Objective: To explore the effect of adenovirus-mediated delivery of an antiangiogenic fragment of human thrombospondin 1 (TSP1(f)) on K562 cell growth in nude mice.
Methods: TSP1(f) cDNA was amplified by RT-PCR from normal human peripheral blood mononuclear cells and was used as transgene to construct a adenoviral vector (ADV-TSP1(f)). Human leukemia K562 cells were cultured and infected with ADV-TSP1(f) or ADV-LacZ. PBS was used as control. TSP1(f) expression/secretion by these infected K562 cells was demonstrated using Western blot analysis. MTT assay was performed to determine the effect of ADV-TSP1(f) infection on K562 cell growth kinetics. Eighteen female Balb/c nude mice were inoculated subcutaneously with human leukemia K562 cells. When the diameter of the tumor reached 5 approximately 7 mm the rats were randomly divided into 3 groups of 6 rats injected intratumorally with ADV-TSP1(f), ADV-LacZ, and PBS respectively. The volume of K562 xenografts was measured every three days during the 3-week treatment. By the end of the 21st day the mice were killed and the tumors were taken to undergo histological examination. The intratumoral microvessel density (MVD) was determined by immunohistochemical staining.
Results: TSP-1f was expressed and secreted efficiently by ADV-TSP1(f)-infected K562 cells. Three weeks after the initial treatment, the volume of K562 xenografts in the mice treated with ADV-TSP1(f), ADV-LacZ, and PBS was (1,108 +/- 179) mm(3), (4,518 +/- 452) mm(3), and (4,666 +/- 458) mm(3) respectively (P < 0.01). The number of CD31+ microvessels counted per x200 field was 34 +/- 9, 36 +/- 7, and 14 +/- 4 in the tumors treated with PBS, ADV.LacZ, and ADV.TSP-1f respectively (P < 0.001).
Conclusion: Adenovirus-mediated TSP-1f gene transfer greatly inhibits K562-derived tumor growth and angiogenesis in mouse xenograft model, and may serve as a new therapy for hematological malignancies.