Liposomal Hexaglutamated Pemetrexed Production

Example 1

Production of Alpha Hexaglutamated Pemetrexed (αHgPMX) Liposomes

Briefly L alpha hexaglutamated pemetrexed (aGR6) and D alpha hexaglutamated pemetrexed (aDGR6) were encapsulated in liposomes by the following procedure. First, the lipid components of the liposome membrane were weighed out and combined as a concentrated solution in ethanol at a temperature of around 65° C. In this example, the lipids used were hydrogenated soy phosphatidylcholine, cholesterol, and DSPE-PEG-2000 (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (polyethylene glycol)-2000]). The molar ratio of HSPC:Cholesterol:PEG-DSPE was approximately 3:2:0.15. Next, the aGR6 or aDGR6 was dissolved in 5% dextrose at a concentration of 150 mg/ml with a pH of 6.5-6.9. The drug solution was heated up to 65° C. The ethanolic lipid solution was injected into the aGR6 or aDGR6 solution using a small-bore needle. During this step the drug solution was well stirred using a magnetic stirrer. The mixing was performed at an elevated temperature (63° C.-72° C.) to ensure that the lipids were in the liquid crystalline state (as opposed to the gel state that they attain at temperatures below the lipid transition temperature Tm=51° C.−54° C.). As a result, the lipids were hydrated and form multiple bilayer (multilamellar) vesicles (MLV) containing aGR6 or aDGR6 in the aqueous core.

Downsizing of MLV's Using Filter Extrusion

The MLVs were fragmented into unilamellar (single bilayer) vesicles of the desired size by high-pressure extrusion using three passes through stacked (track-etched polycarbonate) membranes. The first pass was performed through stacked membranes consisting of two layers with a pore size of 200 nm. The remaining two passes were through the stacked membranes consisting of three layers with a pore size of 100 nm. During extrusion, the temperature was maintained above the Tm to ensure plasticity of the lipid membranes. As a result of the extrusion, large and heterogeneous in size and lamellarity MLVs turned into small, homogenous (90-125 nm) unilamellar vesicles (ULV) that sequestered the drug in their interior. A Malvern Zetasizer Nano ZS instrument (Southborough, Mass.) with back scattering detector(90°) was used for measuring the hydrodynamic size (diameter) at 25° C. in a quartz micro cuvette. The samples were diluted 50-fold in formulation matrix before analysis.

Purification of Liposomes

After the ULV's containing aGR6 or aDGR6 had been produced, the extra-liposomal free drug was removed using columns for small volume or tangential flow diafiltration against a suitable buffer for large volume. Although any buffer solution can be used, in this example the buffer used was 5 mM HEPES, 145 mM Sodium Chloride, pH 6.7. Upon completion of purification, filter sterilization was performed using a 0.22 micron filter.

Production of Alpha Hexaglutamated Pemetrexed (αHgPTX) Liposomes

Briefly L alpha hexaglutamated pemetrexed (aG6) and D alpha hexaglutamated pemetrexed (aDG6) were encapsulated in liposomes by the following procedure. First, the lipid components of the liposome membrane were weighed out and combined as a concentrated solution in ethanol at a temperature of around 65° C. In this example, the lipids used were hydrogenated soy phosphatidylcholine, cholesterol, and DSPE-PEG-2000 (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy (poly-ethylene glycol)-2000]). The molar ratio of HSPC:Cholesterol:PEG-DSPE was approximately 3:2:0.15. Next, the aG6 or aDG6 was dissolved in 5% dextrose at a concentration of 150 mg/ml with a pH of 6.5-6.9. The drug solution was heated up to 65° C. The ethanolic lipid solution was injected into the aG6 or aDG6 solution using a small-bore needle. During this step the drug solution was well stirred using a magnetic stirrer. The mixing was performed at an elevated temperature (63° C.-72° C.) to ensure that the lipids were in the liquid crystalline state (as opposed to the gel state that they attain at temperatures below the lipid transition temperature Tm=51° C.-54° C.). As a result, the lipids were hydrated and form multiple bilayer (multilamellar) vesicles (MLV) containing aG6 or aDG6 in the aqueous core.

Downsizing of MLV's Using Filter Extrusion

The MLVs were fragmented into unilamellar (single bilayer) vesicles of the desired size by high-pressure extrusion using three passes through stacked (track-etched polycarbonate) membranes. The first pass was performed through stacked membranes consisting of two layers with a pore size of 200 nm. The remaining two passes were through the stacked membranes consisting of three layers with a pore size of 100 nm. During extrusion, the temperature was maintained above the Tm to ensure plasticity of the lipid membranes. As a result of the extrusion, large and heterogeneous in size and lamellarity MLVs turned into small, homogenous (90-125 nm) unilamellar vesicles (ULV) that sequestered the drug in their interior. A Malvern Zetasizer Nano ZS instrument (Southborough, Mass.) with back scattering detector(90°) was used for measuring the hydrodynamic size (diameter) at 25° C. in a quartz micro cuvette. The samples were diluted 50-fold in formulation matrix before analysis.

Purification of Liposomes

After the ULV's containing aG6 or aDG6 had been produced, the extra-liposomal gG6 was removed using columns for small volume or tangential flow diafiltration against a suitable buffer for large volume. Although any buffer solution can be used, in this example the buffer used was 5 mM HEPES, 145 mM Sodium Chloride, pH 6.7. Upon completion of purification, filter sterilization was performed using a 0.22 micron filter. The typical characteristics of liposomal derivatives are shown in the table below.

A dose response study was performed using liposomes containing hexaglutamated pemetrexed that were prepared essential as described above.

Cell viability was determined by CellTiter-Glo® (CTG) luminescent cell viability assay on Day 3 (48 hour) and Day 4 (72 hour). This assay determines the number of viable cells in culture based on quantifying ATP that is present within, which in turn signals the presence of metabolically active cells. The CTG assay uses luciferase as a readout. To assess cell viability Dose response inhibition of pemetrexed, HGP and liposomes on different cancer cell growth were investigated using CellTiter-Glo® luminescent cell viability assay. Human cancer cells were harvested, counted and plated at a same cell density on Day 0. A series of 8 dilutions of each test article were added to the cells on Day 1. Dose response curve were generated and fit using GraphPad Prism and IC50 of each test article were calculated. A lower the IC50 is, the more potent the test article is in term of cancer cell growth inhibition.

Cells were seeded into 96-well plate at a cell density of 5×10⁴ cells per well in 100 μl of fresh media on Day 0. Eight serial 2-fold dilutions of each test article in culture medium were generated and added to cells in triplicate on Day 1. In addition, three wells of cells were treated with vehicle (HBS for free drug or empty liposome for liposomal HGP) alone as a control.

On Days 3 and 4, 100 μl of CellTiterGlo® Reagent were added to each well and incubated at room temperature for 15 minutes. Luciferase luminescence were recorded for each well. In addition, 8 serial 2-fold dilutions of the vehicle (HBS or empty liposome) in culture medium were added into empty wells and included in the assay to generate the background luminescence signals. Luciferase signals were normalized by subtracting the background luminescence signal out of the read-outs respectively.

Human Normal Primary Bone Marrow CD34+ Cells were obtained from ATCC. (ATCC Catalog Number PCS-800-012). Cells were thawed at 37° C. for 1 minute and then placed on ice. The cells were then resuspended in StemSpan SFEM (Stem Cell Tech Catalog Number 9650) plus 10% heat inactivated fetal bovine serum (Corning 35-015-CV). The cells were plated into 96 well culture plates at a density of 2.5×10⁴ cells/well. The following day, live cells were collected via centrifugation and resuspended in neutrophil growth media (StemSpan SFEM plus 10% Heat Inactivated fetal bovine serum plus 100 ng/ml human stem cell factor (Sigma Catalog Number H8416), 20 ng/ml human granulocyte colony-stimulation factor (Sigma Catalog Number H5541), and 10 ng/ml human recombinant IL3 (Sigma SRP3090) at a density of 2.5×104 cells/well. Cells were incubated at 37° C. for 10 days. Fresh media was added every two days. Mature neutrophils were then collected and plated in 96 well plates at a density of 1×10⁴ cells/well and incubated at 37° C. overnight. The next day, test article or vehicle was resuspended in neutrophil growth media and added to the plates. The cells were then incubated for either 48 hours or 72 hours at 37° C. and then assayed at each time point using the Cell Titer Glo Assay (Promega Catalog #G7572).

Methodologies used for cell line AML12 (non-cancerous liver cells) and CCD841 (non-cancerous colon epithelial cells) are similar to the methods used for cancer cells.

Results

In a set of dose response experiments, 6 cell lines representing different types of cancers, namely HT-29 (colon cancer), H2342 (NSCLC, adenocarcinoma subtype), H292 (NSCLC, adenocarcinoma subtype), SW620 (CRC), H1806 (triple negative breast cancer) and OAW28 (ovarian cancer), were studied (FIG. 2). Treatment consisted of exposure for 48 hours using 2 different encapsulated derivatives of liposomal alpha pemetrexed hexaglutamate, namely liposomal alpha L hexaglutamate (liposomal aG6) and its mirror image, liposomal alpha D hexaglutamate (liposomal aDG6) also referred to as its corresponding enantiomer.

The relative potency of the above mentioned derivatives as compared to pemetrexed, following exposure over 48 hours, is represented in FIG. 2. The relative potency of treatment using the various derivatives, as shown in this figure was calculated by dividing the IC50 of pemetrexed by the IC50 of the liposomal alpha pemetrexed hexaglutamate for each cell line. As shown in this figure, in all cell lines, the potency of liposomal alpha pemetrexed hexaglutamate well exceeded that of pemetrexed. By way of example, consider the NSCLC cell line H292. As shown in the figure, the potency of liposomal alpha pemetrexed hexaglutamate was ≥50-fold that of pemetrexed. This suggests that a 2% or lower dose of the liposomal alpha pemetrexed hexaglutamate could have the same treatment effect as a 100% dose of pemetrexed.

As stated in some instances increased uptake of payload can be achieved by targeting the liposomal delivery vehicle using antibody such as Folate Receptor Alpha. By way of example in the next two experiments Liposomal L Gamma G₆/Lps Hexa gG6 was encapsulated using the methods previously described above. Subsequently, pemetrexed, liposomal gamma pemetrexed hexaglutamate derivatives (Liposomal L gamma G6/Lps Hexa gG6) and Folate Receptor Alpha Targeted Liposomal L Gamma G6 (Liposomal gG6-FR1Ab), Free (unencapsulated) L gamma G6 were tested for cytotoxic activity on representative cell lines in non small cell lung cancer cells (NCI-H2342) and colorectal cancer cells (HT-29) as shown in FIG. 3 and FIG. 4 respectively. These data show that both liposomal L gamma pemetrexed hexaglutamate and Folate Receptor Alpha Targeting liposomal L gamma pemetrexed hexaglutamate are more potent than pemetrexed in both cell lines. In general Folate Receptor Alpha Antibody targeting liposomes show the highest potency. By contrast free L gamma G6 has the lowest potency due to its inability to traffic across cell membranes effectively.

Cancer cell viability studies comparing the liposomal alpha pemetrexed hexaglutamate derivatives (liposomal L alphaG6/Lps Hexa aG6 and liposomal D alphaG6/Lps Hexa aDG6) and pemetrexed for cytotoxic activity on representative cell lines in breast, lung and ovarian cancer are shown in FIGS. 5-7. These data show that both liposomal alpha L pemetrexed hexaglutamate and liposomal alpha D pemetrexed hexaglutamate are more potent than pemetrexed. Further, as an indicator of efficacy, the results of the experiments on the same cell lines depicted at various dose levels ranging from 16 to 128 nM in FIGS. 8-10. As shown in these figures, at each of these dose ranges, liposomal alpha L pemetrexed hexaglutamate and liposomal alpha D pemetrexed hexaglutamate are superior to pemetrexed in terms of inhibiting cancer cells for the lung and breast cancer cell lines. In the ovarian cancer cell line, pemetrexed at the dose of 128 nM, appears to be equally effective as liposomal alpha pemetrexed hexaglutamate, whereas the liposomal alpha pemetrexed hexaglutamate at the dose of 32 nM and 64 nM has a better treatment effect than pemetrexed; at 16 nM the treatment effect is lower and similar in magnitude for liposomal alpha pemetrexed hexaglutamate and pemetrexed.

The major toxicities seen in patients treated with pemetrexed is bone marrow suppression which manifests as a decrease in blood counts including neutrophil counts (a type of white blood cells). There is also some adverse effect on the lining of the mouth and gut that manifests as diarrhea and mucositis, as well as an adverse effect on the liver in some instances. To assess the above-mentioned toxicities, treatment of the liposomal alpha pemetrexed hexaglutamate derivatives (L and D) and pemetrexed was measured at 48 hours on CD34+ cells that were differentiated into neutrophils, CCD841 colon epithelium cells and AML12 liver cells. As shown in FIG. 11, liposomal alpha pemetrexed hexaglutamate is significantly less toxic to differentiating human neutrophils in contrast to pemetrexed. This is also supported by neutrophil counts that are better preserved following treatment with the liposomal alpha L pemetrexed hexaglutamate or liposomal alpha D pemetrexed hexaglutamate compared to pemetrexed, at dose ranges from 16 nM to 128 nM (FIG. 12). Strikingly, there does not appear to be any toxicity to the liver cells following treatment with liposomal L alpha pemetrexed hexaglutamate or liposomal alpha D pemetrexed hexaglutamate at the dose levels studied (FIG. 13). In contrast, pemetrexed at all doses studied is leading to a reduction in the liver cell counts of approximately 40%. And finally, the same trend is seen following treatment of epithelial colon cells (FIG. 14). As shown in this figure, pemetrexed at all doses studied is leading to approximately a ≥50% decrease in the number of cells compared to approximately a 20% or less decrease after treatment with liposomal alpha L pemetrexed hexaglutamate and liposomal alpha D pemetrexed hexaglutamate.

Example 3

Methods

Production of Targeted Gamma Hexaglutamated Pemetrexed (HGP) Liposomes

Gamma HGP (gG6) was encapsulated in liposomes and the liposomes were downsized and purified according to procedures essentially as set forth above in Example 1.

Antibody Conjugation

Activated liposomes were prepared by adding DSPE-PEG-maleimide to the lipid composition. The liposomes contain four different lipids: hydrogenated soy phosphatidylcholine (HSPC), cholesterol, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG-2000), and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[maleimide (polyethylene glycol)-2000] (DSPE-PEG-maleimide), in ratios of 3:2:0.1125:0.0375.

Antibody thiolation was accomplished through use of Traut's reagent (2-iminothiolane) to attach a sulfhydryl group onto primary amines Antibody was suspended in PBS at a concentration of 0.9-1.6 mg/ml. Traut's reagent (14 mM) was added to antibody solution at a final concentration of 1-5 mM and then removed through dialysis after one-hour incubation at room temperature. Thiolated antibody was added to activated liposomes at a ratio of 60 g/mol phosphate lipids, and the reaction mixture was incubated for one hour at room temperature and over-night at 4 uL-cysteine was used to terminate the reaction and unconjugated antibody was removed through dialysis.

Exemplary direct and post insertion antibody-liposome conjuation methods are provided below.

Exemplary Antibody Conjugation Method 1: Direct Conjugation

Antibody or its fragments, such as Fab or scFv, can be conjugated directly onto thiol-reactive liposome. Thiol-reactive liposomes are prepared by adding DSPE-PEG-maleimide to the lipid composition. The liposomes contain four different lipids: hydrogenated soy phosphatidylcholine (HSPC), cholesterol, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DSPE-PEG-2000), and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[maleimide (polyethylene glycol)-2000] (DSPE-PEG-maleimide), in ratios of 3:2:0.1125:0.0375.

Antibody (or its fragments, such as Fab or scFv) thiolation is accomplished through use of Traut's reagent (2-iminothiolane) to attach a sulfhydryl group onto primary amines Antibody (or its fragment) is suspended in PBS at a concentration of 0.9-1.6 mg/ml. Traut's reagent (14 mM) is added to antibody (or its fragment) solution at a final concentration of 1-5 mM and then removed through dialysis after one-hour incubation at room temperature. Thiolated antibody (or its fragment) is added to thiol-reactive liposome at a ratio of 60 g/mol phosphate lipids, and the reaction mixture is incubated for one hour at room temperature and over-night at 4° C. L-cysteine is used to terminate the reaction and unconjugated antibody (or its fragment) is removed through dialysis.

Antibody or its fragments, such as Fab or scFv, which contains a cysteine residue at the C-terminal can be conjugated directly onto the liposome by incubating a reduced antibody (or its fragment) with thiol-reactive liposome. Antibody (or its fragment) with a cysteine tail is dissolved and reduced by a 10-20 mM reducing reagent (such as 2-mercaptoethylamine, cysteine, or dithioerythritol) at pH<7. The excess reducing reagent is removed thoroughly by size exclusion chromatography or dialysis. The purified and reduced antibody (or its fragment) can be directly conjugated to the thiol-reactive liposome.

Exemplary Antibody Conjugation Method 2: Post Insertion

Antibody or its fragments, such as Fab or scFv, which contains a cysteine residue at the C-terminal can be conjugated and incorporated into the liposome through a “post insertion” method. Micelles of thiol-reactive lipopolymer (such as DSPE-PEG-maleimide) is prepared by dissolving in an aqueous solution at 10 mg/ml. Antibody (or its fragment) with a cysteine tail is dissolved and reduced by a 10-20 mM reducing reagent (such as 2-mercaptoethylamine, cysteine, or dithioerythritol) at pH<7. The excess reducing reagent is removed thoroughly by size exclusion chromatography or dialysis. The purified and reduced antibody (or its fragment) is then incubated with the micelles of thiol-reactive lipopolymers at a molar ratio of 1:4. At the end of the reaction, the excess maleimide groups are quenched by a small amount of cysteine (1 mM) or mercaptoethanol. Unconjugated antibody (or its fragment) is removed by size exclusion chromatography. Purified conjugated micelles is then incubated with liposome at 37° C. or elevated temperature.

Physical Characteristics of the Nanoparticles

Cell viability was determined by CellTiter-Glo® (CTG) luminescent cell viability assay on Day 3 (48 hour) and Day 4 (72 hour). This assay determines the number of viable cells in culture based on quantifying ATP that was present within, which in turn signals the presence of metabolically active cells. The CTG assay uses luciferase as a readout. To assess cell viability Dose response inhibition of pemetrexed, HGP and liposomes on different cancer cell growth were investigated using CellTiter-Glo® luminescent cell viability assay. Human cancer cells were harvested, counted and plated at a same cell density on Day 0. A series of 8 dilutions of each test article were added to the cells on Day 1. Dose response curve were generated and fit using GraphPad Prism and IC50 of each test article were calculated. A lower the IC50 is, the more potent the test article was in term of cancer cell growth inhibition.

Cells were seeded into 96-well plate at a cell density of 5×10⁴ cells per well in 100 μl of fresh media on Day 0. Eight serial 2-fold dilutions of each test article in culture medium were generated and added to cells in triplicate on Day 1. In addition, three wells of cells were treated with vehicle (HBS for free drug or empty liposome for liposomal HGP) alone as a control.

On Days 3 and 4, 100 μl of CellTiterGlo® Reagent were added to each well and incubated at room temperature for 15 minutes. Luciferase luminescence were recorded for each well. In addition, 8 serial 2-fold dilutions of the vehicle (HBS or empty liposome) in culture medium were added into empty wells and included in the assay to generate the background luminescence signals. Luciferase signals were normalized by subtracting the background luminescence signal out of the read-outs respectively.

Human Normal Primary Bone Marrow CD34+ Cells were obtained from ATCC. (ATCC Catalog Number PCS-800-012). Cells were thawed at 37° C. for 1 minute and then placed on ice. The cells were then resuspended in StemSpan SFEM (Stem Cell Tech Catalog Number 9650) plus 10% heat inactivated fetal bovine serum (Corning 35-015-CV). The cells were plated into 96 well culture plates at a density of 2.5×10⁴ cells/well. The following day, live cells were collected via centrifugation and resuspended in neutrophil growth media (StemSpan SFEM plus 10% Heat Inactivated fetal bovine serum plus 100 ng/ml human stem cell factor (Sigma Catalog Number H8416), 20 ng/ml human granulocyte colony-stimulation factor (Sigma Catalog Number H5541), and 10 ng/ml human recombinant IL3 (Sigma SRP3090) at a density of 2.5×10⁴ cells/well. Cells were incubated at 37° C. for 10 days. Fresh media was added every two days. Mature neutrophils were then collected and plated in 96 well plates at a density of 1×10⁴ cells/well and incubated at 37° C. overnight. The next day, test article or vehicle was resuspended in neutrophil growth media and added to the plates. The cells were then incubated for either 48 hours or 72 hours at 37° C. and then assayed at each time point using the Cell Titer Glo Assay (Promega Catalog #G7572).

Methodologies used for cell line AML12 (non-cancerous liver cells) and CCD841 (non-cancerous colon epithelial cells) are similar to the methods used for cancer cells.

Results:

The dose response relationship of free pemetrexed gamma hexaglutamate (gG6), (non-targeted) liposomal gamma hexaglutamate (liposomal gG6), pemetrexed and folate receptor alpha targeting antibody (FR1Ab) liposomal pemetrexed gamma hexaglutamate (liposomal gG6-FR1Ab), in the NCI H2342 non-small cell lung cancer (NSCLC), adenocarcinoma subtype is shown in FIG. 3. The output is percentage of viable cells after 48 hours of treatment as measured by luciferase luminescence. As shown in this FIG. 3, the free pemetrexed gG6 appears to be the least potent as measured by IC50. Both the liposomal pemetrexed gG6 and the liposomal pemetrexed gG6-FR1Ab are 7-fold and 40-fold more potent, respectively, than free pemetrexed.

Similar data is shown for the HT-29 colon cancer cell line in FIG. 4 that depict cell viability expressed as a percentage. As shown in this figure, free pemetrexed gG6 appears to be the least potent. In this instance, the liposomal pemetrexed gG6 is twice as potent as pemetrexed and the liposomal pemetrexed gG6-FR1Ab is 5-fold more potent than free pemetrexed.