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A high-density cell culture method was successfully established in P. pastoris with the alcohol oxidase I (AOXI) promoter in order to produce large quantities of recombinant human angiostatin (AS) which has been reported to have antiangiogenic activity. A preliminary study on fermentation conditions in shaking flasks indicated that adequacy of biomass is beneficial to obtain more products. The fermentation was carried out in a 10 l bioreactor with 5 l modified growth medium recommended by Invitrogen at 30 degrees C. The cells were first grown in glycerol-PTM4 trace salts for 24 h. When the cell density reached A(600) = 125, methanol-PTM4 trace salts was added to induce the expression of AS. During the fermentation, dissolved oxygen level was maintained at 20-30%, pH was controlled at 5 by the addition of 7 M NH(4)OH and the biomass was maintained at about A(600) = 200. After 60 h of induction, the secreted AS was 153 mg/l. The recombinant AS inhibited the angiogenesis on CAM and suppressed the growth of B16 melanoma in C57BL/6J mice (P \0.01).

Pichia pastoris is an efficient host for the expression and secretion of heterologous proteins and the most important feature of P. pastoris is the existence of a strong and tightly regulated promoter from the alcohol oxidase I (AOX1) gene. The AOX1 promoter (pAOX1) has been used to express foreign genes and to produce a variety of recombinant proteins in P. pastoris. However, some efforts have been made to develop new alternative promoters to pAOX1 to avoid the use of methanol. The glyceraldehyde-3-phosphate dehydrogenase promoter (pGAP) has been used for constitutive expression of many heterologous proteins. The pGAP-based expression system is more suitable for large-scale production because the hazard and cost associated with the storage and delivery of large volume of methanol are eliminated. Some important developments and features of this expression system will be summarized in this review.

Canstatin-N DNA fragment amplified from human genome was inserted into the MCS of pGAP9K*, an intracellular expression vector of Pichia pastoris, to generate pGAP9K*-can-N which was then transformed into P. pastoris GS115 by electroporation. A transformant was chosen as an engineering strain from the plate containing G418 (700 μg/ml). D-sorbitol was selected as the only carbon source. The fermentation was carried out in a 50 L bioreactor at a 20 L working volume. After 48 h fermentation with continuous feeding of 25% (w/v) D-sorbitol and 0.8% PTM4, the cell grew to A(600)=178 and intracellularly expressed Canstatin-N reached 780 mg/L. Snail enzyme was combined with water to crack P. pastoris and to release intracellular proteins. The purified recombinant Canstatin-N inhibited CAM angiogenesis and induced significant apoptosis of the human umbilical vein endothelial cell (EVC340).