VASCULAR ENDOTHELIAL GROWTH FACTOR/VASCULAR PERMEABILITY FACTOR (VEGF/VPF) IS AN AUTOCRINE GROWTH FACTOR FOR AIDS-KS

Abstract

Background: Kaposi's sarcoma (KS) is the most common tumor associated with HIV-1 infection. KS develops in approximately 30% of AIDS cases. The principal features of KS tumor are abnormal vascularization and the proliferation of endothelial cells and spindle(tumor) cells. Cells derived from Kaposi's sarcoma induce vascular lesions and display enhanced vascular permeability when inoculated subcutaneously in the nude mouse. This finding suggests that angiogenesis and capillary permeability play an important role in the development and progression of Kaposi's sarcoma. Methods: Several phosphothionate modified VEGF antisense oligonucleotides from different regions of VEGF were synthesized. Several control and AIDS-KS cell lines were treated with various concentration of VEGF antisense oligonucleotides and both DNA synthesis and cell proliferation was measured. VEGF mRNA was also examined by Northern and RT-PCR. VEGF protein was measured by ELISA. Expression of VEGF receptors (Flt-1 and KDR) were examined by RT-PCR. The in vivo studies were carried out in Balb/c Nu+/NU+ athymic nude mice. The VEGF antisense or scrambled VEGF oligonucleotides were injected intra-peritoneally daily for five consecutive days and the size of tumors were examined on day 14. Results: We found that all AIDS-KS cell lines expressed high levels of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF). AIDS-KS cells and primary tumor tissues also expressed high levels of Flt-1 and KDR, the receptors for VEGF, while the skin of the same patients did not show receptor expression. We further demonstrated that of the five different VEGF antisense oligonucleotides two of them (AS-1 and AS-3) specifically blocked VEGF mRNA and protein production and inhibited KS cell growth in a dose dependent manner. The IC50 of AS-1 and AS-3 oligonucleotides in AIDS-KS cells were 2.6 µM and 2.45 µM respectively. VEGF antisense oligonucleotides AS-1 and AS-3 were also examined on various control cell lines and the data showed that the antisense growth inhibitory effects were limited only to the KS cell lines. We have also studied both VEGF antisense (AS-1 and AS-3) and scrambled oligonucleotidesin vivo and found that both antisense oligonucleotides inhibited tumor growth in nude mice while the scrambled oligonucleotide had no significant effect. Conclusion: These results show that VEGF is an autocrine growth factor for AIDS-KS cells. Inhibitors of VEGF or its cognate receptors may thus be candidates for therapeutic intervention.