Disposition Kinetics Of Nolatrexed In Animals

Nolatrexed is a novel lipophilic thymidylate synthase (TS) inhibitor, designed and synthesized by means of computer-aided drug design based on the three-dimensional structure of the active site of TS determined by X-ray crystallography.Unlike the classical folate-based TS inhibitors, the drug does not contain the negatively-charged glutamate side chain and enters the cells mainly via passive diffusion rather than by using the reduced folate carrier for transportation. Thus nolatrexed is devoid of the disadvantage of classical folate-based TS inhibitors that use the reduced folate carrier for entry into the cells and need to be polyglutamylated for the enhanced action, showing promising clinical applications as a non-classical TS inhibitor. Nolatrexed demonstrated strong anti-tumor effect in in vitro studies, including proliferative inhibition of most tumor cell lines and effectiveness to those tumor cells that have already developed resistance to other anti-tumor chemotherapeutics.Clinically applied as a single agent, nolatrexed could yield complete remmision (CR) or partial remmision (PR) in patients with some carcinomas such as head and neck and liver tumors. However, as a rule, cancers are clinically treated with anti-tumor drugs in combination. It is, therefore, quite evident that nolatrexed should be used in combination with other anti-tumor drugs. How the drug is rationally combined with others is one of the key problems to be solved in the future studies. To this end, the present studies use animals as subjects to investigate the disposition kinetics of the drug so as to provide useful data for further clinical trials.High performance liquid chromatography (HPLC) with ultraviolet detector was exploited to determine the concentrations of nolatrexed in biological samples from mice, rats and dogs administered intravenously with the drug. After analysis of the correlation between effects and concentrations, recovery and precision, it \vas confirmed that the method applied and the settings of HPLC selected satisfied the requirements for the pharmacokinetic study.Mice were injected intravenously with nolatrexed dihydrochloride in the dosages of 40. 80 and 160 mg/kg. The elimination half-lives(ti:,) of plasma drug concentrations were 1.59, 2.18 and 3.53 h; the areas under the curve(AUC), 57.2, 174.6 and 442.3 ug玥/ml; the apparent volumes of distribution(Vd), 1.77, 1.63 and 0.85 L/kg; and the clearances (CL). 0.73, 0.46 and 0.34 L/(kg玥), respectively, displaying non-linear kinetics profile. While in Beagle dogs, nolatrexed dihydrochloride were administered intravenously with 20mg/kg, the pharmacokinetic parameters were 2.41-2.90 h for elimination half-life (), 54.2-66.3 ug h/ml for area under the curve(AUC), 0.22-0.41 L/kg for apparent volume of distribution(Vd) and 0.29-0.37 /(kg h) for clearance(CL)It was observed that nolatrexed was mainly distributed in blood flow-rich organs such as heart, lungs, liver, kidneys and spleen. The drug in most tissues gave its peak concentrations in 15 min, and then the amount decreased in 1 h, further falling off in 4 h after intravenous injection to mice with 80 mg/kg.Mice or rats (used for bile excretion test) were administered intravenously with nolatrexed dihydrochloride at 80 mg/kg. The unchangeddrug in urine, feces and bile accounted for 2.8%, 10.7% and 5.6% of the total administered dose respectively. Four metabolites were found in urine by mass spectrum analysis and most of them are hydroxides.It was demonstrated in vitro that nolatrexed was bound to human plasma protein to a degree of more than 95%, indicating that dosage adjustment may be required when given in combination with other drugs showing high plasma protein binding rate.