Interferon-alpha is implicated in the transcriptional regulation of vascular endothelial growth factor

Enhancing the anti-angiogenic action of histone deacetylase inhibitors

Background

Histone deacetylase inhibitors (HDACIs) have many effects on cancer cells, such as growth inhibition, induction of cell death, differentiation, and anti-angiogenesis, all with a wide therapeutic index. However, clinical trials demonstrate that HDACIs are more likely to be effective when used in combination with other anticancer agents. Moreover, the molecular basis for the anti-cancer action of HDACIs is still unknown. In this study, we compared different combinations of HDACIs and anti-cancer agents with anti-angiogenic effects, and analysed their mechanism of action.

Results

Trichostatin A (TSA) and α-interferon (IFNα) were the most effective combination across a range of different cancer cell lines, while normal non-malignant cells did not respond in the same manner to the combination therapy. There was a close correlation between absence of basal p21^WAF1 expression and response to TSA and IFNα treatment. Moreover, inhibition of p21^WAF1 expression in a p21^WAF1-expressing breast cancer cell line by a specific siRNA increased the cytotoxic effects of TSA and IFNα. In vitro assays of endothelial cell function showed that TSA and IFNα decreased endothelial cell migration, invasion, and capillary tubule formation, without affecting endothelial cell viability. TSA and IFNα co-operatively inhibited gene expression of some pro-angiogenic factors: vascular endothelial growth factor, hypoxia-inducible factor 1α and matrix metalloproteinase 9, in neuroblastoma cells under hypoxic conditions. Combination TSA and IFNα therapy markedly reduced tumour angiogenesis in neuroblastoma-bearing transgenic mice.

Conclusion

Our results indicate that combination TSA and IFNα therapy has potent co-operative cytotoxic and anti-angiogenic activity. High basal p21^WAF1 expression appears to be acting as a resistance factor to the combination therapy.

AIDS-associated Kaposi's sarcoma: is there still a role for interferon alfa?

Interferon alfa (IFNalpha) was one of the first agents to be used therapeutically in AIDS-associated Kaposi's sarcoma (KS) more than 25 years ago, and induces tumor regression in a subset of patients. Although much has been learned about the clinical role of IFNalpha in KS treatment, little is currently known about the mechanism(s) by which IFNalpha causes KS regression. This is despite a growing understanding of both KS pathogenesis and relevant IFNalpha activities. To a large extent other agents have supplanted IFNalpha as treatments for KS, but there may still remain a therapeutic role for IFNalpha, possibly in combination with other agents targeting angiogenesis and/or HHV-8-encoded human gene homologs that encode proteins involved in cell cycle regulation and signaling.

Constitutive and inducible expression and regulation of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF), which was originally discovered as vascular permeability factor, is critical to human cancer angiogenesis through its potent functions as a stimulator of endothelial cell survival, mitogenesis, migration, differentiation and self-assembly, as well as vascular permeability, immunosuppression and mobilization of endothelial progenitor cells from the bone marrow into the peripheral circulation. Genetic alterations and a chaotic tumor microenvironment, such as hypoxia, acidosis, free radicals, and cytokines, are clearly attributed to numerous abnormalities in the expression and signaling of VEGF and its receptors. These perturbations confer a tremendous survival and growth advantage to vascular endothelial cells as manifested by exuberant tumor angiogenesis and a consequent malignant phenotype. Understanding the regulatory mechanisms of both inducible and constitutive VEGF expression will be crucial in designing effective therapeutic strategies targeting VEGF to control tumor growth and metastasis. In this review, molecular regulation of VEGF expression in tumor cells is discussed.