pH-Sensitive Amphiphilic Diblock Polyphosphoesters with Lactate Units: Synthesis and Application as Drug Carriers.

pH-sensitive amphiphilic diblock polyphosphoesters containing lactic acid units were synthesized by multistep one-pot polycondensation reactions. They comprise acid-labile P(O)-O-C and C(O)-O-C bonds, the cleavage of which depends on the pH of the medium. The structure of these copolymers was characterized by 1H, 13C {H}, 31P NMR, and size exclusion chromatography (SEC). The newly synthesized polymers self-assembled into the micellar structure in an aqueous solution. The effects of the molecular weight of the copolymer and the length of the hydrophobic chain on micelle formation and stabilityand micelle size were studied via dynamic light scattering (DLS). Drug loading and encapsulation efficiency tests using doxorubicin revealed that hydrophobic drugs can be delivered by copolymers. It was established that the molecular weight of the copolymer, length of the hydrophobic chain and content of lactate units affects the size of the micelles, drug loading, and efficiency of encapsulation. A copolymer with 10.7% lactate content has drug loading (3.2 ± 0.3) and efficiency of encapsulation (57.4 ± 3.2), compared to the same copolymer with 41.8% lactate content (1.63%) and (45.8%), respectively. It was demonstrated that the poly[alkylpoly(ethylene glycol) phosphate-b-alkylpoly(ethylene glycol)lactate phosphate] DOX system has a pH-sensitive response capability in the result in which DOX was selectively accumulated into the tumor, where pH is acidic. The results obtained indicate that amphiphilic diblock polyphosphoesters have potential as drug carriers.

Phosphoric Acid Triester Micelles: Characterization and Self-Assembly.

In this study, we analyzed the properties of amphiphilic alkyldi(methoxy poly(ethylene glycol) (MePEG)350-lactate) phosphates based on ethyl lactate, the monomethyl ether of poly(ethylene glycol)350, and alkyldichloro phosphates. Interestingly, these triesters combine two biodegradable bonds, -P(O)-O-C and -C(O)-O-C-, and include hydrophilic (MePEG350-lactate) and hydrophobic (R-aliphatic chain of alcohols) moieties. The properties of these esters resemble those of phospholipids. After being placed in an aqueous solution, they self-assembled. We also determined the effects of ester composition on micelle formation, stability, and size using dynamic light scattering. Solubilization tests using Sudan III or doxorubicin hydrochloride (Dox·HCl) revealed that they could be incorporated into the hydrophobic cores of dodecyl di(MePEG350-lactate) phosphate and hexadecyl di(MePEG350-lactate) phosphate. Notably, dodecyl di(MePEG350-lactate) phosphate was stable for five days, whereas hexadecyl di(MePEG350-lactate) phosphate was stable for seven days in phosphate-buffered saline. Moreover, Dox·HCl release rates from the micelles were approximately 30-40, 70-80, and 90-100% after 1, 5, and 28 d, respectively.

Synthesis and Characterization of Amphiphilic Diblock Polyphosphoesters Containing Lactic Acid Units for Potential Drug Delivery Applications.

Multistep one-pot polycondensation reactions synthesized amphiphilic diblock polyphosphoesters containing lactic acid units in the polymer backbone. At the first step was synthesized poly[poly(ethylene glycol) H-phosphonate-b-poly(ethylene glycol)lactate H-phosphonate] was converted through one pot oxidation into poly[alkylpoly(ethylene glycol) phosphate-b-alkylpoly(ethylene glycol)lactate phosphate]s. They were characterized by 1H, 13C {H},31P NMR, and size exclusion chromatography (SEC). The effects of the polymer composition on micelle formation and stability, and micelle size were studied via dynamic light scattering (DLS). The hydrophilic/hydrophobic balance of these polymers can be controlled by changing the chain lengths of hydrophobic alcohols. Drug loading and encapsulation efficiency tests using Sudan III and doxorubicin revealed that hydrophobic substances can be incorporated inside the hydrophobic core of polymer micelles. The micelle size was 72-108 nm when encapsulating Sudan III and 89-116 nm when encapsulating doxorubicin. Loading capacity and encapsulation efficiency depend on the length of alkyl side chains. Changing the alkyl side chain from 8 to 16 carbon atoms increased micelle-encapsulated Sudan III and doxorubicin by 1.6- and 1.1-fold, respectively. The results obtained indicate that these diblock copolymers have the potential as drug carriers.

Thermoresponsive Polyphosphoester via Polycondensation Reactions: Synthesis, Characterization, and Self-Assembly.

Using a novel strategy, amphiphilic polyphosphoesters based on poly(oxyethylene H-phosphonate)s (POEHP) with different poly(ethylene glycol) segment lengths and aliphatic alcohols with various alkyl chain lengths were synthesized using polycondensation reactions. They were characterized by 1H NMR, 13C {H} NMR 31P NMR, IR, and size exclusion chromatography (SEC). The effects of the polymer structure on micelle formation and stability, micelle size, and critical micelle temperature were studied via dynamic light scattering (DLS). The hydrophilic/hydrophobic balance of these polymers can be controlled by changing the chain lengths of hydrophilic PEG and hydrophobic alcohols. A solubilizing test, using Sudan III, revealed that hydrophobic substances can be incorporated inside the hydrophobic core of polymer associates. Loading capacity depends on the length of alkyl side chains. The results obtained indicate that these structurally flexible polymers have the potential as drug carriers.

Poly(Alkyloxyethylene-Lactate Phosphate) for Delivery of Doxorubicin: Synthesis and Characterization.

BACKGROUND/AIM: Serious side effects are associated with the use of doxorubicin. Nanoparticles as carriers for anticancer drugs are useful for reducing side effects and improving therapeutic effects. In this study, a polymer for preparing doxorubicin-containing nanoparticles was developed. Using a novel strategy, a biodegradable poly(oxyethylene glycol lactate H-phosphonate) based on dimethyl H-phosphonate and poly(ethylene glycol)-lactate (PEG-lactate) was synthesized. MATERIALS AND METHODS: Poly(hexadecanyloxyethylene - lactate phosphate) was obtained via chlorination of poly(oxyethylene glycol - lactate H-phosphonate) with trichloroisocyanuric acid and the addition of 1-hexadecanol. The polymer was characterized by 1H NMR and 31P NMR. RESULTS: The results of 1H NMR and 31P NMR showed that the polymer was successfully synthesized, and the yield was 46.9%. CONCLUSION: Poly(hexadecanyloxyethylene - lactate phosphate) has potential as a drug carrier.

Polyphosphoester-based Paclitaxel Complexes: Biological Evaluation.

BACKGROUND: Polymer drug delivery systems designed to reduce systemic side-effects are clinically important. Polyphosphoesters are biodegradable polymers with versatile structure that could afford reactive sites or polar functions for drug immobilization. MATERIALS AND METHODS: The drug-polyphosphester systems were characterized by nuclear magnetic resonance and infrared spectroscopy, differential scanning calorimetry and dynamic light scattering. In vitro and in vivo experiments were performed to assess the biological activity of the immobilized drug. RESULTS: Two water-soluble polyphosphoester-based delivery systems of paclitaxel were synthesized. The conjugate with paclitaxel covalently bonded to the polymer, had attenuated activity in vitro. The second system comprised of macromolecular aggregates incorporating the drug via hydrogen bonding. The physical complex achieved a certain level of antitumor activity in vivo and no decrease of body weight - evidence for reduction of the systemic toxic effect associated with paclitaxel treatment. CONCLUSION: The physical complex was found to be a promising carrier for delivery of toxic anticancer agents, e.g. paclitaxel.

Polymer complex of WR 2721. Synthesis and radioprotective efficiency.

Polymer complex constructed from WR 2721 and poly(hydroxyoxyethylene phosphate) was synthesized. The structure of complex formed was elucidated by (1)H-, (13)C, (31)P NMR and FT-IR spectroscopy. The radioprotector was immobilized via ionic bonds. Radioprotective efficacy was evaluated by clonal survival of stem cells in crypts of mouse small intestine, and incidence and latency of the acute radiation induced bone marrow syndrome. Protection factors were assessed for WR 2721 and for the polymer complex. Protection factors for the polymer complex ranged from 2.6 for intestinal stem cell survival to 1.35 for 30 day survival (LD50) following whole body radiation exposure. In all cases, the polymer complex was a significantly better radiation protector than the parent compound.

Low cytotoxicity and clastogenicity of some polymeric aminophosphonate derivatives.

Poly(oxyethylene aminophosphonate)s synthesized on the basis of biodegradable poly(phosphorester)s and Schiff bases were tested in vitro for antitumor activity against a panel of six human epithelial cancer cell lines, for cytotoxicity to mouse fibroblast cells and in vivo for clastogenicity and antiproliferative effects. The polymers showed lower cytotoxicity, both in vivo and in vitro and lower clastogenicity in vivo than the corresponding low-molecular aminophosphonates. The biological activities of the tested polymers correlate with their low in vitro antitumor activity.

Polyphosphoester conjugates of dinuclear platinum complex: synthesis and evaluation of cytotoxic and the proapoptotic activity.

Macromolecular conjugates of a dinuclear platinum complex with a spermidine bridge were synthesized using poly(oxyethylene H-phosphonate)s as precursor polymer. The complex species were attached to the polymer chain via a phosphoramide bond resulting from the reaction between the H-phosphonate groups and the middle amino group of the spermidine moiety. (1)H and (31)P{H} DOSY NMR spectral data were used to prove the conjugation reaction and to characterize the new species. The conjugates exhibited profound cytotoxicity in a panel of five chemosensitive human tumor cell lines and one cisplatin-resistant model (HL-60/CDDP), and were found to induce apoptotic cell death. A flow cytometric analysis encountered a cisplatin-dissimilar modulation of the cell cycle progression in KG-1 leukemic cells, following exposure to the dinuclear agents. Moreover, the novel compounds displayed less pronounced inhibitory activity against cultured murine renal epithelial cells, as compared to cisplatin.

A polyphosphoester conjugate of melphalan as antitumoral agent.

The low molecular weight of many chemotherapeutics causes their untargeted distribution in the body and fast renal clearance, which leads to a loss of therapeutic activity and to unspecific toxic side effects. Therefore, there is a growing interest in conjugating anticancer drugs to water soluble polymers and thus, take advantage of the 'enhanced permeability and retention' (EPR) effect in tumors. In this study, water soluble polyphosphoesters were used as polymer carriers of melphalan hydrochloride (hydrochloride of p-bis(2-chloroethyl)amino-L-phenylalanine), which is a multifunctional alkylating agent. Melphalan was chemically immobilized by covalent bonding to poly(oxyethylene H-phosphonate) under Atherton-Todd reaction conditions. Novel polymer-melphalan complexes with ionic and hydrogen bonds were designed as controls, basing on two other biodegradable polyphosphoesters: poly(hydroxyoxyethylene phosphate) and poly(methyloxyethylene phosphate). The structure of the formed products was elucidated by (1)H, (13)C, (31)P NMR and FT-IR spectroscopy. The cytotoxic effect of the melphalan formulations was evaluated on different tumor cell lines. The novel polymer formulations showed a concentration dependent antitumoral activity, comparable to the effect of unmodified melphalan. The polymer-melphalan conjugate was also evaluated in vivo in the human hepatocellular carcinoma HuH7 xenograft mouse model. It improved the therapeutic efficacy of pure melphalan without causing side effects.

In vitro antitumour activity, genotoxicity, and antiproliferative effects of aminophosphonic acid diesters and their synthetic precursors.

The Schiff bases N-furfurylidene-p-toluidine and N-(4-dimethylaminobenzilidene)-p-toluidine, and the recently synthesized aminophosphonic acid diesters p-[N-methyl-(diethoxyphosphonyl)-(2-furyl)]toluidine and p-[N-methyl(diethoxyphosphonyl)-(4-dimethylaminophenyl)]toluidine were tested for in vitro antitumour activity on six human epithelial cancer cell lines. The genotoxicity and antiproliferative activity of these compounds were tested in mice. The aminophosphonates showed high in vitro antitumour activity towards the breast cancer-derived cell lines (MCF-7 and MDA-MB-231), the cervical carcinoma cell line (HeLa), and the human colon adenocarcinoma cell line (HT-29). In addition, the Schiff base N-furfurylidene-p-toluidine significantly inhibited the growth of bladder carcinoma cells (647-V) and the hepatocellular carcinoma line HepG2, and U-shaped dose-response curves were observed after treatment of 647-V and MCF-7 cells. All studied compounds had a moderate genotoxic and antiproliferative activity in vivo.

Diethyl [(9-anthr-yl)(4-methyl-anilino)meth-yl]phospho-nate.

The title compound, C(26)H(28)NO(3)P, crystallized with two independent mol-ecules in the asymmetric unit. The structural features (bond lengths and angles) of the two mol-ecules are almost identical. The inter-planar angle between the anthracene and toluidine rings is similar in the two mol-ecules, with values of 82.92 (5) and 80.70 (5)°. In the crystal, both molecules form inversion dimers linked by pairs of N-H⋯O hydrogen bonds. Three of the four ethyl groups are disordered over two sets of sites, the major components having occupancies of 0.748 (15), 0.77 (4) and 0.518 (19).

rac-Dimethyl [(9-anthr-yl)(4-methyl-anilino)meth-yl]phospho-nate.

The title compound, C(24)H(24)NO(3)P, crystallizes as a racemate with two mol-ecules in the asymmetric unit. The structural features (bond lengths and angles) of the two mol-ecules are almost identical. The dihedral angle between the anthracene and toluidine rings is similar in the two mol-ecules, with values of 48.36 (9) and 51.15 (9)°. The methyl groups of one of the meth-oxy groups in one mol-ecule is disordered over two sets of sites, the major component having a site occupancy of 0.636 (3). In the crystal, both molecules are linked into inversion dimers by pairs of N-H⋯O hydrogen bonds.

Recent synthesis of aminophosphonic acids as potential biological importance.

Aminophosphonic acids are an important group of medicinal compounds, and their synthesis has been a focus of considerable attention in synthetic organic chemistry as well as medicinal chemistry. Although the phosphonic and carboxylic acid groups differ considerably with respect to shape, size, and acidity, alpha-aminophosphonic acids are considered to be structural analogues of the corresponding amino acids and the transition state mimics peptide hydrolysis. This review summarizes recent developments in the synthesis, characterization and biological activity of alpha-aminophosphonic acid and N-analogues. An account of both uses will be presented, emphasizing one of the potential future developments, and some implications in medicinal chemistry are also disclosed. In addition, a brief account on the characterization of N-(phosphonomethyl) glycine derivatives will be presented.

HPLC study on the stability of bendamustine hydrochloride immobilized onto polyphosphoesters.

Novel water soluble polymer complexes of bendamustine hydrochloride, a bifunctional alkylating agent with antimetabolic and cytotoxic activity, were developed using biodegradable polymer carriers-poly(oxyethylene H-phosphonate), poly(methyloxyethylene phosphate) and poly(hydroxyoxyethylene phosphate). Bendamustine hydrochloride was immobilized onto polyphosphoesters via covalent, ionic and hydrogen bonding. The structure of the complexes formed was elucidated by (1)H, (13)C, (31)P NMR and FT-IR spectroscopy. The chemical stability of bendamustine hydrochloride in the novel complexes was studied by HPLC analysis based on a validated method with appointed analytical parameters such as specificity, repeatability, limit of quantitation, limit of detection and linearity. The results from the HPLC indicate that in neutral (pH 7) and alkaline (pH 9) media bendamustine hydrochloride in the polymer complexes is more stable than the pure bendamustine hydrochloride. The enhanced stability of the immobilized drug is explained with the drug interaction with the polymer carriers or their degradation products.

Novel N-(phosphonomethyl) glycine derivatives: Design, characterization and biological activity.

A series of Calpha,alpha-disubstituted cyclic derivatives of N-(phosphonomethyl) glycine have been synthesized and characterized. They exhibited moderate clastogenicity, low antiproliferative activity on mice bone marrow cells and well expressed cytotoxicity against human tumor cell lines. The 8- and 12-membered cyclic analogs proved superior to the remaining compounds and were found to trigger apoptotic cell death in DOHH-2 cells. The latter compound caused 50% inhibition of the viability of hemobastose-derived cell lines at concentrations ranging from 20 to 67 microM.

[(4,4-Dimethyl-2-oxo-1,3-oxazolidin-3-yl)methyl]phosphonic acid.

The title compound, C6H12NO5P, was synthesized as an intermediate phase in a search for new N-(phosphonomethyl)glycine derivatives. The molecules are held together by O-H...O hydrogen bonds, forming chains along the b axis in the crystal structure. The observed molecular structure is compared with that calculated by the density functional theory method.

Novel alpha-aminophosphonic acids. Design, characterization, and biological activity.

Novel alpha-aminophosphonic acids are synthesized reacting 1,3-oxazolidin-2-one derivatives with formaldehyde and phosphorus trichloride. Treatment of N-(phosphonomethyl)oxazolidinones with aqueous NaOH gave the expected alpha-aminophosphonic acids. The oxidation of (2-hydroxy-1,1-dimethylethylamino)methyl phosphonic acid in the presence of CdO and water resulted in N-phosphonomethyl-2-methyl-1-propanoic acid. Their structures were proved by means of IR, 1H, 13C, and 31P NMR spectroscopy. The genotoxic, clastogenic, and antiproliferative effects of newly synthesized original aminophosphonic acids were investigated for the first time.

Immobilization of aminothiols on poly(oxyalkylene phosphates). Formation of poly(oxyethylene phosphates)/cysteamine complexes and their radioprotective efficiency.

The necessity to apply near-toxic amounts of radioprotective drugs to achieve adequate protection during radiation treatments represents a major problem in human medicine. One of the promising strategies to suppress the toxicity of these drugs involves their incorporation into biocompatible polymers. In this study cysteamine (Cy) was attached to poly(oxyethylene phosphate), POEP, via an ionic bond. Radioprotection of E. coli B cells by this substance and its acute toxicity on male C57 BL mice were measured. The toxicity of Cy immobilized within the poly(oxyethylene phosphate) was significantly lower in comparison to pure Cy while its radioprotective efficiency remained high at half the maximum tolerable dose. The high radioprotective efficiency of the Cy/POEP complexes was further confirmed on mice at different polymer molecular weight characteristics, drug immobilization degrees, application times, and doses. It was found that POEP with molecular weight 4700 Da and containing 24% repeating units with attached Cy has the highest protection potential combined with a depot effect.