Recombinant Human
Thrombopoietin
Endogenous thrombopoietin
(TPO) is a cytokine which promotes platelet production by regulating growth and maturation
of megakaryocztes, therefore increases the platelet level in the circulation. Nowadays the
recombinant human thrombopoietin is preferred as agent of therapy for Thrombocytopenic
purpura and radiation-induced or chemical-induced thrombocytopenia.
rhTPO is a full-length
molecule identical to natural form. It is a single chain, composed of 353 amino acids and
including 21 amino acids in the signal peptide. rhTPO is glycoprotein, its molecular size
is 70-120KD.
The development of rhTPO
was initiated in 1995 .The process of development and pre-clinical studies were completed
at the end of 1998. The application for clinical trails was approved as new drug of Class
I by State Drug and Food Administration (SFDA) of China In 1999. The whole clinical study
(Phase I, II and III) has been already completed until May, 2003.
The human cDNA containing
TPO ORF was cloned from fetal lung cDNA library. rhTPO was expressed in Chinese Hamster
Ovary cell Line (CHO). Fermentation was carried out in a large-scale, continuous perfusion
cell culture system using packed-bed bioreactors (Celligen Plus). To ensure high purity,
rhTPO was purified by multi-step method. The overall recovery rate was 16-25%. The
specific activity of rhTPO in bulk was 280,000 IU/mg. Impurity: Residual DNA (<100pg/50¦Ìg), Endotoxin
(<10EU/50¦Ìg). Finally rhTPO was formulated with human serum albumin (HSA) and other
additives in the environment of pH: 6.4-7.4. Aqua dose form, 50¦Ìg/Vial, stored at
2-8 Celsius degree.
The clinical study
demonstrated that rhTPO was well tolerated by patients. It could accelerate the platelet
recovery after radiotherapy or chemotherapy, decrease the requirement for platelet
transfusion significantly. rhTPO was safe and effective in the treatment of
radiation-induced or chemical-induced Thrombocytopenia. There was no influence of rhTPO on
HB, WBC, the function of kidney or liver, no influence on platelet form, platelet
aggregation function or coagulation. Only a few slight adverse events occurred during
clinical study. Low titer of antibody was observed in a few patients, but it didn't have
neutralizing ability.
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