Polymer-drug Conjugates Research Articles

Synthesis of a Therapeutic Amphiphilic Copolymer of SN38 via RAFT Polymerization and Its Self-Assembly to Peptomicelles for Fighting against Colon Adenocarcinoma

Colorectal cancer (CRC) is the fourth most frequent type and third most lethal malignancy in the world. To increase the efficacy of chemotherapy while reducing its side effects, the self-assembly of polymer–drug conjugates can minimize systemic toxicity while enhancing therapeutic efficiency. In the present study, polyglutamic acid (PGA) was used to prepare the conjugate of a hydrophobic anticancer agent, SN38, by forming an ester bond between phenolic hydroxyl groups of SN38 and the activated carboxylic acid of PGA. Then, a polyhydroxypropyl methacrylamide (PHPMA) block was synthesized starting from the end of the PGA chain via the “grafting from” approach, implementing reversible addition–fragmentation chain transfer (RAFT) polymerization. The amphiphilicity of the synthesized block copolymer will induce self-assembly into peptomicelle (polypeptide-based micellar structure) structures. Then, the prepared SN38-conjugated PGA-PHPMA peptomicelles were tagged with an AS1411 aptamer to provide guided drug delivery to colon adenocarcinoma. The synthesis of the therapeutic diblock copolymer was confirmed by 1H-NMR. The DLS analysis showed the sizes of 61.44 and 59.10 nm with dispersity (Đ) values of 0.44 and 0.32 for targeted and nontargeted peptomicelles, respectively. In vitro drug release experiments of the prepared system showed a controlled release profile, which was significantly accelerated in citrate buffer (pH 5.4) in comparison with that of phosphate-buffered saline (PBS, 1×, pH 7.4). An in vitro cytotoxicity experiment (MTT) illustrated a higher cytotoxicity for aptamer-targeted peptomicelles in comparison with that of nontargeted ones against H29 and C26 as nucleolin-positive cell lines, which was statistically significant, while no difference was identified between the toxicity of aforementioned formulation against CHO as a nucleolin-negative cell line (p > 0.05). In vivo study on mice bearing C26 colon carcinoma confirmed the superior therapeutic index of the aptamer-targeted peptomicelles in comparison with nontargeted peptomicelles in terms of tumor growth suppression and survival rate. Polypeptide-based self-assembled therapeutic structures as an innovative platform represent a capable chemotherapy approach.

Reduction-Sensitive Dextran-Paclitaxel Polymer-Drug Conjugate: Synthesis, Self-Assembly into Nanoparticles, and In Vitro Anticancer Efficacy.

Delivery systems that can encapsulate a precise amount of drug and offer a spatiotemporally controlled drug release are being actively sought for safe yet effective cancer therapy. Compared to polymer nanoparticle (NP)-based delivery systems that rely on physical drug encapsulation, NPs derived from stimuli-sensitive covalent polymer-drug conjugates (PDCs) have emerged as promising alternatives offering precise control over drug dosage and spatiotemporal drug release. Herein, we report a reduction-sensitive PDC "Dex-SS-PTXL" synthesized by conjugating dextran and paclitaxel (PTXL) through a disulfide bond-bearing linker. The synthesized Dex-SS-PTXL PDC with a precise degree of substitution in terms of the percentage of repeat units of dextran covalently conjugated to PTXL (27 ± 0.6%) and the amount of drug carried by the PDC (39 ± 1.4 wt %) was found to self-assemble into spherical NPs with an average size of 110 ± 34 nm and a ζ-potential of -14.09 ± 8 mV. The reduction-sensitive Dex-SS-PTXL NPs were found to release PTXL exclusively in response to the reducing agent concentration reflective of the intracellular reducing environment of the tumor cells. Challenging BT-549 and MCF-7 cells with Dex-SS-PTXL NPs revealed significant cytotoxicity, while the IC50 values and the mode of action (mitotic arrest) of Dex-SS-PTXL NPs were found to be comparable to those of free PTXL, highlighting the active nature of the intracellularly released drug. The developed PDC with its unique ability to self-assemble into NPs and stimuli-responsive drug release can enhance the success of the NP-based drug delivery systems during clinical translation.

The effect of spacers in dual drug-polymer conjugates toward combination therapeutic efficacy

Recently, a great effort has been made to perfect the therapeutic effect of solid tumor, from single-agent therapy to combined therapy and many other polymer-drug conjugations with dual or more anticancer agents due to their promising synergistic effect and higher drug level accumulation towards tumor tissues. Different polymer-drug spacers present diverse therapeutic efficacy, therefore, finding an appropriate spacer is desirable. In this study, dual drugs that are doxorubicin (DOX) and mitomycin C (MMC) were conjugated onto a polymer carrier (xyloglucan) via various peptide or amide bonds, and a series of polymers drug conjugates were synthesized with different spacers and their effect on tumor treatment efficacy was studied both in vitro and in vivo. The result shows that the synergistic effect is better when using different linker to conjugate different drugs rather than using the same spacer to conjugate different drugs on the carrier. Particularly, the finding of this works suggested that, using peptide bond for MMC and amide bond for DOX to conjugate dual drugs onto single XG carrier could improve therapeutic effect and synergy effect. Therefore, in polymer-pharmaceutical formulations, the use of different spacers to optimize the design of existing drugs to enhance therapeutic effects is a promising strategy.

Radiolabeling of a polypeptide polymer for intratumoral delivery of alpha-particle emitter, 225Ac, and beta-particle emitter, 177Lu

IntroductionRadiotherapy of cancer requires both alpha- and beta-particle emitting radionuclides, as these radionuclide types are efficient at destroying different types of tumors. Both classes of radionuclides require a vehicle, such as an antibody or a polymer, to be delivered and retained within the tumor. Polyglutamic acid (pGlu) is a polymer that has proven itself effective as a basis of drug-polymer conjugates in the clinic, while its derivatives have been used for pretargeted tumor imaging in a research setup. trans-Cyclooctene (TCO) modified pGlu is suitable for pretargeted imaging or therapy, as well as for intratumoral radionuclide therapy. In all cases, it becomes indirectly radiolabeled via the bioorthogonal click reaction with the tetrazine (Tz) molecule carrying the radionuclide. In this study, we report the radiolabeling of TCO-modified pGlu with either lutetium-177 (177Lu), a beta-particle emitter, or actinium-225 (225Ac), an alpha-particle emitter, using the click reaction between TCO and Tz. MethodsA panel of Tz derivatives containing a metal ion binding chelator (DOTA or macropa) connected to the Tz moiety directly or through a polyethylene glycol (PEG) linker was synthesized and tested for their ability to chelate 177Lu and 225Ac, and click to pGlu-TCO. Radiolabeled 177Lu-pGlu and 225Ac-pGlu were isolated by size exclusion chromatography. The retention of 177Lu or 225Ac by the obtained conjugates was investigated in vitro in human serum. ResultsAll DOTA-modified Tzs efficiently chelated 177Lu resulting in average radiochemical conversions (RCC) of >75%. Isolated radiochemical yields (RCY) for 177Lu-pGlu prepared from 177Lu-Tzs ranged from 31% to 55%. TLC analyses detected <5% unchelated 177Lu for all 177Lu-pGlu preparations over six days in human serum. For 225Ac chelation, optimized RCCs ranged from 61 ± 34% to quantitative for DOTA-Tzs and were quantitative for the macropa-modified Tz (>98%). Isolated radiochemical yields (RCY) for 225Ac-pGlu prepared from 225Ac-Tzs ranged from 28% to 51%. For 3 out of 5 225Ac-pGlu conjugates prepared from DOTA-Tzs, the amount of unchelated 225Ac stayed below 10% over six days in human serum, while 225Ac-pGlu prepared from macropa-Tz showed a steady release of up to 37% 225Ac. ConclusionWe labeled TCO-modified pGlu polymers with alpha- and beta-emitting radionuclides in acceptable RCYs. All 177Lu-pGlu preparations and some 225Ac-pGlu preparations showed excellent stability in human plasma. Our work shows the potential of pGlu as a vehicle for alpha- and beta-radiotherapy of tumors and demonstrated the usefulness of Tz ligation for indirect radiolabeling.

Emerging targeted drug delivery strategies toward ovarian cancer.

Ovarian cancer is a high-mortality malignancy in women. The contemporary clinical chemotherapy with classic cytotoxic drugs, targeted molecular inhibitors would mostly fail when ovarian cancer cells become drug-resistant or metastasize through the body or when patients bare no more toleration because of strong adverse effects. The past decade has spotted varying targeted delivery systems including antibody-drug conjugates (ADCs), peptide/folate/aptamer-drug conjugates, polymer-drug conjugates, ligand-functionalized nanomedicines, and dual-targeted nanomedicines that upgrade ovarian cancer chemo- and molecular therapy effectively in preclinical/clinical settings via endowing therapeutic agents selectivity and bypassing drug resistance as well as lessening systemic toxicity. The targeted delivery approaches further provide means to potentiate emergent treatment modalities such as molecular therapy, gene therapy, protein therapy, photodynamic therapy, dual-targeting therapy and combination therapy for ovarian cancer. This review highlights up-to-date development of targeted drug delivery strategies toward advanced, metastatic, relapsed, and drug resistant ovarian cancers.

Thiolated Chitosan-Centella asiatica Nanocomposite: A Potential Brain Targeting Strategy Through Nasal Route.

The major challenge associated with the treatment of neurological disorders is the inefficiency of drugs to enter the Central Nervous System (CNS). Polymer-drug conjugates are now being tailored to overcome this hindrance associated with conventional drugs. The study aimed at developing polymer hybrid nasal nanocomposite for enhanced delivery of Centella to the CNS. Thiolated chitosan was complexed with Centella to form a composite using EDAC hydrochloride. The composite was characterized by FTIR, XRD, NMR, and MS. Further, this composite was converted into a nanoformulation by the ionic-gelation method, characterized, and subjected to ex vivo permeation studies. Additionally, MTT assay was performed using Human Uumbilical cord Vein Endothelial Cells (HUVECs) mimicking Blood-Brain Barrier (BBB) to establish the safety of nanocomposite. The targeting efficacy was predicted by molecular docking studies against receptors associated with BBB. The FTIR, XRD, NMR, and MS studies confirmed the chemical conjugation of thiolated chitosan with Centella. Nanocomposite characterization through SEM, AFM, and DLS confirmed the size and stability of the developed nanocomposite having a zeta potential of - 14.5mV and PDI of 0.260. The nanocomposite showed no signs of nasal ciliotoxicity and good permeation of 89.44 ± 1.75% (mean ± SD, n = 3) at 8h across the nasal mucosa. MTT assay showed that the nanocomposite had lesser toxicity compared to the free drug (IC50 of Centella-269.1μg/mL and IC50 of CTC nanocomposite-485.375μg/mL). The affinity of polymer to the BBB receptors as proved by docking studies suggests the ability of polymer-based nanocomposite to concentrate in the brain post nasal administration.

Supramolecular Organization of Polymer Prodrug Nanoparticles Revealed by Coarse-Grained Simulations.

Drug-polymer conjugates that can self-assemble into nanoparticles are promising drug delivery systems that improve the drug bioavailability and allow their controlled release. However, despite the possibility of reaching high drug loadings, the efficiency of the drug release, mediated by cleavage of the drug-polymer linker, is a key parameter to obtain significant anticancer activity. To overcome the limitations of experimental characterizations and to gain a better understanding of such systems, we conducted a coarse-grained molecular dynamics simulation study on four representative drug-polymer conjugates obtained by the "drug-initiated" method and studied their supramolecular organization upon self-assembly. The prodrugs were composed of either a gemcitabine or a paclitaxel anticancer drug, either a propanoate or a diglycolate linker, and a polyisoprene chain. Our simulations gave crucial information concerning the spatial organization of the different components (e.g., drug, linker, polymer, etc.) into the nanoparticles and revealed that the linkers are not fully accessible to the solvent. Notably, some cleavage sites were either poorly hydrated or partially solvated. These observations might account for the low efficiency of drug release from the nanoparticles, particularly when the linker is too short and/or not hydrophilic/solvated enough. We believe that our theoretical study could be adapted to other types of polymer prodrugs and could guide the design of new polymer prodrug nanoparticles with improved drug release efficiency.

Synthesis of L-DOPA conjugated doxorubicin-polyethylenimine nanocarrier and evaluation of its cytotoxicity on A375 and HepG2 cell lines

Objective(s): Polyethylenimine (PEI) is one of the most-extensively investigated cationic polymers for gene and drug delivery. Recently, great attention has been directed to design of carriers for co-delivery of nucleic acids and small molecules. These delivery systems are able to overcome the limitations of gene or drug delivery alone. The aim of this study is to prepare a targeted nano-carrier for co-delivery of doxorubicin (Dox) and gene using polyethylenimine. Materials and Methods: In order to prepare the ligand-containing polymer conjugates, succinic anhydride was conjugated onto the hydroxyl group of Dox through an ester bond following the protection of Dox amines by Fmoc. Drug-polymer conjugates were then coupled with L-DOPA in order to prepare the targeted nanocarriers to the cells through Large Amino Acid Transporter-1 (LAT-1). The PEI derivatives were characterized using 1H-NMR. The toxicity of conjugated polymer, Dox and PEI was assessed on HepG2 and A375 cell lines with different expression level of LAT-1 transporters using MTT assay. Results: The chemical structure of PEI conjugate was confirmed by 1H-NMR. The cytotoxicity measurement demonstrated a cell line-dependent toxicity profile at the concentrations tested in this study. It was shown that there was no significant difference in cell-induced toxicity between conjugated polymer and its parent form in A375 cell line while the cytotoxicity of conjugated polymer was significantly lower than the parent PEI in HepG2 cells.Conclusion: These results provide promising evidence for further evaluation of PEI conjugate for co-delivery of drug and gene via LAT-1 transporters.

Zwitterionic Block Copolymer Prodrug Micelles for pH Responsive Drug Delivery and Hypoxia-Specific Chemotherapy.

Tirapazamine (TPZ) and its derivatives (TPZD) have shown their great potential for efficiently killing hypoxic cancer cells. However, unsatisfactory clinical outcomes resulting from the low bioavailability of the low-molecular TPZ and TPZD limited their further applications. Precise delivery and release of these prodrugs via functional nanocarriers can significantly improve the therapeutic effects due to the targeted drug delivery and enhanced permeability and retention (EPR) effect. Herein, zwitterionic block copolymer (BCP) micelles with aldehyde functional groups are prepared from the self-assembly of poly(2-methacryloyloxyethyl phosphorylcholine-b-poly(di(ethylene glycol) methyl ether methacrylate-co-4-formylphenyl methacrylate) [PMPC-b-P(DEGMA-co-FPMA)]. TPZD is then grafted onto PMPC-b-P(DEGMA-co-FPMA) to obtain a polymer-drug conjugate, PMPC-b-P(DEGMA-co-FPMA-g-TPZD) (BCP-TPZ), through the formation of a pH-responsive imine bond, exhibiting a pH-dependent drug release profile owing to the cleavage of the imine bond under acidic conditions. Outstandingly, BCP-TPZ shows around 13.7-fold higher cytotoxicity to hypoxic cancer cells in comparison to normoxic cancer cells evaluated through an in vitro cytotoxicity assay. The pH-responsiveness and hypoxia-specific cytotoxicity confer BCP-TPZ micelles a great potential to achieve precise delivery of TPZD and thus enhance the therapeutic effect toward tumor-hypoxia.

Photo- and Acid-Degradable Polyacylhydrazone-Doxorubicin Conjugates.

Light-mediated polymer degradation has attracted considerable attention in various applications, including photo-patterning, tissue engineering and photo-triggered drug delivery. In this study, we report the synthesis and characterization of a new, linear, main-chain photo- and acid-degradable copolymer based on acylhydrazone linkages. The polymer was synthesized via a step-growth copolymerization of adipic acid dihydrazide with a bifunctional poly(ethylene glycol) bearing benzaldehyde end-groups, under mild acidic conditions, to afford a hydrophilic PEG-alt-adipic acid (PEG-alt-AA) alternating copolymer. The synthesized polymer was characterized by size exclusion chromatography, proton nuclear magnetic resonance and attenuated total reflection-Fourier transform infrared spectroscopies. The main-chain photo- and acid-induced degradation of the copolymer in dimethylsulfoxide and water, respectively, was verified by UV-vis spectroscopy at light intensities as low as 0.1 mW cm−2 at λ = 254 nm. Next, a model anticancer drug, doxorubicin (DOX), was chemically linked to the polymer chain end(s) via acylhydrazone bond(s), resulting in amphiphilic PEG-alt-adipic acid-DOX (PEG-alt-AA-DOX) polymer–drug conjugates. The conjugates were self-assembled in water to form spherical nanoparticles, as evidenced by scanning and transmission electron microscopies. The irradiation of the self-assembled PEG-alt-AA-DOX conjugates with UV light and the decrease of the solution pH resulted in the disruption of the assemblies due to the photolysis and acidolysis of the acylhydrazone bonds, and the release of the therapeutic cargo.

PH/ROS Dual-Responsive Polymer–Drug-Based Nanocarriers: Click-Reaction Preparation and Fluorescence Imaging-Guided Chemotherapy and Photodynamic Therapy

In the past decades, polymer-drug conjugates of anticancer agents have gained much attention due to their enhanced aqueous solubility, improved pharmacokinetics, and better drug utilization than their conventional insoluble counterparts. Several polymer-drug conjugates have entered the third phase of clinical trials yet suffer from inherent deficiencies, including uncontrolled drug release and unclear degradation mechanisms. In this study, a pH/reactive oxygen species (ROS) dual-responsive PEG-doxorubicin (DOX) conjugate (denoted as TPD) was synthesized through acyl alkynyl-amine click reaction by PEG dipropiolate (PEGB), amine-terminated thioketal (TKL), and doxorubicin (DOX). Due to the generated ene-amine and thioketal in the backbone, the prepared amphiphilic TPD not only has a high drug loading ratio for photosensitizer chlorin e6 (Ce6) but also has the sensitivity to the acidic tumor microenvironment (TME) and ROS. Considering the complex conditions of TME, the prepared TPD@Ce6 nanoparticles (NPs) might respond to the relatively low pH and release Ce6 initially, and upon laser radiation, Ce6 produces abundant singlet oxygen (1O2) to achieve a programmable accelerated release of DOX and more Ce6 at the tumor site. In addition, the NIR fluorescence of DOX could monitor drug delivery and controlled release. The developed TPD@Ce6 NPs can realize the targeted tumor in combination therapy with negligible cytotoxicity on normal tissues.

Combretastatin A4-combined photodynamic therapy for enhanced tumor therapeutic efficacy

The limitation of traditional photodynamic therapy (PDT) such as the inherent hypoxia, the light penetration and the photosensitizer’s activity make it difficult to achieve a satisfactory therapeutic effect. To overcome these restrictions and enhance the antitumor therapeutic effect, the combination of PDT with other means offers a promising strategy to improve the efficacy of PDT. Herein, biodegradable poly (L-glutamic acid) (PLG) was used to chemically conjugate hydrophobic photosensitizers (TPP-NH2) and vascular disrupting agents (CA4) to prepare polymer-drug conjugates PT and PC, respectively. Both the solubility of drug and the endocytosis ability of nanoparticles have been enhanced. When the tumor was treated by PC and PT simultaneously, the conjugated TPP-NH2 and CA4 would be released from the internalized PC and PT due to the degradation of PLG. Under laser irradiation, the released TPP-NH2 could mainly kill the marginal tumor cells by generating cytotoxic singlet oxygen, while the released CA4 caused necrosis in the central region of the tumor by blocking the blood vessels. In vivo and in vitro analysis showed that this combined administration strategy exhibited more satisfied anti-proliferative effect compared to monotherapy, providing an effective strategy to develop synergistic cancer therapy.

Abstract 1068: SDX-7320, a novel inhibitor of methionine aminopeptidase 2 (MetAP2), inhibits MCF-7 tumor growth in combination with palbociclib (Ibrance®)

Abstract Small molecule MetAP2 inhibitor TNP-470 previously showed clinical anti-tumor activity, however CNS side effects and poor drug-like properties limited its development. SDX-7320 is a polymer-drug conjugate of a novel MetAP2 inhibitor (SDX-7539), intended to improve biodistribution (limit CNS penetration) and pharmacokinetics relative to small molecule MetAP2 inhibitors. SDX-7320 has recently completed a phase I trial in late-stage cancer patients (NCT02743637). SDX-7320 was previously shown to inhibit the growth of syngeneic EO771 triple-negative breast cancers (TNBC) accelerated by obesity/metabolic dysfunction (“metabo-oncology”). In addition SDX-7320 synergized with the PI3Kα inhibitor alpelisib (Piqray®) to block the growth of ER+/Her2- MCF-7 xenografts. Here, we show that SDX-7320 inhibits the growth of MCF-7 xenografts alone and in combination with the CDK4/6 inhibitor Palbociclib (Ibrance®). Nude mice were implanted with slow release estrogen pellets and then injected with MCF-7 cells in the fourth mammary gland. Treatment began (n=10/group) when tumors exceeded 100 mm³: SDX-7320 (sc/q4d, 8 mg/kg), palbociclib (po, qd, 20 or 40 mg/kg), SDX-7320 plus palbociclib (20 mg/kg), SDX-7320 plus palbociclib (40 mg/kg). MCF-7 tumor growth inhibition at day 31 relative to vehicle-treated mice: SDX-7320, 29% (NS); palbociclib, 24% and 54% at 20 and 40 mg/kg respectively (NS); SDX-7320 plus palbociclib (20 mg/kg), 64% (p&amp;lt;0.05); and SDX-7320 plus palbociclib (40 mg/kg), 82%, (p&amp;lt;0.01). Tumor samples were homogenized in RIPA buffer containing protease and phosphatase inhibitors for analysis of proteins (by WES). Cell-cycle proteins (cyclin E1, E2, cdk2, cdk4) were decreased in tumor tissue from SDX-7320-treated mice relative to vehicle, and were typically lower in tumors from mice treated with SDX-7320 plus palbociclib (40 mg/kg) compared to either vehicle-treated or SDX-7320-treated mice. A key growth factor-signaling protein Akt was reduced in SDX-7320-treated groups (alone and in combination) as was estrogen receptor alpha (ERα). pAkt (S473) was lowest in SDX-7320-treated tumors and in tumors treated with SDX-7320 plus palbociclib (40 mg/kg). The autophagy marker LC3B was elevated in response to palbociclib (20 and 40 mg/kg) but in combination with SDX-7320, the increase was significantly attenuated. Intracellular pathways and proteins linked to emergence of resistance to palbociclib include cell cycle (cyclin E1), growth factor and hormone signaling (Akt, ERα) and autophagy (LC3B). The protein changes observed (representative of these pathways) suggest that combining SDX-7320 with palbociclib (Ibrance®) may extend the period of progression-free survival in patients with ER+/Her2- breast cancer relative to treatment with palbociclib (Ibrance®) alone. Citation Format: Peter Cornelius, Benjamin Mayes, Pierre Dufour, Sara Little, Andrew Slee, Raphael Nir, Adam Nir, Bradley J. Carver, James Shanahan. SDX-7320, a novel inhibitor of methionine aminopeptidase 2 (MetAP2), inhibits MCF-7 tumor growth in combination with palbociclib (Ibrance®) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1068.

Polymer based Drug Delivery Systems- benchtop to Bedside Transition

Research in the field of polymers and polymeric materials has garnered immense attention in the past few decades due to the versatile functional and structural capabilities of polymers which often can be manipulated for applications in the field of therapy and diagnosis for a host of diseases and disorders. Polymer therapeutics comprises polymer-drug and polymer-protein conjugates as well as supramolecular systems used as drug delivery systems. Although the pharmacological industry invests immensely in the design and discovery of novel drug molecules, small molecular drugs are often inefficient in targeting many diseases like deep seated low vasculature tumours, metastasized cancers and various autoimmune diseases. Coupled with a rapid clearance rate, low solubility, drug resistance and high off target toxicity these small molecular drugs often present modest benefits for a host of common diseases. In order to improve the therapeutic index of pre-existing drugs and shortening the translation from preclinical validation to clinical approval, a vast area of drug delivery research focuses on the improvement of drug carriers by various alterations. The major challenges currently faced by drug delivery systems include a low payload, transition through the desmoplastic barrier for solid tumours and high hepatic and renal clearance. In order to address these issues numerous polymer–protein and polymer-drug conjugates have been engineered and have reported to enhance the stability and pharmacokinetic properties of the active drugs. Highly toxic anticancer drugs like doxorubicin, cis-platin and gemcitabine have successfully been coupled with high molecular weight polymers to formulate targeted drug delivery agents, some of which have undergone successful clinical trials. Apart from PEGylated polymers, dendritic polymers and polyplexes with DNA or RNA moieties have also been considered as candidates for improving the therapeutic index of various drugs. Ongoing efforts in the development of polymer-based therapeutics are promising and open new horizons for personalized medicine for effective cure of various life-threatening diseases.

Folic Acid-Targeted Paclitaxel-Polymer Conjugates Exert Selective Cytotoxicity and Modulate Invasiveness of Colon Cancer Cells.

Although selective tumor delivery of anticancer drugs has been sought by exploiting either passive targeting or by ligand-mediated targeting, a selective anticancer therapy remains an unmet medical need. Despite the advances which have been achieved by nanomedicines, nanosystems such as polymer-drug conjugates still miss the goal of clinical efficacy. In this study, we demonstrated that polymer-drug conjugates require a thoroughly chemical design and the right targeting agent/polymer ratio to be selective and effective towards cancer cells. In particular, two PEG conjugates carrying paclitaxel and targeted with different folic acid (FA)/PEG ratios (one or three) were investigated. The cytotoxicity study in positive (HT-29) and negative (HCT-15) FA receptor (FR)-cell lines demonstrated that the conjugates with one or three FAs were 4- or 28-fold more active in HT-29 cells, respectively. The higher activity of the 3-FA conjugate was confirmed by its strong impact on cell cycle arrest. Furthermore, FA targeting had a clear effect on migration and invasiveness of HT-29 cells, which were significantly reduced by both conjugates. Interestingly, the 3-FA conjugate showed also an improved pharmacokinetic profile in mice. The results of this study indicate that thorough investigations are needed to optimize and tune drug delivery and achieve the desired selectivity and activity towards cancer cells.

Discovery of dual targeting PEGylated BG-P1600-TAT to norepinephrine transporter (NET) and thyrointegrin αvβ3 in the treatment of neuroblastoma

Polymer-drug conjugates are growing in interest as novel anticancer agents for targeted cancer therapy. The aim of this study was to synthesize a poly(ethylene glycol) (PEG) conjugated anticancer drug for neuroblastoma, which is the most common extracranial solid tumor of childhood and the deadliest tumor of infancy. In our previous studies, we designed and synthesized a dual targeting agent using benzylguanidine (BG) conjugated with the high affinity thyrointegrin αvβ3 antagonist TriAzole Tetraiodothyroacetic acid (TAT) via non-cleavable bonding to PEG400 to make BG-P400-TAT and its derivatives as agents against neuroblastoma. Here, we improved the pharmacodynamic properties and increased the solubility by changing the polymer length to 1600 molecular weight. The TAT group, which acts as an integrin αvβ3 antagonist, and the BG group, which can be taken up by neuroblastoma cells through the norepinephrine transporter (NET) system, are conjugated to PEG1600 to make BG-PEG1600-TAT. The binding affinity of BG-PEG1600-TAT was 40-fold higher to integrin αvβ3 versus BG-P400-TAT and was associated with greater anticancer activities against neuroblastoma cells (SK-N-F1 and SKNAS) implanted in SCID mice along with broad spectrum anti-angiogenesis activities versus the FDA approved anti-Vascular Endothelial Growth Factor (VEGF) monoclonal antibody Avastin (bevacizumab). In conclusion, our novel dual targeting of NET and αvβ3 receptor antagonist, BG-P1600-TAT demonstrated broad spectrum anti-angiogenesis and anti-cancer activities in suppressing neuroblastoma tumor progression and metastasis. Thus, BG-PEG1600-TAT represents a potential clinical candidate for targeted therapy in neuroblastoma management.

Saturation Transfer Difference NMR Spectroscopy for the Elucidation of Supramolecular Albumin-Polymer Interactions.

Albumin has consistently demonstrated its potential for enhancing the delivery of drugs and polymer-drug conjugates, binding via supramolecular forces within its multiple binding sites. Herein, we introduce saturation transfer difference (STD-NMR) as a method to identify the interactions between a polymer library and bovine serum albumin (BSA). With STD-NMR, the binding ability of polymers can be quickly screened by focusing on their individual structural features, making this technique more suitable for high throughput screening in comparison to traditional fluorescence studies.

Hyaluronic acid conjugates for topical treatment of skin cancer lesions.

Skin cancer is one of the most common types of cancer in the United States and worldwide. Topical products are effective for treating cancerous skin lesions when surgery is not feasible. However, current topical products induce severe irritation, light-sensitivity, burning, scaling, and inflammation. Using hyaluronic acid (HA), we engineered clinically translatable polymer-drug conjugates of doxorubicin and camptothecin termed, DOxorubicin and Camptothecin Tailored at Optimal Ratios (DOCTOR) for topical treatment of skin cancers. When compared to the clinical standard, Efudex, DOCTOR exhibited high cancer-cell killing specificity with superior safety to healthy skin cells. In vivo studies confirmed its efficacy in treating cancerous lesions without irritation or systemic absorption. When tested on patient-derived primary cells and live-skin explants, DOCTOR killed the cancer with a selectivity as high as 21-fold over healthy skin tissue from the same donor. Collectively, DOCTOR provides a safe and potent option for treating skin cancer in the clinic.

Fabrication of Doxorubicin Conjugated Methoxy Poly(ethylene glycol)-block-poly(ε-caprolactone) Nanoparticles and Study on Their in vitro Antitumor Activities

The purpose of this study was to develop a novel drug-polymer conjugation (mPEG-b-PCL-DOX) and study on its toxicity, bio-safety, and in vitro antitumor activity of mPEG-b-PCL-DOX. The polymer methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) (mPEG-b-PCL) was prepared by ring-opening polymerization. Then, succinic anhydride was reacted with mPEG-b-PCL via esterification reaction to produce mPEG-b-PCL-COOH. Finally, the polymer mPEG-b-PCL-DOX was obtained by conjugating DOX to mPEG-b-PCL-COOH by amidation. The Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (1H NMR) spectra were used to study the structures of obtained polymers. Transmission electron microscope (TEM) and Dynamic laser scattering (DLS) were employed to monitor the morphology and size distribution of mPEG-b-PCL-DOX nanoparticles (NPs). The mPEG-b-PCL-DOX NPs were administrated to KM rats by intraperitoneal injection to study the bio-safety of final NPs. The cell uptake and in vitro anti-tumor activity of final NPs were carried out with HCT116 cells as models. FTIR and 1H NMR spectra confirmed the obtaining of mPEG-b-PCL-DOX. The fabricated NPs were in round shapes with an average diameter of 300 nm. These NPs did not induce hemolysis and physiological or pathological changes in rats’s organs. Finally, cell teats showed that these NPs could be endocytosed by HCT 116 cells, and they had better anti-tumor effects than free DOX did. Therefore, the mPEG-b-PCL-DOX NPs had a potential application in anti-cancer therapy.

Nanoparticles Composed of PEGylated Alternating Copolymer-Combretastatin A4 Conjugate for Cancer Therapy.

Chemotherapy using vascular targeting agents is an emerging new approach for cancer therapy. Combretastatin A4 (CA4) is a leading vascular-disrupting agent that targets the tumor blood vasculature for clinical tumor elimination. However, the extremely poor water solubility of CA4 hinders its biomedical applications. In this study, nanoparticles composed of novel PEGylated alternating copolymer-CA4 conjugates are designed to improve the therapeutic efficiency of CA4. First, an alternating copolymer with an alkene-pendant is synthesized by mPEG-OH-initiated ring-opening copolymerization. Then, side carboxyl groups are introduced by a thio-ene "click" chemical reaction, followed with CA4 conjugation through the Yamaguchi-reaction, resulting in the target copolymer, mPEG-b-P(PA-alt-GCA4). Interestingly, the polymer-drug conjugates can self-assemble into nanoparticles with an average diameter of 55.6nm. The in vitro drug release and cytotoxicity of the obtained CA4-NPs toward 4T1 cells are investigated. Finally, the antitumor efficiency is evaluated in a 4T1-tumor bearing murine model. The in vivo test results demonstrate that CA4-NPs inhibited tumor growth much more efficiently at doses of 30 and 60mg kg-1 , compared with the control group.