Pharmacology of the novel antiangiogenic peptide ATN-161 (Ac-PHSCN-NH2): observation of a U-shaped dose-response curve in several preclinical models of angiogenesis and tumor growth.

PURPOSE: ATN-161 (Ac-PHSCN-NH(2)) is an integrin-binding peptide that is currently in phase II trials in cancer patients. This peptide has been shown to have antitumor activity in a number of different preclinical models. EXPERIMENTAL DESIGN: In this study, we examined the binding, biodistribution, and dose and biomarker response of ATN-161 in several animal models. RESULTS: ATN-161 bound to the beta subunit of a number of different integrins implicated in tumor growth and progression, which depended on its cysteine thiol. The peptide had antiangiogenic activity in the Matrigel plug model, and this activity could be reversed by inhibitors of protein kinase A, an effector of alpha(5)beta(1)-dependent angiogenesis. A labeled analogue of ATN-161, ATN-453, localized to neovessels but not to preexisting vasculature in vivo. The half-life of the peptide when localized to a tumor was much longer than in plasma. Dose-response studies in the Matrigel plug model of angiogenesis or a Lewis lung carcinoma model of tumor growth showed a U-shaped dose-response curve with 1 to 10 mg/kg given thrice a week, being the optimal dose range of ATN-161. Two additional pharmacodynamic models of angiogenesis (dynamic contrast-enhanced magnetic resonance imaging and measurement of endothelial cell progenitors) also revealed U-shaped dose-response curves. CONCLUSIONS: The presence of a U-shaped dose-response curve presents a significant challenge to identifying a biologically active dose of ATN-161. However, the identification of biomarkers of angiogenesis that also exhibit this same U-shaped response should allow the translation of those biomarkers to the clinic, allowing them to be used to identify the active dose of ATN-161 in phase II studies.

Angiogenesis blockade as a new therapeutic approach to experimental colitis.

BACKGROUND: Neoangiogenesis is a critical component of chronic inflammatory disorders. Inhibition of angiogenesis is an effective treatment in animal models of inflammation, but has not been tested in experimental colitis. AIM: To investigate the effect of ATN-161, an anti-angiogenic compound, on the course of experimental murine colitis. METHOD: Interleukin 10-deficient (IL10(-/-)) mice and wild-type mice were kept in ultra-barrier facilities (UBF) or conventional housing, and used for experimental conditions. Dextran sodium sulphate (DSS)-treated mice were used as a model of acute colitis. Mice were treated with ATN-161 or its scrambled peptide ATN-163. Mucosal neoangiogenesis and mean vascular density (MVD) were assessed by CD31 staining. A Disease Activity Index (DAI) was determined, and the severity of colitis was determined by a histological score. Colonic cytokine production was measured by ELISA, and lamina propria mononuclear cell proliferation by thymidine incorporation. RESULT: MVD increased in parallel with disease progression in IL10(-/-) mice kept in conventional housing, but not in IL10(-/-) mice kept in UBF. Angiogenesis also occurred in DSS-treated animals. IL10(-/-) mice with established disease treated with ATN-161, but not with ATN-163, showed a significant and progressive decrease in DAI. The histological colitis score was significantly lower in ATN-161-treated mice than in scrambled peptide-treated mice. Inhibition of angiogenesis was confirmed by a significant decrease of MVD in ATN-161-treated mice than in ATN-163-treated mice. No therapeutic effects were observed in the DSS model of colitis. ATN-161 showed no direct immunomodulatory activity in vitro. CONCLUSION: Active angiogenesis occurs in the gut of IL10(-/-) and DSS-treated colitic mice and parallels disease progression. ATN-161 effectively decreases angiogenesis as well as clinical severity and histological inflammation in IL10(-/-) mice but not in the DDS model of inflammatory bowel disease (IBD). The results provide the rational basis for considering anti-angiogenic strategies in the treatment of IBD in humans.

A non-RGD-based integrin binding peptide (ATN-161) blocks breast cancer growth and metastasis in vivo.

PURPOSE: Integrins are expressed by numerous tumor types including breast cancer, in which they play a crucial role in tumor growth and metastasis. In this study, we evaluated the ability of ATN-161 (Ac-PHSCN-NH2), a 5-mer capped peptide derived from the synergy region of fibronectin that binds to alpha5beta1 and alphavbeta3 in vitro, to block breast cancer growth and metastasis. EXPERIMENTAL DESIGN: MDA-MB-231 human breast cancer cells were inoculated s.c. in the right flank, or cells transfected with green fluorescent protein (MDA-MB-231-GFP) were inoculated into the left ventricle of female BALB/c nu/nu mice, resulting in the development of skeletal metastasis. Animals were treated with vehicle alone or by i.v. infusion with ATN-161 (0.05-1 mg/kg thrice a week) for 10 weeks. Tumor volume was determined at weekly intervals and tumor metastasis was evaluated by X-ray, microcomputed tomography, and histology. Tumors were harvested for histologic evaluation. RESULT: Treatment with ATN-161 caused a significant dose-dependent decrease in tumor volume and either completely blocked or caused a marked decrease in the incidence and number of skeletal as well as soft tissue metastases. This was confirmed histologically as well as radiographically using X-ray and microcomputed tomography. Treatment with ATN-161 resulted in a significant decrease in the expression of phosphorylated mitogen-activated protein kinase, microvessel density, and cell proliferation in tumors grown in vivo. CONCLUSION: These studies show that ATN-161 can block breast cancer growth and metastasis, and provides a rationale for the clinical development of ATN-161 for the treatment of breast cancer.