[Gene transfer of murine Flt3 ligand mediated by adenoviral vector efficiently induces growth inhibition of murine liver cancer].

ABSTRACT

OBJECTIVE: To observe the in vivo therapeutic effects of murine Flt3 ligand (mFL) mediated by recombinant adenoviral vector on murine liver cancer. METHODS: Murine liver cancer cell line Hepal-6 was infected with adenovirus in vitro. The infection efficacy was measured by green fluorescence protein (GFP) expression and the amount of mFL in supernatant was measured by ELISA 48 hrs following infection of Hepal-6. AdmFL, Ad-null, and PBS were added into the culture of Hepal-6 cells, the number of cells was counted every other day for 14 days. A murine liver cancer model was established by subcutaneous inoculation of Hepal-6 cells. A single dosage of 1 x 10(9) expression forming unit (efu) of Ad-mFL, Ad-null or PBS was injected intratumorally. The tumor volume and survival rate were measured twice a week. Twenty days after treatment of adenoviral vectors, three treated mice with their tumor disappearing were killed and their spleen was taken. The splenocytes from these tumor free mice were adoptively transferred to naive mice to whom Hepal-6 cells were inoculated 3 days thereaftter and then the tumor volume was measured once a week.for 4 weeks. 38 days after administration of adenoviral vectors, tumor free animals were rechallenged by parental Hepal-6 cells or syngenic EL4 lymphoma cells at the opposite sites of the original inoculation sites, and the tumor volume was also measured once a week for 4 weeks. RESULTS: Adenoviral vector efficiently infected Hepal-6 cells in intro, and lead to the secretion of high levels of mFL protein (80.5 +/- 7.3 ng/10(6)/24 h) in the supernatant. The growth of Hepal-6 tumor was significantly inhibited by one single intratumoral administration of Ad-mFL in 90% of the treated mice, and the tumor gradually grew in the two other groups. Two of the 7 mice (30%) in PBS group died in 17 days, 14% still lived in 37 days, and all died within 45 days. The mice in the Ad-null group began to die since the 21(st) day, only 11% of them were still alive in 60 days. All mice in the Ad-mFL group were alive at the 60(th) day after tumor implantation. Adoptive transfer of splenocytes to the animals receiving Ad-mFL treatment protected effectively them against a subsequent challenge with the identical tumor cells. Rechallenge of the Ad-mFL cured mice with the parental Hepal-6 cells resulted in complete inhibition of tumor growth. The growth of inoculated EL4 lymphoma cells gradually grew equally in the controls and the experimental mice. CONCLUSION: FL gene transfer mediated by recombinant adenoviral vector has potent therapeutic effects on Hepal-6 liver cancer, and develops long-lasting specific antitumor immunity, which may become a potent cancer gene therapy candidate for further clinic application.