Combination of Paclitaxel and Nitric Oxide as a Novel Treatment for the Reduction of Restenosis

The combination of a nitric oxide (NO) donor and a paclitaxel-NO donor conjugate coated on a vascular stent was tested in a rabbit iliac artery model of stenosis as a potential therapy for restenosis. Paclitaxel was conjugated with a NO donor at the 7-position to give compound 7. An adamantane-based NO donor 14 was synthesized and combined with 7 to provide a burst of NO in the first few critical hours following injury to the vessel wall. Both 7 and 14 demonstrated antiproliferative activity (IC(50) = 20 nM and 15 microM, respectively) and antiplatelet activity (IC(50) = 10 and 1 microM, respectively). Stents were coated with a layer of a polymer containing test compounds. The total amount of NO eluted from the stents after a 6 h implantation in the rabbit iliac artery was 35%, 95%, and 69% of the original content for the stents coated with 7, 14, and the combination of 7 and 14, respectively. The antistenotic activity of 7 and 14 was determined in a 28-day rabbit model with two control groups (uncoated stents and polymer-coated stents) and two study groups (paclitaxel-coated stents and stents coated with the combination of 7 and 14). Polymer-coated stents caused inflammation and increased stenosis by 39% when compared to the uncoated stents. The stents coated with 7 plus 14 were as good as the uncoated stents, 41% better than the polymer-coated stents and 34% better than the paclitaxel-coated stents. These data indicate a beneficial effect of adding NO to an antiproliferative agent (paclitaxel) and suggest a potential therapeutic combination for the treatment of stenotic vessel disease.

Design, synthesis, and bioactivities of steroid-linked taxol analogues as potential targeted drugs for prostate and breast cancer

The female steroid hormone 3,17beta-estradiol (2) was selected as an agent to target taxol (1) to estrogen receptor (ER) positive breast cancer cells. Estradiol-taxol conjugates (ETC) were synthesized through linkages from the 11- or 16-position of estradiol to the 2'-, 7-, or 10-position of taxol. All conjugates were cytotoxic to the A2870 ovarian cancer cell line, although less so than taxol. The MCF-7 breast cancer cell line (ER-alpha positive) and MDA-MB-231 breast cancer cell line (ER-alpha negative) were also used to evaluate the selectivity and cytotoxicity of these conjugates. One conjugate showed some selectivity for ER positive cells, but it was less potent than taxol. Two ETC hemisuccinates were also prepared to improve the solubility of the conjugates. The corresponding Na and triethanolammonium salts were slightly more cytotoxic than the acid form but were much less cytotoxic than the corresponding ETC.

Synthesis and Biological Evaluation of PaclitaxelThiocolchicine Hybrids

The bifunctional taxoid-colchicinoid hybrids 6-8 were synthesized and evaluated in assays of cytotoxicity and tubulin assembly/disassembly. All compounds showed a high degree of cytotoxicity, but, while 6 and 7 behaved as bifunctional tubulin binders not unlike an equimolecular mixture of taxol and thiocolchicine, 8 was surprisingly devoid of tubulin activity, acting on a distinct and yet to identify molecular target.

O?N intramolecular acyl migration reaction in the development of prodrugs and the synthesis of difficult sequence-containing bioactive peptides

N-Ointramolecular acyl migration in Ser- or Thr-containing peptides is a well-known side reaction in peptide chemistry. It results in the mutual conversion of ester and amide bonds. Our medicinal chemistry study focused on the fact that the O-acyl product can be readily converted to the original N-acyl form under neutral or slightly basic conditions in an aqueous buffer and the liberated ionized amino group enhances the water solubility of O-acyl products. Because of this, we have developed a novel class of "O-N intramolecular acyl migration"-type water-soluble prodrugs of HIV-1 protease inhibitors. These prodrugs released the parent drugs via a simple chemical mechanism with no side reaction. In this study, we applied this strategy to important cancer chemotherapeutic agents, paclitaxel and its derivatives, to develop water-soluble taxoid prodrugs, and found that these prodrugs, 2'-O-isoform of taxoids, showed promising results with higher water solubility and proper kinetics in their parent drug formation by a simple pH-dependent chemical mechanism with O-N intramolecular acyl migration. These results suggest that this strategy would be useful in toxicology and medical economics. After the successful application of O-N intramolecular acyl migration in medicinal chemistry, this concept was recently used in peptide chemistry for the synthesis of "difficult sequence-containing peptides." The strategy was based on hydrophilic O-acyl isopeptide synthesis followed by the O-N intramolecular acyl migration reaction, leading to the desired peptide. In a model study with small, difficult sequence-containing peptides, synthesized "O-acyl isopeptides" not only improved the solubility in various media and efficiently performed the high performance liquid chromatography purification, but also altered the nature of the difficult sequence during SPPS, resulting in the efficient synthesis of O-acyl isopeptides with no complications. The subsequent O-N intramolecular acyl migration of purified O-acyl isopeptides afforded the desired peptides as precipitates with high yield and purity. Further study of the synthesis of a larger difficult sequence-containing peptide, Alzheimer's disease-related peptide (A beta 1-42), surprisingly showed that only one insertion of the O-acyl group drastically improved the unfavorable nature of the difficult sequence in A beta 1-42, and achieved efficient synthesis of 26-O-acyl isoA beta 1-42 and subsequent complete conversion to A beta 1-42 via the O-N intramolecular acyl migration reaction of 26-O-acyl isoA beta 1-42. This suggests that our new method based on O-N intramolecular acyl migration is an important method for the synthesis of difficult sequence-containing bioactive peptides.

Asymmetric Sulfur Ylide Mediated Aziridination: Application in the Synthesis of the Side Chain of Taxol

[reaction: see text] Sulfur ylide methodology has been used to construct the Taxol side chain with a high degree of enantioselectivity via a trans-aziridine followed by stereospecific rearrangement of the trans-benzoylaziridine into a trans-oxazoline.

A novel approach of water-soluble paclitaxel prodrug with no auxiliary and no byproduct: design and synthesis of isotaxel

A novel water-soluble paclitaxel prodrug, isotaxel 2, that realizes a higher water-solubility and the formation of paclitaxel through a simple pH-dependent chemical mechanism via the O-N acyl migration was synthesized and showed promising results in water-solubility and kinetics. This prodrug, a 2'-O-benzoyl isoform of paclitaxel, has no additional functional auxiliaries released during conversion to paclitaxel, which would be a great advantage in toxicology and medical economics.

Synthesis of novel macrocyclic docetaxel analogues. Influence of their macrocyclic ring size on tubulin activity

This work describes the synthesis of a series of novel macrocyclic taxoids 3 and 3(H) designed to mimic the docetaxel solid-state ("nonpolar") conformation. These compounds, bearing 18-, 20-, 21-, and 22-membered rings connecting the C-2 OH and C-3' NH moieties, were constructed by ring-closing olefin metathesis of the taxoid-omega,omega'-dienes 4. Biological evaluation of these new taxoids showed that activity is dependent on the ring size, and only the 22-membered ring taxoid 3d exhibits significant tubulin binding. Synthesis of the open-chain analogues 7 and 7(H) and comparison of their biological activities with macrocyclic taxoids show that the carbon tether between C-2 OH and C-3' NH does not hamper tubulin binding. Computational studies of the conformational behavior of the macrocyclic taxoids 3 indicate that the 18-, 20-, and 21-membered-ring 3a-c adopt mainly conformations that are not recognized by tubulin. The most active taxoid 3d appears to adopt a conformation that is between the "nonpolar" and T-shaped forms.

Biodistribution, radiation dose estimates, and in vivo Pgp modulation studies of 18F-paclitaxel in nonhuman primates

Multidrug resistance (MDR) associated with increased expression and function of the P-glycoprotein (Pgp) efflux pump often causes chemotherapeutic failure in cancer. To provide insight into both the dynamics of the pump and the effects of MDR, we radiolabeled paclitaxel, a substrate for the Pgp pump, with (18)F to study MDR in vivo with PET. We obtained biodistribution and radiation dose estimates for (18)F-paclitaxel (FPAC) in monkeys and studied the effects of a Pgp blocker (XR9576, tariquidar) on FPAC kinetics.

METHODS

Paired baseline and Pgp modulation (2 mg/kg XR9576) 4-h whole-body dynamic PET scans were obtained in 3 rhesus monkeys after injection of FPAC. Measured residence times were extrapolated to humans and radiation dose estimates were obtained using MIRDOSE3.1. The postmodulator area under the time-activity curves (AUCs) and Logan plot slopes, a measure of tracer distribution volume (equilibrium tissue-to-plasma ratio) that is inversely proportional to tracer efflux, were compared with baseline values to determine changes in FPAC distribution.

RESULTS

Cumulative activities of the organs sampled accounted for 80% of the injected dose. The critical organ is gallbladder wall (0.19 mGy/MBq [0.69 rad/mCi]), followed by liver (0.14 mGy/MBq [0.52 rad/mCi]); the effective dose is 0.022 mSv/MBq (0.083 rem/mCi). XR9576 preinfusion changed the Logan plot slope for liver by +104% (P = 0.02), lung by +87% (P = 0.11), and kidney by -14% (P = 0.08). Changes in the mean AUC (normalized to the plasma AUC) were +54% (P = 0.08), +97% (P = 0.04), and -12% (P = 0.02), respectively, for liver, lung, and kidney. No significant difference was found in the metabolite-corrected plasma AUC (normalized to the injected dose) between the baseline and XR9576 modulator studies (P = 0.69).

CONCLUSION

Under Radioactive Drug Research Committee guidelines, 266 MBq (7.2 mCi) FPAC can be administered to humans up to 3 times a year. The increase in FPAC accumulation in liver and lung after XR9576 is consistent with Pgp inhibition and demonstrates the potential of FPAC to evaluate MDR.

Hydrogen peroxide from the oxidative burst is not involved in the induction of taxol biosynthesis in Taxus chinensis cells

In cell suspension cultures of Taxus chinensis, 40 mg/l fungal elicitor from Aspergillus niger and 20 microM HgCl2 elicited 5.7 and 3.6 mg/l taxol, which was a 9-fold and 5-fold increase vs. compared with the control, respectively. The fungal elicitor induced hydrogen peroxide (H2O2) accumulation but HgCl2 did not, indicating that H2O2 was not necessary for enhancement of taxol induced by elicitor. Compared with the treatment with fungal elicitor alone, exogenous catalase, ascorbic acid, diphenylene iodonium and superoxide dismutase induced a 0.45, 0.4, 0.7 and 1.4-fold H2O2, but elicited taxol production, which was 0.98, 1.2, 1.1 and 0.9-fold, respectively, vs. non-treated cells Elicitor-induced taxol production was not accorded with the amount of H2O2 production.

Semi-synthesis of an O-glycosylated docetaxel analogue

A 7beta-O-glycosylated docetaxel analogue was semi-synthesized from 9-dihydro-13-acetylbaccatin III, the most abundant taxane isolated from the needles of Taxus canadensis. It was shown to be more bioactive than paclitaxel according to the tubulin assay. It had a reduced potency in the MCF7 cell line cytotoxicity assay compared to paclitaxel, but it demonstrated better activity against the drug resistant cell line MCF7-ADR. In addition, the presence of one sugar moiety on C-7 doubled the water solubility versus that of paclitaxel.

Synthesis and biological evaluation of C-3'NH/C-10 and C-2/C-10 modified paclitaxel analogues

Concurrent modifications on the C-3'NH/C-10, and C-2/C-10 positions on paclitaxel were carried out as a way of investigating possible synergistic effects. The biological activities of these analogues were evaluated in both a microtubule assembly assay and human ovarian cancer (A2780) and prostate cancer (PC3) cytotoxicity assay. In some cases the doubly modified analogues were more active than would have been predicted based on the activity of the singly modified analogues, indicating probable synergistic effects.

Synthesis and HSA binding characterisation of the water soluble 7-succinylpaclitaxel

A water soluble paclitaxel analogue, the 7-hemisuccinylpaclitaxel, was synthesised and its binding to human serum albumin (HSA) was characterised by difference circular dichroism and optical biosensor methodologies. The carboxylate group was introduced at paclitaxel C-7 position to improve the drug water solubility without significantly changing the biological activity. The paclitaxel analogue showed a relatively low affinity to HSA (3.5x10(4) M(-1)), while no significant interactions were evidenced with selective markers for the most characterised binding sites on the carrier, suggesting a non-selective binding to low affinity binding sites.

Synthesis and biological evaluation of 4-deacetoxy-1,7-dideoxy azetidine paclitaxel analogues

Three novel 4-deacetoxy-1,7-dideoxy azetidine paclitaxel analogues were synthesized through a convenient route that employed hydroboration-amination and intramolecular S(N)2-type substitution reaction from a natural taxoid taxinine. All analogues have been tested for cytotoxicity against three human tumor cell lines. None of them showed remarkable cytotoxicity compared to paclitaxel against tested tumor cell lines.

Effect of 9,10-cyclic acetal stereochemistry on feasible operation of the alpha-ketol rearrangement in highly functionalized paclitaxel (Taxol) precursors

The convergent, stereocontrolled synthesis of enantiopure stereoisomeric 9,10-cyclic acetals, whose designed role was to serve as potential precursors to Taxol, is reported. These advanced intermediates are multiply functionalized and carry a bridgehead alpha-ketol array which was key to isomerization into the proper framework. In agreement with relative strain energy values obtained by MM3 calculations, a dichotomy was observed between these two families. While the trans-fused acetals failed to undergo bridge migration, their cis counterparts did so efficiently. In fact, isomerization was sufficiently rapid that oxygenation at C2 was now precluded. The operation of several unusual transannular hydride shifts is also detailed.

A trifunctional catalyst for one-pot synthesis of chiral diols via Heck coupling-N-oxidation-asymmetric dihydroxylation: application for the synthesis of diltiazem and taxol side chain

A heterogeneous bifunctional catalyst composed of OsO4(2-)-WO4(2-) and a trifunctional catalyst comprising PdCl4(2-)-OsO4(2-)-WO4(2-), designed and prepared by an ion-exchange technique using layered double hydroxides (LDH) as an ion-exchanger and their homogeneous bifunctional analogue, K2OsO4-Na2WO4 and trifunctional analogue, Na2PdCl4-K2OsO4-Na2WO4, devised for the first time are evaluated for the synthesis of chiral vicinal diols. These bifunctional and trifunctional catalysts perform asymmetric dihydroxylation-N-oxidation and Heck-asymmetric dihydroxylation-N-oxidation, respectively, in the presence of Sharpless chiral ligand, (DHQD)2PHAL in a single pot using H2O2 as a terminal oxidant to provide N-methylmorpholine oxide (NMO) in situ by the oxidation of N-methylmorpholine (NMM). The heterogeneous bifunctional catalyst supported on LDH (LDH-OsW) displays superior activity to afford diols with higher yields over the other heterogeneous catalysts developed by the ion exchange on quaternary ammonium salts covalently bound to resin (resin-OsW) and silica (silica-OsW) or homogeneous catalysts in the achiral dihydroxylation reactions. The LDH-OsW and its homogeneous analogue are found to be very efficient in performing a simultaneous asymmetric dihydroxylation (AD)-N-oxidation of a wide and varied range of aromatic, cyclic, and mono, di-, and trisubstituted olefins to obtain chiral vicinal diols with higher yields and ee's using H2O2. Further, the use of OsO4(2-)-WO4(2-) catalysts as such or in the supported form offers a simplified procedure for catalyst recycling, which shows consistent activity for a number of cycles. In this process, Os(VI) is recycled to Os(VIII) by a coupled electron transfer-mediator (ETM) system based on NMO-WO4(2-) using H2O2, leading to a mild and selective electron transfer. The one-pot biomimic synthesis of chiral diols is mediated by a recyclable trifunctional heterogeneous catalyst (LDH-PdOsW) consisting of active palladium, tungsten, and osmium species embedded in a single matrix. This protocol, which provides prochiral olefins and NMO in situ by Heck coupling and N-oxidation of NMM, respectively, required for the AD, unfolds a low cost process. We extended the present method to the one-pot synthesis of trisubstituted chiral vicinal diols with moderate to excellent ee's by AD of trisubstituted olefins that are obtained by in situ Heck arylation of disubstituted olefins. The heterogeneous trifunctional catalysts offers chiral diols with unprecedented ee's and excellent yields in the AD of prochiral cinnamates, which are obtained in situ from acrylates and halobenzenes for the first time. The new variants such as LDH support and Et3N*HX inherently composed in the heterogeneous multicomponent system and slow addition of H2O2 facilitates the hydrolysis of osmium monogylcolate ester to subdue the formation of bisglycolate ester to achieve higher ee's. Without resorting to recrystallization, the chiral diols of cinnamates thus synthesized with 99% ee's and devoid of osmium contamination are directly put to use in the synthesis of diltiazem and Taxol side chain with an overall improved yield to demonstrate the synthetic utility of the trifunctional heterogeneous catalyst. The high binding ability of the heterogeneous osmium catalyst enables the use of equimolar ratio of ligand to osmium to give excellent ee's in AD in contrast to the homogeneous osmium system in which the excess molar quantities of the expensive chiral ligand to osmium are invariably used. Further, the XRD, FT-IR, UV-vis DRS, and XPS studies indicate the retention of the coordination geometries of the specific divalent anions anchored to LDH matrix in their monomeric form during the ion exchange and after the reaction.

Synthesis and biological evaluation of paclitaxel-C225 conjugate as a model for targeted drug delivery

Tumor-targeted drug delivery is an attractive strategy in cancer treatment. We have previously reported a paclitaxel model conjugate using a bombesin receptor-recognizing peptide in which the drug cytotoxicity against H1299 human nonsmall cell lung cancer was enhanced compared to unconjugated taxol. In an effort to expand the development of tumor-recognizing taxanes, paclitaxel (PTX, taxol) was conjugated to the anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibody (MAb) Erbitux (C225) to serve as a model MAb-mediated drug delivery compound. Thus, paclitaxel was derivatized at its 2'-hydroxy function by introduction of a succinate linker, and the carboxyl group of the latter was covalently attached to C225 through amide bond formation. The final product conjugate (PTXC225) was analyzed mass spectrometrically for assessment of the drug-to-antibody ratios. Cytotoxicity screening of the drug-antibody conjugate against A431, UM-SCC-1, and UM-SCC-6 cells indicated an enhancement in cytocidal effect of paclitaxel as compared to those of the free drug, the intact antibody, and a physical mixture of the two (the controls). In A431 cells, the conjugate showed 25.2% +/- 2.2% of apoptosis induction as compared to little or no apoptosis caused by the controls. Biodistribution analysis of the PTXC225 in tumor-implanted nude mice and a tyrosine-kinase assay showed that conjugation of the drug did not interfere with the immunoreactivity of the antibody. The 24-h tumor uptake of C225 and PTXC225 were 11.7% +/- 6.0% and 7.1% +/- 3.6% of the injected dose per gram of tissue (%ID/g), respectively, which were not significantly different. Also, in A431-implanted nude mice, the conjugate and C225 showed tumor growth inhibition effects of 57.2% and 41.2%, respectively, against a saline-treated control, which were not significantly different from each other. This lack of difference in the in vivo antitumor activity of the MAb-delivered drug and free PTX may be due to either a relatively low dose of the antibody-delivered drug (346 microg/kg), or an untimely release of it, or both. The tumor growth inhibition pattern of the conjugate, however, was identical to that of C225, indicating that the attachment of PTX did not affect the antigen-binding and growth inhibitory features of the MAb. These preliminary results demonstrate the potential of tumor-targeted delivery of taxol as a promising strategy in cancer treatment and warrant further work to develop more suitable drug-MAb linkers as well as improved dosage and treatment protocols.

Cephalosporin prodrugs of paclitaxel for immunologically specific activation by L-49-sFv-beta-lactamase fusion protein

Paclitaxel conjugates of 7-phenylacetamidocephalosporanic acid were prepared as prodrugs for site specific activation by targeted beta-lactamase. Immunologically specific activation of the prodrug 5 containing 3,3-dimethyl-4-amino-butyric acid as linker in combination with the fusion protein L-49-sFv-beta-lactamase was demonstrated in vitro on 3677 melanoma cells.

New highly active taxoids from 9beta-dihydrobaccatin-9,10-acetals. Part 3

We synthesized novel water-soluble and orally active taxane analogues, 7-deoxy-9beta-dihydro-9,10-O-acetal taxanes. Cytotoxicities of the synthetic compounds were greater than those of paclitaxel and docetaxel, especially against resistant cancer cell lines expressing P-glycoprotein. In addition, some compounds showed potent antitumor effects against B16 melanoma BL6 in vivo by both iv and po administration.

Fluoro-, bromo-, and iodopaclitaxel derivatives: synthesis and biological evaluation

Paclitaxel (Taxol) is a clinically important chemotherapeutic agent. We describe the synthesis of fluoro-, bromo-, and iodopaclitaxel and their [(18)F]fluoro-, [(76)Br]bromo-, and [(124)I]iodo- analogues. [(18)F]Fluoropaclitaxel shows high uptake and rapid clearance from tissues in rats. Preadministration of paclitaxel in normal rats significantly increases (p < 0.005) retention of [(18)F]fluoropaclitaxel and [(76)Br]bromopaclitaxel in blood (33.0%), heart (32.0%), lung (37.6%) kidney (142.4%); and blood (33.4%), lung (42.3%), kidney (62.4%), respectively. [(18)F]Fluoropaclitaxel uptake in the brain of mdr1a/1b(-/-) mice is increased 1400% (p < 1.3e-07) relative to wild-type controls. Preadministration of paclitaxel or XR9576, a modulator, had little effect on the biodistribution in these mdr1a/1b(-/-) mice. As a result, [(18)F]fluoropaclitaxel will be a useful radiopharmaceutical for the study of multidrug resistant tumors.

A new paclitaxel prodrug for use in ADEPT strategy

A new paclitaxel prodrug intended for use in Antibody-Directed Prodrug Therapy (ADEPT) or Prodrug Monotherapy (PMT) has been prepared. This prodrug was originally designed to be activated into the drug by human beta-glucuronidase. In order to enhance the liberation rate of paclitaxel, an elongated spacer system including a nitro-aromatic derivative and a N,N'-methylethylenediamine was incorporated between the sugar moiety and the drug. Indeed, this new prodrug proved to be activated significantly faster than a former paclitaxel prodrug containing a conventional spacer.

Synthesis of C-3' methyl taxotere (docetaxel)

Protected (3R,4S)-N-Boc-3-hydroxy-4-methyl-4-phenylazetidin-2-one has been synthesized stereoselectively and used to esterify protected 10-desacetylbaccatin III to give, following removal of the protecting groups, novel C-3' methyl taxotere (docetaxel).

A de novo enantioselective total synthesis of (-)-laulimalide

An enantioselective total synthesis of the naturally occurring anticancer agent (-)-laulimalide is described. The synthesis is characterized by extensive use of new reaction methodologies based on catalytic asymmetric acyl halide-aldehyde cyclocondensation (AAC) reactions and transformations of the derived enantioenriched beta-lactones. The synthesis also incorporates a unique allenylstannane glycal acetate alkylation and chemoselective ring-closing metathesis reaction.