Cytotoxic titanium and vanadium complexes

Abstract

The present application provides a family of highly resistant and water-stable Titanium and Vanadium complexes, which may be administered directly without a further hydrolysis step and which solubility and cell-penetration characteristics may be modifiable by reducing their particle size to the nanoscale.

Claims

1. A metal complex selected from: ##STR00109##

2. A composition comprising a metal complex according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 present the ORTEP drawings of compound 3 in 50% probability ellipsoids; H-atoms and solvent molecule were omitted for clarity.

(3) FIG. 2 depicts dependence of OVCAR cell viability following a three days incubation period on administered concentration of compound 3, compound 4 and the hydrolysis product of compound 4 administered in a nanoformulated form.

(4) FIGS. 3A-B depict dependence of HT-29 cell viability following a three days incubation period on administered concentrations of compound 1 (FIG. 3A) and compound 2 (FIG. 3B).

(5) FIGS. 4A-B depict dependence of HT-29 (FIG. 4A) and OVCAR-3 (FIG. 4B) cell viability following a three days incubation period on administered concentrations of compounds 5-9.

(6) FIG. 5 depicts dependence of HT-29 and OVCAR-3 cell viability following a three days incubation period on administered concentrations of compound 50.

(7) FIG. 6 depicts dependence of HT-29 and OVCAR-3 cell viability following a three days incubation period on administered concentrations of compound 63.

(8) FIGS. 7A-B depict dependence of average tumor size on time following administration of compound 3 (FIG. 7A) and compound 5 (FIG. 7B): 100 g per mouse per injection, IP, every other day for 4 weeks, to a group of 5 mice previously treated with HT-29-human colon adenocarcinoma (5*10.sup.6 cells, SC) relative to untreated control.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) As noted hereinabove, titanium(IV) based anticancer complexes were the first to enter clinical trials following platinum compounds, demonstrating high antitumor activity toward a range of cancer cells with reduced toxicity. The recently introduced cytotoxic bis(alkoxo)salan Ti.sup.IV complexes had been determined to be: (a) substantially more hydrolytically stable than known Ti.sup.IV complexes; and (b) markedly more active than (bzac).sub.2Ti(OiPr).sub.2, Cp.sub.2TiCl.sub.2, and cis-platin toward variety of cancer-derived cell lines. Nevertheless, these complexes ultimately hydrolyzed to release the labile alkoxo ligands in the biological environment to give polynuclear products. These products although were inactive when administered directly, surprisingly showed high cytotoxicity when formulated into nano-particles.

(10) Vanadium complexes have also previously been shown to lead to cytotoxic compounds. Vanadium(V) complexes based on salan ligands with a labile alkoxo group showed high cytotoxicity but low stability in water.

(11) Herein, the inventors of the present application describe a novel approach which stands against the presently acceptable notion that labile groups are necessary for increased cytotoxicity and provide support to the fact that labile ligands are not be required for cytotoxicity of Ti and V complexes unlike for cis-platin.

(12) It has also been found that reducing the particle size of the complexes of the invention to the nanometric range accelerated intercellular permeability, increased solubility and the dissolution rate. Nanoparticles of Ti and V complexes of the invention were obtained by a rapid conversion of a volatile oil-in-water microemulsion into a dry powder composed of nanoparticles. Rapid evaporation of the volatile droplets containing the complex yielded the powder, which was easily dispersible in an aqueous medium to form stable nanometric dispersions. Notably, the surfactants used were approved by FDA for incorporation into pharmaceutical dosage forms.

(13) Under the notion that labile ligands were not essential for cytotoxicity, pre-designed inert and hydrolytically stable cytotoxic complexes are highly advantageous because the hydrolysis step and the accompanying undesired release of side products such as free labile ligands are eliminated. Thus, tris- and tetrakis-phenolato ligands were prepared and afforded the monomeric octahedral complexes compound 3 and compound 4 (Scheme 2).

(14) ##STR00108##

(15) .sup.1H NMR confirmed that a single product of each complex had formed and the X-ray structure of compound 3 featured an octahedral C.sub.2-symmetrical complex (FIG. 1).

(16) TABLE-US-00002 TABLE 2 Mean particle size measured for 0.2 wt % dispersion in water and IC.sub.50 (M) values toward OVCAR and HT-29 cancer cells for the nanoformulated complexes of the invention. Particle size OVCAR HT-29 HU-2 Complex (nm) (M) (M) (M) compound 4 9.0 0.6 70 22 54 16 compound 3 5.3 0.3 14 4 12 2 0.8 1

(17) Comparative hydrolysis measurements by .sup.1H NMR were carried by monitoring the integration of selected signals with time following addition of 10% D.sub.2O to [D8]THF solution of the complexes. The t.sub.1/2 value for isopropoxo hydrolysis for compound 4 was ca. 100 hours, markedly higher than the value previously reported for analogous complexes of two labile ligands obtained under similar conditions (ca. 5 hours). Compound 3 demonstrated even higher stability, where no substantial hydrolysis was observed for over a week. As expected, the decrease in the number of labile ligands dramatically increased the hydrolytic stability of the complexes.

(18) Compound 3, compound 4, and the hydrolysis product of compound 4 were all inactive when measured directly on HT-29 and OVCAR-1 cells. However, when formulated into nanoparticles, both were cytotoxic (FIG. 2, Table 2). Particularly, the most stable complex compound 3 exhibited the highest cytotoxicity, with IC.sub.50 values that are comparable to those of the most active salan bis(alkoxo) derivatives. Additionally, compound 3 also showed particularly high cytotoxicity toward the multi-drug-resistant (MDR) cells HU-2.

(19) Compound 1 and compound 2 were synthesized similarly. Importantly, these complexes showed cytotoxic activity independent of formulations, even when administered directly (FIGS. 3A-B). The hydrolytic stability of these complexes is similarly high, where no decomposition is observed for days in water solutions.

(20) FIGS. 4A-B depict dependence of HT-29 (FIG. 4A) and OVCAR-3 (FIG. 4B) cell viability following a three days incubation period on administered concentrations of compounds 5-9.

(21) Similar results have been obtained for the various vanadium(V) complexes of the invention. Ligands were generally prepared according to known procedures, and the complexes were obtained by reacting the ligands with a vanadium precursor under inert conditions and possibly with the addition of base. As demonstrated in Table 3, vanadium complexes compounds 5-9 exhibited a remarkable cytotoxic activity which is significantly higher than that of cis-platin toward ovarian and colon cells. These vanadium complexes with no labile ligands demonstrated the activity also when administered directly, independent of particular formulations. Moreover, these complexes are stable for weeks in the presence of water.

(22) The vanadium(V) complex compound 50 (FIG. 5) and the vanadium(IV) complex compound 63 (FIG. 6) also showed high activity independent of formulations (Table 3).

(23) FIGS. 7A-B depict dependence of average tumor size on time following administration of compound 3 (FIG. 7A) and compound 5 (FIG. 7B): 100 g per mouse per injection, IP, every other day for 4 weeks, to a group of 5 mice previously treated with HT-29-human colon adenocarcinoma (5*10.sup.6 cells, SC) relative to untreated control.

(24) TABLE-US-00003 TABLE 3 Cytotoxic activity of vanadium complexes of the invention administered without formulations as compared to cis-platin. IC50 and maximal inhibition values Complex OVCAR-3 HT-29 Cis-platin 8.8 2.1 (91%) 12.2 2.3 (90%) compound 5 0.3 0.1 (88%) 1.9 0.6 (97%) compound 6 0.3 0.1 (90%) 2.5 0.7 (98%) compound 7 .sup.3.2 (95%) compound 8 0.6 0.2 (85%) 0.7 0.1 (94%) compound 9 .sup.1.3 (84%) 2.0 0.4 (99%) compound 50 2.8 0.5 (87%) 4.6 0.8 (96%) compound 63 4.3 1.4 (87%) 5.8 0.3 (97%)

(25) The results presented herein attest to the ability of the biologically friendly Ti species to form complexes that are stable for weeks in an aqueous environment and are highly cytotoxic. Similarly, vanadium complexes can also demonstrate this desired combination of features. The results presented herein provide a well-established understanding that unlike for cis-platin, ligand lability is not a pre-requisite for cytotoxicity of Ti and V complexes, which serves as a particular advantage in this case due to the rich aquatic chemistry of Ti and V compounds. Thus, stable Ti and V complexes are certainly attainable and may lead to high activity in a controlled manner without accompanying release of undesired products. For this reason, administering the stable active species directly is advantageous over receiving it through a hydrolysis step.

(26) Ligands and complexes were generally synthesized according to published procedures. All ligands were dried at 80 C. under vacuum for over 12 hours before complexation. All solvents were distilled using K or K/benzophenone under nitrogen, or dried over aluminum column on an M. Braun drying system SPS-800. All experiments requiring dry atmosphere were performed in an M. Braun dry-box or under nitrogen atmosphere using Schlenck line techniques.

(27) Microemulsions were prepared by dissolving Ti or V complexes in n-butyl acetate (purchased from Sigma-Aldrich Chemical Company Inc.) and adding soybean phosphatidylcholine (at least 92% purity, Lipoid S75, supplied by Lipoid, Switzerland), ammonium glycyrrhizinate (purchased from Sigma-Aldrich Chemical Company Inc), dipotassium glycyrrhizinate (obtained from TCI, Japan) and isopropyl alcohol (purchased from Sigma-Aldrich Chemical Company Inc.) to the resultant solution as to create an oil phase. Water was then added and the mixture and was allowed to equilibrate at 25 C. until transparent isotropic system was formed.

(28) Microemulsion compositions used as templates for the nanopowder preparation were: Ti complex 1.5 wt %, n-butyl acetate (volatile solvent) 23.5 wt %, isopropyl alcohol 25 wt %, ammonium glycyrrhizinate (surfactant) 6 wt %, soybean phosphatidylcholine (surfactant) 4 wt %, dipotassium glycyrrhizinate (surfactant) 5 wt % and water 35 wt %. The resultant system was homogeneous, optically transparent and exhibited no birefringence.

(29) All solvents were evaporated from the microemulsion at a temperature of 473 C. and absolute pressure <1 mbar using a DW-3 Lyopholizer (Heto-Drywinner, Denmark). The samples were kept under these conditions for 72 hours. Dry solvent-free powders were consequently obtained. The composition of these powders was: salan TiIV complex 9.1 wt %, ammonium glycyrrhizinate 36.4 wt %, soybean phosphatidylcholine 24.2 wt %, dipotassium glycyrrhizinate 30.3 wt %.

(30) The dry powder obtained at the end of the freeze-drying process was dispersed at 0.2% in distilled water. The sample was manually shaken for 15 seconds. Particle size distribution by volume was measured at room temperature by dynamic light scattering using a Nano-ZS Zetasizer (Malvern, UK). A 633 nm wavelength laser beam was used to illuminate the sample and the light scattering was detected at 173 angle by the Non-Invasive Back-Scatter (NIBS) technology. The advantages of the backscatter detection are: (a) Ability to measure particle size at high concentration; (b) Elimination of dust and impurity effect. Size measurements of the dispersion were performed in triplicate.

(31) As a reference, nanopowder without the complexes was prepared similarly, dispersed in water, and the particle size was 4.90.2 nm, much smaller than that of the nanoparticles with the reagent tested.

(32) NMR data were recorded using AMX-400 or AMX-500 MHz Bruker spectrometer. X-ray diffraction data were obtained with a Bruker SMART APEX CCD diffractometer, running the SMART software package. After collection, the raw data frames were integrated by the SAINT software package. The structures were solved and refined using the SHELXTL software package. Hydrolysis studies by NMR were performed using a solution of the complex in [D.sup.8]THF and adding 10% D.sub.2O. The results were verified by including p-dinitrobenzene as an internal standard.

(33) Cytotoxicity was measured on HT-29 colon and OVCAR ovarian cells obtained from ATCC Inc. using the methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay. Cells (0.6106) in medium (contains: 1% penicillin/streptomycin antibiotics; 1% L-glutamine; 10% fetal bovine serum (FBS) and 88% medium RPMI-1640, all purchased from Biological Industries Inc.) were seeded into a 96-well plate and allowed to attach for a day. The cells were consequently treated with the reagent tested at 10 different concentrations. Solutions/dispersions of the reagents were prepared either by dissolving 8 mg of the nonformulated reagent in 200 L of THF or by dispersing 8 mg of formulated reagent in 200 L of medium, with further diluting to obtain the different concentrations. A total of 20 L of the resulting system were diluted with 180 L of medium. Consequently, 10 L of each final system were added to each well already containing 200 L of the above solution of cells in the medium to give final concentration of up to 200 mg/L. Control wells were treated with similar amounts of THF or medium. After a standard of 3 days incubation at 37 C. in 5% CO.sub.2 atmosphere, MTT (0.1 mg in 20 L) was added and the cells were incubated for additional 3 hours. The MTT solution was then removed, and the cells were dissolved in 200 L isopropanol. The absorbance at 550 nm was measured by a Bio-Tek EL-800 microplate reader spectrophotometer. Each measurement was repeated at least 33 times, namely, three repeats per plate, all repeated at least 3 times on different days (9 repeats altogether). IC.sub.50 values were determined by a non-linear regression of a variable slope (four parameters) model.

(34) All ligands have been prepared following published or modified procedures. Ligand L5 was obtained based on a published procedure [27].

(35) Ligand L6 was obtained by reacting one equivalent of N,N-Bis(2-hydroxyethyl) ethylenediamine with two equivalents of 2-hydroxy-5-nitrobenzyl bromide and five equivalents of triethylamine in THF. The reaction was stirred overnight and the precipitate formed was expelled by filtration. The filtrate was evaporated and the product was obtained as a yellow powder after recrystallized in ethanol.

(36) Ligand L17 was synthesized by refluxing 3,4-dimethylphenol (2.44 g, 20 mmol) with formaldehyde (4 ml, 40 mmol) and N-methylethylenediamine (0.58 ml, 6.67 mmol) for 24 hours in methanol (20 ml). The solution was allowed to cool to room temperature and the colorless precipitate was collected by filtration to produce the ligand in 40% yield.

(37) .sup.1H NMR (400 MHz, CDCl.sub.3): =6.77 (s, 2H; Ar), 6.68 (s, 1H; Ar), 6.63 (s, 1H; Ar), 6.59 (s, 2H; Ar), 3.62 (s, 4H; CH2), 3.58 (s, 2H; CH2), 2.71 (t, J=3.6 Hz, 2H; CH2), 2.68 (t, J=3.6 Hz, 2H; CH2), 2.22-2.08 ppm (m, 21H; CH3); 13C NMR (100 MHz; CDCl3): =155.5, 154.0, 137.5, 137.2, 131.5, 130.1, 127.6, 127.1, 119.6, 119.1, 117.8, 117.7, 61.2, 55.7, 53.6, 50.6, 41.6, 19.7, 18.8 ppm; Anal. Calcd for C.sub.30H.sub.40N.sub.2O.sub.3: C, 75.59; H, 8.46; N, 5.88. Found: C, 75.40; H, 8.50; N, 5.80.

(38) Compound 4 was synthesized by mixing Ti(OiPr).sub.4 (0.050 g, 0.18 mmol) dissolved in dry THF (5 ml) with L17 (0.072 g, 0.18 mmol) dissolved in dry THF (5 ml) under an inert atmosphere. The two solutions were allowed to mix at room temperature for 2 hours. The solvent was removed under reduced pressure to give the product as a yellow solid in a quantitative yield.

(39) .sup.1H NMR (400 MHz, CDCl3): =6.90 (s, 1H; Ar), 6.84 (s, 1H; Ar), 6.66 (s, 1H; Ar), 6.65 (s, 1H; Ar), 6.47 (s, 1H; Ar), 6.44 (s, 1H; Ar), 4.95 (sept, J=6.0 Hz, 1H; CHCH3), 4.61 (d, J=13.2 Hz, 2H; CH2), 4.41 (d, J=12.6 Hz, 1H; CH2), 3.40 (d, J=13.6 Hz, 1H; CH2), 3.37 (d, J=13.6 Hz, 1H; CH2), 3.03 (dt, J=14.0, 4.4 Hz, 1H; CH2), 2.73 (d, J=12.6 Hz, 1H; CH2), 2.49 (dt, J=12.6, 4.4 Hz, 1H; CH2), 2.26 (dd, J=14.0, 4.4 Hz, 1H; CH2), 2.23-2.09 (m, 21H; CH3), 1.78 (dd, J=14.0, 4.4 Hz, 1H; CH2), 1.23 (d, J=6.0 Hz, 3H; CHCH3), 1.22 ppm (d, J=6.0 Hz, 3H; CHCH3); 13C NMR (125 MHz; CDCl3): =161.1, 160.4, 160.2, 138.7, 138.2, 137.2, 131.0, 130.6, 130.4, 126.8, 126.0, 125.9, 122.0, 121.9, 121.4, 118.6, 118.0, 117.3, 78.8, 66.0, 65.1, 64.1, 59.3, 50.9, 44.2, 25.5, 25.5, 20.1, 19.9, 19.8, 19.0, 19.0 ppm; Anal. Calcd for C.sub.33H.sub.44N.sub.2O.sub.4Ti: C, 68.27; H, 7.64; N, 4.83. Found: C, 68.04; H, 7.55; N, 4.69.

(40) Compound 3 was synthesized similarly, by reacting Ti(OiPr).sub.4 (0.050 g, 0.18 mmol) with L15 (R=o,p-Me) (0.126 g, 0.18 mmol) in dry THF under an inert atmosphere.

(41) .sup.1H NMR (500 MHz, [D8]THF): =7.32 (d, J=2.5 Hz, 2H; Ar), 7.27 (d, J=2.5 Hz, 2H; Ar), 7.14 (d, J=2.5 Hz, 2H; Ar), 6.90 (d, J=2.5 Hz, 2H; Ar), 4.66 (d, J=13.5 Hz, 2H; CH2), 3.91 (d, J=14.0 Hz, 2H; CH2), 3.73 (d, J=14.0 Hz, 2H; CH2), 3.67 (d, J=14.0 Hz, 2H; CH2), 2.97 (m, 4H; CH.sub.2); 13C NMR (125 MHz; [D.sub.8]THF): 6=157.4, 155.9, 130.3, 130.1, 129.6, 129.3, 128.3, 128.2, 125.5, 124.2, 123.0, 122.7, 66.1, 61.4, 59.4 ppm; Anal. Calcd for C.sub.30H.sub.20Cl.sub.8N.sub.2O.sub.4Ti: C, 44.82; H, 2.51; N, 3.48. Found: C, 44.71; H, 3.02; N, 4.05.

(42) Crystal data for compound 3: C.sub.30H.sub.20Cl.sub.8N.sub.2O.sub.4Ti.0.5(C.sub.7H.sub.8), M=846.02, Triclinic, a=8.701(2), b=9.167(2), c=22.742(4) , =80.004(3), =85.872(3), =77.098(3). V=1740.1(5) .sub.3, T=173(1) K, space group P, Z=2, (MoK)=0.902 mm-1, 18949 reflections measured, 7523 unique (R.sub.int=0.1017), R(F. 2) for [I>2(I)]=0.1149, R.sub.w for [I>2(I)]=0.2190.

(43) Compound 1 and compound 2 were obtained similarly by reacting one equivalent of the ligand L6 and L5, respectively, with one equivalent of Ti(OiPr).sub.4 in THF at room temperature under nitrogen atmosphere for several hours. The product precipitated from the solution and was isolated by decantation.

(44) Ligands L7-L11 were prepared by modifying a previously published procedure [28]. Salicylaldehyde (or a substituted salicylaldehyde) was reacted in a 2:1 ratio with ethylene diamine and reduced with sodium borohydride to produce a salan compound. This compound was refluxed with an equimolar amount of the corresponding salicylaldehyde, and reduced with sodium borohydride to give the pentadentate tris(phenolato) ligand. The ligand was purified by extraction with ethyl acetate and crystallization from cold methanol.

(45) Compound 5-9 were prepared by reacting equimolar amounts of Vanadium(V) trisisopropoxide oxide and the pentadentate tris(phenolato) ligand L7-L11, respectively.

(46) Ligand L50 was synthesized according to a previously published procedure [29]. 2,4-dimethylphenol was heated with hexamethylenetetramine in the presence of p-toluenesulfonic acid for 2 days. The resulting ligand was crystallized from cold methanol.

(47) Compound 50: The complex was prepared by reacting equimolar amounts of Vanadium(V) trisisopropoxide oxide and the tetradentate tris(phenolato) ligand L50 in the presence of catalytic amount of triethylamine.

(48) Ligand L63 was synthesized according to a previously published procedure [30].

(49) Compound 63 was prepared as described previously [31]. Ligand L63 was reacted with equimolar amounts of VOSO.sub.4.5H.sub.2O in an aquatic solution, in the presence of sodium acetate to receive the required complex, which was collected by filtration.