Coupling of the antiviral agent zidovudine to polyaspartamide and in vitro drug release studies

[Synthesis and cell biological properties of polyaspartic acid drug/gene vector]

OBJECTIVE

Taking polysuccinimide as the main chain, amine side chain and alkyl side chain were grafted to prepare the drug/gene co-delivery vector. The property of the polymers with various side links were investigated to select an optimal vector.

METHODS

Poly-D, L-polysuccinimide was synthesized by polymerization reaction of D, L-aspartic acid as monomer. Therefore, N, N-dimethylenedipropyl-triamine and 3, 3'-diaminodipropylamine were grafted with dodecylamine/adecylamine/octadecylamine at different proportions by ring-opening reaction to obtain amphiphilic PEECs. The structure of the material was confirmed by ¹H NMR; the particle size and surface potential of the micelles were measured by dynamic light scattering; the critical micelle concentration (CMC) was determined by pyrene fluorescent probe; the RNA blocking ability was characterized by agarose gel electrophoresis; the release behavior of the PEECs was examined and the cytotoxicity, cellular uptake and gene silencing efficiency of the PEECs were studied at the cellular level.

RESULTS

A series of PEECs with different grafting rates was successfully synthesized. The particle sizes and surface potential of the PEEC derived micelles were between 250 nm and 350 nm and 27 mV and 45 mV, respectively, with a small CMC value. The RNA binding ratio of PEECs was at a mass ratio of about 0.8:1. MTT assay demonstrated that PEEC micelles had certain cytotoxicity. PEECs had excellent micelle formation, drug-loading and gene binding abilities, particularly, PEEC₁₆-2 showed high gene silencing efficiency at the cellular level.

CONCLUSIONS

PEECs are able to co-delivery drug and gene, and PEEC₁₆-2 micelles have the best ability of drug encapsulation and gene delivery.

Human Vault Nanoparticle Targeted Delivery of Antiretroviral Drugs to Inhibit Human Immunodeficiency Virus Type 1 Infection

"Vaults" are ubiquitously expressed endogenous ribonucleoprotein nanoparticles with potential utility for targeted drug delivery. Here, we show that recombinant human vault nanoparticles are readily engulfed by certain key human peripheral blood mononuclear cells (PBMC), predominately dendritic cells, monocytes/macrophages, and activated T cells. As these cell types are the primary targets for human immunodeficiency virus type 1 (HIV-1) infection, we examined the utility of recombinant human vaults for targeted delivery of antiretroviral drugs. We chemically modified three different antiretroviral drugs, zidovudine, tenofovir, and elvitegravir, for direct conjugation to vaults. Tested in infection assays, drug-conjugated vaults inhibited HIV-1 infection of PBMC with equivalent activity to free drugs, indicating vault delivery and drug release in the cytoplasm of HIV-1-susceptible cells. The ability to deliver functional drugs via vault nanoparticle conjugates suggests their potential utility for targeted drug delivery against HIV-1.

Synthesis and characterization of N-Mannich based prodrugs of ciprofloxacin and norfloxacin: In vitro anthelmintic and cytotoxic evaluation

Prodrugs, the inert derivatives of existing drugs have successfully contributed to the modification of their physicochemical properties. The improved antimicrobial potential due to enhanced lipophilicity of some of the synthesized prodrugs of antibacterial agents by various schemes has already been reported. In the current study, synthesis, characterization, and biological evaluation of some more lipid based prodrugs/compounds of ciprofloxacin and norfloxacin has been carried out. The synthesized prodrugs/compounds have been screened for anthelmintic activity using Indian earthworms and cytotoxic activity against human lung cancer cell lines A-549 employing sulforhodamine B (SRB) assay method. The prodrugs FQF1, 6b, 6c, and 6k were found to possess promising anthelmintic activity due to improved partition coefficient. Growth of selected cells lines was found to decrease with increase in concentration of prodrugs as compared to parent drug. Prodrug, 6k having GI₅₀ value 28.8, has been proved to be the most active among all the synthesized prodrugs. Results of present investigation reveal that some of the synthesized prodrugs/compounds were found to possess promising biological activity.

Investigation on the controlled synthesis and post-modification of poly-[(N-2-hydroxyethyl)-aspartamide]-based polymers

We report the controlled synthesis of PHEA-based polymers and enhanced the post-modification reactivity by reducing the intramolecular hydrogen bonding.

Tumor-Selective Macromolecular MRI Contrast Agents

Tumor-selective macromolecular ligands containing 5-(p-Carbonyloxyphenyl)-10,15,20-triphenylporphyrin (HPTP) moiety (PHEA-DTPAHPTP and PAEA-DTPA-HPTP) were prepared by the incorporation of diethylenetriaminepentaacetic acid (DTPA) and 5-(p-hydroxylphenyl)-10,15, 20-triphenylporphyrin (HPTP) as the tumor-selective group in poly [α,β-(N-(2-hydroxyethyl)-L-aspartamide)] (PHEA) and poly-[α-β-(N-(2-aminoethy1)-L-aspartamide)] (PAEA). These ligands were further complexed with gadolinium chloride to form two tumor-selective macromolecular MRI contrast agents PHEA-Gd-DTPA-HPTP and PAEA-Gd-DTPA-HPTP. Relaxivity studies showed that both the polyaspartamide-gadolinium complexes possess higher relaxation effectiveness than that of the clinically used Gd-DTPA. Magnetic resonance imaging of tumors in mice indicated that these two polyaspartamide MRI contrast agents containing 5-(p-Carbonlyoxyphenyl)-10,15,20-triphenylporphyrin moiety can significantly enhance the contrast MRIs of Hepatoma (H22) and Ehrlich ascites carcinoma after injection and are taken up selectively by these cancers in mice.

Study on the Anticancer Drug 5-Fluorouracil-Conjugated Polyaspartamide Containing Hepatocyte-Targeting Group

Anticancer conjugates of 5-fluorouracil (5-Fu) and polyaspartamide, containing pyridoxamine as the hepatocyte-targeting group, were synthesized and characterized. Their sustained release properties and biodistribution were evaluated. The 5-Fu was targeted to specific organs, such as the liver, and had a sustained in vitro release rate in PBS. In vitro cytotoxicity assay showed that the polymeric drugs exhibited low cytotoxicity to the human liver cells (L-02). These polymeric drugs possess high anticancer efficiencies and induced apoptosis in the human hepatic tumor cells (Bel-7204).

Multifunctional Environmental Smart Fertilizer Based on l-Aspartic Acid for Sustained Nutrient Release

Fertilizer is one of the most important elements of modern agriculture. However, conventional fertilizer, when applied to crops, is vulnerable to losses through volatilization, leaching, nitrification, or other means. Such a loss limits crop yields and pollutes the environment. In an effort to enhance nutrient use efficiency and reduce environmental pollution, an environmental smart fertilizer was reported in the current study. Poly(aspartic acid) and a degradable macro-cross-linker based on l-aspartic acid were synthesized and introduced into the fertilizer as a superabsorbent to improve the fertilizer degradability and soil moisture-retention capacity. Sustained release behavior of the fertilizer was achieved in soil. Cumulative release of nitrogen and phosphorus was 79.8% and 64.4% after 30 days, respectively. The water-holding and water-retention capacities of soil with the superabsorbent are obviously higher than those of the control soil without superabsorbent. For the sample of 200 g of soil with 1.5 g of superabsorbent, the water-holding capacity is 81.8%, and the water-retention capacity remains 22.6% after 23 days. All of the current results in this study indicated that the as-prepared fertilizer has a promising application in sustainable modern agriculture.

A facile method for synthesizing water-soluble and superior sustained release anti-HIV prodrug SCs-d4T

To efficiently deliver stavudine (d4T) for AIDS therapy, chitosan-stavudine conjugate (Cs-d4T) was synthesized. However, its poor water-solubility limited its clinical application. In this study, a sulphonated chitosan-stavudine conjugate (SCs-d4T) was synthesized with a mild SO3·Py complex sulphonation strategy. Chemical characteristics and morphology of Cs-d4T and SCs-d4T were performed by NMR, XRD, FTIR, ICP-AES and SEM. SCs-d4T demonstrated satisfactory solubility (106-bold of Cs-d4T solubility), good anti-HIV activity (6-fold of d4T anti-HIV activity), and well sustained release ability. The major release product O-isopropyl-5'-H-phosphonate of d4T (d4T-P-H) showed higher anti-HIV activity than d4T. For further evaluating the influence of linker and sulphonation strategy on anti-HIV activity, chitosan grafted with d4T by succinyl linker (Cs-sd4T) and SCs-d4T sulphonated by oleum were also prepared. The result showed that the O-isopropyl monophosphate linker of Cs-d4T and SO3·Py complex sulphonation strategy revealed higher anti-HIV activity than succinyl linker of Cs-sd4T and oleum sulphonation strategy, respectively.

Polymeric anti-HIV therapeutics

The scope of this review is to highlight the application of polymer therapeutics in an effort to curb the transmission and infection of the human immunodeficiency virus (HIV). Following a description of the HIV life cycle, the use of approved antiretroviral drugs that inhibit critical steps in the HIV infection process is highlighted. After that, a comprehensive overview of the structure and inhibitory properties of polymeric anti-HIV therapeutic agents is presented. This overview will include inhibitors based on polysaccharides, synthetic polymers, dendritic polymers, polymer conjugates as well as polymeric DC-SIGN antagonists. The review will conclude with a section that discusses the applications of polymers and polymer conjugates as systemic and topical anti-HIV therapeutics.

Self-delivery multifunctional anti-HIV hydrogels for sustained release

None of the clinical trials of anti-HIV gels based on conventional polymers or lipid emulsions has been successful, suggesting the need of new molecular design of the anti-HIV gels. This paper reports the conversion of anti-HIV prodrugs into self-delivery supramolecular hydrogels. By covalently conjugating reverse transcriptase inhibitors to a versatile self-assembly motif, the hydrogelators that self-assemble to form supramolecular nanofibers as the matrices of hydrogels in a weak acidic condition are obtained. Upon the treatment of prostate acid phosphatase (PAP), the hydrogels exhibit drastically enhanced elasticity. The hydrogelators are biocompatible and able to release the inhibitors under physiological condition. The use of the self-assembly motif as a self-delivery agent containing non-steroid anti-inflammatory drug (NSAID) renders this hydrogel to be both anti-inflammatory and anti-HIV. This work illustrates an unprecedented approach for designing multifunctional supramolecular hydrogels that may serve as potential anti-HIV hydrogels for sustained drug release.

Poly(HEMA-Zidovudine) conjugate: a macromolecular pro-drug for improvement in the biopharmaceutical properties of the drug

A macromolecular pro-drug of a known anti-viral agent Zidovudine (AZT) was synthesized and evaluated as a sustained drug delivery system. The pro-drug was synthesized by coupling the drug to 2-hydroxyethyl methacrylate (HEMA) through a succinic spacer to get a monomeric drug conjugate which was polymerized to obtain the polymeric pro-drug. The pro-drug was subjected for in-vitro drug release study in buffers of pH 1.2 and 7.4. The hydrolytic stability of the pro-drug to pepsin was assessed in simulated gastric fluid (SGF, pH 1.2) and to α-chymotrypsin in simulated intestinal fluid (SIF, pH 7.4). The results showed that the drug release from the polymeric backbone takes place in a sustained manner over a period of 24 h, and the amount of drug released was comparatively higher at pH 7.4. Plasmatic hydrolysis studies of succinylzidovudine showed nearly complete release of AZT. At all pH conditions in the presence and absence of α-chymotrypsin, AZT was released preferentially in comparison with the succinyl derivative. The in-vivo release studies in rabbits after oral administration of AZT conjugate demonstrated a sustained release of parent drug over a period of 24 h. The pro-drug provided a significant increase in the area under the plasma concentration time curve as compared to free drug and extended the plasma half-life from 1.06 h to 8.08 h. This study suggested that, after oral administration, the drug-polymer conjugate can release AZT for prolonged periods, thus improving the pharmacokinetics of AZT and decreasing the fluctuation in plasma drug levels that can lead to toxicity.

Synthesis, nanosizing and in vitro drug release of a novel anti-HIV polymeric prodrug: chitosan-O-isopropyl-5'-O-d4T monophosphate conjugate

A novel approach to improve the antiviral efficacy of nucleoside reverse transcriptase inhibitors (NRTIs) and reduce their side effects was developed by constructing a nanosized NRTI monophosphate-polymer conjugate using d4T as a model NRTI. Firstly, a novel chitosan-O-isopropyl-5'-O-d4T monophosphate conjugate with a phosphoramidate linkage was efficiently synthesized through Atherton-Todd reaction under mild conditions. The anti-HIV activity and cytotoxicity of the polymeric conjugate were evaluated in MT4 cell line. Then the conjugate nanoparticles were prepared by the process of ionotropic gelation between TPP and chitosan-d4T conjugate to improve their delivery to viral reservoirs, and their physicochemical properties were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS) techniques and X-ray diffraction (XRD). In vitro drug release studies in pH 1.1 and pH 7.4 suggested that both chitosan-d4T conjugate and its nanoparticles prefer to release d4T 5'-(O-isopropyl) monophosphate than free d4T for prolonged periods, which resulted in the enhancement of anti-HIV selectivity of the polymeric conjugate relative to free d4T due to bypassing the metabolic bottleneck of monophosphorylation. Additionally, the crosslinked conjugate nanoparticles can prevent the coupled drug from leaking out of the nanoparticles before entering the target viral reservoirs and provide a mild sustained release of d4T 5'-(O-isopropyl) monophosphate without the burst release. The results suggested that this kind of chitosan-O-isopropyl-5'-O-d4T monophosphate conjugate nano-prodrugs may be used as a targeting and sustained polymeric prodrugs for improving therapy efficacy and reducing side effects in antiretroviral treatment.

Glycosilated Macromolecular Conjugates of Antiviral Drugs with a Polyaspartamide

Two new polymeric conjugates for specific liver targeting were prepared by conjugation of sugar moieties and antiviral drugs to alpha, beta-poly[N-2-(hydroxyethyl)-DL-aspartamide] (PHEA). PHEA-galactopyranosylphenylthiocarbamide-mono-O-succinylganciclovir (conjugate 7) and PHEA-mannopyranosylphenylthiocarbamide-O-succinylacyclovir (conjugate 8) were synthesized according to a multi-step procedure which allowed for obtaining high product yield and process standardization. Conjugate 7 contained 7.5 and 8.5% of galactose and ganciclovir (substituent/repeating unit, mol/mol), respectively, and conjugate 8 contained 14.2 and 10.8% of mannose and acyclovir, respectively. In vitro studies demonstrated that both acyclovir and ganciclovir are released from the polymeric adducts at a release rate, which depended on the incubation medium. Though a detailed study evidenced that the two bioconjugates undergo different hydrolysis pathways, in both cases high drug release rate was found in plasma, while the glycosidic moiety was not released. Pharmacokinetic studies carried out by intravenous administration of the bioconjugates to Balb/c mice demonstrated that the conjugation of glycosidic moieties promotes the disappearance of the polymer from the bloodstream. The two derivatives displayed a different pharmacokinetic profile. In particular, the mannosyl conjugation promoted the rapid disposition of the macromolecule in the kidneys and in the liver, while prevented the accumulation in the spleen. On the contrary, the galactosyl derivative was found to dispose in the liver at the same extent of the naked polymer. Few considerations on the different behavior of the conjugates were reported.

A novel anti-HIV dextrin-zidovudine conjugate improving the pharmacokinetics of zidovudine in rats

The aim of this study was to investigate a newly synthesized dextrin-zidovudine (AZT) conjugate designed as a sustained release prodrug of AZT for parenteral administration. AZT was first reacted with succinic anhydride to form a succinoylated AZT which was subsequently coupled with dextrin to yield the dextrin-AZT conjugate. The structure of the conjugate was characterized by FT-IR and (1)H-NMR spectroscopy. The drug content of the conjugate was 18.9 wt.%. The release in vitro of free AZT and succinoylated AZT was investigated in buffer solutions at pH 5.5 and 7.4 and in human plasma. AZT and succinoylated AZT release from the conjugate was 1.4% (pH 5.5), 41.7% (pH 7.4) and 78.4% in human plasma after 24 h. Release was complete in human plasma after 48 h. A pharmacokinetic study in rats following intravenous administration of the conjugate showed prolonged plasma levels of AZT compared to free AZT. The use of the conjugate extended the plasma half-life of AZT from 1.3 to 19.3 h and the mean residence time from 0.4 to 23.6 h. Furthermore, the conjugate provided a significant greater area under the plasma concentration-time curve and reduced the systemic clearance of AZT. This study suggested the potential of this novel dextrin-AZT conjugate as a new intravenous preparation of AZT.

Self-assembled drug delivery systems 2. Cholesteryl derivatives of antiviral nucleoside analogues: synthesis, properties and the vesicle formation

Self-assembled drug delivery systems (SADDS) are defined as the self-aggregates of amphiphilic prodrugs. Prodrug, molecular self-assembly and nanotechnology are involved in SADDS manufacturing. But the knowledge of the self-assembly of amphiphilic prodrugs and the formation rules of SADDS is very limited. In this paper, five cholesteryl derivatives of antiviral nucleoside analogues were synthesized, involving antiviral acyclovir, didanosine and zidovudine, and the different acyl linkers, succinyl, adipoyl and phosphoryl. The derivatives are typical amphiphiles with nucleosides as polar heads and long-chained lipids as hydrophobic tails. The derivatives showed the similar soluble behavior, and the solubility highly depended on the types of solvents. Two forces, hydrogen bonding and hydrophobic interaction in alcohol solutions could improve the derivatives dissolving. However, the molecular self-assembly of derivatives could prefer to happen in the noncompetitive solvents including chloroform and tetrahydrofuran (THF) based on the intermolecular hydrogen bonding between nucleobase moieties, which could greatly increase their solubility. The derivatives formed nanosized vesicles based on hydrophobic interaction after injecting their THF solutions into water. The volume ratios of polar heads and hydrophobic tails of amphiphiles could determine the vesicle size, and the amphiphiles with large ratios would prefer to form small vesicles. The self-assembled vesicles would likely become SADDS.

An efficient vector for gene delivery: α,β-poly (3-dimethylaminopropyl-d,l-aspartamide)

PSI, as the potential peptide-like intermediate, is subject to simple chemical modification in order to obtain good non-viral carriers for gene delivery. This paper describes the facile synthesis and preliminary evaluation of alpha,beta-poly (3-dimethylaminopropyl-D,L-aspartamide) (PDAI) as a vector. Reaction of PSI with 3-dimethylamino-1-propylamine afforded PDAI in N,N-dimethylformamide (DMF) solution. Such biophysical properties of PDAI/DNA complexes as the particle size and the zeta potential were determined by dynamic light scattering assay. The complexes prepared at weight ratios ranging from 2 to 3 have an average size of around 200 nm and a zeta potential of around 10.0 mV. Gel electrophoresis assays confirmed that PDAI could compact DNA to form the complexes and protect DNA from enzymatic degradation by DNase I at the weight ratio above 2.0. Furthermore, PDAI was found to transfect HepG2 cells at a much higher efficiency than commercially available polyethylenimine (PEI) (W(w)=75,000 Da). MTT cytotoxicity assay demonstrated that PDAI also showed much less toxicity than did PEI, suggesting that PDAI is a new class of transfection reagent to be used as a safe vector.

Recent advances in delivery systems for anti-HIV1 therapy

In the last years, different non-biological and biological carrier systems have been developed for anti-HIV1 therapy. Liposomes are excellent potential anti-HIV1 carriers that have been tested with drugs, antisense oligonucleotides, ribozymes and therapeutic genes. Nanoparticles and low-density lipoproteins (LDLs) are cell-specific transporters of drugs against macrophage-specific infections such as HIV1. Through a process of protein transduction, cell-permeable peptides of natural origin or designed artificially allow the delivery of drugs and genetic material inside the cell. Erythrocyte ghosts and bacterial ghosts are a promising delivery system for therapeutic peptides and HIV vaccines. Of interest are the advances made in the field of HIV gene therapy by the use of autologous haematopoietic stem cells and viral vectors for HIV vaccines. Although important milestones have been reached in the development of carrier systems for the treatment of HIV, especially in the field of gene therapy, further clinical trials are required so that the efficiency and safety of these new systems can be guaranteed in HIV patients.

Synthesis and in vitro antitumor effect of diclofenac and fenoprofen thiolated and nonthiolated polyaspartamide-drug conjugates

This paper reports the synthesis and antiproliferative effects of new thiomer-diclofenac and fenoprofen conjugates, hydrophilic, bioadhesive, polymeric prodrugs, as well as antiproliferative effects of diclofenac, fenoprofen and a series of previously described polymer-fenoprofen conjugates on five tumor cell lines. Thiolated and nonthiolated polyaspartamides were the chosen polymeric components. Drug-loading ranged from 5.6 to 22.4%, and the amount of SH groups ranged from 6.9 to 45.6micromol g(-1). Tensile studies demonstrated a clear correlation between the amount of thiol and the mucoadhesive properties of the conjugates. The growth-inhibitory activity of the tested polymer-drug conjugates demonstrates that polyaspartamide-type polymers, especially thiolated polymers, enable inhibition of tumor cell growth with significantly lower doses of the active substance.

Synthesis of poly(ethylene glycol)-metaxalone conjugates and study of its controlled release in vitro

Metaxalone (Met), a drug for treatment of pain and stiffness due to muscular injuries, was covalently linked to poly(ethylene glycols) (PEG) via a chloroacetyl chloride spacer. The average weight molecular weights used for PEG are 4000, 6000 and 10,000, respectively, and the procedure of chemical modification for PEGs was conducted by a two-step protocol: (1) synthesis of N-chloroacetyl-metaxalone; (2) synthesis of PEG(4000)-Met, PEG(6000)-Met and PEG(10000)-Met. The controlled drug release studies were performed in buffer solutions with pH values equal to 1.1, 7.4 and 10.0. The results demonstrate that, in the same condition, the rate of hydrolysis for PEG(10000)-Met is the slowest among three prodrugs, and more amount of metaxalone can be detected releasing from prodrug matrices at the presence of alpha-chymotrypsin in a buffer solution with pH 8.0. It was also found that these novel prodrugs can effectively improve the metaxalone's pharmacokinetics, and furthermore can markedly increase its half-life period.

Bioadhesive Properties of a Polyaminoacidic Hydrogel: Evaluation by ATR FT-IR Spectroscopy

The bioadhesive properties of a novel chemical hydrogel based on a polymer of protein-like structure, have been investigated by using ATR FT-IR spectroscopy. In particular, the copolymer PHG obtained by partial derivatization of PHEA with GMA was chemically crosslinked by UV irradiation at 313 nm. Crosslinked PHG was treated with water to obtain a swelled sample, named PHG-UV gel, that was brought into contact with a phosphate buffer/citric acid solution at pH 7.0 in the absence or in the presence of mucin at various concentrations (0.01, 0.1 and 1 wt.-%). Preliminary dynamic swelling studies have evidenced the occurrence of an interaction between the PHG-UV gel and the glycoprotein. This result was confirmed by ATR FT-IR measurements. A diffusion model using a solution of Ficks' second law was employed to determine the diffusion coefficient of water into PHG-UV gel as a consequence of adsorption and/or interdiffusion which occur at the PHG-UV gel/mucin solution interface. Experimental results suggest a potential use of PHG-UV gel to prepare bioadhesive devices.

Polyaspartamide Gadolinium Complexes Containing Sulfadiazine Groups as Potential Macromolecular MRI Contrast Agents

Both diethylenetriaminepentaacetic acid (DTPA) and sulfadiazine (SD) were incorporated into polyaspartamides with different side chains, including poly-alpha,beta-[N-(2-hydroxyethyl)-L-aspartamide] (PHEA), poly-alpha,beta-[N- (3-hydroxypropyl)-L-aspartamide] (PHPA), poly-alpha,beta-[N-(2-aminoethy1)-L-aspartamide] (PAEA), poly-alpha,beta-[N-(4-aminobuty1)-L-aspartamide] (PABA), and poly-alpha,beta-[N-(6-aminohexyl)-L-aspartamide] (PAHA). The polyaspartamide ligands containing DTPA and SD groups were further reacted with gadolinium chloride to give the corresponding macromolecular gadolinium complexes. Experimental data of 1H NMR, IR, UV, and elemental analysis exhibited the formation of the polyaspartamide ligands and gadolinium complexes. Relaxivity studies indicated that the macromolecular chelates possess higher relaxivities than that of the clinically used Gd-DTPA. MR imaging showed that the macromolecular chelate PAEA-Gd-DTPA-SD greatly enhanced the contrast of MR images of hepatoma in the lower limb of mice and provided prolonged intravascular duration. Thus the polyaspartamide gadolinium complex containing SD groups is expected to be used as the potential macromolecular MRI contrast agents for hepatoma in mice.

Macromolecular prodrugs XI. Synthesis and characterization of polymer-estradiol conjugate

Estradiol-3-benzoate (EB), an ester derivative of the main oestrogen hormone estradiol, was chemically modified and bound to poly(alpha,beta-(N-2-hydroxyethyl-DL-aspartamide))-poly(alpha,beta-(N-2-aminoethyl-DL-aspartamide)) copolymer (PAHA). EB was first converted to estradiol-3-benzoate-17-(benzotriazole-1-carboxylate), which readily reacted with amino groups in PAHA affording the polymer-drug conjugate PAHA-EB. In PAHA-EB estradiol moiety was covalently bound to the polymeric carrier by carbamate linkage, through non-toxic ethylenediamine spacer. The synthesized compound is a potential hydrosoluble estradiol prodrug.

Synthesis and characterization of thiomers of polyaspartamide type

Synthesis of poly[alpha,beta-(N-2-hydroxyethyl-DL-aspartamide)]-thioglycolic acid (PHEA-TGA) conjugate as a new polyaspartamide thiomer is described. The parent polymer PHEA is chemically modified by introducing sulphydryl-bearing compound thioglycolic acid. By varying the reaction conditions several batches of PHEA-TGA conjugates were prepared and analyzed. Tensile studies revealed that total work of adhesion of PHEA-TGA increased more than twice compared to the unmodified polymer. Microparticles prepared from the thiolated polymer preserved its bioadhesive properties.

Tamoxifen-loaded polymeric micelles: preparation, physico-chemical characterization and in vitro evaluation studies

Several samples of polymeric micelles, formed by amphiphilic derivatives of PHEA, obtained by grafting into polymeric backbone of PEGs and/or hexadecylamine groups (PHEA-PEG-C(16) and PHEA-C(16)) and containing different amount of Tamoxifen, were prepared. All Tamoxifen-loaded polymeric micelles showed to increase drug water solubility. TEM studies provided evidence of the formation of supramolecular core/shell architectures containing drug, in the nanoscopic range and with spherical shape. Samples with different amount of encapsulated Tamoxifen were subjected to in vitro cytotoxic studies in order to evaluate the effect of Tamoxifen micellization on cell growth inhibition. All samples of Tamoxifen-loaded polymeric micelles showed a significantly higher antiproliferative activity in comparison with free drug, probably attributable to fluidification of cellular membranes, caused by amphiphilic copolymers, that allows a higher penetration of the drug into tumoral cells. To gain preliminary information about the potential use of prepared micelles as Tamoxifen drug delivery systems, studies evaluating drug release ability of micelle systems in media mimicking biological fluids (buffer solutions at pH 7.4 and 5.5) and in human plasma were carried out. These studies, performed evaluating the amount of Tamoxifen that remains in solution as a function of time, showed that at pH 7.4, as well as in plasma, PHEA-C(16) polymeric micelles were able to release lower drug amounts than PHEA-PEG(5000)-C(16) ones, while at pH 5.5, the behavior difference between two kind of micelles was less pronounced.

Poly(hydroxyethylaspartamide) derivatives as colloidal drug carrier systems

Poly(hydroxyethylaspartamide) (PHEA) derivatives bearing at the polyaminoacidic backbone poly(ethyleneglycol) (2000 or 5000 Da) or both poly(ethyleneglycol) and hexadecylalkylamine as pendant moieties were investigated as polymeric colloidal drug carriers. The ability of the PHEA derivatives to solubilize hydrophobic drugs was investigated using paclitaxel, amphotericin B and methotrexate. The results demonstrated that the drug solubility depends on both macromolecule composition and drug physicochemical properties. In particular, PEG/hexadecylalkylamine co-grafting increased significantly the solubilization properties of PHEA for the considered drugs while the conjugation of PEG only did not endow PHEA with drug carrier properties. A stability study carried out with paclitaxel/PHEA-PEG(5000)-hexadecylalkylamine demonstrated that the drug/carrier system is characterized by physicochemical instability, which is strictly related to the incubation pH. However, the carrier was found to partially prevent drug degradation. Investigations performed using murine myeloid leukaemia NFS-60 cell line showed that paclitaxel loaded PHEA-PEG(5000)-hexadecylalkylamine possesses high pharmacological activity with IC(50) value of 22.3 ng/ml. Pharmacokinetic studies carried out by intravenous administration of paclitaxel loaded PHEA-PEG(5000)-hexadecylalkylamine to Balb/c mice demonstrated that the carrier modifies the in vivo paclitaxel fate. In particular, PHEA-PEG(5000)-hexadecylalkylamine prolonged the drug distribution and elimination phase of 6 and 17 times, respectively; in addition, it increased the systemic availability (AUC) by about 30 times.

Gemfibrozil encapsulation and release from microspheres and macromolecular conjugates

The purpose of this study was to evaluate and compare the ability of the macromolecular conjugates and microspheres to modify the release rate of gemfibrozil (Gem). Gem was covalently linked to two similar polymers: poly[alpha,beta-(N-2-hydroxyethyl-DL-aspartamide)] (PHEA) and poly[alpha,beta-(N-3-hydroxypropyl-DL-aspartamide)] (PHPA) by an ester linkage. The polymer-drug conjugates obtained (PHEA-G(1-3) and PHPA-G) differ in weight-average molecular weight, length of spacer and Gem content. Microspheres, composed of chitosans of different molecular weight alone or as a mixture with (2-hydroxypropyl)methylcellulose (HPMC), PHEA or PHPA and with different theoretical polymer/drug ratio (2:1 and 3:1, w/w) were prepared by spray drying. The microparticulate systems were morphologically characterised by scanning electron microscopy, particle size analysis and Gem content was determined. In vitro dissolution tests were performed to evaluate the feasibility of conjugates and microspheres in modulating Gem release. The results obtained show that microspheres are always suitable to modulate Gem release and that the best conditions are achieved by microspheres composed of the low molecular weight chitosan (CL) combined with PHPA or HPMC with either 2:1 or 3:1 (w/w) polymer/drug ratio. The PHEA-G conjugates exhibited rapid Gem release within less than 2 h, while the PHPA-G conjugate showed sustained Gem release profiles over a 10-h period.