Water-soluble Paclitaxel Research Articles

Synthesis of Ester-Linked Paclitaxel-Glycoside Conjugate as a Water-Soluble Paclitaxel Derivative—Maltoside Modification of Paclitaxel through Ester-Linker (Ester-Spacer)

To synthesize a water-soluble paclitaxel derivative, the anomers of diols of allyl 2,3,4-tri- O-benzyl-6- O-tritylglycoside (maltoside) were prepared, which can be separated by chromatographic procedure. One anomer was converted into α-glycosyloxyacetic acid (maltosyloxyacetic acid) by oxidative cleavage of the diol and subsequent oxidation. Ester-linked paclitaxel-glycoside conjugate, 7-glycolylpaclitaxel 2″- O-α-maltoside, was provided by condensation of 2′-TES paclitaxel with α-glycosyloxyacetic acid (maltosyloxyacetic acid) followed by deprotection of hydroxy groups.

Utilization of green formulation technique and efficacy estimation on cell line studies for dual anticancer drug therapy with niosomes.

The aim of the present study was to prepare niosome formulations for the simultaneous encapsulation, dual drug therapy, of two anticancer drugs by the ecological probe sonication method. Poloxamer and sorbitan monostearate were used as surface active agents in niosomes, and the water soluble doxorubicin and poorly-water soluble paclitaxel were used as anticancer drugs. Thorough physicochemical analysis were performed for the niosomes, and their cytotoxicity and activity were evaluated on MCF-7 and PC3-MM2 cancer cell lines. Prepared niosomes were small in size with sizes ranging from 137 nm to 893 nm, and entrapment efficiencies were high, ranging from 91.24% to 99.99%. During the four weeks stability testing, the particle size remained stable. The niosomal formulations showed in vitro sustained drug release profiles for doxorubicin and clearly increased the dissolution rate of poorly water soluble paclitaxel. The incorporation of both the drugs into niosomes improved cell penetration and antiproliferative activity of the drugs PC3-MM2 cell lines. As a conclusion, doxorubicin and paclitaxel loaded niosome formulations resulted in relatively stable, small sized niosomes with improved drug release profiles, low toxicity, better cell penetration and antiproliferative activity. The niosomes showed synergistic effect due to the presence of both drugs, which can overcome multidrug resistance.

Nanoformulated water-soluble paclitaxel to enhance drug efficacy and reduce hemolysis side effect.

Surgery, chemotherapy, and radiotherapy are the three top cancer treatment modalities. Paclitaxel (PTX) is one of the most widely used chemotherapy drugs. However, its clinical applications have been significantly limited due to: (i) serious hemolysis effect of currently available commercial paclitaxel formulations and (ii) its water insolubility. An easy way to deliver paclitaxel by a new nanocarrier system using pluronic copolymers of P123/F68 and Sorbitan monopalmitate (Span 40) was reported in our previous research article. The characterization of the formulation and analysis of drug release and cellular uptake were also presented. In this article, we reported discoveries of our follow-up invivo antitumor and invitro hemolytic study discoveries. The experimental results showed that the nanoformulated PTX achieved much better tumor suppression performance while reducing hemolysis side effects. This newly formulated drug can significantly improve patient outcomes in cancer chemotherapy.

Paclitaxel–Nanodiamond Nanocomplexes Enhance Aqueous Dispersibility and Drug Retention in Cells

Nanodiamonds (NDs) with 5 nm crystalline structures have been recognized as emerging carbon delivery vehicles due to their biocompatible inertness, high surface-to-volume ratio, and energy absorbance properties. In this study, carboxylated nanodiamond (ND-COOH) was reduced to hydroxylated nanodiamond (ND-OH) for stable and pH-independent colloidal dispersity. The poorly water-soluble paclitaxel (PTX) was physically loaded into ND-OH clusters, forming amorphous PTX nanostructure on the interparticle nanocage of the ND substrate. Stable physical PTX loading onto the ND substrate with stable colloidal stability showed enhanced PTX release. ND-OH/PTX complexes retained the sustained release of PTX by up to 97.32% at 70 h, compared with the 47.33% release of bare crystalline PTX. Enhanced PTX release from ND substrate showed low cell viability in Hela, MCF-9, and A549 cancer cells due to sustained release and stable dispersity in a biological aqueous environment. Especially, the IC50 values of ND-OH/PTX complexes and PTX in Hela cells were 0.037 μg/mL and 0.137 μg/mL, respectively. Well-dispersed cellular uptake of suprastructure ND-OH/PTX nanocomplexes was directly observed from the TEM images. ND-OH/PTX nanocomplexes assimilated into cells might provide convective diffusion with high PTX concentration, inducing initial necrosis. This study suggests that poorly water-soluble drugs can be formulated into a suprastructure with ND and acts as a highly concentrated drug reservoir directly within a cell.

Synthesis of pH-sensitive, water-soluble paclitaxel prodrugs based on norbornene-functional polylactide by copper-free click chemistry

ABSTRACTIn this study, a novel polymeric prodrug based on norbornene-functional polylactide with functionalized paclitaxels (LEV-PTXL) covalently conjugated to water-soluble polymer carrier via a pH-sensitive hydrazone bond was developed. A series of water-soluble PTXL prodrugs with decent drug contents of 17.3 and 24.7 wt% (denoted as PTXL prodrugs 1 and 2) were prepared. The molecular structures and characteristics were confirmed by 1H NMR, Fourier transform infrared, and gel permeation chromatography. In vitro release studies showed that PTXL release rate from polymeric prodrug were significantly accelerated under acidic medium, due to the acid-cleavable hydrazone linkage. As illustrated by cytotoxicity study, while the corresponding polymer carrier was nontoxic, the polymeric prodrug exhibited higher therapeutic efficacy toward MCF-7 and A549 (IC50 = 0.19 and 4.94 µg PTXL equiv/mL, respectively) cancer cells. The norbornene-functional polylactide-based polymeric prodrug has appeared as a novel anticancer nanomedicine for cancer therapy.

Design, synthesis, and evaluation of water-soluble morpholino-decorated paclitaxel prodrugs with remarkably decreased toxicity

Novel water-soluble paclitaxel prodrugs were designed and synthesized by introducing morpholino groups through different linkers. These derivatives showed 400–20,000-times greater water solubility than paclitaxel as well as comparable activity in MCF-7 and HeLa cell lines. The prodrug PM4 was tested in the S-180 tumor mouse model, with paclitaxel as the positive control. The results showed that PM4 had comparable antitumor activity as paclitaxel, with tumor inhibition of 54% versus 56%, and remarkably decreased toxicity. The survival rate of treated mice was 8/8 in the PM4 group, compared to 3/8 in the paclitaxel group.

Abstract 4461: Anti-cancer activity of immunoliposomes encapsulated effective amount of glycosylated paclitaxel with novel loading strategy

Abstract Targeted liposomal drug delivery is considered to enhance the therapeutic effects of anti-cancer agents because high amount of drug could be administered with least side effects. However, significant hydrophobic compounds such as paclitaxel (PTX) are not suitable for efficient encapsulating. We conferred water-solubility of PTX by coupling glucose at 7-OH to produce glycosylated PTX (gPTX). gPTX appeared to have a 10-fold higher solubility than PTX in 40% ethylene glycol (EG) and in Cremophor® EL/Ethanol/PBS (12:12:76 volume%) (CEP). The maximal solubility of gPTX in these solvents was 1.1 and 20.0 mg/ml, respectively. An anti-cancer activity of PTX is due to inhibit tubulin depolymerization. We confirmed tubulin polymerization activity of gPTX in vitro. The activity of gPTX to stabilize tubulin polymerization was lower than that of PTX by only 10%. We successfully prepared gPTX-encapsulated liposome (gPTX-L) with the remote loading method by solubility gradient between 40% EG and CEP. The encapsulation efficiency and loading efficiency were 70.8 % and 8.0 mol% (drug mol / initial lipid mol). Then, trastuzumab was conjugated on the surface of gPTX-L to prepare immunoliposome (gPTX-IL) for targeting HER2 positive cancer cells. The particle size of gPTX-IL was around 150 nm and Z potential was -8.1 mV. We evaluated cellular cytotoxicity of PTX, gPTX, gPTX-L and gPTX-IL in HER2 positive cancer cell lines, SK-BR-3 and HT-29, and HER2 negative cancer cell line, MDA-MB-231, by MTT assay. The IC50 values after 72 hours drug-exposure showed gPTX-L exhibited lower IC50 values than free-gPTX in all cell line, which indicated gPTX-L internalized with liposomal formulation contained high concentration of gPTX. Furthermore, gPTX-IL exhibited lower IC50 values than gPTX-L in HER2 positive cancer cell lines but no significant statically difference in this assay condition. We then evaluated the time required to inhibit the growth at the half maximal level (IT50) at the minimum concentration to show maximal cytotoxicity after 72 hours drug-exposure. gPTX-IL showed the shortest IT50 values of 6.4 and 4.7 h in SK-BR-3 and HT-29 cells, respectively. On the other hand, gPTX-IL showed the same IT50 value of gPTX-L in MDA-MB-231 cells. We then evaluated the anti-cancer efficacy of the formula in vivo using tumor bearing ICR-nu/nu mice. The mice were intravenously injected at the dose of 150 mg/kg of gPTX in a day, which was the lethal dose of free-gPTX. While gPTX-L and free-trastuzumab did not inhibit tumor growth, gPTX-IL significantly decreased tumor volume with low side effects. We further evaluated dose dependency of gPTX-IL using tumor bearing BALB/c-nu/nu mice. The doses of over 100 mg/kg decreased tumor volume and the dose of 150 mg/kg showed the most efficient anti-cancer activity. Collectively, the gPTX-IL with novel encapsulation strategy should be a candidate of highly efficient targeting drug delivery system. Citation Format: Tsukasa Shigehiro, Tomonari Kasai, Akifumi Mizutani, Hiroshi Murakami, Katsuhiko Mikuni, Tadakatsu Mandai, Hiroki Hamada, Masaharu Seno. Anti-cancer activity of immunoliposomes encapsulated effective amount of glycosylated paclitaxel with novel loading strategy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4461. doi:10.1158/1538-7445.AM2014-4461

Compatibility between Paclitaxel and Polymer Carrier

Several polymer-based drug delivery systems are being developed to enhance the extremely low water-solubility of paclitaxel (PTX). It is believed that there is a positive correlation between the compatibility of polymer-drug and the solubilization. In recent years, solubility parameters for polymer and drug were used to evaluate degree of compatibility between a drug and a polymer, which were measured using various experimental methods or estimated using the group contribution menthod (GCM). In this study, degree of compatibility between PTX and polymers were estimated by molar free energy of mixing (Δ̗mix) that was calculated through computer simulation. It is found that the degree of compatibility is: PTX-PTRP > PTX-PLBG > PTX-PLGA > PTX-PCL > PTX-PLA. It has been demonstrated that the result of this study is in accord with the Similar Dissolve Mutually Theory.

Abstract LB-8: A novel remote loading method with solubility gradient to encapsulate effevtive amount of taxanes into liposomes.

Abstract Targeted liposomal drug delivery is considered to enhance the therapeutic effects of anti-cancer agents because high amount of drug could be administered with least side effects. However, water-insoluble hydrophobic and non-weak base chemical compounds such as paclitaxel (PTX) are not suitable for efficient encapsulating. We conferred water-solubility of PTX by coupling glucose at 7-OH to produce 7-alpha-glucosyloxyacetylpaxcitacel (gPTX). gPTX showed enhanced water-solubility with the 40 % ethylene glycol (EG) in PBS and with the CEP buffer (Cremophor EL and Ethanol in PBS). The maximal solubility of gPTX in these solvents was 1 and 20 mg/ml, respectively. We prepared gPTX encapsulated liposome (gPTX-L) with remote loading method by solubility gradient between 40 % EG and CEP buffer. gPTX efficiently encapsulated into liposomes. The encapsulation efficiency and loading efficiency were 72.9 % and 8.5×10−2 drug mol / initial lipid mol. Then, trastuzumab was conjugated on the surface of gPTX-L to prepare immunoliposome (gPTX-IL) for targeting HER2 overexpressing cancer cells. The particle size of gPTX-IL was under 150 nm and Z potential was -3.07 mV. We evaluated IC50 values by MTT assay after 72 hours exposure. The IC50 values of PTX, gPTX, gPTX-L and gPTX-IL for SK-BR-3 cells were 5.5, 18.9, 6.6 and 5.3 nM, respectively. gPTX-IL exhibited the highest toxicity in these paclitaxel formulations. Similarly, the IC50 values for HT-29 cells were 1.3, 11.0, 7.6 and 6.8 nM, respectively. We then evaluated the time required for each formula to inhibit the growth at the half maximal level (IT50) at the minimum concentration to show maximal cytotoxicity (IC100) after 72 hours exposure. gPTX-IL showed the shortest IT50 values of 1.6 and 1.1 h in SK-BR-3 and HT-29 cells respectively. We then evaluated in vivo distribution of liposome and immunoliposome encapsulating HSA conjugated Cy5.5 in ICR-nu/nu mice bearing HT-29 cell tumors. Both liposome and immunoliposome accumulated at the tumor site, but immunoliposome exhibited less accumulation at liver than liposome. Based on these results, we then evaluated the anti-cancer efficacy of the formula in vivo using tumor bearing ICR-nu/nu mice. While gPTX-L and free trastuzumab did not inhibit tumor growth, gPTX-IL decreased tumor volume and inhibited tumor growth with low side effects at the dose of 150 mg/kg gPTX, which was the lethal dose of naked gPTX exhibiting 25% survival rate of mice one week after the injection of gPTX. Collectively, the gPTX-encapsulated immunoliposome with novel encapsulation strategy should be an excellent candidate of highly efficient drug delivery system of cancer treatment targeting HER2. Citation Format: Tsukasa Shigehiro, Tomonari Kasai, Akifumi Mizutani, Hiroshi Murakami, Katsuhiko Mikuni, Tadakatsu Mandai, Hiroki Hamada, Masaharu Seno. A novel remote loading method with solubility gradient to encapsulate effevtive amount of taxanes into liposomes. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-8. doi:10.1158/1538-7445.AM2013-LB-8

Water-soluble paclitaxel by conjugation to hyperbranched polyglycidols

Chemical conjugates composed of paclitaxel (PTXL) and hyperbranched polyglycidols (HBP) were synthesized using glutaric anhydride as a “bridge” with esterification in dimethylformamide. A series of HBP–PTXL conjugates (HPCs) were synthesized using different molecular weights of HBP and varying ratios of HBP to PTXL, and they were characterized. An intact form of PTXL was regenerated from HPCs under acidic or basic pH conditions. Furthermore, water-soluble HPCs exhibit a more pronounced cytotoxic effect against cancer cells, suggesting that these HPCs can be utilized as tumor-specific therapeutic agents in the form of an injectable drug.

Killed Bacillus subtilis spores expressing streptavidin: a novel carrier of drugs to target cancer cells

Carriers of drugs in cancer therapy are required to reduce side-effects of the drugs to normal cells. Here we constructed killed recombinant Bacillus subtilis spores (SA1) that expressed streptavidin as a chimeric fusion to the spore coat protein CotB and used the spores as bioparticle carrier. When bound with biotinylated cetuximab these spores could specifically target to the epidermal growth factor receptor on HT 29 colon cancer cells, thereby delivered paclitaxel to the cells with 4-fold higher efficiency, as indicated by fluorescent intensity of paclitaxel Oregon Green 488 bound to HT29 cells. Based on real-time monitoring of cell index, the IC50 of growth of HT29 cells by paclitaxel-SA1-cetuximab was estimated to be 2.9 nM approximately 5-fold lower than water-soluble paclitaxel (14.5 nM). Instability of DNA content was observed when cells were treated with 16 nM paclitaxel-SA1-cetuximab, resulting in a 2-fold enhancement in polyploidy cells. Thus, by targeting the release of paclitaxel to HT29 cells, spore-associated cetuximab augmented the inhibitory effect of paclitaxel on cell division and proliferation. The SA1 could be used as a “universal” drug carrier to target specific biomarkers on cancer cells by conjugating with suitable biotinylated antibodies.

Abstract 5700: Preparation and evaluation of glycosylated paclitaxel loaded in tastuzumab-immunoliposome

Abstract Targeted drug delivery is considered to enhance the therapeutic effects of anti-cancer agents because high amount could be administered with least side effects. However, water-insoluble hydrophobic chemical compounds such as paclitaxel are not suitable for efficient drug delivery. We conferred water-solubility of paclitaxel by coupling glucose at 7-OH to produce 7-alpha-glucosyloxyacetylpaclitaxel (7-GLG-PT). Although the 7-GLG-PT showed lower cytotoxicity than paclitaxel, encapsulation of 7-GLG-PT into liposomes was more efficient than that of paclitaxel. In our experiment, paclitaxel encapsulated liposomes was not detectable. Trastuzumab was then conjugated on the surface of 7-GLG-PT liposomes to prepare immunoliposome (GLG-PT-IL). The GLG-PT-IL exhibited cytotoxicity on SK-BR-3 cells overexpressing HER2. The IC50 values of paclitaxel, 7-GLG-PT, 7-GLG-PT liposome and GLG-PT-IL were 6, 126, 130 and 94 nM, respectively. From this evaluation, the concentration of each formula to suppress the cell growth completely was estimated around 30 to 300 nM. At these concentrations, the time required for each formula to suppress the growth at the half maximal level was evaluated. GLG-PT-IL showed the shortest time of 5 hours, which was one third of the others when compared with paclitaxel, 7-GLG-PT and 7-GLG-PT liposome. The specific targeting potential of the immunoliposome on SK-BR-3 cells was assessed. The accumulation on the cell surface was competitively inhibited by the excess amount of free tastuzumab. The endocytosis of the immunoliposomes was simultaneously confirmed by time-lapse imaging. Thus GLG-PT-IL has been successfully demonstrated to target the HER2-overexpressing cancer cells specifically suppressing their growth. Trastumab itself is considered to induce the antibody dependent cellular cytotoxicity, so that the endocytosis of HER2 may not be always necessary. However, HER2-mediated endocytosis was induced by the immunoliposomes while single trastuzumab did not show the endocytosis in SK-BR-3 cells. In this context together with the results demonstrated in this study, the 7-GLG-PT immunoliposome should be a promising candidate of highly efficient drug delivery system of cancer treatment targeting HER2. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5700. doi:1538-7445.AM2012-5700

A dose‐finding study with a novel water‐soluble formulation of paclitaxel for the treatment of malignant high‐grade solid tumours in dogs

A new formulation of water-soluble paclitaxel (Paccal® Vet) has been developed for canine cancer patients, without the need for pre-medication (traditionally required in non-water-soluble paclitaxel formulations). The objective of the study was to determine a clinically safe and efficacious dose of Paccal Vet and to estimate progression-free and overall survival and to evaluate single-dose pharmacokinetics in tumour-bearing dogs. A positive risk:benefit ratio was established for Paccal Vet administered at 150 mg m(-2) intravenous (IV) for three or more treatment cycles. Preliminary efficacy was demonstrated by best objective response rate (86%), median time to response (14 days) and median progression-free survival (131 days). Paccal Vet was associated with expected adverse events (AE) (e.g. myelosuppression), however the majority were transient, clinically silent and manageable. This is the first clinical report of a water-soluble formulation of paclitaxel suggesting successful administration and being safely used without pre-medication in dogs.

Synthesis and biological evaluation of a peptide–paclitaxel conjugate which targets the integrin αvβ6

The integrin αvβ6 is an emergent biomarker for non-small cell lung cancer (NSCLC) as well as other carcinomas. We previously developed a tetrameric peptide, referred to as H2009.1, which binds αvβ6 and displays minimal affinity for other RGD-binding integrins. Here we report the use of this peptide to actively deliver paclitaxel to αvβ6-positive cells. We synthesized a water soluble paclitaxel–H2009.1 peptide conjugate in which the 2′-position of paclitaxel is attached to the tetrameric peptide via an ester linkage. The conjugate maintains its specificity for αvβ6-expressing NSCLC cells, resulting in selective cytotoxicity. Treatment of αvβ6-positive cells with the conjugate results in cell cycle arrest followed by induction of apoptosis in the same manner as free paclitaxel. However, initiation of apoptosis and the resultant cell death is delayed compared to free drug. The conjugate demonstrates anti-tumor activity in a H2009 xenograft model of NSCLC with efficacy comparable to treatment with free paclitaxel.

Insights into the Interaction of Discodermolide and Docetaxel with Tubulin. Mapping the Binding Sites of Microtubule-Stabilizing Agents by Using an Integrated NMR and Computational Approach

The binding interactions of two antitumor agents that target the paclitaxel site, docetaxel and discodermolide, to unassembled α/β-tubulin heterodimers and microtubules have been studied using biochemical and NMR techniques. The use of discodermolide as a water-soluble paclitaxel biomimetic and extensive NMR experiments allowed the detection of binding of microtubule-stabilizing agents to unassembled tubulin α/β-heterodimers. The bioactive 3D structures of docetaxel and discodermolide bound to α/β-heterodimers were elucidated and compared to those bound to microtubules, where subtle changes in the conformations of docetaxel in its different bound states were evident. Moreover, the combination of experimental TR-NOE and STD NMR data with CORCEMA-ST calculations indicate that docetaxel and discodermolide target an additional binding site at the pore of the microtubules, which is different from the internal binding site at the lumen previously determined by electron crystallography. Binding to this pore site can then be considered as the first ligand-protein recognition event that takes place in advance of the drug internalization process and interaction with the lumen of the microtubules.

Development of a novel prodrug of paclitaxel that is cleaved by prostate-specific antigen: An in vitro and in vivo evaluation study

In developed countries, prostate cancer is the third most common cause of death from cancer in men. Unfortunately, whilst accumulating clinical data have suggested that taxanes may prolong the survival in a subset of men with prostate carcinoma, the dose and duration of administration of these drugs are limited by their significant systemic toxicities due to a lack of tumour selectivity. In an attempt to improve both the water solubility and tumour-targeting properties of paclitaxel (Taxol®), we set out to develop a water soluble paclitaxel prodrug that is activated specifically by prostate-specific antigen (PSA) which is almost exclusively expressed in prostate tissue and prostate carcinoma making it an ideal molecular target for prodrug strategies. Using albumin as a drug carrier, we describe a novel albumin-binding prodrug of paclitaxel, EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-Leu-PABC-paclitaxel [EMC: ε-maleimidocaproyl; PABC: p-aminobenzyloxycarbonyl] that was synthesised by reacting EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-OH with H-Leu-PABC-paclitaxel. This prodrug was water soluble and was bound to endogenous and exogenous albumin. Moreover, incubation studies with PSA demonstrated that the albumin-bound form of the prodrug was cleaved rapidly at the P1–P1′ scissile bond releasing the paclitaxel-dipeptide H-Ser-Leu-PABC-paclitaxel. Last but not least, due to the incorporation of a PABC self-eliminating linker, this dipeptide was rapidly degraded to liberate paclitaxel as a final cleavage product within a few hours in prostate tumour tissue homogenates. Of note was that the albumin-bound form of the prodrug was approximately three-fold more active in killing PSA-positive LNCaP cells than paclitaxel. In addition, orientating toxicity studies in mice showed that the maximum tolerated dose of the novel paclitaxel prodrug was twice that of conventional paclitaxel. When tested in vivo in an orthotopic mouse model of human prostate cancer using luciferase-transduced LNCaP LLN cells, both paclitaxel and the new paclitaxel prodrug showed distinct antitumour efficacy on the primary tumour and metastases that was significantly better than the effect of doxorubicin which was used as a comparison and showed no antitumour efficacy. The new paclitaxel prodrug (3 × 24 mg paclitaxel equivalents) showed comparable antitumour activity on the primary tumour to paclitaxel at its maximum-tolerated dose (3 × 12 mg/kg), reduced circulating PSA levels and demonstrated a better antitumour effect on lung metastases but not on bone metastases.

Novel pH-sensitive polyacetal-based block copolymers for controlled drug delivery

The principal aim of this study was to synthesize and characterize pH-sensitive biodegradable triblock copolymers containing a hydrophobic polyacetal segment for controlled drug delivery. Poly(ethylene glycol)–poly(ethyl glyoxylate)–poly(ethylene glycol) (PEG–PEtG–PEG) triblock copolymers with PEG molecular weights 500 (PEtG–PEG 500) and 750 (PEtG–PEG 750) were synthesized by PEtG end-capping with methoxy PEG via a carbamate linkage. Synthesized amphiphilic PEG–PEtG–PEG was characterized by 1H NMR spectroscopy. Molecular weights of PEtG–PEG 500 and PEtG–PEG 750 were determined to be 2823 and 3387, respectively, by gel permeation chromatography. The polymers with a biodegradable polyacetal block underwent pH-dependent degradation via an acid-catalyzed hydrolysis. Paclitaxel (PTX)-loaded polymeric micelles were prepared by a dialysis method and the amount of PTX incorporated into the polymeric micelle formulations was 45,000 times greater than the water solubility of PTX at room temperature. The polymeric micelles prepared from the amphiphilic PEG–PEtG–PEG triblock copolymers have released the loaded PTX in a pH-dependent manner. The novel PEtG-based amphiphilic block copolymers can find applications for targeted and controlled drug delivery to the acidic environments found in tumors and intracellular compartments.

Synthesis and Characterization of a Fluorescent Water-Soluble Paclitaxel Prodrug

A fluorescence susceptible water-soluble paclitaxel was synthesized by a condensation reaction between PEGylated paclitaxel (namely, PP7) and 1-pyrene butyric acid (PBA) in order to obtain a better understanding of the mechanism of action of paclitaxel as well as of the environment of the paclitaxel-binding site. The reaction was performed successfully and the resulting paclitaxel was characterized by FT-NMR, analytical-HPLC, UV spectro photometry, and fluorescence spectrometry. The synthesized paclitaxel analogue showed a high susceptibility to fluorescence in both excitation and emission spectra. And we have investigated the time-resolved fluorescence behavior of them in different solvents and at different excitation wavelengths.

Abstract LB-39: Development of a novel water-soluble prodrug of paclitaxel that is cleaved by prostate-specific antigen (PSA): In vitro and in vivo evaluation

Abstract In developed countries, prostate cancer is the second most frequently diagnosed cancer, and the third most common cause of death from cancer in men. Unfortunately, while accumulating clinical data have suggested that the taxanes may prolong the survival in a subset of men with prostate carcinoma, the dose and duration of administration of these drugs are limited by their significant systemic toxicities due to a lack of tumor selectivity. Besides prostate cancer, paclitaxel (Taxol®) is currently showing a promising antitumor activity against a variety of human tumors. In an attempt to improve both the water solubility and tumor targeting properties of paclitaxel, we set out to develop a water soluble paclitaxel prodrug that is activated specifically by prostate-specific antigen (PSA) which is solely expressed in prostate tissue and prostate carcinoma with high levels up to mg/g present in human prostate carcinoma. Using albumin as an efficient carrier for drug delivery, we describe a novel albumin-binding prodrug of paclitaxel, EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-Leu-PABC-Paclitaxel [EMC: -maleimidocaproyl; PABC: p-aminobenzyloxycarbonyl] that was synthesized by reacting EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-OH with H-Leu-PABC-Paclitaxel. This prodrug exhibited excellent water-solubility and was bound rapidly to the cysteine-34 position of endogenous and exogenous albumin. Moreover, incubation studies with PSA demonstrated that the albumin-bound form of the prodrug was cleaved rapidly at the P1-P‘1 scissile bond releasing the paclitaxel-dipeptide H-Ser-Leu-PABC-Paclitaxel. Above all, due to the incorporation of a PABC self-eliminating linker, this dipeptide was rapidly degraded to liberate paclitaxel as a final cleavage product within a few hours in prostate tumor tissue homogenates. Of note was that the albumin-bound form of the prodrug was approximately 4-fold more active in killing PSA-positive LNCaP cells than paclitaxel. In addition, orientating toxicity studies in mice showed that the maximum tolerated dose of the novel paclitaxel prodrug was twice that of conventional paclitaxel. Therefore, the in vivo efficacy of the prodrug (24 mg/kg paclitaxel equivalents) in comparison to free paclitaxel (12 mg/kg) is currently being evaluated in a mouse model of human prostate cancer using luciferase transduced LNCaP LN cells orthotopically implanted in SCID mice. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-39.

Pharmacokinetic Behavior and Biodistribution of Paclitaxel-Loaded Lipid Nanosuspension

In this study, paclitaxel-loaded lipid nanosuspension (PxLN) was prepared and the in vivo profiles after intravenous administration in rats were investigated. We compared the manufacturing processes depending on the temperature: PxLN-H for a hot homogenization process and PxLN-C for solidification of lipid-drug mixtures by liquid nitrogen. Both formulations showed submicron size distribution and the similar drug loading efficiency of about 70%. In vitro release of PxLNs and Taxol performed by a dialysis diffusion method showed similar pattern for PxLN-H and Taxol, but the reduced release profile for PxLN-C. PxLN or Taxol was intravenously administered to the rats at a dose of 5 mg/kg as paclitaxel. The drug in blood samples were assayed by the HPLC/MS/MS method. The AUC of PxLN-H was 3.4-fold greater than that of Taxol. PxLN-H gave higher biodistribution in all tissues than did Taxol. In addition, it maintained the higher drug concentration for 12 h. This lipid nanosuspension might be a promising candidate for an alternative formulation for the parenteral delivery of poorly water-soluble paclitaxel.