| One of the first choice of drugs in treatment for acute promyelocytic leukemia(APL) was ATRA which was used as the representative of differentiation inducingagent. However, a series of side-effects of ATRA such as the retinoic acid syndromeemerged during the further application in clinical. A series of retinoids derivatives weresynthesized by our laboratory using ATRA as a model acid. ATPR has shown itsanti-proliferation and differentiation induction effect on many cancer cells afterscreening of the activity. The drug and the body have a two-way interaction. Thepharmacokinetics of ATPR was investigated in order to study the interaction betweenATPR and the body. We focus on investigating the mechanism of intestine absorptionand tissue distribution of ATPR in order to clarify the pharmacokinetics characteristicsof ATPR of antitumor effect and provide the experimental basis for the dosage regimendesign in clinical and the design of the formulation of ATPR.Objective: To investigate the pharmacokinetic characteristics of ATPR in rats.Methods:1. The experiment of intestine absorption: Set up ATPR (0.1,0.25,0.5,1.0mg/ml)groups, ATPR (0.25mg/ml) added with verapamil group and ATRA (0.25mg/ml) group. Perfusate was collected at different time after perfusion and using HPLC systemfor detection of ATPR and ATRA after management. The absorption rate constants (Ka)and effective permeability coefficients (Peff) were caculated.2. The experiment of time course: Rats in the single dose groups were given ATPRwith low, middle and high dosages or ATRA through intravenous or intragastricadministration, respectively. Blood samples were collected in heparinized tubes througheither medial or lateral canthus of rat at different time. Pharmacokinetic parameters ofATPR were assessed on the seventh day after the administration of multiple dailymiddle dose to rats. After the seventh dose, blood samples were obtained through thesame time schedule as that of the single dose groups. Blood samples were centrifuged toobtain plasma samples for high performance liquid chromatography (HPLC) assay. Themain pharmacokinetic parameters were calculated and the pharmacokinetic parametersof ATPR or ATRA between the single doses and repeated doses were compared,respectively.3. The experiment of tissue distribution: Rats were given ATPR with middle dosageor ATRA through intravenous or intragastric administration, respectively. Brain, liver,spleen, kidney, heart, fat, lung and intestine tissues were obtained after administration atdifferent times, respectively. The tissues were made into homogenates preparation withnormal sodium and the concentrations of ATPR in the tissues were determined by HPLCmethod. Calculate the drug concentration in different tissues.4. The experiment of possible mechanisms of metabolism: Use HepG2cells as thehuman hepatoma cell model. Set up ATRA (1000nmol/L) group, ATPR (1000nmol/L)group, the control group, the solvent group (containing0.01%ethanol), ATPR of thedifferent concentration groups (1000、100、10、1、0.1nmol/L) and ATPR at different times groups(0、4、12、24、48、72h). The mRNA expression of CYP26A1in differentgroups was detected by reverse transcription polymerase chain reaction (RT-PCR) andthe protein expressions of CYP26A1were detected through Western Blot.Results：1. The experiment of intestine absorption: With the increase of drug concentration,the Kaand Peffof ATPR which were first increased and then decreased, respectively.The Kaand Peffhad no significant changes when P-gp inhibitor was added in perfusate(P>0.05). There had no significant difference (P>0.05) of Kaand Peffin the fourintestinal segments and compared with those of ATRA, there had no significantdifference (P>0.05) in the four intestinal segments.2. The experiment of time course: The area under the plasma concentration-time curve(AUC) and maximum plasma concentration (Cmax) of ATPR increased proportionallywith the dose but the mean residence time (MRT), the elimination half-life (T1/2) and theclearance (CL) remained unchanged (P>0.05) within the tested doses after single doseadministration. Compared to those of ATRA, T1/2, AUC, MRT and Cmaxof ATPRincreased significantly, while the CL was much lower (P <0.05). After multiple dailyadministration, the plasma concentration-time curve of ATPR showed an increasingtrend in parallel compared with that of single dose administration. AUC and CmaxofATPR increased significantly but CL declined significantly.3. The experiment of tissue distribution: The concentration of ATPR was high in liver,spleen and lung tissues and much lower levels in heart, kidney, fat and brain tissuesafter intravenous administration. However, it was observed higher drug concentration inlung tissue and lower drug concentration in liver, heart, kidney, fat and brain tissues after intravenous injection of ATRA. The highest concentration of ATPR was observedin intestines and the highest concentration of ATRA was observed liver tissue after oraladministration.4. The experiment of possible mechanisms of metabolism: The mRNA and proteinexpression of CYP26A1in HepG2cells were both increased with the increase of theconcentration of ATPR and reached the peak at12h. The expression of CYP26A1increased significantly (P <0.01) after the management of ATPR and ATRA comparedwith the control group and that of ATRA group increased more significantly.Conclusion:1. The experiment of intestine absorption: The intestinal absorption of ATPR isprobably an active transport or facilitated diffusion process with a good absorption inthe whole intestinal sections.2. The experiment of time course: Whether single or multiple dose administration,compared with ATRA, ATPR was able to maintain a high plasma concentration level forlong time. ATPR would be beneficial for extending dosing interval and for the treatmentof APL and some concentration-dependent effect and could be considered asmonotherapy in clinical in the future.3. The experiment of tissue distribution: ATPR was distributed to the liver tissuequickly after administration and the targeting in liver was higher, suggesting that ATPRmaight have a beneficial advantage on anti-proliferation and differentiation inductioneffects on liver cancer cells.4. The experiment of possible mechanisms of metabolism: ATPR could induce the expression of CYP26A1in HepG2cells in vitro. The inducing effect enhanced with theincrease of drug concentration. It showed that the inducing effect on the expression ofCYP26A1of ATPR was much lower than that of ATRA. The above results indicatedthat ATPR displayed an advantage in overcoming the accelerated metabolism due toinducing the expression of metabolic enzymes. |
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