Thyroid hormone has been recently shown to induce tumor growth and angiogenesis via a plasma-membrane hormone receptor on integrin alphaVbeta3. The receptor is at or near the Arg-Gly-Asp (RGD) recognition site on the integrin that is important to extracellular matrix (ECM) protein and vascular growth factor interactions with the integrin. In the present study, we examined the possibility that tetraiodothyroacetic acid (tetrac), a deaminated, non-agonist thyroid hormone analog that binds to the integrin receptor, may modulate vascular growth factor-induced angiogenesis in the absence of thyroid hormone. Angiogenesis models were studied in which VEGF or FGF2 (1-2 microg/ml) induced tube formation in human dermal microvascular endothelial cells (HDMEC), stimulated new blood vessel branch formation in the chick chorioallantoic membrane (CAM) and induced angiogenesis in the mouse matrigel model. In all models, tetrac (1-10 microM) and at 10 microg in mouse matrigel inhibited the pro-angiogenesis activity of VEGF and FGF2 by more than 50%. RT-PCR revealed that tetrac (1-3 microM) decreased abundance of angiopoietin-2 mRNA, but not angiopoietin-1 mRNA, in VEGF-exposed endothelial cells, suggesting that specific angiogenic pathways are targeted by tetrac. Tetrac is a novel, inexpensive small molecule whose anti-angiogenic activity in the present studies is proposed to reflect inhibition, via the integrin RGD recognition/thyroid hormone receptor site, of crosstalk between plasma-membrane vascular growth factor receptors and integrin alphaVbeta3.

e14643 Background: Uncontrolled proliferation, enhanced angiogenesis and the development of resistance to therapy are hallmarks of cancer; therefore, the development of approaches to simultaneously target these three processes would be the most desirable. Previous work from our laboratory has demonstrated that NapSul-Ile-Trp-CHO (NSITC), a specific inhibitors of cathepsin L, and its analogs strongly inhibited cancer cell proliferation and suppressed the development of drug resistance in vitro (Zheng X. et al., 2004 Cancer Res. 64:1773–80). In the present study, we sought to investigate the validity of these observations in vivo, and to dissect the underlying mechanism(s). Methods: Nude mice (Strain CD1) bearing xenografts of doxorubicin resistant neuroblastoma cell line SKN-SH/R were challenged with doxorubicin (1.5 mg/Kg) alone, NSITC (20 mg/kg) alone or the combination of both. The effect of NSITC on tumor angiogenesis was also investigated using the Chick Chorioallantoic Membrane (CAM). Putative mechanisms by which NSITC inhibits cellular proliferation, drug resistance and angiogenesis were studied using cancer and endothelial cells maintained in culture. Results: The in vivo data indicated that doxorubicin alone had no effect on tumor growth, however NSITC alone exerted 40% inhibition and the combination of both drugs reduced tumor growth by about 90%. NSITC also caused a 125% inhibition of blood vessel branching in the CAM model (at 1 μg/CAM). Investigation of the underlying mechanisms of its action revealed that at low concentration, NSITC forces cancer cells into senescence, preventing them from developing resistance to classical anticancer agents, and at high concentrations, it induced autophagic cell death. NSITC also strongly inhibited the proliferation and invasion of endothelial cells in a dose dependent manner with more than 90% inhibition at 20 μM. Conclusions: Overall, these findings suggest that NSITC has multi-anticancer functions and thus, may represent a potential drug candidate for the treatment of aggressive malignancies. No significant financial relationships to disclose.

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