Therapeutic inhibition of angiogenesis

Extracellular cadherin repeat domains EC1 and EC5 of T-cadherin are essential for its ability to stimulate angiogenic behavior of endothelial cells

T-cadherin (T-cad) promotes survival, proliferation, and migration of endothelial cells and induces angiogenesis. We aimed to identify domains of T-cad functionally relevant to its effects on endothelial cell behavior. To specifically target the functional properties of the 5 cadherin repeat domains (EC1-EC5) of T-cad, endothelial cells were transduced with lentivectors containing specific T-cad-domain-deletion mutant constructs (DeltaI, DeltaII, DeltaIII, DeltaIV, DeltaV). Empty (E) lentivector-transduced cells served as control. Similarly to overexpression of native T-cad, cells expressing DeltaII, DeltaIII, or DeltaIV displayed elevated levels of p-Akt and p-GSK3beta and increased proliferation rates (for DeltaII, DeltaIII) vs. E. DeltaI- and DeltaV-transduced cells exhibited reduced levels of p-Akt and p-GSK3beta and retarded growth rates vs. E. Stimulatory effects of native T-cad overexpression on Akt and GSK3beta phosphorylation were dose dependently inhibited by coexpression of DeltaI or DeltaV. Subsequent functional analyses compared only DeltaI-, DeltaII-, and DeltaV-mutant constructs with E as a negative control. Unlike DeltaII cells, DeltaI and DeltaV cells failed to exhibit homophilic ligation and deadhesion responses on a substratum of T-cad protein. In the wound assay, migration was increased for DeltaII cells but impaired for DeltaI and DeltaV cells. In endothelial cell-spheroid assay, angiogenic sprouting was augmented for DeltaII cells but inhibited for DeltaI and DeltaV cells. We conclude that EC1 and EC5 domains of T-cad are essential for its proangiogenic effects. DeltaI and DeltaV constructs may serve as dominant-negative mutants and as potential tools targeting excessive angiogenesis.

Evaluation of a xenogeneic VEGF vaccine in dogs with soft tissue sarcoma

Active immunization against pro-angiogenic growth factors or their receptors is an emerging strategy for controlling tumor growth and angiogenesis. Previous studies in rodent tumor models have indicated that immunization against xenogeneic growth factors is more likely to induce effective anti-tumor responses than immunization against the autologous growth factor. However, the effectiveness or safety of the xenogeneic vaccination approach has not been previously assessed in a clinically relevant outbred, spontaneous tumor model. Therefore, we investigated the safety and anti-tumor and anti-angiogenic effects of a xenogeneic vascular endothelial cell growth factor (VEGF) vaccine in pet dogs with spontaneous cancer. Nine dogs with soft tissue sarcoma were immunized with a recombinant human VEGF vaccine over a 16-week period. The effects of immunization on antibodies to human and canine VEGF, circulating VEGF concentrations, tumor microvessel density (MVD), and tumor growth were assessed. The xenogeneic VEGF vaccine was well-tolerated by all dogs and resulted in induction of humoral responses against both human and canine VEGF in animals that remained in the study long enough to receive multiple immunizations. Three of five multiply immunized dogs also experienced sustained decreases in circulating plasma VEGF concentrations and two dogs had a significant decrease in tumor MVD. The overall tumor response rate was 30% for all treated dogs in the study. We conclude therefore that a xenogeneic VEGF vaccine may be a safe and effective alternative means of controlling tumor growth and angiogenesis.

Alphastatin downregulates vascular endothelial cells sphingosine kinase activity and suppresses tumor growth in nude mice bearing human gastric cancer xenografts

AIM: To investigate whether alphastatin could inhibit human gastric cancer growth and furthermore whether sphingosine kinase (SPK) activity is involved in this process.

METHODS: Using migration assay, MTT assay and Matrigel assay, the effect of alphastatin on vascular endothelial cells (ECs) was evaluated in vitro. SPK and endothelial differentiation gene (EDG)-1, -3, -5 mRNAs were detected by reverse transcription-polymerase chain reaction (RT-PCR). SPK activity assay was used to evaluate the effect of alphastatin on ECs. Matrigel plug assay in nude mice was used to investigate the effect of alphastatin on angiogenesis in vivo. Female nude mice were subcutaneously implanted with human gastric cancer cells (BGC823) for the tumor xenografts studies. Micro vessel density was analyzed in Factor VIII-stained tumor sections by the immunohistochemical SP method.

RESULTS: In vitro, alphastatin inhibited the migration and tube formation of ECs, but had no effect on proliferation of ECs. RT-PCR analysis demonstrated that ECs expressed SPK and EDG-1, -3, -5 mRNAs. In vivo, alphastatin sufficiently suppressed neovascularization of the tumor in the nude mice. Daily administration of alphastatin produced significant tumor growth suppression. Immunohistochemical studies of tumor tissues revealed decreased micro vessel density in alphastatin-treated animals as compared with controls.

CONCLUSION: Downregulating ECs SPK activity may be one of the mechanisms that alphastatin inhibits gastric cancer angiogenesis. Alphastatin might be a useful and relatively nontoxic adjuvant therapy in the treatment of gastric cancer.