug conjugates are discussed. This short personal perspective summarises some of the important challenges facing polymer therapeutics in R&D today, and future opportunities to improve successful translation.