Tpiao Mechanism of Action

Pharmacology: Thrombopoietin (TPO) is an endogenous cytokine which can stimulate the growth and differentiation of megalokaryocyte. It can increase the quantity of platelet through its stimulative function on each growth phase of megalokaryocyte including multiplication of pro-cell, development and maturation of polyploid megalokaryocyte. Recombinant human thrombopoietin (rhTPO) is a full-length glycosylated thrombopoietin which is expressed in China hamster ovary (CHO) cell line via recombinant genetic technology. It has similar pharmacological function on increasing the quantity of platelet with endogenous thrombopoietin.
The rhTPO 150 units/Kg or 600 units/Kg is separately injected with human serum albumin 20 microgram/kg to macaque which is created as the model of bone marrow restrain after they were irradiated with great dosage systemic radiation of ⁶⁰Coγ. Such administration is given once per day and for 20 days. The testing result shows that rhTPO can increase the average value of platelet count, shorten the time of low value period and increase the congregated rate of peripheral blood platelet in low value. Its lowest effective dosage is 150 units/kg/day. Balb/c rats, which were injected with carboplatin (150 mg/Kg) by intraperitoneal injection to be model of thrombocytopenia, are given. The rhTPO (1.1 x 10² units, 1.1 x 10³ units and 1.1 x10⁴ units/kg) and physiological saline separately once per day for 10 days, rhTPO therapy can improve the platelet decreasing caused by carboplatin obviously when the dose is ≥1.1 x 10³ units/kg.
In vitro culture system with normal human bone marrow and IIEL and DAMI cell series expressed by the antigen of megakaryotic, rhTPO can especially enhance the expression of megakaryocytic series and CD41 antigen of monocyte of normal human bone marrow and promote the production of CFU-Meg.
Pharmacokinetics: Pharmacokinetic Study on Single SC Administration of rhTPO to Normal Volunteers: The healthy volunteers were randomly divided into 3 dosage groups (150 units/kg, 300 units/kg and 600 units/kg). Each group consists of 8 cases and totally 24 subjects. The results showed that the absorption and elimination basically conform to linear pharmacokinetics characters. The t_½ ka of 3 dosage groups were 2.5±1.1 hr, 3.2±2.6 hr and 4.2±2.4 hr respectively and T_max were 9.0±1.9 hr, 10.8±2.4 hr and 11.8±5.4 hr respectively. The elimination of rhTPO was slow and the t_½ in vivo was longer. The elimination t_½ of three dosage was similar separately as 46.3±6.9 hr, 40.2±9.4 hr and 38.7±11.9 hr.
Pharmacokinetic Study on Multiple Administration of rhTPO: 8 patients were divided into 2 groups. Group 1 received the administration every other day (SC rhTPO 1 microgram/kg, equal to 300 units/kg, totally 7 times) and group 2 received administration each day (SC rhTPO 1 microgram/kg equal to 300 units/kg, totally 14 times). Each group consists of 4 subjects. Along with the increase of administration frequency, each patient's rhTPO blood concentration increased accordingly. The C_min of group 1 and group 2 reached respective steady-state concentration 1637± 969 picogram/mL after 5 times and 2906± 1736 pg/mL after 7 times of administration. The C_max changing tendency of 2 groups kept the same as that of C_min. The steady-state C_max were 2135± 1095 picogram/mL and 4193±3436 pg/mL separately. There wasn't obvious difference in kinetics parameters eg, AUC, T_peak and t_½ after the first time administration and the last time administration. It indicated that this drug basically had not the time-dependent pharmacokinetics change. In the condition of multiple SC injection of rhTPO, the blood concentration increase level was in positive correlation to the accumulative dosage of rhTPO. Within 14 times of administration, rhTPO did not show the tendency of accumulation.
Clinical Study: Phase 1 Clinical Study: 27 healthy volunteers received single SC injection of rhTPO for tolerance study. These 27 volunteers were randomly divided into 4 dosage groups, respectively given 75 units/kg, 150 units/kg, 300 units/kg and 600 units/kg. The cases in each group were 3,6,9 and 9. The efficacy of rhTPO was dependant on dosage to increase platelet level for single SC injection. Within the range of 150 units/kg-600 units/kg, the average increase of platelet level is 24-52% than prior to administration. Occasionally, the 100% increase of platelet level occurred. The count of platelet increased to the peak after 10-14 days' administration and returned to the baseline (level prior to administration) after 21 days' administration. One case was found to have transient lower fever and inertia and one case had drowsiness, but both regressed naturally. Once case had transient mild ALT and AST increase and recovered 1 week later.
Additionally 7 blood tumor patients received continuous SC injection for tolerance study. The dosage was 300 units/kg, once per day, in conjunctive 7-14 days. The platelet level of total patients increased to different degree and reached the peak 14-28 days after administration. Once patient was found to get pain in right tibia 7 days after administration. After 2 days' treatment according to the disease, the pain relieved and no similar phenomena appeared in later period of administration. One case had transient mild ALT and AST increase and returned to normal 1 week later.
Class 2 Clinical Study: Random crossing and self-control methods were adopted to 62 solid tumor patients receiving chemotherapy. During treatment course rhTPO was administered to the patients 6-24 hrs after chemotherapy. The dosage was 300 units/kg, once per day for 7-14 days. In control period, no rhTPO was applied after chemotherapy as self-control. The descendent minimum of blood platelet during treatment course and self-control period were 61±51x 10⁹/L and 48±35x10⁹/L (P<0.05) respectively. The maximum of the recovered platelet count after chemotherapy were 260±164 x 10⁹/L and 152±81 x 10⁹/L (P<0.001) respectively. After chemotherapy, the median days needed for platelet count recovering to more than 75x10⁹/L were 14 days and 18 days separately (P<0.001). The adverse effect of rhTPO was rare and mild. Two cases of patients had side effects related to rhTPO eg, fever after administration and the highest to 38.8°C, which faded naturally or the body temperature recovered to normal after stopping administration. The rhTPO has taken no obvious effect to hemoglobin, red blood cell and white blood cell count recovery after administration; no obvious effect to blood platelet shape, blood platelet aggregation function, liver and kidney function. Seven cases of patients monitoring for anti-rhTPO antibody during administration course. Among them was detected to have lower titer (1:5) antibody in serum 14th days after administration, and no influence to the function of increasing platelet level of rhTPO was found.
Phase 3 Clinical Trial: In the multiple centers clinical trial of phase 3, among 311 subjects of patients, random crossing self-control methods were applied to 92 cases of solid tumor patients with platelet decrease after receiving chemotherapy. During treatment course rhTPO was administered to patients 6-24 hrs after chemotherapy. The dosage was 300 units/kg, once per day for 7-14 days. In control period, no rhTPO was applied after chemotherapy as self-control. The descendent minimum of blood platelet during treatment course and self-control period were 66±41x10⁹/L and 55±27x10⁹/L (P<0.001) respectively. The maximum of the recovered platelet count after chemotherapy, the median days needed for platelet count recover to ≥75 x 10⁹/L were 11 days and 16 days separately (P<0.001). The results showed that after chemotherapy, when the platelet reduced, rhTPO could obviously increase platelet count, reduce the descendent minimum of blood platelet, and speed up the recovery of platelet count. Among 92 cases of solid tumor patients, 42 cases of patients were found that their platelet count obviously descended after chemotherapy in control period. According to the statistic result to this group, the median minimum counts of blood platelet descendent after chemotherapy between administration period and control period were separately 50 x 10⁹/L and 32 x 10⁹/L (P<0.001). The median maximum counts of platelet recovery after chemotherapy were 204 x 10⁹/L and 114 x 10⁹/L (P<0.001) respectively. The median counts with platelet level lower than 50 x 10⁹/L after chemotherapy were 1 day and 6 days (P<0.001). For the related adverse effect in phase 3 clinical study, see Adverse Reactions.
Result of phase 3 Clinical Study: The minimum of descendent platelet count after chemotherapy (x10⁹/L): 66±41 for treatment period and 55±27 for the control period. The maximum of recovered platelet count after chemotherapy (x10⁹/L): 266±126 for the treatment period and 146±56 for control period. The median days needed for platelet recovery to or more than 75x10⁹/L after chemotherapy: 11 for the treatment period and 16 for control period.
Toxicology: Acute toxicology: rhTPO were separately injected slowly to rat and mice through vein in tail at the dosage of 1.35 x 10⁵ units/kg (correspond to 900 and 1500 times of recommended dosage on clinical use). No obvious toxicity reaction and death was found during 14 days after injection. No abnormality was found in main organs after histopathology test.
Chronic toxicity: rhTPO was continuously injected to wistar rats by SC at the dosage of 1.5 x 10⁴ units/kg, 7.5 x 10³ units/kg and 1.5 x 10³ units/kg (separately corresponding to 100 times, 50 times, and 10 times of recommended dosage on clinical use) for 35 days. Two control groups were separately injected with 0.5% human serum albumin and physiological saline. The testing results of general situation, food intake, classification of leukocytes, clotting time, routine uronoscopy and histopathology showed that there was no distinct difference between rhTPO treatment group and control group at different time point. 3 weeks after injection, total quantity of peripheral blood platelet continuously decreased obviously along with the week increase of administration especially for the high dosage group. Meganucleus series of bone marrow of high and medium dosage group recuperated slowly after finish of administration. It was demonstrated that obvious cumulative intoxication occurred in high and medium dosage group after injection for 2 weeks. Cumulative intoxication occurred in low dosage group after injection for 4 weeks but disappeared in 2 weeks after stop administration, meganucleus series of bone marrow also recovered obviously 1.5 x 10³ units/kg should be the dosage with which rhTPO is injected to rats by SC without obvious side and toxic effect. The rhTPO, 0.5% human serum albumin and physiological saline were separately injected to 24 rhesus monkeys for 30 days. The rhTPO was administered at the dosage of 9 x 10² units/kg, 1.8 x 10³ units/kg and 5.4 x 10³ units/kg (separately corresponding to 6 times, 12 times and 36 times of recommended dosage on clinical use). Such rhesus monkeys were observed for 58 days after injection (30 days of administration, 28 days after stop of administration). The observing demonstrated that there was no distinctive difference between male and female rhesus monkeys on general circulation, orexia, weight, body temperature, biochemical analysis of blood serum, urine test, ECG and histopathology. Among them, the administration of middle and high dosage rhTPO caused one condition that the total count of peripheral blood platelet radically increased in the earlier period and then turned to dramatically decrease and the recovery of blood platelet quantity was slow. It indicated that large dosage and long-term continuous administration with lower dosage in 30 days did not show obvious accumulation of toxicity to the rhesus monkeys.9 x 10² units/kg body weight should be the dosage with which rhTPO is injected to rhesus monkeys without obvious side and toxic effect.