HPMA based macromolecular therapeutics: Internalization, intracellular pathway and cell death depend on the character of covalent bond between the drug and the peptidic spacer and also on spacer composition

Dye labeling for optical imaging biases drug carriers' biodistribution and tumor uptake

Biodistribution analyses of nanocarriers are often performed with optical imaging. Though dye tags can interact with transporters, e.g., organic anion transporting polypeptides (OATPs), their influence on biodistribution was hardly studied. Therefore, this study compared tumor cell uptake and biodistribution (in A431 tumor-bearing mice) of four near-infrared fluorescent dyes (AF750, IRDye750, Cy7, DY-750) and dye-labeled poly(N-(2-hydroxypropyl)methacrylamide)-based nanocarriers (dye-pHPMAs). Tumor cell uptake of hydrophobic dyes (Cy7, DY-750) was higher than that of hydrophilic dyes (AF750, IRDye750), and was actively mediated but not related to OATPs. Free dyes' elimination depended on their hydrophobicity, and tumor uptake correlated with blood circulation times. Dye-pHPMAs circulated longer and accumulated stronger in tumors than free dyes. Dye labeling significantly influenced nanocarriers' tumor accumulation and biodistribution. Therefore, low-interference dyes and further exploration of dye tags are required to achieve the most unbiased results possible. In our assessment, AF750 and IRDye750 best qualified for labeling hydrophilic nanocarriers.

Poly(styrene-co-maleic Acid) Micelle of Photosensitizers for Targeted Photodynamic Therapy, Exhibits Prolonged Singlet Oxygen Generating Capacity and Superior Intracellular Uptake

Targeted therapy by using nanomedicines based on the enhanced permeability and retention (EPR) effect is becoming a promising anticancer strategy. Many nano-designed photosensitizers (PSs) for photodynamic therapy (PDT) have been developed which show superior therapeutic potentials than free PS. To further understand the advantages of nano-designed PS, in this study, we used styrene-co-maleyl telomer (SMA) as a polymer platform to prepare a micellar type of PS with two well-characterized PSs—rose bengal (RB) and methylene blue (MB)—and evaluated the outmatching benefits of SMA-PS micelles, especially focusing on the singlet oxygen (¹O₂) generation capacity and intracellular uptake profiles. In aqueous solutions, SMA-PS self-assembles to form micelles by non-covalent interactions between PS and SMA. SMA-PS micelles showed discrete distributions by dynamic light scattering having a mean particle size of 18–30 nm depending on the types of SMA and different PSs. The hydrodynamic size of SMA-PS was evaluated by Sephadex chromatography and it found to be 30–50 kDa. In the presence of human serum albumin, the sizes of SMA-PS remarkably increased, suggesting the albumin-binding property. ¹O₂ generation from the SMA-PS micelle was determined by electron spin resonance, in which the SMA-PS micelle showed comparatively more photo-stable, and consequently a more durable and constant, ¹O₂ generation capability than free PS. Moreover, intracellular uptake of SMA-PS micelles was extensively faster and higher than free PS, especially in tumor cells. Taken together, SMA-PS micelles appear highly advantageous for photodynamic therapy in addition to its capacity in utilizing the EPR effect for tumor targeted delivery.

HPMA-based polymeric conjugates in anticancer therapeutics

Polymer therapeutics has gained prominence due to an attractive structural polymer chemistry and its applications in diseases therapy. In this review, we discussed the development and capabilities of N-(2-hydroxypropyl) methacrylamide (HPMA) and HPMA-drug conjugates in cancer therapy. The design, architecture, and structural properties of HPMA make it a versatile system for the synthesis of polymeric conjugations for biomedical applications. Research suggests that HPMA could be a possible alternative for polymers such polyethylene glycol (PEG) in biomedical applications. Although numerous clinical trials of HPMA-drug conjugates are ongoing, yet no product has been successfully brought to the market. Thus, further research is required to develop HPMA-drug conjugates as successful cancer therapeutics.

Intracellular trafficking and cytotoxicity of a gelatine-doxorubicin conjugate in two breast cancer cell lines

Details of intracellular pathways of cytotoxicity remain unclear for doxorubicin conjugates being studied to treat breast cancer tumours. A high molecular weight gelatine-doxorubicin conjugate was investigated with an emphasis on lysosome participation. The conjugate was synthesised and characterised. Cell uptake and cellular localisation in MCF-7 and triple negative breast cancer (TNBC) MDA-MB-231 cells were determined with fluorescence microscopy. Nuclear content of released DOX was determined by UHPLC. Cytotoxicity was determined by the MTT assay. Lysosome membrane permeabilization (LMP) was followed by lysosomal release of fluorescently labelled dextran. After incubation at an equivalent 10 µM DOX, conjugate lysosome accumulation was substantial in both cell lines by 24 h, at which time the conjugate cytotoxic effect was first observed. By 48 h, the conjugate was nearly fourfold more toxic in TNBC than in MCF-7 cells. The MCF-7 nucleus drug content from conjugate released DOX was small but confirmed intra-lysosomal drug release. The conjugate induced LMP in 100% of TNBC cells but LMP was virtually absent in MCF-7 cells. These results suggest that the conjugate induces cytotoxicity by a lysosomal pathway in MDA-MB-231 cells and has potential for treatment of TNBC tumours. Support: NIH/NCI R15CA135421, the Agnes Varis Trust for Women's Health.

Fluorescence Imaging as a Tool in Preclinical Evaluation of Polymer-Based Nano-DDS Systems Intended for Cancer Treatment

Targeted drug delivery using nano-sized carrier systems with targeting functions to malignant and inflammatory tissue and tailored controlled drug release inside targeted tissues or cells has been and is still intensively studied. A detailed understanding of the correlation between the pharmacokinetic properties and structure of the nano-sized carrier is crucial for the successful transition of targeted drug delivery nanomedicines into clinical practice. In preclinical research in particular, fluorescence imaging has become one of the most commonly used powerful imaging tools. Increasing numbers of suitable fluorescent dyes that are excitable in the visible to near-infrared (NIR) wavelengths of the spectrum and the non-invasive nature of the method have significantly expanded the applicability of fluorescence imaging. This chapter summarizes non-invasive fluorescence-based imaging methods and discusses their potential advantages and limitations in the field of drug delivery, especially in anticancer therapy. This chapter focuses on fluorescent imaging from the cellular level up to the highly sophisticated three-dimensional imaging modality at a systemic level. Moreover, we describe the possibility for simultaneous treatment and imaging using fluorescence theranostics and the combination of different imaging techniques, e.g., fluorescence imaging with computed tomography.

HPMA Copolymer-Drug Conjugates with Controlled Tumor-Specific Drug Release

Over the past few decades, numerous polymer drug carrier systems are designed and synthesized, and their properties are evaluated. Many of these systems are based on water-soluble polymer carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, or multidrug resistance inhibitors, all covalently bound to a carrier by a biodegradable spacer that enables controlled release of the active molecule to achieve the desired pharmacological effect. Among others, the synthetic polymer carriers based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are some of the most promising carriers for this purpose. This review focuses on advances in the development of HPMA copolymer carriers and their conjugates with anticancer drugs, with triggered drug activation in tumor tissue and especially in tumor cells. Specifically, this review highlights the improvements in polymer drug carrier design with respect to the structure of a spacer to influence controlled drug release and activation, and its impact on the drug pharmacokinetics, enhanced tumor uptake, cellular trafficking, and in vivo antitumor activity.

Intracellular Fate Investigation of Bio-Eliminable Polymeric Nanoparticles by Confocal Laser Scanning Microscopy

This is a study of the in vitro cytotoxicity and intracellular fate of poly[(glycylglycinemethacrylamide)-co-N-(2-hydroxypropylmethacrylamide y)] bio-eliminable polymer samples and relative nanoparticles in Balb/c 3T3 cloned A31 mouse embryo fibroblasts cell line by using Confocal Laser Scanning Microscopy (CLSM). Nanoparticles were prepared by co-precipitating the polymers with fluorescein labeled human serum albumin (HSA-FITC) as the fluorescent probe and as the model protein drug. The toxicity of the polymers containing 25, 50 and 100%, respectively, of (glycylglycinemethacrylamide) x (GGMA) was investigated in terms of cytoskeleton morphology by exposing cells to various concentrations of polymers for 24 h. Under normal culture conditions, fibroblast cells exhibit characteristic spreading and shape, however, when the cell cultures were subjected to chemical, metabolic or physical stress, their morphology changed reducing their visibility. The polymers with the lower glycine content exert a lower toxicity even at high concentrations [8.5mg/mL]. The cellular uptake of nanoparticles was determined by incubating fibroblasts with HSA-FITC loaded particles and HSA-FITC alone at three different time points. The results indicate that nanoparticles were up-taken by the cells in a time dependent fashion. Preliminary evaluation of the intracellular fate of the prepared nanoparticles indicate their possible lysosomal escape.

Polymer—Doxorubicin Conjugate with a Synthetic Peptide Ligand Targeted on Prostate Tumor

In this study, the synthesis, physico-chemical characterization, and antiproliferative effects of a polymer—doxorubicin conjugate targeted by the amide of peptide sequence CPLHQRPMC are described. This sequence is discovered using the phage display method to achieve high affinity to prostate cancer cell line PC3MM2. The peptide is bound to N-(2-hydroxypropyl)methacrylamide-based copolymer carrier via a hydrophilic undeca(ethylene oxide) spacer. Doxorubicin is attached to the polymer using a pH-sensitive hydrazone bond which proves to be stable at a physiological pH 7.4 but quickly hydrolyzes at pH 5.0. The polymer—drug conjugate exhibits significant antiproliferative activity against human metastatic prostate cancer cell line PC3MM2 in vitro. The addition of a second polymer with the targeting peptide but without doxorubicin to the incubation media leads to a decrease in the cytotoxicity of 32% induced by the first polymer. This finding indicates a receptor-specific endocytosis of the polymeric drug.

Synthesis and Properties of Star HPMA Copolymer Nanocarriers Synthesised by RAFT Polymerisation Designed for Selective Anticancer Drug Delivery and Imaging

High-molecular-weight star polymer drug nanocarriers intended for the treatment and/or visualisation of solid tumours were synthesised, and their physico-chemical and preliminary in vitro biological properties were determined. The water-soluble star polymer carriers were prepared by the grafting of poly(amido amine) (PAMAM) dendrimers by hetero-telechelic N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers, synthesised by the controlled radical Reversible Addition Fragmentation chain Transfer (RAFT) polymerisation. The well-defined star copolymers with Mw values ranging from 2 · 10(5) to 6 · 10(5) showing a low dispersity (approximately 1.2) were prepared in a high yield. A model anticancer drug, doxorubicin, was bound to the star polymer through a hydrazone bond, enabling the pH-controlled drug release in the target tumour tissue. The activated polymer arm ends of the star copolymer carrier enable a one-point attachment for the targeting ligands and/or a labelling moiety. In this study, the model TAMRA fluorescent dye was used to prove the feasibility of the polymer carrier visualisation by optical imaging in vitro. The tailor-made structure of the star polymer carriers should facilitate the synthesis of targeted polymer-drug conjugates, even polymer theranostics, for simultaneous tumour drug delivery and imaging.

Nanoparticles in drug delivery: mechanism of action, formulation and clinical application towards reduction in drug-associated nephrotoxicity

INTRODUCTION

Over the past few decades, nanoparticles (NPs) have gained immeasurable interest in the field of drug delivery. Various NP formulations have been disseminated in drug development in an attempt to increase efficacy, safety and tolerability of incorporated drugs. In this context, NP formulations that increase solubility, control release, and/or affect the in vivo disposition of drugs, were developed to improve the pharmacokinetic and pharmacodynamic properties of encapsulated drugs.

AREAS COVERED

In this article, important properties related to NP function such as particle size, surface charge and shape are disseminated. Also, the current understanding of how NP characteristics affect particle uptake and targeted delivery is elucidated. Selected NP systems currently used in delivery of drugs in biological systems and their production methods are discussed as well. Emphasis is placed on current NP formulations that are shown to reduce drug-induced adverse renal complications.

EXPERT OPINION

Formulation designs utilizing NP-encapsulated drugs offer alternative pharmacotherapy options with improved safety profiles for current and emerging drugs. NPs have been shown to increase the therapeutic index of several entrapped drugs mostly by decreasing drug localization and side effects on organs. Recent studies on NP-encapsulated chemotherapeutic and antibiotic medications show enhanced therapeutic outcomes by altering drug degradation, increasing systemic circulation and/or enhancing cell specific targeting. They may also reduce the distribution of encapsulated drugs into the kidneys and attenuate drug-associated adverse renal complications. The usefulness of NP formulation in reducing the nephrotoxicity of nonsteroidal anti-inflammatory drugs is an under explored territory that deserves more attention.

Targeting of multidrug-resistant human ovarian carcinoma cells with anti-P-glycoprotein antibody conjugates

A monoclonal antibody (mAb) to P-glycoprotein (Pgp), UIC2, is used as a targeting moiety for N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer/drug [(meso chlorin e(6) mono(N-2-aminoethylamide) (Mce(6)) or doxorubicin (DOX)] conjugates to investigate their cytotoxicity towards the Pgp-expressing human ovarian carcinoma cell line A2780/AD. The binding, internalization, and subcellular trafficking of a fluorescein labeled UIC2 targeted HPMA copolymer are studied and show localization to the plasma membrane with limited internalization. The specificity of the UIC2-targeted HPMA copolymer/drug conjugates are confirmed using the sensitive cell line A2780 that does not express Pgp.

Synthetic polymers as drug-delivery vehicles in medicine

Cancerous diseases present a formidable health problem worldwide. While the chemotherapy of cancer, in conjunction with other treatment modalities, has reached a significant level of maturity, efficacious use of such agents is still restricted by numerous pharmacological deficiencies, such as poor water solubility, short serum circulation lifetimes, and low bioavailability resulting from lack of affinity to cancer tissue and inadequate mechanisms of cell entry. More critically still, most drugs suffer from toxic side effects and a risk of drug resistance. The class of platinum anticancer drugs, although outstandingly potent, is particularly notorious in that respect. Among the countless methods developed in recent years in an effort to overcome these deficiencies, the technology of polymer-drug conjugation stands out as a particularly advanced treatment modality. The strategy involves the bioreversible binding, conjugating, of a medicinal agent to a water-soluble macromolecular carrier. Following pharmacokinetic pathways distinctly different from those of the common, nonpolymeric drugs, the conjugate so obtained will act as a prodrug providing safe transport of the bioactive agent to and into the affected, that is, cancerous cell for its ultimate cell-killing activity. The present treatise will acquaint us with the pharmacological fundamentals of this drug delivery approach, applied here specifically to the metalorganic platinum-type drug systems and the organometallic ferrocene drug model. We will see just how this technology leads to conjugates distinctly superior in antiproliferative activity to cisplatin, a clinically used antitumor agent used here as a standard. Polymer-drug conjugation involving metal-based and other medicinal agents has unquestionably matured to a practical tool to the pharmaceutical scientist, and all indications point to an illustrious career for this nascent drug delivery approach in the fight against cancer and other human maladies.

Spectral analysis of doxorubicin accumulation and the indirect quantification of its DNA intercalation

There is a wide range of techniques utilizing fluorescence of doxorubicin (Dox) commonly used for analysis of intracellular accumulation and destiny of various drug delivery systems containing this anthracycline antibiotic. Unfortunately, results of these studies can be significantly influenced by doxorubicin degradation product, 7,8-dehydro-9,10-desacetyldoxorubicinone (D*) forming spontaneously in aqueous environment, whose fluorescence strongly interfere with that of doxorubicin. Here, we define two microscopy techniques enabling to distinguish and separate Dox and D* emission based either on its spectral properties or on fluorescence lifetime analysis. To analyze influx and nuclear accumulation of Dox (free or polymer-bound) by flow cytometry, we propose using an indirect method based on its DNA intercalation competition with Hoechst 33342 rather than a direct measurement of doxorubicin fluorescence inside the cells.

Doxorubicin attached to HPMA copolymer via amide bond modifies the glycosylation pattern of EL4 cells

To avoid the side effects of the anti-cancer drug doxorubicin (Dox), we conjugated this drug to a N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer backbone. Dox was conjugated via an amide bond (Dox-HPMA(AM), PK1) or a hydrazone pH-sensitive bond (Dox-HPMA(HYD)). In contrast to Dox and Dox-HPMA(HYD), Dox-HPMA(AM) accumulates within the cell's intracellular membranes, including those of the Golgi complex and endoplasmic reticulum, both involved in protein glycosylation. Flow cytometry was used to determine lectin binding and cell death, immunoblot to characterize the presence of CD7, CD43, CD44, and CD45, and high-performance anion exchange chromatography with pulsed amperometric detector analysis for characterization of plasma membrane saccharide composition. Incubation of EL4 cells with Dox-HPMA(AM) conjugate, in contrast to Dox or Dox-HPMA(HYD), increased the amounts of membrane surface-associated glycoproteins, as well as saccharide moieties recognized by peanut agglutinin, Erythrina cristagalli, or galectin-1 lectins. Only Dox-HPMA(AM) increased expression of the highly glycosylated membrane glycoprotein CD43, while expression of others (CD7, CD44, and CD45) was unaffected. The binding sites for galectin-1 are present on CD43 molecule. Furthermore, we present that EL4 treated with Dox-HPMA(AM) possesses increased sensitivity to galectin-1-induced apoptosis. In this study, we demonstrate that Dox-HPMA(AM) treatment changes glycosylation of the EL4 T cell lymphoma surface and sensitizes the cells to galectin-1-induced apoptosis.

Cytotoxicity and immunostimulation: double attack on cancer cells with polymeric therapeutics

The successful treatment of cancer with conventional drugs is frequently complicated by the resistance of tumor cells to such a non-specific therapy. Over the last few years, immunotherapy has gained attention as a tumor-specific approach. Recent findings demonstrated that some conventional cytostatics stimulate local anticancer responses. New anticancer drugs, including their polymeric derivatives, are currently being developed with the aim of destroying tumors more effectively and more specifically. Among these, the water-soluble conjugates of doxorubicin with N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer carrier have emerged as efficient therapeutics because they are able to not only directly destroy cancer cells but also elicit systemic tumor-specific anticancer responses. Here, we discuss new insights into their mechanisms of immune surveillance, which could suggest novel approaches to cancer therapy.

Peptide-targeted polyglutamic acid doxorubicin conjugates for the treatment of alpha(v)beta(6)-positive cancers

Most chemotherapeutics exert their effects on tumor cells as well as their healthy counterparts, resulting in dose limiting side effects. Cell-specific delivery of therapeutics can increase the therapeutic window for treatment by maintaining the therapeutic efficacy while decreasing the untoward side effects. We have previously identified a peptide, named H2009.1, which binds to the integrin alpha(v)beta(6). Here, we report the synthesis of a peptide targeted polyglutamic acid polymer in which the high affinity alpha(v)beta(6)-specific tetrameric H2009.1 peptide is incorporated via a thioether at the N-terminus of a 15 amino acid polymer of glutamic acid. Doxorubicin is incorporated into the polymer via an acid-labile hydrazone bond. Payloads of four doxorubicin molecules per targeting agent are achieved. The drug is released at pH 4.0 and 5.6 but the conjugate is stable at pH 7.0. The conjugate is selectively internalized into alpha(v)beta(6) positive cells as witnessed by flow cytometric analysis and fluorescent microscopy. Cellular uptake is mediated by the H2009.1 peptide, as no internalization of the doxorubicin-PG polymer is observed when it is conjugated to a scrambled sequence control peptide. Importantly, the conjugate is more cytotoxic toward a targeted cell than a cell line that does not express the integrin.

Synthesis of Degradable Functional Poly(ethylene glycol) Analogs as Versatile Drug Delivery Carriers

Poly(ethylene glycol) (PEG) is widely used as a water soluble carrier for polymer-drug conjugates. Herein, we report degradable linear PEG analogs (DPEGs) carrying multifunctional groups. The DPEGs were synthesized by a Michael addition based condensation polymerization of dithiols and PEG diacrylates (PEGDA) or dimethacrylates (PEGDMA). They were stable at pH 7.4 but quickly degraded at pH 6.0 and 5.0. Thus, DPEGs could be used as drug carriers without concern for their retention in the body. DPEGs could be made to carry such functional groups as terminal thiol or (meth)acrylate and pendant hydroxyl groups. The functional groups were used for conjugation of drugs and targeting groups. This new type of PEG analog will be useful for drug delivery and the PEGylation of biomolecules and colloidal particles.

Liberation of doxorubicin from HPMA copolymer conjugate is essential for the induction of cell cycle arrest and nuclear fragmentation in ovarian carcinoma cells

Despite intensive study, the molecular mechanism for cell toxicity of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-bound doxorubicin remains unclear. Moreover, the ability of the released drug to accumulate in the nucleus has also been questioned. We have hypothesized that the pattern of cell cycle progression is a useful indicator for the presence of free doxorubicin in the nucleus and its interaction with nuclear DNA. The effects of HPMA copolymer-bound doxorubicin on cell cycle progression were evaluated in this study in cultured human ovarian cancer A2780 cells. We determined that P-GFLG-DOX, but not P-GG-DOX, initiates cell cycle arrest and nuclear fragmentation in the same manner as free DOX, but with a time-delay. Our data indicate that drug release from the conjugate is required for the apoptotic activity associated with the conjugate.