Polymer conjugates as therapeutics: future trends, challenges and opportunities

A Facile and Green Approach for the Preparation of Amine-Functionalized Poly(ethylene glycol) by Reducing Poly(ethylene glycol) Azide with Dithiothreitol

A facile and green approach for the preparation of PEGn-NH2s from PEGn-N3s in water with DTT as the reduction reagent has been developed, avoiding the introduction of metal ions and difficulties in purification compared to the traditional synthesis process of PEGn-NH2s. A series of high-purity linear and multiarm PEGn-NH2s with different molecular weights were synthesized, demonstrating the versatility of this method. Additionally, HS-PEG45-NH2 with high fidelity of thiol and amine was easily prepared through the one-step two functional group conversion of N3-PEG45-S-S-PEG45-N3, and the PEG-based NH2-PEG@AuNPs were also prepared. This technology will promote the application of PEGn-NH2s in the fields of medicine and biomaterials.

Jellyfish-inspired smart tetraphenylethene lipids with unique AIE fluorescence, thermal response, and cell membrane interaction

Smart lipids with fluorescence emission, thermal response, and polyethylene glycolation (PEGylation) functions can be highly valuable for formulation, image-traceable delivery, and targeted release of payloads. Herein, a series of jellyfish-shaped amphiphiles with a tetraphenylethene (TPE) core and four symmetrical amphiphilic side chains were conveniently synthesized and systematically investigated as smart lipids. Compared with regular amphiphilic TPE lipids and phospholipids, the unprecedented jellyfish-shaped molecular geometry was found to enable a series of valuable capabilities, including sensitive and responsive aggregation-induced emission of fluorescence (AIE FL) and real-time FL monitoring of drug uptake. Furthermore, the jellyfish-shaped geometry facilitated the concentration-dependent aggregation from unimolecular micelles at low concentrations to "side-by-side" spherical aggregates at high concentrations and a unique mode of AIE. In addition, the size and the arrangement of the amphiphilic side chains were found to dominate the aggregate stability, cell uptake, and thus the cytotoxicity of the amphiphiles. This study has unprecedentedly developed versatile smart TPE lipids with precise structures, and unique physicochemical and biological properties while the peculiar structure-property relationship may shed new light on the design and application of AIE fluorophores and functional lipids in biomedicine and materials science.

Separation of Molar Weight-Distributed Polyethylene Glycols by Reversed-Phase Chromatography—Analysis and Modeling Based on Isocratic Analytical-Scale Investigations

The separation of polyethylene glycols (PEGs) into single homologs by reversed-phase chromatography is investigated experimentally and theoretically. The used core–shell column is shown to achieve the baseline separation of PEG homologs up to molar weights of at least 5000 g/mol. A detailed study is performed elucidating the role of the operating conditions, including the temperature, eluent composition, and degree of polymerization of the polymer. Applying Martin’s rule yields a simple model for retention times that holds for a wide range of conditions. In combination with relations for column efficiency, the role of the operating conditions is discussed, and separations are predicted for analytical-scale chromatography. Finally, the approach is included in an efficient process model based on discrete convolution, which is demonstrated to predict with high accuracy also advanced operating modes with arbitrary injection profiles.

Monodisperse and Polydisperse PEGylation of Peptides and Proteins: A Comparative Study

Although PEGylation is widely used in biomedicine with great success, it suffers from many drawbacks, such as polydispersity, nonbiodegradability, and loss of precursor potency. Recently, the search for polyethylene glycol (PEG) substitutes has attracted considerable attention. Some of the substitutes partially address the drawbacks of PEGs, but sacrifice the "stealth" effect of PEGs and bring in new issues. Herein, we developed monodisperse oligoethylene glycol (M-OEG) polyamides over 5000 Da as biodegradable and monodisperse PEGylation (M-PEGylation) agents, which provided M-PEGylated peptides and proteins with high monodispersity and a biodegradable PEG moiety. Compared to regular PEGylated proteins with a complex "stealth" cloud of PEG, the hydrogen bond interactions between the M-OEG polyamides and proteins provided the M-PEGylated protein with a biodegradable "stealth" cloak. The monodisperse and biodegradable M-PEGylation strategy as well as the peculiar protein-M-OEG polyamide interactions may shed light on many long-lasting issues during the development of PEGylated biologic drugs, such as monodispersity, biodegradability, and tunable conformation.

Peptidic Monodisperse PEG "Comb" as Multifunctional "Add-On" Module for Imaging-Traceable and Thermo-Responsive Theranostics

Monodisperse polyethylene glycols-modified (M-PEGylated) biomaterials exhibit high structural accuracy, biocompatibility, and fine-tunable physicochemical properties. To develop "smart" drug delivery systems in a controllable and convenient manner, a peptidic M-PEG "comb" with fluorinated L-lysine side chains and a fluorescent N-terminal is conveniently prepared as a ¹⁹ F magnetic resonance imaging (¹⁹ F MRI) and fluorescence dual-imaging traceable and thermo-responsive "add-on" module for liposomal theranostics in cancer therapy. The peptidic M-PEG "comb" has high biocompatibility, thermo-responsivity with a sharp lower critical solution temperature, an aggregation-induced emission fluorescence, and high ¹⁹ F MRI sensitivity. As a highly branched amphiphile, it self-assembles and firmly anchors on the doxorubicin-loaded liposomal nanoparticles, which M-PEGylates the liposomes and facilitates the thermo-responsive drug release and drug tracking with dual-imaging technologies. In a rodent xenograft model of human liver cancer HepG2 cells, the M-PEGylated liposomes exhibit long in vivo half time, low toxicity, high tumor accumulation, "hot spot" ¹⁹ F MRI, and therapeutic efficacy. With accurately programmable chemical structure, fine-tunable physicochemical and biological properties to meet the demands of diagnosis, drug delivery, and therapy, the M-PEG "comb" is promising as a versatile "add-on" module for rapid and convenient formulation of various "smart" theranostics.

Monodisperse polyethylene glycol "brushes" with enhanced lipophilicity, and thermo and plasma stability

A convenient strategy was developed for highly branched and multifunctionalized peptidic monodisperse polyethylene glycol "brushes", which exhibit remarkable physicochemical and biological properties and potential as versatile biomaterials.

Monodisperse oligoethylene glycols modified Camptothecin, 10-Hydroxycamptothecin and SN38 prodrugs

Camptothecin, which represents a class of natural products with high anticancer activity, suffers low water solubility which hampers its clinic application. To address this issue, monodisperse polyethylene glycols were employed to modify this class of natural products, including Camptothecin, 10-Hydroxycamptothecin, and SN38. Through selective modification with a series of monodisperse polyethylene glycols, 31 Camptothecin derivatives, including 9 ethers and 22 carbonates, were prepared using a macrocyclic sulfate-based strategy with high efficacy. Monodisperse polyethylene glycols modification provided the Camptothecin derivatives with high purity and fine-tunable water solubility. Through the physicochemical and biological assays, a few novel prodrugs with good solubility, cytotoxicity, and valuable drug release profile were identified as promising anticancer drug candidates.

One-pot synthesis of monodisperse dual-functionalized polyethylene glycols through macrocyclic sulfates

Dual-functionalization of monodisperse oligoethylene glycols, especially hetero-functionalization, provides a series of highly valuable intermediates for life and materials sciences. However, the existing methods for the preparation of these compounds suffer excessive protecting and activating group manipulation as well as tedious purification. Here, a one-pot dual-substitution strategy with macrocyclic sulfates of polyethylene glycols as the key intermediates was developed for the convenient and scalable preparation of a series of homo-functionalized and hetero-functionalized oligoethylene glycols in just 1 step. A high synthetic efficacy was achieved by avoiding the protecting and activating group manipulation and the intermediate purification.

Metabolomics facilitates the discrimination of the specific anti-cancer effects of free- and polymer-conjugated doxorubicin in breast cancer models

Metabolomics is becoming a relevant tool for understanding the molecular mechanisms involved in the response to new drug delivery systems. The applicability of this experimental approach to cell cultures and animal models makes metabolomics a useful tool for establishing direct connections between in vitro and in vivo data, thus providing a reliable platform for the characterization of chemotherapeutic agents. Herein, we used metabolomic profiles based on nuclear magnetic resonance (NMR) spectroscopy to evaluate the biochemical pathways involved in the response to a chemotherapeutic anthracycline drug (Doxorubicin, Dox) and an N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-conjugated form (HPMA-Dox) in an in vitro cell culture model and an in vivo orthotopic breast cancer model. We also used protein expression and flow cytometry studies to obtain a better coverage of the biochemical alterations associated with the administration of these compounds. The overall analysis revealed that polymer conjugation leads to increased apoptosis, reduced glycolysis, and reduced levels of phospholipids when compared to the free chemotherapeutic drug. Our results represent a first step in the application of integrated in vitro and in vivo metabolomic studies to the evaluation of drug delivery systems.

Polymer Therapeutics: Biomarkers and New Approaches for Personalized Cancer Treatment

Polymer therapeutics (PTs) provides a potentially exciting approach for the treatment of many diseases by enhancing aqueous solubility and altering drug pharmacokinetics at both the whole organism and subcellular level leading to improved therapeutic outcomes. However, the failure of many polymer-drug conjugates in clinical trials suggests that we may need to stratify patients in order to match each patient to the right PT. In this concise review, we hope to assess potential PT-specific biomarkers for cancer treatment, with a focus on new studies, detection methods, new models and the opportunities this knowledge will bring for the development of novel PT-based anti-cancer strategies. We discuss the various "hurdles" that a given PT faces on its passage from the syringe to the tumor (and beyond), including the passage through the bloodstream, tumor targeting, tumor uptake and the intracellular release of the active agent. However, we also discuss other relevant concepts and new considerations in the field, which we hope will provide new insight into the possible applications of PT-related biomarkers.

Solid Phase Stepwise Synthesis of Polyethylene Glycols

Polyethylene glycol (PEG) and derivatives with eight and twelve ethylene glycol units were synthesized by stepwise addition of tetraethylene glycol monomers on a polystyrene solid support. The monomer contains a tosyl group at one end and a dimethoxytrityl group at the other. The Wang resin, which contains the 4-benzyloxy benzyl alcohol function, was used as the support. The synthetic cycle consists of deprotonation, Williamson ether formation (coupling), and detritylation. Cleavage of PEGs from solid support was achieved with trifluoroacetic acid. The synthesis including monomer synthesis was entirely chromatography-free. PEG products including those with different functionalities at the two termini were obtained in high yields. The products were analyzed with ESI and MALDI-TOF MS and were found close to monodispersity.

Cancer Nanotechnology: Opportunities for Prevention, Diagnosis, and Therapy

Nanotechnological innovations over the last 16 years have brought about the potential to revolutionize specific therapeutic drug delivery to cancer tissue without affecting normal tissues. In addition, there are new nanotechnology-based platforms for diagnosis of cancers and for theranostics, i.e., integrating diagnosis with therapy and follow-up of effectiveness of therapy. This chapter presents an overview of these nanotechnology-based advancements in the areas of prevention, diagnosis, therapy, and theranostics for cancer. In addition, we stress the need to educate bio- and medical students in the field of nanotechnology.

Influence of Block versus Random Monomer Distribution on the Cellular Uptake of Hydrophilic Copolymers

The use of polymers has revolutionized the field of drug delivery in the past two decades. Properties such as polymer size, charge, hydrophilicity, or branching have all been shown to play an important role in the cellular internalization of polymeric systems. In contrast, the fundamental impact of monomer distribution on the resulting biological properties of copolymers remains poorly studied and is always only investigated for biologically active self-assembling polymeric systems. Here, we explore the fundamental influence of monomer distribution on the cellular uptake of nonaggregating and biologically passive copolymers. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was used to prepare precisely defined copolymers of three hydrophilic acrylamide monomers. The cellular internalization of block copolymers was compared with the uptake of a random copolymer where monomers are statistically distributed along the chain. The results demonstrate that monomer distribution in itself has a negligible impact on copolymer uptake.

Amide bond-containing monodisperse polyethylene glycols beyond 10 000 Da

Monodisperse polyethylene glycols above 4000 Da, including the longest one to date (10 262 Da), can be prepared from oligoethylene glycol-containing ω-amino acids through solid phase synthesis.

Enabling cytoplasmic delivery and organelle targeting by surface modification of nanocarriers

Nanocarriers are designed to specifically accumulate in diseased tissues. In this context, targeting of intracellular compartments was shown to enhance the efficacy of many drugs and to offer new and more effective therapeutic approaches. This is especially true for therapies based on biologicals that must be encapsulated to favor cell internalization, and to avoid intracellular endosomal sequestration and degradation of the payload. In this review, we discuss specific surface modifications designed to achieve cell cytoplasm delivery and to improve targeting of major organelles; we also discuss the therapeutic applications of these approaches. Last, we describe some integrated strategies designed to sequentially overcome the biological barriers that separate the site of administration from the cell cytoplasm, which is the drug's site of action.

In vivo evaluation of a mucoadhesive polymeric caplet for intravaginal anti-HIV-1 delivery and development of a molecular mechanistic model for thermochemical characterization

CONTEXT AND OBJECTIVE

The aim of this study was to develop, characterize and evaluate a mucoadhesive caplet resulting from a polymeric blend (polymeric caplet) for intravaginal anti-HIV-1 delivery.

MATERIALS AND METHODS

Poly(lactic-co-glycolic) acid, ethylcellulose, poly(vinylalcohol), polyacrylic acid and modified polyamide 6, 10 polymers were blended and compressed to a caplet-shaped device, with and without two model drugs 3'-azido-3'-deoxythymidine (AZT) and polystyrene sulfonate (PSS). Thermal analysis, infrared spectroscopy and microscopic analysis were carried out on the caplets employing temperature-modulated DSC (TMDSC), Fourier transform infra-red (FTIR) spectrometer and scanning electron microscope, respectively. In vitro and in vivo drug release analyses as well as the histopathological toxicity studies were carried out on the drug-loaded caplets. Furthermore, molecular mechanics (MM) simulations were carried out on the drug-loaded caplets to corroborate the experimental findings.

RESULTS AND DISCUSSION

There was a big deviation between the Tg of the polymeric caplet from the Tg's of the constituent polymers indicating a strong interaction between constituent polymers. FTIR spectroscopy confirmed the presence of specific ionic and non-ionic interactions within the caplet. A controlled near zero-order drug release was obtained for AZT (20 d) and PSS (28 d). In vivo results, i.e. the drug concentration in plasma ranged between 0.012-0.332 mg/mL and 0.009-0.256 mg/mL for AZT and PSS over 1-28 d.

CONCLUSION

The obtained results, which were corroborated by MM simulations, attested that the developed system has the potential for effective delivery of anti-HIV-agents.

Chemotherapy-Induced Cardiotoxicity: Pathophysiology and Prevention

Along with the remarkable progress registered in oncological treatment that led to increased survival of cancer patients, treatment-related comorbidities have also become an issue for these long-term survivors. Of particular interest is the development of cardiotoxic events, which, even when asymptomatic, not only have a negative impact on the patient`s cardiac prognosis, but also considerably restrict therapeutic opportunities. The pathophysiology of cytostatic-induced cardiotoxicity implies a series of complex and intricate mechanisms, whose understanding enables the development of preventive and therapeutic strategies. Securing cardiac function is an ongoing challenge for the pharmaceutical industry and the physicians who have to deal currently with these adverse reactions. This review focuses on the main mechanism of cardiac toxicity induced by anticancer drugs and especially on the current strategies applied for preventing and minimizing the cardiac side effects.

Polymeric micelles for pH-responsive delivery of cisplatin

Methoxy poly(ethylene oxide)-block-poly-(α-carboxylate-ε-caprolactone) (PEO-b-PCCL) was used to develop pH-responsive polymeric micelles for the delivery of cisplatin (CDDP). Micelles were prepared through complexation of CDDP with the pendant carboxyl groups on the poly(ε-caprolactone) core, perhaps through coordinate bonding. The obtained micelles were characterized using dynamic light scattering (DLS) measurement for size and stability. The in vitro release of CDDP at different pHs (7.4, 6.0 and 5.0) was evaluated. The in vitro cell uptake as well as cytotoxicity of developed micelles against two breast cancer cell lines, i.e. MDA-MB-435 and MDA-MB-231, were also assessed and compared to free CDDP as control. DLS results showed PEO-b-PCCL to form stable micelles with an average diameter of <50 nm upon complexation with CDDP. Developed polymeric micelles were capable of slowly releasing CDDP in physiological pH. However, CDDP release from polymeric micelles was triggered upon exposure to electrolytes and/or acidic pHs mimicking that of extracellular tumor microenvironment or intracellular organelles. Consistent with the slow release of CDDP from its polymeric micellar formulation, polymeric micellar CDDP exhibited lower cytotoxicity and CDDP intracellular uptake compared to free drug. The results indicate a great potential for the developed formulation in platinum therapy of breast cancer.

CD44-tropic polymeric nanocarrier for breast cancer targeted rapamycin chemotherapy

In contrast with the conventional targeting of nanoparticles to cancer cells with antibody or peptide conjugates, a hyaluronic acid (HA) matrix nanoparticle with intrinsic-CD44-tropism was developed to deliver rapamycin for localized CD44-positive breast cancer treatment. Rapamycin was chemically conjugated to the particle surface via a novel sustained-release linker, 3-amino-4-methoxy-benzoic acid. The release of the drug from the HA nanoparticle was improved by 42-fold compared to HA-temsirolimus in buffered saline. In CD44-positive MDA-MB-468 cells, using HA as drug delivery carrier, the cell viability was significantly decreased compared to free rapamycin and CD44-blocked controls. Rat pharmacokinetics showed that the area under the curve of HA nanoparticle formulation was 2.96-fold greater than that of the free drug, and the concomitant total body clearance was 8.82-fold slower. Moreover, in immunocompetent BALB/c mice bearing CD44-positive 4T1.2neu breast cancer, the rapamycin-loaded HA particles significantly improved animal survival, suppressed tumor growth and reduced the prevalence of lung metastasis.

FROM THE CLINICAL EDITOR

This study demonstrates increased efficiency of rapamycin delivery and consequential treatment effects in a breast cancer model by hyaluronic acid - L-rapamycin conjugates with intrinsic tropism for CD44-positive cells.

Cathepsin B-cleavable doxorubicin prodrugs for targeted cancer therapy (Review)

Doxorubicin (DOX) is one of the most effective cytotoxic anticancer drugs used for the treatment of hematological malignancies, as well as a broad range of solid tumors. However, the clinical applications of this drug have long been limited due to its severe dose-dependent toxicities. Therefore, DOX derivatives and analogs have been developed to address this issue. A type of DOX prodrug, cleaved by cathepsin B (Cat B), which is highly upregulated in malignant tumors and premalignant lesions, has been developed to achieve a higher DOX concentration in tumor tissue and a lower concentration in normal tissue, so as to enhance the efficacy and reduce toxicity to normal cells. In this review, we focused on Cat B-cleavable DOX prodrugs and discussed the efficacy of these prodrugs, demonstrated by preclinical and clinical developments.

Multifunctional dendritic polymers in nanomedicine: opportunities and challenges

Nanotechnology has resulted in materials that have greatly improved the effectiveness of drug delivery because of their ability to control matter on the nanoscale. Advanced forms of nanomedicine have been synthesized for better pharmacokinetics to obtain higher efficacy, less systemic toxicity, and better targeting. These criteria have long been the goal in nanomedicine, in particular, for systemic applications in oncological disorders. Now, the "holy grail" in nanomedicine is to design and synthesize new advanced macromolecular nanocarriers and to translate them from lab to clinic. This review describes the current and future perspectives of nanomedicine with particular emphasis on the clinical targets in cancer and inflammation. The advanced forms of liposomes and polyethylene glycol (PEG) based nanocarriers, as well as dendritic polymer conjugates will be discussed with particular attention paid to designs, synthetic strategies, and chemical pathways. In this critical review, we also report on the current status and perspective of dendritic polymer nanoconjugate platforms (e.g. polyamidoamine dendrimers and dendritic polyglycerols) for cellular localization and targeting of specific tissues (192 references).

Nanomaterials: applications in cancer imaging and therapy

The application of nanomaterials (NMs) in biomedicine is increasing rapidly and offers excellent prospects for the development of new non-invasive strategies for the diagnosis and treatment of cancer. In this review, we provide a brief description of cancer pathology and the characteristics that are important for tumor-targeted NM design, followed by an overview of the different types of NMs explored to date, covering synthetic aspects and approaches explored for their application in unimodal and multimodal imaging, diagnosis and therapy. Significant synthetic advances now allow for the preparation of NMs with highly controlled geometry, surface charge, physicochemical properties, and the decoration of their surfaces with polymers and bioactive molecules in order to improve biocompatibility and to achieve active targeting. This is stimulating the development of a diverse range of nanometer-sized objects that can recognize cancer tissue, enabling visualization of tumors, delivery of anti-cancer drugs and/or the destruction of tumors by different therapeutic techniques.

Bifunctional conjugates comprising β-cyclodextrin, polyethylenimine, and 5-fluoro-2'- deoxyuridine for drug delivery and gene transfer

Earlier reports indicated that the conjugates (PEI(600)-CD, PC) of β-cyclodextrin and low-molecular-weight polyethylenimine (PEI, M(w) 600) can be used as efficient gene carriers in glioma cancer therapy. Incorporating anticancer drugs onto PC conjugates may endow them with new and interesting properties for great applications. In this work, FU-PEI(600)-CD (FPC) conjugates comprising PC and 5-fluoro-2'-deoxyuridine (FdUrd) were prepared as new bifunctional anticancer prodrugs with improved therapeutic effects, as well as good gene transfer efficiency. In comparison with free FdUrd, FPC could inhibit proliferation and enhance cytotoxicity on glioma cells. The results of hematoxylin and eosin (HE) staining indicated that C6 cells treated with FPC shrunk more seriously. Unlike FdUrd, cell cycle analysis indicated that C6 cells were primarily arrested in the G1 phase in the presence of FPC. Cellular uptake of FPC in C6 cells was about 10 times higher than that of FdUrd. In addition, the in vitro and in vivo gene transfection indicated that FPC still exhibited good gene expression efficiency. With the ability to deliver drugs and transfer genes, such bifunctional FPC conjugates may have great potential applications in combination therapy of cancers.

Polymer–drug conjugates for novel molecular targets

Polymer therapeutics can be already considered as a promising field in the human healthcare context. The discovery of the enhanced permeability and retention effect by Maeda, together with the modular model for the polymer–drug conjugate proposed by Ringsdorf, directed the early steps of polymer therapeutics towards cancer therapy. Orthodox anticancer drugs were preferentially chosen in the development of the first conjugates. The fast evolution of polymer chemistry and bioconjugation techniques, and a deeper understanding of cell biology has opened up exciting new challenges and opportunities. Four main directions have to be considered to develop this ‘platform technology’ further: the control of the synthetic process, the exhaustive characterization of the conjugate architectures, the conquest of combination therapy and the disclosure of new therapeutic targets. We illustrate in this article the exciting approaches offered by polymer–drug conjugates beyond classical cancer therapy, focusing on new, more effective and selective targets in cancer and in their use as treatments for other major human diseases.

Structural characterization of photopolymerizable binary liposomes containing diacetylenic and saturated phospholipids

The use of liposomes to encapsulate materials has received widespread attention for drug delivery, transfection, diagnostic reagent, and as immunoadjuvants. Phospholipid polymers form a new class of biomaterials with many potential applications in medicine and research. Of interest are polymeric phospholipids containing a diacetylene moiety along their acyl chain since these kinds of lipids can be polymerized by Ultra-Violet (UV) irradiation to form chains of covalently linked lipids in the bilayer. In particular the diacetylenic phosphatidylcholine 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) can form intermolecular cross-linking through the diacetylenic group to produce a conjugated polymer within the hydrocarbon region of the bilayer. As knowledge of liposome structures is certainly fundamental for system design improvement for new and better applications, this work focuses on the structural properties of polymerized DC8,9PC:1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes. Liposomes containing mixtures of DC8,9PC and DMPC, at different molar ratios, and exposed to different polymerization cycles, were studied through the analysis of the electron spin resonance (ESR) spectra of a spin label incorporated into the bilayer, and the calorimetric data obtained from differential scanning calorimetry (DSC) studies. Upon irradiation, if all lipids had been polymerized, no gel-fluid transition would be expected. However, even samples that went through 20 cycles of UV irradiation presented a DSC band, showing that around 80% of the DC8,9PC molecules were not polymerized. Both DSC and ESR indicated that the two different lipids scarcely mix at low temperatures, however few molecules of DMPC are present in DC8,9PC rich domains and vice versa. UV irradiation was found to affect the gel-fluid transition of both DMPC and DC8,9PC rich regions, indicating the presence of polymeric units of DC8,9PC in both areas. A model explaining lipids rearrangement is proposed for this partially polymerized system.

Molecules that modulate Apaf-1 activity

Programmed cell death, apoptosis, is a highly regulated cellular pathway, responsible for the elimination of cells in the organism that are no longer needed or extensively damaged. Defects in the regulation of apoptosis could be at the molecular basis of different diseases, either when it is insufficient or excessive. The formation of the macromolecular complex, apoptosome, is a key event in this pathway, which has also been defined as the intrinsic apoptosis pathway. The apoptosome is a holoenzyme multiprotein complex formed by cytochrome c-activated apoptotic protease-activating factor (Apaf-1), dATP, and procaspase-9. Recent studies have produced a wealth of information about the regulation and functions of Apaf-1, but additional studies aimed at elucidating its role as a signaling device at the crosstalk between different signaling pathways are needed to take advantage for the development of modulators of apoptosis pathways and possible therapeutic applications.

Polymers for drug delivery systems

Polymers have played an integral role in the advancement of drug delivery technology by providing controlled release of therapeutic agents in constant doses over long periods, cyclic dosage, and tunable release of both hydrophilic and hydrophobic drugs. From early beginnings using off-the-shelf materials, the field has grown tremendously, driven in part by the innovations of chemical engineers. Modern advances in drug delivery are now predicated upon the rational design of polymers tailored for specific cargo and engineered to exert distinct biological functions. In this review, we highlight the fundamental drug delivery systems and their mathematical foundations and discuss the physiological barriers to drug delivery. We review the origins and applications of stimuli-responsive polymer systems and polymer therapeutics such as polymer-protein and polymer-drug conjugates. The latest developments in polymers capable of molecular recognition or directing intracellular delivery are surveyed to illustrate areas of research advancing the frontiers of drug delivery.