Pemetrexed

Enzyme Assays and Methods. :

TS activity is assayed using a spectrophotometric method, which involved monitoring the increase in absorbance at 340 nm resulting from formation of the product, 7,8-dihydrofolate. The assay buffer contains 50 mM N-tris[hydroxymethyljmethyl-2-aminoethanesulfonic acid, 25 mM MgC1₂, 6.5 mM formaldehyde, 1 mM EDTA, and 75 mM 2-mercaptoethanol, pH 7.4. The concentrations of deoxyuridylate monophosphate, 6R-MTHF, and hIS are 100 μM, 30μM and 30 nM (1.7 milliunits/mL), respectively. At the 6R-MTHF concentration, an uninhibited reaction and six concentrations of inhibitor are assayed. K_{i app} values are determined by fitting the data to the Morrison equation using nonlinear regression analysis with the aid of the program ENZFITTER. K_i values are calculated using the equation: K_{i app}= K_i(1 + [S]/K_m), where [S] is equal to 30 μM and K_m is equal to 3 μM. DHFR activity is assayed spectrophotometrically by monitoring the dis appearance of the substrates NADPH and 7,8-dihydrofolate at 340 nm. The reaction takes place at 25°C in 0.5 mL of 50 mM potassium phosphate buffer, which contains 150 mM KC1 and 10 nM 2-mercaptoethanol, pH 7.5, and 14 nM (0.34 milliunitlmL) DHFR. The NADPH concentration is 10 μM and 7,8-dihydrofolate is varied at 5, 10, or 15 μM. At each 7,8-dihydrofolate concentration, an uninhibited reaction and seven concentrations of inhibitor are assayed. The ENZFITI'ER microcomputer program is used to obtain K_{i app} values by fitting the data to the Morrison equation by nonlinear regression analysis. K_{i app}= K_i(1 + [S]/K_m), where [S] is equal to the concentration of 7,8-dihydrofolate used and K_m of 7,8-dihydrofolate is equal to 0.15 μM. GARFT activity is assayed spectrophotometrically by monitoring the increase of absorbance resulting from formation of the product 5,8-dideazafolate at 295 nm. The reaction solvent contains 75 mM HEPES, 20% glycerol, and 50 mM a-thioglygerol, pH 7.5, at 25°C. The concentrations of substrates and enzyme used are 10 μM α,β-glycinamide ribonucleotide, 0-10 μM 10-formyl-5,8-dideazafolic acid, and 10 nM (1.9 milliunits/mL) GARFT. K_i values are calculated using the Enzyme Mechanism program of the Beckman DU640 spectrophotometer, which uses nonlinear regression analysis to fit data to the Michaelis-Menten equation for competitive inhibition.

• Cell lines: CCRF-CEM leukemia, GC3/C1 colon carcinoma, and HCT-8 ileocecal carcinoma cells.
• Concentrations: 0-30 μM
• Incubation Time: 72 hours
• Method: Dose-response curves are generated to determine the concentration required for 50% inhibition of growth (IC50). Pemetrexed disodium is dissolved initially in DMSO at a concentration of 4 mg/mL and further diluted with cell culture medium to the desired concentration. CCRF-CEM leukemia cells in complete medium are added to 24-well Cluster plates in a total volume of 2.0 mL. Pemetrexed disodium at various concentrations are added to duplicate wells so that the final volume of DMSO is 0.5%. The plates are incubated for 72 hour at 37 °C in an atmosphere of 5% CO₂ in air. At the end of the incubation, cell numbers are determined on a ZBI Coulter counter. For several studies, IC50s are determined for each compound in the presence of either 300 μM AICA, 5 μM thymidine, 100 μM hypoxanthine, or combination of 5 μM hymidine plus 100 μM hypoxanthine. For adherent tumor cells, a modification of the original MTT colorimetric assay is used to measure cell cytotoxicity. The human tumor cells are seeded in 100 μL assay medium/well in 96-well flat-bottomed tissue culture plates. The assay medium contains folic acid-free RPMI 1640 supplemented with 10% FCS and either 2 nM folinic acid or 2.3 μM folic acid as the sole folate source. Well 1A is left blank. Stock solutions of antifolates are prepared in Dulbecco's PBS at 1 mg/mL, and a series of 2-fold dilutions are subsequently made in PBS. Ten-μL aliquots of each concentration are added to triplicate wells. Plates are incubated for 72 hours at 37 °C in a humidified atmosphere of 5% CO₂-in-air. MTT is dissolved in PBS at 5 mg/mL, 10 μL of stock MTF solution are added to each well of an assay, and the plates are incubated at 37 °C for 2 additional hours. Following incubation, 100 μL of DMSO are added to each well. After thorough formazan solubilization, the plates are read on a Dynatech MR600 reader, using a test wavelength of 570 nm and a reference wavelength of 630 nm. The IC50 is determined as the concentration of drug required to inhibit cell growth by 50% compared to an untreated controls.
  (Only for Reference)

• Animal Models: EMT-6 mammary carcinoma, the human HCT 116 colon carcinoma, and the human H460 non-small cell lung carcinoma are injected s.c. into the nude mice.
• Formulation: Pemetrexed disodium is dissolved in DMSO and then diluted in water.
• Dosages: 100 mg/kg or 150 mg/kg
• Administration: Administered via i.p.
  (Only for Reference)