[Experimental study of dually targeting gene therapy system for pituitary adenomas].

OBJECTIVE

To construct a dually targeting gene therapy system for pituitary adenomas and investigate its effect.

METHODS

Promoter hGHp containing human growth hormone gene was obtained from human genome and cloned into the plasmid pcDNA3.1/His A with the promoter cut to construct the recombinant plasmid pcDNA3.1/His A-hGHp. HSV-TK gene was obtained from the plasmid pcDNA3.1/His A-TK and integrated into the plasmid pcDNA3.1/His A-hGHp to construct the recombinant plasmid pcDNA3.1/His A-hGHp-TK. A GE7 gene delivery system-mediated human growth hormone promoter controlled gene therapy system was constructed by adding the mixture of GE7-polylysine and HA20-polylysine into the DNA solution. Human growth hormone-secreting pituitary adenoma cells of the GH3 line, human myeloma cells of the U-2OS line, and human oophoroma cells of the HO8910PM line were cultured and transfected with PBS or GE7 packaged pcDNA3.1/HisA-TK or pcDNA3.1/HisA-hGHp-TK. Western blotting was used to examine the expression of PBS or GE7 packaged pcDNA3.1/HisA-TK or pcDNA3.1/HisA-hGHp-TK protein, MTT method was used to detect the cell survival rate. Another GH3, U-2OS, and HO8910PM cells were cultured and transfected with PBS or GE7 packaged pcDNA3.1/HisA-TK or pcDNA3.1/HisA-hGHp-TK and then ganciclovir (GCV) was added. MTT method was used to examine the cell survival rates. GH3 cells were injected subcutaneously into the right axilla of 200 SD nude rats loaded with human pituitary adenoma. Three weeks after the rats were randomly divided into 5 equal groups: PBS group in which PBS was injected into the tumor and GCV was injected peritoneally; GE7 group in which GE7-polylysine and HA20-polylysine were injected into the tumor and GCV was injected peritoneally; without TK group in which GE7-packaged pcDNA3.1/His A-hGHp was injected into the tumor and GCV was injected peritoneally; without GCV group in which GE7-packaged pcDNA3.1/His A-hGHp-TK was injected into the tumor and PBS was injected peritoneally; and treatment group in which GE7-packaged pcDNA3.1/His A-hGHp-TK was injected into the tumor and GCV was injected peritoneally. Peritoneal injection lasted 21 days for all groups. On the days 3, 7, 14, and 21 eight rats from each group were killed to measure the volume of tumor. The survival rate of the rest 8 rats was observed.

RESULTS

A dually targeting gene therapy system for pituitary adenoma was composed successfully. HSV-TK protein was expressed in the GH3 cells but not in the U-2OS and HO8910PM cells after transfection of GE7-packaged pcDNA3.1/HisA-hGHp-TK; and was expressed in the GH3 and HO8910PM cells but not in the U-2OS cells after transfection of GE7-packaged pcDNA3.1/HisA-TK. Transfection of GE7-packaged pcDNA3.1/HisA-hGHp-TK and addition of GCV significantly decreased the survival rate of the GH3 cells, but did not influence the survival rates of the U-2OS and HO8910PM cells. Transfection of GE7-packaged pcDNA3.1/HisA-TK and addition of GCV significantly decreased the survival rate of GH3 and HO8910PM cells but did not influence the survival of the U-2OS and HO8910PM cells. When the GH3 cells were transfected with GE7-packaged pcDNA3.1/HisA-hGHp-TK with the addition of GCV of the concentration of 4 mg/L the survival rate decreased to 10%, when the GCV concentration was raised to 8 mg/L the survival rate of the GH3 cells was < 5%. Three days after the beginning of treatment the tumor volume of different groups of rats increased at different degrees and the tumor was smallest in the treatment group in comparison with the other groups (all P < 0.05). Seven days after the beginning of treatment the tumor volume of the treatment group significantly decreased and the tumors of the other groups still increased (all P < 0.001). The survival time of the treatment group was over 120 days, significantly longer than those of the other groups (all about 40 days).

CONCLUSION

GE7 system-mediated hGHp controlled gene therapy system is hopeful to be the targeted therapeutic strategy for pituitary adenomas.