Clinical experience with anthracycline antibiotics-HPMA copolymer-human immunoglobulin conjugates

Targeted Drug Delivery Biopolymers Effectively Inhibit Breast Tumor Growth and Prevent Doxorubicin-Induced Cardiotoxicity

The anticancer agent doxorubicin(dox) has been widely used in the treatment of a variety of hematological malignancies and solid tumors. Despite doxorubicin’s efficiency in killing tumor cells, severe damage to healthy tissues, along with cardiotoxicity, limits its clinical use. To overcome these adverse side effects, improve patient safety, and enhance therapeutic efficacy, we have designed a thermally responsive biopolymer doxorubicin carrier that can be specifically targeted to tumor tissue by locally applying mild hyperthermia (41 °C). The developed drug vehicle is composed of the following: a cell penetrating peptide (SynB1) to promote tumor and cellular uptake; thermally responsive Elastin-like polypeptide (ELP); and the (6-maleimidocaproyl) hydrazone derivative of doxorubicin (DOXO-EMCH) containing a pH-sensitive hydrazone linker that releases doxorubicin in the acidic tumor environment. We used the in vivo imaging system, IVIS, to determine biodistribution of doxorubicin-delivered ELP in MDA-MB-231 xenografts in nude mice. Tumor bearing mice were treated with a single IV injection of 10 mg/kg doxorubicin equivalent dose with free doxorubicin, thermally responsive SynB1 ELP 1-DOXO, and a thermally nonresponsive control biopolymer, SynB1 ELP 2-DOXO. Following a 2 h treatment with hyperthermia, tumors showed a 2-fold higher uptake when treated with SynB1 ELP 1-DOXO compared to free doxorubicin. Accumulation of the thermally non-responsive control SynB1 ELP2 –DOXO was comparable to free doxorubicin, indicating that an increase in dox accumulation with ELP is due to aggregation in response to thermal targeting. Higher levels of SynB1 ELP1–DOXO and SynB1 ELP2 –DOXO with respect to free doxorubicin were observed in kidneys. Fluorescence intensity from hearts of animals treated with SynB1 ELP1–DOXO show a 5-fold decrease in accumulation of doxorubicin than the same dose of free doxorubicin. SynB1-ELP1-DOXO biopolymers demonstrated a 6-fold increase in tumor/heart ratio in comparison to free doxorubicin, indicating preferential accumulation of the drug in tumors. These results demonstrate that thermally targeted polymers are a promising therapy to enhance tumor targeting and uptake of anticancer drugs and to minimize free drug toxicity in healthy tissues, representing a great potential for clinical application.

Tumor Stimulus-Responsive Biodegradable Diblock Copolymer Conjugates as Efficient Anti-Cancer Nanomedicines

Biodegradable nanomedicines are widely studied as candidates for the effective treatment of various cancerous diseases. Here, we present the design, synthesis and evaluation of biodegradable polymer-based nanomedicines tailored for tumor-associated stimuli-sensitive drug release and polymer system degradation. Diblock polymer systems were developed, which enabled the release of the carrier drug, pirarubicin, via a pH-sensitive spacer allowing for the restoration of the drug cytotoxicity solely in the tumor tissue. Moreover, the tailored design enables the matrix-metalloproteinases- or reduction-driven degradation of the polymer system into the polymer chains excretable from the body by glomerular filtration. Diblock nanomedicines take advantage of an enhanced EPR effect during the initial phase of nanomedicine pharmacokinetics and should be easily removed from the body after tumor microenvironment-associated biodegradation after fulfilling their role as a drug carrier. In parallel with the similar release profiles of diblock nanomedicine to linear polymer conjugates, these diblock polymer conjugates showed a comparable in vitro cytotoxicity, intracellular uptake, and intratumor penetration properties. More importantly, the diblock nanomedicines showed a remarkable in vivo anti-tumor efficacy, which was far more superior than conventional linear polymer conjugates. These findings suggested the advanced potential of diblock polymer conjugates for anticancer polymer therapeutics.

Polymer nanomedicines

Polymer nanomedicines (macromolecular therapeutics, polymer-drug conjugates, drug-free macromolecular therapeutics) are a group of biologically active compounds that are characterized by their large molecular weight. This review focuses on bioconjugates of water-soluble macromolecules with low molecular weight drugs and selected proteins. After analyzing the design principles, different structures of polymer carriers are discussed followed by the examination of the efficacy of the conjugates in animal models and challenges for their translation into the clinic. Two innovative directions in macromolecular therapeutics that depend on receptor crosslinking are highlighted: a) Combination chemotherapy of backbone degradable polymer-drug conjugates with immune checkpoint blockade by multivalent polymer peptide antagonists; and b) Drug-free macromolecular therapeutics, a new paradigm in drug delivery.

HPMA-Copolymer Nanocarrier Targets Tumor-Associated Macrophages in Primary and Metastatic Breast Cancer

Polymeric nanocarriers such as N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers deliver drugs to solid tumors and avoid the systemic toxicity of conventional chemotherapy. Because HPMA copolymers can target sites of inflammation and accumulate within innate immune cells, we hypothesized that HPMA copolymers could target tumor-associated macrophages (TAM) in both primary and metastatic tumor microenvironments. We verified this hypothesis, first in preliminary experiments with isolated bone marrow macrophage cultures in vitro and subsequently in a spontaneously metastatic murine breast cancer model generated from a well-established, cytogenetically characterized 4T1 breast cancer cell line. Using our standardized experimental conditions, we detected primary orthotopic tumor growth at 7 days and metastatic tumors at 28 days after orthotopic transplantation of 4T1 cells into the mammary fat pad. We investigated the uptake of HPMA copolymer conjugated with Alexa Fluor 647 and folic acid (P-Alexa647-FA) and HPMA copolymer conjugated with IRDye 800CW (P-IRDye), following their retroorbital injection into the primary and metastatic tumor-bearing mice. A significant uptake of P-IRDye was observed at all primary and metastatic tumor sites in these mice, and the P-Alexa647-FA signal was found specifically within CD11b⁺ TAMs costained with pan-macrophage marker CD68. These findings demonstrate, for the first time, a novel capacity of a P-Alexa647-FA conjugate to colocalize to CD11b⁺CD68⁺ TAMs in both primary and metastatic breast tumors. This underscores the potential of this HPMA nanocarrier to deliver functional therapeutics that specifically target tumor-promoting macrophage activation and/or polarization during tumor development. Mol Cancer Ther; 16(12); 2701-10. ©2017 AACR.

The Light at the End of the Tunnel-Second Generation HPMA Conjugates for Cancer Treatment

It is almost four decades since N-(2-hydroxypropyl)methacrylamide (HPMA) - based copolymers arose as drug carriers. Although fundamentals have been established and significant advantages have been proved, the commercialization of this platform technology was hampered due to modest outcome of clinical trial initiated with PK1, the symbol of first generation polymer-drug conjugates. In this review, we illustrate the exciting progress and approaches offered by more effective 2^nd generation HPMA-based polymer-drug conjugates in cancer treatment. For example, a new synthetic strategy endorses inert HPMA polymer with biodegradability, which permitted to prepare high molecular weight HPMA-drug conjugates with simple linear architecture while maintaining good biocompatibility. As expected, extended long-circulating pharmacokinetics and enhanced antitumor activities were achieved in several preclinical investigations. In addition, greater inhibition of tumor growth in combination regimes exhibits the remarkable capability and flexibility of HPMA-based macromolecular therapeutics. The review also discusses the main challenges and strategies for further translation development of 2^nd generation HPMA-based polymer-drug conjugates.

Backbone Degradable N-(2-Hydroxypropyl)methacrylamide Copolymer Conjugates with Gemcitabine and Paclitaxel: Impact of Molecular Weight on Activity toward Human Ovarian Carcinoma Xenografts

Degradable diblock and multiblock (tetrablock and hexablock) N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-gemcitabine (GEM) and -paclitaxel (PTX) conjugates were synthesized by reversible addition-fragmentation chain-transter (RAFT) copolymerization followed by click reaction for preclinical investigation. The aim was to validate the hypothesis that long-circulating conjugates are needed to generate a sustained concentration gradient between vasculature and a solid tumor and result in significant anticancer effect. To evaluate the impact of molecular weight of the conjugates on treatment efficacy, diblock, tetrablock, and hexablock GEM and PTX conjugates were administered intravenously to nude mice bearing A2780 human ovarian xenografts. For GEM conjugates, triple doses with dosage 5 mg/kg were given on days 0, 7, and 14 (q7dx3), whereas a single dose regime with 20 mg/kg was applied on day 0 for PTX conjugates treatment. The most effective conjugates for each monotherapy were the diblock ones, 2P-GEM and 2P-PTX (Mw ≈ 100 kDa). Increasing the Mw to 200 or 300 kDa resulted in decrease of activity most probably due to changes in the conformation of the macromolecule because of interaction of hydrophobic residues at side chain termini and formation of "unimer micelles". In addition to monotherapy, a sequential combination treatment of diblock PTX conjugate followed by GEM conjugate (2P-PTX/2P-GEM) was also performed, which showed the best tumor growth inhibition due to synergistic effect: complete remission was achieved after the first treatment cycle. However, because of low dose applied, tumor recurrence was observed 2 weeks after cease of treatment. To assess optimal route of administration, intraperitoneal (i.p.) application of 2P-GEM, 2P-PTX, and their combination was examined. The fact that the highest anticancer efficiency was achieved with diblock conjugates that can be synthesized in one scalable step bodes well for the translation into clinics.

Biodegradable Poly(ester-urethane) Carriers Exhibiting Controlled Release of Epirubicin

PURPOSE

The purpose of this study was to develop the perspective biodegradable poly(ester-urethane) (PUR) carriers based on "predominantly isotactic" and atactic polylactides (PLAs), and poly(ε-caprolactone) (PCL), for the controlled release of epirubicin (EPI).

METHODS

The biodegradable PURs containing different soft segments as new and effective carriers of EPI have been obtained. The preliminary studies on toxicity and degradation of obtained polymers, and the release of the EPI from PUR carriers were carried out.

RESULTS

We found that the kinetic release of EPI from the obtained PUR carriers tested in vitro at 37°C and pH 7.4 was strongly dependent on the kind of the polyesters, used as the soft segment in PURs synthesis. Furthermore, we demonstrated that the EPI was released from various synthesized carriers in a rather regular manner, according to the diffusion-degradation and degradation mechanisms. Importantly, in some cases, the kinetics of the EPI release was nearly zero-order.

CONCLUSION

The results show that the obtained PURs are very effective and perspective carriers and might be potentially applied in the technology of high controlled EPI delivery systems.

Development of biodegradable polyesters with various microstructures for highly controlled release of epirubicin and cyclophosphamide

In this study, "predominantly isotactic", disyndiotactic, and atactic polylactides (PLAs) and poly(ε-caprolactone)s (PCLs) were loaded with anticancer agents, epirubicin (EPI) and cyclophosphamide (CYCLOPHO), to investigate their properties as highly controlled delivery devices. It was found that the kinetic release of drugs from the obtained polyester matrices tested in vitro at 37°C and pH7.4 was strongly dependent on average molecular weight (M_n) of the polymers as well as the PLAs' microstructure. EPI and CYCLOPHO were released from various obtained matrices according to the diffusion, diffusion-degradation, and degradation mechanisms in a rather regular and continuous manner. Importantly, in some cases, the kinetics of the EPI and CYCLOPHO release was nearly zero-order, suggesting predominantly polymer degradation. It is shown that the drug release profiles can be tailored by a controlled design of the microstructure and M_n of polyesters, allowing use of the synthesized matrices for the development of highly controlled biodegradable anticancer drug delivery systems.

Self-Assembling Doxorubicin Prodrug Forming Nanoparticles and Effectively Reversing Drug Resistance In Vitro and In Vivo

Doxorubicin (DOX) is a widely used chemotherapeutic drug to treat a range of cancers. However, its unfavorable effects, particularly the cardiotoxicity and the induction of multidrug resistance (MDR), significantly limit its clinical applications. Herein, a novel doxorubicin prodrug, PEG_2K -DOX, is synthesized by conjugating a deprotonated doxorubicin molecule with the polyethylene glycol (PEG, MW: 2K) chain via pH-responsive hydrazone bond, and its potential as a better alternative than doxorubicin is evaluated. The data show that the amphiphilic PEG_2K -DOX can self-assemble into stable nanoparticles with a high and fixed doxorubicin loading content (≈20 wt%), a favorable size of 91.5 nm with a narrow polydispersity (PDI = 0.14), good stability, and pH-dependent release behavior due to the acid-cleavable linkage between PEG and doxorubicin. Although doxorubicin hardly accumulates in MDR cells, PEG_2K -DOX nanoparticles significantly increase the cellular uptake and cell-killing activity of doxorubicin in two MDR cancer cell lines MCF-7/ADR and KBv200, with the IC₅₀ values dropped to 1.130% and 42.467% of doxorubicin, respectively. More impressively, PEG_2K -DOX nanoparticles exhibit significantly improved plasma pharmacokinetics, increased in vivo therapeutic efficacy against MDR xenograft tumors, and better in vivo safety compared with doxorubicin. PEG_2K -DOX nanoparticles hold the promise to become a better alternative than doxorubicin for cancer treatment, especially for MDR tumors.

FRET-trackable biodegradable HPMA copolymer-epirubicin conjugates for ovarian carcinoma therapy

To develop a biodegradable polymeric drug delivery system for the treatment of ovarian cancer with the capacity for non-invasive fate monitoring, we designed and synthesized N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-epirubicin (EPI) conjugates. The polymer backbone was labeled with acceptor fluorophore Cy5, while donor fluorophores (Cy3 or EPI) were attached to HPMA copolymer side chains via an enzyme-cleavable GFLG linker. This design allows elucidating separately the fate of the drug and of the polymer backbone using fluorescence resonance energy transfer (FRET). The degradable diblock conjugate (2P-EPI) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using a bifunctional chain transfer agent (Peptide2CTA). The pharmacokinetics (PK) and therapeutic effect of 2P-EPI (Mw ~100 kDa) were determined in mice bearing human ovarian carcinoma A2780 xenografts. Compared to 1st generation conjugate (P-EPI, Mw <50 kDa), 2P-EPI demonstrated remarkably improved PK such as fourfold terminal half-life (33.22 ± 3.18 h for 2P-EPI vs. 7.55 ± 3.18 h for P-EPI), which is primarily attributed to the increased molecular weight of the polymer carrier. Notably, complete tumor remission and long-term inhibition of tumorigenesis (100 days) were achieved in mice (n=5) treated with 2P-EPI. Moreover, in vitro cell uptake and intracellular drug release were determined via FRET intensity changes. The results establish a solid foundation for future in vivo tracking of drug delivery and chain scission of polymeric conjugates by FRET imaging.

Synthesis, DNA-binding, and photocleavage properties of a serious of porphyrin-daunomycin hybrids

It is widely accepted that the pharmacological activities of anthracyclines antitumor agents express when the quinone-containing chromophore intercalates into base pairs of the duplex DNA. We have successfully synthesized and investigated the DNA-interactions of hybrids composed with quinone chromophore and cationic porphyrin. Herein, a clinic anticancer drug, daunomycin, is introduced to the porphyrin hybrids through different lengths of amide alkyl linkages, and their interactions and cleavage to DNA were studied compared with the previous porphyrin-quinone hybrids. Spectral results and the determined binding affinity constants (Kb) show that the attachment of daunomycin to porphyrin could improve the DNA-binding and photocleaving abilities. The porphyrin-daunomycin hybrids may find useful employment in investigating the ligand-DNA interaction.

Acid-triggered drug release from micelles based on amphiphilic oligo(ethylene glycol)–doxorubicin alternative copolymers

We prepared pH-sensitive amphiphilic oligo(ethylene glycol)–doxorubicin alternative conjugates for the controlled release of doxorubicin.

A core-shell albumin copolymer nanotransporter for high capacity loading and two-step release of doxorubicin with enhanced anti-leukemia activity

The native transportation protein serum albumin represents an attractive nano-sized transporter for drug delivery applications due to its beneficial safety profile. Existing albumin-based drug delivery systems are often limited by their low drug loading capacity as well as noticeable drug leakage into the blood circulation. Therefore, a unique albumin-derived core-shell doxorubicin (DOX) delivery system based on the protein denaturing-backfolding strategy was developed. 28 DOX molecules were covalently conjugated to the albumin polypeptide backbone via an acid sensitive hydrazone linker. Polycationic and pegylated human serum albumin formed two non-toxic and enzymatically degradable protection shells around the encapsulated DOX molecules. This core-shell delivery system possesses notable advantages, including a high drug loading capacity critical for low administration doses, a two-step drug release mechanism based on pH and the presence of proteases, an attractive biocompatibility and narrow size distribution inherited from the albumin backbone, as well as fast cellular uptake and masking of epitopes due to a high degree of pegylation. The IC50 of these nanoscopic onion-type micelles was found in the low nanomolar range for Hela cells as well as leukemia cell lines. In vivo data indicate its attractive potential as anti-leukemia treatment suggesting its promising profile as nanomedicine drug delivery system.

Nano-sized albumin-copolymer micelles for efficient doxorubicin delivery

We present the discovery of a nano-sized protein-derived micellar drug delivery system based on the polycationic albumin precursor protein cBSA-147. The anticancer drug doxorubicin (DOX) was efficiently encapsulated into nanosized micelles based on hydrophobic interactions with the polypeptide scaffold. These micelles revealed attractive stabilities in various physiological buffers and a wide pH range as well as very efficient uptake into A549 cells after 1 h incubation time only. In vitro cytotoxicity was five-times increased compared to free DOX also indicating efficient intracellular drug release. In addition, multiple functional groups are available for further chemical modifications. Based on the hydrophobic loading mechanism, various classical anti-cancer drugs, in principle, could be delivered even synergistically in a single micelle. Considering these aspects, this denatured albumin-based drug delivery system represents a highly attractive platform for nanomedicine approaches towards cancer therapy.

Controlled drug release through a plasma polymerized tetramethylcyclo-tetrasiloxane coating barrier

A plasma polymerized tetramethylcyclo-tetrasiloxane (TMCTS) coating was deposited onto a metallic biomaterial, 316 stainless steel, to control the release rate of drugs, including daunomycin, rapamycin and NPC-15199 (N-(9-fluorenylmethoxy-carbonyl)-leucine), from the substrate surface. The plasma-state polymerized TMCTS thin film was deposited in a vacuum plasma reactor operated at a radio-frequency of 13.56 MHz, and was highly adhesive to the stainless steel, providing a smooth and hard coating layer for drugs coated on the substrate. To investigate the influence of plasma coating thickness on the drug diffusion profile, coatings were deposited at various time lengths from 20 s to 6 min, depending on the type of drug. Atomic force spectroscopy (AFM) was utilized to characterize coating thickness. Drug elution was measured using a spectrophotometer or high-performance liquid chromatography (HPLC) system. The experimental results indicate that plasma polymerized TMCTS can be used as an over-coating to control drug elution at the desired release rate. The drug-release rate was also found to be dependent on the molecular weight of the drug with plasma coating barrier on top of it. The in vitro cytotoxicity test result suggested that the TMCTS plasma coatings did not produce a cytotoxic response to mammalian cells. The non-cytotoxicity of TMCTS coating plus its high thrombo-resistance and biocompatibility are very beneficial to drug-eluting devices that contact blood.

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.